SnAgCu/Cu焊点热循环失效行为研究

Failure Behavior of SnAgCu/Cu Solder Joint Subjected to Thermal Cycling

摘要:

对热循环条件下SnAgCu/Cu焊点的热力疲劳行为进行了研究。基于热循环条件下实际倒装焊点的位移分析，设计了单焊点试样及其热力耦合加载装置。利用电阻应变测量法研究了–40~125 ℃热循环条件下焊点的变形行为。以电阻变化率为损伤参量，确定了焊点的损伤演变规律以及焊点热疲劳寿命。基于此，采用基于应变的Coffin-Manson模型确定了焊点寿命与非弹性应变之间的关系。结果表明焊点随加载应变范围的增大而出现加速破坏。最后，对热循环过程中SnAgCu/Cu焊点的微观组织演变进行了扫描电镜观察分析，旨在进一步揭示焊点失效的本质。

Abstract:

Thermomechanical fatigue of SnAgCu/Cu solder joints subjected to thermal cycling was investigated. Based upon an analysis of displacements for flip-chip solder joints subjected to temperature cycling, a special bimetallic loading frame with single solder joints has been designed, which allows for the strain measurements of an individual solder joint during thermal cycling. The strain-stress relationship for the solder joint, characterized by hysteresis loops, was determined by strain gauge measurement during thermal cycling from –40 to 125 oC. The failure process was characterized by resistance change of the solder joints, and the number of cycles to failure was determined when the variable D=1-R0/R approximately reached 0.5. The results show that the failure process of solder joints is accelerated with the increase of strain range applied. Coffin-Masson law was applied to characterize the relationship between solder joint life and inelastic strain range, and the model parameters were determined for SnAgCu/Cu solder joint. In addition, the microstructure evolution of the solder joints during thermal cycling was analyzed by Scanning Electron Microscopy, which gave the microscopic explanation for the failure mechanism of SnAgCu/Cu solder joints.