An investigation of process parameters in the dam-bar cutting of integrated circuit packages

The rapid evolution of micorelectronics is placing greater demands on the packaging technology of integrated circuits (IC), the trend being towards higher lead counts, smaller lead width, finer lead pitch and thinner leadframes. These demands impose stringent requirements on the quality of dam-bar cutting, the latter being a mechanical trimming process in which the dam bar btween the leads of an IC package after post-molding process is pierced out. The leadframe thickness and the area of cutting are in the order of one tenth of a millimeter and cutting is performed at a much higher speed than that found in conventional blanking and piercing processes. In this work, a purposely built single-punch dam-bar cutting press was constructed. The effects of percentage punch-die clearance, punch shear and the plastic anisotropy of the leadframe materials on the cutting force and energy, and the quality of the sheared edge of the dam-bar, were studied. The optimum punch-die clearance for minimum cutting energy was established. The cutting force, energy and burr height were found to be affected by the plastic anisotropy of the virgin leadframe materials. These findings can be applied in the design of trimming tools used in the dam-bar cutting of IC packages.