**1.3. Lead free packaging materials**

Large number of Pb-free solder alloys have been developed and studied where Sn is the major fraction. The most popular Pb-free alloy system candidates are narrated in detail in a review paper in Ref. [7]. In the present state, the advanced solders that have been developed so far are mostly Sn coupled with other elements like Cu, Ag, Zn, Bi, Sb, Ni.[8–14] Among all the binary eutectic Pb-free alloys, Sn–Ag, Sn–Zn, and Sn–Cu are considered to be the potential candidates to replace Sn–Pb. For ternary alloys, the most commonly used system is Sn–Ag– Cu which is proved the most effective due to its lower melting temperature and superior mechanical properties compared to the other combinations.[15] However, there exist some issues of reliability such as the formation of brittle/needle type intermetallics of Ag3Sn and Cu6Sn5 in ternary alloys which damages the mechanical and soldering properties.[5, 16] These Sn-rich alloys are sensitive to tin whisker growth if prolonged for a long time which is known to cause short circuiting in electronic devices. The major driving force for tin whisker growth is known to be the internal residual stresses due to the inherent compounds like Cu6Sn5, Cu3Sn with time.[5]
