ISO Solder Alloy 721 (Sn96Ag2.5Bi1Cu0.5)
Solder alloy 721 is a tin-based soldering alloy. Cited properties are appropriate for the as-fabricated (no temper or treatment) condition. 721 is the ISO numeric designation for this material. Older literature may refer to this material as S-Sn96Ag2,5Bi1Cu0,5, but this is now discouraged.
It has a moderately low ductility among the tin-based solder alloys in the database.
The graph bars on the material properties cards below compare solder alloy 721 to: tin-based solder alloys (top), all alloys in the same category (middle), and the entire database (bottom). A full bar means this is the highest value in the relevant set. A half-full bar means it's 50% of the highest, and so on.
Mechanical Properties
Elastic (Young's, Tensile) Modulus
51 GPa 7.3 x 106 psi
Elongation at Break
17 %
Poisson's Ratio
0.36
Shear Modulus
19 GPa 2.7 x 106 psi
Tensile Strength: Ultimate (UTS)
50 MPa 7.3 x 103 psi
Thermal Properties
Latent Heat of Fusion
61 J/g
Melting Completion (Liquidus)
220 °C 420 °F
Melting Onset (Solidus)
210 °C 420 °F
Specific Heat Capacity
220 J/kg-K 0.053 BTU/lb-°F
Thermal Conductivity
56 W/m-K 32 BTU/h-ft-°F
Thermal Expansion
22 µm/m-K
Electrical Properties
Electrical Conductivity: Equal Volume
14 % IACS
Electrical Conductivity: Equal Weight (Specific)
17 % IACS
Otherwise Unclassified Properties
Density
7.4 g/cm3 460 lb/ft3
Embodied Carbon
17 kg CO2/kg material
Embodied Energy
280 MJ/kg 120 x 103 BTU/lb
Common Calculations
Stiffness to Weight: Axial
3.8 points
Stiffness to Weight: Bending
17 points
Strength to Weight: Axial
1.9 points
Strength to Weight: Bending
4.1 points
Thermal Diffusivity
34 mm2/s
Thermal Shock Resistance
3.2 points
Alloy Composition
Sn | 95 to 96.6 | |
Ag | 2.3 to 2.7 | |
Bi | 0.8 to 1.2 | |
Cu | 0.3 to 0.7 | |
Sb | 0 to 0.1 | |
In | 0 to 0.1 | |
Pb | 0 to 0.070 | |
Au | 0 to 0.050 | |
As | 0 to 0.030 | |
Fe | 0 to 0.020 | |
Ni | 0 to 0.010 | |
Cd | 0 to 0.0020 | |
Al | 0 to 0.0010 | |
Zn | 0 to 0.0010 |
All values are % weight. Ranges represent what is permitted under applicable standards.
Followup Questions
Similar Alloys
Further Reading
ISO 9453: Soft solder alloys - Chemical compositions and forms