Solder ( / 'sɒdə(r) / or / 'sɒldə(r) /) is a fusible A fusible alloy is a metal alloy capable of being easily fused, i.e. easily meltable, at relatively low temperatures. Fusible alloys are commonly, not necessarily, eutectic alloys metal alloy An alloy is a partial or complete solid solution of one or more elements in a metallic matrix. Complete solid solution alloys give single solid phase microstructure, while partial solutions give two or more phases that may be homogeneous in distribution depending on thermal history. Alloys usually have different properties from those of the with a melting point or melting range of 90 to 450 degree Celsius Celsius is a temperature scale that is named after the Swedish astronomer Anders Celsius (1701–1744), who developed a similar temperature scale two years before his death. The degree Celsius (°C) can refer to a specific temperature on the Celsius scale as well as a unit to indicate a temperature interval (a difference between two temperatures (190 to 840 °F Fahrenheit is the temperature scale proposed in 1724 by, and named after, the physicist Daniel Gabriel Fahrenheit . Today, the temperature scale has been replaced by the Celsius scale in most countries. It is still in use in few nations, such as United States and Belize), used in a process called soldering Soldering is a process in which two or more metal items are joined together by melting and flowing a filler metal into the joint, the filler metal having a relatively low melting point. Soft soldering is characterized by the melting point of the filler metal, which is below 400 °C . The filler metal used in the process is called solder where it is melted to join metallic surfaces. It is especially useful in electronics Electronics is the branch of science and technology which makes use of the controlled motion of electrons through different media and vacuum. The ability to control electron flow is usually applied to information handling or device control. Electronics is distinct from electrical science and technology, which deals with the generation, and plumbing Plumbing is the skilled trade of working with pipes, tubing and plumbing fixtures for drinking water systems and the drainage of waste. A plumber is someone who installs or repairs piping systems, plumbing fixtures and equipment such as water heaters. The plumbing industry is a basic and substantial part of every developed economy due to the need. Alloys that melt between 180 and 190 °C (360 and 370 °F) are the most commonly used. By definition, using alloys with melting point above 450 °C (840 °F) is called brazing Brazing is a metal-joining process whereby a filler metal is heated above and distributed between two or more close-fitting parts by capillary action. The filler metal is brought slightly above its melting temperature while protected by a suitable atmosphere, usually a flux. It then flows over the base metal (known as wetting) and is then cooled. Solder can contain lead and/or flux In metallurgy, a flux is a chemical cleaning agent that facilitates soldering, brazing, and welding by removing oxidation from the metals to be joined. Common fluxes are: ammonium chloride or rosin for soldering tin; hydrochloric acid and zinc chloride for soldering galvanized iron ; and borax for brazing or braze-welding ferrous metals. Different but in many applications solder is now lead free.

The word solder comes from the Middle English Middle English is the name given by historical linguists to the diverse forms of the English language in use between the late 11th century and about 1470, when the Chancery Standard, a form of London-based English, began to become widespread, a process aided by the introduction of the printing press into England by William Caxton in the late 1470s word soudur, via Old French Old French was the Romance dialect continuum spoken in territories that span roughly the northern half of modern France and parts of modern Belgium and Switzerland from the 9th century to the 14th century. It is a direct descendent of Old Gallo-Romance. It was then known as the langue d'oïl to distinguish it from the langue d'oc (Occitan language, solduree and soulder, from the Latin Latin or sometimes Roman is an Italic language originally spoken in Latium and Ancient Rome. Although often considered a dead language, in view of the fact that it has no native speakers, a small number of scholars can fluently speak it and it continues to be taught in schools and universities and has been, and currently is, used in the process of solidare, meaning "to make solid".

Eutectic A eutectic system is a mixture of chemical compounds or elements that has a single chemical composition that solidifies at a lower temperature than any other composition. This composition is known as the eutectic composition and the temperature is known as the eutectic temperature. On a phase diagram the intersection of the eutectic temperature alloys melt at a single temperature. Non-eutectic alloys have markedly different solidus In chemistry, materials science, and physics, the solidus is the locus of temperatures below which a given substance is completely solid (crystallized). The solidus is applied, among else, to metal alloys, ceramics, and natural rocks and minerals and liquidus The liquidus temperature, TL or Tliq, is mostly used for glasses, alloys and rocks. It specifies the maximum temperature at which crystals can co-exist with the melt in thermodynamic equilibrium. Above the liquidus temperature the material is homogeneous. Below the liquidus temperature more and more crystals begin to form in the melt if one waits temperature, and within that range they exist as a paste of solid particles in a melt of the lower-melting phase. The pasty state causes some problems during handling; it can however be exploited as it allows molding of the solder during cooling, e.g. for ensuring watertight joint of pipes, resulting in a so called wiped joint.

