Characterization of Indium addition on Sn-Bi-Sb Lead free Solder alloy

4231 | P a g e C o u n c i l f o r I n n o v a t i v e R e s e a r c h A u g u s t 2 0 1 6 w w w . c i r w o r l d . c o m Characterization of Indium addition on Sn-Bi-Sb Lead free Solder alloy S. Mosaad , A. R. Mohamed, Mustafa Kamal (1,*) Physics Department, Faculty of Science, Suez Canal University, Egypt saramosaad@windowslive.com 2 Physics Department, Faculty of Science, Port Said University, Egypt raoufahmed@yahoo.com 3 Metal Physics lab. Physics Department, Faculty of Science, Mansoura University, Egypt kamal42200274@yahoo.com Abstract


Introduction
In recent years, substantial efforts were made to develop lead-free solders that are suitable substitutes for classic tin-lead eutectic solders [1].There is a growing need for solders that can be used for applications with more demanding service conditions such as in Sealing in cryogenic applications, Soldering or fusing applications High-end device cooling by reduces operating temperatures.For these purposes, it is necessary to evaluate the properties of candidate solder alloys that are related to manufacturing and reliability.There are many different metals and metal alloys that can be used as solders and a set of binary alloys have been chosen as candidates for lead-free solders those are: Sn-Bi, Sn-Sb, Sn-Cu, and Sn-Zn.Among the ternary compositions, the Sn-Bi-Zn is used in making printing wiring boards [2].However all of these eutectic compositions have a melting temperature above 473 K.Among the commercial Lead-free alloys, Sn-58 wt% Bi eutectic alloy may be a favorable alloy especially for electronics and telecommunications.In fact, this alloy, which has the eutectic temperature of 412 K and has a higher ultimate tensile stress and shear strength over Sn-Pb eutectic [3,4].Bismuth has also been used as the alloying element in ternary Sn-Zn-Bi Sn-Ag-Bi and Sn-Bi-Cu systems to provide suitable substitutes for Sn-Pb solder alloys [5, 6, 7, and 8].
Indium also chosen in solder alloys because of Indium is ductile and malleable that makes it to deform and fill in the uneven microstructure of two mating parts, by only moderate pressure.This ductility and malleability is retained at cryogenic temperatures so that an assembly can maintain the effective seal, even in harsh environments.At relatively high thermal conductivity of 86W/mK at 85°C, indium is widely used in the applications of thermal management to dissipate the heat produced by electronic components.Indium compensates for different coefficients of thermal expansion (CTE) during bonding dissimilar parts.At small percentages, indium can improve the thermal fatigue performance of solders that used in electronics assembly.Indium alloys enable solders to withstand drop tests better than other low melting alloy.Several indium-containing alloys that melt at temperatures less than 180°C, could be used as step soldering or applications that require lower reflow temperatures.Indium has a low vapor pressure, making it suitable for use in high vacuum applications.
The effect of Sn on reversibility of liquid -liquid transition in Bi-Sb-Sn alloys had been done by Xianfen Li et al and the results show that Sn plays an important role on the reversibility of liquid-liquid transition [8].Dragan Manasijevic et al have studied experimentally the phase equilibria and thermodynamics of the Bi-Sb-Sn ternary system [9].Y.S. Hor and R.J. Cava have reported the thermoelectric properties of Sn-doped Bi-Sb that small amounts of Sn doping dramatically decrease the thermal conductivity of the alloy system using melt stoichiometric mixtures of elemental Bi,Sb and Sn in 4mm inner diameter quartz tube [10].Alberto Torres et al had performed and studied the effects of adding of Sb (0, 3 and 6wt.%) of Sn-Bi eutectic solder alloys on structure, melting, corrosion and mechanical properties [11].Thermodynamic C o u n c i l f o r I n n o v a t i v e R e s e a r c h A u g u s t 2 0 1 6 w w w .c i r w o r l d .c o m database for phase diagram in Sn-Sb-Bi ternary alloy system have been investigated by Ohnuma et al and thermodynamic calculation on the Sn-Sb-Bi showed by [12][13][14][15][16][17][18].
The aim of this study was to investigate the effects of In content on structure, electrical, thermal and mechanical properties of all melt-quenched ribbons of Sn70-x-Bi15-Sb15-Inx (where x= 0, 1, 3, 5, 7, and 9 in at.%) that promote the application of SnBiSbIn series alloys on the functionality industry.

