Measurement of Backside Flip Chip Die Stresses using Piezoresistive Test Die

Thermal cycling of flip chip assemblies is one of the commonly used tests to identify potential reliability concerns. The CTE mismatch among dissimilar materials in a flip-chip assembly produces thermo-mechanical stresses, which can lead to failures such as solder cracking, interfacial delamination, die cracking, etc. Although much work has been done in understanding the eutectic solder fatigue failure during thermal cycling, not much work has been done in understanding the stresses induced during underfill cure and the subsequent evolution of these stresses during thermal cycling. In this ongoing research, a comprehensive theoretical and experimental study has been carried out to understand the development and evolution of stresses on the active side of the die during thermal cycling.