Information AboutSolder |
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The word solder comes from the Middle English word ''soudur'', via Old French ''soldure'' and ''soulder'', from the Latin ''solidare'', meaning '‘to make solid’'. LEAD SOLDER Tin / Lead 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 Strength s. At the retail level, the two most common alloys are 60/40 Sn / Pb and 63/37 Sn/Pb. The 63/37 ratio is notable in that it is a Eutectic mixture, which means: # It is has the lowest melting point (183 °C or 361.4 °F) of all the tin/lead alloys; and # The melting point is truly a ''point'' — not a range. At an eutectic composition, the liquid solder solidifies as an eutectic, which consists of fine grains of nearly pure lead and nearly pure tin phases, but in no way is it an intermetallic, since there are no tin/lead intermetallics, as can be seen from a tin/lead equilibrium diagram. {Link without Title} In plumbing, a higher proportion of lead was used. This had the advantage of making the alloy solidify more slowly, so that it 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. Since even small amounts of lead have been found detrimental to health, lead in plumbing solder was replaced by Copper or Antimony , with Silver often added, and the proportion of tin was increased (see '' Lead-free Solder '' below). HARD SOLDER As used for Brazing , is generally a copper/ Zinc or copper/silver alloy, and melts at higher temperatures. In silversmithing or jewelry making, special hard solders are used that will pass Assay . They contain a high proportion of the metal being soldered and lead is not used in these alloys. These solders also come in a variety of hardnesses, known as 'enamelling', 'hard', 'medium' and 'easy'. Enamelling solder has a high melting point, close to that of the material itself, to prevent the joint Desoldering during firing in the enamelling 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 soldering a new joint. Easy solder is also often used for repair work for the same reason. Flux or rouge is also used to prevent joints desoldering. FLUX CORE SOLDER Solder often comes pre-mixed with, or is used with, Flux , a reducing agent designed to help remove impurities (specifically Oxidised metals) from the points of contact to improve the electrical connection. For convenience, solder is often manufactured as a hollow tube and filled with flux. Most cold solder is soft enough to be rolled and packaged as a coil making for a convenient and compact solder/flux package. The two principal types of flux are acid flux, used for metal mending, and rosin flux, used in electronics, where the corrosiveness of the vapours that arise when acid flux is heated could damage components. 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 Deionised Water and detergent, instead of hydrocarbon solvents. Since solder can occasionally splash (due to the superheated flux inside or from contact with water in the cleaning sponge), it is recommended that Safety Goggles be worn when soldering. Though small solder splashes on skin are painful, they usually do not cause lasting harm. For large scale work additional protective clothing may be needed. LEAD-FREE SOLDER According to the European Union Waste Electrical And Electronic Equipment Directive (WEEE) and Restriction Of Hazardous Substances Directive (RoHS), lead had to be eliminated from electronic systems by July 1 2006 , leading to much interest in lead-free solders. These contain tin, copper, silver, and sometimes Bismuth , Indium , Zinc , Antimony , and other metals in varying amounts. The lead-free replacements for conventional Sn60/Pb40 solder have higher melting points, requiring re-engineering of most components and materials used in electronic assemblies. Lead-free solder joints may produce mechanically weaker joints depending on service and manufacture conditions, which may lead to a decrease in reliability using such solders. " Tin Whiskers " are another problem with many lead-free solders, where slender crystals of tin slowly grow out of the solder joint. These whiskers can bridge a short circuit years after a device's manufacture.
Different elements serve different roles in the solder alloy:
SEE ALSO EXTERNAL LINKS
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