Experimental procedures
The materials used in the present work are Sn, Sb, Bi, and In fragments, with purity was better than 99.99% produced by a single copper roller (200 mm in diameter) melt-spinning technique [19][20][21][22][23].The process parameters such as the ejection temperature, and the linear speed of the wheel were fixed at 873 K and 30.4 ms −1 respectively.X-ray diffraction analysis (XRD) was carried out with a XPERT-PRO X-ray diffractometer, using Cu-Kα radiation of λ = 1.5406Å. Differential Scanning Calorimetry (DSC) was carried out in a Shimadzu (DSC-50) with heating rate at 10 K•min −1 .The temperature dependence of resistivity (TDR) was measured by four probe method using micro ohmmeter of type BS407.The BS407 uses a four terminal measurement system via high quality Kelvin Clip leads with sensitivity is 1 μΩ.The heating range starts from room temperature up to 480 K with heating rate of 5 K•min −1 .Elastic moduli, the internal friction and the thermal diffusivity of melt-spun ribbons were examined in air atmosphere with a modified dynamic resonance method [24].

2-
Results and Discussion   Figure 1(e) show Sn63-Bi15-Sb15-In7 alloy and figure 1(f) show Sn61-Bi15-Sb15-In9 alloy, It quite clear that, in these two alloys, the all intermediate phases are exist and which may be evidence that In atomic percent become enough for the exists of all phases.XRD analysis is shown in Table 1.In general each unit cell contains an integer number of atoms and the crystal structure is attributed to a crystallographic system for a crystal tin.In practice, a cell containing a non-integer number of atoms as indicated in Table (II), it is well known that cell, usually contains point defects.The distribution of point defects could have a short range order and it varies from cell to cell.

Structure
The uniform macro strain causes a shift of the direction lines to new 2ϴ positions .This non-uniform micro strain causes a broadening of the corresponding diffraction line [25].Line width B, both full width at half maximum (FWHM) and integral breadth, were used a Williamson-Hall plot [26] as illustrated in figure (3).To find information about the crystallite size Deff and local lattice distortion < Σ 2 > in tin phases, the following equation may be used: The 1/Deff and 5 < Σ 2 > ½ parameters are given in Table (II ).For the Sn phase is immeasurably low, leads to a good crystallization state.The results are discussed predominantly in terms of the size and strain values obtained.

Thermal Analysis
Figure (4) shows the DSC curves for as-quenched melt-spun pure Sn70-x-Bi15-Sb15-Inx (x = 0, 1, 3, 5, 7 and 9 in at %) alloys.The endothermic peak due to melting was obtained, the melting temperature Tm and the enthalpy of fusion ΔHm have been determined.ΔHm was obtained from the integral under the DSC peak of melting as given by equation: Where, Cp is the heat capacity at constant pressure, T0 and Tf are known as onset melting temperature and final melting temperature of the specimen, respectively.The pasty range is very important parameter in solder, the highest value calculated to be 15.5 for Sn63-Bi15-Sb15-In7 alloy and the lowest value is 7.59 for Sn69-Bi15-Sb15-In1 alloy.

Table (III).
The DSC Details for as-quenched melt-spun alloys.

Electrical properties
Figure (5) shows the temperature dependence of resistivity obtained for as-quenched melt-spun Sn70-x-Bi15-Sb15-Inx , x = 0, 1, 3, 5, 7, and 9) alloy in the temperature range from 300 to 450 K.The behavior is metallic, that mean the resistivity increases by increasing temperature.The resistivity at room temperature ρ is found to be 239.088* 10 -8 Ω.m for Sn70-Bi15-Sb15 alloy.By increasing In content, the resistivity decreases linearly up to 92.5 * 10 -8 (Ω.m), which shown in Table (IV) and figure 6 (a).The temperature coefficient of resistivity TCR was calculated to be 14.05 × 10 -3 K -1 for Sn70-Bi15-Sb15 alloy.The TCR decreased due to the addition of In as shown in figure 6 (b).
Table (V) gives a list of the electrical conductivities and other transport parameters of the studied quenched ribbons from the melt.Values of the concentrations of conduction electrons, mobility (μ) , collision time (ι) and mean free Path (l) are also given accordingly to the quantum theory [29] .

