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ISO Solder Alloy 123 (Pb95Sn5)

Solder alloy 123 is a lead-based soldering alloy. Cited properties are appropriate for the as-fabricated (no temper or treatment) condition. 123 is the ISO numeric designation for this material. Older literature may refer to this material as S-Pb95Sn5, but this is now discouraged.

It has a moderately low heat capacity among lead-based solder alloys. In addition, it has a fairly low electrical conductivity and a very high ductility.

The graph bars on the material properties cards below compare solder alloy 123 to: lead-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

18 GPa 2.6 x 106 psi

Elongation at Break

45 %

Poisson's Ratio


Shear Modulus

6.2 GPa 0.91 x 106 psi

Tensile Strength: Ultimate (UTS)

28 MPa 4.0 x 103 psi

Thermal Properties

Latent Heat of Fusion

26 J/g

Melting Completion (Liquidus)

310 °C 600 °F

Melting Onset (Solidus)

300 °C 570 °F

Specific Heat Capacity

130 J/kg-K 0.032 BTU/lb-°F

Thermal Conductivity

23 W/m-K 13 BTU/h-ft-°F

Thermal Expansion

29 µm/m-K

Electrical Properties

Electrical Conductivity: Equal Volume

8.8 % IACS

Electrical Conductivity: Equal Weight (Specific)

7.1 % IACS

Otherwise Unclassified Properties

Base Metal Price

75 % relative


11 g/cm3 690 lb/ft3

Embodied Carbon

4.5 kg CO2/kg material

Embodied Energy

74 MJ/kg 32 x 103 BTU/lb

Embodied Water

500 L/kg 59 gal/lb

Common Calculations

Stiffness to Weight: Axial

0.9 points

Stiffness to Weight: Bending

7.8 points

Strength to Weight: Axial

0.69 points

Strength to Weight: Bending

1.8 points

Thermal Diffusivity

16 mm2/s

Thermal Shock Resistance

3.8 points

Alloy Composition

Lead (Pb)Pb 93.5 to 95.5
Tin (Sn)Sn 4.5 to 5.5
Antimony (Sb)Sb 0 to 0.5
Bismuth (Bi)Bi 0 to 0.1
Silver (Ag)Ag 0 to 0.1
Indium (In)In 0 to 0.1
Copper (Cu)Cu 0 to 0.080
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 0.0050
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