An effective method for improving IC package die failure during assembly punch processing

摘要

Singulation by a punch process is a major manufacturing step in the package assembly process. The punch process induces dynamic stress waves in the package which transfer stress to the die. This could be a potential factor to crack or pop the die during punching. The objective of this paper is to investigate an effective method to minimize stress transfer. This method uses a pre-groove technique in the lead frame design to reduce the punch stress during singulation. A 3D transient dynamic large deformation finite element method is used to determine what stresses are going to be induced during singulation of the package, to check if the package can withstand punch induced stress waves and to determine potential design weaknesses both with and without the pre-groove. Different locations of the pre-groove, different shape parameters of the groove and different punch contact shapes are simulated and studied to get the optimized results. Tests of the punching process including a group of samples with and without pre-groove have been developed. The results show that dynamic stresses transferred to die without groove are much greater than with the groove, there is an optimized shape and location of the groove that may reduce stress to a maximum degree. While changing the design of punch contact head, such as narrowing the width of contact punch head area, it also reduced the die stresses in punching singulation, but not as significantly as with pre-groove cases. Both modeling and testing have confirmed that pre-groove is an effective method to remove the die crack/pop failure.