中文摘要：

将QFN（Quad Flat No-Lead）封装器件通过表面贴装技术焊接到PCB（Printed Circuit Board）的过程中,熔化的焊点在器件与PCB间形成液桥。为了提高焊接的成功率,不仅要在PCB上设计合理的焊盘尺寸,还要了解液化焊点的形态及受力情况。利用毛细力学的理论,根据液态焊点的形态特征,建立焊点受力模型,在液态焊点体积恒定的条件下求解焊点的形态微分方程。根据液桥的形态特征参数和刚度特性曲线的变化,分析芯片的可焊接区间,并通过与Surface Evolver（SE）的仿真结果进行对比以证明方法的有效性。

英文摘要：

In the process of a Quad Flat No-Lead package is soldered to Printed Circuit Board（ PCB） through Surface mount technology,molten solder joint forming a liquid bridge between package and PCB. With a view to increasing the success rate of the welding,not only is a reasonable size of the pad designed on the PCB,but also the shape and stress of the solder joints have to be understood. In this paper,employing the theory of the capillary mechanics and according to the shape characteristics of the molten solder joint,a mechanical model for the solder is developed. Under the condition of a molten solder joint with a constant volume,the differential equations defining the shape of the solder are solved. According to the changes of the shape parameters and the stiffness characteristic curves,the welding interval is analyzed. By comparing the Surface Evolver（ SE） simulations with those of the method employed in this paper,the validity of the method is demonstrated.