Copper thick-film substrates for power electronic applications

Abstract

Substrates for high power electronic systems are dominated by DCB-technology. Recently, new copper thick-film pastes have been proposed for use as high power substrates. They are compatible with Al2O3- and pre-oxised AlN-substrates. This paper investigates production processes to build up highly reliable power modules and explores basis electrical and thermal properties of thick-film copper substrates. Fired copper film thicknesses of 300 μm have been produced by subsequent print-dry-fire cycles. Smooth surfaces and copper films with a density of about 70 % of bulk copper have been produced. A power module comprising of 650 V IGBTs, diodes and an intelligent hall sensor with copper traces and spaces of 200 μm is presented. Wire bonding processes on copper thick-films with 500 μm aluminium wire and 400 μm copper wire are discussed. Test units with a 1200 V IGBT were built up. The IGBT was attached at 250 °C and a pressure of 15 MPa using a novel silver sinter paste. This paste can be directly used on copper. The current-carrying capacity of the thick-film test samples was found to be reduced by 10% in comparison to the DCB test device. No significant difference was found in the performance of both technologies in active power pulse tests lasting a few seconds. The number of cycles for test devices with sintered chips, bonded with 400 μm copper wire bonds exceeded 450,000 cycles in a cycles from 25 °C up to 150 °C.