Effect of Strain Rate on Tensile Behavior of Sn-9Zn-xAg-ySb; {(x, y) = (0.2, 0.6), (0.2, 0.8), (0.6, 0.2), (0.8, 0.2)} Lead-Free Solder Alloys

Shihab Uddin¹, Md. Abdul Gafur^2*, Mohammad Obaidur Rahman¹

¹Department of Physics, Jahangirnagar University, Savar, Dhaka, Bangladesh.
²Pilot Plant and Process Development Centre, Dhaka, Bangladesh.

DOI: 10.4236/msa.2023.144016                

Abstract

The tensile properties of Sn-9Zn-xAg-ySb; {(x, y) = (0.2, 0.6), (0.2, 0.8), (0.6, 0.2), (0.8, 0.2)} lead-free solders were investigated. All the test samples were annealed at 150°C for 1 hour. The tests are carried out at room temperature at the strain rate of 4.17 × 10^-3 s^-1, 20.85 × 10^-3 s^-1, and 208.5 × 10^-3 s^-1. It is seen that the tensile strength increases and the ductility decrease with increasing the strain rate over the investigated range. From the strain rate change test results, the strain sensitivity values are found in the range of 0.0831 to 0.1455 due to the addition of different alloying elements.

Keywords

Lead-Free Solder, Strain Rate, Strain Sensitivity, Ductility, Tensile Properties

1. Introduction

Lead-based solder alloys are using for a long time in electronic and optoelectronic packaging all over the world due to their excellent wetting property, decent melting temperature, suitable electrical and mechanical properties, and low cost [1] [2] . Due to the toxicity of lead, it pollutes the groundwater and causes lead poisoning. Therefore, it is harmful to human beings and to the environment, and its use is prohibited [3] - [10] . Because of environmental and health perturbation, legislations, environmental regulations like Waste Electrical and Electronic Equipment (WEEE), Restriction of the use of Hazardous Substances (RoHS), and marketing forces at home and abroad made the electronics industries restless about the lead-free solder alloys to replace the traditional lead-based solders [11] - [18] . The researchers are giving the most attention to the Sn-Ag and Sn-Zn alloys, because of their excellent performance, reliability, cost, and resource. In comparison with Sn-Ag solders Sn-Zn solders have many benefits, such as low melting point (198˚C), satisfactory mechanical strength, low cost, and available supply. So there is a great opportunity to think about the Sn-Zn solder [19] - [27] . Sn-Zn-based solder alloys may be a good alternative to lead-based solders because of their better mechanical properties. The mechanical properties of Sn-9Zn eutectic alloy is better than that of traditional solder alloys and it has a lower melting point of 199.8˚C [28] . As the Sn-9Zn eutectic alloy has many advantages, it is predicted as a suitable replacement for leaded solder alloys. Nowadays a large number of studies on Sn-9Zn-xNi [29] , Sn-9Zn-(Cu & Al) [30] , Sn-9Zn-xAg [31] , Sn-9Zn-xCr [32] , Sn-9Zn-xGa [33] , Sn-9Zn-xBi [34] , Sn-9Zn- xAl and Sn-9Zn-xCu [35] , are done to find out an alternative of Sn-Pb alloys. But Sn-9Zn eutectic alloy has some negative points, such as worst corrosion behavior, poor oxidation resistance, and low wettability than the Sn-Pb eutectic solder [36] . Due to these poor behaviors, Sn-9Zn eutectic alloy cannot occupy the position of Sn-Pb solders [37] [38] . Despite so many weak sides, using of Sn-9Zn eutectic alloy is spreading day by day. So further studies are required to investigate its material properties such as melting temperature, solderability, creep resistance, thermal fatigue, corrosion behavior, mechanical strength, ductility, and so on. The mechanical properties of a solder alloy are very significant, as such properties determine the thermal fatigue and fracture of the solder joint. Therefore, it is necessary to investigate the solder’s mechanical properties (tensile strength, yield strength, and ductility). The aim of this study is to investigate the tensile properties of Sn-9Zn-0.2Ag-0.6Sb, Sn-9Zn-0.2Ag-0.8Sb, Sn-9Zn-0.6Ag- 0.2Sb and Sn-9Zn-0.8Ag-0.2Sb solders under different test conditions. Especially the effects of strain rate at room temperature on the tensile properties are examined.

