Sn-Ag3.0-Cu0.5/Cu金属间化合物生长行为及其对PBGA焊点热疲劳可靠性的影响

Growth Behavior of Sn-Ag3.0-Cu0.5/Cu Intermetallic Compounds and Their Effect on the Thermal Fatigue Reliability of PBGA Solder Joints

利用SMT全自动回流焊机和高温恒温试验箱,制备出经2次回流焊且不同时效处理时间的Sn-Ag3.0-Cu0.5/Cu焊点试件,对其金属间化合物(IMC)的厚度进行测量,发现其厚度的增长与时效时间的平方根近似成线性关系。采用统一粘塑性Anand本构模型来描述焊点的力学性能,运用有限元计算软件ANSYS对PBGA构件进行热循环模拟,对其在不同IMC厚度下的应力和应变响应进行分析。结果表明,芯片右下方焊点右上角热循环结束后累积的等效塑性应变最大,是整个PBGA构件的关键焊点;随着IMC厚度的增加,关键焊点热循环过程中的等效应力水平不断降低,相应剪切塑性应变范围Δγ不断增大,热疲劳寿命Nf则不断降低;升温和高温保温过程中剪切塑性应变的增加量构成了剪切塑性应变范围Δγ,且不同IMC厚度下升温段剪切塑性应变增加量占Δγ的比例基本维持在95%左右。

The Sn-Ag3.0-Cu0.5/Cu solder joint samples subjected to 2 reflows and different aging time were prepared using,SMT full-automatic reflow machine and high constant-temperature test chamber,the thicknesses of the intermetallic compounds （IMC） of the samples were measured.The results show that the thickness increment of IMC is approximately proportional to the square root of aging time.A series of thermal cycling simulations were conducted with finite element software ANSYS to examine the stress/strain behaviors of PBGA solder joints with various IMC thickness,and the solder balls were characterized by Anand unified viscoplastic constitutive model.The simulated results show that there is the most cumulative plastic strain at the top right corner of the solder ball right beneath the edge of chip,which is considered as the critical solder joint of PBGA.With increasing thickness of IMC,the equivalent stress level of the critical solder joint decreases during the thermal cycling process,the shear plastic strain range △γ increases and the corresponding thermal fatigue life Nf decreases.The shear plastic strain increment during the heating process and holding process constitutes △γ and the percentage of △γ basically maintains at the level of 95% in different IMC thicknesses.