Flip-Chip Underfill Packaging Considering Capillary Force, Pressure Difference, and Inertia Effects

This study aims to enhance the flow rate and reduce the filling time in flip-chip underfill packaging by combining capillary force, pressure difference, and inertia effects. In the designed underfill apparatus, the capillary force effect is developed by surface tension, the pressure difference between the inlet and the outlet is established using a pump or a vacuum, and the inertia force is achieved via circular rotation. The governing equations containing the three analyzed effects are derived and solved using a dimensionless technique. The analytical results indicate that for the general gap height of approximately $10-1000μm$⁠, the pressure difference and inertia effects dominate the driving force and provide a significant reduction in the filling time. However, for a gap height of less than $1μm$⁠, the driving force is dominated by the capillary effect. The present results confirm that the productivity of the flip-chip underfill packaging process can be enhanced through the appropriate control of the capillary force, pressure difference, and inertia effects.