Flip-chip on flex integrated power electronics modules for high-density power integration

Three-dimensional flip-chip on flex (FCOF) integrated power electronics modules (IPEMs) have been fabricated for highdensity power applications. In this FCOF-IPEM structure, solder-bumped devices were flip-soldered to a flexible substrate with electrical circuits etched on both sides. One side of the flex provides interconnection to power devices while the other is used to construct a simple gate-drive circuit; via holes through the flex integrate the power stage and gate-drive together. Solder-bumped MOSFET devices were obtained by a metallization processing and were used in the FCOF power module construction to improve thermal performance, power density, and integration. With this packaging approach, the multiple solder bumps, instead of the thin, long bonding wires were utilized to connect the power devices to the flex substrate and to improve heat dissipation, lower parasitic oscillations, and reduce package size. Reliability of solder joints has been dealt with through selection of materials, such as use of flexible substrates and underfill encapsulation, and design of joint shape for lower thermomechanical stresses. A comparative study of continuous switching test results have shown that the FCOF-IPEMs have better electrical performance than commercial wire bonded power modules.