Final Meeting of the COST Action 531 Lead-Free Solder Materials May 17th – 18th, 2007 Vienna, Austria Report presented by Z. Moser

Within COST 531 Program realized from 2003 – 2006 at the Institute of Metallurgy and Materials, Polish Academy of Sciences in Kraków, Poland the following general research has been undertaken : “Experimental determination and modeling of physicochemical properties of multi-component alloys on the tin base “. Within this research two studies has been realized: : “ Influence of Sb additions on surface tension and density of Sn-Ag-Cu-Sb alloys. Experiment vs. modeling”. a.Z. Moser, W. Gasior, J. Pstruś, “ Surface tension and density of Sn based Sn-Ag-Cu alloys with Sb additions”, Proceedings of COST Action 531 Lead-free Solder Materials, Mid-term Meeting, Lausanne 2005, February 24-25, Switzerland, b. Z.Moser, W.Gąsior, J.Pstruś, I.Ohnuma, K.Ishida, “ Influence of Sb additions on surface tension and density of Sn-Sb, Sn-Ag-Sb and Sn-Ag-Cu-Sb alloys”. Experiment vs. modeling, International Jounal of Materials Research, Zeitschrift fuer Metallkunde, 97, 2006, p Dedicated to Professor Dr. Ferdinand Sommer on the occasion of his 65 th birthday.

: “ Influence of In additions on surface tension and density of the Sn-Ag-Cu-In alloys. Experiment vs. modeling”. This research has been realized jointly with Slovak Academy of Sciences (Pavol Sebo). a.Z. Moser, W. Gąsior, J. Pstruś, “Influence of In additions on surface tension and density of In-Sn, Sn-Ag-In and Sn-Ag-Cu-In liquid solders. Experiment vs. Modeling”. COST 531, MC Meeting ( ) & WG Meeting, ( ). Genoa, Italy. b. Zbigniew Moser, Pavol Sebo, Władysław Gąsior, Peter Svec and Janusz Pstruś, “Wettability Studies of Sn-Ag-Cu-In Liquid Solders and Interaction with Cu Substrate”, Program and Abstracts Calphad XXXVI The Pennsylvania State University, State College, Pennsylvania, USA, May 6 -11, 2007, p.35, This joint research will be presented to day.

Wettability Studies of Sn-Ag-Cu-In Liquid Solders and Interaction with Cu Substrate Zbigniew Moser*, Pavol Sebo**, Władysław Gąsior*, Peter Svec*** and Janusz Pstruś* *Institute of Metallurgy and Materials Science, Polish Academy of Sciences, Kraków, Reymonta Street 25, POLAND **Institute of Materials and Machine Mechanics, Slovak Academy of Sciences, Racianska 75, , Bratislava 3, SLOVAKIA ***Institute of Physics, Slovak Academy of Sciences, Dubravska cesta 9, Bratislava 45, SLOVAKIA Plan of presentation: 1. Introduction 2. Surface tension and density measurements of the (Sn3.13Ag0.74Cu) + In liquid alloys 3. Modeling of the surface tension 4. Contact angles measurements of the (Sn3.13Ag0.74Cu) + In liquid alloys 5. Interaction studies of the quaternary alloys with Cu substrate 6. Conclusions 7. Final remarks

