為了避免熱應力所造成之疲勞破壞，覆晶元件在製程中，會在晶片與基板之間填入底膠，本文主要以實驗方法及數值模擬來探討流體以表面張力充填底膠之現象。
實驗方法分別利用平行平板及毛細管，探討流體充填體積與時間之關係。實驗結果顯示，垂直平行板間之流體上升之初始速度近似定值，隨著時間的增加，速度急速的由快轉慢，到最後因表面張力與重力平衡而變成零。相對的，則水平放置的不同管徑之毛細管，因不受重力影響，實驗結果顯示，流體一開始以爆衝方式流入，達到極值後，流速便隨著時間而下降，最後漸漸平緩，流速以近似定值前進。
若觀察充填時間，由毛細管實驗得到流體前端位置平方與時間成正比，其斜率主要與流體性質有關。若以長度50cm之毛細管為例，發現管徑愈小，充填時間則愈長，兩者成反比關係，主要是流體前端之毛細壓力所造成之結果；管徑愈小，毛細壓力相對就愈大，因此使流體前進之壓力梯度也愈小。
以有限差分法模擬之結果與經驗公式之流體前端位置來比較，兩者差異值會隨著時間增大而漸漸縮小，以間距0.05公分來看充填長度50cm，最大差值為0.27cm，最小值為0.01cm。
此外，以7.5 × 5.8 cm2，間距為60μm之晶片模擬實際充填情形，以點膠式對不同位置做底膠充填。實驗發現，邊緣部分對充填時間有重要的影響，然而流體前端不規則，容易發生氣孔包覆於流體中。

To improve the reliability due to CTE mismatch of flip chip electronic components, the underfill encapsulant is usually filled into the gap between the chip and the substrate. The underfill driven by the capillary force is the emphatic topic in this study. In order to know the dispensing process due to capillary effect, this study combines experiments with numerical investigations to explore this phenomenon.
Two vertical parallel plates and horizontal capillaries are used to experimentally find the relation between the dispensing volume and time. In the vertical parallel plates, experimental results indicate that the initial speed is almost constant and then drops off rapidly as time proceeds further. The fluid keeps on climbing up until equilibrium between surface tension and gravity is reached. In contrast, in the horizontal capillaries, where no gravity effect exists, surface tension effects were investigated by changing the diameter of the capillary. The results show a burst-like fluid filling behavior initially. Then, upon reaching a speed limit, the speed of flow front starts to drop off to a constant velocity as time proceeds further. Overall speaking, the square of flow front is proportional to the underfill time. On the other hand, the dispensing time increases as the diameter decreases.
Comparing the results of finite difference method to those of empirical formula, the deviation of flow front decreases as time increases. Taking the case of the gap of 0.05cm as an example, the maximum deviation is 0.27cm, and the minimum deviation is 0.01cm.
For the case with a die of 7.5 × 5.8 cm2, and a bump height of 60μm, filling time depends on the dispensing location. Experimental results indicate that the die edge has an important effect. However, an irregular shape of the flow front can occur and can lead voids inside the fluid if the dispensing speed is too fast.

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