Effect of Chip Metallization and Process Parameters on the Die Attach Properties of Direct Bonded Power Devices

In this paper, the direct bonding is investigated as a die attach technology for commercial power devices depending on chip metallization and process parameters. For that purpose, insulated gate bipolar transistors (IGBT) with different backside metallization such as Ag, Pd and Au were attached onto Ag metallized direct bonded copper (DBC) substrates. The resulting Ag/Ag, Pd/Ag and Au/Ag joints were examined using mandrel bending test, scanning acoustic microscopy (SAM) and cross-section analysis with scanning electron microscopy (SEM). The results show that the bonding strength of the interconnect increases for longer process time and higher temperature and depends on the combination of metallization. To estimate the reliability of the resulting joints, power cycling tests of direct bonded IGBTs were performed using thin Al wire bonds for topside interconnection. Twenty samples were subjected to a temperature swing of 110K reaching up to 651,000 cycles before end of life. Failure analysis revealed a degradation either of the Al wire bonds or of the backside metallization of the IGBT.