為了因應現在對電子產品多功能且高效能的要求，三維立體封裝被視為一項可用來突破莫爾定律的技術，然而在電子產品使用過程中，許多的電晶體同時運作，加上晶片堆疊的影響，使得產生大量的焦耳熱，為了排散這些廢熱，勢必會在模組建立一溫度梯度，由溫度梯度所導致的原子移動也就是熱遷移，將會成為一個很重要的議題。而鎳因為其在焊錫中擴散及反應較慢的關係，所以常被使用為金屬墊片的材料。在接合過程中鎳與錫反應會生成Ni3Sn4介金屬化合物以達到接合的效果，但介金屬化合物本質較脆，過多的介金屬化合物產生會降低材料的機械性質，因此了解熱遷移對介金屬化合物介面反應的影響便是一大重要課題。實驗中我們使用對稱的Ni/SnAg/Ni三明治結構來研究在熔融焊錫中鎳原子的擴散行為，以模擬元件對接時可能的介面反應，並以將試片與散熱鰭片放置在加熱板上進行回焊測試的方式，在熔融態焊錫內部建立一大小約為160 °C/cm的溫度梯度。實驗結果發現熱端介面反應被抑制，而冷端介面反應卻被加速，造成冷端生成的介金屬化合物厚度大於熱端，我們推測這異常的介面成長是因為在受溫度梯度的影響之下，鎳原子會傾向往冷端移動而導致。此外，我們也觀察到在熔融態焊錫中，冷、熱兩端介金屬化合物的生成速率皆呈現兩階段不同速率的現象，而從動力學角度分析，這是因為化學勢梯度與熱遷移驅動力互相競爭的關係。在反應初期第一階段，由於介金屬化合物厚度很薄的關係，化學勢梯度驅動力很大，所以冷、熱兩端介金屬化合物厚度皆隨時間增厚，而冷端反應較熱端更快。然而，在反應的第二階段，也就是經過120分鐘的回焊之後，冷端介金屬化合物成長速率減慢，熱端介金屬化合物的厚度會達到一平衡值不再成長，表示此時化學位能與熱遷移力達到動態平衡。最後根據熱遷移的通量公式，可以求得鎳在熔融焊錫中Q*值(Heat of Transport)為+0.76 kJ/mole。同時我們也得知在256.5度時，達動態平衡的臨界條件為熱端介金屬化合物厚度與銲錫內部溫度梯度的乘積要等於489.18 μm×°C/cm。而當達到動態平衡之後反應仍然持續進行並消耗金屬墊層，此時熱端金屬墊層消耗速率為0.134 μm/h。

To meet the demands of high performance and small feature sizes of electronic products, three-dimensional integrated circuit (3DIC) technology is proposed as a promising way to overcome Moore’s law. However, due to multiple transistors work at a same time and the effect of chips stacking, the joule heating will become a big concern. To remove heat, a temperature gradient must be established across the solder joint; therefore it is critical to understand thermomigration induced failure in Pb-free microbumps. Nickel, commonly used as under bump metallization (UBM) in electronic packaging, would react with solder to form Ni3Sn4 intermetallic compound (IMC) during the reflowing process. However, large amount of IMC may deteriorate the mechanical properties of solder. In this study we aim on understanding the interfacial reaction of Ni3Sn4 IMC under thermomigration in molten solder. To simulate the diffusion behavior of Ni atoms during device assembly, a temperature gradient of about 160 °C/cm was established by employing a heat sink and Ni/SnAg/Ni sandwich structures to investigate the interfacial reaction of IMC in molten-state micro-scale solders. The results show that the growth of IMC at hot end was hindered, whereas the growth of IMC at cold side was accelerated, which indicates that under a temperature gradient, Ni atoms tend to move from the hot side toward the cold side. In addition, we observed two-stage growth behavior of IMC under a temperature gradient in molten-state solders. The growth kinetic analysis suggests that the chemical potential gradient and thermomigration driving force compete with each other. At Stage I, the initial thickness of IMC is thin Therefore, the chemical potential gradient dominates the interfacial reaction and the Ni3Sn4 at both ends grow with test time. However, dynamic equilibrium is attained at hot end from Stage II, where the growth rate of IMC at the cold end slows down and the IMC thickness at hot end remains unchanged after 120 minutes of reflow. The molar heat of transport (Q*) of Ni in molten SnAg solder was calculated to be +0.76 kJ/mole. The critical product of ∂x(∂T/∂x) is 489.18 μm×°C/cm at 256.5 °C and the Ni interface moving velocity due to UBM consumption is calculated to be 0.134 μm/h at the hot end when dynamic equilibrium is achieved

Abstract I
摘要 III
致謝 V
Table of content VI
Table caption Page VIII
Figure Caption Page IX
1. Introduction 1
2. Literature review 4
2.1. Evolution of electronic packaging technology 4
2.2. Issues of 3D-IC packaging technology 8
2.3. Thermomigration 10
2.3.1. Theory of thermomigration 10
