Abstract:
In this study, Sn-Cu-Ni-Ge solder alloy was selected for the purpose of lead-free
solder joint reliability comparison with Sn-Ag solder alloy on Ball Grid Array (BGA)
packages. Ball impact shear and pull tests were performed as assembly, after high
temperature storage and multiple reflow to examine the mechanical strength of the
solder joint. Sn-Ag alloy performed higher shear and pull strength due to the thinner
intermetallic layer formed. Sn-Ag showed zero intermetallic brittle fracture in pull test
at variable stress condition. In comparison with Sn-Ag, Sn-Cu-Ni-Ge alloy showed
95-100% brittle fracture. The difference in the strength was due to the intermetallic
compound (IMC). The smaller IMC thickness and area of Sn-Ag alloy was due to
lower reaction rate of Ni and Sn. As a result, Sn-Ag could provide a better and more
reliable solder joint system.
