最近這幾年，隨著電晶體閘極寬度的微縮發展所需投資的成本不斷飆升，而為了突破此瓶頸，讓晶片整體效能持續提升，開始轉向電子封裝技術的發展，透過多晶片的堆疊和異質整合，進一步擴大先進封裝的發展潛力。以目前先進封裝的發展趨勢而言，若將晶片接點的間距微縮至10微米，便能在晶圓上提供更高密度的I/O接點，晶片堆疊通過微銲點接合技術實現，而整個構裝系統的效能將取決於微銲點的性質表現，暫態液相接合(transient liquid phase bond)便是一種深具前景的技術，將整個銲點轉為全介金屬化合物，其特點為提供卓越的焊點強度和可靠的耐高溫特性。本研究透過由鎳基板溶解之鎳摻雜和溫度梯度的雙重效應來改善介金屬化合物 (intermetallic compounds) 的晶粒結構，並輔以機械測試和破斷面分析驗證其對傳統Cu/SAC/Cu暫態液相接合結構的強化效果。
藉由鎳基板取代熱端或冷端的銅基板，也就是Cu/SAC305/Cu、Cu/SAC305/Ni、Ni/SAC305/Cu這三種微結構進行討論，透過鎳溶解於銲料中優化晶粒結構。在一般Cu/SAC/Cu結構中，Cu6Sn5的晶粒生長具有強烈的擇優取向，且傾向成長為粗大化晶粒，這些性質易讓破裂路徑不受阻礙地筆直前進，造成微銲點的機械性質表現不佳。而鎳摻雜可有效改善這些缺陷，尤其是當鎳基板位於冷端時，機械強度相較於Cu/SAC/Cu大幅提升103.28%。此外，當鎳基板處於熱端或冷端時，全金屬間化合物銲點的微結構卻呈現出差異極大的結果，本研究透過溫度梯度和濃度梯度的交互作用來探討此差異產生的機制。
進而為了模擬電子元件長期處在工作溫度下對微銲點結構的變化，透過長時間的時效熱處理來觀察這三種參數的微結構變化，可發現優化後的Cu6Sn5晶粒結構依然可大幅度保留，而原本呈現層狀結構的Cu3Sn則被轉為網狀形貌。代表藉由鎳摻雜優化後的接點展現出良好的熱穩定，且網狀的Cu3Sn結構也能夠增加該結構的強度。後續的機械測試也應證出含鎳之微銲點具有最佳表現。
鎳添加於熱端或冷端的基板分別造成之效應將在本研究中深入討論，並期望藉由此法所改造的晶粒結構對於強化先進封裝之微銲點可靠度係一個具有前瞻性的途徑。

In recent years, the cost of investing in the development of transistor gate width scaling has continued to soar, prompting a shift towards the development of electronic packaging technology to break through this bottleneck and enable the continuous improvement of the overall performance of chips. Through the stacking of multiple chips and heterogeneous integration, the development potential of advanced packaging can be further expanded. According to the current trend of advanced packaging development, if the pitch of joints between chip is reduced to 10 μm, higher density I/O contacts can be provided on the wafer, and chip stacking can be achieved through micro-bump bonding technology. The performance of the entire packaging system will depend on the properties of the micro-bumps, and transient liquid phase (TLP) bonding is a promising technique that converts the entire solder joint into a full intermetallic compounds (IMCs), offering excellent solder joint strength and reliable high-temperature characteristics. This study aimed to improve the grain structure of intermetallic compounds through a dual effect of dissolved Ni addition from Ni substrate and a temperature gradient, and then to verify its strengthening effect on the traditional Cu/SAC/Cu transient liquid phase bonding structure through mechanical testing and fracture surface analysis.
Three microstructures, Cu/SAC305/Cu, Cu/SAC305/Ni, and Ni/SAC305/Cu, were discussed by replacing the Cu substrate at the hot or cold end with a Ni substrate and optimizing the grain structure by dissolving Ni atoms into the solder. In the Cu/SAC/Cu structure, the growth of Cu6Sn5 grains has a strong preferred orientation and tends to grow into coarse grains, which can easily allow the cracking path to advance unobstructedly, leading to poor mechanical properties of the micro-bump. Ni doping can effectively improve these concerns, especially when the Ni substrate is located at the cold end, the mechanical strength is significantly improved by 103.28% as compared to Cu/SAC/Cu. In addition, when the Ni substrate is at the hot or cold end, the microstructure of the full intermetallic compounds solder joints exhibits significantly different results. This study was intended to explore the mechanism causing this difference through the interaction of temperature and concentration gradients.
To simulate the structural changes of micro joints of electronic components under long-term working temperatures, long-term aging heat treatment was used to observe the microstructure changes of these three parameters. It was found that the optimized Cu6Sn5 grain structure was still largely retained, while the originally layered Cu3Sn was transformed into a network-like morphology. This indicates that the joint optimized by Ni doping shows good thermal stability, and the network-like Cu3Sn structure can also increase the strength of the joint. Subsequent mechanical tests also confirmed the effectiveness of Ni doping in enhancing the mechanical properties of the micro-bumps.
This study will address the effects of Ni addition on the hot and cold ends of the substrate. The aim is to explore the transformative benefits of this approach on the grain structure and its potential to enhance the reliability of the micro-bumps in advanced packaging.

