- Email: [email protected]
Phase equilibria in the Au–In–Sn ternary system
CALPHAD: Computer Coupling of Phase Diagrams and Thermochemistry 33 (2009) 17–22
Contents lists available at ScienceDirect
CALPHAD: Computer Coupling of Phase Diagrams and Thermochemistry journal homepage: www.elsevier.com/locate/calphad
Phase equilibria in the Au–In–Sn ternary system G. Borzone a,∗ , N. Parodi a , G. Cacciamani a , A. Watson b a
DCCI-University of Genova and INSTM, Genova, Italy
b
IMR/SPEME, University of Leeds, UK
article
info
Article history: Received 22 June 2008 Received in revised form 15 August 2008 Accepted 13 September 2008 Available online 1 October 2008 Dedicated to the memory of Prof. Riccardo Ferro Keywords: Phase diagram DSC Au–In–Sn ternary system Solder alloys
a b s t r a c t Phase equilibria of the Au–In–Sn system have been investigated by Differential Scanning Calorimetry (DSC), metallographic examination, Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDS) measurements. The 130 ◦ C isothermal section of the phase diagram was studied. The ternary diagram shows six three-phase fields, and one ternary Au4 In3 Sn3 phase, which melts incongruently at 382 ◦ C and shows a homogeneity range between 21 and about 30 at.% In, at constant Au/Sn ratio. The DSC results have been combined with microstructural observations and thermodynamic modelling [G. Cacciamani, G. Borzone, A. Watson, Thermodynamic modelling and assessment of the Au–In–Sn system, CALPHAD 33(1) (2009) 100–108] and seven invariant reactions have been identified. © 2008 Elsevier Ltd. All rights reserved.
1. Introduction The effects of the interfacial reactions between solder and substrate material under operating conditions are very important to the performance of solder joints. Many electronic components and printed circuit boards are plated with a variety of thicknesses of gold, ranging from 10 to 15 to several hundred micrometers. In order to produce an electrically and metallurgically sound joint when soldering to gold-plated components and boards, the wetting capability of the solder in the presence of a suitable flux must be considered. For long-term reliability of a soldered assembly, a solder joint must not be brittle or susceptible to fatigue. The interaction and diffusion of gold in Sn-based soldering is in fact of particular interest, since gold forms a very brittle AuSn4 intermetallic phase. Indium alloys offer the advantages of reduced intermetallic phase formation, the capability of gold soldering (for the repair of jewellery, for example) and thermal fatigue resistance in the joints produced. Thus, the aim of this work is to study alloys of the Au–In–Sn system, which is important in order to understand the chemistry of electrical contacts made from lead-free In–Sn alloys and Au containing substrates.
∗ Corresponding address: Dipartimento di Chimica e Chimica Industriale, Via Dodecaneso 31, 16146 Genova, Italy. Tel.: +39 010 3536153; fax: +39 010 3625051. E-mail address: [email protected] (G. Borzone). 0364-5916/$ – see front matter © 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.calphad.2008.09.008
This contribution reports the results of experimental investigation of the phase diagram of the Au–In–Sn system, but in order to define the phase diagram completely, both computational and experimental approaches should be performed, and to this end, key experiments reported here and thermodynamic modelling that will be published elsewhere [1], have been combined in a recursive procedure. 2. Literature data A complete description of the ternary phase diagram is not available. The existence of the ternary phase Au4 In3 Sn3 , hP10-Pt2 Sn3 type, having a congruent melting point at about 430 ◦ C was reported by Schubert et al. [2,3], who also investigated a portion of the ternary system. The alloys were examined as cast and following heat treatment at 250 ◦ C, or between 100 and 350 ◦ C. Humpston [4] studied the AuIn–AuSn section and found a two-phase region below about 325 ◦ C. All of these data have been critically assessed by Haussmann [5]. An assessed isothermal section (for approximately 250 ◦ C) has been presented by Prince [6]. It is worth noting that the published phase diagram is not an equilibrium diagram, because no samples were annealed at or quenched from that temperature. As stated by Prince [6], the assessed version may be considered only as ‘‘a guide to the 250 ◦ C isothermal for alloys whose compositions are on the Au-rich side of a line joining AuIn2 to AuSn4 . For alloys on the Au-poor side of this line the equilibria
18
G. Borzone et al. / CALPHAD: Computer Coupling of Phase Diagrams and Thermochemistry 33 (2009) 17–22
are to be interpreted as equivalent to the 100 ◦ C section’’. The liquidus surface is not known. Information on the limiting binary systems was obtained from the literature [7–10]. 3. Experimental The metals used were indium ingot 99.999 mass%, tin 99.999 mass% and gold 99.99+ mass% nominal purity. Samples were prepared at compositions given in Table 1 by melting pieces of the constituent metals in alumina crucibles in an induction furnace under an argon atmosphere. The sample mass was about 1–2 g. The alloys were generally annealed at 130 ◦ C for 15 days or one month or more in order to reach the equilibrium state, and then quenched into cold water. Several samples were annealed at 300 ◦ C for several days, then at 130 ◦ C for 1 month followed by water quenching. On the basis of results obtained from the modelling, carried out in parallel in order to predict liquidus temperatures, the samples were subjected to thermal analysis by using a Setaram DSC111 apparatus with heating and cooling rates of 5, 3, 1 or 0.3 ◦ C/min. The DSC samples were prepared by sealing 500–700 mg of the alloys under Ar in tantalum crucibles. The calorimeter was calibrated by measuring the melting temperature of metallic In, Sn, Pb and Zn (99.999 mass% purity) and the temperature was obtained with an accuracy of Tm ± 0.5 ◦ C. The microstructure of all of the samples, either as cast, after annealing or after DSC analysis, was investigated by optical and scanning electron microscopy (SEM). An electron microscope (Zeiss EVO-40) equipped with an OXFORD INCA Energy 300 analyser, which allowed local chemical analysis by Energy dispersive X-ray (EDS), was employed. For quantitative EPMA (electron probe microanalysis), the samples were analysed using an acceleration voltage of 20 kV using cobalt as calibration standard for the beam current, gain and resolution of the spectrometer. The X-ray intensities were corrected for ZAF (Z Absorption Fluorescence) effects using pure elements as standards. The samples were observed by means of a back-scattered electron detector (BSE). Microanalysis (EPMA) was used to check the overall composition of the samples, the uniformity of chemical composition and the composition of the coexisting phases. 4. Results and discussion The phase equilibria in the ternary Au–In–Sn system were studied by a combination of the methods described above. Altogether, 34 ternary alloys were prepared with overall compositions as given in Table 1, where all the experimental results are presented. The corresponding partial isothermal section at 130 ◦ C is shown in Fig. 1. No samples were prepared in the In–Sn rich-region of the system and hence this part of the section is omitted in the figure. The results of DSC analysis are given in Table 1, together with details of the experimental conditions employed. The temperatures reported in Table 1 represent average values of the thermal effects detected during first and second heating. Usually, pronounced undercooling effects were observed for all of the investigated alloys, and the relevant phase diagram information was, in general, taken from the heating curves. The stability fields of the different phases at 130 ◦ C shown in Fig. 1 agree in some part with the general features of the isothermal section at approximately 250 ◦ C proposed by Prince [6] and the corresponding two and three phase equilibria. However, in this work, a larger extension in the ternary system than had been previously reported was observed for the solid solutions based on the binary compounds. A typical feature is their extension into the
Fig. 1. Isothermal section of Au–In–Sn system at 130 ◦ C showing the τ1 (Au4 In3 Sn3 ) ternary phase: The three-phase fields are marked by ∗.
