QFP结构中引脚焊缝界面端的奇异性热应力问题研究

Researches on Thermal Stresses at the Interface Edge of a QFP Welded Joint

由于引脚、印制电路板和焊接剂的热-机材料属性不同,在受到热载荷或机械载荷时,引脚焊接界面端会产生奇异性应力,有可能产生界面开裂。为了基于界面端奇异场来评价QFP结构引脚界面端力学行为,采用数值方法求解引脚焊缝任意角度尖劈界面端的应力强度系数。具体步骤为:首先,基于高次内插有限元特征分析法确定两相任意角度尖劈界面端的奇异性指数和应力角分布函数,并引入常数热应力项,获得热-机耦合奇异性应力场表达式;采用有限元分析技术和最小二乘拟合法来获得应力强度系数的数值解。考察了热-机材料属性对热载荷下焊接剂/印制电路板界面端应力强度系数的影响。结果表明:弹性模量、泊松比和材料热膨胀系数等均对应力强度系数有影响,适当的做出调整可以使界面端呈现良好的热应力状态。

Due to the mismatches of thermomechanical properties among the pin,PCB and solder of a QFP welded joint,singular thermal stresses,which are an inducement of interfacial delamination,will occur at the interface edges of these materials.In order to evaluate the local mechanical behavior of the QFP welded joint,in the paper,singular thermal stresses as well as the corresponding generalized stress intensity factors（GSIFs） at the interface edge of an arbitrary bi-material wedge is determined numerically based on the analytical solu-tion and the FEM.Firstly,A ad hoc FE eigenanalysis method is used to solve the eigensolusions of singular stress fields,i.e.,the singularity stress orders and the angular variations of stresses,and these eigensolusions together with a constant stress term are used to established the expression of the singular thermal stress field at the interface edge.In numerical examples,the effects of elastic modulus,poisson’s ratios and thermal expan-sion coefficients on SIFs at the interface edge of the QFP welded joint are considered,and it is found that the local thermal stress states can be improved by selecting solder with suitable material constants.