This research seeks to characterize the micro-mechanical behavior of Sn-Ag-Cu solder bumps/joints generated by fine pitch flip chip assembly processes. The solder bumps and joints that were aged at either 80 °C or 150 °C for up to 440 hours (∼18 days); have been studied by an analysis using micro-shear testing and nano-indentation techniques. The shear test of the aged bumps showed a slight increase in shear strength after an initial period of aging (∼50 hours) as compared to the non-aged bumps, but a decrease after longer aging (e.g. 440 hours). A brittle Ag3Sn phase formed as large stick-like features in the body of bulk solder and near the interface of solder/UBM during the initial aging, and is attributed with the increase of shear strength, along with the refinement of the bump microstructure. However, as the time of aging extended, the solder bumps were softened due to grain growth and re-crystallization. It was found that the formation of brittle phases in the body of solder and along the interfaces caused localized stress concentration, which can significantly affect joint reliability. In addition, Nano-testing identified a large lamellar Au-rich structure, formed in the solder and interface of the solder/PCB in the joints after the aging process at 150 °C. These are believed to be detrimental to joint reliability.

Issue Section:
Research Paper
Keywords:
solders, flip-chip devices, ageing, indentation, fine-pitch technology, shear strength, tin alloys, silver alloys, copper alloys
Topics:
Flip-chip, Nanoindentation, Shear (Mechanics), Solders, Tin, Flip-chip devices, Intermetallic compounds, Testing, Reliability, Shear strength
1.
Bradley, E., 2003, “Lead Free Solder Assembly: Impact and Opportunity,” Proceedings of the 53rd Electronic Components & Technology Conference, New York, IEEE, pp. 41–46.
2.
Hua, F., 2003, “Pb-Free Solder Challenges in Electronics Packaging and Assembly,” Proceedings of the 53rd Electronic Components & Technology Conference, New York, IEEE, pp. 58–63.
3.
Kim, N., Jung, S. Y., and S., Oh, 2003, “Reliability of the Pb-Free Solder Bump on Electroless Ni Under Bump Metallurgies,” Proceedings of the 53rd Electronic Components & Technology Conference, New York, IEEE, pp. 77–82.
4.
Liu, C., Geggel, M., Conway, P. P., and Hendriksen, M., 2002, “Micro-Scale Mechanical Properties of Fine Feature Flip Chip with Lead Free Solders,” Proceedings of the International Symposium on Electronic Materials and Packaging, Kaohsiung, Taiwan, pp. 259–266.
5.
Liu, C., Li, D., and Conway, P. P., 2003, “Characterization of Intermetallics Ageing in Flip Chip Solder Bumps,” Proceedings of the 53rd Electronics Components and Technology Conference (ECTC’53), New York, IEEE, pp. 1767–1771.
6.
Huang, Z., Conway, P. P., Liu, C., and Thomson, R. C., 2003, “Inter-Dependence of Processing and Alloy Composition on the Reliability of Sn-Based Lead Free Solders in Fine Pitch FCOB Interconnection,” SEMI Technology Symposium; 28th International Electronics Manufacturing Technology (STS: IEMT), July 16–18, San Jose, CA.
7.
Kang, S. K., Choi, W. K., Shih, D. Y., Lauro, P., Henderson, D. W., Gosselin, T., and Leonard, D. N., 2002, “Interfacial Reactions, Microstructure and Mechanical Properties of Pb-Free Solder Joints in PBGA Laminates,” Proceedings of the 52nd Electronic Components & Technology Conference, New York, IEEE, pp. 146–153.
8.
Jeon, Y. D., Nieland, S., Ostmann, A., Reichl, H., and Paik, K. W., 2002, “Studies on the Interfacial Reactions between Electroless NiUBM and 95.5Sn-4.0Ag-0.5Cu Alloy,” Proceedings of the 52nd Electronic Components & Technology Conference, New York, IEEE, pp. 740–746.
9.
Zeng
,
K.
, and
Tu
,
K. N.
,
2002
, “
Six Cases of Reliability Study of Pb-Free Solder Joints in Electronic Packaging Technology
,”
Mater. Sci. Eng., R.
,
38
, pp.
55
–
105
.
10.
Goyal, D., Lane, T., Kinzie, P., Panichas, C., Chong, K. M., and Villalobos, O. 2002, “Failure Mechanism of Brittle Solder Joint Fracture in the Presence of Electroless Nickel Immersion Gold (ENIG) Interface,” Proceedings of the 52nd Electronic Components & Technology Conference, New York, IEEE, pp. 732–739.
11.
Jang, S. Y., Wolf, J., Kwon, W. S., and Paik, K. W., 2002, “UBM (Under Bump Metallization) Study for Pb-Free Electroplating Bumping: Interface Reaction and Electromigration,” Proceedings of the 52nd Electronic Components & Technology Conference, New York, IEEE, pp. 1213–1220.
12.
Balkan, H., D. Patterson, et al., 2002, “Flip-chip Reliability: Comparative Characterization of Lead Free (Sn/Ag/Cu) and 63Sn/Pb Eutectic Solder,” Proceedings of the 52nd Electronic Components & Technology Conference, New York, IEEE, pp. 1263–1269.
13.
Chung, C. K., Aspandiar, R., Leong, K. F., and Tay, C. S., 2002, “The Interactions of Lead (Pb) in Lead Free Solder (Sn/Ag/Cu) System,” Proceedings of the 52nd Electronic Components & Technology Conference, pp. 168–175.
14.
Zhang, F., Chum, C. C., and Li, M., 2002, “Effect of Au on Interfacial Reactions of Eutectic SnPb and SnAgCu Solders with Al/Ni(V)/Cu Thin Film Metallization,” Proceedings of the 52nd Electronic Components & Technology Conference, New York, IEEE, pp. 726–731.
15.
Oliver
,
W. C.
, and
Pharr
,
G. M.
,
1992
, “
An Improved Technique for Determining Hardness and Elastics Modulus Using Load and Displacement Sensing Indentation Experiments
,”
J. Mater. Res.
,
7
(6), June, pp.
1564
–
1583
.
16.
Beake
,
B. D.
,
Goodes
,
S. R.
,
Smith
,
J. F.
, et al.,
2002
, “
Investigating the Fracture Resistance and Adhesion of DLC Films with Micro-impact Testing
,”
Diamond Relat. Mater.
,
11
(8), August, pp.
1606
–
1609
.
17.
Li, D., Liu, C., and Conway, P. P., 2003, “Direct Soldering onto the UBM of Electroless Deposited Ni-P with Sn-Pb and Pb-free Alloys,” Proceedings of EMAP 2003, International Symposium on Electronic Materials and Packaging, November 17–20, Singapore, pp. 269–276.
18.
Yau, E. W. C., Gong, J. F., Hong, B. F. W., and Chan, P. C. H., 2003, “A Reliability Comparison of Lead Free and Eutectic Solder for Stencil Printing Based Flip-Chip Applications,” Proceedings of the 53rd Electronics Components and Technology Conference (ECTC’53), New York, IEEE, pp. 323–330.
19.
Kang, S. K., Choi, W. K., Shih, D. Y., Henderson, D. W., and Gosselin, T., 2003, “Formation of Ag3Sn Plates in Sn-Ag-Cu Alloys and Optimization of Their Alloy Composition,” Proceedings of the 53rd Electronics Components and Technology Conference (ECTC’53), New York, IEEE, pp. 64–70.
Copyright © 2004
 by ASME
You do not currently have access to this content.