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Solder joints are subjected to varied stress cycle circumstances in the electronic packaging service life but are also influenced by aging. There has been limited investigation into the influence of aging and varying cycles on SnAgCu-Bi (SAC-Bi) solder joint fatigue. Cyclic fatigue tests were performed on solder joints of several alloys, including SnAgCu (SAC305), SnAgCu-Bi (SAC-Q), and SnCu-Bi (SAC-R). Individual solder joints were cycled under varying stress levels, alternating between mild and harsh stress levels. At least seven samples were prepared for each alloy by alternating between 25 mild stress (MS) cycles and three harsh stress (HS) cycles until the solder joint broke off. The impact of aging on Bi-doped solder joints fatigue under varied amplitude stress was examined and predicted for 10 and 1000 h under 125 °C. Because of the "Step-up" phenomenon of inelastic work, a new fatigue model was developed based on the common damage accumulation (CDA) model. The experimental results revealed that aging reduced the fatigue life of the tested solder alloys, particularly that of SAC305. According to the CDA model, all solder alloys failed earlier than expected after aging. The proposed model uses the amplification factor to assess inelastic work amplification after switching between the MS and HS cycles under varying stress amplitude conditions. The amplification factor for the SAC-Bi solder alloys increased linearly with fracture initiation and substantially followed crack propagation until the final failure. Compared with existing damage accumulation models, the proposed fatigue model provides a more accurate estimation of damage accumulation. For each case, the cut-off positions were examined. The SAC-Q amplification factor increased linearly to 83% of its overall life, which was much higher than that of SAC305 and SAC-R. This study identified three distinct failure modes: ductile, brittle, and near intermetallic compound (IMC) failure. It was also observed that SAC-Q with an organic solderability preservatives (OSP) surface finish was more susceptible to brittle failure owing to the excessive brittleness of the alloy material. [ABSTRACT FROM AUTHOR]

The surface finish (SF) becomes a part of the solder joint during assembly and improves the component's reliability. Furthermore, the SF influences the solder joint's reliability by affecting the thickness of the intermetallic compound (IMC) layer at the solder interface and copper pads. In this experiment, five different alloys are used and compared with the SAC305 alloy, two of which, Innolot and SAC-Bi, are bi-based solder alloys. This study includes three common SFs: electroless nickel immersion gold (ENIG), immersion silver (ImAg), and organic solderability preserve (OSP). The performance of three surface finishes is examined in terms of component characteristic life. All of the boards were isothermally aged for twelve months at 125 °C. The boards were then exposed to 5000 cycles of thermal cycling at temperatures ranging from −40–+125 °C. Most of the current research considers only one or two factors affecting the reliability of the electronic package. This study combines the effect of multiple factors, including solder paste content, SF, isothermal aging, and thermal cycling, to ensure that the test conditions represent real-world applications. In addition, the electronics packages are assembled using commercialized alloys. The current study focuses on a high-performance alloy already present in the electronic market. The failure data were analyzed statistically using the Weibull distribution and design of experiments (DOE) analysis of variance (ANOVA) techniques. The findings reveal that the micro and uniformly distributed precipitates in solder microstructures are critical for high-reliability solder joints. Re-crystallization of the thermally cycled solder joints promotes the local formation of numerous new grains in stress-concentrated zones. As the fracture spreads along these grain boundaries and eventually fails, these new grains participate in crack propagation. Aging significantly worsens this situation. Finally, although the ENIG surface finish with its Ni layer outperforms other SFs, this does not imply that ENIG is more reliable in all solder paste/sphere/finish combinations. [ABSTRACT FROM AUTHOR]

