Investigation of electroless copper plating with high plating coverage in small BVH for next generation fine pattern SAP

Abstract

Printed wiring board (PWB) used for package substrates are required to have higher circuit densities. We anticipate that PWB circuit patterns and blind via hole (BVH) will continue to be miniaturized due to higher density requirements. The electroless copper plating solution generally used has less chemical material supply to the inside of the BVH than the surface of the substrate. As a result, the copper thickness at the bottom of the BVH tends to be thinner than that on the surface of the substrate. It is difficult to uniformly deposit the electroless copper plating in the BVH on the package substrate by the semi-additive process (SAP), especially when the BVH are becoming smaller. Therefore, we investigated additives that suppress the electroless copper plating deposition on the surface of the substrate and additives that improve the permeability of the plating solution into the BVH. Two additives have been discovered that dramatically improve the plating uniformity in the small BVH compared to the conventional bath. In addition, we used this plating solution with the new additives to evaluate the internal stress and peel strength of the electroless copper plating film. As a result, it was confirmed that both internal stress and peel strength were improved compared to the conventional bath.