ternary system in the direction parallel to the In–Sn axis. AuSn4 dissolves up to 6 at.% In, while AuSn2 dissolves up to 1 at.% In. In agreement with Humpston [4], the AuIn–AuSn section was confirmed as not being pseudo-binary and a considerable solubility of indium in AuSn (up to about 16 at.%) and extensive solubility of Sn in AuIn (up to 20.0 at.%) was observed. The AuIn2 phase dissolves up to 22 at.% Sn. A limited amount of Sn solubility (up to 2 at.%) in the Au3 In phase was also observed. A maximum solubility of indium in Sn of up to 1 at.% was observed. The six three-phase fields determined at 130 ◦ C in the region investigated are: AuSn2 –AuSn–Au4 In3 Sn3 , AuSn–Au4 In3 Sn3 –AuIn, AuSn–Au7 In3 –AuIn, AuIn– Au4 In3 Sn3 –AuIn2 , AuSn2 –Au4 In3 Sn3 –AuIn2 , and AuIn2 –AuSn2 –AuSn4 . The primary crystallization areas have been determined on the basis of the information obtained by metallographic analysis, see Table 1. From the DSC results, seven invariant reactions have been identified, 4 of them involving the liquid phase. This observation has been supported by thermodynamic modelling that will be published elsewhere [1]. The invariant reactions are listed in Table 2 together with the corresponding temperature and reaction type. The recorded liquidus temperatures indicate a decrease in the slope of the liquidus surface, from the Au–In binary system to the Sn-rich corner. The alloys investigated in the Sn-rich part of the system, showed only the solid state invariant reaction U13 , AuSn4 + γ (In, Sn) → AuIn2 + (β Sn), which takes place at 196 ◦ C. The tie-lines related to samples 2 and 3 are shown in Fig. 1. Fig. 2 shows the DSC thermograms obtained for samples 6 and 20. Concerning the Au4 In3 Sn3 ternary phase, thermal and metallographic analyses suggest incongruent melting, in contrast with the literature. Samples having a composition close to the Au4 In3 Sn3 phase (19 and 20) showed on cooling, as reported by Schubert et al. [2], a liquidus temperature of 430 ◦ C, followed by a number of transformations below the liquidus (see the DSC effects recorded in Fig. 2). However, on the basis of the present studies, the formation of the Au4 In3 Sn3 phase was related to the L + AuIn2 + AuSn → Au4 In3 Sn3 P1 invariant reaction at 382 ◦ C. Correspondingly, a large region of primary crystallization of AuIn2 and a small region for Au4 In3 Sn3 were observed. On the basis of the EPMA analyses, the
G. Borzone et al. / CALPHAD: Computer Coupling of Phase Diagrams and Thermochemistry 33 (2009) 17–22
19
Table 1 Experimental results of DSC, phases observed and EDS compositions of the investigated Au–In–Sn ternary alloys Sample
Alloy composition by EPMA at.% Au In Sn
Thermal treatment
Phases
Microprobe analysis at.% Au In
Sn
1
2.3
0.7
97
As cast
Primary crystals of (β Sn)
0.0
0.0
100
DSC 1 ◦ C/min
AuSn4−x Inx
20.0
4.0
76.0
2
4.0
8.0
88.0
130 ◦ C, 30 days
Primary crystals of AuIn2−x Snx (β Sn) 33.3 0.2
DSC 3 C/min
46.7 2.0
20.0 97.8
◦
3
5.0
10.5
84.5
130 ◦ C, 15 days
Primary crystals of AuIn2−x Snx (β Sn)
5.2
80.5
130 ◦ C, 54 days
48.5 5.5
6
28.0
26.0
11.0
16.0
61.0
58.0
130 ◦ C, 35 days
130 ◦ C, 54 days
DSC 1 ◦ C/min 7
27.5
16.5
56.0
◦
130 C, 20 days
DSC 1 ◦ C/min sample not in equilibrium 8
27.0
17.0
56.0
◦
130 C, 30 days
Large primary crystals of Au4 In3 Sn3 AuSn4−x Inx AuSn2−x Inx sample not in equilibrium Primary crystals of AuIn2−x Snx Au4 In3 Sn3 AuSn4−x Inx Au4 In3 Sn3 AuIn2−x Snx AuSn4−x Inx
20.0 0.0
6.0 1.0
74.0 99.0
40.5 20.5 33.0
20.0 3.0 2.0
39.5 76.5 65.0
33.8 40.3 20.0
46.8 28.1 6.0
19.4 31.6 74.0
40.6 34.7 20.7
28.4 44.0 6.3
31.0 21.3 73.0
Primary crystals of AuIn2−x Snx AuSn2−x Inx AuSn4−x Inx
33.5 33.5 20.0
44.5 1.0 6.0
22.0 65.5 74.0
28.0
17.0
55.0
130 ◦ C, 20 days sample not in equilibrium
Au4 In3 Sn3 AuIn2−x Snx AuSn4−x Inx
41.0 34.0 20.7
30.0 42.0 6.0
29.0 24.0 73.3
10
28.6
20.0
51.4
130 ◦ C, 30 days sample not in equilibrium
Primary crystals of AuIn2−x Snx Au4 In3 Sn3 AuSn4−x Inx
34.0 40.3 20.0
45.0 24.4 6.5
21.0 35.3 73.5
130 ◦ C, 30 days
Primary crystals of AuIn2−x Snx Au4 In3 Sn3 AuSn4−x Inx
34.0 39.5 20.3
45.5 24.9 6.2
20.5 35.6 73.5
30.0
22.5
47.5
DSC 1 C/min sample not in equilibrium ◦
12
13
33.4
33.7
24.4
22.8
42.2
43.5
130 ◦ C, 20 days sample not in equilibrium see Fig. 3
Primary crystals of AuIn2−x Snx Au4 In3 Sn3 AuSn4−x Inx
33.5 39.2 19.0
46.5 32.1 6.8
20.0 28.7 74.2
130 ◦ C, 20 days
AuIn2−x Snx Au4 In3 Sn3 AuSn4−x Inx
33.5 40.0 19.0
49.0 29.8 6.8
17.5 30.2 74.2
DSC 1 ◦ C/min 14
44.6
4.6
50.8
◦
130 C, 20 days DSC 1 C/min
AuSn1−x Inx AuSn2−x Inx
