In a BGA/CSP type electronic part having a matrix-shaped array of solder pads on its back surface, the solder pads at first two corners on one side of the array are connected with each other by an inner pattern wire, and the solder pads at the other, second two corners on the opposite side are also connected with each other by an inner pattern wire. In a printed wiring board having a matrix-shaped array of connection pads on its top surface, pattern wires are extended from the connection pads at four corners of the connection pad array to form test lands. Further, the connection pads, at two of the corners, to be bonded with the solder pads at one of the first two corners and at one of the second two corners confronting the one of the first two corners are connected with each other by a pattern wire on the board. Thus, after the BGA/CSP type electronic part is mounted in position on the printed wiring board, the state of the connection between the BGA/CSP type electronic part and the printed wiring board can be confirmed by checking the state of continuity between the test lands connected with the connection pads at the other two corners of the connection pad array.