本研究係探討錫銀銅覆晶接合銲錫隆點，於通電條件之下，電遷移及熱致遷移對銲錫隆點結構產生之影響。本實驗每一測試組件中共有三個銲錫隆點，其中二個銲錫隆點進行通電實驗，電子流方向相反，另外一個銲錫隆點沒有電流通過，以為實驗對照組，藉由比較通電流與未通電流的銲錫隆點，進而了解電子與熱在通電過程中對於原子移動的影響。進行通電實驗的條件是在環境溫度120oC、電流密度1.2x104A/cm2下，於不同通電時間將試片取出，利用電子顯微鏡(SEM)觀察微組織變化，以及藉由X-ray能量分佈光譜儀(EDX)分析其組成成份。

　　通電過程中，電遷移效應(electromigration)與熱致遷移效應(thermomigration)同時發生，但是實驗結果顯示原子之移動由熱致遷移效應所主導，無論電子流的方向為何，甚至沒有電子流通過銲錫隆點，銲錫之組成原子皆往較低溫之基板端(substrate)遷移，於鋁導線/底層金屬（under bump metal，UBM）附近處，亦即陽極端產生孔洞(Void)。

　　熱致遷移效應導致錫原子往基板端(冷)遷移，於鋁導線/UBM附近處形成孔洞以及凹陷區域，於基板端附近形成幾乎純錫的突起物(hillock)，鋁原子被驅使往基板端(冷)遷移，導致於鋁導線產生大量裂縫(crack)，電遷移效應造成基板端無電鍍Ni-P層的消秏；電遷移效應抑制銲錫隆點/UBM(Cu/Ni-P/Au)間Cu-Ni-Au-Sn介金屬化合物(IMC)的成長；熱致遷移效應則促進IMC的成長。

　　為了說明散熱之重要性，本研究在一冷卻條件(-5°C)進行電遷移實驗，結果發現在此冷卻條件(-5°C)下有效抑制缺陷之生成，由此進一步說明適當散熱降低質量遷移效應(mass transfer)。

　The present work investigated the behaviors of electromigration and thermomigration in the Sn-3.0Ag-0.5Cu Pb-free flip chip solder bumps at 120°C by applying a three-bump set therein the electrical current flows in different directions. The third bump mainly experienced heat transfer from the Al trace without current flowing for comparison. The solder bumps were examined at specified period of current stressing using SEM (Scanning Electron Microscope) and EDX (Energy Dispersive X-ray Spectroscopy).

　Voids formed on the Al trace/ solder interface regardless of the direction of electron flow. Voids also formed at the interface even though the current flowed along the Al trace. Thermomigration overwhelms electromigration and results in mass diffusion when counter flow of electron and thermal gradient exists. The thermal gradient throughout the bump drives the mass transfer of Sn and Al. Thermomigration results in the formation of voids on the Al trace/ solder interface and the accumulation of Sn on the substrate side. Due to the migration of Al through the IMC layer into the solder bump, the cracks are formed at the Al trace.

　The electrical current resulted in the consumption of Ni in some local areas. The formation of intermetallic compound at the substrate side (metallized with Cu/Ni-P/Au) was suppressed when the electron flow and thermal gradient were in the opposite direction. On the other hand, the solder mass was forced to migrate to the substrate when the current flowed toward the substrate or along the Al trace.

　In order to illustrate the importance of heat dissipation, a set of joints was stressed with current at an environmental temperature of –5oC. The comparison between the as produced bump and current stressed bump indicated that no visible defect exists either at the cathode or at the anode even after 600 hours. These observations further emphasized the significance of heat dissipation in reducing the migration defect.

1. C. Y. Liu, Chih Chen, C. N. Liao, and K. N. Tu, “Microstructure- Electromigration Correlation in a Thin Stripe of Eutectic SnPb Solder Stressed between Cu Electrodes”, Applied Physics Letters, Vol. 75, No. 1, 1999, pp. 58〜60.
2. C. Y. Liu, Chih Chen, and K. N. Tu, “Electromigration in Sn-Pb Solder Strips as a Function of Alloy Composition”, Journal of Applied Physics, Vol. 88, No. 10, 2000, pp. 5703〜5709.
