Corrosion Resistance of Copper-Coated Contacts

Abstract

Corrosion of electronic components can produce a wide range of failure signatures, from intermittent electrical faults to complete functional breakdown. This paper presents an investigation on the exposure of a simple connector-coating system. The system consists of a copper contact coated with a nickel layer underneath a gold finish layer. The system was characterized using the following techniques: optical microscopy, atomic force microscopy ͑AFM͒, scanning electron microscopy ͑SEM͒, energy dispersive X-ray spectroscopy ͑EDAX͒, secondary ion mass spectroscopy ͑SIMS͒ and focused ion beam ͑FIB͒. After initial characterization, the connector was exposed to 2, 4, 7, 15, and 30 days in an aggressive environment consisting of 90% relative humidity, 40°C, and 4 ppm H 2 S. Digital images of the corrosion products that developed on the contacts after exposure clearly demonstrated localized corrosion by-products present on the connector surface. SEM, EDAX, and SIMS analysis of the corrosion sites demonstrated the presence of copper sulfide and nickel sulfur corrosion product, which suggest a two-step mechanism: first, the Ni layer is attacked by the aggressive environment at the sites where the gold layer is not available, followed by the diffusion of copper through the nickel layer. FIB cross-sectional analysis revealed that surface defects in the gold layer resulted in sites for corrosion initiation and subsequent development of a thick copper sulfide layer of approximately 5 m. It is concluded that this copper connector coating system does not prevent the formation of insulating corrosion products on the surface of the connector in a very aggressive environment.

Corrosion of RoHS-Compliant Surface Finishes in Corrosive Mixed Flowing Gas Environments

“…This is consistent with the porosity corrosion mechanism operating for medium-phosphorus ENIG, whereby the corrosion product, copper sulfide, creeps out of the pores in the ENIG layer and migrates onto the adjacent surface. 10,11,20 The corrosion products were confirmed by EDS to be predominately copper and sulfur for both ENIG surface finishes (Figs. 3b and 4b).…”

“…A FEI 200 focused ion beam (FIB) microscope was used to obtain cross-sections. 20 Auger depth profiles were performed using a PerkinElmer 610.…”

Corrosion of Electronics: Lead‐Free Initiatives

“…The chlorine attacked the submicrometer defects in the Au layer. These defects opened and led to the subsequent corrosion of theNi andCu alloysubstrate layer [30] (as seen in Fig. 41.1).…”

Accelerated Testing of Electronics to Simulate Long‐Term Worldwide Environments

“…Despite all the efforts to understand the corrosion rates and the formation of the different corrosion layers [23] and the effect of the environment on those materials (particularly for electronic applications [24]), very little has been done to take into consideration environmental data from developing countries to develop more realistic accelerated atmospheric corrosion tests (AACTs) that will mimic the environments typically found in developing countries. This subject will be discussed in more detail in the next section.…”