A comparison study of SnAg and SnCuNiGe alloy on mechanical strength of lead-free bga solder joint on selectively plated Ni/Au finish

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.