Warpage Observation of Liquid Compression Mold Underfill on Strip Substrate

Liquid Compression Mold Underfill (LCMUF) is a liquid encapsulation material that was developed to encapsulate wafer-level packages of 12-inch silicon wafers using a compression molding machine. In this report, we applied it to a package of FR-4 strip substrate using a compression molding machine for wider application of LCMUF. To encapsulate the strip substrate, the process used Mold Underfill (MUF) with a transfer molding machine is commonly applied. In comparison, the compression molding process with LCMUF has the advantages of waste reduction of encapsulation material, low risk of chip misalignment, low heat damage to mounted components, and good flowability to chip gaps. On the other hand, since the warpage of the strip substrate after molding may cause problems during subsequent processes, such as grinding and dicing, it is essential to reduce the warpage of the strip substrate. Therefore, we optimized the Coefficient of Thermal Expansion (CTE) property of LCMUF and succeeded in reducing the warpage of the strip substrate after compression molding. Moreover, this LCMUF also shows good flowability to chip gap between mounted chip and strip substrate uniformly without voids.