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Solder (,〔(【引用サイトリンク】title=solder )〕 〔 or in North America 〔Oxford American Dictionary〕) is a fusible metal alloy used to join together metal workpieces and having a melting point below that of the workpiece(s). Soft solder is typically thought of when solder or soldering is mentioned, with a typical melting range of .〔Frank Oberg, Franklin D. Jones, Holbrook L.Horton, Henry H. Ryffel (ed) ''Machinery's Handbook 23rd Edition'' Industrial Press Inc., 1988, ISBN 0-8311-1200-X, page 1203〕 It is commonly used in electronics, plumbing, and assembly of sheet metal parts. Manual soldering uses a soldering iron or soldering gun. Alloys that melt between are the most commonly used. Soldering performed using alloys with a melting point above is called 'hard soldering', 'silver soldering', or brazing. For certain proportions an alloy becomes eutectic and melts at a single temperature; non-eutectic alloys have markedly different ''solidus'' and ''liquidus'' temperatures, and within that range they exist as a paste of solid particles in a melt of the lower-melting phase. In electrical work, if the joint is disturbed in the pasty state before it has solidified totally, a poor electrical connection may result; use of eutectic solder reduces this problem. The pasty state of a non-eutectic solder can be exploited in plumbing as it allows molding of the solder during cooling, e.g. for ensuring watertight joint of pipes, resulting in a so-called 'wiped joint'. For electrical and electronics work solder wire is available in a range of thicknesses for hand-soldering, and with cores containing flux. It is also available as a paste or as a preformed foil shaped to match the workpiece, more suitable for mechanized mass-production. Alloys of lead and tin were universally used in the past, and are still available; they are particularly convenient for hand-soldering. Lead-free solder, somewhat less convenient for hand-soldering, is often used to avoid the environmental effect of lead. Plumbers often use bars of solder, much thicker than the wire used for electrical applications. Jewelers often use solder in thin sheets which they cut into snippets. The word solder comes from the Middle English word ''soudur'', via Old French ''solduree'' and ''soulder'', from the Latin ''solidare'', meaning "to make solid". With the reduction of the size of circuit board features, the size of interconnects shrinks as well. Current densities above 104 A/cm2 are often achieved and electromigration 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. Contact with molten solder can cause 'solder embrittlement' of materials, a type of liquid metal embrittlement. == Lead solder == Tin/lead 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 and shear strengths. Alloys commonly used for electrical soldering are 60/40 Tin/lead (Sn/Pb) which melts at 〔http://www.farnell.com/datasheets/315929.pdf〕 and 63/37 Sn/Pb used principally in electrical/electronic work. The 63/37 is a eutectic alloy, which: # has the lowest melting point () of all the tin/lead alloys; and # the melting point is truly a ''point'' — not a range. In plumbing, a higher proportion of lead was used, commonly 50/50. This had the advantage of making the alloy solidify more slowly. With the pipes being physically fitted together before soldering, the solder could be wiped over the joint to ensure watertightness. Although lead water pipes were displaced by copper when the significance of lead poisoning 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 couple of copper and lead promotes corrosion of the lead and tin. Tin, however, is protected by insoluble oxide. Since even small amounts of lead have been found detrimental to health, lead in plumbing solder was replaced by silver (food grade applications) or antimony, with copper often added, and the proportion of tin was increased (see Lead-free solder.) The addition of tin—more expensive than lead—improves wetting properties of the alloy; lead itself has poor wetting characteristics. High-tin tin-lead alloys have limited use as the workability range can be provided by a cheaper high-lead alloy. In electronics, components on printed circuit boards (PCBs) are connected to the printed circuit, and hence to other components, by soldered joints. For miniaturized PCB joints with surface mount components, solder paste has largely replaced solid solder. Lead-tin solders readily dissolve gold plating and form brittle intermetallics.〔 Sn60Pb40 solder oxidizes on the surface, forming a complex 4-layer structure: tin(IV) oxide on the surface, below it a layer of tin(II) oxide with finely dispersed lead, followed by a layer of tin(II) oxide with finely dispersed tin and lead, and the solder alloy itself underneath. Lead, and to some degree tin, as used in solder contains small but significant amounts of radioisotope impurities. Radioisotopes undergoing alpha decay are a concern due to their tendency to cause soft errors. Polonium-210 is especially problematic; lead-210 beta decays to bismuth-210 which then beta decays to polonium-210, an intense emitter of alpha particles. Uranium-238 and thorium-232 are other significant contaminants of alloys of lead.〔〔 ==Lead-free solder== On July 1, 2006 the European Union Waste Electrical and Electronic Equipment Directive (WEEE) and Restriction of Hazardous Substances Directive (RoHS) came into effect prohibiting the inclusion of significant quantities of lead in most consumer electronics produced in the EU. In the US, manufacturers 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 to 20 °C higher,〔 though there are also solders with much lower melting points. There are drop-in replacements for silkscreen with solder paste soldering operations. It may be desirable to use minor modification of the solder pots (e.g. titanium liners or impellers) used in wave-soldering, to reduce maintenance cost due to increased tin-scavenging of high-tin solder. Lead-free solder may be less desirable for critical applications, such as aerospace and medical projects, because its properties are less thoroughly known. "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 75% of 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.〔 Lead-free solder has a higher Young's modulus than lead-based solder, making it more brittle when deformed. When the PCB on which the electronic components are mounted is subject to bending stress due to warping, the solder joint deteriorates and fractures can appear. This effect is called solder cracking.〔http://product.tdk.com/en/techjournal/archives/vol05_mlcc/contents06.html〕 Another fault is Kirkendall voids which are microscopic cavities in solder. When two different types of metal that are in contact are heated, dispersion occurs (see also Kirkendall effect). Repeated thermal cycling cause the formation of voids which tends to cause solder cracks. Lead-free solder can cause short life cycles of products, as well as planned obsolescence.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Solder」の詳細全文を読む スポンサード リンク
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