In this study, we developed the Molded Underfill (MUF) technology for system in package (SiP) module with fine pitch flip chip in RF application, in which two flip chips, LC filter, and additional passive components are integrated side-by-side. This study covered not only MUF reliability performance but also MUF design study focused on the void free methodology to minimize void between flip chip bumps in the SiP module. The investigation comprises several aspects: A design study that present a printed circuit board (PCB) and epoxy molding Compound (EMC) selection approach, air vent design of cavity vacuum molding, and void formation mechanism by mold flow simulation and DOE(Design of Experiment) of several SIP module layouts.

The test vehicle used for this study of MUF by vacuum transfer molding shown as SiP module (8.2×7.7×1.13mm) which was sawn from 52.70×68.70×0.75mm mold area of 118.5*75.5*0.38 substrate. One segment mold inside (52.70× 68.70×0.75mm) had 35ea SiP modules (7X5 unit array). In addition, one SiP module included one Flip chip RF/BB IC(6.51×5.81×0.41mm) which had 339ea bumps and 95um Bump height, one Flip chip RF switch (0.705×0.705× 0.33mm) which had 4 bumps and 85um bump height, 1.6×0.8×0.6mm size of LC filter, and total 25ea passives.

In the end, SAT result of void, moisture sensitivity test, thermal cycle test and pressure cooker test had also been carried out for reliability evaluation. The test result shows that the optimized SiP module with fine flip pitch has a good reliability performance.

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