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

•Serious warpage of IGBT power module is induced from assembly processes.•A pre-bending substrate with a curve opposite the warp is proposed.•Design is validated by FEA and related actual measurements.•Increasing DBC thickness of Al2O3 layer reduces warps and bonded solder stresses.•A thicker base plate is suggested to reduce warping of the entire packaging structure.

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.

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