Defects Induced in Copper by Cathodic Charging of Hydrogen

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Abstract
Scanning and transmission electron microscopes were used to study the effect of cathodic charging of hydrogen on the defect structure of bulk copper foils. Cathodic charging of hydrogen over an extended period of time (∼24h) resulted in a considerable reduction in the ductility of copper foils. This ductility reduction was accompanied by the formation of blisters, dislocations, and hydrogen gas bubbles, and their densities decreased with increasing depth from the foil surface. This observation is similar to the case of hydrogen‐sensitive metals such as iron‐base alloys, and it indicates that copper is embrittled by cathodic charging of hydrogen. In addition, a part of the lost ductility was found to be recoverable by low‐temperature (150°C) annealing. This recovery is attributed to the reduced hydrogen gas pressure resulting from the outdiffusion of molecular hydrogen trapped inside the gas bubbles. This investigation was performed as part of an effort to understand the mechanism of embrittlement of electroless copper deposits used in the manufacture of printed wiring boards.
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