ESCA Analysis of Ageing of Metallic Surfaces: Solderability of Nickel Silver

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Abstract
Because of recent interest in nickel silver (copper‐zinc‐nickel alloy) in electronic applications, this alloy was chosen for an ageing‐solderability study. An Auger/ESCA study was performed on the surface of samples of nickel silver to determine the chemical nanostructure at various degrees of ageing (0–2 years). During this time a redistribution of the three constituent metals occurred, with migration of copper to the surface. All three metal constituents oxidised at different rates. Additionally, the thickness of the surface carbon layer increased with time. The effect of physical abrading (cleaning by erasing) of the samples on solderability, ageing, and chemical surface was also studied. After erasure, all samples appeared similar to one another and close to the original composition, and the copper oxide layer was completely removed. All the cleaned surfaces, when returned to the atmosphere, experienced air oxidation of copper to copper oxide in less than two days. Angle‐resolved ESCA studies were performed to determine the concentration gradient close to the surface. Nickel was not evenly distributed with depth, but was more concentrated on the surface of the cleaned samples. Solderability studies on nickel silver samples showed no improvement with chemical treatment, attesting to the creation of a resistant passivation layer.