Ambient Effects on Gold-Aluninum Bonds

It has been observed that gold-aluminum bond degradation is dependent upon the ambient gas that exists in an integrated circuit package. Hermetic samples, which characteristically exhibit severe bond degradation when subjected to a stress of 250°C for 50 hours, were found to have an order of magnitude improvement in time-to-failure when subjected to the same temperature stress, but with the bonds exposed to an open air ambient. A bond pull strength of less than 1.0 gram was used as a failure criteria. Significant metallurgical effects were observed to correspond to the bond strength data. Mass spectrometry techniques were used to gas analyne both degraded and unstressed samples in an effort to determine the gas which causes the severe degradation. Although many residual gases were observed in the hermetic samples, none could consistently explain the observed effect. The analysis leads to the conclusion that there was no gas in the hermetic samples causing the degradation. Rather, it was concluded that the presence of oxy, gen substantially extends the life of gold-aluminum bonds.