Isothermal Aging Effects on the Thermal reliability Performance of Lead-Free Solder Joints

2012 ◽  
Vol 2012 (1) ◽  
pp. 000801-000808 ◽  
Author(s):  
Jiawei Zhang ◽  
Zhou Hai ◽  
Sivasubramanian Thirugnanasambandam ◽  
John L. Evans ◽  
M. J. Bozack
Keyword(s):  
Elevated Temperature ◽  
Isothermal Aging ◽  
Elevated Temperatures ◽  
Solder Joints ◽  
Bulk Solder ◽  
Lead Free ◽  
Aging Effects ◽  
Thermal Reliability ◽  
Free Solder ◽  
The Impact

Electronics assemblies containing solder joints are often exposed to elevated temperatures for prolonged periods of time. The time-at-temperature stress impacts the overall package reliability of the assembled circuitry due to evolving materials, microstructural, and mechanical properties. It is especially important to understand the impact of isothermal aging on the long term behavior of lead (Pb)-free solder joints which operate in harsh environments. In this study, we have explored the effects of elevated temperature isothermal aging on the reliability of Sn-Ag-Cu (SAC) assemblies on board level packages. As the isothermal aging temperature increases, the Weybull characteristic lifetime for SAC 105 and 305 solder joints is drastically reduced compared to Sn-37Pb.In parallel mechanical studies on bulk solder specimens, the creep rate for SAC105, 305 rapidly increases with aging. A full test matrix with varying aging temperatures and solder alloys was considered. Package sizes ranged from 19mm, 0.8mm pitch ball grid arrays (BGAs) to 5mm, 0.4mm pitch μBGAs. The test structures were built on three different board finishes (ImSn, ImAg and SnPb). Storage condition temperatures were 25°C, 55°C, 85°C and 125°C with aging over time periods of 0, 6, and 12 months. Subsequently, the specimens were thermally cycled from −40°C to 125°C with 15 min dwell times at the high temperature. It was found that the thermal performance of lead-free fine-pitch packages significantly degrades up to 55–60% after aging at elevated temperature. The dominant failure mode can be associated with the growth of Cu6Sn5 intermetallic compounds (IMC) during the aging, particularly on the pad side.

Nanoindentation Measurements of the Mechanical Properties of Individual Phases Within Lead Free Solder Joints Subjected to Isothermal Aging

2018 ◽  
Author(s):  
Abdullah Fahim ◽  
Sudan Ahmed ◽  
Jeffrey C. Suhling ◽  
Pradeep Lall
Keyword(s):  
Mechanical Properties ◽  
Isothermal Aging ◽  
Solder Joints ◽  
Bulk Solder ◽  
Lead Free ◽  
Nanoindentation Test ◽  
Lead Free Solder ◽  
Free Solder ◽  
The Individual ◽  
Sac Solder

Exposure of lead free solder joints to high temperature isothermal aging conditions leads to microstructure evolution, which mainly includes coarsening of the intermetallic (IMC) phases. In our previous work, it was found that the coarsening of IMCs led to degradation of the overall mechanical properties of the SAC solder composite consisting of β-Sn matrix and IMC particles. However, it is not known whether the isothermal aging changes properties of the individual β-Sn and IMC phases, which could also be affecting to the overall degradation of properties. In this study, the aging induced variations of the mechanical properties of the β-Sn phase, and of Sn-Cu IMC particles in SAC solder joints have been explored using nanoindentation. SAC solder joints extracted from SuperBGA (SBGA) packages were aged for different time intervals (0, 1, 5, 10 days) at T = 125 °C. Nanoindentation test samples were prepared by cross sectioning the solder joints, and then molding them in epoxy and polishing them to prepare the joint surfaces for nanoindentation. Multiple β-Sn grains were identified in joints using optical polarized microscopy and IMCs were also observed. Individual β-Sn grains and IMC particles were then indented at room temperature to measure their mechanical properties (elastic modulus and hardness) and time dependent creep deformations. Properties measured at different aging time were then compared to explore aging induced degradations of the individual phases. The properties of the individual phases did not show significant degradation. Thus, IMC coarsening is the primary reason for the degradation of bulk solder joint properties, and changes of the properties of the individual phases making up the lead free solder material are negligible.

