The purpose of this paper was to attempt to confirm the root cause of unstable stitch pull strength in PQFN package and propose some permanent solutions for it.
A screen experiment was designed to find the key process out of the manufacturing flow; a non‐destructive detaching method and cross section polishing were used to inspect the bond integrity; Auger analysis assisted with argon ion sputter was tried to confirm the contamination; finally the manufacturing processes were redesigned to prevent the contamination.
Some first aids of process optimization got little improvement; the screen experiment of processes found solder die bonding was the one resulted into a poor bond integrity which was demonstrated by non‐destructive detaching method and cross section inspection; Auger analysis assisted with argon ion sputter detected that there was a tin layer thicker than 20 nm coated on the bonding surface and the wire bondability of gold wire on this tin coating was poor; the lead frame was redesigned to prevent the wetting and flowing of tin and got a perfect performance.
Because of the limitation of time and resources, the proposed solutions for this issue could be studied more deeply.
This paper set up an example how to find out the root cause from the complex manufacturing process flow and put forward a quick solution accordingly for the issue.
