Investigators: Gery Stafford and Sandra Claggett

Technical Description:

The loss of solderability of printed wiring boards and component leads during storage is a major problem that costs the electronics industry millions of dollars each year. It is clear that surface oxidation is involved, but the nature of the various oxides and their role in the degradation process are obscure. This project focuses on the electrochemical evaluation of artificially aged copper.

Technical Objectives:

• Determine the electrochemical method (galvanostatic or potentiostatic transient) which provides the most accurate and reliable description of the aged copper surface.

• Determine the reduction potentials for Cu₂O and CuO in an electrolyte comprising 1.0 mol/L LiClO₄ and 0.1 mol/L LiOH.

• Electrochemically evaluate the surface oxide of copper after exposure to four different accelerated aging procedures. Analysis should provide information about the oxidation state and amount of oxide present on the surface.

Anticipated Outcome:

• Determine the electrochemical signature for each of the aging procedures and provide comparisons based on both the oxidation state and quantity of surface oxide present.

Accomplishments for FY 1995:

• In 1.0 mol/L LiClO₄ and 0.1 mol/L LiOH, the reduction potentials of Cu₂O and CuO are approximately 0.25V apart. However, the reduction potentials for each species varies with oxide thickness, presumably due to the semi-conducting nature of the oxide. Galvanostatic experiments, involving very small currents, yield the most reliable and reproducible reduction transients.

• The amount and valence of oxide formed on copper coupons aged under different conditions can be determined by galvanostatic reduction. Reproducibility within a given set of coupons is quite good. Cu2O was the primary species detected for all levels of aging; however, two of the aging conditions resulted in 1-2 monolayers of CuO on the outer surface.

Impact and Technical Highlights:

• Electrochemical reduction is an excellent technique for determining the oxidation state of copper, both qualitatively and quantitatively. These measurements can be performed directly on printed wiring boards and component leads and may eventually be used to assess solderability.

Back to Table of Contents

Last modified: Mon Jan 06 09:46:15 1997 Metallurgy Webmeister