Abstract
This study focuses on the internal stress in the nickel deposit during electroplating through the additive-free Watts bath electrolyte mixed with and without supercritical carbon dioxide (Sc-CO2). The results showed that the Ni films plated in Sc-CO2 had brighter, smoother surface and higher hardness than plated in conventional electrolyte without Sc-CO2. However, there existed more nano-sized pinholes via TEM and AFM measurements in the Sc-CO2 specimens. It was found that during electroplating the Sc-CO2 occluded into the coating through the nano-sized pinholes/voids influenced the internal stress of the deposit. On the other hand, the periodic plating characteristics of the Sc-CO2 electroplating led to higher relative peak magnitude of Ni {111} over {200} in crystalline orientation revealed in X-ray diffraction patterns. As a result, the internal stress in the nickel film plated through the Sc-CO2 method was significantly higher than that in the conventional one. Moreover, the more CO2 volume fraction used in Sc-CO2 electroplating resulted in even higher internal stress of nickel film.
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