A toast rack or toastrack is a serving piece having vertical partitions (usually from five to eight in number) connected to a flat base, used for holding slices of toast . It often has a central ring handle for carrying and passing round the table.
105-545: The term toast rack is also used in other fields, notably railways and architectural design, usually as a derivative term for objects resembling a toast rack (see below). The earliest known examples of toast racks date from the 1770s. They have been made in large quantities since then and are still being made today. By maintaining air gaps between the slices, the toast rack allows water vapor to escape from hot toast instead of condensing into adjacent slices and making them soggy. However, this increased air flow can also mean that
210-422: A filler metal called solder . The soldering process involves heating the surfaces to be joined and melting the solder, which is then allowed to cool and solidify, creating a strong and durable joint. Soldering is commonly used in the electronics industry for the manufacture and repair of printed circuit boards (PCBs) and other electronic components. It is also used in plumbing and metalwork , as well as in
315-602: 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
420-426: 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
525-646: A catalytic tip to heat a bit, without flame, are used for portable applications. Hot-air guns and pencils allow rework of component packages (such as surface mount devices) which cannot easily be performed with electric irons and guns. For non-electronic applications, soldering torches use a flame rather than a soldering tip to heat solder. Soldering torches are often powered by butane and are available in sizes ranging from very small butane/oxygen units suitable for very fine but high-temperature jewelry work, to full-size oxy-fuel torches suitable for much larger work such as copper piping. Common multipurpose propane torches,
630-830: A complex circuit board in one operation, vastly reducing production cost of electronic devices. Musical instruments, especially brass and woodwind instruments, use a combination of soldering and brazing in their assembly. Brass bodies are often soldered together, while keywork and braces are most often brazed. The solderability of a substrate is a measure of the ease with which a soldered joint can be made to that material. Some metals are easier to solder than others. Copper, zinc, brass, silver and gold are easy. Iron, mild steel and nickel are next in difficulty. Because of their thin, strong oxide films, stainless steel and some aluminium alloys are even more difficult to solder. Titanium , magnesium , cast irons , some high-carbon steels , ceramics , and graphite can be soldered but it involves
735-400: A flame or carbon arc torch to achieve the melting of the filler. Soft solder filler metals are typically alloys (often containing lead ) that have liquidus temperatures below 350 °C (662 °F). In this soldering process, heat is applied to the parts to be joined, causing the solder to melt and to bond to the workpieces in a surface alloying process called wetting . In stranded wire,
840-460: 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
945-418: 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
1050-430: A heated iron whereas the other methods typically require a higher temperature torch or a furnace to melt the filler metal. Different equipment is usually required since a soldering iron cannot achieve high enough temperatures for hard soldering or brazing. Brazing filler metal is stronger than silver solder, which is stronger than lead-based soft solder. Brazing solders are formulated primarily for strength, silver solder
1155-422: A joint. A good solder joint produces an electrically conductive, water- and gas-tight join. Each type of solder offers advantages and disadvantages. Soft solder is so called because of the soft lead that is its primary ingredient. Soft soldering uses the lowest temperatures (and so thermally stresses components the least) but does not make a strong joint and is unsuitable for mechanical load-bearing applications. It
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#17328555273351260-577: A large thermal mass to store enough heat for soldering large areas before needing re-heating in the fire; the larger the head, the longer the working time. The copper surface of the tool must be constantly cleaned and re-tinned during use. Historically, soldering coppers were standard tools used in auto bodywork, although body solder has been mostly superseded by spot welding for mechanical connection, and non-metallic fillers for contouring. During WW2 and for some time afterwards SOE forces used small pyrotechnic self-soldering joints to make connections for
1365-404: A lesser extent steel and zinc. This mechanical soldering is similar to a low temperature brazing operation, in that the mechanical characteristics of the joint are reasonably good and it can be used for structural repairs of those materials. The American Welding Society defines brazing as using filler metals with melting points over 450 °C (842 °F) — or, by the traditional definition in
1470-783: 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 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