50.5 34.0
6.0 1.0
43.5 65.0
◦
15
40.2
9.5
50.3
130 ◦ C, 20 days
DSC 1 ◦ C/min
205 206.8 207
Liquidus
192
150 194 196
U13
221
Liquidus
139 194 196
U13
206 215 225
–
Liquidus
207 261
201 251
Liquidus
211 261 346 384 388
203 260 327
U12 U8
377
Liquidus
211 230 263 363 387
9
11
211 220 224
18.2 94.4
Large primary crystals of AuSn4−x Inx (β Sn)
DSC 1 ◦ C/min 5
Reaction
160 33.3 0.1
DSC 1 C/min
14.3
Cooling
209 212 228
◦
4
Heating
Primary crystals of AuSn1−x Inx AuSn2−x Inx Au4 In3 Sn3
50.5 33.8 40.8
12.0 1.5 21.0
37.5 64.7 38.2
212 259 368 393 407
260 405 420
197 261 337 364 382
U8
Liquidus
204 260 343
U8
395
Liquidus
260 383
U8 P1
416
Liquidus
253 301 307 422
U7 407
Liquidus
230 247 248 301
U7 (continued on next page)
20
G. Borzone et al. / CALPHAD: Computer Coupling of Phase Diagrams and Thermochemistry 33 (2009) 17–22
Table 1 (continued) Sample
16
17
18
19
Alloy composition by EPMA at.% Au In Sn
40.0
46.6
37.5
40.0
10.8
4.4
15.0
29.0
49.2
49.0
47.5
31.0
Thermal treatment
◦
130 C, 20 days
130 ◦ C, 20 days
130 ◦ C, 20 days
130 ◦ C, 20 days
DSC 5 ◦ C/min
20
38.7
30.6
30.7
300 ◦ C,20 days DSC 5 ◦ C/min
21
39.0
31.0
30.0
22
39.5
31.0
29.5
23
40.0
30.5
29.5
24
25
38.0
52.0
33.0
21.0
28.0
27.0
130 ◦ C, 20 days
◦
130 C, 40 days
130 ◦ C, 20 days
130 ◦ C, 20 days
53.0
19.5
27.5
130 ◦ C, 20 days
DSC 0.3 ◦ C/min
27
49.0
25.0
26.0
130 ◦ C, 50 days
DSC 1 ◦ C/min 28
29
30
31
49.5
58.0
62.0
45.2
25.0
18.3
17.0
34.0
25.5
23.7
21.0
20.8
130 ◦ C, 50 days
130 ◦ C, 54 days
130 ◦ C, 30 days
As cast
Microprobe analysis at.% Au In
50.0 33.5 40.0
12.0 1.5 21.0
38.0 65.0 39.0
Two phase sample AuSn1−x Inx AuSn2−x Inx
50.5 34.0
5.5 1.0
44.0 65.0
Two phase sample AuSn2−x Inx Au4 In3 Sn3
34.0 40.0
1.0 25.0
65.0 35.0
Almost single phase few small primary crystals of AuIn1−x Snx and Au4 In3 Sn3 Almost single phase Au4 In3 Sn3 Small quantity of AuIn2−x Snx
Cooling
Reaction
354 407
394
Liquidus
253 350 50.0 40.0
36.5 31.0
13.5 29.0
39.5
28.7
31.8
33.5
42.4
24.1
Almost single phase Au4 In3 Sn3 very Small quantity of AuIn2−x Snx
39.0
30.0
31.0
33.1
46.9
20.0
AuIn1−x Snx AuIn2−x Snx Au4 In3 Sn3
50.0 33.3 39.2
36.0 47.5 30.2
14.0 19.2 30.6
50.2 34.0 38.8
36.2 48.7 28.1
13.6 17.3 33.1
Two phase sample AuIn2−x Snx Au4 In3 Sn3
33.3 40.0
45.7 29.5
21.0 30.5
Primary crystals of AuIn1−x Snx AuSn1−x Inx Au7 In3−x Inx
50.5 50.5 71.0
29.5 15.0 29.0
20.0 34.5 0.0
Primary crystals of AuIn1−x Snx AuSn1−x Inx Au3 In1−x Snx
52.0 52.0 75.0
28.5 18.0 24.0
19.5 30.0 1.0
Two phase sample AuIn1−x Snx AuSn1−x Inx
Heating Sn
Primary crystals of AuSn1−x Inx AuSn2−x Inx Au4 In3 Sn3
Few primary crystals of AuIn1−x Snx and few AuIn2−x Snx Large quantity of Au4 In3 Sn3
see Fig.4 26
Phases
51.0 50.5
29.5 18.5
19.5 31.0
Two phase sample AuIn1−x Snx AuSn1−x Inx
50.0 50.0
31.2 16.0
19.5 34.0
Two phase sample AuSn1−x Inx Au3 In1−x Snx
50.0 75.0
15.0 24.0
35.0 1.0
Two phase sample Au3 In1−x Snx AuSn1−x Inx
75.0 50.0
23.0 12.0
2.0 38.0
Primary crystals of AuIn1−x Snx AuSn1−x Inx Au4 In3 Sn3
49.5 48.2 39.8
38.2 12.4 33.7
12.3 39.4 26.5
254 384 402
P1
429 454
430
U2 Liquidus
230 382 430 452
240 380 414 430
P1 U2 Liquidus
364 369 372 427 443 450
360
423
Liquidus
296 430 468 470
430 457 465
U2 Liquidus
G. Borzone et al. / CALPHAD: Computer Coupling of Phase Diagrams and Thermochemistry 33 (2009) 17–22
21
Table 1 (continued) Sample
32
Alloy composition by EPMA at.% Au In Sn 63.5
16.0
20.5
Thermal treatment
Phases
◦
130 C, 30 days
Two phase sample Au3 In1−x Snx AuSn1−x Inx
DSC 3 ◦ C/min 33
34
46.0
46.0
34.0
34.0
20.0
20.0
130 ◦ C, 40 days
130 ◦ C, 40 days
DSC 5 ◦ C/min
Microprobe analysis at.% Au In
Sn
75.0 50.0
2.0 38.0
23.0 12.0
Two phase sample AuIn1−x Snx Au4 In3 Sn3
50.0 40.0
37.5 31.0
12.5 29.0
Two phase sample AuIn1−x Snx Au4 In3 Sn3
50.6 40.0
37.4 31.0
12.0 29.0
Heating
Cooling
Reaction
309 330 373 400
310 360 381
Liquidus
384 397 414 437 484
383 398 412 433 446
U2 Liquidus
Table 2 Invariant reactions in the Au–In–Sn system determined in this work and according to the thermodynamic modelling [1] Reaction
Type
T /◦ C
L + AuIn → AuIn2 + AuSn L + AuSn + AuIn2 → Au4 In3 Sn3 L + AuSn → AuSn2 + Au4 In3 Sn3 L + Au4 In3 Sn3 → AuIn2 + AuSn4 AuIn2 + AuSn → Au4 In3 Sn3 + AuIn Au4 In3 Sn3 + AuSn4 → AuIn2 + AuSn2 AuSn4 + γ (In, Sn) → AuIn2 + (β Sn)
U2 P1 U7 U8 U11 U12 U13
430 382 301 260 296 205 196
Fig. 3. SEM image (BSE mode) of the microstructure of the 33.4 at.% Au, 24.4 at.% In, 42.2 at.% Sn sample (sample 12, Table 1) showing the incomplete reaction: light grey phase AuIn2−x Snx (1); white elongated crystals τ1 (2), dark grey phase AuSn4−x Inx (3).
