Application of via post interconnection for build up printed circuit board

Recently, printed circuit boards (PCBs) have been downsized and electronic circuits have become more dense, because of the tendency for electronic component miniaturization. With the shrinkage of PCBs, the build up process has become an important production technique in PCB preparation. For the build up technique, each of the electric circuit layers is electrically connected with via holes. The via holes are metallized by means of electroless plating and electroplating of copper. In the electroless plating process with miniaturization of via hole diameter, if the via hole deposition uniformity is decreased, the electrical reliability between the layers significantly deteriorates. Accordingly, the authors investigated build up printed circuit boards using via posts, which are metallized using the Cu electroplating method. The shear strength between electroplated via posts and electrolessly plated underlayers was evaluated. It was found that electroplated via posts with higher shear strength are obtained by optimization of the pretreatment process and electroplating conditions. In particular, it was important that oxide films on the copper underlayer were removed for improved shear strength.