1575-428: A metal chassis, while large irons have tips too cumbersome for working on printed circuit boards (PCBs) and similar fine work. A 25-watt iron will not provide enough heat for large electrical connectors, joining copper roof flashing, or large stained-glass lead came. On the other hand, a 100-watt iron may provide too much heat for PCBs. Temperature-controlled irons have a reserve of power and can maintain temperature over
1680-583: A non-conductive substrate. Electrical components may be fixed to conductive pads on the outer layers, generally by means of soldering , which both electrically connects and mechanically fastens the components to the board. Another manufacturing process adds vias , drilled holes that allow electrical interconnections between conductive 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
1785-446: 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
1890-636: 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. The Austrian engineer Paul Eisler invented
1995-839: A process similar to joining carbides: they are first plated with a suitable metallic element that induces interfacial bonding. Soldering filler materials are available in many different alloys for differing applications. In electronics assembly, the eutectic alloy with 63% tin and 37% lead (or 60/40, which is almost identical in melting point) has been the alloy of choice. Other alloys are used for plumbing, mechanical assembly, and other applications. Some examples of soft-solder are tin-lead for general purposes, tin-zinc for joining aluminium , lead-silver for strength at higher than room temperature, cadmium-silver for strength at high temperatures, zinc-aluminium for aluminium and corrosion resistance, and tin-silver and tin-bismuth for electronics. A eutectic formulation has advantages when applied to soldering:
2100-595: 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 its Cledo Brunetti Award for early key contributions to
2205-409: A pump in a bath of liquid solder produces an elevated "wave" of solder which the part is quickly passed through. Wave soldering uses surface tension to keep solder from bridging the insulating gaps between the copper lines of flux-coated printed wiring boards / printed circuit boards . The electric soldering iron is widely used for hand-soldering, consisting of a heating element in contact with
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#17328555273352310-407: A torch or other high temperature source and darkened goggles to protect the eyes from the bright light produced by the white-hot work. It is often used to repair cast-iron objects, wrought-iron furniture, etc. Soldering operations can be performed with hand tools, one joint at a time, or en masse on a production line. Hand soldering is typically performed with a soldering iron , soldering gun , or
2415-418: A torch, or occasionally a hot-air pencil. Sheetmetal work was traditionally done with "soldering coppers" directly heated by a flame, with sufficient stored heat in the mass of the soldering copper to complete a joint; gas torches (e.g. butane or propane) or electrically heated soldering irons are more convenient. All soldered joints require the same elements of cleaning of the metal parts to be joined, fitting up
2520-433: A very mild 'no-clean' flux might be perfectly acceptable for production equipment, but not give adequate performance for more variable hand-soldering operations. Different types of soldering tools are made for specific applications. The required heat can be generated from burning fuel or from an electrically operated heating element or by passing an electric current through the item to be soldered. Another method for soldering
2625-436: A wide range of work. A soldering gun heats a small cross-section copper tip very quickly by conducting a large AC current through it using a large cross-section one-turn transformer; the copper tip then conducts the heat to the part like other soldering irons. A soldering gun will be larger and heavier than a heating-element soldering iron of the same power rating because of the built-in transformer. Gas-powered irons using
2730-440: 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,
2835-451: Is fire retardant , the dielectric constant (e r ), the loss tangent (tan δ), the tensile strength , the shear strength , the glass transition temperature (T g ), 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
2940-437: 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
3045-402: 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 a 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 or between sheet layers of
3150-477: 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. Often encountered materials: Less-often encountered materials: Copper thickness of PCBs can be specified directly or as
3255-420: Is also unsuitable for high-temperature applications as it loses strength, and eventually melts. Silver soldering, as used by jewelers, machinists and in some plumbing applications, requires the use of a torch or other high-temperature source, and is much stronger than soft soldering. Brazing provides the strongest of the non-welded joints but also requires the hottest temperatures to melt the filler metal, requiring
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3360-468: 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
