Investigation of the Effects of High Temperature Aging on Mechanical Behavior and Microstructural Changes in Lead Free Solders

2019 ◽  
Author(s):  
Jing Wu ◽  
Mohammad S. Alam ◽  
Jeffrey C. Suhling ◽  
Pradeep Lall
Keyword(s):  
Ostwald Ripening ◽  
Solder Joints ◽  
Particle Diameter ◽  
Lead Free ◽  
Average Particle ◽  
Lead Free Solder ◽  
Aging Effects ◽  
Sac305 Solder ◽  
Free Solder

Abstract Aging effects are common in lead free solder joints within electronic assemblies that are exposed to isothermal environments for extended periods. Such exposures lead to evolution of the solder microstructure, which results in changes in the mechanical properties and creep behavior of the solder joints. In our recent investigations, we have been utilizing Scanning Electron Microscopy (SEM) to better understand aging induced degradations. The microstructural evolutions were observed in SAC305 and SAC_Q (SAC+Bi) alloys exposed to isothermal conditions at T = 125 °C for several different regions from several different joints. The microstructures in several fixed regions of interest were recorded after predetermined time intervals of aging, which were 1 hour (up to 24 hours) and 10 hours (up to 150 hours) for the short term aging samples; and 250 hours (up to 2500 hours) for the long term aging samples. Using the recorded images and imaging processing software, the area and diameter of each IMC particle was tracked during the aging process. As expected, the quantitative analysis of the evolving SAC_Q microstructure showed that the particles coalesced during aging leading to a decrease in the number of particles. This caused an increase in the average diameter of the particles of slightly more than 100% for long term aging of 2500 hours. For SAC305, the average particle diameter was found to increase at three times the rate (increase of 200% after 2500 hours of aging). Thus, coarsening of IMC particles was greatly mitigated in the SAC_Q alloy relative to that observed in SAC305. Immediately after reflow solidification, Bismuth rich phases were present in the SAC_Q joints. During aging at T = 125 °C, the bismuth was observed to quickly go into solution both within the beta-Sn dendrites and in the intermetallic rich regions between dendrites. This resulted in solid solution strengthening of the lead free solder. It was also found that the aging-induced presence of bismuth in solution within the beta-Sn matrix provided an increased resistance to the Ostwald ripening diffusion process that coarsens the Ag3Sn IMC particles. The combination of these two effects in the SAC+Bi alloy lead to greatly improved resistance to aging induced effects relative to the SAC305 solder alloy. Finally, we have compared the time dependent evolution of microstructure with the degradation in strength during aging for of the two solder alloys, and good correlations were observed.

Effect of Aging on the Properties of Intermetallic Layers in SAC+Bi Solder Joints

2021 ◽  
Author(s):  
Mohammad Ashraful Haq ◽  
Mohd Aminul Hoque ◽  
Jeffrey C. Suhling ◽  
Pradeep Lall
Keyword(s):  
Solder Joints ◽  
Lead Free ◽  
Lead Free Solder ◽  
Aging Condition ◽  
Sac305 Solder ◽  
The Poor ◽  
Free Solder ◽  
Lead Free Solders ◽  
Overall Reliability ◽  
Intermetallic Layers

Abstract A major problem faced by electronic packaging industries is the poor reliability of lead free solder joints. One of the most common methods utilized to tackle this problem is by doping the alloy with other elements, especially bismuth. Researches have shown Bismuth doped solder joints to mostly fail near the Intermetallic (IMC) layer rather than the bulk of the solder joint as commonly observed in traditional SAC305 solder joints. An understanding of the properties of this IMC layer would thus provide better solutions on improving the reliability of bismuth doped solder joints. In this study, the authors have used three different lead free solders doped with 1%, 2% and 3% bismuth. Joints of these alloys were created on copper substrates. The joints were then polished to clearly expose the IMC layers. These joints were then aged at 125 °C for 0, 1, 2, 5 and 10 days. For each aging condition, the elastic modulus and the hardness of the IMC layers were evaluated using a nanoindenter. The IMC layer thickness and the chemical composition of the IMC layers were also determined for each alloy at every aging condition using Scanning Electron Microscopy (SEM) and EDS. The results from this study will give a better idea on how the percentage of bismuth content in lead free solder affects the IMC layer properties and the overall reliability of the solder joints.