3. Q. T. Huynh, C. Y. Liu, Chih Chen, and K. N. Tu, “Electromigration in Eutectic SnPb Solder Lines”, Journal of Applied Physics, Vol. 89, No. 8, 2001, pp. 4332〜4335.
4. T. Y. Lee and K. N. Tu, “Electromigration of Eutectic SnPb Solder Interconnects for Flip Chip Technology”, Journal of Applied Physics, Vol. 89, No. 6, 2001, pp. 3189〜3194.
5. T. Y. Lee and K. N. Tu, “Electromigration of Eutectic SnPb and Sn3.8Ag0.7Cu Flip Chip Solder Bumps and Under-Bump Metallization”, Journal of Applied Physics, Vol. 90, No. 9, 2001, pp. 4502〜4508.
6. H. Ye, C. Basaran, and D. Hopkins, “Thermomigration in Sn-Pb Solder Joints Under Joule Heating During Electric Current Stressing”, Applied Physics Letters, Vol. 82, No. 7, 2003, pp. 1045〜1047.
7. V. B. Fiks, “On the Mechanism of the Ions in Metals”, Soviet Physics-Solid State, Vol. 1, 1959, pp. 14〜28.
8. H. B. Huntington and A. R. Grone, “Current-Induced Marker Motion in Gold Wires”, Journal of Physics and Chemistry of Solids, Vol. 20, No. 1, 1961, pp. 76〜87.
9. A. R. Grone, “Current-Induced Marker Motion in Copper”, Journal of Physics and Chemistry of Solids, Vol. 20, No. 1, 1961, pp. 88〜93.
10. C. Bosvieux and J. Friedel, “Sur L’Electrolyse Des Alliages Metalliques”, Journal of Physics and Chemistry of Solids, Vol. 23, 1962, pp. 123〜136.
11. R. V. Penney, “Current-Induced Mass Tranaport in Aluminum”, Journal of Physics and Chemistry of Solids, Vol.25, 1964, pp. 335〜345.
12. K. A. Koh and S. J. Chua, “Electromigration in Aluminum/Silicon/Copper Metallization due to the Presence of a Thin Oxide Layer ”, Journal of Electronic Materials, Vol. 26, No. 9, 1997, pp. 1070〜0175.
13. W. C. Shih and A. L. Greer, “Transmission Electron Microscopy of Al-Cu Interconnects during In-Situ Electromigration Testing”, Thin Solids Films, Vol. 292, 1997, pp. 103〜117.
14. X. Y. Liu, C. L. Liu, and L. J. Borucki, “A New Investigation of Copper’s Role in Enhancing Al-Cu Interconnect Electromigration Resistance from an Atomistic View”, Acta materialia, Vol. 47, No.11, 1999, pp. 3227〜3231.
15. H. W. Wanh, B. S. Chiou, and J. S. Jiang, “Electromigratio in Sputtered Copper Films on Polyimide”, Journal of Materials Science : Maerials in Electronics, Vol. 10, 1999, pp. 267〜271.
16. H. B. Huntington, “Diffusion in Solids : Recent Developments”, edited by A. S. Nowick and J. J. Burton, Academic Press, New York, 1975, pp. 303〜352.
17. R. S. Sorbello, “A Pseudopotential Based Theory of the Driving Forces for Electromigration in Metals”, Journal of Physics and Chemistry of Solids, Vol. 34, 1973, pp. 937〜950.
18. Y. H. Lin, C. M. Tsai, Y. C. Hu, Y. L. Lin, and C. R. Kao, “Electromigration-Induced Failure in Flip-Chip Solder Joints”, Journal of Electronic Materials, Vol. 34, No. 1, 2005, pp. 27〜33.
19. H. B. Huntington, C. K. Hu, and S. N. Mei, “Diffusion in Solids : Recent Developments”, edited by M. A. Dayanada and G. E. Murch, TMS, Warrendale, PA, 1984, pp. 301〜348.
20. P. S. Ho and T. Kwok, “Electromigration in Metals”, Reports on Progress in Physics, Vol. 52, No. 3, 1989, pp. 301〜348.
