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ISO Solder Alloy 601 (IEC B520, In52Sn48)

Solder alloy 601 is an alloy that does not fit into any substantial classification group in the database. Cited properties are appropriate for the as-fabricated (no temper or treatment) condition. B520 is the IEC 60672 type for this material. 601 is the ISO numeric designation. Older literature may refer to this material as S-In52Sn48, but this is now discouraged.

It has the lowest melting temperature among alloys in the same category. In addition, it has the highest ductility and the lowest tensile strength.

The graph bars on the material properties cards below compare solder alloy 601 to: minor element 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

31 GPa 4.5 x 106 psi

Elongation at Break

83 %

Poisson's Ratio


Shear Modulus

11 GPa 1.6 x 106 psi

Tensile Strength: Ultimate (UTS)

12 MPa 1.7 x 103 psi

Thermal Properties

Latent Heat of Fusion

43 J/g

Melting Completion (Liquidus)

120 °C 240 °F

Melting Onset (Solidus)

120 °C 240 °F

Specific Heat Capacity

230 J/kg-K 0.054 BTU/lb-°F

Thermal Conductivity

34 W/m-K 20 BTU/h-ft-°F

Thermal Expansion

23 µm/m-K

Electrical Properties

Electrical Conductivity: Equal Volume

12 % IACS

Electrical Conductivity: Equal Weight (Specific)

14 % IACS

Otherwise Unclassified Properties


7.3 g/cm3 460 lb/ft3

Embodied Water

1330 L/kg 160 gal/lb

Common Calculations

Stiffness to Weight: Axial

2.3 points

Stiffness to Weight: Bending

14 points

Strength to Weight: Axial

0.45 points

Strength to Weight: Bending

1.6 points

Thermal Diffusivity

20 mm2/s

Thermal Shock Resistance

1.2 points

Alloy Composition

Indium (In)In 51 to 52.5
Tin (Sn)Sn 47.5 to 48.5
Bismuth (Bi)Bi 0 to 0.1
Silver (Ag)Ag 0 to 0.1
Antimony (Sb)Sb 0 to 0.1
Lead (Pb)Pb 0 to 0.070
Copper (Cu)Cu 0 to 0.050
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

Further Reading

ISO 9453: Soft solder alloys - Chemical compositions and forms