| 摘要 |
PROBLEM TO BE SOLVED: To realize higher density in a horizontal direction and also improve electrical connection reliability by making the diameter of a via hole used for inter-layer connection smaller (not exceeding about 100μm), SOLUTION: An insulating layer is provided on the surface of a first circuit of an internal layer board on which the circuit is formed a second circuit is formed on the surface of the insulating layer, and the first circuit and the second circuit are connected together with a via hole, for constitution. The form of the via hole is made into a mortar-shape in which the diameter of the via hole grows larger as it approaches from the first circuit side to the second circuit side and further the angle made by a wall surface of the via hole and the surface on which the first circuit is formed is made 45 degree or less. |
