Effect of Ag on IMC Growth and Shear Strength of Sn-3.5Ag/Cu microbumps

In three-dimensional interconnect packaging field, the size of copper pillar bumps (CPB) has dropped to 20 μm or even smaller, so exploring the growth mechanism and mechanical properties of small, high-density bumps becomes an important issue. In this research, uniform Sn-3.5Ag/Cu and Sn/Cu bumps were prepared by multilayer electroplating and the effect of Ag on Sn/Cu interfacial reaction during aging at 150 °C as well as shear strength of bumps were investigated. During the aging, Ag
₃
Sn formed between Sn/Cu
₆
Sn
₅
interface in Sn-3.5Ag/Cu bump which inhibited the grain boundary diffusion of Cu and the growth of Cu
₆
Sn
₅
. The intermetallic compounds (IMC) growth rate of Sn-3.5Ag/Cu and Sn/Cu bumps were calculated as 1.19×10
^-17
m
²
/s and 2.55×10
^-17
m
²
/s. Meanwhile, Ag had adverse influence on Cu
₆
Sn
₅
shear strength in Sn-3.5Ag/Cu compared with that in Sn/Cu microbump before aging for 400h, which was ascribed to the balance between precipitation and pinning effect of Ag
₃
Sn.