SnPbvalues describe: 63Sn-37Pb
Why it's out
Marginal vapor pressure, creep, and flux residues that outgas forever.
Where it hides
Ad hoc electrical joints: use crimps, spot welds, or vacuum-rated solder practice.
Properties
The values below are candidate: compiled from the sources named, not yet individually validated.
Provisional provenance: O'Hanlon, A User's Guide to Vacuum Technology.
Wet cleaning
| Recipe | if it must be present: ultrasonic flux removal in IPA, then a long bake |
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| Forbidden | no-clean flux, which is not vacuum-clean |
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| Limit | flux residue, which outgasses far longer than the alloy |
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Vacuum and outgassing
| Outgassing, unbaked (10 h) | 5e-8 mbar·L/s/cm² |
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| Outgassing, baked | not bakeable |
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| Vapour pressure | lead evaporates slowly above 300 °C, but the flux is the real problem |
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Temperature
| Bake, assembled | 80 °C |
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| Braze / H2 firing | 183 reflow °C |
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| Metallurgical limit | THE CONDEMNING NUMBER: melts at 183 °C, so it caps the bakeout of every system it touches |
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Thermal
| CTE | 25 ppm/K |
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| Thermal conductivity | 50 W/m·K |
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| Specific heat | 180 J/kg·K |
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| Emissivity | 0.1 |
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| Melting / softening | 183 °C |
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Mechanical
| Strength | 30–50 tens MPa |
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| Tensile | 30–50 MPa |
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| Elongation | 30 % |
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| Young's modulus | 30 GPa |
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| Density | 8.4 g/cm3 |
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Electrical and magnetic
| Relative permeability | ~1.0 |
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| Resistivity | 15 µΩ·cm |
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Engineering
| Joining | soldered |
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| Process notes | present in legacy feedthroughs and assemblies |
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| Availability and cost | commodity |
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Sources · 1
- O Hanlon, A Users Guide to Vacuum Technology
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