電子產品尺寸微小化使得銲點在通電狀態極有可能面臨熔融失效；此外，為了因應無鉛化需求，開發耐電流負荷的無鉛銲料乃成為急需著手的目標。為了調查電子產品的銲料在高電流密度場合的表現，本研究的實驗試料皆以Sn為基底，主要探討純Sn、Sn基共晶合金(Sn-9Zn、Sn-3.5Ag、Sn-3Ag-0.5Cu、Sn-0.7Cu和Sn-37Pb)以及不同組成二元Sn-xZn ( x = 7, 9, 20, 30, 40, 50, 60, 70, 80, 90, 100 wt.%)系合金之通電誘發組織變化與熔融破壞機制的關係。
純Sn通電誘發的初始熔融軌的確切位置難以斷定是在晶界處或晶粒內部。基於電流密度和熱兩者分佈不均質的關係，使得純Sn熔融軌跡彼此連結構成更大範圍的網狀熔融路徑，以高角度方式穿越晶界，進一步持續側向擴張形成廣闊分佈的熔融區進而導致熔斷破壞。另一方面，純Sn透過加熱方式誘發熔融現象亦為網狀熔融路徑。
各Sn基共晶合金通電誘發熔融行為的共通性為熔融區起始於共晶相，再延伸到初晶相(-Sn)進而使彼此熔融區互相連結導致熔斷破壞。然而，共晶相熔解溫度(Teutectic)以及共晶相體積率對於臨界熔斷電流密度(CFCD)的影響程度似乎不如其他因素如每單位共晶相體積熔解所需要的潛熱值(△H+→L)、導電度以及散熱程度(或導熱度)。另外，Sn-9Zn絕大部分電、熱性質優於其他Sn基共晶合金，其中以Sn-37Pb皆為最低。另一方面，初晶富Zn相於通電過程中未發生熔融現象。通電熔斷實驗結果顯示，各Sn基共晶合金之CFCD值依序為Sn-9Zn > Sn-3.5Ag > Sn-0.7Cu > Sn-3Ag-0.5Cu > Sn-37Pb。因此，以Sn-9Zn共晶銲料最有可能應用在高電流密度場合。
各Sn基共晶合金的熔融特徵並非如同純Sn大範圍的網狀熔融路徑。此外，相較於純Sn，各Sn基共晶合金個別相具有不同的電、熱性質和體積率，使得熔融區的連結形式更具多樣性進而使熔融區較不易連結。因此，大部分的Sn基共晶合金(Sn-37Pb除外)的CFCD值皆高於純Sn。
進一步調查二元Sn-xZn合金在通電熔融實驗的線性相關統計顯示，CFCD值與導電度、△Hf以及Sn/Zn共晶相體積率皆有良好的相關性。通電過程中，初晶富Zn相並未發生熔融現象，此外主導Sn-xZn合金之通電熔融特性絕大部份取決於Sn/Zn共晶相。當Zn含量從7 wt.% (亞共晶組成)添加到9 wt.% (共晶組成)，樹枝狀-Sn初晶相逐漸減少並轉而由富Zn相晶出。由於初晶-Sn亦為熔融相，使得Sn-9Zn合金之CFCD大於Sn-7Zn。當Zn含量從9 wt.%添加到30、70 wt.% (過共晶組成)以及100 wt.% (純Zn)，欲使愈高Zn含量試料發生熔斷，仰賴Sn/Zn共晶相熔融區的連結路徑可能因富Zn相不發生熔融而受到阻礙，因此二元Sn-xZn系合金之CFCD是隨Zn含量增加而提升。

Microminiaturization of electronic products may lead solder joints to fusion failure during the electrification. Additionally, developing current-resistant lead-free solders is imperative for lead-free issues. In order to investigate how solders act in high-current densty occasions, Sn-based test specimens were used for this research, and it mainly investigated the relationship between electrification-induced microstructural change and electrification-fusion mechanism for pure Sn, Sn-based eutectic alloys (Sn-9Zn, Sn-3.5Ag, Sn-0.7Cu, Sn-3Ag-0.5Cu and Sn-37Pb) and Sn-xZn alloys (x = 7, 9, 20, 30, 40, 50, 60, 70, 80, 90, 100 wt.%).
