Control of the adhesion strength between nickel replica and copper mold by electrochemical nucleation of lead
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The failure to release nickel replica from its copper mold occurs sometimes, in particular, when nickel replica is thin, large and has microstructures such as micro prism arrays. The failure is induced by improper adhesion strength between nickel replica and its copper mold. When the adhesion strength becomes too strong, the release of nickel replica from its copper mold can lead to poor surface finish or severe damages on nickel replica and/or copper mold; when the adhesion strength becomes too weak, premature release of nickel replica can happen due to internal stress that has been built up during electrochemical deposition, leading to the failure of electroforming process. To address this challenge, this paper proposes a simple and effective electrochemical approach to control the adhesion strength. The approach is to electrochemically deposit a certain density of lead nuclei on copper mold before electrochemically depositing nickel. Our experiments indicate that: (1) lead nuclei density can be conveniently controlled by nucleation duration time and electrical current; (2) lead nuclei density affects significantly the adhesion strength and hence can be used to control the adhesion strength; (3) the release of nickel replica from its copper mold becomes easy and the associated surface roughness is improved significantly when an optimal lead nuclei density is electrochemically deposited on its copper mold.
KeywordsOptical mold Micro prism arrays Electroforming Lead nucleation Surface roughness Adhesion strength
This work was supported by the Natural Science Foundation of Fujian Province of China (No: 2017J01700) and Key Project of Fujian Province of China (No: 2017H0025).
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