Are Dark Spots on Gold Plating Cosmetic or a Reliability Risk?

This case study demonstrates how a correlative analytical workflow was used to determine whether dark spots on a gold-plated electrical contact represented cosmetic discoloration or contamination that could compromise wire bond reliability. Conductive atomic force microscopy (AFM) revealed that the visible dark spots corresponded to relatively flat regions, while the brighter areas contained conductive islands approximately 10–20 nm tall. Photo-induced force microscopy (PiFM) identified localized siloxane (PDMS)-related chemistry on the raised islands and distinct CH₂-rich chemistry in the surrounding regions, indicating multiple surface species. Time-of-flight secondary ion mass spectrometry (TOF-SIMS) mapped widespread PDMS residue, handling-related contamination, and trace surface elements, but found no direct correlation between the visible spots and localized chemistry. Together, the results showed that the discoloration arose from a combination of nanoscale topography, surface contamination, and roughness rather than electrically insulating defects, helping the customer determine that the observed spots were cosmetic rather than a functional threat to wire bond performance.