3465-451: 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
3570-443: Is commonly referred to as "The Toast Rack" by local estate agents and residents, owing to its appearance on street plans which seems to resemble the shape of a toast rack. The 'toast rack passenger carriage' has been a design feature of railways since their inception, with the name particularly common on miniature and light railways, where it refers to open-sided carriages (with or, especially on miniature railways, without roofs) where
3675-418: Is equivalent in quality to an 8-layer through-hole PCB, so HDI technology can reduce costs. HDI PCBs are often made using build-up film such as ajinomoto build-up film, which is also used in the production of flip chip packages. Some PCBs have optical waveguides, similar to optical fibers built on the PCB. A basic PCB consists of a flat sheet of insulating material and a layer of copper foil , laminated to
3780-632: Is estimated to reach $ 79 billion by 2024. 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
3885-519: Is fully separated from the next by upright seats, again resembling the toast rack design. At these larger gauges the coaches may be fully enclosed, or 'semi-open' (with roofs and sides, but unglazed windows). Many railways have examples of toast rack carriages, and some (for example the Vale of Rheidol Railway in Wales ) are known for a distinct preference for the design in their rolling stock fleet. On tramways of
3990-565: Is often referred to as "The Toast Rack", due to its unusual architectural design. The appearance is compounded by the fact that the building was constructed to house a department of domestic science. A neighbouring building, by the same architect, is said to resemble a fried egg. The building was Grade II listed in 1998 and was described by the prolific architectural critic, Nikolaus Pevsner as "a perfect piece of pop architecture". An affluent block of streets in Wandsworth , South West London (SW18),
4095-481: Is somewhat absorbed by the surrounding metal, resulting in a joint that is actually stronger than the metal being joined. The metal being joined must be perfectly flush, as silver solder cannot normally be used as a filler and will not fill gaps. Another difference between brazing and soldering is how the solder is applied. In brazing, one generally uses rods that are touched to the joint while being heated. With silver soldering, small pieces of solder wire are placed onto
4200-468: 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 US, copper foil thickness
4305-409: Is to facilitate the soldering process. One of the obstacles to a successful solder joint is an impurity at the site of the joint; for example, dirt, oil or oxidation . The impurities can be removed by mechanical cleaning or by chemical means, but the elevated temperatures required to melt the filler metal (the solder) encourages the work piece (and the solder) to re-oxidize. This effect is accelerated as
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4410-426: Is to place solder and flux at the locations of joints in the object to be soldered, then heat the entire object in an oven to melt the solder; toaster ovens and hand-held infrared lights have been used by hobbyists to replicate production soldering processes on a much smaller scale. A third method of soldering is to use a solder pot where the part (with flux) is dipped in a small heated iron cup of liquid solder, or
4515-421: Is used by jewelers to protect the precious metal and by machinists and refrigeration technicians for its tensile strength but lower melting temperature than brazing, and the primary benefit of soft solder is the low temperature used (to prevent heat damage to electronic components and insulation). Since the joint is produced using a metal with a lower melting temperature than the workpiece, the joint will weaken as
4620-450: Is usually described as easy, medium, or hard in reference to its melting temperature, not the strength of the joint. Extra-easy solder contains 56% silver and has a melting point of 618 °C (1,145 °F). Extra-hard solder has 80% silver and melts at 740 °C (1,370 °F). If multiple joints are needed, then the jeweler will start with hard or extra-hard solder and switch to lower-temperature solders for later joints. Silver solder
4725-449: The glass transition temperature the resin in the composite softens and significantly increases thermal expansion; exceeding T g then exerts mechanical overload on the board components - e.g. the joints and the vias. Below T g 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
4830-404: The liquidus and solidus temperatures are the same, so there is no plastic phase, and it has the lowest possible melting point. Having the lowest possible melting point minimizes heat stress on electronic components during soldering. And, having no plastic phase allows for quicker wetting as the solder heats up, and quicker setup as the solder cools. A non-eutectic formulation must remain still as
4935-399: 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
5040-499: The "iron" (a larger mass of metal, usually copper) which is in contact with the working tip made of copper. Usually, soldering irons can be fitted with a variety of tips, ranging from blunt, to very fine, to chisel heads for hot-cutting plastics rather than soldering. Plain copper tips are subject to errosion/dissolution in hot solder, and may be plated with pure iron to prevent that. The simplest irons do not have temperature regulation. Small irons rapidly cool when used to solder to, say,