Isothermal Aging Effects on the Mechanical Shock Performance of Lead-Free Solder Joints

2011 ◽  
Vol 1 (5) ◽  
pp. 714-721 ◽  
Author(s):  
Hongtao Ma ◽  
Tae-Kyu Lee ◽  
Dong Hyun Kim ◽  
H G Park ◽  
Sang Ha Kim ◽  
...  
Keyword(s):  
Isothermal Aging ◽  
Solder Joints ◽  
Lead Free ◽  
Lead Free Solder ◽  
Mechanical Shock ◽  
Aging Effects ◽  
Free Solder

Nanomechanical Characterization of Aging Effects in Solder Joints in Microelectronic Packaging

2013 ◽  
Author(s):  
Mohammad Hasnine ◽  
Muhannad Mustafa ◽  
Jing Zou ◽  
Jeffrey C. Suhling ◽  
Barton C. Prorok ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Solder Joints ◽  
Bulk Solder ◽  
Lead Free ◽  
Lead Free Solder ◽  
Aging Effects ◽  
Single Grain ◽  
Free Solder ◽  
Aging Phenomena ◽  
Sac Solder

The mechanical properties of a lead free solder are strongly influenced by its microstructure, which is controlled by its thermal history including solidification rate and thermal aging after solidification. Due to aging phenomena, the microstructure, mechanical response, and failure behavior of lead free solder joints in electronic assemblies are constantly evolving when exposed to isothermal and/or thermal cycling environments. Through uniaxial testing of miniature bulk solder tensile specimens, we have previously demonstrated that large changes occur in the stress-strain and creep behaviors of lead free solder alloys with aging. Complementary studies by other research groups have verified aging induced degradations of SAC mechanical properties. In those investigations, mechanical testing was performed on a variety of sample geometries including lap shear specimens, Iosipescu shear specimens, and custom solder ball array shear specimens. While there are clearly aging effects in SAC solder materials, there have been limited prior mechanical loading studies on aging effects in actual solder joints extracted from area array assemblies (e.g. PBGA or flip chip). This is due to the extremely small size of the individual joints, and the difficulty in gripping them and applying controlled loadings (tension, compression, or shear). In the current work, we have explored aging phenomena in actual solder joints by nano-mechanical testing of single SAC305 lead free solder joints extracted from PBGA assemblies. Using nanoindentation techniques, the stress-strain and creep behavior of the SAC solder materials have been explored at the joint scale for various aging conditions. Mechanical properties characterized as a function of aging include the elastic modulus, hardness, and yield stress. Using a constant force at max indentation, the creep response of the aged and non-aged solder joint materials has also been measured as a function of the applied stress level. With these approaches, aging effects in solder joints were quantified and correlated to the magnitudes of those observed in testing of miniature bulk specimens. Our results show that the aging induced degradations of the mechanical properties (modulus, hardness) of single grain SAC305 joints were similar to those seen previously by testing of larger “bulk” solder specimens. However, due to the single grain nature of the joints considered in this study, the degradations of the creep responses were significantly less in the solder joints relative to those in larger uniaxial tensile specimens. The magnitude of aging effects in multi-grain lead free solder joints remains to be quantified. Due to the variety of crystal orientations realized during solidification, it was important to identify the grain structure and crystal orientations in the tested joints. Polarized light microscopy and Electron Back Scattered Diffraction (EBSD) techniques have been utilized for this purpose. The test results show that the elastic, plastic, and creep properties of the solder joints and their sensitivities to aging are highly dependent on the crystal orientation. In addition, an approach has been developed to predict tensile creep strain rates for low stress levels using nanoindentation creep data measured at very high compressive stress levels.

