不同体积无铅微尺度焊点的蠕变力学性能

采用基于动态力学分析仪的精密蠕变试验方法,对比研究了5.34×107 μm3与7.07×106 μm3两种体积相差近一个数量级的无铅Sn-3.0Ag-0.5Cu微尺度焊点的高温蠕变力学行为与蠕变性能.结果表明,所有微尺度焊点的蠕变曲线均呈现初始蠕变、稳态蠕变和加速蠕变阶段.虽然微尺度焊点的体积存在较大差异,但是它们的蠕变激活能与蠕变应力指数均非常接近.此外,在相同的试验温度与拉伸应力作用下,大体积微尺度焊点的稳态蠕变速率相对小体积焊点更大,而蠕变寿命则呈现完全相反的趋势.

Creep properties of microscale lead-free solder joints with different volumes

Adopting accurate creep testing method based on dynamic mechanical analyzer (DMA Q800, TA-Instruments),high temperature creep mechanical behaviors and properties of lead-free Sn-3.0Ag-0.5Cu microscale solder joints with volumes of 5.34×107 μm3 and 7.07×106 μm3 were investigated under two different service conditions. One condition was keeping the tensile stress (20 MPa) constant at four different temperatures (100,125,135,and 145℃), and the other was keeping the temperature (145℃) constant under four different tensile stresses (8,12,16,and 20 MPa). The experimental results show that all strain-time creep curves of microscale solder joints included three typical stages-primary creep,secondary creep (steady creep) and tertiary creep. Also, the creep activation energy and creep stress exponent value were very close to each other, though the volumes of the Sn-based solder joints were obviously different, this was mainly because the lattice diffusion was thought as the creep mechanism during the high temperature creep process. In addition, under the same testing temperature and same loading stress, the steady creep rate of the Sn-3.OAg-0.5Cu microscale solder joints with large volume was much higher than that of the smaller ones, however, the creep lifetime had totally opposite trends due to more defects in the larger solder joints.