This chapter discusses the evolution of lead free (Pb-free) solder, from tin-silver-copper (SAC) system with silver content of 3.0, 3.8, and 4.0 to low SAC system such as SAC0307 and SAC105 and the emerge of high reliability Pb-free solder. The discussion covers the reason and the driving force of industries implementing this change. The solder composition has evolved further recently to fulfill high reliability requirement of certain sectors such as automotive, aerospace, and military which are preparing to go green in soldering technology. This kind of high reliability solder involves additional microalloying of tin (Sn)-based solder in making it to be more robust. In this chapter, the author will introduce the techniques used by solder makers and researchers in enhancing the Pb-free solder strength in the recent evolution. Recently, attention has been drawn to low temperature joining technology again such as silver sintered joint and liquid-phase diffusion bonding material used in high power density and high junction temperature-integrated circuits. Pb-free joining material is required to replace the high Pb solder, which is still commonly used in such high-power devices.
Part of the book: Soldering Materials