Wafer level embedding technology for 3D wafer level embedded package
This paper presents the development of wafer level embedding process for a three dimensional (3D) embedded micro wafer level package (EMWLP). Wafer level embedding process was carried out by using compression molding machine and low-cost granular epoxy molding compound (EMC). Various molding process parameters such as molding time and temperature and three EMCs of different CTEs were analyzed to achieve reliable 3D EMWLP. Several molding process issues, such as warpage, die-sweep, EMC penetration, and die-shift, were faced during embedding process development. A large warpage of more than 1 mm and die-shift of more than 600 µm were found to occur in reconstructed molded wafer. Wafer level embedding process was optimized to reduce warpage and die-shift problems. A significant reduction in warpage (∼ 30 %) and die-shift (∼ 88 %) were achieved after embedding process optimization. The detail of process optimization is presented in the paper. Reconstructed molded wafers were subjected to various reliability tests, such as thermal cycle (TC), moisture sensitivity test-level 3 (MST-L3), and highly accelerated stress test (HAST). Scanning acoustic microscopy (SAM) analysis of molded wafers was carried out to analyze the void formation and delamination in molded wafers. No major void or delamination was observed in reconstructed wafer after molding as well as after reliability tests.