Temperature cycling aging studies of Zn-based solders for high-temperature applications

Power semiconductor packages are prone to reliability issues related to microstructural changes, thermal fatigue and thermo-mechanical stresses during high temperature operation. This paper evaluates the reliability of various Pb-free Zn-Al-based solder alloys used as die-attached solder during thermal cycling aging. Minimal interfacial intermetallic compounds (IMCs) growth was observed after 1500 thermal cycles. However, brittle solder cracks were observed in the solder joint after prolonged thermal cycling aging, with preferential cracks occurring near the edges of the Si die-solder interface and surrounding solder defects such as voids and delaminations. Thermo-mechanical FE simulation shows an increase of stresses of at least 50%-61% for void and delamination in various locations within the solder interface. Simulated stress contour plots concurred with crack initiation sites observed during failure analysis of the thermal cycle aged die-attached leadframes.