Metals Binary Alloys Multicomponent Alloys Pb Sn In Ag Bi Sb Cu Zn Al Au Pb – Sn Ag – Sn Ag – In Bi – Sn In – Sn Ag – Bi Sb – Sn Sn – Zn Ag – Sb Cu – Sn Cu – Sb (Sn-Ag) eut +In (Sn-Ag) eut +Bi (Sn-Ag) eut +Cu (Sn-Ag) eut +Sb (Sn-Ag) eut +Cu+Sb (Sn-Ag) eut +Cu+Bi (Sn 3.13Ag 0.74Cu)+In This study Table 1. The investigated liquid metals and alloys Fig. 1. The first window of the SURDAT database [1] Z. Moser, W. Gąsior, A. Dębski and J. Pstruś, Database of lead – free soldering materials, edited by IMIM PAS and printed by Orekop, Kraków 2007, ISBN [2] J.A.V. Butler, The Thermodynamics of the Surfaces of Solutions, Proceedings of the Royal Society of London series A, CXXXV, (1932) [3] Liu X.J., Inohana Y., Ohnuma I., Kainuma R., Ishida K., Moser Z., Gąsior W., Pstruś J., Experimental Determination and Thermodynamic Calculation of the Phase Equilibria and Surface tension of the Ag-Sn-In System, J. Electron. Mater., 31, (2002), [4] P. Sebo, P. Stefanik, Kovove Mater., Effect of In Addition on Sn-Ag Solder, Its Wetting and Shear Strength of Copper Joints, 43, (2005) (Decreasing of contact angles adding 6.6 and 9 mass.% In to (Sn-Ag) eut ) [5] M. E. Loomans, S.Vaynmann, G. Ghosh, M. E. Fine, J. Electronic Mater. 23 (1994) (Similar decreasing of contact angles by In additions). [6] S. Hwang, Lead-free Implementation and Production, A Manufacturing Guide, McGraw-Hill, (2005), ISBN , Chapter Three: Selecting Lead-free Alloys for Solder Interconnections. (From meniscographic studies with flux wetting force and wetting time of Sn 4.1 Ag0.5Cu 4In ( mass.%) nearly equivalent to Sn-Pb eutectic). 1. Introduction

The main aim is to confirm the previous observation of In additions to (Sn-Ag) eut on wettability and to extend it in the presented studies of quaternary alloys (Sn 3.13Ag 0.74Cu) + In combining surface tension, density and modeling of surface tension from Krakow, Poland with contact angles and interaction of liquid alloys with Cu substrate using flux undertaken in Bratislava, Slovakia within COST 531 Program. The starting material was nearly eutectic alloy (Sn 3.13Ag 0.74Cu) with 2, 3, 4, 15, 30, 50 and 75 at.% In.

2. Surface tension and density measurements of the (Sn3.13Ag0.74Cu) + In liquid alloys The density and surface tension measurements of the (Sn3.13Ag0.74Cu) + In liquid alloys at In concentrations ( 2, 3, 4, 15, 30, 50 and 75 at.%) by the maximum bubble pressure method and dilatometric technique were conducted in the temperature range from 158 °C to 936 °C. Results are presented in Tables 2 and 3 and in Figures 2 and 3. In Figures 4 and 5 are shown isotherms of surface tension and density. As indicated in the introduction no change of both temperature dependence of the surface tension and density is observed. The preliminary results were presented in Genoa [1]. [1] COST Action 531, MC Meeting (25/02/2006) & WG Meeting, (23-24/02/2006) in Genoa, Italy.

X In σ=A+B∙T mN∙m -1 σ 523K mN∙m -1 σ 1023K mN∙m -1 Err(a) mN∙m -1 Err(b) mN∙m∙K -1 0* ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±11.3 ±7.8 ±9.0 ±9.9 ±8.0 ±10.4 ±9.6 ±11.1 ±18.5 ±11.9 ± ± ± ± ± ± ± ± ± * - Sn 3.13Ag 0.74Cu X In % at ρ=A+B∙T g∙cm -3 ρ 523K g∙cm -3 ρ 1023K g∙cm -3 Err(a) g∙cm -3 Err(b) g∙cm -3 ∙K -1 0* ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±0.03 ±0.028 ±0.036 ±0.050 ±0.088 ±0.076 ±0.063 ±0.067 ±0.022 ±0.032 ± ± ± ± ± ± ± ± Table 2. Temperature dependencies of the density of the liquid quaternary (Sn 3.13Ag 0.74Cu)+In and ternary alloys with the calculated errors of the A and B parameters and the densities calculated at 523 K and 1032 K Table 3. Temperature dependencies of the surface tension of the liquid quaternary (Sn 3.13Ag 0.74Cu)+In and ternary alloys with the calculated errors of the A and B parameters and the surface tension calculated at 523 K and 1032 K

Fig. 2. The temperature dependencies of the density of (Sn 3.13Ag 0.74Cu) + In liquid alloys Fig. 3. The temperature dependencies of the surface tension of (Sn 3.13Ag 0.74Cu) + In liquid alloys

