科研之友
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摘要
Due to the increase of board thickness and the decrease of hole diameter (aspect ratio greater than 20), the highfrequency high-speed printed circuit board (HFHSPCB) required for 5G/6G communications brings new challenges to micro-hole drilling process. In this paper, the failure mode and failure mechanism of HFHSPBC large aspect ratio micro-hole drilling process (0.2 mm diameter micro-hole and 4.14 mm thickness HFHSPCB) were studied. Experimental results showed that micro-drill fracture was the main failure mode of the process, while observations of the micro-drill cutting edge and the fractured micro-drill surface suggested that the cause of fracture was not tool wear. Further analysis of thrust force and torque during drilling revealed that, the microdrill fracture was not due to excessive thrust force as known for traditional PCB drilling, but excessive torque caused by friction and chip removal resistance during drilling. Micro-drill fracture occurred only in the speed conversion stage where material removal was zero but drilling torque was the maximum. Based on the microdrill fracture analysis, a non-equal-step peck drilling process was proposed to control the drilling torque below the limit value. Compared to direct drilling or equal-step peck drilling, this non-equal-step peck drilling method greatly prolonged micro-drill life, realized near-zero micro-drill fracture, and largely enhanced microhole quality.
