半導在體封裝技術中，打線技術是最為成熟且廣泛運用於各項電子產品。隨著電子產品的縮小或高效能需求，打線材料必須克服更多隨之而來的挑戰。然而，金價的提升以及銅線在製程及應用上問題，使得銀線與銀合金線逐漸成為新一代的打線材料以提供價格及應用上的優勢。但是在過去的文獻資料中，鮮少探討銀合金打線與鋁金屬薄膜在電流下之影響。本論文探討銀鈀合金線與鋁墊打線系統在不同打線參數下的拉力測試及通電測試，同時也研究電遷移實驗下打線系統的微結構及形貌之改變。實驗結果顯示，適當的超音波震盪及楔型接點位置可以有效提升打線系統的可靠度。另一方面，試片在電遷移的實驗中被施予8x104 A/cm2之電流密度在環境溫度150℃及175℃下。我們發現在電遷移實驗中存在兩種不同的電阻對時間的關係。我們認為孔洞的生成影響電阻變化呈凹向上的趨勢，快速的介金屬化合物生成主導電阻改變呈凹向下的趨勢。同時我們更進一步透過模擬來分析接點內部的電流密度分布情形，發現在球型接點的角落和楔型接合處有最大的電流密度，此發現和球型接點處的孔洞位置相同。在電遷移的實驗中也發現明顯的極化效應，當電子流方向從鋁流向銀時，可以發現接點上有大量的突起物。然而當接點中的電子流方向從銀流向鋁或是沒有施加電流時，接點外觀並無明顯變化。我們推測此極化效應的形成原因是因為接點的幾何效應伴隨著電遷移所造成的壓應力影響接點有顯著的形貌改變，而在電子流方向相反及未通電的接點則因並無接點幾何上的縮減而沒有產生形貌上的變化。同時，壓應力也使動態再結晶的現象顯著地發生在銀合金線靠近電子流方向從鋁流向銀的接點。在微結構中，我們觀察到電子流方向也會影響介金屬化合物的生成。在相同實驗條件下的試片中，當電子流方向與化學位能方向相同時，介金屬化合物的厚度較厚，反之則較薄。而未通電的打線系統則因為溫度較低，介金屬化合物的成長速度最慢。除此之外，研究結果指出銀鈀合金打線系統在環境溫度157.2℃下未通電之介面反應為擴散控制機制。

The light-emitting diode (LED) is regarded as one of the energy-efficient electronic devices to environment. At the same time, wire bonding technology is utilized in LED package assembly. Gold wire bonding has been widely utilized in semiconductor packaging industry for electrical connections. However, since the gold price is soaring in past ten years, the alternative materials, such as copper and silver, are the candidates to replace gold. The silver alloy wire has shown many advantages, including excellent electrical and thermal properties. Nevertheless, not many studies have reported electromigration (EM) induced failure of silver alloy wire. This study employed silver alloy wires with 25.4 μm diameter bonded on 4 μm thick aluminum metallization of die pads to investigate their interfacial reaction and failure mechanism under current stressing of 8 x 104 A/cm2 at ambient temperature of 150℃ and 175℃. The bond pull test (BPT) was conducted before the EM test to understand the impact of various wire bonding parameters on electrical and mechanical properties. In addition, the resistance evolution of sample during current stressing and the microstructure of joint interface between silver alloy wire and Al bond pad were examined. In EM tests, two different resistance versus time curves were found and were attributed to void formation and rapid IMCs growth, respectively. The results exhibited that the polarity effect of distinct surface morphology on ball bonds and the different thickness of intermetallic compounds (IMCs) existed at the interface between the silver alloy wire and Al metallization pad. We propose that abnormal protrusions formation was observed at bond joints with electron flow from Al to Ag in samples due to flux divergence caused by the change in volume of ball bond. However, the surface morphology of bond joints with electron flow from Ag to Al and at isothermal condition did not change dramatically. The phenomena of dynamic recrystallization inside the wire can also be observed after current stressing. Again, dynamic recrystallization was more severe inside the wire adjacent to ball bonds when current flowed from Al to Ag. Moreover, different thickness of IMCs were observed at ball bonds with two different direction of electron flow. Meanwhile, the results of ANSYS simulation verified the current crowding effect might happen at the juncture of the ball bond and the heel of wedge bond on bump. The samples annealed at various time periods without current stressing showed the interfacial reaction between silver alloy wire and Al metallization is diffusion-controlled.

Content
摘要 I
Abstract III
致謝 V
List of Figures IX
List of Tables XIII
Chapter 1 Introduction 1
Chapter 2 Literature Review 4
2-1 Bonding process 4
2-1-1 Thermosonic ball and wedge bonding 5
2-1-2 Bond Stitch on Ball (BSOB) 7
2-1-3 Bond Pull Test (BPT) 9
2-2 Material issues & Phase Evolution of IMCs 12
2-2-1 Wire bonding material 12
2-2-2 Silver and Silver alloy wire 13
2-2-3 Ag-Al system 15
2-3 Electromigration (EM) 19
2-3-1 Electromigration in silver 19
2-3-2 Electromigration in wire bond 22
2-3-3 Joule Heating 26
2-3-4 Polarity effect 27
2-4 Motivation 29
Chapter 3 Experimental Details 30
3-1 Specimen Preparation 30
3-2 Bond Pull Test (BPT) 33
3-3 Electromigration Test 34
3-4 Joule Heating Test 37
3-5 Simulation 38
Chapter 4 Results 40
4-1 Bond Pull Test (BPT) 40
4.2 As-bonded 44
4-3 Joule Heating Measurement 46
4-4 EM Test of Resistance versus Time (RVT) curves 48
4-5 Morphology and Microstructure for group Ⅰ (concave-up type) 52
4-5-1 Morphology of bond joints for group Ⅰ 52
4-5-2 Microstructure of ball bonds for group Ⅰ 56
4-6 Morphology and Microstructure for group Ⅱ (concave-down type) 60
4-6-1 Morphology of bond joints for group Ⅱ 60
4-6-2 Microstructure of ball bonds for group Ⅱ 64
4-7 Morphology and Microstructure for sample F 68
4-8 Comparison of sample B at 150℃ and sample F at 175℃ under EM test 71
4-8-1 Comparison of morphology of ball bonds of sample B and sample F 71
4-8-2 Comparison of microstructure of wires of sample B and sample F 73
4-9 The growth of IMCs 77
4-10 Simulation 80
Chapter 5 Discussion 83
5-1 Polarity effect 83
5-1-1 Formation of protrusions after current stressing 83
5-1-2 Dynamic recrystallization 87
5-1-3 IMCs formation 89
5-2 RVT curves for group Ⅰ(concave-up) and group Ⅱ (concave-down) 93
5-3 Kinetics of IMCs at isothermal condition 95
Chapter 6 Conclusions 100
Reference 102
Appendix A 109
Appendix B 110

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