Processing and Characterization of Module to Heatspreader Interface

To successfully implement a packaging concept, it is imperative to resolve many challenging issues related to materials and processing, which will result in improved thermal management of the power electronics modules. Almost every parameter of a power device is a function of temperature. The heat generated by these active devices, which reduces circuit efficiency, may also degrade circuit performance or cause the circuit to fail prematurely. Therefore, packaging engineers must design the mechanical assembly to address the trade-offs of efficiency, reliability and, cost versus thermal performance. In high-power electronics modules, the heat generated by the power devices is transferred to the ambient environment by attaching a heat spreader to the semiconductor package. Once the heat spreader is selected, it has to be attached optimally to the semiconductor package to ensure efficient thermal management through the thermal interface. In most power electronics modules, solder or thermally conductive epoxy is used to eliminate the air gaps by conforming to surface irregularities; however, these bonding agents introduce interfaces and/or interlayers of finite thickness. While strong interfaces are necessary to ensure mechanical integrity of the bonded components, they are responsible for lowering the electrical and thermal conductivities of the assemblage. Thermal resistance of the joint is directly proportional to the interface thickness and inversely proportional to the thermal conductivity of the interface material as well as to the area of the heat transfer. Moreover, these layers are quite non-uniform and consist of voids, which introduces anomalous thermal spreading.