Microvia Formation for Multi-Layer PWB by Laser Direct Drilling: Improvement of Drilled Hole Quality of GFRP Plates

Microvia formation technology using lasers has become the dominant method for drilling microvia that are called blind via-holes (BVHs) in printed wiring boards (PWBs). Laser direct drilling (LDD), which is direct drilling of the outer copper foil by laser, has attracted attention as a novel method. In particular, when copper and resin with different processing thresholds are simultaneously drilled, an overhang defect occurs on the drilled hole. On the other hand, aramid fiber reinforced plastics (AFRP) have been replaced by glass fiber reinforced plastics (GFRP) as the material used for the build-up layer because of its cost performance. Moreover, the PWB quality of the particle incrustations around the drilled holes has problems in the manufacturing process. However, the LDD process of such a composite has not been clarified. Therefore, we investigated it by detailed observation using a high-speed camera. We estimated the overhang length using the finite element method (FEM) and experimentally and analytically evaluated the effects of filler contented build-up layers. As a result, we improved drilled-hole quality by using prototype PWBs made of GFRP with filler in the build-up layer.