SnAgCu无铅焊点低周疲劳行为研究（英文）

Low Cycle Fatigue Behavior of SnAgCu Solder Joints

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 mechanical fatigue tests on 96.5Sn-3Ag-0.5Cu lead-free solder joints were carried out using a micro-uniaxial fatigue testing system at 25 °C with different frequencies（1-10 Hz） and a wide range of strain（2%-8%）. The results show that the low cycle fatigue（LCF） life of the solder joint follows the Coffin-Manson equation in different strain ranges. Frequency-modified Coffin-Manson equation can describe the frequency effect on the fatigue life of lead-free solder joints. The analysis of failure process show that the fatigue cracks initiate at the interfaces between the solder and inter-metallic compound（IMC） around the edge of the joints, and then propagate within the solder along the solder/IMC interfaces proximately. Fracture morphologies of solder joints under different frequencies mainly consist of an initiated region, a propagation region and a final fracture region. The fracture mechanism of the final fracture region transforms from inter-granular fracture to trans-granular fracture with increasing of frequency.