打線接合製程中銅線有著取代金線的潛力，本研究以15μm級微細銅導線打線接合後，對拉伸斷線特性進行調查，並藉nano-indentation測試結球後硬度分布以探討組織變化之間關係；對15μm線而言，結球後奈米硬度為1.2~1.45GPa。考慮實際應用，實驗採用退火線材，組織特徵為等軸晶。實驗結果顯示，放電結球後組織可區分為：1.球部(柱狀晶組織) 2.熱影響區(粗大化等徑晶) 3.退火區(等軸晶組織)。雖然結球前後線材降伏強度變化不明顯，但是結球後抗拉強度則是整體略微下降，強度變動幅度增大；特別是結球後線材的延伸率大幅劣化。
由於結球後有一熱影響區域且強度較低，不論在結球後拉伸測試或是接合後拉伸測試，實驗結果皆確認此為銅線斷線位置。接合後拉伸斷裂的位置集中在熱影響區100μm以內，為容易滑移的等徑晶和粗大等軸晶組織。值得注意的是在靠近頸縮的附近，遠離頸部的斷裂可觀察到退火雙晶的存在；靠近頸部的斷裂則是緊鄰球部柱狀晶。
本研究亦針對鍍鋁基板和鍍金基板進行打線接合。在未熱處理前，金基板和500nm鋁基板皆能達到良好鍵结，但是200nm鋁基板部份試片因為鋁膜的破裂，在拉力測試後出現界面斷裂。金膜與500nm鋁膜基板，接合試片在經過175℃熱處理24hr、72hr後，亦未看出接合強度的下降，同樣能維持良好接合品質。此結果也顯示，當銅線線徑減少到15μm，接合過程對基板造成的下壓力較小，所需的鋁膜能夠減少到500nm。

Copper wire is getting well accepted as a reliable design alternative to the gold wire in the wire bonding process. In this study, 15μm copper wires are bonded to substrates by thermosonic process, and the tensile fracture characteristics of FAB samples and bonded samples are investigated. On the other hand, the relationships between hardness and microstructure after EFO process are also studied with nano-indentation. It is reported that the nano-hardness of 15μm wire is 1.2~1.45GPa.
Considering practical applications, the 15μm wires we use are all fully annealed, and its microstructures are mainly equiaxed grains. After EFO process, the wire microstructure can be divided into three parts: (1) FAB with columnar grains (2) HAZ with coarse equal-diameter grains (3) annealing zone with equiaxed grains. Besides, according to tensile test, it shows a reduction of UTS, and elongation decreases extremely. Also, EFO process causes the distribution of tensile data show a larger range.
Because of lower strength, HAZ is the position of fracture in tensile test for FAB samples and bonded samples. After bonding, tensile fracture took place at equal–diameter grains and coarse grains within 100μm HAZ away from bonds. The experiments show that necking is near a twin when fracture is far from bonds, or near columnar grains when fracture is close to bonds.
In this study, the 15μm copper wires are bonded to aluminum pad and Gold pad. Before isothermal ageing, it is discovered that the bonded samples for 200nm Al pad have poor pull strength with metal lift. After isothermal ageing at 175℃ for 24hrs and 72hrs, it is shown that bonds for Au pad and 500nm Al pad still have good bondability. This result suggests that the thickness of Al pad can be reduce to 500nm for 15μm copper wires.

1. Herman, “Wire Bonding in Microelectronics Materials, Processes, Reliability, and Yield, 2nd ed.”, McGraw-Hill (1997), pp1-10.
2. 陳博彥，「微細銅導線放電結球特性與打線接合強度要因探討」，國立成功大學材料科學與工程研究所碩士論文，民國九十七年。
3. Klaus Dieter Lang, George G. Harman, Martin Schneider Ramelow, “Modern Wire Bonding Technologies – Ready for The Challenges of Future Microelectronic Packaging”, www.izm.fraunhofer.de (2004).
4. Petar Ratchev, Serguei Stoukatch, Bart Swinnen, “Mechanical Reliability of Au and Cu Wire Bonds to Al, Ni/Au and Ni/Pd/Au Capped Cu Bond Pads”, Microelectronics Reliability 46 (2006), pp1315–1325.
5. Ivy Wei Qin, “Wire Bonding Tutorial -Advances in Bonding Technology ”, Advanced Packaging (July, 2005).
6. 陳昭亮，張昫揚，「密集角距封裝之金線結球參數分析研究」，興大工程學刊，第十二卷，第二期（民國九十年），127-141頁。
7. 王元亭，「放電結球細微銅導線抗拉強度之韋伯解析研究」，國立成功大學材料科學與工程研究所碩士論文，民國九十四年。
8. 李志中，「線上熱處理銅導線經放電結球前後之微觀組織及拉伸性質探討」，國立成功大學材料科學與工程研究所碩士論文，民國九十五年。
9. H.A. Mohamed, J. Washburn, “Mechanism of Solid State Pressure Welding”, Welding Journal, Vol. 54 (Sep. 1975), pp302-310.