Mechanical Properties
Elastic modulus (E), Shear modulus (G), Bulk modulus (B) and Poisson's ratio are calculated by dynamic resonance method for Sn70-x-Sb15-Bi15-Inx alloys, x=0, 1, 3, 5, 7 and 9 at.%) [30,31].It is investigated that (E) increases gradually with increasing the amount of In present which shown as in figure (7) up to 39.02708 GPa to Sn61-Sb15-Bi15-In9 alloy.It has been found that the additions of In in SnSbBiIn as melt-quenched ribbons improve the elastic moduli and it is attributed to the substantial refinement of the solidification microstructure.The mechanical results are shown in Table (VI).It is seen that there is a gradual increase in values of the mechanical properties with the amount of In content.
It was found that, the existence of metastable structural configurations at the interface and the internal strain distribution can obviously affect the mechanical behavior.This part reports some results of elasticity or internal friction measurements coupled to thermal diffusivity analysis on Sn70-x-Sb15-Bi15-Inx melt-quenched ribbons using chill-block melt-spin technique [32][33].There are several equations to do these analyses.It is easy to show that the logarithmic decrement δ of the free vibration amplitude is simply related to the internal friction Q -1 . When the damping is small, the internal friction Q -1 is expressed by the formula: Where, δ is the logarithmic decrement and defined as the natural logarithm of the ratio of successive amplitudes.Then: Where, A1 and A2 are the amplitudes at times t1 and t2, f is the natural frequency of the free -vibrating system, Δ E is the energy lost per cycle and E is the stored vibration energy.
The internal friction is very sensitive to the small changes in the mechanical state of the melt-spun ribbons and it can be used to measure thermal diffusivity.From the frequency f , at which the peak damping occurs, thermal diffusivity Dth is simply related to the frequency f by the formula : Where, T is the absolute temperature [34].The mathematical formula that relates thermal diffusivity Dth to thermal conductivity K is given by: Where, Cp is heat capacity and it is the temperature-dependent at constant pressure, and ρ is the density, as shown in Table (VIII).A typical values of thermal conductivity in units (W.m -1 .k - ).The information is necessary for modeling the optimum conditions during processing.

Conclusion
From the present study the data shows that:  From the analysis of X-ray diffraction result has proved that Sn70-x-Sb15-Bi15-Inx , the alloy composed of tetragonal Sn , rhombohedral Bi phases, with a few lines form Sb phase, In phase, Bi3In5, and SnSb, InSb, In0.2Sn0.8intermetallic compounds.


It is found that by increasing Indium content, the electrical resistivity value of SnBiSbIn melt-spun alloys decreases linearly.The scattering centers of the electrons decrease which leads to an increase of orderly atomic arrangement.The result is a net increase in the electrical conductivity.


The temperature coefficient of resistivity (TCR) decreases with increasing Indium content.

Figure 1 (Figure 1
Figure 1(b) shows for Sn69-Bi15-Sb15-In1 alloy, it is clear that Sb phase and SnSb Intermetallic compound are disappeared and there is an existence of new Intermetallic compound, these are, InSb with Orthorhombic crystal structure (S.G.: Pmmn), and Bi3In5 Intermetallic phase with Tetragonal unit cell (S.G.: 14/mcm).It is notice that Sn phase and Bi phase exist in these positions.

Figure 2 (
Figure 2(a) shows the variation of the axial ratio c/a with In concentration and figure 2(b) shows the variation of the volume of unit cell of Sn phase with In concentrations.It is clear that, there is a drop at axial ratio at Sn65-Bi15-Sb15-In5 alloy without these point all values of axial ratio increased by increasing In concentration.From the figure 2 (b), it is clear that the volume of unit cell of Sn has a variation and the highest value belongs to Sn67-Bi15-Sb15-In3 alloy and the lowest value belongs to Sn63-Bi15-Sb15-In7.

Figure 2 .
Figure 2. (a) The variation of c/a with Incc concentration; (b) The variation of v with In concentration
C o u n c i l f o r I n n o v a t i v e R e s e a r c h A u g u s t 2 0 1 6 w w w .c i r w o r l d .c o m decreases by increasing In concentration from 473 K for Sn70-Bi15-Sb15 to 432.65 K for Sn61-Bi15-Sb15-In9 alloy.The enthalpy of fusion ΔHm and the entropy ΔS decreases by increasing In for all alloys except for Sn65-Bi15-Sb15-In5 and Sn69-Bi15-Sb15-In1 alloys.
e s e a r c h A u g u s t 2 0 1 6 w w w .c i r w o r l d .c o m the thickness of the ribbon .The measured values for internal friction Q -1 and thermal diffusivity Dth are listed in Table(VI).The data indicate that the internal friction is quite small and rapidly decrease friction in higher In content for Sn61-Bi15-Sb15-In9 in atomic percent for melt-quenched ribbons.Increasing indium concentrations the thermal diffusivity Dth is increasing.


Melting temperature decreases with increasing Indium content.Alloys have thermal stability because there is no phase change before melting peaks and there is a good pasty range in alloy.C o u n c i l f o r I n n o v a t i v e R e s e a r c h A u g u s t 2 0 1 6 w w w .c i r w o r l d .c o m  It has been found that the additions of In in SnBiSb as melt quenched ribbons improve the elastic moduli and it is attributed to the substantial refinement of the solidification microstructure. Internal friction decreases by increasing Indium content. Sn61-Bi15-Sb15-In9 has best physically prosperities, such as high values of electrical resistivity, elastic moduli and poisson's ratio, with lower melting point comparison with Sn-Pb eutectic which is indicated in table IX.