高溫熔融無鉛銲錫壓電噴墨印刷為一種非接觸式直接輸出成形的技術，可以噴印出微米等級的銲錫微液滴，因此廣泛被運用在電子封裝、生物晶片及微電子元件的製造上。由於在高溫製程下壓電材料的不穩定性，因此需要具備對噴墨製程原理及機制的了解，才能作為調整參數時的理論基礎。此外，銲錫隆點的形狀受到銲錫微液滴撞擊基板的行為影響，因此利用高速攝影機觀察銲錫微液滴撞擊不同表面處理過的基板，以探討其對銲錫隆點的影響。
本研究透過實驗和數值模擬方法來觀察及探討高溫熔融無鉛銲錫的壓電噴墨製程。透過商用流體力學計算軟體Flow-3D的輔助分析，得知施加一雙脈衝電壓波形，會在噴嘴上方產生壓力變化曲線，影響液滴的形態。其產生的正壓力會造成液柱的出現，後續的負壓區壓力變化則會造成液柱的斷裂，劇烈變化的負壓區造成斷裂時的不穩定，影響液滴的穩定生成。雙脈衝波形中的techo值決定毛細管內原先的壓力波及tfinalrise時所造成壓力的重合性，tfinalrise產生的負壓可抵消掉原來壓力波形中的負壓震盪，以平緩液滴頸縮及斷裂的過程，穩定液滴的生成。
除了分析壓力變化外，流體速度也是判斷液滴生成的方法。在單脈衝波形中要形成單一液滴的條件，可以調整tdwell以造成管內流體向外流動的速度與tfall時所造成流體速度互相重合，以產生足夠的向下動量來形成液柱。在雙脈衝波形中，控制techo可以調整流體往回拉的力量，有助於拉斷液柱，而形成單一液滴。比較不對稱電壓的雙脈衝波形，發現過大的向下動量造成液柱大量被擠出，若無足夠的拉力則會造成衛星液滴的出現；向下動量不足時，過大的拉力則是會造成液滴飛行速度太慢。因此可以得到負向電壓較大的不對稱電壓雙脈衝波形有助於生成穩定的單一液滴，因為其具有互相抗衡的向下動量以及拉力。
利用高速攝影系統的觀測，可以觀察到熔融銲錫微液滴撞擊經過不同表面處理基板的現象。當微銲錫液滴撞擊在覆有一層OSP層的銅墊上，則其間的界面熱傳係數便小於最小值4.07×104 W/m2•K，無法及時凝固而反彈離開。當撞擊無OSP層銅墊時，則微液滴會撞擊銅墊並在銅墊上凝固，為了達最小表面能而產生反覆的擴張及回彈的行為，隨著凝固銲錫的向上增加，液體的減少，震盪趨於不明顯，造成銲錫隆點的表面有下深上淺的皺褶出現。

This study investigated the droplet formation mechanism of molten lead-free solder under various process conditions of the ink-jet printing. Experimentally, the effects of a bipolar pulse waveform on droplet formation were observed through flash microscopic method. The numerical model was used to calculate for the detailed information concerning the droplet formation after the reliability of the numerical model has been verified. A single droplet can be obtained by applying a negative pressure variation to reduce the pressure shock in the negative pressure period which influences the contraction and break-up of the liquid thread. Fluid propagating velocity was also used to discuss the droplet formation mechanism in this study. A sufficient outward momentum of the fluid at the nozzle and a pulling force to pinch off the liquid thread were found to be essential for generating a single droplet. An asymmetric voltage of a bipolar waveform can be used to enhance the outward momentum and the pulling force of the fluid. The solder bumping process of a single molten micro-droplet was recorded using a high-speed digital camera. A droplet was observed to rebound on a copper pad coated with a layer of organic solderability preservatives, which was suspected to decease the interfacial heat transfer coefficient lower than a minimal value, 4.07×104 W/m2•K. It was found that the surface ripples on the solder bump was caused by the interaction of the fluid flow and the heat transfer/solidification processes in the bumping process.

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