2017 年 83 巻 853 号 p. 16-00374
Recently, the diameter of through hole on printed circuit board (PCB) has become smaller with downsizing of electric devices. However, the drilling small diameter through hole includes some problems such as hole position accuracy and hole bending. Entry sheet is used to improve drill centering, drill guidance and reduction of burrs when drilling PCB. Series of drilling tests of PCB are carried out to investigate the effect of entry sheet on hole position accuracy, hole bending and chip-evacuation using three kinds of materials of entry sheet; aluminum, aluminum clad with lubricant and resin. The thrust during drilling entry sheet and the wear of the drill are measured. The hole position accuracy and hole bending examined after the drilling tests. The chips evacuation behavior out of drilled hole with the drill is filmed by a high-speed motion camera and the shape of chips produced is observed by a microscope. The amount of chisel wear and flank wear of the drill is not almost affected by the kinds of sheets. The hole position accuracy of entry side is worse as the maximum thrust during drilling entry sheet is increasing. The rate of increase of the amount of hole bending to the hit number of hole when using high rigid and high lubricant entry sheet decreases rather than that when using low rigid and low lubricant entry sheet. The evacuation out of drilled hole with the drill in case of drilling with aluminum clad with lubricant is better than that in case of drilling with aluminum.