2. Experimental Procedure

2.1. Preparation of the Samples

Raw materials for preparing the alloys, pure tin (99.5 wt%), pure zinc (99.5 wt %), pure silver (99.5 wt%), and pure antimony (99.5 wt%) are available in the local market. At the first calculated amount of tin, zinc, silver, and antimony are weighted. Then tin is placed in a clay graphite crucible and melted in a muffle furnace at the temperature of 250˚C for 10 minutes. After melting the tin, zinc, silver, and antimony are added and the temperature is upgraded to 500˚C for 10 minutes. The melted solder alloy was chill cast in the preheated (300˚C) cast iron mold having the dimension of 250 mm × 10 mm × 10 mm followed by cooling in the air. Each solder is cast as a rectangular ingot. Before casting, the melt was homogenized by stirring at 500˚C.

2.2. Heat Treatment

The as-cast alloys are sectioned and annealed at the temperature of 150˚C for 60 minutes followed by furnace cooling to remove the micro-segregation effects. Then the tensile test samples are prepared from the ingots of the solder. The dimensions of the samples are gauge length 8 mm, thickness 2 mm, and width 3 mm as shown in Figure 1.

2.3. Tensile Tests

The tensile test is performed in a Universal Testing Machine (brand: Hounsfield, SR. No. H10KS-0572) at three different cross-head speeds: 2, 10, and 100 mm/ min which are equal to the nominal strain rates of 4.17 × 10⁻³, 20.85 × 10⁻³ and 208.5 × 10⁻³ s⁻¹ respectively. The test is carried out up to the failure of the samples at room temperature. Test curves only for one sample of each alloy are presented here as typical test curves; those for the other samples exhibited a similar shape and appearance and are not given. The averages of three consistent test results are taken as the tensile value for the corresponding alloy.

3. Results and Discussion

The chemical compositions of the alloys are measured with BRUKER S1TITAN Handheld XRF Analyzer, shown in Table 1 (wt%).

3.1. Effect of Strain Rate on Ultimate Tensile Strength

The investigation was conducted with four alloys. All the test samples are annealed at 150˚C for 1 hour and a significant effect is observed. Table 2 summarizes the results of the tensile tests and each datum is the average of the results of the three samples. In two alloys (alloy-1, alloy-2) Sb content was varied and in the other two alloys (alloy-3, alloy-4) Ag content was varied. The tensile tests were conducted at three strain rates (4.17 × 10⁻³ s⁻¹, 20.85 × 10⁻³ s⁻¹, and 208.5 × 10⁻³ s⁻¹). It is very clear that the strain rate plays an important role and affects

Figure 1. Dimensions of the tensile specimen.

Table 1. Chemical compositions of the solder alloys (wt%).

Table 2. Tensile properties at different strain rates.

stress levels. The ultimate tensile strength (UTS) increases with increasing the strain rate over the investigated range at room temperature as shown in Figure 2.

Table 2 and Figure 3 show that alloy-1 with less Sb displays higher tensile strength than alloy-2 with more Sb all over the strain rates. On the other hand, alloy-4 having more Ag displays higher tensile strength than alloy-3 having less Ag.

An approximate linear relevance is performed between the tensile strength and the strain rate as shown in Figure 4. The strength-strain rate relationship follows the equation given below:

σ = kέ^m (1)

where σ is the tensile strength, έ is the strain rate, k is a constant, and m is called the strain rate hardening exponent or strain sensitivity [39] . The values of m, k, and R² are obtained from the logarithmic plotting of Equation (1) as shown in Figure 4 and those are summarized in Table 3.

The value of m for Sn-37Pb is much greater than that of these four investigated lead-free solders [40] . As the value of m describes the ability to stop necking, the lead-free solders are lower capable to arrest necking [41] . As the values of m are less than 0.3, superplastic behavior will not occur in these lead-free solders [42] . The obtained results are in good agreement with the previous results [43] [44] .

3.2. Effect of Strain Rate on Ductility

Figure 5 displays the variation of % elongation with the strain rate of the alloys. It was observed that at the strain rate for which the ultimate tensile strength is maximum, the ductility values of the alloys go through the minimum.

