Gold dendrite simulation: root cause determination

While dendritic growth for Ag, Sn, and other metals provides jeopardy for the exterior of packaged integrated circuits, we observed Au dendrites inside ceramic packages. The key factors controlling growth kinetics are a combination of bias and two residual chemicals: one hygroscopic component from the die attach material, and gold plating salts. We found dendritic growth rate to be linear with plating salt concentration during laboratory simulations, but were unable to measure the current density dependence. However, the key factor was the presence or absence of residual nonylphenol, tracked down to an inadequate die attach bake schedule. Laboratory simulations produced the same dendrite morphology as seen for failed units. Furthermore, we found dendritic growth would occur only if all three factors were present-bias, nonylphenol, and the plating salts.