This paper discusses an experimental effort to investigate potential failure mechanisms associated with humidity cycling conditions of polymer-overlaid high-density interconnects.  Cut (cross-sectioned) and uncut test modules (GE TEG4 and NASA SEC) were subjected to 100 cycles (1,600 hours) of humidity cycling between 45% and 95% relative humidity at steady-state temperatures of 23^oC and 85^o C.  The results of environmental scanning electron microscopic investigation and optical microscopic investigation indicated interfacial delimitation at certain locations.  Electrical measurements showed that electrical resistance changed less than 10%.

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