Development of high current transfer-mold type power module with high heat-cycle durability [motor drive applications]

High current transfer-molded type power modules have been developed for industrial motor drive systems. The key issue in this development was to improve the heat dissipation characteristics of the existing transfer-molded package construction. To achieve this, a new concept of directly soldering power chips onto heat spreaders has been adopted. However, the strain on solder joints by heat-cycling stress became an issue in the development process. It has been solved by creating specially designed dimples on copper heat spreaders integrated in the structure and using a new resin, which has a linear expansion coefficient close to that of the metal. The durability of a new transfer molded type high-current power module, which has been developed based on the novel structural concept, has been ascertained by heat cycling and other tests. In this paper, the authors describe some major aspects of the new design and provide results of confirmatory tests performed on the device.