Investigation of pre-bending substrate design in packaging assembly of an IGBT power module

Abstract

Serious warpage and a high level of thermal stress or strain resulting from the heavy coefficients of the thermal extension mismatch between direct bonded copper (DBC) and a copper-base plate are obviously introduced into module structures in the packaging of the power modules of an insulated gate bipolar transistor (IGBT) during multi-temperature cycles of assembly. The aforementioned phenomenon is unfavorable in maintaining the long-term reliability of an IGBT power module because failure modes such as burn-out of connected wires among IGBT chips and growth of cracks in the soldered materials between the DBC and base plate could occur. A pre-bending substrate with a curve opposite the warp direction is proposed in this paper to eliminate warping as well as to achieve suitable co-planarity. The proposed design is found to be effective via finite element method-based simulation validated by experimental measurements. A thick base plate is also recommended to reduce warping of the entire packaging structure based on the predictive results of parametric analyses of the thickness of the Al2O3 and copper-base plates.