According to the package board of the present invention, each soldering pad formed on the top surface of the package board, on which an IC chip is to be mounted, is small (133 to 170 .mu.m in diameter), so the metallic portion occupied by the soldering pads on the surface of the package board is also small. On the other hand, each soldering pad formed on the bottom surface of the package board, on which a mother board, etc. are to be mounted, is large (600 .mu.m in diameter), so the metallic portion occupied by the soldering pads on the surface of the package board is also large. Consequently, a dummy pattern 58M is formed between conductor circuits 58U and 58U for forming signal lines on the IC chip side surface of the package board thereby to increase the metallic portion on the surface and adjust the rate of the metallic portion between the IC chip side and the mother board side of the package board, protecting the package board from warping in the manufacturing processes, as well as during operation.