Damage Evolution in Lead Free Solder Joints in Isothermal Fatigue

2015 ◽  
Vol 137 (2) ◽  
Author(s):  
Awni Qasaimeh ◽  
Sa’d Hamasha ◽  
Younis Jaradat ◽  
Peter Borgesen
Keyword(s):  
Crack Initiation ◽  
Mechanical Response ◽  
Solder Joints ◽  
Fatigue Testing ◽  
Hysteresis Loops ◽  
Damage Function ◽  
Lead Free ◽  
Lead Free Solder ◽  
Sac305 Solder ◽  
Free Solder

The extrapolation and generalization of accelerated test results for lead free solder joints require the identification of a damage function that can be counted on to apply beyond the region of the test. Individual ball grid array (BGA) scale Sn3Ag0.5Cu (SAC305) solder joints were subjected to isothermal shear fatigue testing at room temperature and 65 °C. The resulting mechanical response degradation and crack behavior, including strain hardening, crack initiation, and propagation, were correlated with the inelastic work and effective stiffness derived from load–displacement hysteresis loops. Crack initiation was found to scale with the accumulated work, independently of cycling amplitude and strain rate. The subsequent damage rate varied slightly with amplitude.

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

Characterization of aging effects in lead free solder joints using nanoindentation

2013 ◽  
Author(s):  
Mohammad Hasnine ◽  
Muhannad Mustafa ◽  
Jeffrey C. Suhling ◽  
Barton C. Prorok ◽  
Michael J. Bozack ◽  
...  
Keyword(s):  
Solder Joints ◽  
Lead Free ◽  
Lead Free Solder ◽  
Aging Effects ◽  
Free Solder

Investigation of Aging Induced Evolution of the Microstructure of SAC305 Lead Free Solder

2017 ◽  
Author(s):  
Nianjun Fu ◽  
Jing Wu ◽  
Sudan Ahmed ◽  
Jeffrey C. Suhling ◽  
Pradeep Lall
Keyword(s):  
Cross Sections ◽  
Particle Diameter ◽  
Lead Free ◽  
Average Particle ◽  
Lead Free Solder ◽  
Average Particle Diameter ◽  
Free Solder ◽  
Induced Changes ◽  
Lead Free Solders ◽  
Particle Area

The most well-known and widely observed microstructural changes during aging are the coarsening of Ag3Sn and Cu6Sn5 intermetallic compounds (IMCs) present in the eutectic regions between β-Sn dendrites. In this investigation, Scanning Electron Microscopy (SEM) has been utilized to examine aging induced coarsening of IMCs occurring within lead free solders. Unlike many prior studies, fixed regions in the solder joint cross-sections were monitored throughout the aging process, rather than examining different samples and/or different regions after the various aging exposures. Sn-3.0Ag-0.5Cu (SAC305) lead free solder samples were formed with reflowed (RF) and water quenched (WQ) cooling profiles and resulting initial microstructures, and then polished microscopy cross-sections were prepared. Nanoindentation marks were added to the cross-sections at certain locations to facilitate locating the fixed regions of interest in subsequent microscopy observations. After preparation, the samples were then aged at T = 125 °C, and the microstructures were observed and recorded in the selected regions after various aging exposures using SEM. In addition, the coarsening of IMCs during aging has been quantitatively analyzed. Particularly, the aging induced changes in number of IMCs, total area of all IMCs, average particle area, and average particle diameter have been quantified for fixed regions in the samples.

Cu6Sn5 and Cu3Sn lntermetallics Study in the Sn-40Pb/Cu System during Long-term Aging

2010 ◽  
Vol 7 (2) ◽  
pp. 1
Author(s):  
Ramani Mayappan ◽  
Zainal Arifin Ahmad
Keyword(s):  
Solder Joints ◽  
Intermetallic Layer ◽  
Lap Joints ◽  
Lead Free ◽  
Lead Free Solder ◽  
Cu6sn5 Phase ◽  
Planar Shape ◽  
Cu6sn5 Layer ◽  
Free Solder

