The Nature and Rate of Creepage of Copper Sulfide Tarnish Films over Gold

Abstract

Tarnish films that form on copper surfaces at high humidity can creep over adjoining gold surfaces, causing increases in the contact resistance of the gold. In many cases, however, when gold‐plated contacts having exposed areas of copper are removed from equipment used for extended periods of time in environments known to contain sulfiding compounds, there has been little or no evidence of creepage. This protection against tarnish is caused by a naturally formed oxide and has been duplicated in the laboratory. When copper sulfide tarnish films do creep over gold surfaces, distinctive periodic bands are formed. The humidity dependence of the rate and maximum distance of the creepage have been studied.

Electronic Materials, Components, and Devices

“…The corrosion products in both cases creep over the gold contact surface, increasing the contact resistance markedly. The creep rate of the copper corrosion product is a strong function of the relative humidity [19]. Corrosion product creep has been explained by postulating a local galvanic cell action that is enhanced by the high diffusivity of silver in silver iodide and of the electrons in the substrate metal to the advancing edge of the corrosion product [20].…”

Modeling pore corrosion in normally open gold- plated copper connectors.

“…This meniscus is called the halo region [32], and has been observed to exhibit a large contact resistance (< 10 Ohms) as well, at least for late times with large blooms. In some cases this creep corrosion is the dominant mode for corrosion product growth [33,34,35]. The mechanism for this type of corrosion is not known presently.…”