Abstract
We have developed a fine-pitch wiring technology for a package substrate by introducing a chromium compound adhesion promotion layer on the surface of smooth epoxy resin. In order to apply this technology to the manufacturing of multi-layer circuit boards, new via formation process is investigated. The outline of this via formation process is as follows: First, a copper foil with an adhesion layer is laminated on the epoxy resin. Then, the copper foil is removed using a liquid etchant to leave the adhesion layer. Next, the adhesion layer is covered with a dry film resist (DFR) layer and then, CO2 laser is exposed over the DFR layer to form via holes. The smear is removed using a plasma treatment. Finally, the DFR layer is removed. In this study, the effect of the plasma condition on the smear removal rate and that of the type of DFR remover on the adhesion layer are investigated. As a result, we find that the smear is effectively removed by the plasma treatment with an O2/CF4 mixture gas and that the amine-type DFR remover does not damage the adhesion layer. This will be a new via formation process with a high adhesion strength.
