The effect research of PCB microvia design on thermal fatigue life of WLCSP solder joints

With the development of integrated circuit to miniaturization, the diameter of the solder joints becomes smaller and smaller and the microvias in the high density PCB also become more and more. The design of the microvia has impacted on the fatigue life of the solder joints. This paper establishes the 3D Finite Element Method symmetric models of WLCSP through studying the influence of the parameters such as diameter, depth and quantity of the microvias on thermal fatigue life of WLCSP solder joints with FEM. 0.4mm is chosen for the diamiters in the models, the Microvias are designed based on Huawei PCB design standard and 5 is chosen for the proportion of thickness and aperture. Paper describes the 3.5Sn95Pb visoplastic material properties using ANSYS built-in ANAND constitutive model and analysis the deformation and stress distribution and strain behavior of the solder joint in different microvia designs throughing the FEM. The results show that: the PCB with microvias has a shorter lifetime of the solder joints than those without miropores. If the depth of the microvias gets deeper and the proportion of thickness and aperture greater, the solder joints thermal fatigue life will get smaller. The existence of the microvias in the PCB is equivalent to reduce the thickness of the PCB, which makes the whole of the substrate deflection increased and the shear stress range and the plastic strain range in the position of the maximum stress bigger.