Edge tail length effect on reliability of DBC substrates under thermal cycling

Purpose - Direct-bond-copper (DBC) substrates crack after about 15 thermal cycles from −55 to 250°C. The purpose of this paper is to study the phenomenology of thermal-cracking to determine the suitability of DBC for high-temperature packaging.Design methodology approach - The thermal plastic strain distribution at the edge of the DBC substrate was analyzed by using a finite element method with the Chaboche model for copper. The parameters of the Chaboche model were verified by comparing with the three-point bending test results of DBC substrate. The thermal analyses involving different edge tail lengths indicated that susceptibility to cracking was influenced by the edge geometry of the DBC substrate.Findings - Interface cracking was observed to initiate at the short edge of the bonded copper and propagated into the ceramic layer. The interface crack was caused by the accumulation of thermal plastic strain near the short edge. The edge tail can decrease the thermal strain along the short edge of the DBC substrate. Thermal cycling lifetime was improved greatly for the DBC substrate with 0.5 mm edge tail length compared with that without edge tail.Research limitations implications - The thermal cracking of DBC substrates should be studied at the microstructure level in the future.Originality value - Thermal cycling induced failure of DBC was analyzed. A method of alleviating the thermal plastic strain distribution on the weakest site and improving the thermal fatigue lifetime of DBC substrates under thermal cycling was proposed.