Thermal ratchetting effect of AMB-AlN ceramic substrate: Experiments and calculations

Active-metal-brazing aluminium nitride (AMB-AlN) ceramic substrate with high thermal conductivity can provide a good alternative to conventional substrates in the high-temperature applications. However, the reliability of ceramic substrate when exposed to thermal cycling is still an issue. The aim of this study is to address the cyclic growth of warpage and stress of AMB-AlN ceramic substrate subjected to cyclic thermal loading (20-200-20 degrees C), which is of great significance for exploring the failure mechanism of ceramic substrate. The experimental results show that there is a hysteresis between the curves of bending height in the heating and cooling process, which can be explained by the Bauschinger effect. In addition, after five thermal cycles, the bending height of the ceramic substrate accumulates, showing a thermal ratcheting effect. By performing finite element analysis, it is also demonstrated that the warpage and stress of the ceramic substrate accumulates during the cyclic process. Furthermore, the stress on the ceramic layer is caused by the sum of the equivalent plastic strain of the copper layer and the filler metal, which is related to the thickness of the copper layer and the filler metal.