The failure of one solder joint out of the hundreds of joints in a system compromises the reliability of the electronics assembly. Thermal cycling is a result of both creep–fatigue mechanisms working together. To better understand the failure process in thermal cycling, it is crucial to analyze both the effects of creep and fatigue mechanisms in a methodical manner. In this work, individual solder junctions are subjected to accelerated shear fatigue testing to investigate the effects of creep and fatigue on joint dependability at room temperature. A modified fixture is used to conduct fatigue tests on an Instron 5948 micromechanical tester. SAC305 joints with an OSP surface finish were cycled under stress control at first, and then the strain was maintained for a set amount of time. In this investigation, three stress amplitudes of 16, 20, and 24 MPa are used, together with varying residence periods of 0, 10, 60, and 180 s. The fatigue life of solder junctions is described for each testing condition using the two-parameter Weibull distribution. Additionally, as a function of stress amplitude and residence time, a dependability model is created. For each testing scenario, the progression of the stress–strain loops was studied. By quantifying relevant damage metrics, such as plastic work per cycle and plastic strain at various testing circumstances, the damage due to fatigue is distinguished from creep. To investigate the relationships between plastic work and plastic strain with fatigue life, the Coffin–Manson and Morrow Energy model is used. The results indicate that using greater stress magnitudes or longer dwell periods significantly shortens fatigue life and dramatically increases plastic work and plastic strain. The housing impact is significant; in some circumstances, testing with a longer dwelling period and lower stress amplitude resulted in more damage than testing with a shorter dwelling period and higher stress levels. When illustrating the fatigue behavior of solder junctions under various stress amplitudes or dwellings, the Coffin–Manson and Morrow Energy model were both useful. In the end, general reliability models are developed as functions of plastic work and plastic strain. [ABSTRACT FROM AUTHOR]

The mechanical and fatigue properties of microelectronic interconnection materials are important issues in critical applications in the life of electronic assemblies. Due to the growth in the applications of electronic components in new technological products used in tough conditions, evaluating the reliability of solder alloys has become crucial to the prediction of product life. SAC (Sn-Ag-Cu) solder alloys are common lead-free alloys used to form solder joints. In the current study, the reliability of individual SAC305 solder joints in actual setting conditions with an organic solderability preservative (OSP) surface finish was examined using an accelerated shear fatigue test at different load levels (16 MPa, 20 MPa, and 24 MPa). Four operating temperature levels (−10, 25, 60, and 100 °C) were also used. Seven samples were utilized at each experimental condition. An orthogonal array (L12) was employed for this experiment. The fatigue behavior of the SAC305 solder joints in actual setting conditions was described by a two-parameter Weibull distribution. The characteristic life and the shape parameter were extrapolated from the Weibull distribution for each experimental condition. Characteristic life was employed to represent the fatigue resistance of the solder joints. For each sample, the inelastic work per cycle and plastic deformation were determined. The results indicated a notable increase in the inelastic work per cycle and the plastic strain as a result of increasing either the stress load or the working temperature. Combinations of stress amplitude, working temperature, inelastic work, and plastic deformation were applied as inputs to the fuzzy system for computing a comprehensive output measure (COM-Value) using the Mamdani method. A negative relationship was observed between the solder life and the four fuzzy inputs. To fuzzify the inputs of the fuzzy system, two membership functions, "MFs", were formed for each input, and five MFs were set for the output. The center-of-gravity (COG) theorem was utilized as a defuzzification method in the fuzzy inference system. The characteristic life of the solder joints was predicted by the COM-Value, which was used as an independent variable. Finally, The COM-Value was used to generate a general predicted reliability model for SAC305 solder joints with an acceptable model adequacy index. [ABSTRACT FROM AUTHOR]

The reliability of electronic assemblies is a vital criterion used to assure product quality over its lifetime. Weibull distribution is the most common distribution utilized to describe the reliability data. Most of the studies use the Weibull scale parameter, or characteristic life, to compare alternatives and make a selective decision. This may not lead to achieving the optimal parameters which can be problematic because this method doesn't consider the variability behavior of the fatigue life. In this study, a new approach for process parameters selection is proposed to find the optimal parameter values that improve the micro-optimality selection process based on reliability data. In this study, a new approach is proposed based on examining the solder joint reliability by using a multi criteria analysis. The fuzzy logic is utilized as a tool to solve the multi criteria problem that is presented from the proposed approach. The reliability of microelectronic connections in thermal cycling operating conditions is used as a validation case study. In the validation case study, the optimal process parameters are found for ball grid array electronic components. Two levels of the solder sphere materials, three levels of the surface finish, and 10 levels of solder paste alloys are studied as process parameters. Using the proposed approach, four quality responses are employed to assess the reliability data, including the scale parameter, the B10 (life at 10% of the population failure), mean-standard deviation response, and the signal to noise ratio (SNR). The fuzzy logic is applied to solve the multiresponse problem. An optimal process parameter setting that considers different quality characteristics was found for the validation case study. ENIG surface finish, SAC305 solder sphere, and material six were the optimal factor levels that are obtained for the aged CABGA208 component using the proposed approach. [ABSTRACT FROM AUTHOR]

