The use of polymer rich colloids to enable high adhesion electroless copper plating on FR4 substrates

This study is aimed at understanding better the role of palladium catalysts in the electroless copper plating (ECP) process - a prime segment of PCB fabrication. The immense superiority of the Pd nanoparticles over the traditional Sn/Pd or ion-Pd catalysts has been discussed at length in various studies. Here, we are trying to establish a link between the stability of home-made Pd nanoparticles, namely poly vinyl alcohol - capped Pd nanoparticles (PVA-Pd) and the T-peel strength of the copper film obtained by the commercial ECP bath. A wide range of PVA-Pd colloids with varying PVA:Pd ratio have been synthesized. The visible differences between the solutions indicate that ratios with high PVA content tend to be more stable than their PVA deficient counterparts. The weight ratio 0.175 (PVA : Pd) was extremely unstable even after continuous stirring, and had visible Pd precipitates. The ratios 0.25 and 0.5 tend to be stable if they are kept stirring, and show visible particles after being taken off it. The ratios 0.75 and 1 show relatively higher stability, while the ratios like 17.5, 25 and 50 show excellent stability because of being highly viscous. T-Peel results show a direct relationship between the adhesion and polymer content in the catalysts. Higher the ratio, better the adhesion, with ratios like 25 and 50 showing average T-Peel results of approximate 1200 gf'cm. This value approaches that of the copper clad laminate (CCL), massively used in the PCB industries. Our result indicates the excessive amount polymer doesn't interfere with the catalysis and promote T-peel adhesion instead.