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.

The reliability of Sn-Ag-Cu (SAC)-based solder alloys has been extensively investigated after the prohibition of lead in the electronics industry owing to their toxicity. Low-temperature solder (LTS) alloys have recently received considerable attention because of their low cost and reduced defects in complex assemblies. The shear and fatigue properties of individual solder joints were tested using an Instron micromechanical testing system in this research. Two novel solder alloys (Sn-58Bi-0.5Sb-0.15Ni and Sn-42Bi) with low melting temperatures were examined and compared with Sn-3.5Ag and Sn-3.0Ag-0.8Cu-3.0Bi. The surface finish was electroless nickel-immersion gold (ENIG) during the test. Shear testing was conducted at three strain rates, and the shear strength of each solder alloy was measured. A constant strain rate was used for the cyclic fatigue experiments. The fatigue life of each alloy was determined for various stress amplitudes. The failure mechanism in shear and fatigue tests was characterized using scanning electron microscopy/energy-dispersive spectroscopy (SEM/EDS). The results revealed that Sn-3.0Ag-0.8Cu-3.0Bi had superior shear and fatigue properties compared to other alloys but was more susceptible to brittle failure. The shear strain rate affected the failure modes of Sn-3.0Ag-0.8Cu-3.0Bi, Sn-58Bi-0.5Sb-0.15Ni, and Sn-42Bi; however, Sn-3.5Ag was found to be insensitive. Several failure modes were detected for Sn-3.5Ag in both shear strength and fatigue tests.

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.

One of the crucial factors in determining the reliability of an electronic device is fatigue failure of the interconnecting solder joints. In most cases, large bulk samples are used to study the fatigue characteristics of the solder materials. Real solder joints often encountered in ball grid array (BGA) components have only been considered in limited investigations. In this study, a specialized sandwich BGA test vehicle with a 3 × 3 solder joint was connected to the two substrates. The alloys were tested at room temperature using an Instron micromechanical tester in both the stress-controlled and strain-controlled methods. The tests were performed at a constant strain rate. Four stresses and four strain levels of the solder alloy Sn-3.0Ag-0.5Cu (SAC305) were examined using organic solderability preservative (OSP) and electroless nickel-immersion silver (ENIG) surface finishes. The work per cycle and plastic strain range was computed based on a systematic recording of the stress–strain (hysteresis) loops of each sample. A novel approach based on inelastic work is developed to calculate the fatigue life of a BGA assembled test vehicle. The results of the stress-controlled and strain-controlled tests indicated that the OSP surface finishes outperformed the ENIG surface finish. Regardless of the testing process and surface finish, the Coffin–Manson and Morrow energy models were acceptable for SAC305.

In realistic applications, the solder joint is continually subjected to thermal-mechanical stress due to the difference in the coefficient of thermal expansion between the printed circuit board substrate and the electronic packaging components. Creep and fatigue processes were the most common causes of failure in electronic assemblies. Under isothermal aging, creep deformation becomes more prominent. The aged microstructure was recognized by intermetallic coarsening and the appearance of intergranular fracture generated by dynamic recrystallization in the bulk solder joint. In this study, the influence of Bi content on the creep behaviors of solder joints was investigated under various aging conditions. Three lead-free solder alloys, including SAC305, SAC-3Bi, and SAC-6Bi, are tested at room temperature. For each alloy, preliminary micro-indentation tests were conducted to define three stress levels for distinct aging conditions. After each test, displacement versus time data was gathered. A novel approach based on an empirical model was developed to systematically examine the development of the steady-state creep rate. A power dependency prediction model was developed to investigate the relationship between creep strain rate and stress levels. The steady-state creep rate of SAC305 is significantly higher than that of SAC-Bi alloys owing to the presence of bismuth (Bi) in the solid solution at room temperature. The creep properties showed less variation after 100 h of aging. SAC-Bi alloys showed less coarsening of the intermetallic compounds precipitates after aging than SAC305. In the SAC-Bi solder alloys, combinations of precipitate and solid solution hardening mechanisms were observed, while Ag3Sn particles were the dominant strengthening mechanism in the SAC305 alloy system.