SnAgCu无铅焊点低周疲劳行为研究

Low Cycle Fatigue Behavior of SnAgCu Solder Joints

摘要:

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（1Hz~10Hz）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三个特征区域：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。

Abstract:

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