Mechanisms of Atmospheric Copper Sulfidation and Evaluation of Parallel Experimentation Techniques

Abstract

A physics-based understanding of material aging mechanisms helps to increase reliability when predicting the lifetime of mechanical and electrical components. This report examines in detail the mechanisms of atmospheric copper sulfidation and evaluates new methods of parallel experimentation for high-throughput corrosion analysis. Often our knowledge of aging mechanisms is limited because coupled chemical reactions and physical processes are involved that depend on complex interactions with the environment and component functionality. Atmospheric corrosion is one of the most complex aging phenomena and it has profound consequences for the nation's economy and safety. Therefore, copper sulfidation was used as a test-case to examine the utility of parallel experimentation. Through the use of parallel and conventional experimentation, we measured: (1) the sulfidation rate as a function of humidity, light, temperature and O 2 concentration; (2) the primary moving species in solid state transport; (3) the diffusivity of Cu vacancies through Cu 2 S; (4) the sulfidation activation energies as a function of relative humidity (RH); (5) the sulfidation induction times at low humidities; and (6) the effect of light on the sulfidation rate. Also, the importance of various sulfidation mechanisms was determined as a function of RH and sulfide thickness. Different models for sulfidation-reactor geometries and the sulfidation reaction process are presented.

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

“…Rutherford Backscattering (RBS) experiments have verified the mechanism for growth of the copper sulfide film [11]. It was shown that the copper sulfide film grows at the sulfide-water film interface and not at the buried sulfide-copper interface.…”

“…During this stage, sulfide growth is controlled primarily by either gas phase mass transport or by partial surface reaction control [6]. Detailed experiments by Braithwaite et al [11] have shown that the growth rate in this stage is roughly independent of the relative humidity level. This experimental observation is in stark contrast with many other atmospheric corrosion systems where the corrosion rate is typically negligible until a critical relative humidity is reached, at which point sufficient water is present on the surface to support electrochemical reactions.…”

“…The kinetics of the sulfidation reaction in Stage I and II have been found to be effectively independent of relative humidity. However, the transition from Stage I to Stage II has been found to be impacted by the relative humidity [11,12]. Higher humidity promotes a more rapid transition to Stage II (i.e., the length of Stage I growth appears to decrease with increasing relative humidity).…”

“…They missed it, because gas-phase mass transport interfered with the calculation of the sticking coefficient. Previously, we undertook a study to mitigate the mass transport resistance by constructing a stagnation point flow reaction and using a large and varying normal velocity to minimize the mass transport resistance [11,16]. Numerical calculations were then carried out to model the predicted initial growth rates obtained from normal incidence reflectometry to obtain an estimate of the reactive sticking coefficient for the initial sulfidation rate.…”

A Modeling Approach for Predicting the Effect of Corrosion on Electrical-Circuit Reliability

“…9 To formulate the constitutive equations needed to describe these effects and the physicochemical processes ongoing during the sulfidation of an electrical contact, two levels of experimental studies were performed. In the first series, the sulfidation kinetics of bare copper were characterized.…”