Wire sweep improvement in low cost manner

Abstract

Wire sweep had been a generic problem for semiconductor devices since long time ago. In this study, a quantifiable measurable on the gold wire sweeping is developed. Meanwhile, the viscosity curve of Epoxy Mold Compound had been adopted to perform upfront molding-filling analysis to optimize the process and product reliability risk such as short molding and wire sweeping. On the other hand, by implication of Hook's Law F=kx, a simple modification on upgrading the transfer spring mechanism which may improve the EMC feeding also being discussed in this paper. The additional internal force creates by kx and the force by the machine had generated a double transfer force effect to the EMC. This internal force kx are enhancing the smooth feeding of the EMC and reduce the negative impact on chip and wire during mold transfer. As the result, by using current EMC with 17.5um wire size as well as minor modification on the transfer spring, the wire sweeping of SOT 223 package manage to be reduced from 18% to less than 10%. Base on the study, some of the interesting finding and conclusions can be drawn out. Firstly are the optimization of process parameter have the limitation on transfer window, transfer parameter does not give the significant wire sweeping behavior due to the parabolic viscosity properties vs time of the EMC.Anyhow selected result from this parameter is very helpful when we applied the spacer (Hook's Law) to generate the internal force to the spring. Further action also can be carried out to eliminate the sweeping issue, which is by the lower EMC viscosity properties, this action may involve certain cost that lead to overall product cost increases, but it would guarantee the product quality. Finally all the mention method to improve wire sweeping issue in this paper is considering cheap, fast and simple.