The underfill encapsulation process and corresponding underfillflow behavior are studied numerically and experimentally. A 2-D volumeof fluid (VOF) FLUENT model was used to better simulate one-sideunderfill flow compared to a pre-existing analytical model. For thetwo-side underfill flow, a 3-D flow model based on the Hele-Shawapproximation was created to calculate the process time. A 2-Danalytical model was also modified by including a body force to simulateinclined underfill flow. Experiments were performed to verify thenumerical model, and good agreement was observed for the flow time andflow distance relationship for different processes. Experiments atvarying temperatures allowed the inference of the encapsulant's strongtemperature dependent viscosity and of an optimal temperature for theunderfill process. Experimental results also revealed that dispensingfrom more than one side of the chip changed the underfill flow behaviorand thus changed the process time. We also noted that the addition ofcenter bumps increases the fill time compared to just edge bumps.However, for two different densities of center bumps, no significantdifference on the total underfill time was observed
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