Springback in the roller forming of integrated circuit leadframes

The accurate control of springback in the cold forming of narrow strips of integrated circuit leadframes becomes highly essential for the semi-conductor industry in order to be able to meet stringent requirements for very high lead count packages. However, most of the studies on the problems of the springback of sheet metals are based on wide strips. In the present study, a special cantilever-type forming jig has been designed to investigate the springback of narrow strips of steel and copper alloy at various die radii, die angles and die gaps. This forming jig is equipped with an advanced on-line automated imaging system to measure the springback angle of the strips. The springback was found to increase with increase of the die radius, the die angle and the die gap. Significant anisotropy in the sheet materials led to different springback behaviours for different sheet orientations. The findings of this paper can be used as a guideline for designers in the design of tools for the roller forming of integrated circuit leadframes.