Analysis of the Impact of Polyimide Coating on Passivation Reliability by Simulation

In this paper, an advanced 3D FEA model framework with global and local sub-model is developed to investigate the impact of the polyimide coating on passivation reliability. The modeling work consists of two parts: the first part is the transient thermal simulation under a power pulse. The second part is the thermal mechanical stress simulation with the transient temperature input from the first part. Modeling and a small amount of empirical tests are conducted to evaluate the polyimide coating's impact to passivation. The highlights of this work include consideration of silica fillers in mold compound which penetrate through a thin polyimide coating and contact the passivation or being embedded in the passivation slot to show its impact to passivation. Dynamic power pulse modeling shows that the passivation stress is induced by mismatch thermal expansion and temperature gradients generated by power pulses. A modeling DOE scheme, which considers different polyimide thickness, ideal models vs actual models, silica fillers penetrating the polyimide layer, and silica fillers contacting passivation, is fully investigated and studied. The results show the optimal solution with the minimum stress on passivation, which can help to improve the reliability of product, reduce costs in product development and maximize the robustness of our products.