This paper describes micro-drilling processes for printed circuit boards (PCBs) containing fillers with high hardness and high thermal conductivity. Inspired primarily by devices such as digital cameras, laptop computers, and wireless communications devices, the electronics field today is continuously demanding smaller, lighter, and more technologically advanced high performance devices. However, that the increase in semiconductor-generated heat tends to affect such devices negatively. Additionally, from the viewpoint of environmental problems, electric vehicles and LEDs are being developed actively. PCBs are one of the principal components for building such devices. In recent years, PCBs containing alumina fillers with high thermal conductivity have been developed and begun to be widely used. However, when processing these PCBs, the drill tools become severely worn because of the filler's high hardness. We therefore examined the drill wear characteristics. The results show the filler is the main factor that causes drill wear, while the increase in cutting force does not affect it. The cutting force increases with the drill wear linearly. Moreover, the characteristic of PCBs with higher filler content rates is close to that of inorganic material like ceramics.