1. Field of the Invention
The present invention relates to a splitter system for splitting a twin wire used for connecting together pads on a printed circuit board.
2. Description of the Related Art
When a large number of semiconductor electronic elements such as LSI's are mounted on a printed circuit board, sometimes the pattern formed on the printed circuit board is insufficient to enable connection of all of the terminals, due to the excessive number of terminals to be connected. In such a case, or in the event of a design change, wire connection between terminals is carried out on the rear side of the printed circuit board. For this purpose, a twin wire comprising two wires connected together in parallel is used. The twin wire is split into two wires in the vicinity of a wire connecting position and bonded to two adjacent pads, respectively. To supply the twin wire continuously to a wire bonder, the twin wire must be split, at an interval corresponding to a distance between two wire connecting positions, for a length necessary to allow the wires to be bonded to two pads at each wire connecting position.
In a conventional twin wire splitter unit combined with a wire bonder, one end of a twin wire is bonded to a printed circuit board at a bonding tip position. The printed circuit board is then moved with the twin wire being drawn to set the next wire connecting position under the bonding tip. During this movement of the printed circuit board with the twin wire, a splitting means such as a pin is thrust into the center of the twin wire to split the twin wire for a predetermined length. Namely, when the twin wire is fed to the next connecting position, to perform the next bonding operation after completion of the bonding at the previous position, the splitting pin is driven to split the twin wire for a predetermined length. In such a conventional splitter unit, the feed length of the twin wire must be longer than the length of a twin wire feeding path between the bonding position (a position where the bonding tip is located) and the splitting position (a position where the splitting pin is located) to enable the twin wire to be split by the pin at the splitting position. Namely, if the distance between two wire connecting positions on the printed circuit board is short, i.e., the length of twin wire necessary for connection becomes shorter than the length between the bonding and splitting positions, then it is impossible to split the twin wire at the position corresponding to the next bonding position during the feed motion of the twin wire, after a leading end of the wire is bonded.