Creep of eutectic SnAgCu in thermally treated solder joints

The creep behaviour of Sn96.5Ag3.5 and Sn95.5Ag3.8Cu0.7 solder was studied specifically for its dependence on technological and environmental factors. The technological factors considered were typical cooling rates and pad metallizations for soldering joints in electronic packaging. The environmental factors included microstructural changes as a result of thermal aging of solder joints. Creep experiments were conducted on three types of specimens $flip-chip joints, PCB solder joints and bulk specimens. Flip-chip specimens were altered through the selection of various under bump metallizations (Cu vs. NiAu), cooling rates (40 K/min vs. 120 K/min), and thermal storage (24h, 168h, and 1176h at 125°C). PCB solder joints were studied by using a copper pin soldered into a thru-hole connection on a printed circuit board having a NiAu metallization. Bulk specimens contained the pure alloys. The creep behaviour of the SnAg and SnAgCu solders varied in dependence of specimen type, pad metallization and aging condition. Constitutive models for SnAg and SnAgCu solders as they depend on the reviewed factors are provided.