A set of wires prepared for connection
Properly joined thermocouple wires
Thermocouples do a lot for us. We use them for profiling reflow ovens, checking material temperatures, and a host of other temperature related measurements. They see a lot of abuse and they are bound to break with enough rough use. So how do we fix broken thermocouple wires? I have a method that works very well. It may not be the cheapest way to fix the wires but it has the following advantages:
- Pb-free joint
- Highest thermal conductivity of any current method
- Good for use up to 280°C
- Strongest connection (40,000psi tensile strength)
- Requires no specialized equipment
This method can also be used to convert leaded thermocouple wires to pb-free.
Here’s how:
1) Clip the ends of the thermocouple wires so they are even
2) Strip the sheathing back as shown in the picture (1/4inch)
3) Use a razor blade or emery paper to scrape the oxide layer off the wires, then twist the ends together
4) Put a very thin (~.001”) layer of NC 506 flux on the surface of a ceramic coupon and the exposed thermocouple wires
5) Place an 80Au/20Sn preform or a sphere(s) of the correct volume on the flux layer
6) Place the coupon onto a hotplate set to 400°C
7) Bring the wires over to the Au/Sn (which should now be molten)
8) Dip the wires into the solder
9) The solder should wick onto the wires, when it does – remove the wires.
You can leave the no-clean flux residue on the wires, or wipe it off using a solvent and rag. You now have a high-temp pb-free thermocouple.
If you'd like to discuss this with me, click here or just give me a call @ (315) 853-4900 x-7592.