Printed circuit board

A printed circuit board (PCB), also called printed wiring board (PWB), is a medium used to connect or "wire" components to one another in a circuit. It takes the form of a laminated sandwich structure of conductive and insulating layers: each of the conductive layers is designed with an artwork pattern of traces, planes and other features (similar to wires on a flat surface) etched from one or more sheet layers of copper laminated onto and/or between sheet layers of a non-conductive substrate. Electrical components may be fixed to conductive pads on the outer layers in the shape designed to accept the component's terminals, generally by means of soldering, to both electrically connect and mechanically fasten them to it. Another manufacturing process adds vias: plated-through holes that allow interconnections between layers.
Printed circuit boards are used in nearly all electronic products. Alternatives to PCBs include wire wrap and point-to-point construction, both once popular but now rarely used. PCBs require additional design effort to lay out the circuit, but manufacturing and assembly can be automated. Electronic design automation software is available to do much of the work of layout. Mass-producing circuits with PCBs is cheaper and faster than with other wiring methods, as components are mounted and wired in one operation. Large numbers of PCBs can be fabricated at the same time, and the layout has to be done only once. PCBs can also be made manually in small quantities, with reduced benefits.
PCBs can be single-sided (one copper layer), double-sided (two copper layers on both sides of one substrate layer), or multi-layer (outer and inner layers of copper, alternating with layers of substrate). Multi-layer PCBs allow for much higher component density, because circuit traces on the inner layers would otherwise take up surface space between components. The rise in popularity of multilayer PCBs with more than two, and especially with more than four, copper planes was concurrent with the adoption of surface mount technology. However, multilayer PCBs make repair, analysis, and field modification of circuits much more difficult and usually impractical.
The world market for bare PCBs exceeded $60.2 billion in 2014 and is estimated to reach $79 billion by 2024.
History.
Predecessors.
Before the development of printed circuit boards, electrical and electronic circuits were wired point-to-point on a chassis. Typically, the chassis was a sheet metal frame or pan, sometimes with a wooden bottom. Components were attached to the chassis, usually by insulators when the connecting point on the chassis was metal, and then their leads were connected directly or with jumper wires by soldering, or sometimes using crimp connectors, wire connector lugs on screw terminals, or other methods. Circuits were large, bulky, heavy, and relatively fragile (even discounting the breakable glass envelopes of the vacuum tubes that were often included in the circuits), and production was labor-intensive, so the products were expensive.
Development of the methods used in modern printed circuit boards started early in the 20th century. In 1903, a German inventor, Albert Hanson, described flat foil conductors laminated to an insulating board, in multiple layers. Thomas Edison experimented with chemical methods of plating conductors onto linen paper in 1904. Arthur Berry in 1913 patented a print-and-etch method in the UK, and in the United States Max Schoop obtained a patent to flame-spray metal onto a board through a patterned mask. Charles Ducas in 1925 patented a method of electroplating circuit patterns.
Predating the printed circuit invention, and similar in spirit, was John Sargrove's 1936–1947 Electronic Circuit Making Equipment (ECME) that sprayed metal onto a Bakelite plastic board. The ECME could produce three radio boards per minute.
Early PCBs.
The Austrian engineer Paul Eisler invented the printed circuit as part of a radio set while working in the UK around 1936. In 1941 a multi-layer printed circuit was used in German magnetic influence naval mines.
Around 1943 the USA began to use the technology on a large scale to make proximity fuzes for use in World War II. Such fuzes required an electronic circuit that could withstand being fired from a gun, and could be produced in quantity. The Centralab Division of Globe Union submitted a proposal which met the requirements: a ceramic plate would be screenprinted with metallic paint for conductors and carbon material for resistors, with ceramic disc capacitors and subminiature vacuum tubes soldered in place. The technique proved viable, and the resulting patent on the process, which was classified by the U.S. Army, was assigned to Globe Union. It was not until 1984 that the Institute of Electrical and Electronics Engineers (IEEE) awarded Harry W. Rubinstein the Cledo Brunetti Award for early key contributions to the development of printed components and conductors on a common insulating substrate. Rubinstein was honored in 1984 by his alma mater, the University of Wisconsin-Madison, for his innovations in the technology of printed electronic circuits and the fabrication of capacitors. This invention also represents a step in the development of integrated circuit technology, as not only wiring but also passive components were fabricated on the ceramic substrate.
Post-war developments.
In 1948, the USA released the invention for commercial use. Printed circuits did not become commonplace in consumer electronics until the mid-1950s, after the "Auto-Sembly" process was developed by the United States Army. At around the same time in the UK work along similar lines was carried out by Geoffrey Dummer, then at the RRDE.
Motorola was an early leader in bringing the process into consumer electronics, announcing in August 1952 the adoption of "plated circuits" in home radios after six years of research and a $1M investment. Motorola soon began using its trademarked term for the process, PLAcir, in its consumer radio advertisements. Hallicrafters released its first "foto-etch" printed circuit product, a clock-radio, on 1 November 1952.
Even as circuit boards became available, the point-to-point chassis construction method remained in common use in industry (such as TV and hi-fi sets) into at least the late 1960s. Printed circuit boards were introduced to reduce the size, weight, and cost of parts of the circuitry. In 1960, a small consumer radio receiver might be built with all its circuitry on one circuit board, but a TV set would probably contain one or more circuit boards.
Originally, every electronic component had wire leads, and a PCB had holes drilled for each wire of each component. The component leads were then inserted through the holes and soldered to the copper PCB traces. This method of assembly is called "through-hole" construction. In 1949, Moe Abramson and Stanislaus F. Danko of the United States Army Signal Corps developed the "Auto-Sembly" process in which component leads were inserted into a copper foil interconnection pattern and dip soldered. The patent they obtained in 1956 was assigned to the U.S. Army. With the development of board lamination and etching techniques, this concept evolved into the standard printed circuit board fabrication process in use today. Soldering could be done automatically by passing the board over a ripple, or wave, of molten solder in a wave-soldering machine. However, the wires and holes are inefficient since drilling holes is expensive and consumes drill bits and the protruding wires are cut off and discarded.
From the 1980s onward, small surface mount parts have been used increasingly instead of through-hole components; this has led to smaller boards for a given functionality and lower production costs, but with some additional difficulty in servicing faulty boards.
In the 1990s the use of multilayer surface boards became more frequent. As a result, size was further minimized and both flexible and rigid PCBs were incorporated in different devices. In 1995 PCB manufacturers began using microvia technology to produce High-Density Interconnect (HDI) PCBs.
Recent advances.
Recent advances in 3D printing have meant that there are several new techniques in PCB creation. 3D printed electronics (PEs) can be utilized to print items layer by layer and subsequently the item can be printed with a liquid ink that contains electronic functionalities.
HDI (High Density Interconnect) technology allows for a denser design on the PCB and thus potentially smaller PCBs with more traces and/or components in a given area. As a result, the paths between components can be shorter. HDIs use blind/buried vias, or a combination that includes microvias. With multi-layer HDI PCBs the interconnection of several vias stacked on top of each other (stacked vías, instead of one deep buried via) can be made stronger, thus enhancing reliability in all conditions. The most common applications for HDI technology are computer and mobile phone components as well as medical equipment and military communication equipment. A 4-layer HDI microvia PCB is equivalent in quality to an 8-layer through-hole PCB, so HDI technology can reduce costs.
Composition.
A basic PCB consists of a flat sheet of insulating material and a layer of copper foil, laminated to the substrate. Chemical etching divides the copper into separate conducting lines called tracks or "circuit traces", pads for connections, vias to pass connections between layers of copper, and features such as solid conductive areas for electromagnetic shielding or other purposes. The tracks function as wires fixed in place, and are insulated from each other by air and the board substrate material. The surface of a PCB may have a coating that protects the copper from corrosion and reduces the chances of solder shorts between traces or undesired electrical contact with stray bare wires. For its function in helping to prevent solder shorts, the coating is called solder resist or solder mask.
The pattern to be etched into each copper layer of a PCB is called the "artwork". The etching is usually done using photoresist which is coated onto the PCB, then exposed to light projected in the pattern of the artwork. The resist material protects the copper from dissolution into the etching solution. The etched board is then cleaned. A PCB design can be mass-reproduced in a way similar to the way photographs can be mass-duplicated from film negatives using a photographic printer.
FR-4 glass epoxy is the most common insulating substrate. Another substrate material is cotton paper impregnated with phenolic resin, often tan or brown.
When a PCB has no components installed, it is less ambiguously called a "printed wiring board" ("PWB") or "etched wiring board". However, the term "printed wiring board" has fallen into disuse. A PCB populated with electronic components is called a "printed circuit assembly" ("PCA"), "printed circuit board assembly" or "PCB assembly" ("PCBA"). In informal usage, the term "printed circuit board" most commonly means "printed circuit assembly" (with components). The IPC preferred term for an assembled board is "circuit card assembly" ("CCA"), and for an assembled backplane it is "backplane assembly". "Card" is another widely used informal term for a "printed circuit assembly".
For example, expansion card.
A PCB may be printed with a legend identifying the components, test points, or identifying text. Originally, silkscreen printing was used for this purpose, but today other, finer quality printing methods are usually used. Normally the legend does not affect the function of a PCBA.
Layers.
A printed circuit board can have multiple layers of copper which almost always are arranged in pairs. The number of layers and the interconnection designed between them (vias, PTHs) provide a general estimate of the board complexity. Using more layers allow for more routing options and better control of signal integrity, but are also time consuming and costly to manufacture. Likewise, selection of the vias for the board also allow fine tuning of the board size, escaping of signals off complex ICs, routing, and long term reliability, but are tightly coupled with production complexity and cost.
One of the simplest boards to produce is the two-layer board. It has copper on both sides that are referred to as external layers; multi layer boards sandwich additional internal layers of copper and insulation. After two-layer PCBs, the next step up is the four-layer. The four layer board adds significantly more routing options in the internal layers as compared to the two layer board, and often some portion of the internal layers is used as ground plane or power plane, to achieve better signal integrity, higher signaling frequencies, lower EMI, and better power supply decoupling.
