Lead Free

Potential health hazard due to the toxic nature of lead has prompted electronic industry to come up with regulations on its usage. Europe, Japan and now US (not all states) has implemented the regulations suggested by Restriction of Hazards Substances (RoHS) and Waste from Electrical and Electronic Equipment (WEEE) directive. For most applications, due to this, eutectic tin-lead alloy in the solder joint has been replaced with lead free Sn-Ag-Cu (SAC) alloys. Due to this change in technology, there arise new challenges. The microstructure, mechanical response, and failure behavior of lead free solder joints in electronic assemblies are constantly evolving when exposed to isothermal aging and/or thermal cycling environments. It is observed that the material behavior variations of (SAC) lead free solders during room temperature aging (25°C) and elevated temperature aging (125°C) are unexpectedly large and universally detrimental to reliability. Such effects for lead free solder materials are especially important for the harsh applications environments present in high performance computing and in automotive, aerospace, and defense applications.

However, there has been little work in the literature, and the work that has been done has concentrated on the degradation of solder ball shear strength (e.g. Dage Shear Tester). Current finite element models for solder joint reliability during thermal cycling accelerated life testing are based on traditional solder constitutive and failure models that do not evolve with material aging. Thus, there will be significant errors in the calculations with the new lead free SAC alloys that illustrate dramatic aging phenomena. Figure 1 shows the microstructural evolution of mixed formulation solder alloys. For example MIX 10-90 contains 10% Sn-Pb and 90% SAC305 solder alloy.

Figure 1: Microstructure of various mixed formulation ratios of Sn-Pb and SAC305 solder alloy.

Figure 1: Microstructure of various mixed formulation ratios of Sn-Pb and SAC305 solder alloy.

Representative Recent Publications

Reduction of Lead Free Solder Aging Effects using Doped SAC Alloys Cai Z., Zhang Y., Suhling J., Lall P., Johnson W., Bozack M., Electronic Components and Technology Conference, 2010. ECTC 2010. 60th, 1493-1511, 2010.

The Influence of Aging on the Stress-Strain and Creep Behavior of SAC Solder Alloys Zhang Y., Cai Z., Mustafa M., Suhling J., Lall P., Bozack M., Proceedings of ITHERM 2010, Las Vegas, NV, June 2-5, 2010.

Thermo-Mechanical Reliability of SAC Lead-free Alloys Lall P., Hinshaw R., Pandher R., Harsha M., Suhling J., Proceedings of ITHERM 2010, Las Vegas, NV, June 2-5, 2010.

Analysis of the Mechanical Behavior, Microstructure, and Reliability of Mixed Formulation Solder Joints Zhang, Y., Kurumaddali, K., Suhling, J., Lall, P., Bozack, M., Proceedings of 59th Electronic Components & Technology Conference 2009, pp. 759-770, San Diego, California USA, May 25-29, 2009.

The Effects of SAC Alloy Composition on Aging Resistance and Reliability Zhang, Y., Cai, Z., Suhling, J., Lall, P., Bozack, M., Proceedings of 59th Electronic Components & Technology Conference 2009, pp. 370-389, San Diego, California USA, May 25-29, 2009.

Aging Effects In Sac Solder Joints Zhang, Y., Cai, Z., Suhling, J., Lall, P., Bozack, M., Proceedings of the 2009 SEM International Congress and Exposition on Experimental and Applied Mechanics, pp. 1-14, Albuquerque New Mexico USA, June 1-4, 2009.

Material Behavior Of Mixed Formulation Solder Joints Zhang, Y., Kurumaddali, K, Suhling, J., Lall, P., Bozack, M., ASME InterPACK, pp. 1-12, San Francisco, CA, USA, July 19-23, 2009.

Aging Effects On The Mechanical Behavior And Reliability Of SAC Alloys Zhang, Y., Cai, Z., Suhling, J., Lall, P., ASME InterPACK, pp. 1-18, San Francisco, CA, USA, July 19-23, 2009.

The Effects of Aging Temperature on SAC Solder Joint Material Behavior and Reliability Zhang, Y., Chai, Z., Suhling, J., Lall, P., Bozack, M., Proceedings of 58th Electronic Components & Technology Conference 2008, pp. 99-112, Orlando, FL, May 27-30, 2008.

Properties Of Mixed Formulation Solders Zhang, Y., Micthell, C., Suhling, J., Evans, J., Lall, P., Bozack, M., Proceedings of the 2008 SMTA International, pp. 644-651, Orlando, FL, Aug 17-21, 2008.

The Influence of Elevated Temperature Aging on Reliability of Lead Free Solder Joints Ma, H., Suhling, J., Zhang, Y., Lall, P., Bozack, M., Proceedings of 57th Electronic Components & Technology Conference 2007, pp. 653-668, Reno, NV, May 29 - Jun 1, 2007.

Reliability of the Aging Lead Free Solder Joint Ma, H., Suhling, J., Lall, P., Bozack, M., Proceedings of 56th Electronic Components & Technology Conference 2006, pp. 849-864, San Diego, CA, May 30 - Jun 2, 2006.

Evolution Of Lead Free Solder Material Behavior During Isothermal Aging Ma, H., Suhling, J,, Lall, P., Bozack, M., 2006 ASME International Mechanical Engineering Congress and Exposition, pp. 1-16, Chicago, IL, Nov 5-10, 2006.

Effects Of Aging On The Stress-Strain And Creep Behaviors Of Lead Free Solders Ma, H., Suhling, J., Lall, P., Bozack, M., Proceedings of ITHERM 2006, pp. 961-976, San Diego, CA, May30-Jun2, 2006.

Measurement Of The Constitutive Behavior Of Lead Free Solders Abdel-Hady, H., Ma, H., Suhling, J., Islam, S., Lall, P., Proceedings of the 2004 SEM X International Congress & Exposition on Experimental and Applied Mechanics, pp. 1-5, Costa Mesa, CA, Jun 7-10, 2004.