Nanomechanical Behaviors Of Sn-Ag-Cu Solders Joint Under Different Loading Method

With the size of Lead-free solder joints decreasing, the reliability of solder joints is particularly prominent, which the mechanical behavior of solder joint is critical to its reliability. In this paper, through different test of nano-indentation method, the mechanical behaviors of high-silver, low-silver and the modified lead-free BGA solder joints were studied, including the creep behavior of BGA solder joint, the cycle behavior and the mechanical behavior of IMC.Through the load-unload test of nano-indentation method, Creep behavior of the four kinds of BGA solder joint of Sn-3.0Ag-0.5Cu, Sn-0.3Ag-0.7Cu, Sn-0.3Ag-0.7Cu-0.05 La and Sn-0.3Ag-0.7Cu-0.05 Ce was studied. Indention hardness, Young’s modulus and creep sensitive index n is derived. According to the analysis of creep behavior, trace after indentation and 3-D morphology of BGA solder after deep-etching, we can conclude RE(rare-earth) additions significantly improve the creep resistance and the creep controlling factor of SAC lead-free BGA solder joint is the climb of dislocation.Through the cycle load-unload test of nano-indentation method, the effects of different experimental parameters for two kinds of BGA solder joints of Sn-3.0Ag-0.5Cu and Sn-0.3Ag-0.7Cu on cycling performance were all investigated. The results indicated that the cycling performance of Sn-Ag-Cu series Lead-free BGA solder joint was load-dependent, and the cumulative damage of BGA solder joint was increased with the increase of maximum load, especially largely accumulated in the first few cycles, then gradually decreased and stabilized. However, with the cycle number increasing, the deformation resistance of BGA solder joints slightly decreased; the creep displacement increased with the hold time increasing and creep-fatigue interaction will accelerate of BGA solder joints failure; the energy loss of Sn-0.3Ag-0.7Cu BGA solder joints is greater than the Sn-3.0Ag-0.5Cu BGA solder joint, while the indentation hardness showed the opposite trend. The prolonged aging impact the shape of P-h curve. The cumulative damage of BGA solder joint was increased. The indentation hardness of SAC lead-free BGA solder joints is reduced during the cycle load-unload test, and the influence is relevant to the material; the value of ηit on cycle load-unload test is bigger than the value of ηit on load-unload test, cycle load-unload test can weaken the effect of plastic deformation; loading ways impact creep behavior.The thicknesses of interface metal compounds(IMC) of different kinds of BGA solder joint are increased after 25 days of aging. Through the energy spectrum analyses, we can determine three kinds of IMC, including Cu6Sn5, Cu3 Sn and(Cu1-xNix)6Sn5, We can conclude that all of three kinds of IMC show Serrated Rheological Effect in different degree after the nanoindentation experiments on different loading rate, but the rheological degree which is the same interface compounds under different loading rate is different. The trend is more apparent when the loading rate is low. This phenomenon of Cu3 Sn and(Cu1-xNix)6Sn5 is not obvious when the loading rate increase. However, Cu6Sn5 shows the opposite trend. The relation of Young’s modulus of four kinds of IMC: Cu3 Sn >(Cu1-xNix)6Sn5> Cu6Sn5; The relation of indention hardness of four kinds of IMC:(Cu1-xNix)6Sn5> Cu6Sn5> Cu3 Sn.