2.3.2. Joule heating induced temperature gradient in flip chip solder joint. 12
2.3.3. Thermomigration in lead free solder 15
2.3.4. Theromigration of UBM materials 20
2.4. Thermo-compression bonding 24
2.5. Motivation 25
3. Experimental details 27
3.1. Sample preparation 27
3.2. Thermomigration test setup and characterization 28
3.3. Finite element ANSYS simulation 29
4. Results 33
4.1. Simulation of Temperature distribution in Ni/SnAg/Ni sandwich structure 33
4.2. Microstructural evolution of Ni/SnAg/Ni specimen under a temperature gradient 35
4.3. Microstructural evolution of Ni/Sn/Ni specimen under isothermal aging 43
5. Discussion 56
5.1. The growth mechanism of Ni3Sn4 under a temperature gradient 56
5.2. Critical product 65
5.3. Calculation of Heat of transport (Q*) of Ni 66
6. Conclusions 73
References 75

1. L.J. Ladani, Numerical analysis of thermo-mechanical reliability of through silicon vias (TSVs) and solder interconnects in 3-dimensional integrated circuits. Microelectronic Engineering, 2010. 87(2): p. 208-215.
2. C. Chen, H.Y. Hsiao, Y. Chang, F.Y. Ouyang, K.N. Tu, Thermomigration in solder joints. Materials Science and Engineering: R: Reports, 2012. 73(9-10): p. 85-100.
3. H.Y. Chen, C.Chen, Thermomigration of Cu–Sn and Ni–Sn intermetallic compounds during electromigration in Pb-free SnAg solder joints. Journal of Materials Research, 2011. 26(8): p. 983.
4. A.T. Huang, A.M. Gusak, K.N. Tu, Y.S. Lai, Thermomigration in SnPb composite flip chip solder joints. Applied Physics Letters, 2006. 88(14): p. 1911.
5. K.N. Tu, Reliability challenges in 3D IC packaging technology. Microelectronics Reliability 2011. 51(3): p. 517-523.
6. A. Sharif, Y.C. Chan, Dissolution kinetics of BGA Sn–Pb and Sn–Ag solders
with Cu substrates during reflow. Materials Science and Engineering:B, 2004. 106(2): p. 126-131.
7. C.C. Chang, The effects of solder volume and Cu concentration on the consumption rate of Cu pad during reflow soldering. Journal of Alloys and Compounds, 2010. 492(1): p. 99-104.
8. J. Shen, Growth mechanism of Ni3Sn4 in a Sn/Ni liquid/solid interfacial reaction. Acta Materialia, 2009. 57(19): p. 5196-5206.
9. P.E. Tegehall, Review of the impact of intermetallic layers on the brittleness of tin-lead and lead-free solder joints IVF project report 06/07, IVF Industrial Research and Development Corporation, 2006.
10. D.R. Frear, Materials issues in area-array microelectronic packaging. Journal of the Minerals Metals & Materials Society, 1999. 51(3): p. 22-27.
11. C. Ludwig, S. Akad, W. Wien, Math.-Naturwiss, 1856. Kl.20: p. 539.
12. C. Soret, Arch. Sci. Phys. Nat., 1879. Geneve 3: p. 48.
13. P.G. Shewmon, The redistribution of a second phase during annealing in a temperature gradient. Trans. Met. Soc. AIME, 1958. 212: p. 642-7.
14. A. Sawatzky, The diffusion and solubility of hydrogen in the alpha phase of zircaloy-2. Journal of Nuclear Materials, 1960. 2(1): p. 62-68.
15. W. Roush, J. Jaspal, Proceedings of the Electron. Compon. 32nd Conference,San Diego, CA, 1982: p. 342.
16. F.Y. Ouyang, C.L. Kao, In situ observation of thermomigration of Sn atoms to the hot end of 96.5Sn-3Ag-0.5Cu flip chip solder joints. Journal of Applied Physics, 2011. 110(12): p. 3525.
17. X. Gu, Y.C. Chan, Thermomigration and electromigration in Sn58Bi solder joints. Journal of Applied Physics, 2009. 105(9): p. 3537.
18. F.Y. Ouyang, W.C. Jhu, T.C. Chang, Thermal-gradient induced abnormal Ni3Sn4 interfacial growth at cold side in Sn2.5Ag alloys for three-dimensional integrated circuits. Journal of Alloys and Compounds, 2013. 580: p. 114-119.
