The electroless copper plating of small via holes

The Build-up method is becoming an important process with the increase in electric wiring density and miniaturization of the hole diameter. Preparation and circulation of plating solutions become difficult in the via hole with reduction of the hole diameter, so that uniformity of deposits decreases and this leads to lowering the electric reliability between each layer. Therefore the uniformity of electroless copper plating was investigated using small via holes (20-100 mu m phi, 30-230 mu m depth) prepared on the wiring board Uniform deposits were obtained by changing the parameters related to the deposition characteristics. The possibility of via filling by the electroless copper was also investigated.