11 or 13. The identification of the AuSn2 –Au4 In3 Sn3 –AuIn2 and AuIn2 –AuSn2 –AuSn4 three-phase fields is based mainly on the information resulting from the thermodynamic modelling. In fact, only sample 8 of Table 1 belongs to the AuIn2 –AuSn2 –AuSn4 three phase field, while samples 5, 9, 10 and 12 showed a metastable Au4 In3 Sn3 –AuSn4 –AuIn2 three phase field. This may be due to the sluggishness of the Au4 In3 Sn3 + AuSn4 → AuIn2 + AuSn2 invariant solid-state reaction (U12 ), which was observed only in sample 6. Fig. 3 presents a micrograph of sample 12 showing the uncompleted reaction. Fig. 4 shows the micrograph of sample 25; the composition of the sample is very close to the AuIn–AuSn line. Only two phases are shown to be in equilibrium AuIn1−x Snx and AuSn1−x Snx . Fig. 2. DSC thermograms of samples 6 and 20 (see Table 1).
Au4 In3 Sn3 ternary phase shows a small homogeneity range between 21 and about 30 at.% In at constant Au:Sn ratio. The thermal analysis of samples 19 and 20, and samples 6 and 13 lying in the AuIn2 –AuSn2 –AuSn4 three-phase field, showed thermal events at about 382 ◦ C, which corresponds to the P1 invariant reaction related to the formation of the Au4 In3 Sn3 phase. The DSC thermogram of sample 6 indicates the invariant reaction U8 , L + Au4 In3 Sn3 → AuIn2 + AuSn4 followed by the invariant reaction U12 , which takes place in the solid-state at about 205 ◦ C. This effect was not observed in samples 7,
Effects at around 430 ◦ C observed in a number of samples on heating were identified as the reaction U2 , L + AuIn → AuIn2 + AuSn, which is linked via a liquidus monovariant line to the binary eutectic reaction L → AuIn + AuIn2 . The tie-lines determined for samples 29 and 30 are shown in Fig. 1. Samples 14 and 15 showed on heating an effect at 301 ◦ C, corresponding to the invariant reaction U7 , L + AuSn → AuSn2 + Au4 In3 Sn3 . Two additional invariant reactions in the solid-state, U11 at 296 ◦ C (AuIn2 + AuSn → Au4 In3 Sn3 + AuIn) and U13 (AuSn4 + γ (In, Sn) → AuIn2 + (β Sn)) were identified.
22
G. Borzone et al. / CALPHAD: Computer Coupling of Phase Diagrams and Thermochemistry 33 (2009) 17–22
Acknowledgments The Authors would like to dedicate this contribution to the memory of Prof. Riccardo Ferro, who devoted his professional life to the understanding of Materials Chemistry and who played an important role in the Intermetallic community. They are greatly indebted to him for his teaching, scientific work and human qualities and wish to express the high regard in which he was held by all his co-workers. The financial support given by the National Consortium of Materials Science and Technology (INSTM) under PRISMA2004 project and UK EPSRC Platform Grant (GR/R95798) ‘‘Metallurgy at the Interface’’ is gratefully acknowledged. This research is a contribution to the European COST Action 531 ‘‘Lead-free Solder Materials’’. Fig. 4. SEM image (BSE mode) of the microstructure of the 52.0 at.% Au, 21.0 at.% In, 27.0 at.% Sn sample (sample 25, Table 1): grey phase AuIn1−x Snx (1), dark grey phase AuSn1−x Inx (2) and eutectic.
5. Conclusions Through an experimental investigation of the Au–In–Sn phase diagram, this work provides information on the phase composition of the system at 130 ◦ C, the character of low-temperature transformations, and invariant temperatures. The isothermal equilibria at 130 ◦ C and the existence of six three-phase ternary fields have been confirmed by metallographic analysis. One stable ternary phase, Au4 In3 Sn3 , occurs and its incongruent formation at 382 ◦ C has been established. The melting behaviour of the different alloys has been determined and 7 invariant reactions have been identified.
References [1] G. Cacciamani, G. Borzone, A. Watson, Thermodynamic modelling and assessment of the Au–In–Sn system, CALPHAD 33 (1) (2009) 100–108. [2] K. Schubert, H. Breimer, R. Gohle, H.-L. Lukas, H.G. Meissner, E. Stolz, Naturwiss. 45 (1958) 360–361. [3] K. Schubert, H. Breimer, R. Gohle, Z. Metallkd. 50 (1959) 146–153. [4] G. Humpston, The constitution of some ternary Au-based solder alloys, Ph.D. Thesis, Brunel University, UK, 1985. [5] K. Haussmann, in: G. Effenberg, F. Aldinger, A. Prince (Eds.), Ternary Alloys. A Comprehensive Compendium of Evaluated Constitutional Data and Phase Diagrams, vol. 13, VCH Publishers, New York, 1995, pp. 136–138. [6] A. Prince, G.V. Raynor, D.S. Evans (Eds.), Phase Diagrams of Ternary Gold Alloys, Institute of Metals, UK, 1990, pp. 300–302. [7] T.B. Massalski, H. Okamoto, P.R. Subramanian, L. Kacprzak (Eds.), Binary Alloys Phase Diagrams, 2nd ed., vol. 1–3, Metals Park, OH, USA, 1990. [8] N. Moelans, K.C. Hari Kumar, P. Wollants, J. Alloys Compd. 360 (2003) 98–106. [9] H.S. Liu, C.L. Liu, K. Ishida, Z.P. Jin, J. Electron. Mater. 32 (2003) 1290–1296. [10] H.S. Liu, Y. Cui, K. Ishida, Z.P. Jin, CALPHAD 27 (2003) 27–37.
