A circuit board includes a board body of a thickness, and a socket. The board body defines a plurality of through holes therein. The socket includes a first line of short pin groups and a second line of long pin groups engaging the through holes of the board body. The socket defines a slot. The first line of short pin groups and the second line of long pin groups are respectively located on opposite sides of the slot. The first line of short pin groups has a length less than the thickness of the board body. The second line of long pin groups has a length sufficient that the second line of pin groups protrudes the board body.