In multi-layer boards, the layers of material are laminated together in an alternating sandwich: copper, substrate, copper, substrate, copper, etc.; each plane of copper is etched, and any internal vias (that will not extend to both outer surfaces of the finished multilayer board) are plated-through, before the layers are laminated together. Only the outer layers need be coated; the inner copper layers are protected by the adjacent substrate layers.
Component mounting.
"Through hole" components are mounted by their wire leads passing through the board and soldered to traces on the other side. "Surface mount" components are attached by their leads to copper traces on the same side of the board. A board may use both methods for mounting components. PCBs with only through-hole mounted components are now uncommon. Surface mounting is used for transistors, diodes, IC chips, resistors, and capacitors. Through-hole mounting may be used for some large components such as electrolytic capacitors and connectors.
The first PCBs used through-hole technology, mounting electronic components by leads inserted through holes on one side of the board and soldered onto copper traces on the other side. Boards may be single-sided, with an unplated component side, or more compact double-sided boards, with components soldered on both sides. Horizontal installation of through-hole parts with two axial leads (such as resistors, capacitors, and diodes) is done by bending the leads 90 degrees in the same direction, inserting the part in the board (often bending leads located on the back of the board in opposite directions to improve the part's mechanical strength), soldering the leads, and trimming off the ends. Leads may be soldered either manually or by a wave soldering machine. Through-hole manufacture adds to board cost by requiring many holes to be drilled accurately, and it limits the available routing area for signal traces on layers immediately below the top layer on multi-layer boards, since the holes must pass through all layers to the opposite side. Once surface-mounting came into use, small-sized SMD components were used where possible, with through-hole mounting only of components unsuitably large for surface-mounting due to power requirements or mechanical limitations, or subject to mechanical stress which might damage the PCB (e.g. by lifting the copper off the board surface).
Surface-mount technology emerged in the 1960s, gained momentum in the early 1980s, and became widely used by the mid-1990s.
Components were mechanically redesigned to have small metal tabs or end caps that could be soldered directly onto the PCB surface, instead of wire leads to pass through holes. Components became much smaller and component placement on both sides of the board became more common than with through-hole mounting, allowing much smaller PCB assemblies with much higher circuit densities.
Surface mounting lends itself well to a high degree of automation, reducing labor costs and greatly increasing production rates compared with through-hole circuit boards. Components can be supplied mounted on carrier tapes. Surface mount components can be about one-quarter to one-tenth of the size and weight of through-hole components, and passive components much cheaper. However, prices of semiconductor surface mount devices (SMDs) are determined more by the chip itself than the package, with little price advantage over larger packages, and some wire-ended components, such as 1N4148 small-signal switch diodes, are actually significantly cheaper than SMD equivalents.
Electrical properties.
Each trace consists of a flat, narrow part of the copper foil that remains after etching. Its resistance, determined by its width, thickness, and length, must be sufficiently low for the current the conductor will carry. Power and ground traces may need to be wider than signal traces. In a multi-layer board one entire layer may be mostly solid copper to act as a ground plane for shielding and power return. For microwave circuits, transmission lines can be laid out in a planar form such as stripline or microstrip with carefully controlled dimensions to assure a consistent impedance. In radio-frequency and fast switching circuits the inductance and capacitance of the printed circuit board conductors become significant circuit elements, usually undesired; conversely, they can be used as a deliberate part of the circuit design, as in distributed-element filters, antennae, and fuses, obviating the need for additional discrete components. High density interconnects (HDI) PCBs have tracks and/or vias with a width or diameter of under 152 micrometers.
Materials.
Laminates.
Laminates are manufactured by curing layers of cloth or paper with thermoset resin under pressure and heat to form an integral final piece of uniform thickness. They can be up to in width and length. Varying cloth weaves (threads per inch or cm), cloth thickness, and resin percentage are used to achieve the desired final thickness and dielectric characteristics. Available standard laminate thickness are listed in
ANSI/IPC-D-275.
The cloth or fiber material used, resin material, and the cloth to resin ratio determine the laminate's type designation (FR-4, CEM-1, G-10, etc.) and therefore the characteristics of the laminate produced. Important characteristics are the level to which the laminate is fire retardant, the dielectric constant (er), the loss tangent (tan δ), the tensile strength, the shear strength, the glass transition temperature (Tg), and the Z-axis expansion coefficient (how much the thickness changes with temperature).
There are quite a few different dielectrics that can be chosen to provide different insulating values depending on the requirements of the circuit. Some of these dielectrics are polytetrafluoroethylene (Teflon), FR-4, FR-1, CEM-1 or CEM-3. Well known pre-preg materials used in the PCB industry are FR-2 (phenolic cotton paper), FR-3 (cotton paper and epoxy), FR-4 (woven glass and epoxy), FR-5 (woven glass and epoxy), FR-6 (matte glass and polyester), G-10 (woven glass and epoxy), CEM-1 (cotton paper and epoxy), CEM-2 (cotton paper and epoxy), CEM-3 (non-woven glass and epoxy), CEM-4 (woven glass and epoxy), CEM-5 (woven glass and polyester). Thermal expansion is an important consideration especially with ball grid array (BGA) and naked die technologies, and glass fiber offers the best dimensional stability.
FR-4 is by far the most common material used today. The board stock with unetched copper on it is called "copper-clad laminate".
With decreasing size of board features and increasing frequencies, small nonhomogeneities like uneven distribution of fiberglass or other filler, thickness variations, and bubbles in the resin matrix, and the associated local variations in the dielectric constant, are gaining importance.
Key substrate parameters.
The circuitboard substrates are usually dielectric composite materials. The composites contain a matrix (usually an epoxy resin) and a reinforcement (usually a woven, sometimes nonwoven, glass fibers, sometimes even paper), and in some cases a filler is added to the resin (e.g. ceramics; titanate ceramics can be used to increase the dielectric constant).
The reinforcement type defines two major classes of materials: woven and non-woven. Woven reinforcements are cheaper, but the high dielectric constant of glass may not be favorable for many higher-frequency applications. The spatially nonhomogeneous structure also introduces local variations in electrical parameters, due to different resin/glass ratio at different areas of the weave pattern. Nonwoven reinforcements, or materials with low or no reinforcement, are more expensive but more suitable for some RF/analog applications.
The substrates are characterized by several key parameters, chiefly thermomechanical (glass transition temperature, tensile strength, shear strength, thermal expansion), electrical (dielectric constant, loss tangent, dielectric breakdown voltage, leakage current, tracking resistance...), and others (e.g. moisture absorption).
At the glass transition temperature the resin in the composite softens and significantly increases thermal expansion; exceeding Tg then exerts mechanical overload on the board components - e.g. the joints and the vias. Below Tg the thermal expansion of the resin roughly matches copper and glass, above it gets significantly higher. As the reinforcement and copper confine the board along the plane, virtually all volume expansion projects to the thickness and stresses the plated-through holes. Repeated soldering or other exposition to higher temperatures can cause failure of the plating, especially with thicker boards; thick boards therefore require a matrix with a high Tg.
The materials used determine the substrate's dielectric constant. This constant is also dependent on frequency, usually decreasing with frequency. As this constant determines the signal propagation speed, frequency dependence introduces phase distortion in wideband applications; as flat a dielectric constant vs frequency characteristics as is achievable is important here. The impedance of transmission lines decreases with frequency, therefore faster edges of signals reflect more than slower ones.
Dielectric breakdown voltage determines the maximum voltage gradient the material can be subjected to before suffering a breakdown (conduction, or arcing, through the dielectric).
Tracking resistance determines how the material resists high voltage electrical discharges creeping over the board surface.
Loss tangent determines how much of the electromagnetic energy from the signals in the conductors is absorbed in the board material. This factor is important for high frequencies. Low-loss materials are more expensive. Choosing unnecessarily low-loss material is a common engineering error in high-frequency digital design; it increases the cost of the boards without a corresponding benefit. Signal degradation by loss tangent and dielectric constant can be easily assessed by an eye pattern.
Moisture absorption occurs when the material is exposed to high humidity or water. Both the resin and the reinforcement may absorb water; water also may be soaked by capillary forces through voids in the materials and along the reinforcement. Epoxies of the FR-4 materials are not too susceptible, with absorption of only 0.15%. Teflon has very low absorption of 0.01%. Polyimides and cyanate esters, on the other side, suffer from high water absorption. Absorbed water can lead to significant degradation of key parameters; it impairs tracking resistance, breakdown voltage, and dielectric parameters. Relative dielectric constant of water is about 73, compared to about 4 for common circuit board materials. Absorbed moisture can also vaporize on heating, as during soldering, and cause cracking and delamination, the same effect responsible for "popcorning" damage on wet packaging of electronic parts. Careful baking of the substrates may be required to dry them prior to soldering.
Common substrates.
Often encountered materials:
Less-often encountered materials:
Copper thickness.
Copper thickness of PCBs can be specified directly or as the weight of copper per area (in ounce per square foot) which is easier to measure. One ounce per square foot is 1.344 mils or 34 micrometers thickness. "Heavy copper" is a layer exceeding three ounces of copper per ft2, or approximately 0.0042 inches (4.2 mils, 105 μm) thick. Heavy copper layers are used for high current or to help dissipate heat.
On the common FR-4 substrates, 1 oz copper per ft2 (35 µm) is the most common thickness; 2 oz (70 µm) and 0.5 oz (17.5 µm) thickness is often an option. Less common are 12 and 105 µm, 9 µm is sometimes available on some substrates. Flexible substrates typically have thinner metalization. Metal-core boards for high power devices commonly use thicker copper; 35 µm is usual but also 140 and 400 µm can be encountered.
In the USA, copper foil thickness is specified in units of ounces per square foot (oz/ft2), commonly referred to simply as "ounce". Common thicknesses are 1/2 oz/ft2 (150 g/m), 1 oz/ft2 (300 g/m), 2 oz/ft2 (600 g/m), and 3 oz/ft2 (900 g/m). These work out to thicknesses of 17.05 μm (0.67 thou), 34.1 μm (1.34 thou), 68.2 μm (2.68 thou), and 102.3 μm (4.02 thou), respectively.
1/2 oz/ft2 foil is not widely used as a finished copper weight, but is used for outer layers when plating for through holes will increase the finished copper weight Some PCB manufacturers refer to 1 oz/ft2 copper foil as having a thickness of 35 μm (may also be referred to as 35 μ, 35 micron, or 35 mic).
Construction.
Design.
Manufacturing starts from the fabrication data generated by computer aided design, and component information. The fabrication data is read into the CAM (Computer Aided Manufacturing) software. CAM performs the following functions:
