Causes and improvement measures of the lateral-burr defect in stamped power-semiconductor leadframes

The thickness of the leadframe used for power-semiconductor packaging is usually greater than that of microelectronic chips to provide adequate heat dissipation efficiency. Lateral burrs are likely to occur at the notched sharp corners near the wire bonding area. The length of this lateral burr can be larger than the vertical burrs generated by typical punching and exceeds the dimensional tolerance. Whereas in the common stamping practice, both the notching depth and the punch/die clearance are large, and the occurrence of lateral burrs has been rare. This work investigates the causes of lateral burrs in notching and uses the slug-holding punch to constrain the slug-bulging as the improvement measure. Three copper alloy thick plates with a thickness of 0.5 mm were used. Three-dimensional finite element simulation was used to observe the phenomenon of slug-bulging and help evaluate the cause of lateral burrs. The analyses show that the cause of lateral burrs is due to slug-bulging in notching thick plates. Noticeable slug-bulging appears when the notching depth ranges from the susceptible 50% to 100% of plate thickness. The notching experiment confirms that significant lateral burrs are generated when the notching depth is 75% of plate thickness. When the punch/die clearance increases, the volume of the lateral burrs decreases, which is contrary to the phenomenon of vertical burrs generated by typical punching. Under a fixed punch/die clearance, lateral burrs increase with the plate metals with high ductility or aligned to the rolling direction. By notching with a slug-holding punch, the slug-bulging was constrained, and hence the formation of lateral burrs became almost negligible.