Understanding the Atmospheric Degradation of Noble Metal-Plated Connector Materials

The current level of understanding of the atmospheric environmental degradation of gold-plated copper with and without a nickel underplate (and related materials) has limited the effectiveness of mathematical models aimed at predicting device lifetime/reliability. Efforts to understand this phenomenon have focused primarily on modeling the impact of the degradation (e.g.. change in contact resistance). Variability of in-service exposure conditions (e.g.. temperature. humidity, gaseous. and particulate contamination) coupled with the variety of metals of interest and environmental barriers in place (i.e., gaskets, connector geometry. sealants. etc.) hinders the effective application of such empirically based models. The goal of the research presented here was to develop a detailed understanding of the processes that govern the initiation. propagation, and stifling of corrosion/sulfidation sites on noble metal-plated alloys of relevance to electronic connectors. such that current and future process models may be refined to capture accurately the impact of atmospheric corrosion. Gold-plated copper coupons with and without a nickel underplate were exposed to a Battelle Class 2 (ASTM B845 Method G) mixed flowing gas environment. Selected regions of each specimen were mapped optically, cataloging the various corrosion sites located on the surface. A series of sites that were identified as being in various stages of their development were then cross-sectioned using a focused ion beam. Through this study, a qualitative description of the physical manifestation of each stage of the life cycle of an individual defect site that has undergone atmospheric corrosion in gold-plated copper with and without a nickel underplate has been developed.