It is difficult to confirm that whether the electrification-induced initial fusion trace of pure Sn emerges from grain boundary or grain interior. Due to the non-uniform electrical and thermal distribution, fusion traces of pure Sn are interconnected to form larger network-like fusion paths and tend to intersect the grain boundaries in a high-angle manner. Further fusion fracture will happen by sideward spreading of the fusion paths. On the other hand, the heating-induced fusion phenomenon of pure Sn also belongs to network-like fusion paths.
The commomality of electrification-induced fusion behavior in Sn-based eutectic alloys: The fusion region initially emerges from the eutectic phase, extends to the primary phase (-Sn), and then the mutual fusion regions will further interconnect and cause fusion fracture. However, volume fraction of eutectic phase and eutectic temperature (Teutectic) seems to have less effect on critical fusion current density (CFCD) than the fusion latent heat per unit of eutectic phase volume (△H+→L), electrical conductivity, and heat dissipation (or thermal consuctivity). Additionally, the electrical, thermal properties of Sn-9Zn are mostly better than those of the other Sn-based eutectic alloys, and those of Sn-37Pb are the worst. On the other hand, the fusion phenomenon does not occur on primary Zn-rich phases. The result of electrification-fusion test shows the descending CFCD order of Sn-based eutectic alloys is Sn-9Zn > Sn-3.5Ag > Sn-0.7Cu > Sn-3Ag-0.5Cu > Sn-37Pb. Thus, Sn-9Zn has the potential to be applied in hign-current density occasions.
A large area of network-like fusion paths in pure Sn can not be observed in the Sn-based eutectic alloys. Besides, the individual phases of Sn-based eutectic alloys have different electrical, thermal properties and volume fractions, making the fusion connecting form more various but the fusion regions have poorer connectivity than pure Sn. Therefore, most of Sn-based eutectic alloys (except for Sn-37Pb) have higher CFCD value than pure Sn.
The linear regression statistic of electrification-fusion test in Sn-xZn alloys shows CFCD values have good relationship among electrical conductivity, latent heat of eutectic region contained in per unit solder volume (△Hf) and volume fraction of eutectic phase. Fusion phenomenon does not take place in Primary Zn-rich phases during the electrification. Moreover, the dominant influence on electrification-fusion characteristics in Sn-xZn alloys mostly is Sn/Zn eutectic phase. When Zn content increases from 7 wt.% (hypoeutectic) to 9 wt.% (eutectic), dendritic primary -Sn gradually decreases and primary Zn-rich phase crystallizes. Since primary -Sn is also a fusion phase, making Sn-9Zn has higher CFCD than Sn-7Zn. When Zn content increases from 9 wt.% to 30, 70 wt.% (hypereutectic) and 100 wt.% (pure Zn), in order to fuse higher Zn content of Sn-xZn alloys, the fusion-free Zn-rich phase may presumably hinder the connecting path for Sn/Zn eutectic fusion phase from extending further. Thus, the CFCD of Sn-xZn alloys increases with increasing Zn content.

[1] M. Kimura, S. Inoue, T. Shimoda, T. Sameshima, Current
paths over grain boundaries in polycrystalline silicon
films, J. Appl. Phys., 40 (2001), pp. 97-99.
[2] I.A. Blech, E.S. Meieran, Electromigration in thin
aluminum films, J. Appl. Phys., 40 (1968), pp. 485-
491.
[3] Y.M. Hung, C.M. Chen, Electromigration of Sn-9wt.% Zn
solder, J. Electro. Mater., 37 (2008), pp. 887-893.
[4] S.M. Kuo, K.L. Lin, Microstructure evolution during
electromigration between Sn-9Zn solder and Cu, J.
Mater. Res., 22 (2007), pp. 1240-1249.
[5] Y.C. Hsu, C.K. Chou, P.C. Liu, C. Chen,
Electromigration in Pb-free SnAg3.8Cu0.7 solder
stripes, J. Appl. Phys., 98 (2005), pp. 0335231-
0335236.
[6] Y.C. Hu, Y.H. Lin, C.R. Kao, Electomigration failure
in flip chip solder joints due to rapid dissolution of
copper, J. Mater. Res., 18 (2003), pp. 2544-2548.
[7] C.M. Tsai, Y.L. Lin, J.Y. Tsai, Y.S. Lai, C.R. Kao,
Local melting induced by electromigration in flip-chip
solder joints, J. Electro. Mater., 35 (2006), pp.
