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ISO Solder Alloy 501 (IEC C7A3, Sn99Cu0.7Ag0.3)

Solder alloy 501 is a tin-based soldering alloy. Cited properties are appropriate for the as-fabricated (no temper or treatment) condition. C7A3 is the IEC 60672 type for this material. 501 is the ISO numeric designation. Older literature may refer to this material as S-Sn99Cu0,7Ag0,3, but this is now discouraged.

It has a moderately low tensile strength and the highest thermal conductivity among tin-based solder alloys.

The graph bars on the material properties cards below compare solder alloy 501 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

Brinell Hardness


Elastic (Young's, Tensile) Modulus

51 GPa 7.3 x 106 psi

Elongation at Break

22 %

Poisson's Ratio


Shear Modulus

19 GPa 2.7 x 106 psi

Tensile Strength: Ultimate (UTS)

29 MPa 4.3 x 103 psi

Thermal Properties

Latent Heat of Fusion

60 J/g

Melting Completion (Liquidus)

230 °C 440 °F

Melting Onset (Solidus)

220 °C 420 °F

Specific Heat Capacity

220 J/kg-K 0.053 BTU/lb-°F

Thermal Conductivity

67 W/m-K 39 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


7.3 g/cm3 460 lb/ft3

Embodied Carbon

15 kg CO2/kg material

Embodied Energy

260 MJ/kg 110 x 103 BTU/lb

Embodied Water

1390 L/kg 170 gal/lb

Common Calculations

Stiffness to Weight: Axial

3.8 points

Stiffness to Weight: Bending

17 points

Strength to Weight: Axial

1.1 points

Strength to Weight: Bending

2.9 points

Thermal Diffusivity

41 mm2/s

Thermal Shock Resistance

1.9 points

Alloy Composition

Tin (Sn)Sn 98.3 to 99.3
Copper (Cu)Cu 0.5 to 0.9
Silver (Ag)Ag 0.2 to 0.4
Antimony (Sb)Sb 0 to 0.1
Indium (In)In 0 to 0.1
Lead (Pb)Pb 0 to 0.070
Bismuth (Bi)Bi 0 to 0.060
Gold (Au)Au 0 to 0.050
Arsenic (As)As 0 to 0.030
Iron (Fe)Fe 0 to 0.020
Nickel (Ni)Ni 0 to 0.010
Cadmium (Cd)Cd 0 to 0.0020
Aluminum (Al)Al 0 to 0.0010
Zinc (Zn)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