Replacing Sn-Pb solder with lead-free solder is a great challenge in the electronics industry. The presented lead-free solder is Sn based and forms two intermetallic species upon reaction with the Cu substrate, namely Cu6Sn5 and Cu3Sn. The growth of Cu6Sn5 and Cu3Sn intermetallics have been investigated with respect to Sn-40Pb/Cu solder joints. The joints were aged under long-term thermal exposure using single shear lap joints and the intermetallics were observed using scanning electron microscopy. As-soldered solder joints exhibit a single Cu6Sn5 phase, however after aging a Cu3Sn layer below the Cu6Sn5 is observed to manifest. The Cu6Sn5 layer develops with a scalloped morphology, whereas the Cu in layer always develops an undulating planar shape in phase with the Cu6Sn5. The Cu6Sn5 layer begins to transform from a scalloped- to a planar-shape as aging progresses in order to minimize the interfacial energy. The intermetallic layers exhibit a linear dependence on the square root of aging time, which corresponds to diffusion-controlled growth. The activation energy for the growth of the Cu6Sn5 intermetallic layer has been determined to be 56.16 kJ/mol.

Study of Lead Free Solder Joints Subjected to Isothermal Mechanical Shear Cycling

2020 ◽  
Author(s):  
Mohd Aminul Hoque ◽  
Mohammad Ashraful Haq ◽  
Jeffrey C. Suhling ◽  
Pradeep Lall
Keyword(s):  
Printed Circuit Boards ◽  
Solder Joints ◽  
Polarized Light ◽  
Lead Free ◽  
Lead Free Solder ◽  
Circuit Boards ◽  
Sac305 Solder ◽  
Mechanical Cycling ◽  
Before And After ◽  
Free Solder

Abstract Electronic packages are usually subjected to varying temperature conditions, thus subjecting the package to thermal cyclic loadings. As the different components of the package are made up of materials of different Coefficients of Thermal Expansion (CTE), the thermal cyclic loading brings about fluctuating shear stress to arise within the package, ultimately leading to its failure. It has been seen in previous literature that the recrystallization assisted cracking is a major factor that leads to the failure of solder joints when subjected to thermomechanical cycles. In this study, the authors have tried to determine whether the mechanical shear cycling of aged and non-aged samples of SAC305 lead free solder joints undergo a recrystallization phase before its ultimate failure. Arrays (3 × 3) of SAC305 solder joints of roughly 750μm in diameter were reflowed in between two FR-4 printed circuit boards to create a sandwiched structural sample. The samples were then polished to expose the solder joints. A polarized light microscope was utilized to capture the images of the joints before and after the mechanical cycling and analyzed to observe any changes in the microstructure in the form of recrystallization of the tin grains.

Numerical Investigation on Electromigration Oriented Failure of Lead Free Solder Joints With Aging Effects

2019 ◽  
Author(s):  
Tusher Ahmed ◽  
Mohammad Motalab ◽  
Jeffrey C. Suhling
Keyword(s):  
Thermal Aging ◽  
Flip Chip ◽  
Solder Joints ◽  
Mass Diffusion ◽  
Lead Free ◽  
Small Scale ◽  
Time To Failure ◽  
Lead Free Solder ◽  
Aging Effects ◽  
Free Solder

Abstract Lead free solder materials have replaced lead based solder materials nowadays for increased environmental concern. Further miniaturization of electronic solder joints in packages has caused electromigration to dominate among all the reliability issues found in electronic packages. This current investigation deals with the review of mechanical property degradations of SAC305(Sn-96.5Ag-3.0Cu-0.5) solder materials due to thermal aging and their effects on electromigration oriented failure of small scale flip chip solder bumps. Thermal aging causes significant degradation of ultimate strength as well as elastic modulus of the SAC solder material. This degradation in stress-strain relationship plays an utterly important role in electromigration oriented mass diffusion and subsequent failure in the solder joints. This research highlights the linkage between thermal aging oriented strength degradation and its effect on electromigration oriented void propagation rate and time to failure. Structural-electric diffusion analyses with a finite element analysis software have been performed and results derived from different aging conditions (1 to 60 days of aging at 100 °C) at different electromigration temperatures have revealed that mass diffusion due to electromigration and associated stress migration actually reduces with the increment of aging time and thus increases time to failure in case of a flip chip solder joint. Simulation results have been found to be in good agreement with the experimental results available in literatures. These results can pave way to further detailed experimental investigation on effect of thermal aging on electromigration.

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