Structure Optimization and Reliability Investigation on Copper Pillar Interconnections for Double-sided Cooling Power Module

Double-sided power modules provide another heat dissipation channel to meet the demands of rapidly increased power density for power module. However, double-sided structure incurs reliability issues resulting from chip tilt with large area solder during reflowing process, especially in the region of gate pad. Copper pillar interconnection has been proposed to solve this problem by providing anchoring support during reflowing, though it brings higher thermal stress simultaneously. In this work, the height, diameter and pitch of copper pillar interconnection structures in double-sided power module are analyzed via finite element method. Besides, equivalent thermal model, block model and strip model based on FEM are employed to investigate the influence of different copper pillar interconnection structures on thermal and thermomechanical performance. The results indicate that a finer pitch, larger diameter and smaller height of copper pillar interconnections generate smaller thermal resistance and can obviously reduce the thermal stress. Specifically, the maximum junction temperature variation caused by different structures reaches to 7.49°C. The stresses of chip, copper and solder are decreased up to 33.08%, 33.37% and 9.16% respectively with pitch of 200μm, diameter of 130μm and height of 40μm compared to the structure with maximum stress. The stress distribution of chip and copper pillar at different locations are analyzed, and the stress concentration appears at the interface of chip and copper pillar.