Effect of Reflow Profiles on the Board Level Drop Reliability of Pb-Free (SnAgCu) BGA Assemblies

The mechanical reliability of BGA assemblies is sensitive to the intermetallic compounds that are formed at the solder/base metal interfaces. With Pb-free assembly using SnAgCu solder alloys, the reflow temperatures are higher and may degrade the performance of the BGA assemblies compared to tin-lead. In this study, BGA packages with Sn3.8Ag0.7Cu solder balls and either Ni/Au or Cu substrates were assembled to printed circuit boards with Cu pads protected with organic solderability preservative using a standard Pb-free solder paste of the same composition. The reflow profile variables investigated were peak temperature and number of reflow excursions. A subset of the assemblies were subjected to 4-point dynamic bend at high strain rate (>5/sec) to determine the effect of the reflow variables on the board level drop reliability. BGAs with Ni/Au substrates showed improved performance with increasing peak reflow temperature, while those with Cu substrates demonstrated the opposite. There were weak trends seen with number of reflows for both substrates. The intermetallic compound layer development due to the reflow variables is also covered.

[1]  J. N. Tey,et al.  Reaction of Sn-3.5Ag-0.7Cu-xSb solder with Cu metallization during reflow soldering , 2004, IEEE Transactions on Electronics Packaging Manufacturing.

[2]  E. Bradley,et al.  A novel mechanical shock test method to evaluate lead-free BGA solder joint reliability , 2005, Proceedings Electronic Components and Technology, 2005. ECTC '05..

[3]  K. Tu,et al.  Impact reliability of solder joints , 2004, 2004 Proceedings. 54th Electronic Components and Technology Conference (IEEE Cat. No.04CH37546).

[4]  Z. Zhong,et al.  Board level drop test and simulation of TFBGA packages for telecommunication applications , 2003, 53rd Electronic Components and Technology Conference, 2003. Proceedings..

[5]  S. Canumalla,et al.  Intermetallic morphology and damage evolution under thermomechanical fatigue of lead (Pb)-free solder interconnections , 2004, 2004 Proceedings. 54th Electronic Components and Technology Conference (IEEE Cat. No.04CH37546).

[6]  Interfacial reactions, microstructure and mechanical properties of Pb-free solder joints in PBGA laminates , 2002, 52nd Electronic Components and Technology Conference 2002. (Cat. No.02CH37345).

[7]  Zhaowei Zhong,et al.  Advanced experimental and simulation techniques for analysis of dynamic responses during drop impact , 2004, 2004 Proceedings. 54th Electronic Components and Technology Conference (IEEE Cat. No.04CH37546).

[8]  Masazumi Amagai,et al.  High solder joint reliability with lead free solders , 2003, 53rd Electronic Components and Technology Conference, 2003. Proceedings..

[9]  Chwee Teck Lim,et al.  Investigating the drop impact of portable electronic products , 2002, 52nd Electronic Components and Technology Conference 2002. (Cat. No.02CH37345).

[10]  M. Amagai,et al.  High drop test reliability: lead-free solders , 2004, 2004 Proceedings. 54th Electronic Components and Technology Conference (IEEE Cat. No.04CH37546).