| 摘要 |
PROBLEM TO BE SOLVED: To suggest a drill of a small diameter preventing electric connection properties and reliability from being lowered by making it less prone to damage, even if the frequency of use is enhanced, without causing a failure such as a displacement of a formed through hole. SOLUTION: In this drill formed with grooves 20 in a blade part 30 and a body 40, the drill having 40 to 80% of an occupancy rate of metal in cross section at a base end of a cutting edge 30 of the body 40 and 1.50 to 3.50 mm of a radius of curvature in a shaft vertical direction of a deepest part of each of the grooves 20 at the base end is used. The drill has strength not to impede discharging property of chips. When the through hole is provided in a substrate formed by the drill, abnormality and displacement of the shape of the hole are difficult to be caused to make difficult to lower electric connection properties and reliability. COPYRIGHT: (C)2007,JPO&INPIT
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