Lead Free

Potential health hazards due to the toxic nature of lead has prompted the electronics industry to establish regulations regarding its usage. Europe, Japan, and parts of the United States have implemented the regulations suggested by the Restriction of Hazards Substances (RoHS) and Waste from Electrical and Electronic Equipment (WEEE) directives. Due to this, eutectic tin-lead alloy in the solder joint has been replaced with lead free Sn-Ag-Cu (SAC) alloys in most applications. Although this change has resulted in benefits regarding the health and safety on individuals, it also has produced 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 (25°C) aging and elevated temperature (125°C) aging 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 published in the literature, and the work that has been performed and documented has almost solely 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

Fahim, A., Ahmed, S., Suhling, J.C., Lall, P., Nanomechanical Characterization of Intermetallic Compounds in Lead Free Solder Joints, Proceedings of the IEEE 2018 Electronic Components and Technology Conference (ECTC2018), San Diego, CA, May 29-June 1, 2018.

Ahmed, S., Wu, J., Fu, N., Suhling, J.C., Lall, P., Quantification and Modeling of Microstructural Evolution in Lead Free Solders During Long Term Isothermal Aging, Proceedings of the IEEE 2018 Electronic Components and Technology Conference (ECTC2018), San Diego, CA, pp. 162-171, May 29-June 1, 2018.

Chowdhury, M.M., Hoque, M.A., Ahmed, S., Suhling, J.C., Hamasha, S., Lall, P., Effects of Mechanical Cycling on the Microstructure of SAC305 Lead Free Solder, Proceedings of the IEEE 2018 Intersociety Conference on Thermal and Thermomechanical Phenomena in Electronic Systems (ITherm2018), San Diego, CA, pp. 1324-1332, May 29-June 1, 2018.

Hassan, KM Rafidh, Alam, M.S., Basit, M., Suhling, J.C., Lall, P., The Influence of Poisson's Ratio on the Reliability of SAC Lead Free Solder Joints, Proceedings of the IEEE 2018 Intersociety Conference on Thermal and Thermomechanical Phenomena in Electronic Systems (ITherm2018), San Diego, CA, pp. 1207-1216, May 29-June 1, 2018.

Alam, M.S., Hassan, KM Rafidh, Suhling, J.C., Lall, P., High Temperature Mechanical Behavior of SAC and SAC+X Lead Free Solders, Proceedings of the IEEE 2018 Electronic Components and Technology Conference (ECTC2018), San Diego, CA, pp. 1781-1789, May 29-June 1, 2018.

Alam, M.S., Hassan KM Rafidh, Suhling, J.C., Lall, P., A Comparative Study of the High Temperature Mechanical Behavior of Lead Free Solders, Proceedings of the IEEE 2018 Intersociety Conference on Thermal and Thermomechanical Phenomena in Electronic Systems (ITherm2018), San Diego, CA, pp. 1314-1323, May 29-June 1, 2018.

Ahmed, S., Suhling, J.C., Lall, P., Evaluation of Aging Induced Microstructural Evolution in Lead Free Solders Using Scanning Probe Microscopy, Proceedings of the IEEE 2018 Intersociety Conference on Thermal and Thermomechanical Phenomena in Electronic Systems (ITherm2018), San Diego, CA, pp. 1062-1070, May 29-June 1, 2018.

Chowdhury, M.M., Hoque, M.A., Fu, N., Suhling, J.C., Hamasha, S., Lall, P., Characterization of Material Damage and Microstructural Evolution Occurring in Lead Free Solders Subjected to Cyclic Loading, Proceedings of the IEEE 2018 Electronic Components and Technology Conference (ECTC2018), San Diego, CA, pp. 865-874, May 29-June 1, 2018.

Wu, J., Ahmed, S., Suhling, J.C., Lall, P., Investigation of Microstructural Evolution in SAC Solders Exposed to Short-Term and Long-Term Aging, Proceedings of the IEEE 2018 Intersociety Conference on Thermal and Thermomechanical Phenomena in Electronic Systems (ITherm2018), San Diego, CA, pp. 1234-1242, May 29-June 1, 2018.

Fahim, A., Ahmed, S., Suhling, J.C., Lall, P., Mechanical Characterization of Intermetallic Compounds in SAC Solder Joints at Elevated Temperatures, Proceedings of the IEEE 2018 Intersociety Conference on Thermal and Thermomechanical Phenomena in Electronic Systems (ITherm2018), San Diego, CA, pp. 1081-1090, May 29-June 1, 2018.

Hoque, M.A., Chowdhury, M.M., Fu, N., Suhling, J.C., Hamasha, S., Lall, P., Evolution of the Cyclic Stress-Strain and Constitutive Behavior of Doped Lead Free Solder During Fatigue Testing, Proceedings of the IEEE 2018 Intersociety Conference on Thermal and Thermomechanical Phenomena in Electronic Systems (ITherm2018), San Diego, CA, pp. 1387-1395, May 29-June 1, 2018.

Lall, P., Yadav, V., Suhling, J., Locker, D., Effect of Prolonged Storage on High Strain Rate Mechanical Properties of SAC-Q Leadfree Solder at High Operating Temperature, Proceedings of the IEEE 2018 Intersociety Conference on Thermal and Thermomechanical Phenomena in Electronic Systems (ITherm2018), San Diego, CA, pp. 1296-1308, May 29-June 1, 2018.

Lall, P., Yadav V., Zhang, D., Suhling, J., Reliability of SAC Leadfree Solders in Automotive Underhood Temperature-Vibration, Proceedings of the IEEE 2018 Intersociety Conference on Thermal and Thermomechanical Phenomena in Electronic Systems (ITherm2018), San Diego, CA, pp. 1255-1269, May 29-June 1, 2018.