Contents lists available at ScienceDirect
CALPHAD: Computer Coupling of Phase Diagrams and Thermochemistry journal homepage: www.elsevier.com/locate/calphad
Phase equilibria in the Au–In–Sn ternary system G. Borzone a,∗ , N. Parodi a , G. Cacciamani a , A. Watson b a
DCCI-University of Genova and INSTM, Genova, Italy
b
IMR/SPEME, University of Leeds, UK
article
info
Article history: Received 22 June 2008 Received in revised form 15 August 2008 Accepted 13 September 2008 Available online 1 October 2008 Dedicated to the memory of Prof. Riccardo Ferro Keywords: Phase diagram DSC Au–In–Sn ternary system Solder alloys
a b s t r a c t Phase equilibria of the Au–In–Sn system have been investigated by Differential Scanning Calorimetry (DSC), metallographic examination, Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDS) measurements. The 130 ◦ C isothermal section of the phase diagram was studied. The ternary diagram shows six three-phase fields, and one ternary Au4 In3 Sn3 phase, which melts incongruently at 382 ◦ C and shows a homogeneity range between 21 and about 30 at.% In, at constant Au/Sn ratio. The DSC results have been combined with microstructural observations and thermodynamic modelling [G. Cacciamani, G. Borzone, A. Watson, Thermodynamic modelling and assessment of the Au–In–Sn system, CALPHAD 33(1) (2009) 100–108] and seven invariant reactions have been identified. © 2008 Elsevier Ltd. All rights reserved.
1. Introduction The effects of the interfacial reactions between solder and substrate material under operating conditions are very important to the performance of solder joints. Many electronic components and printed circuit boards are plated with a variety of thicknesses of gold, ranging from 10 to 15 to several hundred micrometers. In order to produce an electrically and metallurgically sound joint when soldering to gold-plated components and boards, the wetting capability of the solder in the presence of a suitable flux must be considered. For long-term reliability of a soldered assembly, a solder joint must not be brittle or susceptible to fatigue. The interaction and diffusion of gold in Sn-based soldering is in fact of particular interest, since gold forms a very brittle AuSn4 intermetallic phase. Indium alloys offer the advantages of reduced intermetallic phase formation, the capability of gold soldering (for the repair of jewellery, for example) and thermal fatigue resistance in the joints produced. Thus, the aim of this work is to study alloys of the Au–In–Sn system, which is important in order to understand the chemistry of electrical contacts made from lead-free In–Sn alloys and Au containing substrates.
∗ Corresponding address: Dipartimento di Chimica e Chimica Industriale, Via Dodecaneso 31, 16146 Genova, Italy. Tel.: +39 010 3536153; fax: +39 010 3625051. E-mail address: [email protected] (G. Borzone). 0364-5916/$ – see front matter © 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.calphad.2008.09.008
This contribution reports the results of experimental investigation of the phase diagram of the Au–In–Sn system, but in order to define the phase diagram completely, both computational and experimental approaches should be performed, and to this end, key experiments reported here and thermodynamic modelling that will be published elsewhere [1], have been combined in a recursive procedure. 2. Literature data A complete description of the ternary phase diagram is not available. The existence of the ternary phase Au4 In3 Sn3 , hP10-Pt2 Sn3 type, having a congruent melting point at about 430 ◦ C was reported by Schubert et al. [2,3], who also investigated a portion of the ternary system. The alloys were examined as cast and following heat treatment at 250 ◦ C, or between 100 and 350 ◦ C. Humpston [4] studied the AuIn–AuSn section and found a two-phase region below about 325 ◦ C. All of these data have been critically assessed by Haussmann [5]. An assessed isothermal section (for approximately 250 ◦ C) has been presented by Prince [6]. It is worth noting that the published phase diagram is not an equilibrium diagram, because no samples were annealed at or quenched from that temperature. As stated by Prince [6], the assessed version may be considered only as ‘‘a guide to the 250 ◦ C isothermal for alloys whose compositions are on the Au-rich side of a line joining AuIn2 to AuSn4 . For alloys on the Au-poor side of this line the equilibria
18
G. Borzone et al. / CALPHAD: Computer Coupling of Phase Diagrams and Thermochemistry 33 (2009) 17–22
are to be interpreted as equivalent to the 100 ◦ C section’’. The liquidus surface is not known. Information on the limiting binary systems was obtained from the literature [7–10]. 3. Experimental The metals used were indium ingot 99.999 mass%, tin 99.999 mass% and gold 99.99+ mass% nominal purity. Samples were prepared at compositions given in Table 1 by melting pieces of the constituent metals in alumina crucibles in an induction furnace under an argon atmosphere. The sample mass was about 1–2 g. The alloys were generally annealed at 130 ◦ C for 15 days or one month or more in order to reach the equilibrium state, and then quenched into cold water. Several samples were annealed at 300 ◦ C for several days, then at 130 ◦ C for 1 month followed by water quenching. On the basis of results obtained from the modelling, carried out in parallel in order to predict liquidus temperatures, the samples were subjected to thermal analysis by using a Setaram DSC111 apparatus with heating and cooling rates of 5, 3, 1 or 0.3 ◦ C/min. The DSC samples were prepared by sealing 500–700 mg of the alloys under Ar in tantalum crucibles. The calorimeter was calibrated by measuring the melting temperature of metallic In, Sn, Pb and Zn (99.999 mass% purity) and the temperature was obtained with an accuracy of Tm ± 0.5 ◦ C. The microstructure of all of the samples, either as cast, after annealing or after DSC analysis, was investigated by optical and scanning electron microscopy (SEM). An electron microscope (Zeiss EVO-40) equipped with an OXFORD INCA Energy 300 analyser, which allowed local chemical analysis by Energy dispersive X-ray (EDS), was employed. For quantitative EPMA (electron probe microanalysis), the samples were analysed using an acceleration voltage of 20 kV using cobalt as calibration standard for the beam current, gain and resolution of the spectrometer. The X-ray intensities were corrected for ZAF (Z Absorption Fluorescence) effects using pure elements as standards. The samples were observed by means of a back-scattered electron detector (BSE). Microanalysis (EPMA) was used to check the overall composition of the samples, the uniformity of chemical composition and the composition of the coexisting phases. 4. Results and discussion The phase equilibria in the ternary Au–In–Sn system were studied by a combination of the methods described above. Altogether, 34 ternary alloys were prepared with overall compositions as given in Table 1, where all the experimental results are presented. The corresponding partial isothermal section at 130 ◦ C is shown in Fig. 1. No samples were prepared in the In–Sn rich-region of the system and hence this part of the section is omitted in the figure. The results of DSC analysis are given in Table 1, together with details of the experimental conditions employed. The temperatures reported in Table 1 represent average values of the thermal effects detected during first and second heating. Usually, pronounced undercooling effects were observed for all of the investigated alloys, and the relevant phase diagram information was, in general, taken from the heating curves. The stability fields of the different phases at 130 ◦ C shown in Fig. 1 agree in some part with the general features of the isothermal section at approximately 250 ◦ C proposed by Prince [6] and the corresponding two and three phase equilibria. However, in this work, a larger extension in the ternary system than had been previously reported was observed for the solid solutions based on the binary compounds. A typical feature is their extension into the
Fig. 1. Isothermal section of Au–In–Sn system at 130 ◦ C showing the τ1 (Au4 In3 Sn3 ) ternary phase: The three-phase fields are marked by ∗.