Fig. 4. The isotherms of the density of (Sn 3.13Ag 0.74Cu)+In liquid alloys at 523 K and 1023 K Fig. 5. The isotherms of the surface tension of (Sn 3.13Ag 0.74Cu)+In liquid alloys at 523 K and 1023 K

3. Modeling of the surface tension Two kinds of modeling of surface tension were used for quaternary alloys Sn-Ag-Cu-In, similarly as in previous studies on Sn-Ag-Cu-Sb system [1]. [1] Z.Moser, W.Gąsior, J.Pstruś, I.Ohnuma, K.Ishida, “Influence of Sb additions on surface tension and density of Sn-Sb, Sn-Ag-Sb and Sn-Ag-Cu-Sb alloys. Experiment vs.modeling”, International Jounal of Materials Research, Zeitschrift fuer Metallkunde, 97, (2006), Dedicated to Professor Dr.Ferdinand Sommer on the occasion of his 65th birthday. 1. Butler model with thermodynamic properties of liquid constituent components and surface tension of pure components. This modeling was successfully tested in studies of systems presented in SURDAT database with observation that the experimental temperature dependence of the surface tension is linear, while from modeling slightly curvilinear dependence was calculated. For such procedure in the case of quaternary Sn-Ag-Cu-In system we should know data of six binaries: Cu-In, Cu-Ag, Sn-Ag, Ag-In, Sn-Cu, In-Sn, four ternaries: Sn-Ag-Cu, Sn-Ag-In, Sn-Cu-In, In-Ag-Cu and for quaternary alloy (one quaternary alloy with equal concentration of components 0.25 molar fraction was investigated).

In the case of modeling 2, we are basing on experimental data of surface tension of constituent binary systems with ternary and quaternary correction factors to elaborate the temperature and concentration dependence of the surface tension of the Sn-Ag-Cu-In system. For the remaining, not previously investigated surface tension and density, in this study were determined Cu-In and Cu-Ag, ternaries Sn-Ag-Cu, Sn-Ag-In, In-Ag-Cu and one quaternary alloy with equal concentration of components 0.25 molar fraction. As an example, in Table 4 are presented surface tension data of ternaries and quaternary alloy. Table 4. Temperature dependencies of the surface tension of the liquid quaternary Sn 25Ag 25Cu 25In and ternary alloys Sn 25Ag 25In, Sn 25Ag 25Cu and In 25Ag 25Cu with the calculated errors of the A and B parameters and the surface tension calculated at 973 K and 1273 K X % atσ = A +BT mN·m -1 σ 973K mN·m -1 σ 1273K mN·m -1 Err(A) mN·m -1 Err(B) mN·m -1 ·K -1 Sn25Ag25In Sn25Ag25Cu In25Ag25Cu Sn25Ag25Cu25In = T = T = T = T 560.7± ± ± ± ± ± ± ±12.3 ±13.1 ±8.2 ±12.4 ±26.0 ± ± ± ±0.0227

Fig.6. Comparison of calculations of the surface tension of the quaternary system Sn-Ag-Cu-In by Butler’s model and with temperature-concentration dependence and with one experimental alloy (Table 4) with equal 0.25 molar fractions. Thin lines show the Butler model, while thick correspond to temperature concentration dependence of the surface tension Results of calculations by the Butler model show lower values of the surface tension due to the fact that interaction parameters for Ag-Cu-In and Cu-In-Sn were not taken into calculations. In addition, only the limited amount of alloys for binary and ternary alloys of surface tension was investigated with one quaternary sample. The obtained results from both methods are compared in Fig.6.