10. K.C. Joshi, “The Formation of Ultrasonic Bonds Between Metals”, Welding Journal, Vol. 50 (Dec. 1971), pp840-848.
11. B. Langenecker, “Effects of Ultrasound on Deformation Characteristics of Metals”, IEEE Transactions of Sonics and Ultrasonics, Vol. SU-13, No. 1 (March 1966), pp1-8.
12. H. Saiki, Y. Marumo, H. Nishitake, T. Uemura, T. Yotsumoto, “Deformation Analysis of Au Wire Bonding”, Journal of Material Processing Technology, Vol. 177 (2006), pp709-712.
13. N. Srikanth, J. Premkumar, M. Sivakumar, Y.M. Wong, C.J. Vath, “Effect of Wire Purity on Copper Wire Bonding”, Electronics Packaging Technology Conference (2007), pp755 – 759.
14. S. Murali, N. Srinkanth, C.J. Vath III, “Effect of Wire Size on The Formation of Intermetallics and Kirkendall Voids on Thermal Aging of Thermosonic Wire Bonds”, Materials Letters, Vol. 58 (2004), pp3096- 3101.
15. J.H. Westbrook, R.L. Fleischer, “Intermetallic Compounds Vol.1”, Wiley(2000), pp91-125, 227-275
16. S. Murali, N. Srikanth, C.J. Vath III, “An analysis of Intermetallics Formation of Gold and Copper Ball Bonding on Thermal Aging”, Materials Research Bulletin, Vol. 38 (2003), pp637-646.
17. S. Murali, “Formation and Growth of Intermetallics in Thermosonic Wire Bonds:Significance of Vacancy–Solute Binding Energy”, Journal of Alloys and Compounds, Vol. 426 (2006), pp200–204.
18. C.W. Tan, D. Abdul Razak, “Mechanical and Electrical Properties of Au-Al and Cu-Al Intermetallics Layer at Wire Bonding Interface”, Journal of Electronic Packaging, Vol. 125 (Dec. 2003), pp617-620.
19. C.J. Hang, C.Q. Wang, M. Mayer, Y.H. Tian, Y. Zhou, H.H. Wang, “Growth Behavior of Cu/Al Intermetallic Compounds and Cracks in Copper Ball Bonds During Isothermal Aging”, Microelectronics Reliability, Vol. 48, pp416-424.
20. I.M. Cohen, L.J. Huang, P.S Ayyaswamy, “Melting and Solidification of Thin Wires: A Class of Phase-Change Problems with A Mobile Interface – II. Experimental Confirmation”, International Journal of Heat and Mass Transfer, Vol. 38, No. 9 (1995), pp1647-1659.
21. N. Srikanth, S. Murali, Y.M. Wong, Charles J. Vath III, "Critical Study of Thermosonic Copper Ball Bonding", Thin Solid Films, Vol. 462 (2004), pp339– 345.
22. Y. Ohno, Y. Ohzeki, T. Aso, O. Kitamura, “Factors Governing the Loop Profile in Au Bonding Wire”, Electronic Components and Technology Conference, 1992. Proceedings, 42nd (1992), pp899-902.
23. 林宜璋，「不同退火條件之銅導線經放電結球前後之機械性質與織構分析」，國立成功大學材料科學與工程研究所碩士論文，民國九十六年。
24. T. Baudin, A.L. Etter, R. Penelle, “Annealing Twin Formation and Recrystallization Study of Cold-drawn Copper Wires from EBSD Measurements”, Materials Characterization 58 (2007), pp947-952.
25. G.Y. Chin, W.L. Mammel, “Computer Solutions of Taylor Analysis for Axisymmetric Flow”, Transactions of the Metallurgical Society of Aime, Vol. 239 (1967), pp1400.
26. G. Khatibi, R. Stickler, V. Gröger, B. Weiss, “Tensile Properties of Thin Cu-wires with a Bamboo Microstructure”, Journal of Alloys and Compounds, Vol. 378 (2004) , pp326–328
27. G. G. Zhang, X. F. Ang, Z. Chen, C. C. Wong, “Critical Temperatures in Thermocompression Gold Stud Bonding”, Journal of Applied Physics, Vol. 102, No. 063519 (2007).
28. Narendra J. Noolu, Ivan Lum, Y. (Norman) Zhou, “Roughness Enhanced Au Ball Bonding of Cu Substrates”, IEEE Transactions on Components and Packaging Technologies, Vol. 29, No. 3 (SEPTEMBER 2006).
29. Mohd Rusli Ibrahim Yong Cheng Choi, Larry Lim, Jiang Lu, Low Teck Poh, “The Challenges of Fine Pitch Copper Wire Bonding in BGA Packages”, IEEMT 2006, Putrajaya, Malaysia.