5145-558: 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
5250-690: The United States, above 800 °F (427 °C). Aluminium soldering alloys generally have melting temperatures around 730 °F (388 °C). This soldering / brazing operation can use a propane torch heat source. These materials are often advertised as "aluminium welding", but the process does not involve melting the base metal, and therefore is not properly a weld. United States Military Standard or MIL-SPEC specification MIL-R-4208 defines one standard for these zinc-based brazing/soldering alloys. A number of products meet this specification. or very similar performance standards. The purpose of flux
5355-441: The ambient temperature approaches the melting point of the filler metal. For that reason, the higher temperature processes produce joints which are effective at higher temperatures. Brazed connections can be as strong or nearly as strong as the parts they connect, even at elevated temperatures. "Hard soldering" or "silver soldering" is used to join precious and semi-precious metals such as gold, silver, brass, and copper. The solder
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#17328555273355460-453: 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. 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
5565-437: 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
5670-519: 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
5775-512: The ceramic substrate. In 1948, the US 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
5880-466: The choice of method depends on the application and the materials being joined. Soldering is an important skill for many industries and hobbies, and it requires a combination of technical knowledge and practical experience to achieve good results. There is evidence that soldering was employed as early as 5,000 years ago in Mesopotamia. Soldering and brazing are thought to have originated very early in
5985-757: 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
6090-539: 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
6195-431: 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. 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
6300-464: 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
6405-492: 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
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#17328555273356510-403: 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
6615-454: The essential design is a flat frame with a series of upright seats set at right-angles to the direction of the track, thus forming a crude representation of a toast rack. When the term 'toast rack carriage' is used of larger railways (up to, and sometimes including, standard gauge ) it refers to coaches whose seats are set at right-angles to the track direction, and with no side corridor, central aisle, or corridor connection; thus each compartment
6720-534: The filler metal for each type of soldering can be adjusted to modify the melting temperature of the filler. Soldering differs from gluing significantly in that the filler metals directly bond with the surfaces of the workpieces at the junction to form a bond that is both electrically conductive and gas- and liquid-tight. Soft soldering is characterized by having a melting point of the filler metal below approximately 400 °C (752 °F), whereas silver soldering and brazing use higher temperatures, typically requiring
6825-405: 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. "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
6930-467: The higher temperature silver soldering process. Small mechanical parts are often soldered or brazed as well. Soldering is also used to join lead came and copper foil in stained glass work. Electronic soldering connects electrical wiring to devices, and electronic components to printed circuit boards . Electronic connections may be hand-soldered with a soldering iron. Automated methods such as wave soldering or use of ovens can make many joints on
7035-731: The history of metal-working, probably before 4000 BC. Sumerian swords from c. 3000 BC were assembled using hard soldering. Soldering was historically used to make jewelry, cookware and cooking tools, assembling stained glass , as well as other uses. Soldering is used in plumbing, electronics, and metalwork from flashing to jewelry and musical instruments. Soldering provides reasonably permanent but reversible connections between copper pipes in plumbing systems as well as joints in sheet metal objects such as food cans, roof flashing , rain gutters and automobile radiators . Jewelry components, machine tools and some refrigeration and plumbing components are often assembled and repaired by
7140-412: The horse and early electric age, toastrack cars – usually with roofs and often reversible seats – were common in warm climates or for summer use. On electric tramways, such cars were usually trailers, but motor toastracks did occur. Soldering Soldering ( US : / ˈ s ɒ d ər ɪ ŋ / ; UK : / ˈ s oʊ l d ər ɪ ŋ / ) is a process of joining two metal surfaces together using
7245-447: 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