Initially PCBs were designed manually by creating a photomask on a clear mylar sheet, usually at two or four times the true size. Starting from the schematic diagram the component pin pads were laid out on the mylar and then traces were routed to connect the pads. Rub-on dry transfers of common component footprints increased efficiency. Traces were made with self-adhesive tape. Pre-printed non-reproducing grids on the mylar assisted in layout. The finished photomask was photolithographically reproduced onto a photoresist coating on the blank copper-clad boards.
Modern PCBs are designed with dedicated layout software, generally in the following steps:
Panelization.
Several small printed circuit boards can be grouped together for processing as a panel. A panel consisting of a design duplicated "n"-times is also called an "n"-panel, whereas a "multi-panel" combines several different designs onto a single panel. The outer tooling strip often includes tooling holes, a set of panel fiducials, a test coupon, and may include hatched copper pour or similar patterns for even copper distribution over the whole panel in order to avoid bending. The assemblers often mount components on panels rather than single PCBs because this is efficient. Panelization may also be necessary for boards with components placed near an edge of the board because otherwise the board could not be mounted during assembly. Most assembly shops require a free area of at least 10 mm around the board.
The panel is eventually broken into individual PCBs along perforations or grooves in the panel through milling or cutting. For milled panels a common distance between the individual boards is 2–3 mm. Today depaneling is often done by lasers which cut the board with no contact. Laser depaneling reduces stress on the fragile circuits, improving the yield of defect-free units.
Copper patterning.
The first step is to replicate the pattern in the fabricator's CAM system on a protective mask on the copper foil PCB layers. Subsequent etching removes the unwanted copper unprotected by the mask. (Alternatively, a conductive ink can be ink-jetted on a blank (non-conductive) board. This technique is also used in the manufacture of hybrid circuits.)
The method chosen depends on the number of boards to be produced and the required resolution.
Etching.
The process by which copper traces are applied to the surface is known as "etching" after the subtractive method of the process, though there are also additive and semi-additive methods.
Subtractive methods remove copper from an entirely copper-coated board to leave only the desired copper pattern. The simplest method, used for small-scale production and often by hobbyists, is immersion etching, in which the board is submerged in etching solution such as ferric chloride. Compared with methods used for mass production, the etching time is long. Heat and agitation can be applied to the bath to speed the etching rate. In bubble etching, air is passed through the etchant bath to agitate the solution and speed up etching. Splash etching uses a motor-driven paddle to splash boards with etchant; the process has become commercially obsolete since it is not as fast as spray etching. In spray etching, the etchant solution is distributed over the boards by nozzles, and recirculated by pumps. Adjustment of the nozzle pattern, flow rate, temperature, and etchant composition gives predictable control of etching rates and high production rates. As more copper is consumed from the boards, the etchant becomes saturated and less effective; different etchants have different capacities for copper, with some as high as 150 grams of copper per litre of solution. In commercial use, etchants can be regenerated to restore their activity, and the dissolved copper recovered and sold. Small-scale etching requires attention to disposal of used etchant, which is corrosive and toxic due to its metal content. The etchant removes copper on all surfaces not protected by the resist. "Undercut" occurs when etchant attacks the thin edge of copper under the resist; this can reduce conductor widths and cause open-circuits. Careful control of etch time is required to prevent undercut. Where metallic plating is used as a resist, it can "overhang" which can cause short-circuits between adjacent traces when closely spaced. Overhang can be removed by wire-brushing the board after etching.
In additive methods the pattern is electroplated onto a bare substrate using a complex process. The advantage of the additive method is that less material is needed and less waste is produced. In the full additive process the bare laminate is covered with a photosensitive film which is imaged (exposed to light through a mask and then developed which removes the unexposed film). The exposed areas are sensitized in a chemical bath, usually containing palladium and similar to that used for through hole plating which makes the exposed area capable of bonding metal ions. The laminate is then plated with copper in the sensitized areas. When the mask is stripped, the PCB is finished.
Semi-additive is the most common process: The unpatterned board has a thin layer of copper already on it. A reverse mask is then applied. (Unlike a subtractive process mask, this mask exposes those parts of the substrate that will eventually become the traces.) Additional copper is then plated onto the board in the unmasked areas; copper may be plated to any desired weight. Tin-lead or other surface platings are then applied. The mask is stripped away and a brief etching step removes the now-exposed bare original copper laminate from the board, isolating the individual traces. Some single-sided boards which have plated-through holes are made in this way. General Electric made consumer radio sets in the late 1960s using additive boards. The (semi-)additive process is commonly used for multi-layer boards as it facilitates the plating-through of the holes to produce conductive vias in the circuit board.
Industrial etching is usually done with ammonium persulfate or ferric chloride. For PTH (plated-through holes), additional steps of electroless deposition are done after the holes are drilled, then copper is electroplated to build up the thickness, the boards are screened, and plated with tin/lead. The tin/lead becomes the resist leaving the bare copper to be etched away.
Lamination.
Multi-layer printed circuit boards have trace layers inside the board. This is achieved by laminating a stack of materials in a press by applying pressure and heat for a period of time. This results in an inseparable one piece product. For example, a four-layer PCB can be fabricated by starting from a two-sided copper-clad laminate, etch the circuitry on both sides, then laminate to the top and bottom pre-preg and copper foil. It is then drilled, plated, and etched again to get traces on top and bottom layers.
The inner layers are given a complete machine inspection before lamination because mistakes cannot be corrected afterwards. Automatic optical inspection (AOI) machines compare an image of the board with the digital image generated from the original design data. Automated Optical Shaping (AOS) machines can then add missing copper or remove excess copper using a laser, reducing the number of PCBs that have to be discarded. PCB tracks can have a width of just 10 micrometers.
Drilling.
Holes through a PCB are typically drilled with drill bits made of solid coated tungsten carbide. Coated tungsten carbide is used because board materials are abrasive. High-speed-steel bits would dull quickly, tearing the copper and ruining the board. Drilling is done by computer-controlled drilling machines, using a "drill file" or Excellon file that describes the location and size of each drilled hole.
Holes may be made conductive, by electroplating or inserting hollow metal eyelets, to connect board layers. Some conductive holes are intended for the insertion of through-hole-component leads. Others used to connect board layers, are called vias.
When vias with a diameter smaller than 76.2 micrometers are required, drilling with mechanical bits is impossible because of high rates of wear and breakage. In this case, the vias may be laser drilled—evaporated by lasers. Laser-drilled vias typically have an inferior surface finish inside the hole. These holes are called "micro vias" and can have diameters as small as 10 micrometers. It is also possible with "controlled-depth" drilling, laser drilling, or by pre-drilling the individual sheets of the PCB before lamination, to produce holes that connect only some of the copper layers, rather than passing through the entire board. These holes are called "blind vias" when they connect an internal copper layer to an outer layer, or "buried vias" when they connect two or more internal copper layers and no outer layers. Laser drilling machines can drill thousands of holes per second and can use either UV or lasers.
The hole walls for boards with two or more layers can be made conductive and then electroplated with copper to form "plated-through holes". These holes electrically connect the conducting layers of the PCB. For multi-layer boards, those with three layers or more, drilling typically produces a "smear" of the high temperature decomposition products of bonding agent in the laminate system. Before the holes can be plated through, this smear must be removed by a chemical "de-smear" process, or by "plasma-etch". The de-smear process ensures that a good connection is made to the copper layers when the hole is plated through. On high reliability boards a process called etch-back is performed chemically with a potassium permanganate based etchant or plasma etching. The etch-back removes resin and the glass fibers so that the copper layers extend into the hole and as the hole is plated become integral with the deposited copper.
Plating and coating.
Proper plating or surface finish selection can be critical to process yield, the amount of rework, field failure rate, and reliability.
PCBs may be plated with solder, tin, or gold over nickel.
After PCBs are etched and then rinsed with water, the solder mask is applied, and then any exposed copper is coated with solder, nickel/gold, or some other anti-corrosion coating.
Matte solder is usually fused to provide a better bonding surface for bare copper. Treatments, such as benzimidazolethiol, prevent surface oxidation of bare copper. The places to which components will be mounted are typically plated, because untreated bare copper oxidizes quickly, and therefore is not readily solderable. Traditionally, any exposed copper was coated with solder by hot air (solder) levelling (HASL aka HAL). The HASL finish prevents oxidation from the underlying copper, thereby guaranteeing a solderable surface. This solder was a tin-lead alloy, however new solder compounds are now used to achieve compliance with the RoHS directive in the EU, which restricts the use of lead. One of these lead-free compounds is SN100CL, made up of 99.3% tin, 0.7% copper, 0.05% nickel, and a nominal of 60 ppm germanium.
It is important to use solder compatible with both the PCB and the parts used. An example is ball grid array (BGA) using tin-lead solder balls for connections losing their balls on bare copper traces or using lead-free solder paste.
Other platings used are organic solderability preservative (OSP), immersion silver (IAg), immersion tin (ISn), electroless nickel immersion gold (ENIG) coating, electroless nickel electroless palladium immersion gold (ENEPIG), and direct gold plating (over nickel). Edge connectors, placed along one edge of some boards, are often nickel-plated then gold-plated using ENIG. Another coating consideration is rapid diffusion of coating metal into tin solder. Tin forms intermetallics such as Cu6Sn5 and Ag3Cu that dissolve into the Tin liquidus or solidus (at 50 °C), stripping surface coating or leaving voids.
"Electrochemical migration" (ECM) is the growth of conductive metal filaments on or in a printed circuit board (PCB) under the influence of a DC voltage bias. Silver, zinc, and aluminum are known to grow whiskers under the influence of an electric field. Silver also grows conducting surface paths in the presence of halide and other ions, making it a poor choice for electronics use. Tin will grow "whiskers" due to tension in the plated surface. Tin-lead or solder plating also grows whiskers, only reduced by reducing the percentage of tin. Reflow to melt solder or tin plate to relieve surface stress lowers whisker incidence. Another coating issue is tin pest, the transformation of tin to a powdery allotrope at low temperature.
Solder resist application.
