Recrystallization behaviour of SnAgCu solder joints

The recrystallization behaviour of tin in various SnAgCu solder joints, chip-scale packages (CSPs), 0402 resistors and single-overlap shear specimens was studied. The objective of the study was to determine the effect of solder composition (hypoeutectic, eutectic and hypereutectic SnAgCu), the surface finish of printed circuit board (PCB) and the type of the solder joints on the recrystallization of tin during thermomechanical fatigue and isothermal creep. The results show that after reflow the solder joints consist only of a few tin grains. During thermomechanical fatigue recrystallization nucleates at the locations where the strain is concentrated, i.e. in the neck region of CSP, in the solder between the 0402 resistor and PCB and in the vicinity of voids. The recrystallized grains facilitate the occurrence of intergranular fracture. The results indicate that solder joints with hypoeutectic composition have a tendency to recrystallize more readily than joints with eutectic or hypereutectic composition.