Contributions of chemical interactions and mechanical interlocking for the adhesion of electroplated copper to ABS in the Cr(VI) etching process

A typical step in the electroplating of metals to polymer substrates is the preparation of a substrate surface through sulfochromic acid etching, which is well known for modifying the chemistry and morphology of the treated surfaces. While this process has existed for decades, the relative contributions of chemical interactions and mechanical interlocking towards the final adhesion are not well understood. As sulfochromic acid is toxic and hazardous to the environment and human health, understanding how this acid etching promotes adhesion, and especially what are the real contributions of chemistry and mechanics respectively, becomes critical to be able to replace this treatment with greener techniques. However, such knowledge is still ambiguous, since decoupling the chemical and morphological contributions is challenging because both effects occurred simultaneously during etching. In this study, we proposed various sample preparation strategies to address these issues. First, we minimized the etching duration to achieve similar chemistry as that after the standard etching while avoiding strong modifications in surface morphology. Second, we passivated the etched samples to ensure that most of the adhesion properties of prepared samples are from morphological effects. Results indicated that chemical contribution was critical to ensure good wetting during the electroless plating, while mechanical interlocking was the major contributor (90%) for the ultimate adhesion of electroplated copper to acrylonitrile-butadiene-styrene interfaces.