在覆晶接合技術(flip chip technology)中，銲料(solder bump)與凸塊底金屬層(under bump metallization, UBM)材料的選擇經常用於決定銲接點迴焊(reflow)之後所生成的介金屬化合物(intermetallic compound, IMC)的生成厚度、形貌以及相轉變，許多研究利用添加第四元元素於錫銀銅銲料、改變銲料抑或是改變凸塊底金屬層的材料系統，以達到抑制介金屬化合物的生長、相轉變或是改變形貌，但元素添加或是改變材料系統都會受到新元素的限制，例如氧化或是價格問題，因此，利用凸塊底金屬層的結構改質去影響回焊後的界面反應越來越受重視。
本研究利用直流磁控濺鍍 (DC magnetron sputter)的基材偏壓(substrate bias)調控以製備擁有緻密堆疊特性的鎳膜，不同堆疊緻密性的鎳膜當作凸塊底金屬層，進行相同溫度下，不同時間的回焊，觀察其生成的介金屬化合物的厚度、相轉變程度，並深入探討凸塊底金屬層的結構影響介金屬化合物生成的原因。
利用直流磁控濺鍍的製備不同微結構特性的鎳膜，經由原子力顯微鏡(Atomic Force Microscope, AFM)觀察其濺鍍後的表面粗糙度，透過X光繞射分析(X-ray Diffraction, XRD)分辨其方向性的差異，進一步利用穿透式電子顯微鏡(Transmission Electron Microscope, TEM)驗證其結構緻密程度的差異性，亦結合高解析原子影像(High Resolution image, HR image)和選區繞射圖樣(Selected-Area Diffraction Pattern, SADP)更精確驗證高堆疊致密程度的鎳膜是奈米雙晶結構(nano-twinned structure)。不同結構的鎳膜基板焊錫銀銅銲球經過250 ℃ 的迴焊後，以場發射掃描式電子顯微鏡(Field-Emission Scanning Electron Microscope, FE-SEM)觀察介金屬化合物的生成和相轉變，並計算介金屬化合物的生成厚度和鎳膜的消耗程度。
利用動力學以及熱力學的觀點深入分析並探究鎳膜具高推疊緻密性的奈米雙晶結構抑制介金屬化合物的生成厚度，並有效減緩鎳膜的消耗程度。因此奈米雙晶鎳薄膜為最有潛力的薄膜結構運用在電子封裝的凸塊底金屬層。

In electronic packaging, rapid growth of intermetallic compound (IMC), fast consumption rate of UBM, dual-phase IMC and spalling phenomenon are concerned in the Sn-Ag-Cu (SAC) solder system. Many studies have aimed to improve the characteristics of the SAC solder system, including adding a fourth element to SAC solder or changing to another solder material. Doping other elements to the under bump metallization (UBM) or the alternative material UBM was also employed. All above methods are material control, which would bring to some concerns, such as the issue of oxidation and the cost of the modified process due to the new material system. Beyond the material control, the method of the architecture control by modifying the microstructure of UBM was demonstrated to affect the interfacial reaction in solder joint. The microstructural control of UBM is a potential way to solve the critical issues in the SAC solder system.
With the structural difference of Ni UBM, it is expected that the dense structure of Ni UBM may inhibit its consumption rate of UBM and suppress the growth of IMC during reflow. While the bias voltage applied during coating process, the microstructure of film can be shaped and modulated to the dense structure. When the bias voltage increased to 200 volt, the (111) nanotwinned Ni film was produced due to the high mobility of adatoms and the high energy of ion bombardment during the growing process. By using the nanotwinned structure of Ni film, slow interfacial reactions in solder joint were observed because of the attractive properties of nanotwinned structure. Nanotwinned structure was regarded as a perfect symmetric crystal, which possessed the lower boundary energy and higher activation energy along boundary. As a result, the stable structure of nanotwinned Ni film significantly suppress the formation of interfacial IMC and can be employed as thinner Ni-based UBM in electronic packaging.

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