IC packages are getting smaller year by year. Lead pitches as fine as 0.3 mm are now required. In the assembly of IC packages, the cutting of dam bars to connect leads is traditionally performed using pressing. The limit has been reached however, where pressing can no longer be used to achieve the very fine lead pitches required. YAG laser processing applied to dam bar cutting provides a possible solution.
In dam bar cutting with lasers, the same ease of formation in terms of time as in pressing and an even higher positioning accuracy resulting in finer lead pitch are inevitable requirements. For high speed cutting, an oblong beam transformed from a circular beam using a beam former consisting of cylindrical lenses is used. Each dam bar is cut with one pulse of the oblong spot. High accuracy positioning is ensured by a “Sensing Laser Triggering System”. The SLT consists mainly of a laser diode, photo diode and triggering circuit. The laser diode and photo diode are installed in the laser processing head. The lead position ahead of the laser area to be processed is detected. The laser is triggered by the detected signal, just thereafter. Using the SLT and the oblong beam, a cutting speed of 100 dam/s and positioning accuracy of ±3 μ m can be achieved.