A power module, which includes aninsulating plate soldered to a heatsink, is called adirect-cooled power module. There are severalpackaging technologies to improve a direct-cooledpower module in terms of not only reduction ofthermal resistance but also elongation of lifetime.Among those approaches, this paper describesoptimization of heatsink thickness and prevention ofratchet deformation. The calculation results showthat a thicker heatsink is better to avoid liquidleakage although thicker heatsink provides shortersolder-lifetime. A heatsink with Vickers hardness ofgreater than 60 MPa is expected to prevent ratchetdeformation under the condition of thermal cyclingbetween —40oC and I25oC.
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