Areas that should not be soldered may be covered with solder resist (solder mask). The solder mask is what gives PCBs their characteristic green color, although it is also available in several other colors, such as red, blue, purple, yellow, black and white. One of the most common solder resists used today is called "LPI" (liquid photoimageable solder mask).  A photo-sensitive coating is applied to the surface of the PWB, then exposed to light through the solder mask image film, and finally developed where the unexposed areas are washed away. Dry film solder mask is similar to the dry film used to image the PWB for plating or etching. After being laminated to the PWB surface it is imaged and developed as LPI. Once but no longer commonly used, because of its low accuracy and resolution, is to screen print epoxy ink. In addition to repelling solder, solder resist also provides protection from the environment to the copper that would otherwise be exposed.
Legend / silkscreen.
A legend (also known as "silk" or "silkscreen") is often printed on one or both sides of the PCB. It contains the component designators, switch settings, test points and other indications helpful in assembling, testing, servicing, and sometimes using the circuit board.
There are three methods to print the legend:
Bare-board test.
Boards with no components installed are usually "bare-board tested" for "shorts" and "opens". This is called "electrical test" or "PCB e-test". A short is a connection between two points that should not be connected. An open is a missing connection between points that should be connected. For high-volume production, a fixture such as a "bed of nails" in a rigid needle adapter makes contact with copper lands on the board. The fixture or adapter is a significant fixed cost and this method is only economical for high-volume or high-value production. For small or medium volume production "flying probe" testers are used where test probes are moved over the board by an XY drive to make contact with the copper lands. There is no need for a fixture and hence the fixed costs are much lower. The CAM system "instructs" the electrical tester to apply a voltage to each contact point as required and to check that this voltage appears on the appropriate contact points and only on these.
Assembly.
In assembly the bare board is populated (or "stuffed") with electronic components to form a functional "printed circuit assembly" (PCA), sometimes called a "printed circuit board assembly" (PCBA). In through-hole technology, the component leads are inserted in holes surrounded by conductive "pads"; the holes keep the components in place. In surface-mount technology (SMT), the component is placed on the PCB so that the pins line up with the conductive "pads" or "lands" on the surfaces of the PCB; solder paste, which was previously applied to the pads, holds the components in place temporarily; if surface-mount components are applied to both sides of the board, the bottom-side components are glued to the board. In both through hole and surface mount, the components are then soldered; once cooled and solidified, the solder holds the components in place permanently and electrically connects them to the board.
There are a variety of soldering techniques used to attach components to a PCB. High volume production is usually done with a pick-and-place machine and bulk wave soldering for through-hole parts or reflow ovens for SMT components and/or through-hole parts, but skilled technicians are able to hand-solder very tiny parts (for instance 0201 packages which are 0.02 in. by 0.01 in.) under a microscope, using tweezers and a fine-tip soldering iron, for small volume prototypes. Selective soldering may be used for delicate parts. Some SMT parts cannot be soldered by hand, such as BGA packages. All through-hole components can be hand soldered, making them favored for prototyping where size, weight, and the use of the exact components that would be used in high volume production are not concerns.
Often, through-hole and surface-mount construction must be combined in a single assembly because some required components are available only in surface-mount packages, while others are available only in through-hole packages. Or, even if all components are available in through-hole packages, it might be desired to take advantage of the size, weight, and cost reductions obtainable by using some available surface-mount devices. Another reason to use both methods is that through-hole mounting can provide needed strength for components likely to endure physical stress (such as connectors that are frequently mated and demated or that connect to cables expected to impart substantial stress to the PCB-and-connector interface), while components that are expected to go untouched will take up less space using surface-mount techniques. "For further comparison, see the SMT page."
After the board has been populated it may be tested in a variety of ways:
To facilitate these tests, PCBs may be designed with extra pads to make temporary connections. Sometimes these pads must be isolated with resistors. The in-circuit test may also exercise boundary scan test features of some components. In-circuit test systems may also be used to program nonvolatile memory components on the board.
In boundary scan testing, test circuits integrated into various ICs on the board form temporary connections between the PCB traces to test that the ICs are mounted correctly. Boundary scan testing requires that all the ICs to be tested use a standard test configuration procedure, the most common one being the Joint Test Action Group (JTAG) standard. The JTAG test architecture provides a means to test interconnects between integrated circuits on a board without using physical test probes, by using circuitry in the ICs to employ the IC pins themselves as test probes. JTAG tool vendors provide various types of stimuli and sophisticated algorithms, not only to detect the failing nets, but also to isolate the faults to specific nets, devices, and pins.
When boards fail the test, technicians may desolder and replace failed components, a task known as "rework".
Protection and packaging.
PCBs intended for extreme environments often have a conformal coating, which is applied by dipping or spraying after the components have been soldered. The coat prevents corrosion and leakage currents or shorting due to condensation. The earliest conformal coats were wax; modern conformal coats are usually dips of dilute solutions of silicone rubber, polyurethane, acrylic, or epoxy. Another technique for applying a conformal coating is for plastic to be sputtered onto the PCB in a vacuum chamber. The chief disadvantage of conformal coatings is that servicing of the board is rendered extremely difficult.
Many assembled PCBs are static sensitive, and therefore they must be placed in antistatic bags during transport. When handling these boards, the user must be grounded (earthed). Improper handling techniques might transmit an accumulated static charge through the board, damaging or destroying components. The damage might not immediately affect function but might lead to early failure later on, cause intermittent operating faults, or cause a narrowing of the range of environmental and electrical conditions under which the board functions properly. Even bare boards are sometimes static sensitive: traces have become so fine that it is possible to blow a trace (or change its characteristics) with a static discharge. This is especially true on non-traditional PCBs such as MCMs and microwave PCBs.
Cordwood construction.
Cordwood construction can save significant space and was often used with wire-ended components in applications where space was at a premium (such as fuzes, missile guidance, and telemetry systems) and in high-speed computers, where short traces were important. In cordwood construction, axial-leaded components were mounted between two parallel planes. The name comes from the way axial-lead components (capacitors, resistors, coils, and diodes) are stacked in parallel rows and columns, like a stack of firewood. The components were either soldered together with jumper wire or they were connected to other components by thin nickel ribbon welded at right angles onto the component leads. To avoid shorting together different interconnection layers, thin insulating cards were placed between them. Perforations or holes in the cards allowed component leads to project through to the next interconnection layer. One disadvantage of this system was that special nickel-leaded components had to be used to allow reliable interconnecting welds to be made. Differential thermal expansion of the component could put pressure on the leads of the components and the PCB traces and cause mechanical damage (as was seen in several modules on the Apollo program). Additionally, components located in the interior are difficult to replace. Some versions of cordwood construction used soldered single-sided PCBs as the interconnection method (as pictured), allowing the use of normal-leaded components at the cost of being difficult to remove the boards or replace any component that is not at the edge.
Before the advent of integrated circuits, this method allowed the highest possible component packing density; because of this, it was used by a number of computer vendors including Control Data Corporation. The cordwood method of construction was used only rarely once PCBs became widespread, mainly in aerospace or other extremely high-density electronics.
Types.
Breakout boards.
A minimal PCB for a single component, used for prototyping, is called a breakout board. The purpose of a breakout board is to "break out" the leads of a component on separate terminals so that manual connections to them can be made easily. Breakout boards are especially used for surface-mount components or any components with fine lead pitch.
Advanced PCBs may contain components embedded in the substrate, such as capacitors and integrated circuits, to reduce the amount of space taken up by components on the surface of the PCB while improving electrical characteristics.
Multiwire boards.
Multiwire is a patented technique of interconnection which uses machine-routed insulated wires embedded in a non-conducting matrix (often plastic resin). It was used during the 1980s and 1990s. As of 2010, Multiwire was still available through Hitachi.
Since it was quite easy to stack interconnections (wires) inside the embedding matrix, the approach allowed designers to forget completely about the routing of wires (usually a time-consuming operation of PCB design): Anywhere the designer needs a connection, the machine will draw a wire in a straight line from one location/pin to another. This led to very short design times (no complex algorithms to use even for high density designs) as well as reduced crosstalk (which is worse when wires run parallel to each other—which almost never happens in Multiwire), though the cost is too high to compete with cheaper PCB technologies when large quantities are needed.
Corrections can be made to a Multiwire board layout more easily than to a PCB layout.
Uses.
Printed circuit boards have been used as an alternative to their typical use for electronic and biomedical engineering thanks to the versatility of their layers, especially the copper layer. PCB layers have been used to fabricate sensors, such as capacitive pressure sensors and accelerometers, actuators such as microvalves and microheaters, as well as platforms of sensors and actuators for Lab-on-a-chip (LoC), for example to perform polymerase chain reaction (PCR), and fuel cells, to name a few.
Repair.
Manufacturers may not support component-level repair of printed circuit boards because of the relatively low cost to replace compared with the time and cost of troubleshooting to a component level. In board-level repair, the technician identifies the board (PCA) on which the fault resides and replaces it. This shift is economically efficient from a manufacturer's point of view but is also materially wasteful, as a circuit board with hundreds of functional components may be discarded and replaced due to the failure of one minor and inexpensive part, such as a resistor or capacitor. This practice is a significant contributor to the problem of e-waste.
Legislation.
In many countries (including all European Single Market participants, the United Kingdom, Turkey, and China), legislation restricts the use of lead, cadmium and mercury in electrical equipment. PCBs sold in such countries must therefore use lead-free manufacturing processes and lead-free solder, and attached components must themselves be compliant.
Safety Standard UL 796 covers component safety requirements for printed wiring boards for use as components in devices or appliances. Testing analyzes characteristics such as flammability, maximum operating temperature, electrical tracking, heat deflection, and direct support of live electrical parts.