With the reduction of the size of circuitboard features, the size of interconnects shrinks as well. Current densities above 10⁴ A/cm² are often achieved and electromigration Electromigration is the transport of material caused by the gradual movement of the ions in a conductor due to the momentum transfer between conducting electrons and diffusing metal atoms. The effect is important in applications where high direct current densities are used, such as in microelectronics and related structures. As the structure size becomes a concern. At such current densities the Sn63Pb37 solder balls form hillocks on the anode side and voids on the cathode side; the increased content of lead on the anode side suggests lead is the primary migrating species.^[1]

Contact with molten solder can cause solder embrittlement of the materials, a type of liquid metal embrittlement Liquid metal embrittlement is a phenomenon of practical importance, where certain ductile metals experience drastic loss in tensile ductility or undergo brittle fracture when tested in the presence of specific liquid metals. Generally, a tensile stress, either externally applied or internally present, is needed to induce embrittlement. Exceptions.

Lead solder

Tin Tin is a chemical element with the symbol Sn and atomic number 50. It is a main group metal in group 14 of the periodic table. Tin shows chemical similarity to both neighboring group 14 elements, germanium and lead, like the two possible oxidation states +2 and +4. Tin is the 49th most abundant element and has, with 10 stable isotopes, the largest/lead Lead is a main-group element with symbol Pb and atomic number 82. Lead is a soft, malleable poor metal. It is also counted as one of the heavy metals. Metallic lead has a bluish-white color after being freshly cut, but it soon tarnishes to a dull grayish color when exposed to air. Lead has a shiny chrome-silver luster when it is melted into a solders, also called soft solders, are commercially available with tin concentrations between 5% and 70% by weight. The greater the tin concentration, the greater the solder’s tensile Tensile strength is indicated by the maxima of a stress-strain curve and, in general, indicates when necking will occur. As it is an intensive property, its value does not depend on the size of the test specimen. It is, however, dependent on the preparation of the specimen and the temperature of the test environment and material and shear strengths Shear strength in engineering is a term used to describe the strength of a material or component against the type of yield or structural failure where the material or component fails in shear. At the retail level, the two most common alloys are 60/40 Tin/lead (Sn/Pb) which melts at 370 °F or 188 °C and 63/37 Sn/Pb used principally in electrical/electronic work. The 63/37 ratio is notable in that it is a eutectic A eutectic system is a mixture of chemical compounds or elements that has a single chemical composition that solidifies at a lower temperature than any other composition. This composition is known as the eutectic composition and the temperature is known as the eutectic temperature. On a phase diagram the intersection of the eutectic temperature mixture, which means:

1. It has the lowest melting point (183 °C or 361.4 °F) of all the tin/lead alloys; and
2. The melting point is truly a point — not a range.

At a eutectic A eutectic system is a mixture of chemical compounds or elements that has a single chemical composition that solidifies at a lower temperature than any other composition. This composition is known as the eutectic composition and the temperature is known as the eutectic temperature. On a phase diagram the intersection of the eutectic temperature composition, the liquid solder solidifies at a single temperature. Tin/lead solder solidifies to fine grains of nearly pure lead and nearly pure tin phases In the physical sciences, a phase is a region of space , throughout which all physical properties of a material are essentially uniform. Examples of physical properties include density, index of refraction, and chemical composition. A simple description is that a phase is a region of material that is chemically uniform, physically distinct, and (, there are no tin/lead intermetallics Intermetallics or intermetallic compounds is a term that is used in a number of different ways. Most commonly it refers to solid state phases involving metals. There is a "research definition" adhered to generally in scientific publications, and a wider "common use" term. There is also a completely different use in coordination and no solid solution A solid solution is a solid-state solution of one or more solutes in a solvent. Such a mixture is considered a solution rather than a compound when the crystal structure of the solvent remains unchanged by addition of the solutes, and when the mixture remains in a single homogeneous phase.This often happens when the two elements involved are close of tin in lead or lead in tin, as can be seen from a tin/lead equilibrium diagram A phase diagram in physical chemistry, engineering, mineralogy, and materials science is a type of chart used to show conditions at which thermodynamically distinct phases can occur at equilibrium. In mathematics and physics, "phase diagram" is used with a different meaning: a synonym for a phase space.^[2]

