Analytical Analysis on the Capillary Pressure of Underfill Flow Meniscus During the Flip-Chip Encapsulation Process

In the conventional flip-chip underfill encapsulation process, the underfill fluid is driven into the gap beneath the chip and substrate through capillary action. Particularly, the capillary pressure of the flow front determined the strength of overall capillary flow advancement through the bump array, hence the filling time and subsequently the manufacturing productivity. This paper analytically studied the capillary pressure of the flow front. Accordingly, the variation effects of bump contact angle and bump pitch on the flow front capillary pressure were presented. It was found that the variation trend of capillary pressure along the flow displacement between the region confined by two adjacent bumps is sinusoidal. The magnitude of capillary pressure is positive near bump entrant and acting along the flow direction before the capillary pressure gradually decreasing to oppose the flow advancement. The increasing of contact angle shifted the capillary pressure trend leftward with the peak being lowered, whereas the magnitude of capillary pressure decreases with the increases in bump pitch. Additionally, by studying the capillary pressure of flow meniscus, a new dynamic-based contact line jump criterion was proposed by considered the peak capillary pressure along the underfill advancement. These findings are practically useful for the design optimization of flip-chip package to promote the longevity of electronic package and reduce electronic wastes.