Tin contamination in PQFN package and its effects on wire bondability

• Published in: Microelectronics international 2013-01, Vol.30 (3), p.176-186
• Main Authors: Zong, Fei, Wang, Zhi-jie, Xu, Yan-bo, Niu, Ji-yong, Zhang, Han-min
• Format: Article
• Language: English
• Subjects: Applied sciences; Argon; Augers; Bond strength; Bonding; Contamination; Design of experiments; Design. Technologies. Operation analysis. Testing; Detaching; Electrical & electronic engineering; Electronics; Engineering; Exact sciences and technology; Integrated circuits; Manufacturing; Plasma; Roots; Semiconductor electronics. Microelectronics. Optoelectronics. Solid state devices; Studies; Tin; Wire
• ISSN: 1356-5362; 1758-812X
• DOI: 10.1108/MI-11-2012-0075

Purpose – 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. Design/methodology/approach – 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. Findings – 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. Research limitations/implications – Because of the limitation of time and resources, the proposed solutions for this issue could be studied more deeply. Originality/value – 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.