A Novel Mechanism of Embrittlement Affecting the Impact Reliability of Tin-Based Lead-Free Solder Joints

2009 ◽  
Vol 38 (9) ◽  
pp. 1881-1895 ◽  
Author(s):  
Konstantina Lambrinou ◽  
Wout Maurissen ◽  
Paresh Limaye ◽  
Bart Vandevelde ◽  
Bert Verlinden ◽  
...  
Keyword(s):  
Solder Joints ◽  
Lead Free ◽  
Lead Free Solder ◽  
Free Solder ◽  
Impact Reliability ◽  
The Impact

Effects of Current Stressing and Isothermal Aging on the Tensile Strength of Microscale Lead-Free Solder Joints with Different Joint Volumes

2013 ◽  
Vol 634-638 ◽  
pp. 2800-2803 ◽  
Author(s):  
Li Meng Yin ◽  
Yan Fei Geng ◽  
Zhang Liang Xu ◽  
Song Wei
Keyword(s):  
Tensile Strength ◽  
Current Density ◽  
Isothermal Aging ◽  
Solder Joints ◽  
High Current Density ◽  
Copper Wire ◽  
Lead Free ◽  
Lead Free Solder ◽  
Current Stressing ◽  
Free Solder

Adopting an accurate micro-tensile method based on dynamic mechanical analyzer (DMA) instrument, the tensile strength of three kinds of copper-wire/solder/copper-wire sandwich structured microscale lead-free solder joints that underwent current stressing with a direct current density of 1.0×104 A/cm2 and loading time of 48 hours were investigated, and compared with those solder joints isothermal aged at 100 0C for 48 hours and as-reflowed condition. These three kinds of microscale columnar solder joints have different volumes, i.e., a same diameter of 300 μm but different heights of 100 μm, 200 μm and 300 μm. Experimental results show that both current stressing and isothermal aging degrades the tensile strength of microscale solder joints, and the solder joint with smaller volume obtains higher tensile strength under same test condition. In addition, current stressing induces obvious electromigration (EM) issue under high current density of 1.0×104 A/cm2, resulting in the decreasing of tensile strength and different fracture position, mode and surface morphology of microscale solder joints. The degree of strength degradation increases with the increasing of joint height when keep joint diameter constant, this is mainly due to that electromigration leads to voids form and grow at the interface of cathode, and solder joints with larger volume may contains more soldering defects as well.

Evolution of Lead Free Solder Material Behavior Under Elevated Temperature Aging

2007 ◽  
Author(s):  
Hongtao Ma ◽  
Jeffrey C. Suhling ◽  
Yifei Zhang ◽  
Pradeep Lall ◽  
Michael J. Bozack
Keyword(s):  
Elevated Temperature ◽  
Room Temperature ◽  
Solder Joints ◽  
Material Behavior ◽  
Lead Free ◽  
Lead Free Solder ◽  
Room Temperature Aging ◽  
Free Solder ◽  
Lead Free Solders ◽  
Temperature Aging

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. In our prior work on aging effects (Ma, et al., ECTC 2006), we demonstrated that the observed material behavior variations of SAC405 and SAC305 lead free solders during room temperature aging (25 °C) were unexpectedly large and universally detrimental to reliability. Such effects for lead free solder materials are much more dramatic at the higher aging temperatures (e.g. 100–150 °C) typical of the harsh 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. In the current work, we have explored the effects of elevated temperature isothermal aging on the mechanical behavior and reliability of lead free solders. The effects of aging on mechanical behavior have been examined by performing stress-strain and creep tests on SAC405 and SAC305 samples that were aged for various durations (0–6 months) at several elevated temperatures (80, 100, 125, and 150 °C). Analogous tests were performed with 63Sn-37Pb eutectic solder samples for comparison purposes. Variations of the temperature dependent mechanical properties (elastic modulus, yield stress, ultimate strength, creep compliance, etc.) were observed and modeled as a function of aging time and temperature. In this paper, we have concentrated our efforts on presenting the results for samples aged at 125 °C. In addition, the new elevated temperature aging data were correlated with our room temperature results from last year’s investigation. The results obtained in this work have demonstrated the significant effects of elevated temperature exposure on solder joints. As expected, the mechanical properties evolved at a higher rate and experienced larger changes during elevated temperature aging (compared to room temperature aging). After approximately 200 hours of aging, the lead free solder joint material properties were observed to degrade at a nearly constant rate. We have developed a mathematical model to predict the variation of the properties with aging time and aging temperature. Our data for the evolution of the creep response of solders with elevated temperature aging show that the creep behavior of lead free and tin-lead solders experience a “crossover point” where lead free solders begin to creep at higher rates than standard 63Sn-37Pb solder for the same stress level. Such an effect is not observed for solder joints aged at room temperature, where SAC alloys always creep at lower rates than Sn-Pb solder.

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