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ISO Solder Alloy 191 (Pb93Sn5Ag2)

Solder alloy 191 is a lead-based soldering alloy. Cited properties are appropriate for the as-fabricated (no temper or treatment) condition. 191 is the ISO numeric designation for this material. Older literature may refer to this material as S-Pb93Sn5Ag2, 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 moderately high melting temperature.

The graph bars on the material properties cards below compare solder alloy 191 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

Elastic (Young's, Tensile) Modulus

19 GPa 2.7 x 106 psi

Elongation at Break

32 %

Poisson's Ratio


Shear Modulus

6.5 GPa 0.94 x 106 psi

Tensile Strength: Ultimate (UTS)

29 MPa 4.2 x 103 psi

Thermal Properties

Latent Heat of Fusion

27 J/g

Melting Completion (Liquidus)

300 °C 570 °F

Melting Onset (Solidus)

300 °C 560 °F

Specific Heat Capacity

130 J/kg-K 0.032 BTU/lb-°F

Thermal Conductivity

24 W/m-K 14 BTU/h-ft-°F

Thermal Expansion

29 µm/m-K

Electrical Properties

Electrical Conductivity: Equal Volume

8.8 % IACS

Electrical Conductivity: Equal Weight (Specific)

7.2 % IACS

Otherwise Unclassified Properties


11 g/cm3 690 lb/ft3

Embodied Carbon

5.8 kg CO2/kg material

Embodied Energy

95 MJ/kg 41 x 103 BTU/lb

Common Calculations

Stiffness to Weight: Axial

0.93 points

Stiffness to Weight: Bending

8.0 points

Strength to Weight: Axial

0.72 points

Strength to Weight: Bending

1.9 points

Thermal Diffusivity

16 mm2/s

Thermal Shock Resistance

3.9 points

Alloy Composition

Lead (Pb)Pb 92.4 to 94
Tin (Sn)Sn 4.8 to 5.2
Silver (Ag)Ag 1.2 to 1.8
Antimony (Sb)Sb 0 to 0.2
Bismuth (Bi)Bi 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 0.0020
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