ternary system in the direction parallel to the In–Sn axis. AuSn4 dissolves up to 6 at.% In, while AuSn2 dissolves up to 1 at.% In. In agreement with Humpston [4], the AuIn–AuSn section was confirmed as not being pseudo-binary and a considerable solubility of indium in AuSn (up to about 16 at.%) and extensive solubility of Sn in AuIn (up to 20.0 at.%) was observed. The AuIn2 phase dissolves up to 22 at.% Sn. A limited amount of Sn solubility (up to 2 at.%) in the Au3 In phase was also observed. A maximum solubility of indium in Sn of up to 1 at.% was observed. The six three-phase fields determined at 130 ◦ C in the region investigated are: AuSn2 –AuSn–Au4 In3 Sn3 , AuSn–Au4 In3 Sn3 –AuIn, AuSn–Au7 In3 –AuIn, AuIn– Au4 In3 Sn3 –AuIn2 , AuSn2 –Au4 In3 Sn3 –AuIn2 , and AuIn2 –AuSn2 –AuSn4 . The primary crystallization areas have been determined on the basis of the information obtained by metallographic analysis, see Table 1. From the DSC results, seven invariant reactions have been identified, 4 of them involving the liquid phase. This observation has been supported by thermodynamic modelling that will be published elsewhere [1]. The invariant reactions are listed in Table 2 together with the corresponding temperature and reaction type. The recorded liquidus temperatures indicate a decrease in the slope of the liquidus surface, from the Au–In binary system to the Sn-rich corner. The alloys investigated in the Sn-rich part of the system, showed only the solid state invariant reaction U13 , AuSn4 + γ (In, Sn) → AuIn2 + (β Sn), which takes place at 196 ◦ C. The tie-lines related to samples 2 and 3 are shown in Fig. 1. Fig. 2 shows the DSC thermograms obtained for samples 6 and 20. Concerning the Au4 In3 Sn3 ternary phase, thermal and metallographic analyses suggest incongruent melting, in contrast with the literature. Samples having a composition close to the Au4 In3 Sn3 phase (19 and 20) showed on cooling, as reported by Schubert et al. [2], a liquidus temperature of 430 ◦ C, followed by a number of transformations below the liquidus (see the DSC effects recorded in Fig. 2). However, on the basis of the present studies, the formation of the Au4 In3 Sn3 phase was related to the L + AuIn2 + AuSn → Au4 In3 Sn3 P1 invariant reaction at 382 ◦ C. Correspondingly, a large region of primary crystallization of AuIn2 and a small region for Au4 In3 Sn3 were observed. On the basis of the EPMA analyses, the
G. Borzone et al. / CALPHAD: Computer Coupling of Phase Diagrams and Thermochemistry 33 (2009) 17–22
19
Table 1 Experimental results of DSC, phases observed and EDS compositions of the investigated Au–In–Sn ternary alloys Sample
Alloy composition by EPMA at.% Au In Sn
Thermal treatment
Phases
Microprobe analysis at.% Au In
Sn
1
2.3
0.7
97
As cast
Primary crystals of (β Sn)
0.0
0.0
100
DSC 1 ◦ C/min
AuSn4−x Inx
20.0
4.0
76.0
2
4.0
8.0
88.0
130 ◦ C, 30 days
Primary crystals of AuIn2−x Snx (β Sn) 33.3 0.2
DSC 3 C/min
46.7 2.0
20.0 97.8
◦
3
5.0
10.5
84.5
130 ◦ C, 15 days
Primary crystals of AuIn2−x Snx (β Sn)
5.2
80.5
130 ◦ C, 54 days
48.5 5.5
6
28.0
26.0
11.0
16.0
61.0
58.0
130 ◦ C, 35 days
130 ◦ C, 54 days
DSC 1 ◦ C/min 7
27.5
16.5
56.0
◦
130 C, 20 days
DSC 1 ◦ C/min sample not in equilibrium 8
27.0
17.0
56.0
◦
130 C, 30 days
Large primary crystals of Au4 In3 Sn3 AuSn4−x Inx AuSn2−x Inx sample not in equilibrium Primary crystals of AuIn2−x Snx Au4 In3 Sn3 AuSn4−x Inx Au4 In3 Sn3 AuIn2−x Snx AuSn4−x Inx
20.0 0.0
6.0 1.0
74.0 99.0
40.5 20.5 33.0
20.0 3.0 2.0
39.5 76.5 65.0
33.8 40.3 20.0
46.8 28.1 6.0
19.4 31.6 74.0
40.6 34.7 20.7
28.4 44.0 6.3
31.0 21.3 73.0
Primary crystals of AuIn2−x Snx AuSn2−x Inx AuSn4−x Inx
33.5 33.5 20.0
44.5 1.0 6.0
22.0 65.5 74.0
28.0
17.0
55.0
130 ◦ C, 20 days sample not in equilibrium
Au4 In3 Sn3 AuIn2−x Snx AuSn4−x Inx
41.0 34.0 20.7
30.0 42.0 6.0
29.0 24.0 73.3
10
28.6
20.0
51.4
130 ◦ C, 30 days sample not in equilibrium
Primary crystals of AuIn2−x Snx Au4 In3 Sn3 AuSn4−x Inx
34.0 40.3 20.0
45.0 24.4 6.5
21.0 35.3 73.5
130 ◦ C, 30 days
Primary crystals of AuIn2−x Snx Au4 In3 Sn3 AuSn4−x Inx
34.0 39.5 20.3
45.5 24.9 6.2
20.5 35.6 73.5
30.0
22.5
47.5
DSC 1 C/min sample not in equilibrium ◦
12
13
33.4
33.7
24.4
22.8
42.2
43.5
130 ◦ C, 20 days sample not in equilibrium see Fig. 3
Primary crystals of AuIn2−x Snx Au4 In3 Sn3 AuSn4−x Inx
33.5 39.2 19.0
46.5 32.1 6.8
20.0 28.7 74.2
130 ◦ C, 20 days
AuIn2−x Snx Au4 In3 Sn3 AuSn4−x Inx
33.5 40.0 19.0
49.0 29.8 6.8
17.5 30.2 74.2
DSC 1 ◦ C/min 14
44.6
4.6
50.8
◦
130 C, 20 days DSC 1 C/min
AuSn1−x Inx AuSn2−x Inx