1005-1009.
[8] Y.L. Lin, C.W. Chang, C.M. Tsai, C.W. Lee, C.R. Kao,
Electromigration-induced UBM consumption and the
resulting failure mechanisms in flip-chip solder
joints, J. Electro. Mater., 35 (2006), pp. 1010-1016.
[9] Y.H. Lin, Y.C. Hu, C.M. Tsai, C.R. Kao, K.N. Tu, In
situ observation of the void formatin-and-propagation
mechanism in solder joints under current-stressing,
Acta Mater., 53 (2005), pp. 2029-2035.
[10] H. Ye, C. Basaran, D.C. Hopkins, Damage mechanics of
microelectronics solder joints under high current
densities, Int. J. Solids Struct., 40 (2003), pp. 4021-
4032.
[11] E.C.C. Yeh, W.J. Choi, K.N. Tu, Current-crowding-
induced electromigration failure in flip chip solder
joints, Appl. Phys. Lett., 80 (2002), pp. 580-582.
[12] J.D. Wu, P.J. Zheng, C.W. Lee, S.C. Hung, J.J. Lee, A
study in flip-chip UBM/bump reliability with effects of
SnPb solder composition, Microelectron. Relia., 46
(2006), pp. 41-52.
[13] F.Y. Hung, C.J. Wang, T.S. Lui, L.H. Chen, Electrical
current phase transformation of Sn-9Zn-1Ag alloy,
Mater. Trans., 46 (2005), pp. 1820-1824.
[14] W.H. Wu, S.P. Peng, C.S. Lin, C.E. Ho, Study of DC and
AC electromigration behavior in eutectic Pb-Sn solder
joints, J. Electro. Mater., 38 (2009), pp. 2184-2193.
[15] A.W. Worcester, J.T. O’Reilly, Metals handbook, 10th
ed., ASM, 2 (1990), pp. 543-556.
[16] S. Jin, Developing lead-free solders: a challenge and
opportunity, JOM, 45 (1993), pp. 13-19.
[17] S.S. Kang, A.K. Sarkhel, Lead-free solders for
electronic packaging, J. Electro. Mater., 23 (1994),
pp. 701-707.
[18] M. McCormack, S. Jin, H.S. Chen, D.A. Machusak, New
lead-free Sn-Zn-In solder alloys, J. Elctro. Mater., 23
(1994), pp. 687-690.
[19] J. Glarzer, Microstructure and mechanical properties of
lead-free solder alloys for low-cost electronic
assembly: a review, J. Electro. Mater., 23 (1994), pp.
693-700.
[20] T.L. Gall, Metals handbook, desk ed., ASM, Chap. 30
(1985), pp. 73-76.
[21] P.T. Vianco, D.R. Frear, Issues in the replacement of
lead-bearing, JOM, 45 (1993), pp. 14-19.
[22] S. Vaynman, M.E. Fine, Development of fluxes for lead-
free solders containing zinc, Scripta Mater., 41
(1999), pp. 1269-1271.
[23] 張淑如，『鉛對人體的危害』，勞工安全衛生簡訊，第12期，(民國
84年)，17-18頁。
[24] K.N. Tu, A.M. Gusak, M. Li, Physics and materials
challenges for lead-free solders, J. Appl. Phys., 93
(2003), pp. 1335-1353.
[25] S. Choi, J.G. Lee, F. Guo, T.R. Bieler, K.N.
Subramanian, J.P. Lucas, Creep properties of Sn-Ag
solder joints containing intermetallic particles, JOM.,
53 (2001), pp. 22-26.
[26] N.-C. Lee, Getting ready for lead-free solders,
Soldering and Surface Mount Tech., 26 (1997), pp. 65-
69.
[27] 陳信文，『無鉛銲料簡介』，電子與材料，第1期，(民國88年)，
74-77頁。
[28] Z. Moser, J. Dutkiewicz, W. Gasior, J.Salawa, The Sn-
Zn system, Bull. Alloy Phase Diagrams, 6 (1985), pp.
330-334.
[29] E.P. Wood, K.L. Nimmo, In search of new lead-free
electronic solders, 23 (1994), pp. 709-713.
[30] I. Karakaya, W.T. Thompson, The Ag-Sn system, Bull.
Alloy Phase Diagrams, 8 (1987), pp. 340-347.
