Filler Particle Distribution Impact for Interfacial Delamination of Underfill

As the market trends drive aggressive miniaturization and highly-integrated packaging solutions, Flip Chip (FC) technology has been widely recognized and adopted as the optimal solution. However, with integration and miniaturization come mechanical reliability challenges - primarily interfacial delamination and crack of 1st-level interconnection. Interfacial delamination between polyimide (PI) and underfill (UF - which contains epoxy polymer and filler particles) around the solder bump is one of the dominant issues attributed to open short electrical failure for FC devices. This study develops a predictive mechanical reliability modeling methodology using the FEA-based scheme to capture the local structure impact of filler particle underfill (UF) distribution and correlate it to empirical data obtained from thermal cycle (TC) test data. The methodology constitutes coupling an image-processing technique and light intensity analysis to extract the local difference in PI and UF filler particle distribution from the measured cross-sectional image. The temperature-dependent UF resin mechanical properties were derived using Mori-Taknaka's composite theory model coupled with dynamic mechanical analysis (DMA). In addition, the Anand model was employed to capture the rate-dependent plasticity of the solder material. Silicon validation of the modeling methodology was demonstrated on two real-life IC FC package devices under TC loading conditions. Good correlation between modeling and silicon measurements was achieved, which validates the integrity of the predictive modeling methodology.