| 摘要 |
<p>PROBLEM TO BE SOLVED: To provide a method of easily forming a straight through-hole on a base plate by means of a laser beam. SOLUTION: A pulsative laser beam L is emitted to an insulating base plate 10 in a state where a copper foil 11 having a surface roughness Ra of 0.1μm is arranged on the rear side. The laser beam L is set so that its focal position f is above the irradiation surface of the insulating base plate 10. With the laser beam L emitted, it starts to form a hole in the depth direction from the surface of the insulating plate 10, and finally reaches the copper foil 11 to form a through-hole 13 (tapered hole). With the irradiation continued further, the laser beam L is reflected by the copper foil 11 to irradiate the inner circumferential face of the tapered hole. Therefore, the tapered hole is gradually expanded in diameter from the rear to the surface and finally becomes a straight through- hole 13.</p> |