The reliability of electronic assemblies is exceedingly reliant on the life of solder joints. Many factors may influence the fatigue life and mechanical properties of solder joints. Aging is one of the main factors that adversely affect the reliability of solder joints. In this article, the mechanical reliability of individual SnAgCu solder joints is studied at different aging conditions. The experiments include aging then cycling solder joints in stress-controlled shear fatigue at different stress amplitudes (16, 20, and 24 MPa) until complete failure. The aging conditions include three levels of aging temperatures (50 °C, 100 °C, and 150 °C) and four levels of aging time (2, 10, 100, and 1000 h). The effect of stress amplitude, aging time, and aging temperature on the fatigue life is investigated. The evolutions in the hysteresis loop, including the inelastic work dissipation, are explored by studying the stress–strain diagrams. The results showed that the fatigue life was affected by the stress amplitude, where increasing the stress by a factor of 2 leads to life reduction by a factor of 22. It was also found that increasing the aging time leads to nonlinear life reduction, where the first few hours of aging had the largest effect. Increasing the aging temperatures aggregates the aging time effect and leads to less fatigue resistance. Overall, increasing the aging time, temperature, and/or stress amplitudes leads to an increase in the work dissipation per cycle, which creates more damage and leads to less number of cycles to failure. The effect of these factors was fit into mathematical equations. Then, a general reliability model as a function of those parameters was developed. [ABSTRACT FROM AUTHOR]

Reliability of microelectronic assemblies is typically limited by the fatigue failure of one of the interconnected solder joints. The fatigue behavior of the lead-free solder joints doped with bismuth under different stress loading and aging conditions is not yet understood. This article investigates the effect of adding bismuth on the mechanical reliability of SAC alloys considering different loading and aging conditions. The fatigue behavior and shear strength of individual SAC305 (Sn–3.0Ag–0.5Cu) and SAC-Q (Sn–3.4Ag–0.5Cu–3.3Bi) solder joints are examined and compared. A unique experiment is designed to test the individual solder joints using a micromechanical testing system. The results show that the fatigue life and shear strength of SAC-Q with Bi are much higher than SAC305 regardless of the aging and stress conditions. It was also found that increasing stress amplitude leads to a decrease in the fatigue life for both alloys. The aging time has a negative effect on the fatigue life and shear strength of both alloys. The impact of aging on SAC-Q solder joints is significantly less than that for SAC305. Microstructure analysis shows a substantial amount of precipitates coarsening with aging for SAC305 compared with SAC-Q. Hysteresis loop analysis shows that increasing the cycling stress amplitude and aging time leads to an increase in the work per cycle and plastic strain. Common fatigue models, such as Morrow energy model and Coffin–Manson model, fail to predict the life considering the effect of aging; aging affects the constants of both models. [ABSTRACT FROM AUTHOR]

This study aims to comprehensively understand the influence of bismuth (Bi) content on the shear characteristics of solder joints under various aging conditions and strain rates. Three solder alloys were evaluated (SAC305, SAC-3Bi, and SAC-6Bi) under different aging times (0, 10, 100, and 1000 h) and shear strain rates (0.008, 0.8, and 8 s−1). The aging temperature was 150 °C. Shear tests were performed on individual solder joints using an Instron 5948 micromechanical tester at room temperature. The study developed an empirical model to determine the ultimate shear strength of SAC305 alloys as a function of aging time and strain rate, and assessed shear energy using different failure modes. Microstructural analysis was performed at various aging times to investigate the failure processes associated with each test combination. The results indicate that doping alloys with Bi improves the shear properties of alloys and mitigates the effects of aging. Furthermore, the study observed three failure mechanisms (ductile, brittle, and a combination of both) and found that Bi-containing alloys are more prone to brittle failure at relatively high shear strain rates due to high brittleness. • The effect of Bi content on the shear properties of lead-free alloys was examined under different aging times. • Bi-based alloys showed higher ultimate shear strength than SAC305 under different shear strains. • Bi-based alloys exhibited brittle failure at high strain rates after 100 and 1000 hrs of aging. • A Correlation between the failure modes and shear energy was established. [ABSTRACT FROM AUTHOR]

