Hybrid power modules using a metal matrix composite baseplate: An evaluation

This paper presents an evaluation of the reliability of hybrid power modules using a metal matrix composite baseplate. In this study, we investigate the possible damage in the assemblies by measuring their thermal resistance. Several 2"/spl times/1" power module samples including four bipolar transistors (BUX48) have been realized with the use of a vacuum bake soldering machine allowing reduction of voids in the solder joints. The test vehicles have been submitted to liquid-liquid thermal shocks (+125/spl deg/C/-55/spl deg/C). Every 250 thermal shocks, two samples were extracted in order to measure the thermal resistance. Results show that even after 2700 shocks, only a very small increase in the thermal resistance of the assemblies is observed. In comparison, modules with a copper baseplate show a strong increase in thermal resistance and fail much earlier. As a consequence, in applications where thermal cycling is involved, hybrid power modules with metal matrix composite baseplates will offer much better reliability. SEM observations conducted on cross-sectioned samples and acoustic analysis do not show the typical cracks generally observed in solder joints between the direct bonded copper substrate and the copper baseplate of aged modules.