Hi All,
Do you have any recommendations for a conductive epoxy (electrically) that can be used to glue wires under UHV and cooled down to 4 K? the baking temperature of the system is 150 C.
I have used Stycast 1266 epoxy along with GE7031 varnish to encapsulate heater wires and to glue them in place. To attach electrical leads, I have used In-Sn solder (Pb free). Hope this helps!
Hallo Mohamed,
I used indium to get a good electrical and thermal contact. But In is no epoxy. So it must be soldered. The melting temperature of In is about 150C. This T cannot be exceeded. But In is ideal for low-T applications. The advantages are very good conductivity and it doesn't break - furthermore: if you use epoxy, the sample (wire) is stressed and can disrupt. The vapour pressure of In can be neglected. For UHV is epoxy no recommendation.
With Regard
R. Mitdank
Hello Rüdiger,
Rüdiger Mitdank How much is the baking temperature of your setup? because we bake our system here up to 150 C, so the indium will be a nightmare in this case.
Rüdiger Mitdank Is the 150 C melting point sharp or a range? If it is a sharp one, can you send me a recommended supplier name for this 150 C solder in Germany?
Hi,
The 52%In-48%Sn has a eutectic temperature of 118 deg C.
I am planning to use 97%In-3%Ag wire for measurements on superconductors. This has a melting point of 143 deg C as per the manufacturers data sheet.
Just a note of caution - all my measurements were done in the high vacuum regime (so some of the epoxies I had used were still found to be adequate) and not in the ultra high vacuum you are interested in.
UHV-compatible electrically conductive glues:
- Epotek E4110-LV. Two-component silver epoxy (standard E4110 also works well down to at least 10^-9 mbar, especially since your system will also be cryopumped).
- Epotek H31D-LV. Single-component silver epoxy.
UHV-compatible solder: All-State No. 430. Silver solder, melts at 221C.
You could also use pure indium, as others have suggested, provided that you keep the chamber temperature comfortably below 150C and there is no load/tension on the wire during bakeout. However, indium isn't much fun to solder since it doesn't flow or wet other metals particularly well. Also, bear in mind that it becomes superconducting at 3.4K, so the thermal conductivity of your joint will drop below this temperature.
Dear Mohamed,
as I read, the melting point of "PURE" indium is 156,6°C. This is of course critically, if you bake at 150°C. Perhaps is 140°C sufficient? I bake not more than 130C. The main effect is water and therefore this temperature is high enough .But I recommend a test. The larger problem with indium is the surface tension. Indium tends to coagulate.
Yours
R. Mitdank
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