In plumbing, a higher proportion of lead was used, commonly 50/50. This had the advantage of making the alloy solidify more slowly, so that it could be wiped over the joint to ensure watertightness, the pipes being physically fitted together before soldering. Although lead water pipes were displaced by copper when the significance of lead poisoning Lead poisoning is a medical condition caused by increased levels of the heavy metal lead in the body. Lead interferes with a variety of body processes and is toxic to many organs and tissues including the heart, bones, intestines, kidneys, and reproductive and nervous systems. It interferes with the development of the nervous system and is began to be fully appreciated, lead solder was still used until the 1980s because it was thought that the amount of lead that could leach into water from the solder was negligible from a properly soldered joint. The electrochemical Electrochemistry is a branch of chemistry that studies chemical reactions which take place in a solution at the interface of an electron conductor and an ionic conductor (the electrolyte), and which involve electron transfer between the electrode and the electrolyte or species in solution couple of copper and lead promotes corrosion of the lead and tin, however tin is protected by insoluble oxide. Since even small amounts of lead have been found detrimental to health,^[3] lead in plumbing solder was replaced by silver Silver is a metallic chemical element with the chemical symbol Ag and atomic number 47. A soft, white, lustrous transition metal, it has the highest electrical conductivity of any element and the highest thermal conductivity of any metal. The metal occurs naturally in its pure, free form (native silver), as an alloy with gold and other metals, and (food grade applications) or antimony Antimony ;[note 2] Latin: stibium) is a chemical element with the symbol Sb and an atomic number of 51. It has two stable isotopes, one with seventy neutrons, the other with seventy-two. A silvery lustrous grey metalloid, it is found mainly as antimony sulfide, commonly known as stibnite, with copper Copper is a chemical element with the symbol Cu (Latin: cuprum) and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is rather soft and malleable, and a freshly exposed surface has a pinkish or peachy color. It is used as a thermal conductor, an electrical conductor, a building material, and a often added, and the proportion of tin was increased (see Lead-free solder.)

The addition of tin improves wetting properties of the alloy; lead itself has poor wetting characteristics. Tin however increases the cost of the solder. High-tin tin-lead alloys have limited use as the workability range can be provided by a cheaper high-lead alloy.^[4]

In electronics, the traditional use of solder was to fortify mechanically made electrical contacts An electrical connector is a conductive device for joining electrical circuits together. The connection may be temporary, as for portable equipment, or may require a tool for assembly and removal, or may be a permanent electrical joint between two wires or devices. There are hundreds of types of electrical connectors. In computing, an electrical, e.g. two solid copper wires A wire is a single, usually cylindrical, string of metal. Wires are used to bear mechanical loads and to carry electricity and telecommunications signals. Wire is commonly formed by drawing the metal through a hole in a die or draw plate. Standard sizes are determined by various wire gauges. The term wire is also used more loosely to refer to a twisted together. This was in part due to the higher electrical resistance The electrical resistance of an object is a measure of its attraction to the passage of a steady electric current. An object of uniform cross section will have a resistance proportional to its length and inversely proportional to its cross-sectional area, and proportional to the resistivity of the material of solder versus copper.^[5] Printed circuit boards A printed circuit board, or PCB, is used to mechanically support and electrically connect electronic components using conductive pathways, tracks or traces etched from copper sheets laminated onto a non-conductive substrate. It is also referred to as printed wiring board or etched wiring board. A PCB populated with electronic components is a use solder joints to mount components and create a circuit, also replacing the use of solid solder with solder paste.

Lead-tin solders readily dissolve gold Gold is a chemical element with the symbol Au (from Latin: aurum, "shining dawn", hence adjective, aureate) and an atomic number of 79. It has been a highly sought-after precious metal for coinage, jewelry, and other arts since the beginning of recorded history. The metal occurs as nuggets or grains in rocks, in veins and in alluvial plating and form brittle intermetallics.

