High performance wafer level underfill material with high filler loading

A new wafer level underfill material with filler content of 60 weight % was developed for high performance flip chip applications with lead free solder bumps. Systematic optimization of the viscosity behavior led to good spin coat ability even for the material with high filler loading. The material can be applied onto the bumped wafer with high uniformity up to a thickness of 100 |xm by spin coating. The thickness variation was less than 5%. Additionally, void reduction in the package was realized by optimizing the curing process. By controlling the viscosity during the post-curing step voids in the package can be eliminated. Finally, the package with the new wafer level underfill material exhibited good reliability including during thermal cycling.