Common damage accumulation rules fail to predict the fatigue life of solder joints under realistic service conditions where cycling amplitudes vary over time. A modification of Miner’s rule of linear damage accumulation has been proposed that accounts for effects of amplitude variations in, for example, the vibration of microelectronic assemblies with lead-free solder joints on the average or characteristic fatigue life. We are, however, obviously much more concerned with the first failure across a very large sample set. Prediction of, say, the first failure out of 10000 or a million would require the extrapolation of experimental failure distributions and the assumption of a shape of this distribution. Even qualitative comparisons of accelerated test results and their scatter should account for effects of amplitude variations. We have argued that the long-term life of solder joints in vibration or cyclic bending is limited by the accumulation of inelastic work, and that much can be learned from the low cycle fatigue behavior in shear. Individual ball grid array scale SAC305 and SAC105 solder joints were cycled in shear at room temperature with combinations of two different stress amplitudes. Relying on our modified Miner’s rule and the associated understanding of the effects of amplitude variations, we show that the statistical uncertainty in the fatigue life of solder joints under a specific set of realistic service conditions must be significantly greater than measured in fixed amplitude cycling tests. The predicted failure distribution was best fit by a Weibull distribution over a limited range, but we argue that the assumption of such a distribution is likely to be increasingly conservative when it comes to the prediction of earlier failure. Estimates are provided for the potential errors. [ABSTRACT FROM PUBLISHER]

The fatigue behavior of solder joints in realistic service applications is still not well understood. Service life prediction based on conducting accelerated tests and extrapolating test results therefore involves a high potential for error. Understanding both the evolution of solder joint properties and the damage accumulation has proved to be critical to reliability modeling. Damage accumulation in isothermal cycling is shown to scale with the accumulated inelastic work even in complex cycling scenarios, so that the life of a solder joint ends upon accumulation of a given amount of work. Individual ball grid array solder joints were cycled in shear fatigue experiments with different load amplitudes and strain rates. The effects of load amplitudes and strain rates on the work accumulation and fatigue life were systematically addressed. The correlation between different loading scenarios and the accumulated work to failure was also discussed. The results showed that the accumulated work until the development of a major crack is constant regardless of the load amplitude. After that the accumulated work to failure is lower for larger load amplitudes. For some reason, a larger fraction of the work appears to be dissipating as heat at lower load amplitude, but only during crack growth. On the other hand, the strain rate affects the fraction of the work going to heat even before the development of a major crack. [ABSTRACT FROM PUBLISHER]

Solder joints reliability is a determinant factor for the life of the electronic assemblies. In this study, the reliability of actual SAC305 solder joints is investigated using accelerated shear fatigue tests. The effect of aging time and stress amplitude are studied. Five levels of aging time at 100 °C and three levels of stress amplitudes are applied in the experiments. Two-parameters Weibull distribution is used to describe the fatigue life of the solder joints at each test condition. A numerical model for the solder joints reliability is developed as a function of stress amplitude and aging time. The hysteresis loops at different aging times and stress amplitudes are demonstrated. The relationships between the inelastic work, plastic strain, and fatigue life are identified by exploiting the Coffin-Manson and Morrow Energy models. The results indicate a reduction in fatigue life and an increase in inelastic work and plastic strain when the cyclic stress amplitude is increased. Increasing the aging time has a negative impact on the fatigue life of the solder joint. The Morrow Energy model significantly outperforms the Coffin-Manson model in describing the fatigue behavior of the solder joints regardless of the aging conditions. Finally, a general reliability model as a function of the inelastic work per cycle is introduced. [ABSTRACT FROM AUTHOR]