Microstructure and Properties of Bi-Sn, Bi-Sn-Sb, and Bi-Sn-Ag Solder Alloys for Electronic Applications
Abstract
1. Introduction
2. Materials and Methods
- Bi–Sn binary alloy: Melting was performed in a resistance furnace stabilized at 300 °C. Pre-weighed Bi and Sn were introduced after thermal equilibrium was achieved;
- Bi–Sn–Sb alloy: The furnace was stabilized at 650 °C, and Sb was first introduced and melted, followed by the addition of Sn and Bi to complete the alloy composition;
- Bi–Sn–Ag alloy: Ag was initially melted at 980 °C (peak ~1000 °C), followed by the sequential addition of Bi and Sn.
3. Results and Discussion
3.1. Characterization of Bi-Sn-Based Solder Alloys
3.1.1. Chemical Composition
3.1.2. Microstructural Characterization
3.2. Microhardness Evaluation of Bi-Sn-Based Solder Alloys
3.3. Thermal and Electrical Conductivity of Bi-Sn-Based Solder Alloys
4. Conclusions
- Sb induces granular Sn-Sb intermetallics that may strengthen the structure but degrade thermal transport;
- Ag promotes fine, directional intermetallics (Ag3Sn), enhances electrical conductivity, and moderately reduces thermal conductivity;
- Both Ag and Sb raise electrical conductivity compared to the binary alloy, reflecting complex structural interactions;
- The binary Bi60Sn40 serves as a stable baseline, offering high thermal conductivity and a uniform eutectic structure suitable for low-temperature soldering.
- Ag increases electrical conductivity but slightly lowers thermal conductivity at higher temperatures.
Author Contributions
Funding
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Conflicts of Interest
References
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Chemical Composition (%) | |||
---|---|---|---|
Element | Bi60Sn40 | Bi60Sn35Sb5 | Bi60Sn35Ag5 |
Bi | 59.437 | 59.411 | 58.804 |
Sn | 39.475 | 34.533 | 34.271 |
Sb | 0.0167 | 4.88 | 0.0177 |
Ag | 0 | 0 | 4.93 |
Cu | 0.122 | 0.182 | 1.63 |
Fe | 0.018 | 0.029 | 0.024 |
O.E. * | rem. | rem. | rem. |
Total | 100 | 100 | 100 |
EDS Analysis | Element | Weight % | Atomic % | Net Int. | Error % | Peak-to-Background (P/B) Ratio | Resolution, R | Fluorescence, F |
---|---|---|---|---|---|---|---|---|
Spot 1 | BiL | 100.00 | 100.00 | 349.38 | 12.34 | 205.5412 | 1.1256 | 1.0445 |
Spot 2 | SnL | 31.51 | 44.75 | 411.53 | 7.86 | 167.6377 | 1.0575 | 1.0067 |
BiL | 68.49 | 55.25 | 280.07 | 12.92 | 182.9532 | 1.1144 | 1.0457 | |
Spot 3 | SnL | 2.31 | 3.99 | 18.93 | 45.62 | 9.9665 | 1.0628 | 1.0074 |
BiL | 97.69 | 96.01 | 353.42 | 13.37 | 200.5332 | 1.1248 | 1.0446 | |
Spot 4 | SnL | 82.19 | 89.04 | 1038.78 | 6.83 | 317.0775 | 1.0479 | 1.0056 |
BiL | 17.81 | 10.96 | 44.85 | 32.78 | 38.6640 | 1.0952 | 1.0527 | |
