ISO Solder Alloy 121 (Pb85Sn15)
Solder alloy 121 is a lead-based soldering alloy. Cited properties are appropriate for the as-fabricated (no temper or treatment) condition. 121 is the ISO numeric designation for this material. Older literature may refer to this material as S-Pb85Sn15, but this is now discouraged.
It has a fairly low electrical conductivity among lead-based solder alloys. In addition, it has a fairly low embodied energy and a moderately low heat capacity.
The graph bars on the material properties cards below compare solder alloy 121 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
11
Elastic (Young's, Tensile) Modulus
21 GPa 3.1 x 106 psi
Elongation at Break
25 %
Poisson's Ratio
0.43
Shear Modulus
7.5 GPa 1.1 x 106 psi
Tensile Strength: Ultimate (UTS)
32 MPa 4.7 x 103 psi
Thermal Properties
Latent Heat of Fusion
29 J/g
Melting Completion (Liquidus)
290 °C 550 °F
Melting Onset (Solidus)
230 °C 440 °F
Specific Heat Capacity
140 J/kg-K 0.034 BTU/lb-°F
Thermal Conductivity
31 W/m-K 18 BTU/h-ft-°F
Thermal Expansion
28 µm/m-K
Electrical Properties
Electrical Conductivity: Equal Volume
8.8 % IACS
Electrical Conductivity: Equal Weight (Specific)
7.4 % IACS
Otherwise Unclassified Properties
Base Metal Price
80 % relative
Density
11 g/cm3 670 lb/ft3
Embodied Carbon
5.6 kg CO2/kg material
Embodied Energy
93 MJ/kg 40 x 103 BTU/lb
Embodied Water
580 L/kg 69 gal/lb
Common Calculations
Stiffness to Weight: Axial
1.1 points
Stiffness to Weight: Bending
8.6 points
Strength to Weight: Axial
0.84 points
Strength to Weight: Bending
2.1 points
Thermal Diffusivity
20 mm2/s
Thermal Shock Resistance
3.9 points
Alloy Composition
| Pb | 83.4 to 85.5 | |
| Sn | 14.5 to 15.5 | |
| Sb | 0 to 0.5 | |
| Bi | 0 to 0.25 | |
| Ag | 0 to 0.1 | |
| In | 0 to 0.1 | |
| Cu | 0 to 0.080 | |
| Au | 0 to 0.050 | |
| As | 0 to 0.030 | |
| Fe | 0 to 0.020 | |
| Ni | 0 to 0.010 | |
| Cd | 0 to 0.0050 | |
| 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