Solder wire is a fusible metal with a melting point lower than that of the metal to be soldered. When the solder is melted, the surface of the metal to be soldered can be wetted under the condition that the metal is not melted, and an alloy layer is formed at the contact surface to connect the soldered metals together. In general electronic product assembly, tin-lead solder, commonly known as solder wire, is mainly used.

The temperature requirement for lead-free solder wire is higher than that of lead-free solder wire. The melting point of lead-free solder wire is about 227 degrees. The welding surface tension of lead-free solder wire is large, and the wetting ability is poor. The appearance of wire solder joints is relatively rough, the pores in the solder joints are relatively large, and the requirements for the wetting angle are relatively large. Without the half-moon lead-free solder wire, the requirements for additives are relatively high. It is necessary to improve the activity of the additives and increase the activation temperature requirements. .

The supply of tin raw materials for lead-free solder wire is currently stretched. The current global annual output of solder wire is 230,000 tons, which is widely used in metal connection and surface treatment and plating. The world annual output of lead-free solder wire, the main component of tin, is 210,000 tons, of which 60,000 tons are used as raw materials for solder wire. According to the calculation of mortal tin accounting for 60% of soldering estimates, the annual output of new solder wire should be 100,000 tons, and the remaining 130,000 tons are solder wires that are re-used from residues. Lead-free solder wire cannot be made from lead-containing re-used solder wire, so it must be made with raw tin. Although the density of lead-free solder wire is 10%~20% lighter than the original eutectic solder wire, considering the factors of weight reduction, 200,000 tons of raw materials are still required to produce lead-free solder wire every year.