Lead-Free Solder

Abstract

The motivation for developing lead-free solders is to remove Pb from electronic manufacturing and waste disposal processes. There has been vigorous development of alternative solder alloys largely based upon Sn. These new solder materials have properties that differ from Pb–Sn eutectic solder that have required changes throughout the printed circuit board and package technology and infrastructure. Because solders perform at 80% of its melting temperature, they require performance comparable to superalloys used in jet engines, yet demands on solder joints are continually increasing due to increasing current density and stress states arising from miniaturization. Design with lead-free solder requires die and circuit board design that considers the higher melting temperature, and stronger and anisotropic mechanical properties. As design tools are increasingly based upon computational modeling, fundamental properties of new solder alloys are needed, which recognize the intrinsic anisotropy of tin, effects on property evolution arising from thermal cycling, high current density, environmental boundary conditions such as vibration, residual stress effects, electrochemical attack, and tin whisker formation. These phenomena need to be understood before they can be modeled, and thereby anticipated.