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在25℃下利用单轴微力疲劳试验机对96.5Sn-3Ag-0.5Cu无铅焊点进行不同频率(1~10 Hz)和应变范围(2%~8%)的低周疲劳试验。结果表明,不同应变范围条件下无铅焊点的低周疲劳行为符合Coffin-Manson方程。频率修正的Coffin-Manson方程可以用来描述频率对无铅焊点低周疲劳寿命的影响。疲劳裂纹首先在焊点边缘的钎料与金属间化合物(IMC)之间的界面处萌生,随后,裂纹沿近IMC层的钎料内进行扩展。不同频率条件下焊点的断口形貌主要分为3个特征区域:裂纹萌生区、裂纹扩展区和最终断裂区。随着频率的升高,焊点的断裂机制由沿晶断裂向穿晶断裂转变。
Low-cycle fatigue tests were performed on 96.5Sn-3Ag-0.5Cu lead-free solder joints at different frequencies (1 to 10 Hz) and strain ranges (2% to 8%) at 25 ° C using a uniaxial micro-scale fatigue tester. The results show that the low cycle fatigue behavior of lead-free solder joints with different strain ranges accords with the Coffin-Manson equation. The frequency-corrected Coffin-Manson equation can be used to describe the effect of frequency on the low-cycle fatigue life of lead-free solder joints. The fatigue crack first sprouts at the interface between the solder and the intermetallic compound (IMC) at the edge of the solder joint, and then the crack propagates along the brazing material of the near IMC layer. Fracture morphology of solder joints under different frequency conditions is mainly divided into three characteristic areas: crack initiation zone, crack propagation zone and final fracture zone. As the frequency increases, the fracture mechanism of solder joints transforms from intergranular fracture to transgranular fracture.