The fracture mechanisms of a Sn-Ag-Cu lead-free solder joint and the effects of test parameters on power cycling life were investigated. In this study, three levels of average temperature (348, 373 and 398 K), two levels of each of current on-and-off time (2 s/10 s and 5 s/22 s), and three levels of ΔT_j (75, 100 and 125 K) were used. Because the thermal expansion of the die-attach material was restrained by Si, equibiaxial tensile and compressive creep deformation occurred during power cycling. This deformation generated fatigue cracks in the central part of the die-attach joint, and the cracks connected to each other, resulting in a fatigue crack network. The fracture occupied 70% or more of the die-attach area and was the dominant factor affecting the joint’s fatigue life. As ΔT_j increased, the strain energy density in the central part increased, resulting in a decrease in fatigue life. Although the strain energy density at an average temperature of 398 K decreased by about 10% compared with that at an average temperature of 348 K, the fatigue life decreased to about 40% when the average temperature increased. Continuous dynamic recrystallization occurred during power cycling, leading to fatigue failure in high-energy grain boundaries. Since continuous dynamic recrystallization tended to occur more readily at higher temperatures, the fatigue life decreased with increasing average temperature, even for the same junction temperature range ΔT_j. Moreover, the area of equibiaxial tensile and compressive creep deformation in the die-attach material became larger with increasing current on-and-off times. As a result, the fracture area under long current on-and-off time conditions was increased by about 25% in comparison with that under short current on-and-off time conditions.

研究了Sn-Ag-Cu无铅焊点的断裂机理以及测试参数对功率循环寿命的影响。在这项研究中，平均温度分为三个等级（348、373和398 K），电流通断时间分别为两个等级（2 s / 10 s和5 s / 22 s），以及三个等级ΔT_使用j（75、100和125 K）。由于芯片附着材料的热膨胀受到Si的限制，因此在功率循环过程中会发生等双轴拉伸和压缩蠕变变形。该变形在芯片安装接头的中央部分产生疲劳裂纹，并且裂纹彼此连接，从而形成疲劳裂纹网络。断裂占据了模具附着面积的70％或更多，是影响关节疲劳寿命的主要因素。作为ΔT_j增加，中央部分的应变能密度增加，导致疲劳寿命降低。尽管平均温度为398 K时的应变能密度比平均温度为348 K时降低了约10％，但当平均温度升高时，疲劳寿命降低至约40％。功率循环过程中发生了连续的动态重结晶，导致高能晶界疲劳失效。由于在较高温度下趋于更容易发生连续动态再结晶，因此即使在相同的结温范围ΔT _j下，疲劳寿命也会随着平均温度的升高而降低。。而且，随着电流接通和断开时间的增加，芯片连接材料中的等轴拉伸和压缩蠕变变形的面积变大。结果，与短电流通断时间条件下相比，在长电流通断时间条件下的断裂面积增加了约25％。