A new cutting method was developed for ultra-thin glass, which was difficult to cut by conventional methods. First, a crackless trench line was formed on the glass surface by scribing. Second, an assist crack was formed in the vicinity of the trench line. Then, crack propagation along either side of the trench line was induced from the assist crack. We investigated the crack formation and stress distribution by experiments and finite element method (FEM) to determine the directionality of crack propagation. On the crack propagation side, cracks perpendicular to the glass surface were observed along the trench line. On the other hand, cracks a few tens of microns in size deflecting from the trench line were formed on the other side. Numerical analyses indicated that the symmetrical distribution of shearing stress around the trench line contributed to the directionality of crack propagation. The crack propagation direction and stress distribution could be inverted by scribing conditions.

This study was performed to clarify the effects of flank wear and margin wear on drilled hole quality in printed circuit board (PCB) hole drilling. We performed a series of hole drilling tests in PCBs using a drill with only flank wear and a drill with only margin wear, and investigated the effects of each drill on hole positional accuracy, hole bending, and roughness of the inner wall surface. Compared to flank wear, margin wear resulted in poorer hole position accuracy, hole bending, and roughness of the inner wall surface. As margin wear increased, the cutting force on the Lissajous curve on the plane perpendicular to the drilling direction increased, and hole bending and hole position accuracy deteriorated. When using a drill with margin wear, the reverse taper drill margin rubbing the inner wall of the hole causes fraying of the glass cloth. Therefore, the amount of protrusion of glass cloth on the inner wall of the hole increased, and the roughness of the inner wall of the hole deteriorated.