Table 3. Stress-strain characteristics of the alloys.

Figure 2. Typical stress-strain curves at room temperature showing the effect of different strain rates (a) alloy-1, (b) alloy-2, (c) alloy-3, (d) alloy-4.

Figure 3. Typical stress-strain curves (a-c) of the alloys at the different strain rates (a) Strain rate 4.17 × 10⁻³ s⁻¹ (b) 20.85 × 10⁻³ s⁻¹ (c) 208.5 × 10⁻³ s⁻¹ and (d) average UTS values at various strain rates.

Figure 4. Ln-Ln plot of UTS versus strain rate.

Figure 5. Ductility (% elongation)—strain rate curves of investigated alloys.

3.3. Effect of Strain Rate on Yield Strength

The yield strength-strain rate curves of the alloys are plotted in Figure 6. It is

Figure 6. Yield strength-strain rate curves of investigated alloys (a) average yield strength values at different strain rates (b) Ln-Ln plot of average yield strength versus strain rate.

found that the yield strength (2% proof strengths) of the alloys increases with strain rates. The trend is very similar to that of ultimate tensile strengths. In all the alloys the maximum yield strength was attained at a strain rate of 208.5 × 10⁻³ s⁻¹. The yield strength of alloy-1 is higher than that of alloy-2 and the yield strength of alloy-4 is higher than that of alloy-3 all over the strain rates.

4. Conclusions

The tensile properties of Sn-9Zn-0.2Ag-0.6Sb, Sn-9Zn-0.2Ag-0.8Sb, Sn-9Zn- 0.6Ag-0.2Sb, and Sn-9Zn-0.8Ag-0.2Sb are investigated under the strain rates 4.17 × 10⁻³ s⁻¹, 20.85 × 10⁻³ s⁻¹ and 208.5 × 10⁻³ s⁻¹. The results are summarized as follows:

1) Tensile strength and yield strength increase with the strain rate within the investigated range.

2) The trend of the yield strength is very similar to that of tensile strength.

3) Ductility decreases with increasing the strain rate.

4) The strain sensitivity m is 0.0831 for Sn-9Zn-0.2Ag-0.6Sb, 0.1455 for Sn- 9Zn-0.2Ag-0.8Sb, 0.1274 for Sn-9Zn-0.6Ag-0.2Sb and 0.1346 for Sn-9Zn-0.8Ag- 0.2Sb.

5) All the values of m are less than 0.3, so superplastic behavior will not occur in any of the lead-free solders investigated in this study.

6) Further investigation of the tensile properties of these solder alloys at different temperatures and strain rates is needed to understand the thermodynamic hardening response in more detail.

Acknowledgements

This research work was completed using the resources of the department of Pilot Plant and Process Development Center (PP & PDC), Bangladesh Council of Science and Industrial Research (BCSIR). The authors gratefully acknowledge Prime Ministers Education Assist Trust, Bangladesh for providing financial support to carry out the research successfully.

Conflicts of Interest

The authors declare no conflicts of interest regarding the publication of this paper.

