壓電噴墨製程技術為直接輸出技術的一種，配合精密對位系統與可適用多種墨水材料的特性，可以改善與替代半導體製程部分步驟，應用於3D IC產業晶圓接合上具有開發潛力。為了達到微接點製程低溫化，使用奈米墨水材料進行微接點接合成為發展重點，因此，針對奈米墨水材料的轉移品質進行研究，並且探討噴印厚度對微接點的強度、電性影響。
本研究利用奈米銀墨水為銅對接之接合材料，目的在於製備銅對銅接合導電精微結構，進一步探討噴印厚度與微接點性質之關係。在墨水轉移方面，透過高速攝影機觀察基板溫度對液滴沉積行為影響，找出合適噴印條件；接著，將此噴墨參數應用於銅對銅接合製程，藉由噴印厚度的改變探討微接點強度的影響，並且檢測在不同噴印厚度下電性的差異。此外，藉由提高基板溫度及微液滴噴印時間長短，於相同噴印銅墊片面積下達到增加墨水厚度，在液滴沉積堆疊過程中，觀察液滴的延展寬度、厚度與接觸角的變化，獲得最佳噴印條件及品質。
高固含量商用奈米銀墨水60 wt%，使用壓電噴頭於適當雙脈衝波形參數，可以形成單一顆微液滴，其直徑為52 μm及飛行速度為0.6 m/s。當基板溫度為50 oC，微液滴形成過程不受溫度影響，仍為單一顆穩定液滴；但微液滴沉積於銅墊片後，其延展幅度縮小。在微接點性質方面，當噴印墨水乾燥後厚度為5 μm，有最大之剪切強度可達30.4 MPa，並且有最低特徵接觸電阻為4.5×10-8 Ω∙cm2。在小範圍堆疊液滴方面，基板溫度為70 oC，使用循環式噴印模式可以成功在200 μm的範圍內堆疊成微液柱，其高度達111 μm。

Piezoelectric ink-jet printing technology is a kind of direct writing printing technology. This approach is attractive for replacing conventional processes, such as screen printing and photolithography, if carried out using a precision alignment system and multiple inks, especially with regard to the patterning of conductive tracks, and this is why it can be used for wafer-level 3-D integration bonding. Silver nanoparticle-based inks can be used to lower the temperature of the process, and thus the current study examines the printing performance of such inks and the effects of printing thickness on the shear strength and contact resistance of micro-interconnections.
We fabricated a Cu-to-Cu metallic microstructure by nano silver ink and ink-jet printing. The highly concentrated silver ink was ejected from the piezoelectric printhead by a suitable bipolar waveform. For each pulse cycle, the single droplet diameter was 52 μm with an average velocity of 0.6 m/s. At a substrate temperature of 50 oC, 60 droplets were printed on a Cu pad with diameter 600 μm and the thickness of drying layer was about 5 μm. According to our experimental results, this could provide effective bonding between Cu joints before the thermal compression process, which heated the material to 250 oC for 30 min. Consequently, the joints had a high shear strength of 30.4 MPa with a low specific contact resistance of 4.5×10-8 Ω∙cm2. For the advanced application on a small target, the height of the piled droplets reached to 111 μm within a small diameter of 200 μm when the substrate temperature was increased to 70 oC.

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