50.5 34.0
6.0 1.0
43.5 65.0
◦
15
40.2
9.5
50.3
130 ◦ C, 20 days
DSC 1 ◦ C/min
205 206.8 207
Liquidus
192
150 194 196
U13
221
Liquidus
139 194 196
U13
206 215 225
–
Liquidus
207 261
201 251
Liquidus
211 261 346 384 388
203 260 327
U12 U8
377
Liquidus
211 230 263 363 387
9
11
211 220 224
18.2 94.4
Large primary crystals of AuSn4−x Inx (β Sn)
DSC 1 ◦ C/min 5
Reaction
160 33.3 0.1
DSC 1 C/min
14.3
Cooling
209 212 228
◦
4
Heating
Primary crystals of AuSn1−x Inx AuSn2−x Inx Au4 In3 Sn3
50.5 33.8 40.8
12.0 1.5 21.0
37.5 64.7 38.2
212 259 368 393 407
260 405 420
197 261 337 364 382
U8
Liquidus
204 260 343
U8
395
Liquidus
260 383
U8 P1
416
Liquidus
253 301 307 422
U7 407
Liquidus
230 247 248 301
U7 (continued on next page)
20
G. Borzone et al. / CALPHAD: Computer Coupling of Phase Diagrams and Thermochemistry 33 (2009) 17–22
Table 1 (continued) Sample
16
17
18
19
Alloy composition by EPMA at.% Au In Sn
40.0
46.6
37.5
40.0
10.8
4.4
15.0
29.0
49.2
49.0
47.5
31.0
Thermal treatment
◦
130 C, 20 days
130 ◦ C, 20 days
130 ◦ C, 20 days
130 ◦ C, 20 days
DSC 5 ◦ C/min
20
38.7
30.6
30.7
300 ◦ C,20 days DSC 5 ◦ C/min
21
39.0
31.0
30.0
22
39.5
31.0
29.5
23
40.0
30.5
29.5
24
25
38.0
52.0
33.0
21.0
28.0
27.0
130 ◦ C, 20 days
◦
130 C, 40 days
130 ◦ C, 20 days
130 ◦ C, 20 days
53.0
19.5
27.5
130 ◦ C, 20 days
DSC 0.3 ◦ C/min
27
49.0
25.0
26.0
130 ◦ C, 50 days
DSC 1 ◦ C/min 28
29
30
31
49.5
58.0
62.0
45.2
25.0
18.3
17.0
34.0
25.5
23.7
21.0
20.8
130 ◦ C, 50 days
130 ◦ C, 54 days
130 ◦ C, 30 days
As cast
Microprobe analysis at.% Au In
50.0 33.5 40.0
12.0 1.5 21.0
38.0 65.0 39.0
Two phase sample AuSn1−x Inx AuSn2−x Inx
50.5 34.0
5.5 1.0
44.0 65.0
Two phase sample AuSn2−x Inx Au4 In3 Sn3
34.0 40.0
1.0 25.0
65.0 35.0
Almost single phase few small primary crystals of AuIn1−x Snx and Au4 In3 Sn3 Almost single phase Au4 In3 Sn3 Small quantity of AuIn2−x Snx
Cooling
Reaction
354 407
394
Liquidus
253 350 50.0 40.0
36.5 31.0
13.5 29.0
39.5
28.7
31.8
33.5
42.4
24.1
Almost single phase Au4 In3 Sn3 very Small quantity of AuIn2−x Snx
39.0
30.0
31.0
33.1
46.9
20.0
AuIn1−x Snx AuIn2−x Snx Au4 In3 Sn3
50.0 33.3 39.2
36.0 47.5 30.2
14.0 19.2 30.6
50.2 34.0 38.8
36.2 48.7 28.1
13.6 17.3 33.1
Two phase sample AuIn2−x Snx Au4 In3 Sn3
33.3 40.0
45.7 29.5
21.0 30.5
Primary crystals of AuIn1−x Snx AuSn1−x Inx Au7 In3−x Inx
50.5 50.5 71.0
29.5 15.0 29.0
20.0 34.5 0.0
Primary crystals of AuIn1−x Snx AuSn1−x Inx Au3 In1−x Snx
52.0 52.0 75.0
28.5 18.0 24.0
19.5 30.0 1.0
Two phase sample AuIn1−x Snx AuSn1−x Inx
Heating Sn
Primary crystals of AuSn1−x Inx AuSn2−x Inx Au4 In3 Sn3
Few primary crystals of AuIn1−x Snx and few AuIn2−x Snx Large quantity of Au4 In3 Sn3
see Fig.4 26
Phases
51.0 50.5
29.5 18.5
19.5 31.0
Two phase sample AuIn1−x Snx AuSn1−x Inx
50.0 50.0
31.2 16.0
19.5 34.0
Two phase sample AuSn1−x Inx Au3 In1−x Snx
50.0 75.0
15.0 24.0
35.0 1.0
Two phase sample Au3 In1−x Snx AuSn1−x Inx
75.0 50.0
23.0 12.0
2.0 38.0
Primary crystals of AuIn1−x Snx AuSn1−x Inx Au4 In3 Sn3
49.5 48.2 39.8
38.2 12.4 33.7
12.3 39.4 26.5
254 384 402
P1
429 454
430
U2 Liquidus
230 382 430 452
240 380 414 430
P1 U2 Liquidus
364 369 372 427 443 450
360
423
Liquidus
296 430 468 470
430 457 465
U2 Liquidus
G. Borzone et al. / CALPHAD: Computer Coupling of Phase Diagrams and Thermochemistry 33 (2009) 17–22
21
Table 1 (continued) Sample
32
Alloy composition by EPMA at.% Au In Sn 63.5
16.0
20.5
Thermal treatment
Phases
◦
130 C, 30 days
Two phase sample Au3 In1−x Snx AuSn1−x Inx
DSC 3 ◦ C/min 33
34
46.0
46.0
34.0
34.0
20.0
20.0
130 ◦ C, 40 days
130 ◦ C, 40 days
DSC 5 ◦ C/min
Microprobe analysis at.% Au In
Sn
75.0 50.0
2.0 38.0
23.0 12.0
Two phase sample AuIn1−x Snx Au4 In3 Sn3
50.0 40.0
37.5 31.0
12.5 29.0
Two phase sample AuIn1−x Snx Au4 In3 Sn3
50.6 40.0
37.4 31.0
12.0 29.0
Heating
Cooling
Reaction
309 330 373 400
310 360 381
Liquidus
384 397 414 437 484
383 398 412 433 446
U2 Liquidus
Table 2 Invariant reactions in the Au–In–Sn system determined in this work and according to the thermodynamic modelling [1] Reaction
Type
T /◦ C
L + AuIn → AuIn2 + AuSn L + AuSn + AuIn2 → Au4 In3 Sn3 L + AuSn → AuSn2 + Au4 In3 Sn3 L + Au4 In3 Sn3 → AuIn2 + AuSn4 AuIn2 + AuSn → Au4 In3 Sn3 + AuIn Au4 In3 Sn3 + AuSn4 → AuIn2 + AuSn2 AuSn4 + γ (In, Sn) → AuIn2 + (β Sn)
U2 P1 U7 U8 U11 U12 U13
430 382 301 260 296 205 196
Fig. 3. SEM image (BSE mode) of the microstructure of the 33.4 at.% Au, 24.4 at.% In, 42.2 at.% Sn sample (sample 12, Table 1) showing the incomplete reaction: light grey phase AuIn2−x Snx (1); white elongated crystals τ1 (2), dark grey phase AuSn4−x Inx (3).
