2013 Volume 54 Issue 3 Pages 332-336
Using an organic solderability preservative (OSP), the morphology and microstructure of Sn–9Zn–1Al (SZA) and Sn–8Zn–3Bi (SZB) lead-free solder pastes used to assemble BGA packages with Sn–3.8Ag–0.7Cu (SAC) solder balls on a printed circuit board (PCB) were investigated. The scallop-shaped (Cu,Ag)5Zn8 intermetallic compound (IMC) is formed in both SZA and SZB solder joints, and the belt-shaped (Cu,Ag)5Zn8 IMC is also formed at the interfaces of both SZA/Cu and SZB/Cu. At 125°C, the Zn atoms in the IMC layer have sufficient energy to diffuse towards the Cu pad and react with it. The IMC belt composed of island-shaped compounds formed in the SZA and SZB solder joints and the size of island-shaped compounds and amount of microvoids increased after 1,000 times thermal cycling.