QFP器件微焊点热疲劳行为分析

Analysis on the thermal fatigue behavior of QFP soldered joints

通过数值模拟可知,蠕变应变和塑性应变在时间历程处理过程中,以阶梯状累积增加.基于Shine and Fox模型和Solomon模型,运用等效应变进行SnPb和SnAgCu焊点的疲劳寿命评估,分别为937次和1 391次.结果表明,焊点的拉伸力均随着热循环次数的增加而减小;SnAgCu焊点的热循环可靠性优于SnPb焊点,焊点在热循环后的断裂形式已由韧性断裂转变为脆性断裂.随着热循环次数的增加,焊点界面处的金属间化合物层不断的生长,脆性的金属间化合物使得焊点的可靠性严重削弱,导致焊点的拉伸力下降.

The creep strain and plastic strain of soldered joints in time history are studied and analyzed with numerical simulation method,which are found to be accumulated as ladder form.Based on Solomon and Shine and Fox models,the fatigue life values of the Sn-Pb and SnAgCu soldered joints are evaluated by equivalent strain,which are about 937 and 1 391 respectively.The experimental results showed both in experiment and simulation results indicate that the tensile force of soldered joints will be decreased with the increase of thermal cycling times,the reliability of SnAgCu after thermal cycling is better than that of Sn-Pb, the fracture mode of the soldered joints transforms from toughness fracture into brittle fracture,and the brittle intermetallic compounds at the interface of soldered joints will grow up gradually with the increase of thermal cycling times during thermal cycling process,which give a strong impact to the reliability of soldered joints and reduce the tensile force of soldered joints at the same time.