International Metalworking Companies

IMC International Metalworking Companies B.V., otherwise known as IMC Group, is the holding company of several worldwide manufacturers of metal cutting tools. Together they produces a wide range of carbide inserts, carbide endmills and cutting tools covering all metal cutting applications. The IMC Group is in the automotive, aerospace, die and mold, general engineering, bearing manufacturing and energy industries.
Subsidiaries.
Today, the IMC Group has over 130 subsidiaries in 65 countries.
Primary Subsidiaries:


6-8-6

Under the Whyte notation for the classification of steam locomotives by wheel arrangement, represents the arrangement of six unpowered leading wheels arranged into a three-axle leading truck, eight powered driving wheels, and six unpowered trailing wheels arranged into a three-axle trailing truck.
Other equivalent classifications are:
The only known example of the 6-8-6 wheel arrangement is the experimental Pennsylvania Railroad S2 steam turbine locomotive.


Huhtamaki PPL

Huhtamaki PPL Limited or HPPL (formerly: The Paper Products Limited) is an Indian multinational company specializing in flexible packaging and packaging solutions, founded in 1935 in Lahore. In 1999, the company became part of Huhtamäki Oyj, Finland. It has been involved in the field of packaging for over 80 years.
The company has its registered office in Mumbai, India; and as of 2016, has 14 manufacturing locations across India and sales offices in Mumbai, Delhi, Bangalore and Kolkata.
The company manufactures flexible laminates, films, specialized pouches, cartons, tube laminates, labels, shrink sleeves, rotogravure cylinders, packaging machinery etc. It caters to customers across sectors ranging from food and beverages, personal care to pharmaceuticals, industrial products etc.
History.
The company was founded in 1935 as ‘The Paper Products Limited’ by Mr. Sardarilal Talwar. The company’s first assignment was converting paper into paper products for the British Army Dairy, thus starting flexible packaging.
In the 1960s, the company moved from manufacturing packaging products using paper to using cellophane-based products for bread and biscuit packs, along with twist wraps.
In the 1980s, it started polymer-based packaging and created material for commercial use in the form of flexible packaging.
Products.
The company offers solutions such as Flexible Packaging, Specialised Pouches, Thermoforms, Shrink Sleeve Solutions, Decorative Packaging, Value added cartons and Security Solutions and Promotions.
Awards.
HPPL has received several awards (as The Paper Products Ltd); recent ones being:
Parent company.
Huhtamaki, headquartered in Espoo, Finland is a global packaging manufacturer and supplier for various applications. Its primary outputs include cartons and containers for foods and other consumer goods, disposable tableware and films and laminates for uses such as adhesives, plasters and labels.
It has 71 manufacturing units in 34 countries and a support staff of 15,800 globally. Its net sales in 2015 were approximately €2.7 billion.


CheckInstall

CheckInstall is a computer program for Unix-like operating systems which eases the installation and uninstallation of software compiled from source by making use of package management systems. After software compilation it can automatically generate a Slackware-, RPM-, or Debian-compatible package that can later be cleanly uninstalled through the appropriate package manager.
CheckInstall monitors the installation phase of a normal software build process and notes the files that are added to the system. It then builds a package that contains these files, using additional information gathered from the user. Finally, the files installed by the original run are removed and the package is installed using the system package tools, so the package will be properly registered in the local installed packages database.
The primary benefits provided by CheckInstall versus simply running codice_1 are the ability to remove the package from the system using the system packaging tools, and the ability to install the resulting package on multiple machines. CheckInstall is sometimes cited as a mechanism for creating packages by open source projects instead of creating numerous platform-specific build packages.
Usage.
Checkinstall is usually used after running a configure script and codice_2, as follows:
 ./configure
 make
 sudo checkinstall
After entering some information about the author and a package description, you will get the folder where the generated package has been saved to.


Butt welding

Butt welding is when two pieces of metal are placed end-to-end without overlap and then welded along the joint (as opposed to lap joint weld, where one piece of metal is laid on top of the other, or plug welding, where one piece of metal is inserted into the other). Importantly, in a butt joint, the surfaces of the workpieces being joined are on the same plane and the weld metal remains within the planes of the surfaces.
Common uses.
Butt welding is a commonly used technique in welding that can either be automated or done by hand on steel pieces. Butt welding can also be done with brazing for copper pieces. It is used to attach two pieces of metal together such as pipe, framework in factories, and also flanges. A flange is something that either is internal or external that provided to strengthen a piece of material. In factories butt welding has shown how economical it can be for companies to use when building things out of metal. This is because if they wanted to make something out of metal without welding it together they would have to bend everything and reinforce the structure which costs more than welding the two pieces together. Butt welding is accomplished by heating up two pieces of metal, or applying pressure, or doing both of those. Penetration while welding the metal is important to maintain and with thin pieces of metal this is possible however, with thick pieces edge preparation may have to be done to prepare the metal. Full penetration butt welds are made when they are in the within the parent(bigger, stronger) metal. In butt welding the strongest welds will have the fewest imperfections. To achieve this the heat input is controlled, which decreases the size of the weld. In commercial welding when this is done it also reduces cost but in order to maintain the strength of the weld double butt welds will be used. In butt welding there are two types used to achieve the specific welds and then there are also a variety of joints considered to be butt joints.
Butt welding is best performed with MIG or TIG welding applications due to their natural ability to connect two pieces of metal together. Using different types of welding electrodes for the welder will determine the properties of the weld such as its resistance against corrosion and strength. Electrodes conduct current through the metal being welded in order join the two pieces. The metal determines the type of welding that is required. The electrodes are either heavily or lightly coated. For the heavily coated electrodes are commonly used in structural welding because they are much stronger and corrosion resistant. The lightly coated electrodes are not as structurally sound. Butt welding is performed with the Arc, TIG, or MIG welder held at a slight angle the weld if the weld is laying flat in order to achieve the least amount of porosity in the weld and also to increase the weld's strength. Fillet welding make up about 80 percent of the connection despite being weaker than butt welds. The reason it is used more often is because fillet welds offer more room for error with much larger tolerances. Fillet welding is not a type of butt weld despite its similarities.
Types of butt welding.
Flash.
Flash butt welding is used with machinery and connects multiple pieces of metal together that are miss matched in size and shape. These different sizings can oftentimes cause for breaks in welding process. High voltage current is applied in order to connect the metal pieces together by applying it to both the components known as flashing in order to join them together.
Resistance.
This weld joins the two pieces of metal together by heat that comes from the pressure due to the metals being held together at a preset force. Resistance butt welding is used on joints that are of similar shape and size and often the weld is performed in one movement unlike flash welding.
Types of butt joints.
There are many different types of butt welding joints and they all are named with their particular shape. The joint also known as a square groove weld has many different forms in order to connect pieces of metal together and are all capable of bearing loads. There are many different types of joints such as lap joints, tee joints, butt joints, and also corner joints. Lap joints are two pieces that are end-over-end and welded together whereas butt welds are put end to end and connected that way. Butt welds are connected to each other with the thickness of the parent metal. There are many different kinds of butt welds such as square, single v, double v, single bevel, double bevel, single u, double u, single j, and also a double j. Minimizing the distortions in a weld is important however doing so will minimize the chances of full penetration. In order to get full penetration double welds such as double v, double j, and double u may be used.
Standards.
EN 1993-1-8, which covers the design of joints in the design of steel structures, defines a set of provisions for welding structural steel.


