Finite Volume Method Study on Contact Line Jump Phenomena and Dynamic Contact Angle of Underfill Flow in Flip-Chip of Various Bump Pitches

Abstract

Three distinct flip-chip underfill cases were considered in this work, with each possess a bump pitch of 0.8 mm, 1.0 mm and 1.2 mm. Contact line jump (CLJ) phenomenon during the underfill flow were successfully visualized with the aided of finite volume method (FVM) based simulation. The current simulated underfill flow fronts were qualitatively validated with the existing experimental data. Generally, the attachment process occurs much faster than the detachment process, by a factor of 14. Within the investigated pitches range, shorter bump pitch would yield a slower underfill flow but a faster-completion underfill process. The voiding mechanism during the underfill process were presented. Furthermore, the dynamic contact angle of underfill meniscus were analytically computed from the numerical data. The contact angle is found to be varies sinusoidally with the filling time, while the impact of bump pitch is minimal. Lastly, it is found that the bump pitch of flip-chip does affect the void formation and propagation.