Singular Uniformity after Reflow of Varied-Shaped Flip Chip Solder Bump on Single Substrate

In order to get better electrical performance and layout flexibility, adopting different profiles of solder bumps in flip chip packaging is inevitable. In this study, we mainly compare the effects of reflowed solder bumps coplanarity by altering their contours, magnitudes and volumes. By using Surface Evolver simulating software, we could further analyze and compare the differences in coplanarity between the practical plating-based solder bumps and their final simulating results. Since the plating-based solder bumps are usually prone to suffer rugged mushroom-like structures after plating, extremely influencing their coplanarity after reflow, we thus utilize an extra polishing mechanism after plating to eliminate those annoying mushroom-like structures in order to promote coplanarity after reflow. Utilizing this uniform coplanarity enables us to obtain optimization in solder bumps layout. The final results indicate that the volumes and magnitudes of solder bumps have great impact on bumps' height and fatigue after reflow, while the shapes have relatively minor influence. Finally, combining the simulation results with the practical fabrication models gives us the benefits of getting better design and layout in solder bumps used in the future advanced flip chip packaging.

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