近年來全球人口老化問題日益嚴重，伴隨著勞動力衰退與勞動成本上升，農業與工業對人力需求將漸漸由自動化系統、人工智慧與機器人取代，也因此帶動了高功率模組的發展，催生低成本、高效率工作系統的需求。高功率模組的發展中，構裝的重要性不可言喻，由於傳統構裝中以錫為主的銲料球其熔點過低、易產生因熱膨脹係數不匹配所造成的翹曲現象、低封裝壽命以及低電遷移抵抗能力，因此錫合金銲料球勢必要被取代。為了改善封裝以錫銲料球產生的問題，近年來開發了暫態液相擴接合(transient liquid phase, TLP)以及銀燒結接合技術。其中，TLP技術所需接合時間過長導致難以控制接合品質，而銀燒結技術成本過高且其電遷移抵抗能力較差，因此以銅金屬作為接合材料逐漸受到封裝產業重視。傳統的銅直接接合製程溫度皆需要在高於250 oC以及施加一定的壓力之下才能完成接合。而本研究開發了新式銅膠於低溫50 oC以及無施加接合壓力等條件下完成銅直接接合。 本研究成功將銅膠應用於銅箔基板直接接合、銅柱直接接合以及直徑為100微米銅導線直接接合。利用掃描式電子顯微鏡、穿透式電子顯微鏡、低角度X光繞射、聚焦離子束以及電子背向散射繞射等儀器分析銅膠接合之微結構。銅膠是由經氧化後的微米銅球、抗壞血酸以及明膠共同混合而成，而經氧化後的微米銅球其表面所覆蓋的氧化銅層會被抗壞血酸還原成奈米銅球，而明膠所扮演的角色除了當保護劑防止銅氧化之外，其與奈米銅球之間的交互反應促使了奈米銅球之間產生定向貼附成長機制 (oriented attachment mechanism)，使接合可於50 oC環境下放置30分鐘完成。此外，本研究利用DLVO理論以及動力學推導證實銅膠燒結反應內定向貼附成長機制之存在。;Increasing demands for artificial intelligence, automatic systems, and intelligent robots have driven the development of power module packaging. Due to the issues of low re-melting temperature for Sn-based solder ball, warpage induced by CTE mismatch, low packaging lifetime of Sn-based solder, low electromigration resistance for Ag nanoparticle sintering and high cost of Ag, the Cu direct bonding is a potential method for assembling power electronics. Therefore, the development of Cu direct bonding is a main trend for 3D IC packaging in high-power device. Researchers are seeking new materials and novel approaches for low temperature bonding. Traditional bonding requires a temperature for bonding at around 250 oC or above. Usually low temperature bonding requires additional pressure. This study reports a method that can greatly reduce the warpage of the chip. Bonding without pressure also saves the chip from damage due to stress. In this study, we develop a Cu paste of oxidized micron-size Cu particles and water-based fluid of ascorbic acid and gelatin. The Cu paste is successfully applied to Cu foils, Cu pillars and Cu wires direct bonding at 50 oC for 30 min without bonding pressure. The interfacial reaction is investigated by scanning electron microscopy, focus ion beam, transmission electronic microscopy, grazing incidence X-ray diffraction and electron backscatter diffraction. In the sintering processes, we find that the Cu nanoparticle sintering is controlled by oriented attachment. The DLVO theory and kinetic calculation are employed to verify the oriented attachment mechanism in Cu sintering process. This study suggests a very effective method to achieve sintering of Cu at low temperature without pressure, which would greatly reduce the cost of the processing.
