Conventional hardware plating processes contain metal (e.g., Zn/Cu alloy) injection in a mold, alkaline copper plating, pyrophosphate copper plating, and acidic copper plating. After metal injection in a mold, the metal substrates will be formed with some scratches or pin holes due to the long-term use of the mold. These scratches and pores will make the surface uneven, decrease the brightness of the hardware after electroplating processes. Moreover, it cannot pass the reliability test, such as adhesion and corrosion tests. However, common alkaline copper plating and pyrophosphate copper plating do not have filling ability to solve these problems.

In this work, we are going to use acidic copper plating to improve the surface flatness and solve the problem of pin holes. Blind microvias were used to simulate the pin holes and uneven surface of the hardware. Various plating additives with different concentrations were studied to fill the microvias and simultaneously render the surface to be smooth and bright. We observed the cross-section of the microvia by using an optical microscope (OM) and measured the surface brightness by using a luminance meter to investigate the effect of additives on surface brightness and filling performance.