| Summary: | 碩士 === 國立臺灣科技大學 === 材料科學與工程系 === 105 === The demand for better tool performance in machining printed circuit boards (PCBs) is increasing due to the extensive usage of PCBs in digital electronic products. Therefore, higher density PCBs with smaller hole diameters, produced by small sized drill bits are required. However, the chip adhesion became more serious for drill bits with small diameters e.g. micro-drill bit, leading to a poor drilling performance as well as short drill life.
To improve the drilling performance of micro-drill bits, surface modification, such as coating, have been widely applied. Thin film metallic glasses (TFMGs) have a smooth surface roughness and a low coefficient of friction compared with other coatings due to their disordered atomic structure. Accordingly, TFMGs have become a potential material for the surface treatment for micro-drill bits. In this study, micro-drill bits were pre-cleaned in two different ways, referred to as Group A and Group B. TFMG with Ti buffer layer (TFMG/Ti) and monolithic TFMG coatings were deposited by various deposition parameters using arc ion plating (Ti layer) and magnetron sputtering (TFMG). Effects of four parameters on drilling performance, including sputter etching time, substrate bias, arc deposition time and arc power were evaluated by TFMG/Ti coated drill bits. Moreover, the effects of working pressures and substrate biases were carried out by TFMG-coated drill bits. Drilling test were then evaluated on two kinds of PCBs, different PCBs yielded different drilling performances. For TFMG/Ti coated drill bits, long sputter etching time resulted in damage of drill substrate, due to the severe ion bombardment. Increasing substrate bias resulted in decreases of number and size of microparticles, thus the surface roughness decreased as well. For TFMG-coated drills, the pre-cleaning process was significantly influence on drilling performance. Overall, TFMG-coated drill bits in Group A presented a better drilling performance than those in Group B. TFMG-coated drill bits deposited at high working pressures (5 and 8 mTorr) exhibited better drilling performance. The coated drill bits gave an average enhancement of Cpk up to 18.3% and lower surface roughness variation before and after drilling rest (19.7% presented by coated drills while 111.2% presented by bare drill bits at flutes), compared with bare drill bits. Furthermore, TFMG remained on the flute of coated micro-drill bits, providing a better chip removal.
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