21. S. Y. Kang, P. M. Williams, T. S. Mclaren, and Y. C. Lee, “Studies of Thermosonic Bonding for Flip-chip Assembly”, Materials Chemistry and Physics, Vol. 42, No. 1, 1995, pp. 31〜37.
22. A. Schubert, R. Dudek, H. Walter, E. Jung, A. Golhardt, B. Michel, and H. Reichl, “Reliability Assessment of Flip-Chip Assemblies with Lead-free Solder Joints”, Proceedings-Electronic Components and Technology Conference, 2002, pp. 1246〜1255.
23. J. Baliga, “Flip-Chip Packaging: Prepare For the Ramp-up”, Semiconductor International, Vol. 21, No. 3, 1998, pp. 87.
24. J. H. Lau, Flip Chip Technologies, McGraw-Hill, New York. USA, 1996, Chapter 3
25. J. H. Lau, Flip Chip Technologies, McGraw-Hill, New York. USA, 1996, Chapter 15
26. J. H. Lau, Flip Chip Technologies, McGraw-Hill, New York. USA, 1996, Chapter 6
27. J. H. Lau, Flip Chip Technologies, McGraw-Hill, New York. USA, 1996, Chapter 9
28. J. H. Lau, Flip Chip Technologies, McGraw-Hill, New York. USA, 1996, Chapter 1
29. M. Pecht, Integrated Circuit, Hybrid, and Multichip Module Package Design Guidelines, John Wiley & Sons, New York, USA, 1994, Chapter 7
30. K. L. Lin and Y. T. Liu, “Manufacturing of Solder Bumps with Cu/Ta/Cu as under Bump Metallurgy”, IEEE Transactions on Advanced Packaging, Vol. 22, No. 4, 1999, pp. 580〜585.
31. C. J. Chen and K. L. Lin, “Electroless Ni-Cu-P Barrier between Si/Ti/Al Pad and Sn-Pb Flip-Chip Solder Bumps”, IEEE Transactions on Components and Packaging Technologies, Vol. 24, No. 4, 2001, pp. 691〜697.
32. K. L. Lin, Y. L. Chang, C. C. Huang, F. I. Li, and J. C. Hsu, “Microstructure Evolution of Electroless Ni-P and Ni-Cu-P Deposits on Cu in the Presence of Additives”, Applied Surface Science, Vol. 181, No. 1, 2001, pp. 166〜172.
33. K. L. Lin and Y. C. Liu, “Manufacturing of Cu/Electroless Nickel/Sn-Pb Flip Chip Solder Bumps”, IEEE Transactions on Advanced Packaging, Vol. 22, No. 4, 1999, pp. 575〜579.
34. H. A. Sorkhabi, H. Dolati, N. P. Ahmadi, and J. Manzoori, “Electroless Deposition of Ni-Cu-P Alloy and Study of the Influences of Some Parameters on the Properties of Deposits”, Applied Surface Science, Vol. 185, No. 3, 2002, pp. 155〜160.
35. J. H. Lau, Chip on Board Technologies for Multichip Modules, Van Nostrand Reinhold, New York, USA, 1994, Chap. 5
36. T. B. Massalski, Binary Alloy Phase Diagrams, William W. Scott, Vol. 1, 1986, pp. 964〜965.
37. K. N. Tu and R. D. Thompson, “Kinetics of Interfacial Reaction in Bimetallic Cu-Sn Thin Films”, Acta Matallurgica, Vol. 30, No. 5, 1982, pp. 947〜952.
38. R. A. Gaqliano and M. E. Fine, “Thickening Kinetics of Interfacial Cu6Sn5 and Cu3Sn Layers during Reaction of Liquid Tin with Solid Copper”, Journal of Electronic Materials, Vol. 32, No. 12, 2003, pp. 1441〜1447.
39. L. H. Su, Y. W. Yen, C. C. Lin, and S. W. Chen, “Interfacial Reactions in Molten Sn/Cu and Molten In/Cu couples”, Matallurgical and Materials Transactions B, Vol. 28B, No. 5, 1997, pp. 927〜934.
