CIRCUIT BOARD

摘要

In a circuit board (1) having the ground layer (5) and the signal wiring (3A, 3B) arranged on the ground layer with an insulator layer (2) interposed therebetween, a shield layer (7) composed of a conductive material is formed on an insulation coating layer (4) covering the signal wiring on the side opposite to the ground layer (5). The portion which is above the insulator layer and faces the singnal wiring (3A) requiring a control of a characteristic impedance is configured as an opening (7a) in the shield layer where there is no shield layer arranged. When the signal wiring fulfils the function of single end transmission, the distance U between the opposite outsides of the signal wiring (3A) and the opening edge (7b) of the shield layer is set in the range of 3t1=U=20t1, where the thickness of the insulator layer (2) is t1. With such structure, a circuit board which can control the characteristic impedance of the signal wiring (3A) and can exhibit the effect also in EMI countermeasure is provided.