Study on planarizing process for high aspect ratio via-holes using for electroplating and apply to process for Cu/polyimide multilayer substrates

A low-cost and high-density circuit board process is developed using Cu electroplating, which flattens uneven surfaces. A circuit board is made using the following process: (1) via-holes are made on a polyimide surface acting as an insulation layer; (2) the metal (Cr/Cu) used to supply the electroplating current is deposited by sputtering; (3) reversed line patterns are made by photolithography; (4) reversed line patterns and via-holes are plugged by simultaneous Cu electroplating; and (5) resist and metal are stripped. This new approach can reduce the number of processes compared with previous methods. However, one problem is that voids occur in the via-holes that have been plugged by the Cu electroplating process. We controlled the electroplating current density and electroplating bath conditions to plug the via-holes without voids. In addition, we fabricated a circuit board with two layers of lines. As a result, this new process has been shown to be capable of manufacturing a high-density circuit board.