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Solder is a kind of fusible metal whose melting point is lower than that of the welded metal. When the solder melts, it can wet the welded metal surface under the condition that the welded metal does not melt, and form an alloy layer at the contact surface to connect with the welded metal. It constitutes a path for a circuit. Solders can be distinguished by two types: lead solder and lead-free solder.
Lead solder
That is (Sn, Pb) as the main raw material, solder is eutectic produced by the combination of tin (melting point 232 C) and lead (melting point 327 C). According to user's needs, the manufacturer will add some other metal elements to tin and lead eutectic to increase the properties of eutectic. In tin and lead alloys, except pure tin, pure copper and eutectic components melt at a single temperature, other alloys are melted in one region, so eutectic solder tin is the best kind of tin-lead solder. Traditional tin-lead solder is widely used because of its low eutectic point Sn63/Pb37, its eutectic temperature is 183 C, which is close to the heat resistance of PCB at present, and its good solderability, conductivity and low price. Sn-Pb solder is the main welding material in electronic assembly welding. With its high quality performance and low cost, it has been paid attention to.
Lead free solder
That is (Sn/Cu) as the main raw material of the alloy. According to the market demand, the manufacturer adds some metal elements such as zinc-zinc/silver-Ag/bismuth-Bi/indium-in to increase the performance of the alloy. The liquidus of lead-free alloys is generally higher than that of lead liquidus (about 34 degrees C), i.e. (Sn/0.8Cu alloy liquidus 227 degrees C, Sn/3.5Ag alloy liquidus 221 degrees C, Sn/3.5Ag/0.75Cu liquidus 221 degrees C-219 degrees C, Sn/10Bi liquidus 187 degrees C). A wide range of studies have shown that no lead-free alloys can directly replace lead-tin alloys. Therefore, great efforts have been devoted to the research and development of alloys that can replace lead-tin solders. Although each of these alloys has its own advantages and disadvantages, some of them are likely to replace Lead-Tin Alloys because of their excellent properties. With the rapid development of the world, solder is an indispensable welding material for electronic products. With the enhancement of people's awareness of environmental protection, human society increasingly recognizes that environmental protection is a necessary condition for sustainable development. The formulation and implementation of relevant government decrees, especially the formal entry into force of the EU WEEE and RoHS Directives on Discarded Electronic and Electrical Equipment, make it imperative for us to turn to lead-free assembly of electronic products. Only by turning to lead-free electronic assembly can we keep pace with the international development direction.
