A highly reliable, high-density printed wiring board process called the partly additive process has been developed for manufacturing high-speed digital switching systems. The partly additive process realizes very fine, highly reliable through-holes and circuit patterns at fairly low cost. To realize this process, a specially designed solder-resist that can withstand high temperatures and the high alkalinity of electroless copper plating solution was developed. A new electroless copper plating solution was also developed that can deposite copper having excellent mechanical and electrical properties. The composition of the electroless copper plating solution could be tightly controlled using a newly developed system to automatically monitor and supply solution components accurately.