Three-dimensional flip-chip on flex packaging for power electronics applications

We have extended the concept of flip-chip technology, which is widely used in IC packaging, to the packaging of three-dimensional (3-D) integrated power electronics modules (IPEMs). We call this new approach flip-chip on flex IPEM (FCOF-IPEM), because the power devices are flip-chip bonded to a flexible substrate with control circuits. We have developed a novel triple-stacked solder bump metallurgy for improved and reliable device interconnections. In this multilayer structure, we have carefully selected packaging materials that distribute the thermo-mechanical stresses caused by mismatching coefficients of thermal expansion (CTEs) among silicon chips and substrates. We have demonstrated the feasibility of this packaging approach by constructing modules with two insulated gate bipolar transistors (IGBTs), two diodes, and a simple gate driver circuit. Fabricated FCOF-IPEMs have been successfully tested at power levels up to 10 kW. This paper presents the materials and reliability issues in the package design along with electrical, mechanical, and thermal test results for a packaged IPEM.