Sn60Pb40 solder oxidizes on the surface with forming complex 4-layer structure: tin(IV) oxide Tin dioxide is the inorganic compound with the formula SnO2. The mineral form of SnO2 is called cassiterite, and this is the main ore of tin. With many other names , this oxide of tin is the most important raw material in tin chemistry. This colourless, diamagnetic solid is amphoteric on the surface, below it a layer of tin(II) oxide with finely dispersed lead, below a layer of tin(II) oxide with finely dispersed tin and lead, and the solder alloy itself underneath.^[6]

Some alloys, namely of lead and to some degree tin, contain small but significant amounts of radioisotope A radionuclide is an atom with an unstable nucleus, which is a nucleus characterized by excess energy which is available to be imparted either to a newly-created radiation particle within the nucleus, or else to an atomic electron . The radionuclide, in this process, undergoes radioactive decay, and emits a gamma ray(s) and/or subatomic particles impurities. The radioisotopes undergoing alpha decay Alpha decay is a type of radioactive decay in which an atomic nucleus emits an alpha particle, and thereby transforms into an atom with a mass number 4 less and atomic number 2 less. For example: are a concern due to their tendency to cause soft errors In electronics and computing, an error is a signal or datum which is wrong. Errors may be caused by a defect, usually understood either to be a mistake in design or construction, or a broken component. A soft error is also a signal or datum which is wrong, but is not assumed to imply such a mistake or breakage. After observing a soft error, there. Polonium-210 Polonium is a chemical element with the symbol Po and atomic number 84, discovered in 1898 by Marie Skłodowska-Curie and Pierre Curie. A rare and highly radioactive metalloid, polonium is chemically similar to bismuth and tellurium, and it occurs in uranium ores. Polonium has been studied for possible use in heating spacecraft. It is unstable; is especially problematic; lead-210 beta decays In nuclear physics, beta decay is a type of radioactive decay in which a beta particle is emitted. In the case of electron emission, it is referred to as beta minus (β⁻), while in the case of a positron emission as beta plus (β+). Kinetic energy of beta particles has continuous spectrum ranging from 0 to maximal available energy (Q), which to bismuth-210 which then beta decays to polonium-210 Polonium is a chemical element with the symbol Po and atomic number 84, discovered in 1898 by Marie Skłodowska-Curie and Pierre Curie. A rare and highly radioactive metalloid, polonium is chemically similar to bismuth and tellurium, and it occurs in uranium ores. Polonium has been studied for possible use in heating spacecraft. It is unstable;, an intense emitter of alpha particles Alpha particles consist of two protons and two neutrons bound together into a particle identical to a helium nucleus, which is produced in the process of alpha decay. The alpha particle can be written as He2+, 42He2+ or 42He (as it is possible that the ion gains electrons from the environment. Also, electrons are not important in nuclear chemistry). Uranium-238 Uranium-238 is the most common isotope of uranium found in nature. It is not fissile, but is a fertile material: it can capture a slow neutron and after two beta decays become fissile plutonium-239. U-238 is fissionable by fast neutrons, but cannot support a chain reaction because inelastic scattering reduces neutron energy below the range where and thorium-232 Thorium-232 is the only primordial isotope of thorium and makes up effectively all of natural thorium, with other isotopes of thorium appearing only in trace amounts as relatively short-lived decay products of uranium and thorium are other significant contaminants of lead containing alloys.^[1][7]

Lead-free solder

On July 1, 2006 the European Union The European Union is an economic and political union of 27 member states which are located primarily in Europe. Committed to regional integration, the EU was established by the Treaty of Maastricht in 1993 upon the foundations of the European Communities. With over 500 million citizens, the EU combined generated an estimated 28% share (US$ 16.5 Waste Electrical and Electronic Equipment Directive The directive imposes the responsibility for the disposal of waste electrical and electronic equipment on the manufacturers of such equipment. Those companies should establish an infrastructure for collecting WEEE, in such a way that "Users of electrical and electronic equipment from private households should have the possibility of returning (WEEE) and Restriction of Hazardous Substances Directive The Directive on the restriction of the use of certain hazardous substances in electrical and electronic equipment 2002/95/EC ( listen ; commonly referred to as the Restriction of Hazardous Substances Directive or RoHS) was adopted in February 2003 by the European Union. The RoHS directive took effect on 1 July 2006, and is required to be enforced (RoHS) came into effect prohibiting the intentional addition of lead to most consumer electronics produced in the EU. California recently adopted a RoHS law^[8] and China has a version as well. Manufacturers in the U.S. may receive tax benefits by reducing the use of lead-based solder. Lead-free solders in commercial use may contain tin, copper, silver, bismuth, indium, zinc, antimony, and traces of other metals. Most lead-free replacements for conventional Sn60/Pb40 and Sn63/Pb37 solder have melting points from 5–20 °C higher,^[9] though solders with much lower melting points are available.

