Study and realization of a low force 3D press-pack power module

The purpose of this study concerns the packaging of the vertical power chips used for medium power level modules, from hundreds of W up to several kW. We present a new vision of electrical components packaging that permits to improve the standard switching cell characteristics commonly used in power electronics. We define a generic element that could be the basic element used for the power modules assembly as it is presented in the PEBB approach. The concept developed consists in a 3 Dimension geometrical switching cell packaging. The implementation strategy is based on a low force pressed contact. Then, the feasibility evaluation requires an electrical and a thermal characterization of metal-metal interface in the case of contact under reduced force. A measure bench dedicated to the characterization of joints like the ones in press-pack modules has been realized. We characterized first an Al-Cu pressed contact. Results were compatible with targeted applications. (i.e. thermal contact resistance Rth = 0.15degC.cm2/W and the electrical contact resistance Relec = 0.2 mOmega.cm2). After that we modified the first measure bench to be consistent with the characterization of electro-thermal contacts on both sides of a power diode. The resulting values of thermal and electric contact resistance were still consistent with our application (i.e. Rth = 0.12degC.cm2/W and 0.2 mOmega.cm2 < Relec < 0.9 mOmega.cm2). To validate our concept and substantiate this research, a power module prototype operating under low force clamping, and implemented to emulate a buck chopper function, has been designed and realized. First experimental tests validate the operation and feasibility.

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