| 摘要 |
PURPOSE: To improve adhesion of plating in a blind viahole, hardly affected by a thermal stress, and to enhance connection reliability. CONSTITUTION: A first and a second wiring layer (lower conductor circuit), 2 and 3, and a fourth and a fifth wiring layer (upper conductor circuit), 6 and 7, arranged through the intermediary of insulating layers 4 and 5 are electrically connected through blind viaholes 8 and 9 which serve as connection holes, wherein the viaholes 8 and 9 are so formed as to set their upper openings larger than bottoms in diameter. At this point, the viaholes 8 and 9 may be formed into such shapes that they increase gradually in diameter. The insulating layer is of laminated structure composed of two or more layers where a connection hole is provided at a prescribed position, and the connection hole is so formed as to increase gradually or by steps in diameter from the lower layer to the upper layer. |