[31] K. Suganuma, Y. Nakamura, Microstructure and strength
of interface between Sn-Ag eutectic solder and Cu, J.
Japan Inst. Metals (in Japanese), 59 (1995), pp. 1299-
1305.
[32] K. Suganuma, S.H. Huh, K. Kim, H. Nakase, Y. Nakamura,
Effect of Ag content on properties of Sn-Ag binary
alloy solder, Mater. Trans., 42 (2001), pp. 286-291.
[33] W. Yang, R.W. Messler, L.E. Felton, Microstructure
evolution of eutectic Sn-Ag solder joints, J. Electro.
Mater., 23 (1994), pp. 765-772.
[34] V.I. Igoshev, J.I. Kleiman, D. Shangguan, S. Wong, U.
Michon, Fracture of Sn-3.5%Ag solder alloy under creep,
J. Electro. Mater., 29 (2000), pp. 1356-1361.
[35] W. Yang, L.E. Feltion, R.W. Messler, The effect of
soldering process variables on the microstructure and
mechanical properties of eutectic Sn-Ag/Cu solder
joints, J. Electro. Mater., 24 (1995), pp. 1465-1472.
[36] J.S. Hwang, R.M. Vargas, Solder joint reliability-can
solder creep, Soldering and Surface Mount Tech., 2
(1990), pp. 38-45.
[37] F. Hua, J. Glazer, Lead-free for electronic assembly,
Design and Reliability of Solders and Solder
Interconnections, TMS Annual Meeting, (1997), pp. 65-
73.
[38] J. Glazer, Metallurgy of low temperature lead-free
solders forelectronic assembly, International Mater.
Rev., 40 (1995), pp. 65-93.
[39] K.J. Puttlitz, G.T. Galyon, Impact of the rohs
directive on high-performance electronic systems, J.
Mater. Sci., 18 (2007), pp. 347-365.
[40] Y. Kariya, M. Otsuka, Mechanial fatigue
characteristics of Sn-3.5Ag-X (X=Bi, Cu, Zn and In)
solder alloys, J. Electro. Mater., 27 (1998), pp. 1229-
1235.
[41] N. Saunders, A.P. Miodownik, The Cu-Sn system, Bull.
Alloy Phase Diagrams, 11 (1990), pp. 278-287.
[42] L. Xiao, J. Liu, L. Ye, A. Tholen, Characterization of
mechanical properties of bulk lead free solders,
International Symposium on Advanced Packaging
Materials, (2000), pp. 145-151.
[43] J.W. Yoon, S.W. Kim, S.B. Jung, Effect of reflow time
on interfacial reaction and shear strength of Sn-0.7Cu
solder/Cu and electroless Ni-PBGA joints, J. Alloys
Comp., 385 (2004), pp. 192-198.
[44] J.W. Yoon, S.W. Kim, S.B. Jung, Effects and reflow and
cooling conditions on interfacial reaction and IMC
morphology of Sn-Cu/Ni solder joint, J. Alloys Comp.,
415 (2006), pp. 56-61.
[45] K. Suganuma, Advances in lead-free electronics
soldering, Current Opinion in Sold State and Materials
Science, 5 (2001), pp. 55-64.
[46] 李芳儀，『銅含量對Sn-Ag-Cu無鉛銲錫振動破壞特性之效應』，國立成功
大學材料科學及工程學系，碩士論文，(民國92年)。
[47] Ed.T. Lyman, H.E. Bouer, W.J. Carnes, Metals handbook
Vol. 8 metallography, structures and phase diagrams,
ASM, Metals Park, Ohio, USA, pp. 256.
[48] K.S. Kim, S.H. Huh, K. Suganuma, Effects of
intermetallic compounds on properties of Sn-Ag-Cu lead-
free soldered joints, J. Alloy Compd., 352 (2003), pp.
226-236.
[49] K.S. Kim, S.H. Huh, K. Suganuma, Effects of cooling
speed on microstructure and tensile properties of Sn-
Ag-Cu alloys, Mater. Sci. Eng., A 333 (2002), pp. 106-
114.
[50] S.L. Allen, M.R. Notis, R.R. Chromik, R.P. Vinci,
Microstructural evolution in lead-free solder alloys:
part II. directionally solidified Sn-Ag-Cu, Sn-Cu and
Sn-Ag, J. Mater. Res., 19 (2004), pp. 1425-1431.