7350-427: 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
7455-505: The joint, heating the parts, applying flux, applying the filler, removing heat and holding the assembly still until the filler metal has completely solidified. Depending on the nature of flux material used and the application, cleaning of the joint may be required after it has cooled. Each solder alloy has characteristics that work best for certain applications, notably strength and conductivity, and each type of solder and alloy has different melting temperatures. The term silver solder denotes
7560-467: The joint. These fluxes cannot be used in electronics because their residues are conductive leading to unintended electrical connections, and because they will eventually dissolve small diameter wires. Citric acid is an excellent water-soluble acid-type flux for copper and electronics but must be washed off afterwards. Fluxes for soft solder are currently available in three basic formulations: Flux performance must be carefully evaluated for best results;
7665-646: The lead into the groundwater. Unfortunately, common lead-free solders are not eutectic formulations, melting at around 220 °C (428 °F), making it more difficult to create reliable joints with them. Other common solders include low-temperature formulations (often containing bismuth ), which are often used to join previously soldered assemblies without unsoldering earlier connections, and high-temperature formulations (usually containing silver ) which are used for high-temperature operation or for first assembly of items which must not become unsoldered during subsequent operations. Alloying silver with other metals changes
7770-407: The manufacture of jewelry and other decorative items. The solder used in the process can vary in composition, with different alloys used for different applications. Common solder alloys include tin-lead, tin-silver, and tin-copper, among others. Lead-free solder has also become more widely used in recent years due to health and environmental concerns associated with the use of lead . In addition to
7875-498: 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
7980-491: 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
8085-506: The melting point, adhesion and wetting characteristics, and tensile strength. Of all the brazing alloys, silver solders have the greatest strength and the broadest applications. Specialty alloys are available with properties such as higher strength, the ability to solder aluminum, better electrical conductivity, and higher corrosion resistance. There are three forms of soldering, each requiring progressively higher temperatures and producing an increasingly stronger joint strength: The alloy of
8190-511: The metal prior to heating. A flux, often made of boric acid and denatured alcohol, is used to keep the metal and solder clean and to prevent the solder from moving before it melts. When silver solder melts, it tends to flow towards the area of greatest heat. Jewelers can somewhat control the direction the solder moves by leading it with a torch; it will even sometimes run straight up along a seam. A number of solder materials, primarily zinc alloys, are used for soldering aluminium and alloys and to
8295-498: The need for additional discrete components. High density interconnects (HDI) PCBs have tracks or vias with a width or diameter of under 152 micrometers. 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 4 by 8 feet (1.2 by 2.4 m) in width and length. Varying cloth weaves (threads per inch or cm), cloth thickness, and resin percentage are used to achieve
8400-471: 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
8505-573: 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 United States 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
8610-474: 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 November 1, 1952. Even as circuit boards became available,
8715-403: 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
8820-402: The remote detonation of demolition and sabotage explosives. These consisted of a small copper tube partially filled with solder and a slow-burning pyrotechnic composition wrapped around the tube. The wires to be joined would be inserted into the tube and a small blob of ignition compound allowed the device to be struck like a match to ignite the pyrotechnic and heat the tube for long enough to melt
8925-441: The resin matrix, and the associated local variations in the dielectric constant, are gaining importance. The circuit-board 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
9030-546: The same kind used for heat-stripping paint and thawing pipes, can be used for soldering pipes and other fairly large objects either with or without a soldering tip attachment; pipes are generally soldered with a torch by directly applying the open flame. A soldering copper is a tool with a large copper head and a long handle which is heated with a small direct flame and used to apply heat to sheet metal such as tin plated steel for soldering. Typical soldering coppers have heads weighing between one and four pounds. The head provides
9135-478: 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 lead inserted through holes on one side of
9240-408: 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
