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.

Nanoindentation Characterization of Lead-free Solders and Intermetallic Compounds under Thermal Aging

2010 ◽  
Vol 2010 (1) ◽  
pp. 000314-000318
Author(s):  
Tong Jiang ◽  
Fubin Song ◽  
Chaoran Yang ◽  
S. W. Ricky Lee
Keyword(s):  
Mechanical Properties ◽  
Thermal Aging ◽  
Solder Joints ◽  
Lead Free ◽  
Small Range ◽  
Lead Free Solder ◽  
Solder Alloys ◽  
Aging Test ◽  
Free Solder ◽  
Lead Free Solders

The enforcement of environmental legislation is pushing electronic products to take lead-free solder alloys as the substitute of traditional lead-tin solder alloys. Applications of such alloys require a better understanding of their mechanical behaviors. The mechanical properties of the lead-free solders and IMC layers are affected by the thermal aging. The lead-free solder joints on the pads subject to thermal aging test lead to IMC growth and cause corresponding reliability concerns. In this paper, the mechanical properties of the lead-free solders and IMCs were characterized by nanoindentation. Both the Sn-rich phase and Ag3Sn + β-Sn phase in the lead-free solder joint exhibit strain rate depended and aging soften effect. When lead-free solder joints were subject to thermal aging, Young's modulus of the (Cu, Ni)6Sn5 IMC and Cu6Sn5 IMC changed in very small range. While the hardness value decreased with the increasing of the thermal aging time.

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.

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.

Formation and Mechanical Properties of Intermetallic Compounds in Sn-Cu High-Temperature Lead-Free Solder Joints

2010 ◽  
Vol 654-656 ◽  
pp. 2450-2454 ◽  
Author(s):  
De Kui Mu ◽  
Hideaki Tsukamoto ◽  
Han Huang ◽  
Kazuhiro Nogita
Keyword(s):  
Mechanical Properties ◽  
High Temperature ◽  
Intermetallic Compounds ◽  
Solder Joints ◽  
Nickel Content ◽  
Lead Free ◽  
Lead Free Solder ◽  
Nickel Addition ◽  
Free Solder ◽  
Lead Free Solders

High-temperature lead-free solders are important materials for electrical and electronic devices due to increasing legislative requirements that aim at reducing the use of traditional lead-based solders. For the successful use of lead-free solders, a comprehensive understanding of the formation and mechanical properties of Intermetallic Compounds (IMCs) that form in the vicinity of the solder-substrate interface is essential. In this work, the effect of nickel addition on the formation and mechanical properties of Cu6Sn5 IMCs in Sn-Cu high-temperature lead-free solder joints was investigated using Scanning Electron Microscopy (SEM) and nanoindentation. It was found that the nickel addition increased the elastic modulus and hardness of the (Cu, Ni)6Sn5. The relationship between the nickel content and the mechanical properties of the IMCs was also established.

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.

The Effect of Multiple Reflow Times on Lead-Free Solder Joint Microstructure

2003 ◽  
Author(s):  
Sami T. Nurmi ◽  
Janne J. Sundelin ◽  
Eero O. Ristolainen ◽  
Toivo K. Lepisto¨
Keyword(s):  
Solder Joint ◽  
Solder Joints ◽  
Lead Free ◽  
Lead Free Solder ◽  
Solder Paste ◽  
Snagcu Solder ◽  
Silver Copper ◽  
Free Solder ◽  
Tin Silver Copper ◽  
Lead Free Solders

As environmental issues are raising more interest and are becoming crucial factors in all parts of the world, more and more environmental-friendly electronics products are emerging. Usually this means the introduction of products with lead-free solders. However, the reliability of lead-free solders is still a serious concern despite the vast research done in this field. This paper will describe the interconnect reliability of three kinds of solder joints respectively prepared with lead-free solder paste and lead-free PBGA components, lead-free solder paste and tin-lead-silver PBGA components, and tin-lead solder paste and tin-lead-silver PBGA components. Lead-free and tin-lead solders were composed of eutectic tin-silver-copper and tin-lead, respectively. In addition, the study also presents the effect of multiple reflow times. The study focuses on the microstructures of different assemblies. The particular interest is on the assemblies soldered with lead-free solder paste and tin-lead-silver PBGA components, since the SnPbAg solder on the bumps of the PBGA components were exposed to the reflow profile meant for the lead-free SnAgCu solder. Thus, these SnPbAg solder bumps were in the molten state almost twice as long as the rest of the solders. This had a notable effect on the reliability of these solder joints as we will be showing later in this paper. The test boards were temperature-cycled for 2500 cycles between −40 and +125°C (a 30-minute cycle). PBGA solder joint failures were monitored with a real time monitoring system. Optical and scanning electron microscopy was used to inspect the broken solder joints and their microstructure. The results of tests indicate that the number of reflow times can significantly affect the lifetime of PBGA solder joints. The most notable changes can be seen in the solder joints made with tin-lead-silver PBGA components and tin-silver-copper solder paste soldered with a lead-free reflow profile. The general trend was that the reliability of the solder joints increased in proportion to the number of reflow times. Mainly two factors are believed to have the major effect on the reliability of PBGA solder joints, voids, and microstructural changes in solder.

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.

Effect of aluminum content on structure, transport and mechanical properties of Sn-Zn eutectic lead free solder alloy rapidly solidified from melt.

2015 ◽  
Vol 10 (1) ◽  
pp. 2641-2648
Author(s):  
Rizk Mostafa Shalaby ◽  
Mohamed Munther ◽  
Abu-Bakr Al-Bidawi ◽  
Mustafa Kamal
Keyword(s):  
Mechanical Properties ◽  
Melting Point ◽  
Lead Free ◽  
Al Alloy ◽  
Lead Free Solder ◽  
Pronounced Increase ◽  
Mass Unit ◽  
Size Refinement ◽  
Free Solder ◽  
Lead Free Solders

The greatest advantage of Sn-Zn eutectic is its low melting point (198 oC) which is close to the melting point. of Sn-Pb eutectic solder (183 oC), as well as its low price per mass unit compared with Sn-Ag and Sn-Ag-Cu solders. In this paper, the effect of 0.0, 1.0, 2.0, 3.0, 4.0, and 5.0 wt. % Al as ternary additions on melting temperature, microstructure, microhardness and mechanical properties of the Sn-9Zn lead-free solders were investigated. It is shown that the alloying additions of Al at 4 wt. % to the Sn-Zn binary system lead to lower of the melting point to 195.72 ˚C.  From x-ray diffraction analysis, an aluminium phase, designated α-Al is detected for 4 and 5 wt. % Al compositions. The formation of an aluminium phase causes a pronounced increase in the electrical resistivity and microhardness. The ternary Sn-9Zn-2 wt.%Al exhibits micro hardness superior to Sn-9Zn binary alloy. The better Vickers hardness and melting points of the ternary alloy is attributed to solid solution effect, grain size refinement and precipitation of Al and Zn in the Sn matrix.  The Sn-9%Zn-4%Al alloy is a lead-free solder designed for possible drop-in replacement of Pb-Sn solders.  

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