Spot 5 | SnL | 70.26 | 80.62 | 999.99 | 6.77 | 341.4499 | 1.0502 | 1.0058 |
BiL | 29.74 | 19.38 | 89.68 | 21.60 | 78.9456 | 1.0999 | 1.0501 | |
Spot 6 | SnL | 2.15 | 3.72 | 14.42 | 56.01 | 8.6900 | 1.0628 | 1.0074 |
BiL | 97.85 | 96.28 | 342.71 | 11.76 | 188.3782 | 1.1248 | 1.0446 | |
Spot 7 | SnL | 7.63 | 12.69 | 82.10 | 17.49 | 35.3432 | 1.0618 | 1.0072 |
BiL | 92.37 | 87.31 | 368.21 | 13.08 | 205.4512 | 1.1229 | 1.0447 | |
Spot 8 | SnL | 82.20 | 89.05 | 1386.51 | 6.45 | 414.2416 | 1.0479 | 1.0056 |
BiL | 17.80 | 10.95 | 53.73 | 33.55 | 50.5040 | 1.0952 | 1.0527 |
EDS Analysis | Element | Weight % | Atomic % | Net Int. | Error % | Peak-to-Background (P/B) Ratio | Resolution, R | Fluorescence, F |
---|---|---|---|---|---|---|---|---|
Spot 1 | SnL | 2.74 | 4.73 | 14.75 | 41.77 | 11.3363 | 1.0627 | 1.0074 |
BiL | 97.26 | 95.27 | 436.83 | 11.37 | 191.4222 | 1.1246 | 1.0446 | |
Spot 2 | SnL | 20.20 | 29.05 | 371.86 | 8.01 | 101.1552 | 1.0578 | 1.0071 |
SbL | 9.87 | 13.84 | 185.19 | 11.58 | 49.3374 | 1.0601 | 1.0073 | |
BiL | 69.93 | 57.12 | 351.90 | 13.20 | 175.2969 | 1.1150 | 1.0456 | |
Spot 3 | SnL | 19.99 | 27.99 | 329.99 | 8.73 | 97.1621 | 1.0570 | 1.0072 |
SbL | 14.67 | 20.04 | 235.10 | 11.48 | 71.2188 | 1.0593 | 1.0072 | |
BiL | 65.34 | 51.97 | 291.36 | 13.36 | 160.3760 | 1.1134 | 1.0458 | |
Spot 4 | SnL | 49.87 | 53.12 | 966.44 | 6.79 | 263.7330 | 1.0469 | 1.0074 |
SbL | 38.16 | 39.63 | 701.72 | 7.45 | 202.0403 | 1.0488 | 1.0060 | |
BiL | 11.97 | 7.24 | 43.93 | 39.87 | 36.0446 | 1.0934 | 1.0538 |
EDS Analysis | Element | Weight % | Atomic % | Net Int. | Error % | Peak-to-Background (P/B) Ratio | Resolution, R | Fluorescence, F |
---|---|---|---|---|---|---|---|---|
Spot 1 | AgL | 72.18 | 74.06 | 1356.90 | 7.08 | 332.8965 | 1.0376 | 1.0065 |
SnL | 27.82 | 25.94 | 328.80 | 10.20 | 125.1740 | 1.0429 | 1.0036 | |
Spot 2 | AgL | 68.09 | 71.90 | 1394.17 | 6.89 | 329.1566 | 1.0388 | 1.0063 |
SnL | 25.82 | 24.78 | 340.73 | 9.98 | 121.4951 | 1.0443 | 1.0038 | |
BiL | 6.09 | 3.32 | 11.19 | 63.37 | 16.6575 | 1.0880 | 1.0600 | |
Spot 3 | BiL | 100.00 | 100.00 | 385.37 | 12.23 | 182.3931 | 1.1256 | 1.0445 |
Spot 4 | SnL | 74.24 | 83.54 | 1141.59 | 6.40 | 341.7386 | 1.0494 | 1.0057 |
BiL | 25.76 | 16.46 | 87.96 | 24.13 | 65.6165 | 1.0983 | 1.0509 | |
Spot 5 | SnL | 46.27 | 41.83 | 719.74 | 6.34 | 217.5642 | 1.0465 | 1.0076 |
CuK | 26.03 | 43.95 | 490.31 | 8.35 | 155.4725 | 1.0806 | 1.1170 | |
BiL | 27.69 | 14.22 | 95.13 | 21.38 | 72.2014 | 1.0926 | 1.0415 | |
Spot 6 | SnL | 60.06 | 47.82 | 870.31 | 6.21 | 271.5037 | 1.0414 | 1.0078 |
CuK | 32.97 | 49.03 | 605.53 | 6.40 | 190.4063 | 1.0717 | 1.0779 | |
BiL | 6.97 | 3.15 | 12.27 | 65.61 | 18.4796 | 1.0823 | 1.0416 |