9345-414: 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. Each trace consists of
9450-414: The solder and make the joint. Laser soldering is a technique where a 30–50 W laser is used to melt and solder an electrical connection joint. Diode laser systems based on semiconductor junctions are used for this purpose. Suzanne Jenniches patented laser soldering in 1980. Printed circuit board A printed circuit board ( PCB ), also called printed wiring board ( PWB ),
9555-471: The solder is drawn up into the wire between the strands by capillary action in a process called 'wicking'. Capillary action also takes place when the workpieces are very close together or touching. The joint's tensile strength is dependent on the filler metal used; in electrical soldering little tensile strength comes from the added solder which is why it is advised that wires be twisted or folded together before soldering to provide some mechanical strength for
9660-599: The soldering process, reducing the surface tension of the molten solder and causing it to flow and wet the workpieces more easily. For many years, the most common type of flux used in electronics (soft soldering) was rosin -based, using the rosin from selected pine trees . It was nearly ideal in that it was non-corrosive and non-conductive at normal temperatures but became mildly reactive (corrosive) at elevated soldering temperatures. Plumbing and automotive applications, among others, typically use an acid-based ( hydrochloric acid ) flux which provides rather aggressive cleaning of
9765-408: The soldering temperatures increase and can completely prevent the solder from joining to the workpiece. One of the earliest forms of flux was charcoal , which acts as a reducing agent and helps prevent oxidation during the soldering process. Some fluxes go beyond the simple prevention of oxidation and also provide some form of chemical cleaning (corrosion). Many fluxes also act as a wetting agent in
9870-422: 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
9975-760: The temperature drops through the liquidus and solidus temperatures. Any movement during the plastic phase may result in cracks, resulting in an unreliable joint. Common solder formulations based on tin and lead are listed below. The fraction represent percentage of tin first, then lead, totaling 100%: For environmental reasons and the introduction of regulations such as the European RoHS ( Restriction of Hazardous Substances Directive ), lead-free solders are becoming more widely used. They are also suggested anywhere young children may come into contact with (since young children are likely to place things into their mouths), or for outdoor use where rain and other precipitation may wash
10080-402: 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
10185-419: 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 T g . The materials used determine the substrate's dielectric constant . This constant is also dependent on frequency, usually decreasing with frequency. As this constant determines
10290-546: The toast becomes cold more quickly. The toast rack's design and shape follows prevailing fashion. The dividers were often made from silver wires and these in turn were soldered to either a wire-work or a solid base that sat on four feet. Sometimes the base is separate and was used to dispose of any crumbs that fell. Some ingenious designs were made including expanding or folding types (so as to take up less space). Others had incorporated egg-cups or receptacles for jam or marmalade . A designer renowned for his innovative take on
10395-558: The toast rack was Christopher Dresser (1834–1904), who studied at the Glasgow Government School of Design from the age of 13 and is widely thought of as the 'father of modern design'. Modern designs are often made from stamped and folded stainless steel sheet or from welded stainless wire. Manchester Metropolitan University 's Fallowfield Campus main building, the Hollings Building designed by architect L. C. Howitt,
10500-467: The type of solder that is used. Some soft solders are "silver-bearing" alloys used to solder silver-plated items. Lead-based solders should not be used on precious metals because the lead dissolves the metal and disfigures it. The distinction between soldering and brazing is based on the melting temperature of the filler alloy. A temperature of 450 °C is usually used as a practical demarcation between soldering and brazing. Soft soldering can be done with
10605-462: The type of solder used, the temperature and method of heating also play a crucial role in the soldering process. Different types of solder require different temperatures to melt, and heating must be carefully controlled to avoid damaging the materials being joined or creating weak joints. There are several methods of heating used in soldering, including soldering irons, torches, and hot air guns . Each method has its own advantages and disadvantages, and
10710-511: 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
10815-440: 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 ft , 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 ft (35 μm)
10920-433: 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
11025-426: 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 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
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