Comparison Studies on Joint Process for ENEPIG Surface Finished Chip for Double-sided Cooling Module

With increasing power density, double-sided cooling packaging strategy for power module showed a better choice to maximize the power dissipation than the traditional single side cooling assembly method. However, most commercial chip's front electrode for module assembling is an aluminum metallization layer, which is non compatible for most soldering and other joint process and not suitable for double-sided cooling packaging. Thus, a new metal layer such as Au is required for the following solder process. Electrode metal finish by the process of Electroless nickel-electroless palladium-immersion gold (ENEPIG) has high flatness and excellent solderability with low production costs and particularly without "black pad" compared with the finish by the process of electroless nickel-immersion gold (ENIG). In this paper, we studies on the ENEPIG process as surface finishing for commercial Al electrode type power electronic chip, and three different types of bonding methods (Au80Sn20, SnAg3Cu0.5, Nano-silver paste) were applied to evaluate the electrode-substrate joint quality by shear strength comparison. This work will provide a good reference for chip surface finish process for double-sided cooling packaging and selection of electrode-substrate joint methods.