1973–74 European Cup Winners' Cup

The 1973–74 European Cup Winners' Cup football club tournament was won by Magdeburg in a final victory against defending champions Milan. It was the first–and only–win for an East German side in a European tournament.
First round.
Albania refused to play.
Second leg.
"Sunderland won 3-0 on aggregate."
"Sporting CP won 2-1 on aggregate."
"3-3 on aggregate, Zürich won on away goals."
"Malmö won 11-0 on aggregate."
"Magdeburg won 2-0 on aggregate."
"Baník Ostrava won 3-1 on aggregate."
"Beroe Stara Zagora won 11-1 on aggregate."
"Athletic Bilbao won 2-0 on aggregate."
"AC Milan won 4-1 on aggregate."
"Rapid Wien won 2-1 on aggregate."
"Lyon won 2-0 on aggregate."
"PAOK won 2-1 on aggregate."
"SK Brann won 9-0 on aggregate."
"Glentoran won 4-2 on aggregate."
"Borussia Mönchengladbach won 16-1 on aggregate."
"Rangers won 6-0 on aggregate."
Second round.
Second leg.
"Sporting CP won 3-2 on aggregate."
"1-1 on aggregate, Zürich won on away goals."
"Magdeburg won 3-2 on aggregate."
"Beroe Stara Zagora won 3-1 on aggregate."
"AC Milan won 2-0 on aggregate."
"PAOK won 7-3 on aggregate."
"Glentoran won 4-2 on aggregate."
"Borussia Mönchengladbach won 5-3 on aggregate."
Quarter-finals.
Second leg.
"Sporting CP won 4-1 on aggregate."
"Magdeburg won 3-1 on aggregate."
"Milan won 5-2 on aggregate."
"Borussia Mönchengladbach won 7-0 on aggregate."
Semi-finals.
Second leg.
"Magdeburg won 3-2 on aggregate."
"Milan won 2-1 on aggregate."


Rochester Midland Corporation

Rochester Midland Corporation is a closely-held specialty chemical manufacturing company headquartered in Ogden, New York. It has sales and operations in nearly seventy countries, production facilities in Ogden, New York, Aurora, Illinois. It was founded as Rochester Germicide in 1888.


Apple chip

Apple chips are chips or crisps that are prepared using apple. When stale, apple chips become drier and crispier. Contrary to modern belief, apple chips do not become chewier when stale, only harder. Apple chips may be fried, deep fried, vacuum fried, dehydrated or baked. Apple chips may have a dense and crispy texture, or may be puffed, yet still crispy. Microwave vacuum-drying may be used to prepare apple chips with a puffy and crispy texture. They may be seasoned with cinnamon and sweetened with confectioners sugar. Apple chips may be consumed as a snack food, and may be accompanied with various dips and other foods. Apple chips are mass-produced in the United States.
Use in dishes.
Apple chips may be used in sandwiches and as an ingredient in desserts and sweets, such as cookies. They may also be used as a garnish on dishes.
Manufacturers.
Apple chips are mass-produced by some food manufacturers. Companies that produce them include Seneca Foods, Bare Fruit, Buddy Fruits and Tyrrell's Bare Fruit and Buddy Fruits apple chips are prepared using only apples as their sole ingredient.


List of Hyundai transmissions

Hyundai Transys is an affiliate company of Hyundai Motor Group and produces a number of automobile transmissions, axles and seats in-house.
On January 1, 2019, Hyundai DYMOS and Hyundai Powertech were merged with Hyundai Transys.
Hyundai Powertech was established in 2001 as South Korea's first automatic transmission specialist. It has plants in South Korea, China, and the United States. Its automatic transmissions are used in Hyundai, Kia, Dodge, and Jeep vehicles.
Hyundai DYMOS produces MT based transmissions including DCT and AMT along with axles, 4WD and seats as automotive parts.
Automatic Transmission (AT).
Front wheel.
4-speed automatic.
A4F12/A4CF0.
Rated up to while having a dry weight of .
A4F16/A4CF1.
Rated up to while having a dry weight of .
A4F23/A4CF2.
Rated up to while having a dry weight of .
5-speed automatic.
A5F16.
Rated up to while having a dry weight of .
A5F23/A5GF1.
Rated up to while having a dry weight of .
A5HF1.
Rated up to
6-speed automatic.
A6F17.
Rated up to while having a dry weight of .
A6F18.
Rated up to while having a dry weight of .
A6F22/A6GF1.
Rated up to while having a dry weight of .
A6F24/A6MF1.
Rated up to while having a dry weight of . It is contracted by Chrysler Group LLC for use in 2013–2016 Dodge Dart and 2014-2016 Jeep Compass and Jeep Patriot, the transmission is designed to be maintenance-free under normal use and is assembled in South Korea.
A6F27/A6MF2.
Rated up to while having a dry weight of .
A6F28H/A6FMH/A6MF2H.
For Hybrid applications, rated up to while having a dry weight of .
A6F30.
Rated up to while having a dry weight of .
A6F33/A6LF1.
Rated up to while having a dry weight of .
A6F36/A6LF2.
Rated up to while having a dry weight of .
A6LF3.
Rated up to .
8-speed automatic.
A8F27/A8MF1.
Rated up to while having a dry weight of .
A8F36/A8LF1.
Rated up to while having a dry weight of .
A8F42/A8LF2.
Rated up to while having a dry weight of .
A8FLH.
For Hybrid applications, rated up to (motor only) or total output.
Rear wheel.
5-speed automatic.
A5R25.
Rated up to while having a dry weight of .
A5R35/A5SR1.
Rated up to while having a dry weight of .
A5R45/A5SR2.
Rated up to while having a dry weight of .
8-speed automatic.
A8R40/A8LR1.
Rated up to while having a dry weight of .
A8R50/A8TR1.
Rated up to while having a dry weight of .
Continuously Variable Transmission (CVT).
Kappa CVT.
Rated up to or , supports idle stop and go functions.
Gamma CVT CF18/C0GF1.
Rated up to , supports idle stop and go functions.
CF28.
Rated up to .
Dual Clutch Transmission (DCT).
6-speed dual clutch.
D6GF1.
Rated up to while having a dry weight of . This transmission uses dry clutch.
D6KF1/D6F27H.
For Hybrid applications, rated up to while having a dry weight of . This transmission uses dry clutch.
7-speed dual clutch.
D7GF1/D7F22.
Rated up to while having a dry weight of . This transmission uses dry clutch.
D7UF1/D7F34.
Rated up to while having a dry weight of . This transmission uses dry clutch.
8-speed dual clutch.
D8LF1/D8F48W.
Rated up to . This transmission uses wet clutch.
Automated Manual Transmission (AMT).
5-Speed AMT.
S5F13.
Rated up to .
Manual Transmission (MT).
Front Wheel.
5-speed manual.
M5EF2/M5F13.
Rated up to while having a dry weight of
M5AF3/M5F14.
Rated up to while having a dry weight of
M5CF1/M5F16.
Rated up to while having a dry weight of
M5BF2/M5CF2/M5F19.
Rated up to while having a dry weight of
M5GF1/M5F25.
Rated up to while having a dry weight of
M5GF2.
Rated up to
M5HF2.
Rated up to
6-speed manual.
M6CF1/M6F17.
Rated up to while having a dry weight of
M6CF3/M6F28-1.
Rated up to while having a dry weight of
M6CF4/M6F28-2.
Rated up to while having a dry weight of
M6LF1/M6F44.
Rated up to while having a dry weight of
Rear Wheel.
5-speed manual.
M5R18.
Rated up to while having a dry weight of
M5R23.
Rated up to while having a dry weight of
M5R26.
Rated up to while having a dry weight of
M5R32.
Rated up to while having a dry weight of
M5R36.
Rated up to while having a dry weight of
6-speed manual.
M6R26.
Rated up to while having a dry weight of
M6R34.
Rated up to while having a dry weight of
M6R37.
Rated up to while having a dry weight of
M6R40.
Rated up to .
Reduction Gear.
Shift by Cable (SBC).
G1F24.
Rated up to while having a dry weight of , its used in the Kia Ray EV
G1F30.
Rated up to while having a wet weight of , its used in the Hyundai Avante EV, Kia KX3 EV and Kia Soul EV.
G1F36.
Rated up to while having a wet weight of , its used in the Tucson Fuel Cell EV.
Shift by Wire (SBW).
G1F24.
Rated up to while having a wet weight of , its used in the Hyundai Ioniq EV.
G1F26.
Rated up to while having a wet weight of , its used in the Hyundai Nexo, Hyundai Kona EV (OS), Kia Niro EV and Kia Soul EV.
G1F32.
Rated up to while having a wet weight of .


Semiembossed film

Semiembossed film is used as a liner to the calendared rubber to retain the properties of rubber and also to prevent dust and other foreign matters from sticking to the rubber while calendaring and during storage. It is manufactured with 100% virgin low-density polyethylene. The raw material is extruded and cast on the embossed roll and cooled. It can be of any color. Milky white, French blue, red and yellow are standard colors. The diamond-shaped embossing in the film helps in the easy removal of air between the film and the rubber. Semiembossed film is used by tyre manufacturers, tread and bonding gum manufacturers, conveyor belt manufacturers and other rubber coated fabric manufacturers.
Film embossing process.
Film embossing is a mechanical process in which a flat film is transformed into an embossed product. During the process, thermal and stress fields are applied to the polymer, causing changes in the microstructure and physical dimensions of the material. The engineering analysis of the process requires the study of various aspects relating to the characterization of the microstructure before and after embossing, A variety of techniques were employed to characterize the properties and microstructure of the embossed film in relation to crystallinity, orientation, mechanical properties, and dimensions of the embossed films. The thermal treatment of the polymer film was shown to be the most significant factor in the process. By controlling the thermal treatment of the film, it is possible to manipulate the properties and dimensions of the embossed film. The important aspects: influencing thermal treatment include the radiation heater temperature, preheat roll temperature, line velocity, and film thickness. The initial film orientation and embossing pressure have a minor effect on the final properties of the embossed film. The main effect of the embossing pressure is on the bulk thickness of the embossed film.


