Microstructural characterization of damage in thermomechanically fatigued Sn-Ag based solder joints

Sn-Ag based solder joints of 100-μm thickness were thermomechanically fatigued between −15°C and +150°C with a ramp rate of 25°C/min for the heating segment and 7°C/min for the cooling segment. The hold times were 20 min at high temperature extreme and 300 min at the low temperature extreme. Surface damage accumulation predominantly consisted of shear banding, surface relief due to Sn-grain extrusion, grain boundary sliding, and grain decohesion usually near the solder/substrate interface. Small alloy additions were found to affect the extent of this surface damage accumulation.