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During operation, electronic components are exposed to high temperatures that may last for long periods, depending on the operating duration. Solder joints are one of the components most affected by thermal aging while in service. In this research, the effect of thermal aging duration and temperature on the mechanical properties of 92.8%Sn-3%Ag-0.5%Cu-3.3%Bi (Cyclomax) was investigated. The novelty of this work lies in the study of the important properties of a new generation of Sn-Ag-Cu (SAC) materials (i.e., Cyclomax). Cyclomax is rare in industry and immature in research. To understand the effect of thermal aging, the microstructure was investigated, and changes in it and its mechanical properties were observed. To simulate solder joints in electronic devices, samples of solder balls were prepared and attached to copper pads on electronic boards. Most samples were then treated at 150 °C or 100 °C for up to 1000 h and some samples were left untreated for comparison. A scanning electron microscope (SEM) was used to obtain images of the microstructure. The shear stress–shear strain relationships, including the ultimate shear strength (USS), the modulus of elasticity and the ultimate energy (UE), were investigated. The microstructure images indicated the presence of a layer of Cu6Sn5 on top of the copper pad before thermal aging was applied. The thickness of this layer increased with the application of thermal aging over time. The results for the shear stress–shear strain relationship indicate that all of the USS, the total energy (TE) to shear off the solder balls and the UE decreased at the beginning of the thermal aging and then reversed to increase later. In general, isothermal aging reduces the performance of Cyclomax solder joints in terms of the minimum force and energy required to separate and subsequently damage electronic components. [ABSTRACT FROM AUTHOR]

Many electronic products are subjected to heat for long periods, depending on their operations. Thus, it is expected that the physical and mechanical properties of electronic elements, including the soldering joints, will be affected. In this study, the impact of thermal aging time and temperature on the microstructure and mechanical properties of 96.5Sn–3.0Ag–0.5Cu (SAC305) was investigated. The samples used were SAC305 solder balls attached to copper pads. The research began by examining the microstructure of the aged samples at 150 °C for 100 and 1000 h. Then, this was compared to the microstructure of the same samples without thermal aging. Then, five groups of 10 samples were prepared from a shear stress–shear stain experiment. The first group was as produced, the second group was aged for 2 h, the third group was aged for 10 h, the fourth group was aged for 100 h, and the fifth group was aged for 1000 h. All groups were aged at a temperature of 150 °C. An Instron testing machine was used to plot a shear stress–shear stain curve until the ball was completely sheared off the pad. The mechanical properties, including the ultimate shear strength, the ultimate energy used to shear the ball, and the total energy used to shear the ball at all thermal aging times were then estimated. The results of this study indicated the formation of a layer of Cu6Sn5 over the copper pad, which thickened with thermal aging time. Furthermore, the ultimate and total shear strengths decreased with thermal aging time. The same procedure was repeated to assess the ultimate shear strength at 100 °C. The decrease in ultimate shear strength was more severe with increasing thermal aging temperature. [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]

Solder joints in electronic assemblies are subjected to mechanical cycling in normal operating conditions. Testing individual solder joint in mechanical cycling allows monitoring the evolution of hysteresis loop with time and provides the ability to study the factors that affect the reliability. In this article, the effect of surface finish on the fatigue behaviors of four doped lead-free solder alloys (CycloMax, Innolot, Ecolloy, and SAC-X-Plus) and SAC305 was investigated. Individual solder joints with three surface finishes [organic solderability preservative (OSP), immersion silver (ImAg), and electroless nickel immersion gold (ENIG)] were prepared and subjected to various cyclic shear stress loadings until complete failure. Hysteresis loop was systematically recorded using an Instron machine. Characteristic fatigue life and energy dissipation per cycle were analyzed, and the Morrow energy model was applied to empirically predict the fatigue life as a function of work dissipation. Failure mechanisms were investigated as well using SEM/EDS, and the results were correlated with the fatigue behavior of the solder joints. The results indicated that the fatigue resistance of the solder alloys decreased with the increase in stress amplitude. The fatigue resistance of the solder joints with OSP and ImAg surface finishes outperformed ENIG surface finish. CycloMax with OSP surface finish was associated with the best fatigue resistance, while SAC-X-Plus with ENIG surface finish was associated with the worst fatigue resistance. Three failure modes were detected in this study: ductile, brittle, and near-intermetallic compound (IMC) failure. It was also found that Innolot with ENIG surface finish is more susceptible to brittle failure because of the excessive brittleness associated with this alloy. [ABSTRACT FROM AUTHOR]

