Microstructural evolution and failure analysis of Sn–Bi57–Ag0.7 solder joints during thermal cycling

Abstract

Although many studies have reported the behaviors of thermal cycling of Snbased solder joints, the corresponding mechanism is difficult to describe universally due to the complexity of different cases. In the present study, microstructural evolution and failure of Sn-Bi57-Ag0.7 solder joints caused by thermal cycling between -40 and 85 °C from 0 to 1000 cycles were systematically investigated. The results indicated that the Sn-Bi-Ag solder joint was composed of Sn-rich phase, Bi-rich phase, large numbers of Bi dispersed-particles, and Ag 3 Sn precipitate. With the extension of time during thermal cycling, the microstructure of Sn-Bi-Ag solder joint gradually coarsened and the IMC layer became thicker (from 0.82 to 2.38 lm). However, Sn-Bi-Ag solder joints failed after 3000 thermal cycles. Two different stages of failure were found and the mechanism, related to the increment of thermal mismatch stress, was illuminated. Furthermore, Electron Backscattered Diffraction was used to detailedly elucidate the grain characteristics of the failed Sn-Bi-Ag solder joints, and the effect of thermal stress on orientations of Sn and Bi grains was also revealed. Being different from the orientation change observed in traditional Sn-Bi eutectic solder joints in previous studies, the present results demonstrated that both Sn and Bi grains did not present any preferred orientations after thermal cycling. And the reason of this phenomenon might be attributed to the Ag 3 Sn, which could be regarded as second-phase particles. Our present work would provide theoretical guidance for the development of new Sn-Bi-X solders with high reliabilities.

Reliability modeling of the fatigue life of lead-free solder joints at different testing temperatures and load levels using the Arrhenius model

“…The fatigue life of the microelectronics interconnection materials is a major indicator of the reliability of the electronic assemblies, as a single failure in these connections could result in the destruction of the entire electronic system or a drastic reduction in its operational performance. Solder joints and other interconnection materials are fundamentally subject to various types of thermal and mechanical stresses in real-life applications such as shear, tensile, creep, mechanical and thermal shock, and fatigue stresses 1 – 4 . The thermal cycling phenomenon, which is commonly observed in harsh environmental conditions, is one of the major sources of the combined thermal and mechanical stresses.…”

Evaluation of Solder Joint Reliability in 3D Packaging Memory Devices under Thermal Shock

“…Repeated stresses eventually lead to the formation and growth of interfacial cracks due to the combined damage mechanism of fatigue and creep [30]. Additionally, since the solder joint is affected by both shear stress and temperature, the plastic deformation gradually accumulates inside the solder alloy until the cracks appear [31]. Furthermore, there is a large difference between the CTEs of the epoxy resin and plastic encapsulant inside the chip and the solder joint (the solder joint CTE is 21 × 10 −6 1/K, epoxy resin CTE is 67.1 × 10 −6 1/K and plastic encapsulant CTE is 17.68 × 10 −6 1/K) [32], which results in the solder enduring a large stress to accelerate crack growth for eventual crack [33].…”