Effect of Long-Term Room Temperature Aging on the Fatigue Properties of SnAgCu Solder Joint

Abstract

Solder joints in electronic assemblies are subjected to mechanical and thermal cycling. These cyclic loadings lead to the fatigue failure of solder joints involving damage accumulation, crack initiation, crack propagation, and failure. Aging leads to significant changes on the microstructure and mechanical behavior of solder joints. While the effect of thermal aging on solder behavior has been examined, no prior studies have focused on the effect of long-term room temperature aging (25 °C) on the solder failure and fatigue behavior. In this paper, the effects of long-term room temperature aging on the fatigue behavior of five common lead-free solder alloys, i.e., SAC305, SAC105, SAC-Ni, SAC-X-Plus, and Innolot, have been investigated. Several individual lead-free solder joints on printed circuited boards with two aging conditions (no aging and 4 years of aging) have been prepared and subjected to shear cyclic stress–strain loadings until the complete failure. Fatigue life was recorded for each solder alloy. From the stress–strain hysteresis loop, inelastic work and plastic strain ranges were measured and empirically modeled with the fatigue life. The results indicated that 4 years of room temperature aging significantly decreases the fatigue life of the solder joints. Also, inelastic work per cycle and plastic strain range are increased after 4 years of room temperature aging. The fatigue life degradation for the solder alloys with doped elements (Ni, Bi, Sb) was relatively less compared to the traditional SAC105 and SAC305.

The Effect of Micro-Alloying and Surface Finishes on the Thermal Cycling Reliability of Doped SAC Solder Alloys

“…This IMC layer has continued to develop during the reflow operation, which was detrimental to the strength of the joint owing to its brittle nature. To make matters even worse, the formation of the IMC layer is accelerated by the process of aging [ 5 , 6 ]. To minimize the adverse effects of aging, several elements, including bismuth (Bi), nickel (Ni), antimony (Sb), cobalt (Co), and indium (In), have been micro-alloyed with the SnAgCu (SAC)-based solder alloy [ 7 , 8 , 9 , 10 ].…”

“…However, as they become larger and coarser, their ability to block dislocation motions and grain boundary sliding decreases, lowering the strength and creep resistance of the material. Sinan et al [ 6 ] reported that aging at room temperature had degradation effects. The study revealed that dopants reduced the effects of aging while also increasing the inelastic work per cycle and plastic strain range.…”

“…However, the drop shock test indicated the detrimental effect of Ag with the reduction in the ductility [ 12 ]. The other micro-alloying elements, such as Bi, Ni, and Sb, were also reported to improve the reliability of solder joints [ 2 , 6 , 16 ]. Meanwhile, these elements could prevent the degradation of properties during aging [ 6 , 14 , 15 ].…”

“…The other micro-alloying elements, such as Bi, Ni, and Sb, were also reported to improve the reliability of solder joints [ 2 , 6 , 16 ]. Meanwhile, these elements could prevent the degradation of properties during aging [ 6 , 14 , 15 ]. ENIG surface finishes outperformed OSP and ImAg surface finishes in the thermal cycling test [ 14 ], while the converse conclusion was drawn from the mechanical shear fatigue test [ 16 ].…”