40. S. Bader, W. Gust, and H. Hieber, “Rapid Formation of Intermetallic Compounds by Inter Diffusion in the Cu-Sn and Ni-Sn systems”, Acta Matallurgica, Vol. 43, No. 1, 1995, pp. 329〜337.
41. F. Bartels, J. W. Morris, Jr., G. Dalke, and W. Gust, “Intermetallic Phase Formation in Thin Solid-Liquid Diffusion Couples”, Journal of Electronic Materials, Vol. 23, No. 8, 1994, pp. 787〜790.
42. T. B. Massalski, Binary Alloy Phase Diagrams, William W. Scott, Vol. 1, 1986, pp. 1757〜1759.
43. J. Haimovich, “Intermetallic Compound Growth in Tin and Tin-Lead Platings over Nickel and Its effects on Solderability”, Welding Journal, Vol. 68, No. 3, 1989, pp. s102〜s111.
44. W. J. Tomlinson and H. G. Rhodes, “Kinetics of Intermetallic Compound Growth between Nickel, Electroless Ni-P and Tin at 453 to 493K”, Journal of Materials Science, Vol. 22, No. 5, 1987, pp. 1769〜1772.
45. S. J. Wang and C. Y. Liu, “Study of Interaction between Cu-Sn and Ni-Sn Interfacial Reactions by Ni-Sn3.5Ag-Cu Sandwich Structure”, Journal of Electronic Materials, Vol. 32, No. 11, 2003, pp. 1303〜1309.
46. S. Kim and D. C. Johnson, “Control of Ni-Sn interfacial reactions through reactant design”, Journal of Alloys and Compounds, Vol. 392, No. 1, 2005, pp. 105〜111.
47. J. Y. Park, C. W. Yang, J. S. Ha, C. U. Kim, E. J. Kwon, S. B. Jung, and C. S. Kang, “Investigation of Interfacial Reaction between Sn-Ag Eutectic Solder and Al/Ni/Cu/Ti Thin Film Metallization”, Journal of Electronic Materials, Vol. 30, No. 9, 2001, pp. 1165〜1170.
48. H. F. Hsu and S. W. Chen, “Phase Equilibria of the Sn-Ag-Ni Ternary System and Interfacial Reactions at the Sn-Ag/Ni Joints”, Acta Materialia, Vol. 52, No. 9, 2004, pp. 2541〜2547.
49. C. H. Wang and S. W. Chen, “Isothermal Section of The Ternary Sn-Cu-Ni System and Interfacial Reactions In The Sn-Cu/Ni Couples at 800°C”, Metallurgical and Materials Transactions A, Vol. 34, No. 10, 2003, pp. 2281〜2287.
50. C. H. Lin, C. H. Wang and S. W. Chen, “Phase Equilibria and Solidification Properties of Sn-Cu-Ni Alloys”, Journal of Electronic Materials, Vol. 31, No. 9, 2002, pp. 907〜915.
51. D. R. Frear, J. W. Jang, J. K. Lin, and C. Zhang, “Pb-Free Solders for Flip-Chip Interconnects”, Journal of Metals, Vol. 53, No. 6, 2001, pp. 28〜32.
52. L. H. Su, Y. W. Yen, C. C. Lin, and S. W. Chen, “Interfacial Reaction in Molten Sn/Cu and Molten In/Cu Couples”, Matallurgical and
Materials Transactions B, Vol. 28, No. 5, 1997, pp.927〜934.
53. J. W. Yoon and S. B. Jung, “Interfacial Reactions between Sn-0.4Cu Solder and Cu Substrate during Reflow Reaction”, Journal of Alloys and Compounds, Vol. 396, No. 1, 2005, pp. 122〜127.
54. M. Y. Hsieh and H. B. Huntington, “Electromigration of Copper in Lead”, Journal of Physics and Chemistry of Solids, Vol. 39, No. 8, 1978, pp. 867〜871.
55. D. A. Golopentia and H. B. Huntington, “A Study of Electromigration of Nickel in Lead”, Jorunal of Physics and Chemistry of Solid, Vol. 39, No. 9, 1978, pp. 975〜984.
