Copper wire degradation under the effect of different humidity levels

In this study, the degradation of copper wire under different humidity levels is investigated. Unbiased and biased high temperature and high humidity accelerated stress test (HAST) with a cumulative duration of 960 hours are conducted. The stress tests are carried out at temperature of 130aC and relative humidity (RH) of85%, 50% and simulated dry condition. The test vehicles used are ceramic dual in-line package with and without molding compound encapsulation with bare copper wire bonded directly onto the gold-plated lead frame. From the in-situ electrical testing and failure analysis, significant degradation and failures observed for test packages in 130C 85% RH stress whereas 130aC 50% RH and simulated dry condition have relatively flat response with no failure. There is no significant difference in the electrical results between the biased and unbiased stress test. The degradation observed has been investigated and it is due to the oxidation of copper at stitch bond interface.