References

[1]	Mahmudi, R. and Mahin-Shirazi, S. (2011) Effect of Sb Addition on the Tensile Deformation Behavior of Lead-Free Sn-3.5Ag Solder Alloy. Materials & Design, 32, 5027-5032. https://doi.org/10.1016/j.matdes.2011.05.052
[2]	Abtew, M.D., Selvaduray, G. (2000) Lead-Free Solders in Microelectronics. Materials Science and Engineering: R: Reports, 27, 95-141. https://doi.org/10.1016/S0927-796X(00)00010-3
[3]	Miyaki, M., Kanai, M. and Ogata, S. (1999) Soldering Properties for Lead-Free Solders of Sn-Ag-Cu System Solders. Proceedings of the Third IEMT/IMC Symposium (International Electronic Manufacturing Symposium and the International Microelectronics Conference), Omiya, 21-23 April 1999, 125-130.
[4]	Sobhy, M., El-Refai, A.M. and Fawzy, A. (2015) Effect of Graphin Oxide Nano-Sheets (GONSs) on Thermal, Microstructure and Stress-Strain Characteristics of Sn-5 wt% Sb-1wt% Ag Solder Alloy. Journal of Materials Science: Materials in Electronics, 27, 2349-2359. https://doi.org/10.1007/s10854-015-4032-x
[5]	Ichitsubo, T., Matsubara, E., Fujiwara, K., Yamaguchi, M., Irie, H., Kumanoto, S. and Anada, T. (2005) Control of Compound Forming Reaction at the Interface Between SnZn Solder and Cu Substrate. Journal of Alloys and Compounds, 392, 200-205. https://doi.org/10.1016/j.jallcom.2004.09.043
[6]	Zeng, K. and Tu, K.N. (2002) Six Cases of Reliability Study of Pb-Free Solder Joints in Electronic Packaging Technology. Materials Science and Engineering: R: Reports, 38, 55-105. https://doi.org/10.1016/S0927-796X(02)00007-4
[7]	Kang, S.K. and Sarkhel, A.K. (1994) Lead (Pb)-Free Solders for Electronic Packaging. Journal of Electronic Materials, 23, 701-707. https://doi.org/10.1007/BF02651362
[8]	Mahmudi, R., Geranmayeh, A.R., Khanbareh, H. and Jahangiri, N. (2009) Indentation Creep of Lead-Free Sn-9Zn and Sn-8Zn-3Bi Solder Alloys. Materials & Design, 30, 574-580. https://doi.org/10.1016/j.matdes.2008.05.058
[9]	Yu, D.Q., Xie, H.P. and Wang, L. (2004) Investigation of Interfacial Microstructure and Wetting Property of Newly Developed Sn-Zn-Cu Solders with Cu Substrate. Journal of Alloys and Compounds, 385, 119-125. https://doi.org/10.1016/j.jallcom.2004.04.129
[10]	Liu, C.-Y., Hon, M.-H., Wang, M.-C., Chen, Y.-R., Chang, K.-M. and Li, W.-L. (2014) Effects of Aging Time on the Mechanical Properties of Sn-9Zn-1.5Ag-xBi Lead-Free Solder Alloys. Journal of Alloys and Compounds, 582, 229-235. https://doi.org/10.1016/j.jallcom.2013.08.022
[11]	EL-Daly, A.A. and Hammond, A.E. (2011) Development of High Strength Sn-0.7Cu Solders with the Addition of Small Amount of Ag and In. Journal of Alloys and Compounds, 509, 8554-8560. https://doi.org/10.1016/j.jallcom.2011.05.119
[12]	Forsten, A., Steen, H. and Wilding, I. (2000) Development and Validation of Lead-Free Wave Soldering Process. Soldering & Surface Mount Technology, 12, 29-34. https://doi.org/10.1108/09540910010347872
[13]	Islam, R.A., Chan, Y.C., Jillek, W. and Islam, S. (2006) Comparative Study of Wetting Behavior and Mechanical Properties (Microhardness) of Sn-Zn and Sn-Pb Solders. Microelectronics Journal, 37, 705-713. https://doi.org/10.1016/j.mejo.2005.12.010
[14]	Osório, W.R., Garcia, L.R., Peixoto, L.C. and Garcia, A. (2011) Electrochemical Behavior of a Lead-Free SnAg Solder Alloy Affected by the Microstructure Array. Materials & Design, 32, 4763-4772. https://doi.org/10.1016/j.matdes.2011.06.032