Drop-in replacements for silkscreen with solder paste soldering operations are available. Minor modification to the solder pots (e.g. titanium liners and/or impellers) used in wave-soldering operations may be desired to reduce maintenance costs associated with the increased tin-scavenging effects of high tin solders. Since the properties of lead-free solders are not as thoroughly known, they may therefore be considered less desirable for critical applications, like certain aerospace or medical projects. "Tin whiskers" were a problem with early electronic solders, and lead was initially added to the alloy in part to eliminate them.

Sn-Ag-Cu (Tin-Silver-Copper) solders are used by two thirds of Japanese manufacturers for reflow and wave soldering, and by about ¾ companies for hand soldering. The widespread use of this popular lead-free solder alloy family is based on the reduced melting point of the Sn-Ag-Cu ternary eutectic behavior(217˚C), which is below the Sn-3.5Ag (wt.%) eutectic of 221 °C and the Sn-0.7Cu eutectic of 227 °C (recently revised by P. Snugovsky to Sn-0.9Cu). The ternary eutectic behavior of Sn-Ag-Cu and its application for electronics assembly was discovered (and patented) by a team of researchers from Ames Laboratory, Iowa State University, and from Sandia National Laboratories-Albuquerque.

Much recent research has focused on selection of 4th element additions to Sn-Ag-Cu to provide compatibility for the reduced cooling rate of solder sphere reflow for assembly of ball grid arrays, e.g., Sn-3.5Ag-0.74Cu-0.21Zn (melting range of 217–220 ˚C) and Sn-3.5Ag-0.85Cu-0.10Mn (melting range of 211–215 ˚C).

Tin-based solders readily dissolve gold, forming brittle intermetallics; for Sn-Pb alloys the critical concentration of gold to embrittle the joint is about 4%. Indium-rich solders (usually indium-lead) are more suitable for soldering thicker gold layer as the dissolution rate of gold in indium is much slower. Tin-rich solders also readily dissolve silver; for soldering silver metallization or surfaces, alloys with addition of silvers are suitable; tin-free alloys are also a choice, though their wettability is poorer. If the soldering time is long enough to form the intermetallics, the tin surface of a joint soldered to gold is very dull.^[10]

Flux-core solder

Flux is a reducing agent designed to help reduce (return oxidized metals to their metallic state) at the points of contact to improve the electrical connection and mechanical strength. The two principal types of flux are acid flux, used for metal mending and plumbing, and rosin flux, used in electronics, where the corrosiveness of acid flux and vapors released when solder is heated would risk damaging delicate circuitry.

Due to concerns over atmospheric pollution and hazardous waste disposal, the electronics industry has been gradually shifting from rosin flux to water-soluble flux, which can be removed with deionized water and detergent, instead of hydrocarbon solvents.

In contrast to using traditional bars or coiled wires of all-metal solder and manually applying flux to the parts being joined, some light hand soldering since the mid-20th century has used flux-core solder. This is manufactured as a coiled wire of solder, with one or more continuous bodies of non-acid flux embedded lengthwise inside it. As the solder melts onto the joint, it frees the flux and releases that on it as well.

Hard solder

Hard solders are used for brazing, and melt at higher temperatures. Alloys of copper with either zinc or silver are the most common.

In silversmithing or jewelry making, special hard solders are used that will pass away assay. They contain a high proportion of the metal being soldered and lead is not used in these alloys. These solders vary in hardness, designated as "enameling", "hard", "medium" and "easy". Enameling solder has a high melting point, close to that of the material itself, to prevent the joint desoldering during firing in the enameling process. The remaining solder types are used in decreasing order of hardness during the process of making an item, to prevent a previously soldered seam or joint desoldering while additional sites are soldered. Easy solder is also often used for repair work for the same reason. Flux or rouge is also used to prevent joints from desoldering.

Silver solder is also used in manufacturing to join metal parts that cannot be welded. The alloys used for these purposes contain a high proportion of silver (up to 40%), and may also contain cadmium.

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