When soldering is performed, heat transferred from through hole 6b is caused to bypass a mesh-like copper foil region between non-copper-foil regions and thus the transfer of heat to a solid pattern region around thermal land 13b is delayed. Signal wirings 8e, 8f and signal wirings 8g, 8 are formed along the arrangement directions of non-copper-foil regions 15b, 16b respectively keeping a predetermined spacing between them and disposed to overlap copper foil regions, thus ensuring a current return path by means of opposing ground layer 11.