[15]	Garcia, L.R., Osorio, W.R., Peixoto, L.C. and Garcia, A. (2010) Mechanical Properties of Sn-Zn Lead-Free Solder Alloys Based on the Microstructure Array. Materials Characterization, 61, 212-220. https://doi.org/10.1016/j.matchar.2009.11.012
[16]	Cadirli, E., Boyük, U., Engin, S., Kaya, H., Marasli, N. and ülgen, A. (2009) Experimental Investigation of the Effect of Solidification Processing Parameters on the Rod Spacings in the Sn-1.2wt.% Cu Alloy. Journal of Alloys and Compounds, 486, 199-206. https://doi.org/10.1016/j.jallcom.2009.07.027
[17]	Hwang, J.S. (2001) Environment-Friendly Electronics: Lead-Free Technology. Electrochemical Publications, New York.
[18]	Gao, L.L., Xue, S.B., Zhang, L., Sheng, Z., Feng, J., Dai, W., Yu, S.L. and Zeng, G. (2010) Effect of Alloying Elements on Properties and Microstructures of SnAgCu Solders. Microelectronic Engineering, 87, 2025-2034. https://doi.org/10.1016/j.mee.2010.04.007
[19]	Mavoori, H., Chin, J., Vaynman, S., Moran, B., Keer, L. and Fine, M. (1997) Creep, Stress Relaxation, and Plastic Deformation in Sn-Ag and Sn-Zn Eutectic Solders. Journal of Electronic Materials, 26, 783-790. https://doi.org/10.1007/s11664-997-0252-z
[20]	Ventura, T., Terzi, S., Rappaz, M. and Dahle, A.K. (2011) Effects of Solidification Kinetics on Microstructure Formation in Binary Sn-Cu Solder Alloys. Acta Materialia, 59, 1651-1658. https://doi.org/10.1016/j.actamat.2010.11.032
[21]	Lee, J.-E., Kim, K.-S., Inoue, M., Jiang, J.X. and Suganuma, K. (2008) Effects of Ag and Cu Addition on Microstructural Properties and Oxidation Resistance of Sn-Zn Eutectic Alloy. Journal of Alloys and Compounds, 454, 310-320. https://doi.org/10.1016/j.jallcom.2006.12.037
[22]	Suganuma, K. (2001) Advances in Lead-Free Electronics Soldering. Current Opinion in Solid State and Materials Science, 5, 55-64. https://doi.org/10.1016/S1359-0286(00)00036-X
[23]	Fakpan, K. and Canyook, R. (2017) Effects of Sb and Zn Addition on Mechanical Properties and Corrosion Resistance of Sn-Ag-Cu Solders. Key Engineering Materials, 728, 129-134. https://doi.org/10.4028/www.scientific.net/KEM.728.129
[24]	Wood, E.P. and Nimmo, K.I. (1994) In Search of New Lead-Free Electronic Solders. Journal of Electronic Materials, 23, 709-713. https://doi.org/10.1007/BF02651363
[25]	Lin, F., Bi, W.Z., Ju, G.K. and Wang, W.R. (2011) Evolution of Ag3Sn at Sn-3.0Ag-0.3Cu-0.05Cr/Cu Joint Interfaces during Thermal Aging. Journal of Alloys and Compounds, 509, 6666-6672. https://doi.org/10.1016/j.jallcom.2011.03.134
[26]	McCormack, M. and Jin, S. (1994) Improved Mechanical Properties in New, Pb-Free Solder Alloys. Journal of Electronic Materials, 23, 715-720. https://doi.org/10.1007/BF02651364
[27]	Chantaramanee, S., Sriwittayakul, W. and Sungkhaphaitoon, P. (2018) Effects of Antimony and Indium Addition on Wettability and Interfacial Reaction of Sn-3.0Ag-0.5Cu Lead-Free Solder on Copper Substrate. Materials Science Forum, 928, 188-193. https://doi.org/10.4028/www.scientific.net/MSF.928.188
[28]	Chen, K.I., Cheng, S.C., Cheng, C.H., Wu, S., Jiang, Y.L. and Cheng, T.C. (2014) The Effects of Gallium Additions on Microstructures and Thermal and Mechanical Properties of Sn-9Zn Solder Alloys. Advances in Materials Science and Engineering, 2014, Article ID: 606814. https://doi.org/10.1155/2014/606814
[29]	Billah, M.M. and Shorowordi, K.M. (2012) Effect of Micron Size Ni Particle Addition on Microstructure, Thermal and Mechanical Properties of Sn-9Zn Lead-free Solder Alloy. Applied Mechanics and Materials, 229-231, 271-275. https://doi.org/10.4028/www.scientific.net/AMM.229-231.271