19. H.Y. Chen, C. Chen, K.N. Tu, Failure induced by thermomigration of interstitial Cu in Pb-free flip chip solder joints. Applied Physics Letters, 2008. 93(12): p. 2103.
20. M.Y. Guo, C.K. Lin, C. Chen, K.N. Tu, Asymmetrical growth of Cu6Sn5 intermetallic compounds due to rapid thermomigration of Cu in molten SnAg solder joints. Intermetallics, 2012. 29: p. 155-158.
21. Y.P. Su, F.Y. Ouyang, The growth of Ag3Sn intermetallic compound under a temperature gradient, in Electronics Packaging (ICEP). 2014. p. 634-639.
22. F.Y. Ouyang, K.N. Tu, Y.S. Lai, A.M. Gusak, Effect of entropy production on microstructure change in eutectic SnPb flip chip solder joints by thermomigration. Applied Physics Letters, 2006. 89(22): p. 1906.
23. H. Ye, C. Basaran, D. Hopkins, Thermomigration in Pb–Sn solder joints under joule heating during electric current stressing. Applied Physics Letters, 2003. 82: p. 1045-1047.
24. A.T. Huang, K.N. Tu, Y.S. Lai, Effect of the combination of electromigration and thermomigration on phase migration and partial melting in flip chip composite SnPb solder joints. Journal of Applied Physics, 2006. 100(3): p. 3512.
25. D. Yang, B.Y. Wu, Y.C. Chan, K.N. Tu, Microstructural evolution and atomic transport by thermomigration in eutectic tin-lead flip chip solder joints. Journal of Applied Physics Letters, 2007. 102(4): p. 3502.
26. H.Y. Hsiao, C. Chen, Thermomigration in Pb-free SnAg solder joint under alternating current stressing. Applied Physics Letters, 2009. 94(9): p. 2107.
27. F.Y. Ouyang, J.W. Cheng, Comparison of thermomigration behaviors between Pb-free flip chip solder joints and microbumps in three dimensional integrated circuits: Bump height effect. Journal of Applied Physics, 2013. 113(4): p. 3711
28. L. Ding, Y. Tao, Y. Wu, Thermomigration in Sn58Bi solder joints at low ambient temperature, in Electronics Packaging (ICEP). 2011. p. 944-948.
29. B.F. Dyson, T.R. Anthony, D. Turnbull, Interstitial diffusion of copper in tin. Journal of Applied Physics, 1967. 38(8): p. 3408-3409.
30. Y. Jeong, J. Choi, Y. Choi, N. Islam, Optimization of compression bonding processing temperature for fine pitch Cu-column flip chip devices. Electronic Components and Technology Conference (ECTC), 2014 IEEE 64th, 2014: p. 836-840.
31. M. Smalc, G. Shives, G. Chen, S. Guggari, J. Norley, R. A. Reynolds III, Thermal performance of natural graphite heat spreaders. presented at the ASME 2005 Pacific Rim Technical Conference and Exhibition on Integration and Packaging Conference , San Francisco, California USA, 2005.
32. http://www.efunda.com/materials/elements/TC_Table.cfm?Element_ID=Si.
33. http://www.efunda.com/materials/elements/TC_Table.cfm?Element_ID=Ni.
34. H. P. R. Frederikse, R.J. Fields, A. Feldman, Thermal and electrical properties of copper‐tin and nickel‐tin intermetallics. Journal of Applied Physics, 1992. 72(7): p. 2879
35. M. Abtewa, G. Selvaduray, Lead-free solders in microelectronics. Materials Science and Engineering: R: Reports, 2000. 27: p. 65-141.
36. M.O. Alam, Y.C. Chan, Solid-state growth kinetics of Ni3Sn4 at the Sn–3.5Ag solder∕Ni interface. Journal of Applied Physics, 2005. 98(12): p. 3527.
37. K.N. Tu, A.M. Gusak, Kinetics in nanoscale materials. 2014.
38. M.Y. Kuo, C. Chen, Study of thermomigration of Cu and Ni in molten SnAg microbumps. 2012, National Chiao Tung University
39. K. Masui, M. Kajihara, Influence of Pd on kinetics of solid-state reactive diffusion between Sn and Ni. Journal of Alloys and Compounds, 2009. 485: p. 144-149.
40. D.C. Yeh, H.B. Huntington, Extreme fast-diffusion system: nickel in single-crystal tin. Physical Review Letters, 1984. 53: p. 1469.
41. H.Y. Hsiao, C. Chen, Thermomigration in flip-chip SnPb solder joints under alternating current stressing. Applied Physics Letters, 2007. 90(15): p. 2105.
42. Y.C. Chuang, C.Y. Liu., The effect of thermomigration on phase coarsening in a eutectic SnPb alloy. Journal of Electronic Materials, 2007. 36: p. 1495-1500.