Dynamic flow measurements of capillary underfill through a bump array in flip chip package
This study investigated the dynamic variations of flow and meniscus during underfill process using flow visualization techniques to understand physics of capillary flows. For the quantitative flow visualization, a high speed micro particle image velocimetry (μPIV) was applied to a transparent flip chip specimen with arrayed bump structure. As an underfill liquid, glycerin was filled into the flip chip specimen by capillary action. The present visualization technique offers time-varying movement of meniscus and phase-locked velocity fields frozen to the meniscus position. To observe the dynamic contact angle between parallel plates, an in situ measurement technique was developed in the present study. Then, the filling time was compared with analytical models. From this experiment, it was found that the meniscus velocity and the contact angle vary in-phase according to the position of meniscus. The phase-locked velocity fields show velocity gradients on the meniscus surface which gives rise to the breakdown of equilibrium contact angle. Consequently, the detailed filling time has different behavior from the analytical models.