摘要 i
Abstract iii
Contents v
List of Tables viii
Figure Captions ix
Chapter 1. Introduction 1
1.1 Background 1
1.2 Motivations and Goals 2
Chapter 2. Literature Review 5
2.1 Electronic Package 5
2.2 Solder Bump 7
2.2.1 Pb-free Solder 7
2.2.2 Transient Liquid Phase (TLP) Bonding 9
2.3 Under Bump Metallization (UBM) 10
2.3.1 Cu-based UBM 10
2.3.2 Ni-based UBM 11
2.4 Metallurgical Reaction in Micro-bump 12
2.4.1 Interfacial Reaction in Sn-Ag-Cu/Cu Micro-bump 12
2.4.2 Metallurgical Reaction in Conventional Cu/Solder/Cu Micro-bump 13
2.4.3 Metallurgical Reaction in Ni/Solder/Cu Micro-bump 14
2.5 Properties of Cu6Sn5 IMC at Solder/Cu Interface 14
2.5.1 Preferred Orientation of Cu6Sn5 14
2.5.2 Phase Stability of Cu6Sn5 15
2.6 Metallurgical Reaction and Critical Issues in Conventional Cu/Solder/Cu Micron-sized TLP Bonding 15
2.7 Strengthening Mechanism of Micro-bump 17
2.7.1 Effect of Grain Size 17
2.7.2 Effect of Grain Orientation 18
2.7.3 Effect of Ag3Sn Formation 18
2.8 Effect of Ni on Cu-Sn Metallurgical Reaction 19
2.8.1 Effect of Ni on Cu6Sn5 19
2.8.2 Effect of Ni on Cu3Sn 21
Chapter 3. Experiment Procedures 41
3.1 Optimizing the microstructure of Cu/SAC305/Cu TLP micro-bump via the dual effect of temperature gradient and Ni addition 41
3.1.1 Sample Fabrication for Cu/SAC305/Cu, Cu/SAC305/Ni, and Ni/SAC305/Cu TLP Micro-bumps 41
3.1.2 Microstructure Analysis for Cu/SAC305/Cu, Cu/SAC305/Ni, and Ni/SAC305/Cu TLP Micro-bumps Before and After Aging treatment 42
3.1.3 Mechanical Test for Cu/SAC305/Cu, Cu/SAC305/Ni, and Ni/SAC305/Cu TLP Micro-bumps Before and After Aging Treatment 43
Chapter 4. Results and Discussion 46
4.1 Optimizing the microstructure of Cu/SAC305/Cu TLP micro-bump via the dual effect of temperature gradient and Ni addition 46
4.1.1 Microstructure Observation and Elemental Analysis 46
4.1.2 Grain Orientations and Sizes of Cu-Sn IMCs 49
4.1.3 Specimens with Shorter Reflow Time 51
4.1.4 Mechanical Performance 56
4.2 Retaining advantageous grain structure with Ni addition in Cu/SAC305/Cu TLP micro-bump under isothermal long-term aging treatment 72
4.2.1 Microstructure Evolution and Elemental Analysis 72
4.2.2 Grain Orientations and Grain Sizes of Cu-Sn IMCs 75
4.2.3 Mechanical Performance Before and After Aging Treatment 76
Chapter 5. Conclusion 86
References 89

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