11 or 13. The identification of the AuSn2 –Au4 In3 Sn3 –AuIn2 and AuIn2 –AuSn2 –AuSn4 three-phase fields is based mainly on the information resulting from the thermodynamic modelling. In fact, only sample 8 of Table 1 belongs to the AuIn2 –AuSn2 –AuSn4 three phase field, while samples 5, 9, 10 and 12 showed a metastable Au4 In3 Sn3 –AuSn4 –AuIn2 three phase field. This may be due to the sluggishness of the Au4 In3 Sn3 + AuSn4 → AuIn2 + AuSn2 invariant solid-state reaction (U12 ), which was observed only in sample 6. Fig. 3 presents a micrograph of sample 12 showing the uncompleted reaction. Fig. 4 shows the micrograph of sample 25; the composition of the sample is very close to the AuIn–AuSn line. Only two phases are shown to be in equilibrium AuIn1−x Snx and AuSn1−x Snx . Fig. 2. DSC thermograms of samples 6 and 20 (see Table 1).
Au4 In3 Sn3 ternary phase shows a small homogeneity range between 21 and about 30 at.% In at constant Au:Sn ratio. The thermal analysis of samples 19 and 20, and samples 6 and 13 lying in the AuIn2 –AuSn2 –AuSn4 three-phase field, showed thermal events at about 382 ◦ C, which corresponds to the P1 invariant reaction related to the formation of the Au4 In3 Sn3 phase. The DSC thermogram of sample 6 indicates the invariant reaction U8 , L + Au4 In3 Sn3 → AuIn2 + AuSn4 followed by the invariant reaction U12 , which takes place in the solid-state at about 205 ◦ C. This effect was not observed in samples 7,
Effects at around 430 ◦ C observed in a number of samples on heating were identified as the reaction U2 , L + AuIn → AuIn2 + AuSn, which is linked via a liquidus monovariant line to the binary eutectic reaction L → AuIn + AuIn2 . The tie-lines determined for samples 29 and 30 are shown in Fig. 1. Samples 14 and 15 showed on heating an effect at 301 ◦ C, corresponding to the invariant reaction U7 , L + AuSn → AuSn2 + Au4 In3 Sn3 . Two additional invariant reactions in the solid-state, U11 at 296 ◦ C (AuIn2 + AuSn → Au4 In3 Sn3 + AuIn) and U13 (AuSn4 + γ (In, Sn) → AuIn2 + (β Sn)) were identified.
22
G. Borzone et al. / CALPHAD: Computer Coupling of Phase Diagrams and Thermochemistry 33 (2009) 17–22
Acknowledgments The Authors would like to dedicate this contribution to the memory of Prof. Riccardo Ferro, who devoted his professional life to the understanding of Materials Chemistry and who played an important role in the Intermetallic community. They are greatly indebted to him for his teaching, scientific work and human qualities and wish to express the high regard in which he was held by all his co-workers. The financial support given by the National Consortium of Materials Science and Technology (INSTM) under PRISMA2004 project and UK EPSRC Platform Grant (GR/R95798) ‘‘Metallurgy at the Interface’’ is gratefully acknowledged. This research is a contribution to the European COST Action 531 ‘‘Lead-free Solder Materials’’. Fig. 4. SEM image (BSE mode) of the microstructure of the 52.0 at.% Au, 21.0 at.% In, 27.0 at.% Sn sample (sample 25, Table 1): grey phase AuIn1−x Snx (1), dark grey phase AuSn1−x Inx (2) and eutectic.
5. Conclusions Through an experimental investigation of the Au–In–Sn phase diagram, this work provides information on the phase composition of the system at 130 ◦ C, the character of low-temperature transformations, and invariant temperatures. The isothermal equilibria at 130 ◦ C and the existence of six three-phase ternary fields have been confirmed by metallographic analysis. One stable ternary phase, Au4 In3 Sn3 , occurs and its incongruent formation at 382 ◦ C has been established. The melting behaviour of the different alloys has been determined and 7 invariant reactions have been identified.
References [1] G. Cacciamani, G. Borzone, A. Watson, Thermodynamic modelling and assessment of the Au–In–Sn system, CALPHAD 33 (1) (2009) 100–108. [2] K. Schubert, H. Breimer, R. Gohle, H.-L. Lukas, H.G. Meissner, E. Stolz, Naturwiss. 45 (1958) 360–361. [3] K. Schubert, H. Breimer, R. Gohle, Z. Metallkd. 50 (1959) 146–153. [4] G. Humpston, The constitution of some ternary Au-based solder alloys, Ph.D. Thesis, Brunel University, UK, 1985. [5] K. Haussmann, in: G. Effenberg, F. Aldinger, A. Prince (Eds.), Ternary Alloys. A Comprehensive Compendium of Evaluated Constitutional Data and Phase Diagrams, vol. 13, VCH Publishers, New York, 1995, pp. 136–138. [6] A. Prince, G.V. Raynor, D.S. Evans (Eds.), Phase Diagrams of Ternary Gold Alloys, Institute of Metals, UK, 1990, pp. 300–302. [7] T.B. Massalski, H. Okamoto, P.R. Subramanian, L. Kacprzak (Eds.), Binary Alloys Phase Diagrams, 2nd ed., vol. 1–3, Metals Park, OH, USA, 1990. [8] N. Moelans, K.C. Hari Kumar, P. Wollants, J. Alloys Compd. 360 (2003) 98–106. [9] H.S. Liu, C.L. Liu, K. Ishida, Z.P. Jin, J. Electron. Mater. 32 (2003) 1290–1296. [10] H.S. Liu, Y. Cui, K. Ishida, Z.P. Jin, CALPHAD 27 (2003) 27–37.