Cu electroless deposition (ELD) technology has been widely used in the metallization of non-conductive materials, such as a printed circuit board (PCB) and polyimide film (PI). In the ELD process, industries use traditional Sn/Pd colloid as the catalyst to initiate the Cu ELD. However, palladium is an expensive noble metal. In addition, the residual palladium adsorbed on the resin surface has to be removed after copper patterning to prevent a possible short between two copper lines in the semi-additive process (SAP). This would increase the overall process cost. As a result, we use copper nanoparticle (CuNP) as the catalyst to initiate the Cu ELD on the resin surface and the sidewall of through holes of a PCB. In this work, the stability of the Cu ELD solution is important for industrial production. We select different chelators and reducers to study their effect on the stability of Cu ELD solution under the condition of using CuNP as the catalyst. The stability of the Cu ELD solution was characterized by UV-Vis spectroscopy and electrochemical analysis. The morphology of the ELD Cu layer was imaged by scanning electron microscope (SEM) and optical microscope (OM). Results show that the Cu ELD solution (i.e., formula) is different from that is formulated for Pd catalyst system.

Keywords:

Electroless copper deposition, Copper nanoparticle, Stability, Semi-additive process

Reference:

• Kyung Ju Park, Hyo-Chol Koo, Taeho Lim,a Myung Jun Kim, Oh Joong Kwon, and Jae Jeong Kim, “Evaluation of Stability and Reactivity of Cu Electroless Deposition Solution by In-Situ Transmittance Measurement”, Journal of The Electrochemical Society, vol. 158, pp. D541-D545, 2011.
• Fumihiro Inoue, Harold Philipsen, Alex Radisic, Silvia Armini, Yann Civale, Shoso Shingubara, and Peter Leunissena, “Electroless Copper Bath Stability Monitoring with UV-VIS Spectroscopy, pH, and Mixed Potential Measurements”, Journal of The Electrochemical Society, vol. 159, pp. D437-D441, 2012.