Liquid Compression Mold Underfill Designed for One-Step Encapsulation in Overmold Process

We developed a novel material called Liquid Compression Mold Underfill (hereinafter called LCMUF). The LCMUF is applied to a new one-step wafer level packaging process which conducts both encapsulation of chip gaps and overmolding the entire wafer at one time by wafer-level compression molding machine. Therefore, this new one-step process improves workability and throughput compared with a conventional two-step process. This report focused on a material design for the LCMUF to achieve a chip gap flowability at molding process and reduce a wafer warpage after molding. In investigation 1, we optimized a distribution of filler particle size for the high filler content and the chip gap flowability at molding process. In investigation 2, we tried to decrease binder resin's modulus by applying a flexible epoxy and successfully achieved a low warpage molded wafer. As a result, we developed the LCMUF which enables the one-step process to encapsulate chip gaps and cover the entire chips at mold process simultaneously.