Alloys | Microhardness HV15 (Mean ± SD) |
---|---|
Bi60Sn40 | 14.59 ± 1.69 |
Bi60Sn35Sb5 | 16.36 ± 3.42 |
Bi60Sn35Ag5 | 17.33 ± 2.79 |
Solder Alloy | Temperature (°C) | Thermal Diffusivity α (m2/s) | Thermal Conductivity λ (W/m·K) | Resistivity ρₑ (Ω·m) | Electrical Conductivity σ (S/m) |
---|---|---|---|---|---|
Bi60Sn40 | 25 | 10.75·10−6 | 16.93 | 3.80·10−7 | 2.63·106 |
50 | 11.85·10−6 | 18.94 | 4.45·10−7 | 2.25·106 | |
75 | 12.90·10−6 | 20.93 | 5.10·10−7 | 1.96·106 | |
100 | 13.93·10−6 | 22.93 | 6.35·10−7 | 1.57·106 | |
125 | 14.93·10−6 | 24.93 | 7.60·10−7 | 1.32·106 | |
140 | 16.06·10−6 | 26.93 | 8.35·10−7 | 1.20·106 | |
± s = 21.93 ± 3.74 | |||||
Bi60Sn35Sb5 | 25 | 9.71·10−6 | 13.90 | 1.53·10−7 | 6.52·106 |
50 | 9.11·10−6 | 13.59 | 1.63·10−7 | 6.12·106 | |
75 | 8.66·10−6 | 13.43 | 1.76·10−7 | 5.67·106 | |
100 | 7.23·10−6 | 11.65 | 1.88·10−7 | 5.30·106 | |
125 | 6.81·10−6 | 11.38 | 2.00·10−7 | 4.86·106 | |
140 | 6.22·10−6 | 10.66 | 2.08·10−7 | 4.79·106 | |
± s = 12.44 ± 1.37 | |||||
Bi60Sn35Ag5 | 25 | 11.91·10−6 | 18.28 | 1.52·10−7 | 6.54·106 |
50 | 11.56·10−6 | 18.25 | 1.66·10−7 | 6.15·106 | |
75 | 10.80·10−6 | 17.52 | 1.77·10−7 | 5.69·106 | |
100 | 10.46·10−6 | 17.43 | 1.89·10−7 | 5.33·106 | |
125 | 9.89·10−6 | 16.91 | 2.01·10−7 | 4.98·106 | |
140 | 9.56·10−6 | 16.77 | 2.08·10−7 | 4.81·106 | |
± s = 17.53 ± 0.64 |
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Ilie, A.-A.; Niculescu, F.; Iacob, G.; Pencea, I.; Miculescu, F.; Bololoi, R.; Drăguț, D.-V.; Matei, A.-C.; Ghiţă, M.; Priceputu, A.; et al. Microstructure and Properties of Bi-Sn, Bi-Sn-Sb, and Bi-Sn-Ag Solder Alloys for Electronic Applications. Metals 2025, 15, 915. https://doi.org/10.3390/met15080915
Ilie A-A, Niculescu F, Iacob G, Pencea I, Miculescu F, Bololoi R, Drăguț D-V, Matei A-C, Ghiţă M, Priceputu A, et al. Microstructure and Properties of Bi-Sn, Bi-Sn-Sb, and Bi-Sn-Ag Solder Alloys for Electronic Applications. Metals. 2025; 15(8):915. https://doi.org/10.3390/met15080915
Chicago/Turabian StyleIlie, Andrei-Alexandru, Florentina Niculescu, Gheorghe Iacob, Ion Pencea, Florin Miculescu, Robert Bololoi, Dumitru-Valentin Drăguț, Alexandru-Cristian Matei, Mihai Ghiţă, Adrian Priceputu, and et al. 2025. "Microstructure and Properties of Bi-Sn, Bi-Sn-Sb, and Bi-Sn-Ag Solder Alloys for Electronic Applications" Metals 15, no. 8: 915. https://doi.org/10.3390/met15080915
APA StyleIlie, A.-A., Niculescu, F., Iacob, G., Pencea, I., Miculescu, F., Bololoi, R., Drăguț, D.-V., Matei, A.-C., Ghiţă, M., Priceputu, A., & Ungureanu, C. (2025). Microstructure and Properties of Bi-Sn, Bi-Sn-Sb, and Bi-Sn-Ag Solder Alloys for Electronic Applications. Metals, 15(8), 915. https://doi.org/10.3390/met15080915