Ceramic substrates with aluminum metallization for power application

The reliability of power electronic devices is significantly related to the material properties of the applied substrates which carry the semiconductor chip and the electric interconnections. The most common solution to fulfill the stringent requirements of these devices, with respect to high isolation voltage, good thermal conductivity, high temperature cycling reliability and low cost, is to use ceramic substrates with copper layers on both sides. However, the currently increasing reliability standards in power electronics lead to a situation where common DCB substrates reach their limits in meeting these higher requirements. In previous years, ceramic substrates with aluminum instead of the copper metallization layers (Direct Aluminum Bonding, DAB) were introduced. For DAB substrates, a higher reliability especially for temperature cycling tests was found. In this study, results of Finite Element simulations of DAB substrates are presented. For the DAB samples, significantly lower mechanical stresses inside the ceramic were found in comparison to DCB substrates with the same thermal loading situation, thus explaining the improvements in reliability. In addition, the DAB bonding contacts between the aluminum metallization and the alumina were assessed by Scanning Acoustic Microscopy (SAM) and microstructure analysis on cross sections by Scanning Electron Microscopy (SEM) and Energy Dispersive x-ray spectroscopy (EDS). The results indicate good adhesion between the metal layer and the ceramic due to the found interface microstructure and the lack of defects. Thus, Direct Bonded Aluminium (DAB) substrates provide a promising alternative solution to realize more reliable substrates for power electronic devices, in particular to consider the increasing requirements from automotive and avionic industry.