Shut-off nozzle

Shut-off nozzles are used in the manufacturing process of plastic injection molding. Machine shut-off nozzles serve as the connection between the plasticizing barrel (with reciprocating screw) and the mold. They are mounted on the machineside of the plastic injection molding process, unlike hot runner nozzles which are mounted on the moldside of the process. Machine shut-off nozzles differ from open nozzles because of their closable melt channel.
Reasons for using.
Shut-off nozzles are used to avoid drooling of the melt and stringing, as well as to feed with a retracted nozzle.
Types.
Shut-off nozzles can be self-controlled or externally controlled.
Self-controlled.
The needle keeps the nozzle orifice closed by spring pressure. When the injection pressure increases, the melt will push back on the needle head and try to open the nozzle. Once the melt inside the nozzle reaches a certain amount of pressure, it will succeed in pushing the needle back against the spring. There must, therefore, be a minimum pressure for the opening process to overcome the force of the spring. Once the nozzle opens, the pressure will drop again and the spring-operated needle will close the nozzle tip orifice.
Externally actuated.
The nozzle is opened by external force, independent of the melt-pressure. The shut-off nozzle’s actuation is hydraulically or pneumatically driven. Externally actuated shut-off nozzles can have different ways of closing the melt stream. Due to the fact that they operate independently of melt-pressure, they can be used for a range of applications such as melt pre-compression, physical and chemical foaming and high-speed injection molding.
Needle.
The melt flow is shut off via a melt channel-axis positioned needle moving back and forth according to actuation. This nozzle type shuts off the melt stream directly at the nozzle orifice-mold interface which prevents drooling.
Bolt.
A shut-off bolt, positioned perpendicular to the melt channel moves up and down according to actuation, and thus shuts off/opens the melt flow. This nozzle type has a single melt channel. It therefore does not require rerouting of the melt around the shut-off mechanism. This makes it more suitable for processing of large volumes as well as shear sensitive materials.
Rotary.
This nozzle type is fitted with a rotatable bolt assembly which has a cavity equal in size to the melt channel. In its open position, the bolt cavity is directly aligned with the melt stream. When the actuator rotates the bolt assembly, the cavity becomes misaligned and thus shuts off the melt flow.


Self-lubricating chain

Self-lubricating chains, also referred to as lube-free chains, are commonly found in both roller chain (ANSI Standards, British Standards, and DIN Standards) and conveyor chain varieties, with specialty self-lubricating chains also available. These chains utilize a bush made of an oil-impregnated sintered metal or plastic to provide continuous lubrication to the chain during drive, eliminating the need for further lubrication.
History.
While some of the earliest self-lubricating bearings were developed by Chrysler the earliest self-lubricating chains were bushed chains, which consisted of pins, plates, and sintered bushes. The loss in strength of the bush required it to be made extra thick. This made the outer diameter so large that it did not allow enough room for a roller. These bushed chains suffer from the drawback of lower allowable load and tensile strength compared to regular roller chain, and the outer diameter of the bushes do not rotate when engaging a sprocket and may suffer faster wear and damage.
While various chain manufacturers offered self-lubricating bushed chain designs based on sintered-bush technology since the 1950s, the world's first self-lubricating roller chain was developed and launched by a Japanese chain manufacturer in 1988. After they made further improvements to the oil impregnation and sintering technologies, they received a patent for their lube-free roller chain, as evidenced by Patent #JP20070237969. In the new design, advancements in powder metal bush technology allowed engineers to design a bush that had a smaller diameter yet was stronger, which allowed room for rollers. These rollers improved performance by allowing the chain to articulate more smoothly into sprockets and protect the sintered bushes. Because of these advancements, the self-lubrication style chains achieved strength on par with regular roller chain, with the added benefit of being lube-free.
Powdered metal sintered bearings (in the case of roller chain, the bushes) are self-lubricating because their porosity is impregnated with lubricants during the manufacturing process. In use, frictional heat causes the lubricant to expand and flow out of the pores, forming a film between mating parts. Low coefficients of friction, minimal maintenance and trouble-free service life, low cost, and simple installation are the chief advantages of powdered metal bearings.
Construction.
As with standard roller chains, self-lubricating roller chains consist of five basic parts: inner plates, outer plates, pins, bushes, and rollers. However, the bushes for self-lubricating chains are sintered metal, produced using powder metallurgy. Self-lubricating chains can be manufactured cheaply, quickly, and to precision tolerances. To form the bushings, alloyed powdered metal is mixed, compacted, and sintered. The initial compaction to a large degree dictates the density, shape, dimensions, and mechanical properties of the finished part. Sintered materials have inherent porosity, and the pores have both beneficial and detrimental effects on part performance. The pores act as stress concentration zones and reduce mechanical strength and ductility. However, the pores also reduce noise and vibration and serve as lubricant pockets in lubricated contacts. Sintered bearings and gears are used in many applications where the external lubrication is not possible or not preferred. It is essential that the pores form an interconnected system of controlled size and volume, so that oil is supplied to the entire bearing surface. The rate of oil supply increases with temperature and therefore with increasing speeds of rotation, improving performance.
Applications.
Self-lubrication is ideal in situations where normal lubrication is difficult, troublesome, or impossible. For example, in paper and food processing, lubrication is undesirable due to product contamination. (Chain companies like Tsubaki, Nishiyama and Renold PLC also offer sintered bushes impregnated with food grade lubricant.)
Self-lubricating bushes are used in conveyor chains as well as roller chains for a variety of conveyance applications. These could include not only RS attachment roller chain, but small size conveyor chains and a wide variety of top chains as well.


Design knowledge

There is a large body of knowledge that designers call upon and use during the design process to match the ever-increasing complexity of design problems. Design knowledge can be classified into two categories: product knowledge and design process knowledge.
Product Knowledge.
Product knowledge has been fairly studied and a number of modeling techniques have been developed. Most of them are tailored to specific products or specific aspects of the design activities. For example, geometric modeling is used mainly for supporting detailed design, while knowledge modeling is working for supporting conceptual designs. Based on these techniques, a design repository project at NIST attempts to model three fundamental facets of an artifact representation: the physical layout of the artifact (form), an indication of the overall effect that the artifact creates (function), and a causal account of the operation of the artifact (behavior). The recent NIST research effort towards the development of the basic foundations of the next generation of CAD systems suggested a core representation for design information called the NIST core product model (CPM) and a set of derived models defined as extensions of the CPM (e.g.). The NIST core product model has been developed to unify and integrate product or assembly information. The CPM
provides a base-level product model that is: not tied to any vendor software; open; non-proprietary; expandable; independent of any one product development process; capable of capturing the engineering context that is most commonly shared in product development activities. The core model focuses on artifact representation including function, form, behavior, material, physical and functional decompositions, and relationships among these concepts. The entity-relationship data model influences the model heavily; accordingly, it consists of two sets of classes, called object and relationship, equivalent to the UML class and association class, respectively.
Design Process Knowledge.
Design process knowledge can be described in two levels: design activities and design rationale. The importance of representation for design rationale has been recognized but it is a more complex issue that extends beyond artifact function. The design structure matrix (DSM) has been used for modeling design process (activities) and some related research efforts have been conducted. For example, a web-based prototype system for modeling the product development process using a multi-tiered DSM is developed at MIT. However, few research endeavors have been found on design rationale.
Representation Scenarios.
In terms of representation scenarios, design knowledge can also be categorized into off-line and on-line knowledge. Design process knowledge can be categorized into ontologies.
Off-line Knowledge.
Offline Knowledge refers to existing knowledge representation, including design knowledge in handbook and design ‘‘know-how’’, etc.; the latter refers to the new design knowledge created in the course of design activities by designers themselves. For the off-line knowledge, there are two representation approaches. One is to highly abstract and categorize existing knowledge including experiences into a series of design principles, rationales and constraints. TRIZ is a good instance of this approach. The other is to represent a collection of design knowledge into a certain case for description. Case-based design is an example of this approach. The key issue is on the computerization of the
design knowledge representation. For instance, researchers at the Engineering Design Centre at Lancaster University, UK established a unique knowledge representation methodology and knowledge base vocabulary based on the theory of domains, design principles and computer modeling. They developed a software tool for engineering knowledge management. The tool provides an engineering system designer with the capability to search a knowledge base of past solutions, and other known technologies to explored viable alternatives for product design.
On-line Knowledge.
On-line knowledge representation is capturing the dynamic design knowledge in a certain format for design re-use and archive. A few research efforts have been found in this area. Blessing proposes the process-based support system (PROSUS) based on a model of the design process rather than the product. It uses a design matrix to represent the design process as a structured set of issues and activities. Together with the common product data model (CPDM), PROSUS supports the capture of all outputs of the design activity.
Ontologies.
Ontologies are being used for product representation (e.g.). Research suggests that there is a need to provide computer support that will supply clear and complete design knowledge and also facilitate designer intervention and customization during the decision-making activities in the design process. For example, WebCADET is a design support system that uses distributed Web-based AI tools. It uses the AI as text approach, where knowledge-based systems (KBSs) can be seen as a medium to facilitate the communication of design knowledge between designers. The system can provide support for designers when searching for design knowledge.