4. Contact angles measurements of the (Sn3.13Ag0.74Cu) + In liquid alloys Wetting of copper substrates was studied by sessile drop method. Solder in a cube form was covered by flux and put on the substrate and after melting at given temperature (250, 280 and 320 o C) pictures of drop were taken by digital camera up to 30 minutes. Contact angles were measured by computer. After the drop solidifies, specimen were cut perpendicularly for metallographic studies, discussed in the next section. Typical course of time dependencies of contact angle for pure (not containing In) Sn 3.13Ag 0.74Cu, Sn 2.52Ag 0.57Cu 30In and Sn 1.2Ag 0.27Cu 75In are presented on Figs Except the beginning of wetting, the contact angle practically does not depend on the wetting temperature and with the increase of In concentration is lowered the time to reach the constant values of contact angles, which gradually are decreasing. Due to the observed in Figs.7-9 the negligible differences in contact angles in the temperature interval, in Fig.10 is plotted the change of contact angle after 30 minutes for all investigated alloys. The lowering tendency of the contact angle is observed with some scattering at low In content.

Fig.7. Change of the contact angle for the starting alloy Sn 3.13Ag 0.74Cu Fig. 8. Change of the contact angle for Sn 3.13Ag 0.74Cu + 30 at.% In

Fig. 9. Change of the contact angle for Sn 3.13Ag 0.74Cu + 75 at.% In Fig. 10. Change of contact angles for Sn-Ag-Cu-In alloys after 30 minutes

5. Interaction studies of the quaternary alloys with Cu substrate Metallographic studies of the structure of the boundary between the solder and substrate as well as the structure of the solder itself was studied by electron scanning microscopy (SEM). Energy dispersive X-ray analyzer (EDX) was used to measure the chemical composition of the interface as well as the bulk solder. The same specimen which were used for SEM and EDX investigation were also used for X-ray diffraction phase analysis of the solder and substrate. For low In concentration (up to 15 at.%) Cu interface is formed by Cu 6 Sn 5 phase. For higher concentration of In (30-50 at.%) Cu interface if formed by Cu 41 Sn 11 phase. For highest In concentration (75 at.%) Cu interface is formed by Cu 3 (Sn,In) phase.

6. Conclusions In this presentation, investigating the influence of In on wettability of the alloy Sn 3.13Ag 0.74Cu close to ternary eutectic Sn-Ag-Cu it was confirmed starting from previous data on In-Sn and Sn-Ag-In [1] that due to the nearly the same surface tension and density values of pure In and Sn the beneficial influence of In is reflected by the lowering of the contact angles, with practically no change of temperature dependence of both surface tension and density. Isothermal behaviour of surface tension with “S” shape starting from In-Sn and Sn-Ag-In proceeding into the investigated in this study Sn-Ag-Cu-In is probably in addition connected with the peculiar properties of liquid In-Sn alloys showing extrema on isothermal behaviour of electrical resistivity and viscosity [2] corresponding well to the existence of intermetallic phases in the phase diagram of In-Sn phase diagram. It is the another proof of the mutual correlations between thermodynamic properties, physical properties and the character of the phase diagram. [1] X. J. Liu, Y. Inohana, I. Ohnuma, R. Kainuma, K. Ishida, Z. Moser, W. Gąsior, J. Pstruś, J. Electronic Mater. 31 (2002) [2] B.Predel, M.Hoch, M.Pool, Phase Diagrams and Heterogeneous Equilibria, Springer-Verlag Berlin Heidelberg (2004)

7. Final remarks. 1.Presented today joint results with P. Sebo will be elaborated for Calphad journal. 2.SURDAT database realized in parallel to COST 531 Program has been introduced on website of COST 531 Program. 3.In addition, from financing of COST 531 Program under research entitled “Experimental determination and modeling of physicochemical properties of multi-component alloys on the tin base “ within the additional study has been realized by dr Piotr Ozga: “ The study of a possibility of the electrodeposition of Sn-Ag alloys from aqueous solutions”. a. P.Ozga, “Equilibria in Aqueous Solutions of Ag(I)-Sn(II/IV) in Presence of Strong Complexing Ligands”, CALPHAD XXXIII, Krakow, (Poland) May 30 – June 4, 2004, Abstracts, p b. P.Ozga, “Electrodeposition of Sn-Ag and Sn-Ag-Cu alloys from the thiourea solutions”, Archives of Metallurgy and Materials, 3, (2006), The results of this study were used in habilitation thesis of P. Ozga edited by the Institute of Metallurgy and Materials, ISBN , Krakow, (2006), Special issue of the Archives of Metallurgy and Materials 3/2006 has been devoted to results realized within COST 531 Program.

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