PURPOSE: To improve matching properties of characteristic impedance and to reduce a crosstalk by covering upper, lower, right and left sides of a signal wiring pattern formed on a dielectric layer with ground layers.

CONSTITUTION: In a wiring mounting structure of a thick multilayer board, upper, lower, right and left sides of a signal wiring pattern 1 formed on a dielectric layer 3 are covered with ground layers 5, 4, 2. For example, after a lower conductor 4 is formed on a board 6 by a thick film printing method, a thin film method, etc., a photosensitive dielectric material is formed by a thick film printing method, dried, then a groove for filling a side conductor 2 is formed by a lithography technique, thick film conductor paste is filled, and sintered to form the conductor 2 and a dielectric 3. Then, after the pattern 1 is formed on the dielectric 3 by a thick film printing method and a thin film method, a dielectric layer 3 of an upper layer is formed of a photosensitive dielectric material by a thick film printing method similarly to a dielectric forming method of a lower layer, and an upper conductor 5 is eventually formed by a thick film printing method.