Prediction of filling time in capillary-driven underfill process through 3D numerical analysis

摘要

Underfill, mainly composed of epoxy resin and silica fillers, is used to fill the standoff gap in flip chip to alleviate stress and prevent the solder bumps from crack and fatigue fracture. In this paper, a 3D numerical model is proposed to predict the filling time in capillary-driven underfill process, with the level set method incorporated to capture the interface of the two-phase flow. In the model, the non-Newtonian behaviour of the epoxy resin is described with the power-law constitutive equation and the flow is assumed to be incompressible, laminar and isothermal. By comparing the simulation results with the experiment data, the accuracy of the numerical model is verified. Using the validated model, the effect of the bump pitch on the underfill flow is studied. The bump pitch varies from from 262 μm to 50 μm. The relationship between the flow front location and the filling time is derived.