The effect of gap height on non-Newtonian underfill flow in chip packaging: Experiments and simulations

Underfill encapsulant is important for improving chip device reliability. Gap height is a decisive factor to accelerate the filling speed which directly improves packaging efficiency. In this paper, the effect of gap height on non- Newtonian underfill flow is studied numerically and experimentally. Especially, 2D and 3D finite volume method (FVM) numerical models are used to explore the functional relationships between the gap height and underfill flow pattern, in which volume of fluid (VOF) technique is applied for flow front tracking and the surface tension force is described by continuum surface force (CSF). The simulation results match with experimental results well and help perform a detailed examination of gap height's effects on pressure, velocity, shear rate and viscosity distribution of fluid and morphology of the flow front.