[51] X. Deng, N. Chawla, K.K. Chawla, M. Koopman,Deformation
behavior of (Cu, Ag)-Sn intermetallics by
nanoindetation, Acta Mater., 52 (2004), pp. 4291-4303.
[52] S.L. Allen, M.R. Notis, R.R. Chromik, R.P. Vinci,
Microstructural evolution in lead-free solder alloys:
part I. Cast Sn-Ag-Cu eutectic, J. Mater. Res., 19
(2004), pp. 1417-1424.
[53] B.Y. Wu, Y.C. Chan, H.W. Zhong, M.O. Alam, Effect of
current stressing on the reliability of 63Sn37Pb solder
joints, J. Mater. Sci., 42 (2007), pp. 7415-7422.
[54] J.W. Nah, J.O. Suh and K.N. Tu, Effect of current
crowding and joule heating on electromigration-induced
failure in flip chip composite solder joints tested at
room temperature, J. Appl. Phys. 98 (2005), pp.
0137151-0137156.
[55] J.S. Zhang, Y.C. Chan, Y.P. Wu, H.J. Xi, F.S. Wu,
Electromigration of Pb-free solder under a low level of
current density, J. Alloys Compd., 458 (2008), pp. 492-
499.
[56] B.Y. Wu, Y.C. Chan, Electric current effect on
microstructure of ball grid array solder joint, J.
Alloys Compd., 392 (2005), pp. 237-246.
[57] Y.C. Chan, D. Yang, Failure mechanism of solder
interconnects under current stressing in advanced
electronic packages, Prog. Mater Sci., 55 (2010), pp.
428-475.
[58] H. Ye, C. Basaran, D.C. Hopkins, Mechanical degradation
of microelectronics solder joints under current
densities, Int. J. Solids Struct., 40 (2003), pp. 7269-
7284.
[59] H. Ye, C. Basaran, D.C. Hopkin, Pb phase coarsening in
eutectic Pb/Sn flip chip solder joints under electric
current stressing, Int. J. Solids Struct., 41 (2004),
pp. 2743-2755.
[60] M.O. Alam, C. Bailey, B.Y. Wu, D. Yang, Y.C. Chan, High
current density induced damage mechanisms in electronic
solder joints: a state-of-the-art review, International
Symposium on High Density Packaging and Microsystem
Integration, Shanghai, China, (2007), pp.1-7.
[61] C.H. Wang, S.W. Chen, Electric current effects in flip
chip solder joints, J. Chin. Inst. Chem. Engrs., 37
(2006), pp. 185-191.
[62] 蔡東原，『共晶型錫基合金之高荷電破壞特性探討』，國立成功大學材料
科學及工程學系，碩士論文，(民國93年)。
[63] A.T. Wu, A.M. Gusak, Electromigration-induced grain
rotation in anisotropic conducting beta tin, Appl.
Phys. Lett., 86 (2005), pp. 2419021-2419023.
[64] A.U. Telang, T.R. Bieler, J.P. Lucas, K.N. Subramanian,
L.P. Lehman, Y. Xing, E.J. Cotts, Grain-boundary
character and grain growth in bulk tin and bulk lead-
free solder alloys, J. Electro. Mater., 33 (2004), pp.
1412-1423.
[65] K. Matsugi, G. Sasaki, O. Yanagisawa, Y. Jumagai, K.
Fujii, Electrical and thermal characteristics of Pb-
free Sn-Zn alloys for an AC-low voltage fuse element,
Mater. Trans., 48 (2007), pp. 1105-1112.
[66] J.A. King, Material handbook for hybrid
microelectronics, Artec House , Norwood, USA, (1988).
[67] J. Bilek, J. Atkinson, W. Wakeham, Thermal conductivity
of molten lead free solders, European Microelectronics
and packaging Symposium, (2004).
[68] N. Hidaka, H. Watanabe, M. Yoshiba, M. Shimoda, T.
Asai, M. Ono, Creep behavior and microstructure of Sn-
Ag-Cu-Ni-Ge lead-free solder alloy, Mater. Sci. Tech.,
(2006), pp. 185-197.
[69] R. B. Ross, Metallic materials specification handbook,
3rd ed., E. & F. N. Spon., (1980), pp. 589-619.