Crack initiation and propagation mechanism of Al2O3-DBC substrate during thermal cycling test

Abstract

For high power density modules, improving the reliability and the fatigue lifetime is a real challenge. The direct bonding copper (DBC) substrate is really critical for a suitable and reliable packaging integration, conduct detailed thermo-mechanical analysis and failure mechanism study causes for concern. In this paper, we thoroughly study the failure process of Al2O3-DBC substrate during thermal cycling from −55 °C to 150 °C by experimental, theoretical and finite element numerical methods. The failure phenomenon of DBC substrates were observed by scanning acoustic microscopic. The cross-section sample was tested by microscope and scanning electron microscope to further determine the crack initiation and propagation process and mechanism. It can be found that the crack deviated from original crack direction with a certain angle and propagated into ceramic. After a certain length of crack growth, the crack propagated along the direction parallel to interface and finally caused substrate completely broke. Based on experimental results, we established failure mode of DBC substrate during thermal cycling test, applied interface stress intensity factor K to build interface crack propagation and deflection criterion of DBC substrate, and calculated the interface thermal stress intensity factor for DBC substrate by both theoretical and numerical methods. The analyzed results agreed well with the experimental observations.