Microstructural and mechanical characterization of ceramic substrates with different metallization for power applications

The properties of metalized ceramic substrates, e.g. used in power electronic devices, are mainly influenced by the metallization layer and the interface metal/ceramic. This study presents results from microstructural analyses and mechanical characterization of Direct Aluminum Bonded (DAB) substrates in comparison to Direct Copper Bonded (DCB) substrates. High resolution electron (SEM) and transmission electron microscopy (HRTEM) characterization in combination with crystallographic microanalysis using electron backscatter diffraction (EBSD) show the formation of cupric oxide areas in combination of a complex copper, manganese aluminate system at the aluminum oxide/copper (DCB) interface. For DAB substrates the formation of a ternary Al-Fe-Si phase system was revealed along the aluminum oxide/aluminum interface. The detected interface formation exposed on both substrates indicates strong adhesion bonding strength between alumina/ copper and aluminum, respectively. Based on temperature-dependent Berkovich nanoindentation testing at room temperature to 250 deg C, a decrease of indentation hardness and modulus was shown for both types of metallization. The thermal expansion behavior of both substrates was investigated by a digital image correction method (ARAMIS by GOM) based on grey scale correlation. CTE was found to vary significantly in dependence of the alumina thicknesses and the respective metallization.