This study has investigated the dynamic variations of flow and meniscus during underfill process using flow visualization technique to understand physics of underfill flows. As a quantitative flow visualization technique, μ-PIV(micro particle image velocimetry) was applied. Glycerin was filled into a glass chip which has quadrilateral bump arrangement. It was found that the wetting distance increases rapidly when the meniscus attaches onto the bump and it increases slowly when the meniscus detaches from the bump. The contact angle and the meniscus velocity are in-phase according to the meniscus position. The flow velocity is the fastest between bumps when the meniscus is detached and then the flow velocity continuously gets slow down.
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