Solder is a fusible metal alloy employed to create a permanent bond between metal workpieces. For the adhering and cooling, it requires that an alloy appropriate for use as solder has a lower melting point than the pieces being joined. Solder utilized in making electrical connections also requires having favorable electrical characteristics.

Lead-free solders in commercial use may comprise tin, copper, silver, bismuth, indium, antimony, zinc and traces of other metals. Lead-free solder typically needs flux by mass for adequate wetting ability. Lead-free solder is employed in wave soldering, a slightly modified solder pot may be desirable (e.g. titanium liners or impellers) to decrease maintenance cost because of increased tin-scavenging of high-tin solder.

Tin-silver-copper solders are utilized by two-thirds of manufacturers for reflow and wave soldering. The famous soldering is hand soldering and Cu solder, which is also commonly utilized for solder bumps. The usage of SnCu alloys with additives, for instance, Ni, Ga, Bi, and Co for wave and rework solder applications. Moreover, lead-free solders also employed for reflow applications.

New alloy designs are being developed which use the same concepts as those applied to the development of advanced superalloy for jet engines. Lead-free solders have been performed on circuit board test vehicles. The current Pb-free solder compositions are compatible with the new finishes in terms of solderability and mechanical properties essentials.

Lead-free solders have requisite solderability (i.e., sufficiently low contact angles) to support cost-effective assembly processes for electronic components and printed circuit boards. Sn-Zn Lead-free solders have tensile strength, initial strength, prolonged strength of change than the Sn-Pb solder system is superior. Sn-Bi system the preservation of stability, it can be used with substantially the same Sn-Pb solder flux in the atmosphere in the welding.