Ahmed, S., Suhling, J.C., Lall, P., The Anand Parameters of Aging Resistant Doped Solder Alloys, Proceedings of the IEEE 2017 Intersociety Conference on Thermal and Thermomechanical Phenomena in Electronic Systems (ITherm2017), Orlando, FL, pp. 1416-1424, May 30-June 2, 2017.

Fu, N., Ahmed, S., Suhling, J.C., Lall, P., Visualization of Microstructural Evolution in Lead Free Solders During Isothermal Aging Using Time-Lapse Imagery, Proceedings of the IEEE 2017 Electronic Components and Technology Conference (ECTC2017), Orlando, FL, pp. 429-440, May 30-June 2, 2017.

Alam, M.S., Suhling, J.C., Lall, P., High Temperature Tensile and Creep Behavior of Lead Free Solders, Proceedings of the IEEE 2017 Intersociety Conference on Thermal and Thermomechanical Phenomena in Electronic Systems (ITherm2017), Orlando, FL, pp. 1229-1237, May 30-June 2, 2017.

Fahim, A., Ahmed, S., Suhling, J.C., Lall, P., Nanomechanical Characterization of IMCs Formed in SAC Solder Joints Subjected to Isothermal Aging, Proceedings of the IEEE 2017 Intersociety Conference on Thermal and Thermomechanical Phenomena in Electronic Systems (ITherm2017), Orlando, FL, pp. 1398-1408, May 30-June 2, 2017.

Fu, N., Suhling, J.C., Hamasha, S., Lall, P., Evolution of the Cyclic Stress-Strain and Constitutive Behaviors of SAC305 Lead Free Solder During Fatigue Testing,  Proceedings of the IEEE 2017 Intersociety Conference on Thermal and Thermomechanical Phenomena in Electronic Systems (ITherm2017), Orlando, FL, pp. 1353-1360, May 30-June 2, 2017.

Chowdhury, M.M., Fu, N., Suhling, J.C., Lall, P., Evolution of the Cyclic Stress-Strain Behavior of Doped SAC Solder Materials Subjected to Isothermal Aging, Proceedings of the IEEE 2017 Intersociety Conference on Thermal and Thermomechanical Phenomena in Electronic Systems (ITherm2017), Orlando, FL, pp. 1369-1379, May 30-June 2, 2017.

Ahmed, S., Hasnine, M., Suhling, J.C., Lall, P., Mechanical Characterization of SAC Solder Joints at High Temperature Using Nanoindentation, Proceedings of the IEEE 2017 Electronic Components and Technology Conference (ECTC2017), Orlando, FL, pp. 1128-1135, May 30-June 2, 2017.

Fu, N., Suhling, J.C., Lall, P., Cyclic Stress-Strain Behavior of SAC305 Lead Free Solder: Effects of Aging, Temperature, Strain Rate, and Plastic Strain Rate, Proceedings of the IEEE 2016 Electronic Components and Technology Conference (ECTC2016), Las Vegas, NV, pp. 1119-1127, May 31-June 3, 2016.

Fahim, A., Ahmed, S., Chowdhury, M.M., Suhling, J.C., Lall, P., High Temperature Creep Response of Lead Free Solders, Proceedings of the IEEE 2016 Intersociety Conference on Thermal and Thermomechanical Phenomena in Electronic Systems (ITherm2016), Las Vegas, NV, pp. 1218-1224, May 31-June 3, 2016.

Alam, M.S., Basit, M., Suhling, J.C., Lall, P., Mechanical Characterization of SAC305 Lead Free Solder at High Temperatures, Proceedings of the IEEE 2016 Intersociety Conference on Thermal and Thermomechanical Phenomena in Electronic Systems (ITherm2016), Las Vegas, NV, pp. 755-760, May 31-June 3, 2016.

Fu, N., Suhling, J.C., Mustafa, M., Lall, P., Aging Induced Evolution of the Cyclic Stress-Strain Behavior of Lead Free Solders, Proceedings of the IEEE 2016 Intersociety Conference on Thermal and Thermomechanical Phenomena in Electronic Systems (ITherm2016), Las Vegas, NV, pp. 737-745, May 31-June 3, 2016.

Motalab, M., Mustafa, M., Suhling, J.C., Lall, P., Improved Predictions of Cyclic Stress-Strain Curves for Lead Free Solders using the Anand Viscoplastic Constitutive Model, Proceedings of the IEEE 2016 Intersociety Conference on Thermal and Thermomechanical Phenomena in Electronic Systems (ITherm2016), Las Vegas, NV, pp. 471-480, May 31-June 3, 2016.

Ahmed, S., Basit, M., Suhling, J.C., Lall, P., Effects of Aging on SAC-Bi Solder Materials, Proceedings of the IEEE 2016 Intersociety Conference on Thermal and Thermomechanical Phenomena in Electronic Systems (ITherm2016), Las Vegas, NV, pp. 746-754, May 31-June 3, 2016.

Chowdhury, M.M., Ahmed, S., Fahim, A., Suhling, J.C., Lall, P., Mechanical Characterization of Doped SAC Solder Materials at High Temperature, Proceedings of the IEEE 2016 Intersociety Conference on Thermal and Thermomechanical Phenomena in Electronic Systems (ITherm2016), Las Vegas, NV, pp. 1201-1208, May 31-June 3, 2016.

Basit, M., Ahmed, S., Motalab, M., Roberts, J.C., Suhling, J.C., Lall, P., The Anand Parameters for SAC Solders after Extreme Aging, Proceedings of the IEEE 2016 Intersociety Conference on Thermal and Thermomechanical Phenomena in Electronic Systems (ITherm2016), Las Vegas, NV, pp. 440-447, May 31-June 3, 2016.