56. D. C. Yeh and H. B. Huntington, “Extreme Fast-Diffusion System : Nickel in Single-Crystal Tin”, Physical Review Letters, Vol. 53, No.15, 1984, pp. 1469〜1472.
57. J. Shi and H. B. Huntington, “Electromigration of Gold and Silver in Single Crystal Tin”, Journal of Physics and Chemistry of Solids, Vol. 48, No.8, 1987, pp. 693〜696.
58. Everett C. C. Yeh, W. J. Choi, and K. N. Tu, “Current- Crowding-Induced Electromigration Failure in Flip Chip Solder Joints”, Applied Physics Letters, Vol. 80, No. 4, 2002, pp. 580〜582.
59. Hua Ye, Cemal Basaran, Douglas C, Hopkins, “Mechanical Degradation of Microelectronics Solder Joints under Current Stressing”, International Journal of Solids and Structures, Vol. 40, No. 26, 2003, pp. 7269〜7284.
60. S. K. Kang, W. K. Choi, M. J. Yim, and D. Y. Shih, “Studies of the Mechanical and Electrical Properties of Lead-free Solder Joints”, Journal of Electronic Materials, Vol. 31, No. 11, 2002, pp. 1292〜1303.
61. H. P. R. Frederikse, R. J. Fields, and A. Feldman, “Thermal and Electrical Properties of Copper-Tin and Nickel-Tin Intermetallics”, Journal of Apply Physics, Vol. 72, No. 7, 1992, pp. 2879〜2882.
62. J. Y. Park, C. W. Yang, J. S. Ha, C. U. Kim, E. J. Kwon, S. B. Jung, and C. S. Kang, “Investigation of Interfacial Reaction between Sn-Ag Eutectic Solder and Au/Ni/Cu/Ti Thin Film Metallization”, Journal of Electronic Materials, Vol. 30, No. 9, 2001, pp. 1165〜1170.
63. D. S. Liu, and C. Y. Ni, “A Study on the Electrical Resistance of Solder Joint Interconnections”, Microelectronic Engineering, Vol. 63, No. 4, 2002, pp. 363〜372.
64. J. K. Lin, D. S. Ananda, F. Darrel, G. Yifan, H. Scott, J. W. Jang, L. Lin, M. Dianne, Y. Betty, and Z. Charles, “Characterization of Lead-free Solders and under Bump Metallurgies for Flip-chip Package”, IEEE Transactions on Electronics Packaging Manufacturing, Vol. 25, No. 4, 2002, pp. 300〜307.
65. D. J. Xie, “A New Experimental Method to Evaluate Creep Fatigue Life of Flip-Chip Solder Joints with Underfill”, Microelectronics Reliability, Vol. 40, No. 7, 2000, pp. 1191〜1198.
66. K. D. Kim and D. D. L. Chung, “Effect of Heating on the Electrical Resistivity of Conductive Adhesive and Soldered Joints”, Journal of Electronic Materials, Vol. 31, No. 9, 2002, pp. 933〜939.
67. Z. Tang, and F. G. Shi, “Effect of Preexisting Voids on Electromigration Failure of Flip Chip Solder Bumps”, Microeletronics Journal, Vol. 32, No. 7, 2001, pp. 605〜613.
68. R. V. Gestel, K. D. Zeeuw, L. V. Gemert, and E. Bagerman, “Comparison of Delamination Effects between Temperature Cycling Test and Highly Accelerated Stress Test in Plastic Packaged Devices”, Reliability Physics Symposium 30st Annual Proceedings, International, 1992, pp. 177〜181.
69. P. T. Vianco, K. L. Erickson, and P.L. Hopkins, “Solid State Intermetallic Compound Growth Between Copper and High Temperature, Tin-rich Solders”, Journal of Electronic Materials, Vol. 23, No. 8, 1994, pp. 721〜727.
70. G. Petzow and G. Effenberg, Ternary Alloys, VCH, Vol. 1, 1988, pp. 77.
71. T. B. Massalski, Binary Alloy Phase Diagrams, William W. Scott, Vol. 1, 1986, pp. 168.