Conventionally the solder pads on the IC chip side surface (upper surface) of a package substrate are small (133-170 mu m diameter) and occupy a relatively small metallic part, while the solder pads on the surface (lower surface) of a mother board are large (600 mu m diameter) and occupy a large metallic part. According to the invention, the metallic part on the IC chip side of the package substrate is increased by forming a dummy pattern (58M) between the conductor circuits (58U), (58U) forming signal lines on the IC chip side of the package substrate, and the ratio of the metallic part of the IC chip side to that of the mother board side is adjusted. The package substrate does not warp during the manufacturing process and during the use thereof.