The reliability of an electronic assembly is typically limited by the failure of one of the solder interconnections. One of the key factors that define the quality of solder interconnections is the strength of the solder joint attachment to the printed circuit board (PCB). The ball shear testing is commonly used as a quantitative approach to evaluate the integrity of the solder. Several factors control the shear strength and failure mechanism of solder joints, including the surface finish, solder alloy composition, and speed of shearing (shear strain rate). In this paper, the effect of surface finish on the shear properties of various “microalloyed” SnAgCu-based solder materials was investigated. Individual solder joints were fabricated on a PCB with a solder mask defined configuration. A series of shear testing was conducted at four different strain rates of 0.001, 0.01, 0.1, and 1 s−1. Shear stress–strain curves were recorded for each test, and both shear strength and shear energy were measured. Following the shear testing, fractured top surfaces and cross sections were inspected using SEM/EDS microscopy to characterize the failure mechanism. The results showed that both shear strength and shear energy increase with increasing shear strain rate due to the viscoplasticity of the solder materials. Failure mode analysis indicated the existence of three failure mechanisms, including ductile failure, brittle failure, and mixed failure. Higher occurrence of brittle failure was observed when the shear strain rate is high regardless of surface finish. It was also found that the combination of solder alloy with high silver (Ag) and bismuth (Bi) content and electroless Ni/immersion Au (ENIG) surface finish is more susceptible to brittle failure compared to the rest of solder alloy-surface finish combinations. [ABSTRACT FROM AUTHOR]

One of the crucial factors in evaluating the reliability of an electronic appliance is fatigue failure of the interconnecting solder joints. In most situations, large bulk samples are used to investigate the fatigue characteristics of the solder materials. Only a few studies have examined the solder joints frequently observed in ball grid array (BGA) components. This study implemented a specialized test vehicle in BGA assembly connecting two substrates with nine identical solder joints. Four SAC-based solder alloys were tested using an Instron micromechanical tester in the stress-controlled and strain-controlled methods at room temperature and constant strain rate. At two distinctive stress and strain levels, the fatigue performance of alloys featuring organic solderability preservative (OSP) and electroless nickel-immersion gold (ENIG) surface finishes was investigated. The fatigue results obtained from the stress-controlled and strain-controlled tests were compared. Microstructural analysis was performed using scanning Electron Microscopy (SEM) and energy dispersive spectroscopy (EDS) to identify the precipitates in the bulk solder and the morphologies of IMC layers. The thickness of intermetallic compound (IMC) layers and the failure mode were examined in each case. The results demonstrated that the OSP surface finish significantly outperformed the ENIG surface finish regardless of the testing process and solder alloy. Various failure modes were observed, depending on the solder alloy and IMC layer. • Fatigue of solder joints in BGA was tested in stress and strain-controlled. • Microstructural analysis was performed using SEM/EDS. • The OSP surface finish outperformed the ENIG surface finish. • The interfacial IMC layer of SAC305 with the OSP surface finish was scallop-like • SAC-Q and SAC-I have a brittle failure mode featured with the ENIG finish. [ABSTRACT FROM AUTHOR]

Since the restriction of hazardous substances (RoHS) directive, lead-free soldering has been widely broad adopted. In many applications, lead-free alloys have been substituted for conventional SnPb (Tin-Lead) solder. Among lead-free alloys, SAC305(Sn-3.0Ag-0.5Cu) has gained the highest acceptance as a solder alloy. The fatigue performance of solder joints has become an essential reliability assessment criterion due to the transition to more reliable lead-free alloys from highly predictable lead-based alloys. This study examines the shear fatigue characteristics of sandwich test vehicles for SnPb and SAC305 at different temperatures using both Organic Solderability Preservative (OSP) and Electroless Nickel-Immersion Silver (ENIG) surface finishes. The fatigue experiments were performed using an Instron micromechanical tester at a constant strain rate, and microstructural analysis was carried out using Scanning Electron Microscopy (SEM) to identify the Intermetallic Compound (IMC) morphology and failure mode. The stress-strain (hysteresis) loops of SnPb and SAC305 were measured, and the fatigue life of the specimens was estimated using the strain-life equation at various temperatures. SAC305 was observed to have a better fatigue life than SnPb, particularly at higher strain levels or testing temperatures. The OSP surface finish demonstrated superior fatigue properties compared to the ENIG surface finish. Additionally, elevated testing temperatures were found to accelerate fatigue failure in solder joints. The Arrhenius model was utilized to develop a general empirical model that predicts the fatigue life of SAC305 and SnPb solder alloys with OSP and ENIG surface finishes as a function of the strain level and testing temperature. • The fatigue properties of SAC305 and Sn37Pb solder joints in BGA assembly were examined using the strain-controlled. • The effect of strain level and surface finish was included in this study. • An empirical model was proposed to estimate the fatigue life of solder based on the surface finish, strain, and temperature. • The OSP surface finish outperformed the ENIG surface finish for SAC305 and SnPb at all the testing temperatures. • SAC305 solder alloy performs better than SnPb at higher strain levels or testing temperatures. [ABSTRACT FROM AUTHOR]

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]