The alloy of tin and lead is the one mainly used and other alloys are considered to fulfill any specific requirements as given earlier. The main constituents of the solder alloy are 60% tin and 40% lead, but they also often contain amounts of other relatively low melting metals such as bismuth, indium, and silver.

The extensive use of the Tin / Lead alloy is due the following reasons.

1. The melting point (183⁰ C- 189⁰ C) is low enough to permit the design of components that can endure the high temperatures associated with the soldering process.

2. Though the solder oxidizes quite rapidly, the characteristics of the tin oxide films pose relatively few problems compared with the oxide films of some other low-melting metals.

3. Because of the affinity between tin and many other metals, good wetting can be achieved with the aid of only mildly active fluxes.

4. It provides reasonably good mechanical strength to the solder joint, which can be expected with soft-soldering.

5. Because of the affinity between tin and many other metals, good wetting can be achieved with the aid of only mildly active fluxes. We will discuss fluxes and wetting at a later stage. Given below are some of the solder alloy configurations for various applications.