Gold Dendrite Simulation: Root Cause Determination

Abstract

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.

Propensity of Copper Dendrite Growth on Subassembly Package Components Used in Quad Flat Package

“…Nieman [11] has found that, during biased highly accelerated stress test (HAST), Cu migration is proportional to chloride concentration in adhesive tape and is inversely proportional to conductor spacing. Recently, Kersey and Blish [12] reported Au dendritic growth in ceramic package due to the combined factors of bias and residual components from die-attach adhesive and gold-plate salts. However, most of the works mentioned tend to focus on failure mechanisms under the given stress condition rather than the dependence of Cu migration on subassembly package materials, which is a subject of significant practical interest and needs careful attention.…”