Microstructures Variations of Sn–9Zn–1Al and Sn–8Zn–3Bi Solder Pastes with Sn–3.8Ag–0.7Cu Solder Balls on OSP PCBs after Thermal Cycling Test

抄録

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.