| 摘要 |
PURPOSE:To prevent breakage of a drill and permit accurate drilling by using two kinds of drills with ratios, Lh/D<6 and Lh/D>6 when a hole having a diameter less than 1mm and a ratio of a depth Lh to a diameter D greater than 6 is drilled through a printed circuit board. CONSTITUTION:A prepared hole is drilled through a printed circuit board 1 which is integrally fixed by an upper plate 2 and a lower plate 3 using a short drill 4 having a ratio of an effective length Ld to a diameter (Ld/D) greater than 6, until the hole reaches the board 1 through the upper plate 2. Then, a hole reaching the lower plate 3 through the board 1 is drilled under a guidance of the prepared hole 7 using a drill 5 of a required length having a Ld/D ratio greater than 6 after removing the upper plate 2. With this method, a decented amount is reduced to one half of that of a conventional method using a single drill, whereby an accurate drilling is permitted and drill breakage is reduced. In addition, a small hole having a diameter less than 0.3mm can be drilled. |