Jump rings

Jump rings are (usually metal) rings used to make chains, jewellery and chain mail. They are made by wrapping wire around a mandrel to make a coil, then cutting the coil with wire cutters to make individual rings. The rings can be assembled one by one into chains, earrings, objects such as bowls or ornaments, and chain mail clothing.
The making of items from jump rings is called "chain maille" (""maille" is French for "mesh"").
Jump rings can be described by the following qualities:


Planer (metalworking)

A planer is a type of metalworking machine tool that uses linear relative motion between the workpiece and a single-point cutting tool to cut the work piece. A planer is similar to a shaper, but larger, and with workpiece moving, whereas in a shaper the cutting tool moves.
Applications.
Linear planing.
The most common applications of planers and shapers are linear-toolpath ones, such as:
Helical planing.
Although the archetypal toolpath of a planer is linear, helical cutting can be accomplished by coupling the table's linear motion to simultaneous rotation. The helical planing idea is similar to both helical milling and single-point screw cutting.
Current Usage.
Planers and shapers are now obsolescent, because other machine tools (such as milling machines, broaching machines, and grinding machines) have mostly eclipsed them as the tools of choice for doing such work. However, they have not yet disappeared from the metalworking world. Planers are used by smaller tool and die shops within larger production facilities to maintain and repair large stamping dies and plastic injection molds. Additional uses include any other task where an abnormally large (usually in the range of 4'×8' or more) block of metal must be squared when a (quite massive) horizontal grinder or floor mill is unavailable, too expensive, or otherwise impractical in a given situation. As usual in the selection of machine tools, an old machine that is in hand, still works, and is long since paid-for has substantial cost advantage over a newer machine that would need to be purchased. This principle easily explains why "old-fashioned" techniques often have a long period of gradual obsolescence in industrial contexts, rather than a sharp drop-off of prevalence such as is seen in mass-consumer technology fashions.
Configurations and sizes.
There are two types of planers for metal: double-housing and open-side. The double-housing variety has vertical supports on both sides of its long bed; the open-side variety has a vertical support on only one side, allowing the workpiece to extend beyond the bed. Metal planers can vary in size from a table size of 30"×72" to 20'×62', and in weight from around 20,000 lbs to over 1,000,000 lbs.
History.
Early planing ideas are known to have been underway in France in the 1750s. In the late 1810s, a variety of pioneers in various British shops (including James Fox, George Rennie, Matthew Murray, Joseph Clement, and Richard Roberts) developed the planer into what we today would call a machine tool. The exact details have been contentious and will probably never be known, because the development work being done in various shops was undocumented for various reasons (partially because of proprietary secrecy, and also simply because no one was taking down records for posterity). Roe (1916) provides a short chapter that tells the story as thoroughly as he was able to discover it.


Lead time

A lead time is the latency between the initiation and completion of a process. For example, the lead time between the placement of an order and delivery of new cars by a given manufacturer might be between 2 weeks and 6 months, depending on various particularities. One business dictionary defines "manufacturing lead time" as the total time required to manufacture an item, including order preparation time, queue time, setup time, run time, move time, inspection time, and put-away time. For make-to-order products, it is the time between release of an order and the production and shipment that fulfill that order. For make-to-stock products, it is the time taken from the release of an order to production and receipt into finished goods inventory.
Supply chain management.
A conventional definition of lead time in a supply chain management context is the time from the moment the customer places an order (the moment the supplier learns of the requirement) to the moment it is ready for delivery. In the absence of finished goods or intermediate (work in progress) inventory, it is the time it takes to actually manufacture the order without any inventory other than raw materials. The Chartered Institute of Procurement & Supply identifies "total lead time" as a combination of "internal lead time" (the time required for the buying organisation's internal processes to progress from identification of a need to the issue of a purchase order) and "external lead time" (the time required for the supplying organisation's processes, including any development required, manufacture, dispatch and delivery).
Manufacturing.
In the manufacturing environment, lead time has the same definition as that of Supply Chain Management, but it includes the time required to ship the parts from the supplier. Shipping time is included because the manufacturing company needs to know when the parts will be available for material requirements planning purposes. It is also possible to include within lead time the time it takes for a company to process and have the part ready for manufacturing once it has been received. The time it takes a company to unload a product from a truck, inspect it, and move it into storage ("put-away time") is not trivial. With tight manufacturing constraints or when a company is using Just In Time manufacturing, it is important for supply chain to know how long their own internal processes take.
Lead time consists of:
Example
Company A needs a part that can be manufactured in two days once Company B has received an order. It takes three days for company A to receive the part once shipped, and one additional day before the part is ready to go into manufacturing.
In more detail
Lead Time terminology has been defined in greater detail. The Supply Chain from customer order received to the moment the order is delivered is divided into five lead times.
Example
A restaurant opens up and a customer walks in. A waiter guides him to a table, gives him the menu and asks what he would like to order. The customer selects a dish and the waiter writes it in his notepad. At that moment the customer has made an order which the restaurant has accepted – Order Lead Time and Order Handling Time have begun. Now the waiter marks the order in the cash register, rips the paper from the notepad, takes it into the kitchen and puts into the order queue. The order has been handled and is waiting in the factory (kitchen) for manufacturing. As there are no other customers, the waiter decides to stand outside the kitchen, by the door, waiting for the dish to be prepared and begins calculating Manufacturing Lead Time.
Meanwhile, the chef finishes what he was doing, takes the order from the queue, starts his clock as a mark for the start of Production Lead Time and begins cooking. The chef chops the vegetables, fries the meat and boils the pasta. When the dish is ready, the chef rings a bell and stops his clock. At the same time, the waiter stops calculating Manufacturing Lead Time and rushes through the kitchen door to get the food while it is hot.
When he picks it up, he begins timing the Delivery Lead Time that ends when the dish is served to the customer, who can now happily say that the Order Lead Time was shorter than he had expected.
Possible ways of shortening the lead time:
To best meet the customer needs, a company should work towards the shortest possible lead time in manufacturing, production, and delivery. It can be helped by:
Order lead time.
When talking about Order Lead Time (OLT) it is important to differentiate between the definitions that may exist around this concept. Although they look similar, there are differences between them that help the industry to model the order behavior of their customers. The four definitions are :
OLT formulas.
The OLTRequested will be determined by the difference between the date the customer wants the material in his facilities (wish date) and the date when they provided its order to the supplier.
The OLTQuote will be determined by the difference between the date the customer agree to receive the material in their facilities (Quote date) and the date when the order is provided to the supplier.
The OLTActual will be determined by the difference between the day the provider deliver the material (Delivery date) and the date when they enter the order in the system.
The OLTConfirmed will be determined by the difference between the date the confirmed date by the provider to deliver the material in the customer facilities (Confirmed date) and the date when they provide the order to the supplier.
Average OLT based on volume.
The Average OLT based on Volume (OLTV) is the addition of all the multiplications between the volume of product we deliver (quantity) and the OLT divided by the total quantity delivered in the period of time we are studying for that specific facility.
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By doing this the company will be able to find a relation of volume weighted between the quantities of material required for an order and the time requested to accomplish it. The volume metric could be applied to the 4 types of OLT.
The figure obtained from this calculation will be the average time (e.g. in days) between order placing and the requested delivery date of a specific customer under consideration of the average quantities ordered during that particular time.
Potential application areas for order lead time measurement.
The correct analysis of OLT will give the company:
Project management.
In project management, lead time is the time it takes to complete a task or a set of interdependent tasks. The lead of the entire project would be the overall duration of the critical path for the project.
According to the PMBOK (7th edition) by the Project Management Institute (PMI), lead time is the "time between a customer request and the actual delivery." The lead time is a deliverable metric and a customary measure. The lead time shows the amount of elapsed time from a chunk of work or story entering the backlog, to the end of the iteration or release. A smaller lead time means that the process is more effective and the project team is more productive.
Lead time is also the saved time by starting an activity before its predecessor is completed.
According to the PMBOK (7th edition) by PMI, lead is "The amount of time whereby a successor activity can be advanced with respect to a predecessor activity". An example would be scheduling the start of a 2-week activity dependent with the finish of the successor activity with a lead of 2 weeks so they will finish at the same time.
Journalism.
Lead time in publishing describes the amount of time that a journalist has between receiving a writing assignment and submitting the completed piece. Depending on the publication, lead times can be anything from a couple of hours to many months/years.
Medicine.
Lead time (when referring to a disease) is the length of time between detection of a disease through screening and the moment in time where it would have normally presented with symptoms and led to a diagnosis. An example of this is seen with breast cancer population screening, where women who are asymptomatic have a positive test result with mammography, whereas the underlying disease would have taken many more years to manifest.
Video games.
Lead time in video games can refer to the amount of time certain special, important actions in high-twitch action games, such as using health-recovering items, may need to take in order to be completed successfully. Lead time can be used to prevent players from abusing helpful abilities or items by making them a little more difficult to use safely, requiring some strategy, risk or caution.


Solder alloys

Solder is a metallic material that is used to connect metal workpieces. The choice of specific solder alloys depends on their melting point, chemical reactivity, mechanical properties, toxicity, and other properties. Hence a wide range of solder alloys exist, and only major ones are listed below. Since early 2000s the use of lead in solder alloys is discouraged by several governmental guidelines in the European Union, Japan and other countries, such as Restriction of Hazardous Substances Directive and Waste Electrical and Electronic Equipment Directive.
Solder alloys.
Notes on the above table.
In the Sn-Pb alloys, tensile strength increases with increasing tin content. Indium-tin alloys with high indium content have very low tensile strength.
For soldering semiconductor materials, e.g. die attachment of silicon, germanium and gallium arsenide, it is important that the solder contains no impurities that could cause doping in the wrong direction. For soldering n-type semiconductors, solder may be doped with antimony; indium may be added for soldering p-type semiconductors. Pure tin can also be used.
Various fusible alloys can be used as solders with very low melting points; examples include Field's metal, Lipowitz's alloy, Wood's metal, and Rose's metal.
Properties.
The thermal conductivity of common solders ranges from 30 to 400 W/(m·K), and the density from 9.25 to 15.00 g/cm3.