Failure Mechanisms of Direct Copper Bonding Substrates (DCB)

The instant of macroscopic crack starting and the location of first cracked area are described for direct copper bonding substrates. The first crack appearance is followed by subcritical crack growth in the ceramics. The direction of crack growth changes from mode II to mode I, because of residual stress in the assembly. Crack appears at symmetrical layouts preferential to one side depending on the manufacturing history of the DCB substrate. This effect can have two reasons. First, the loading caused by copper varies on both sides because of the serial bonding process. Second, the strength of the ceramic on both sides is different because of the growth of different interfaces between the copper and the alumina. By characterizing alumina, the same strength on both sides by a four point bending test can be found. Indention fracture experiments do not show a significant different behaviour in different breaking directions. Furthermore, the location of crack occurrence can be changed by the layout of the conductive pad and the aging of the assembly