[30]	Ozyurek, D., Yavuzer, B. and Tuncay, T. (2016) The Effects of Cu and Al on Dry Sliding Wear Properties of Eutectic Sn-9Zn Lead-Free Solder Alloy. Journal of Adhesion Science and Technology, 30, 1662-1670. https://doi.org/10.1080/01694243.2016.1157432
[31]	Huang, H.Z., Huang, Q.S., Peng, S. and Zhou, L. (2010) Effects of Ag Addition on Properties of Sn-9Zn Lead-free Solder Alloys. Rare Metal Materials and Engineering, 39, 1702-1706. https://doi.org/10.1016/S1875-5372(10)60127-0
[32]	Chen, X., Hu, A.M., Li, M. and Mao, D.L. (2008) Study on the Properties of Sn-9Zn-xCr Lead-Free Solder. Journal of Alloys and Compounds, 460, 478-484. https://doi.org/10.1016/j.jallcom.2007.05.087
[33]	Gancarz, T. (2016) Physical, Thermal, Mechanical Properties and Microstructural Characterization of Sn-9Zn-XGa Alloys. Metallurgical and Materials Transactions A, 47, 326-333. https://doi.org/10.1007/s11661-015-3235-3
[34]	Wadud, M.A., Gafur, M.A., Qadir, R. and Rahman, M.O. (2015) Effect of Bismuth Addition on Structure and Mechanical Properties of Tin-9Zinc Soldering Alloy. Materials Sciences and Applications, 6, 792-798. https://doi.org/10.4236/msa.2015.69081
[35]	Yavuzer, B., Ozyurek, D. and Tuncay, T. (2020) Microstructure and Mechanical Properties of Sn-9Zn-xAl and Sn-9Zn-xCu Lead-Free Solder Alloys. Materials Science-Poland, 38, 34-40. https://doi.org/10.2478/msp-2020-0025
[36]	Silva, B.L. and Spinellib, J.E. (2018) Correlations of Microstructure and Mechanical Properties of the Ternary Sn-9wt%Zn-2wt%Cu Solder Alloy. Materials Research, 21, e20170877. https://doi.org/10.1590/1980-5373-mr-2017-0877
[37]	EL-Daly, A.A. and Hammand, A.E. (2010) Elastic Properties and Thermal Behavior of Sn-Zn Based Lead-Free Solder Alloys. Journal of Alloys and Compounds, 505, 793-800. https://doi.org/10.1016/j.jallcom.2010.06.142
[38]	Shalaby, R.M. (2012) Effect of Silicon Addition on Mechanical and Electrical Properties of Sn-Zn Based Alloys Rapidly Quenched from Melt. Materials Science and Engineering: A, 550,112-117. https://doi.org/10.1016/j.msea.2012.04.041
[39]	Plumbridge, W.J. and Gagg, C.R. (1999) Effects of Strain Rate and Temperature on the Stress-Strain Response of Solder Alloys. Journal of Materials Science: Materials in Electronics, 10, 461-469.
[40]	Bai, N., Chen, X. and Fang, Z. (2008) Effect of Strain Rate and Temperature on the Tensile Properties of Tin-Based Lead-Free Solder Alloys. Journal of Electronic Materials, 37, 1012-1019.
[41]	Chan, K.C. and Tong, G.Q. (2001) Strain Rate Sensitivity of a High-Strain-Rate Superplastic Al6061/20SiCW Composite under Uniaxial and Equibiaxial Tension. Materials Letters, 51, 389-395. https://doi.org/10.1016/S0167-577X(01)00326-3
[42]	Shohji, I., Yoshida, T., Takahashi, T. and Hioki, S. (2002) Tensile Properties of Sn-3.5Ag and Sn-3.5Ag-0.75Cu Lead-free Solders. Materials Transactions, 43, 1854-1857. https://doi.org/10.2320/matertrans.43.1854
[43]	El-Daly, A.A. and Hammad, A.E. (2019) Effects of Small Addition of Ag and/or Cu on the Microstructure and Properties of Sn-9Zn Lead-Free Solders. Applied Sciences, 9, Article 2044.
[44]	El-Daly, A.A., Swilem, Y., Makled, M.H., El-Shaarawy, M.G. and Abdraboh, A.M. (2009) Thermal and Mechanical Properties of Sn-Zn-Bi Lead-Free Solder Alloys. Journal of Alloys and Compounds, 484, 134-142. https://doi.org/10.1016/j.jallcom.2009.04.108