CAJ | 학술논문

基于塑性应变能密度概念提出微焊点低周疲劳裂纹萌生、扩展和寿命预测模型，阐明其与连续介质损伤力学的联系，评估应力三轴度对预测模型的影响，并通过试验和数值计算相结合的方法确定出微米尺度球栅阵列(Ball grid array，BGA)结构单颗Sn3.0Ag0.5Cu无铅焊点(高度为500～100μm，焊盘直径为480μm)疲劳裂纹萌生和扩展模型中的相关常数。研究结果表明，疲劳裂纹萌生和扩展循环数与每个循环所产生的塑性应变能密度均呈幂函数关系；应力三轴度会影响疲劳裂纹扩展速率，并最终影响焊点的疲劳寿命；应力三轴度与加载方式有关，拉伸载荷下焊点的应力应变行为受异种材料界面和封装结构力学约束作用的影响，应力三轴度随焊点高度降低而明显升高；而剪切载荷作用下焊点中的力学约束十分有限，焊点高度变化对应力三轴度的影响非常小；测得的高度为100μm焊点的疲劳裂纹扩展相关常数可以很好地用于预测其他不同高度焊点的疲劳寿命，表明所提出的预测模型可以有效地减小由几何结构和体积变化造成的塑性应变能集中现象对焊点疲劳寿命的影响。
기우소성응변능밀도개념제출미한점저주피로렬문맹생、확전화수명예측모형，천명기여련속개질손상역학적련계，평고응력삼축도대예측모형적영향，병통과시험화수치계산상결합적방법학정출미미척도구책진렬(Ball grid array，BGA)결구단과Sn3.0Ag0.5Cu무연한점(고도위500～100μm，한반직경위480μm)피로렬문맹생화확전모형중적상관상수。연구결과표명，피로렬문맹생화확전순배수여매개순배소산생적소성응변능밀도균정멱함수관계；응력삼축도회영향피로렬문확전속솔，병최종영향한점적피로수명；응력삼축도여가재방식유관，랍신재하하한점적응력응변행위수이충재료계면화봉장결구역학약속작용적영향，응력삼축도수한점고도강저이명현승고；이전절재하작용하한점중적역학약속십분유한，한점고도변화대응력삼축도적영향비상소；측득적고도위100μm한점적피로렬문확전상관상수가이흔호지용우예측기타불동고도한점적피로수명，표명소제출적예측모형가이유효지감소유궤하결구화체적변화조성적소성응변능집중현상대한점피로수명적영향。
A plastic strain energy density methodology is proposed to evaluate the initiation and propagation of fatigue crack in lead-free solder joints. The relationships among the plastic strain, plastic strain energy, continuum damage mechanics(CDM) and fatigue life are clarified. Crack growth correlation constants for micro-scale ball grid array(BGA) structure solder joints(with standoff height h in the range 100 to 500μm and a pad diameter 480μm) are determined by a combination of experimental estimation and numerical calculation. The results show that the cycle numbers of crack initiation and propagation have power function relationship with the plastic strain energy density generated in each fatigue cycle. Crack propagation rate is affected by stress triaxiality, which is dependent on loading modes, i.e., stress triaxiality increases dramatically with decreasing h under tensile load because of the mechanical constraint effect arising from interfaces and package structure, while under shear load the standoff height has very limited effect on stress triaxiality. Furthermore, crack growth correlation constants identified in solder joints with h=100μm can be well used to predict fatigue life of solder joints with different geometries, indicating that the fatigue life prediction method proposed in this study can effectively prevent the influence of plastic strain energy concentration caused by structural and volume factors on the prediction of fatigue life of BGA structure solder joints.