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I am looking for the best solder type to connect a wire to a copper substrate. However, the wire is also a mechanical support as well as an electrical connection. Cost is not an issue. The wire is Platinum/Iridium alloy.

Seems there is quite a variety of solder types

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  • \$\begingroup\$ What is the wire made of? Could you braze the wire for the mechanical aspect and add a second short wire with no forces on it for the electrical connection? \$\endgroup\$ – Andrew Morton Jan 18 '17 at 10:29
  • \$\begingroup\$ @AndrewMorton Just edited the question - "The wire is Platinum/Iridium alloy". Only one thin wire allowed, unfortunately \$\endgroup\$ – Dirk Bruere Jan 18 '17 at 10:36
  • \$\begingroup\$ what's the limiting temperature of the wire? Is it just a wire, or the lead to some device which has a temperature limit. Obviously silver solder or brazing is more creep resistance than soft solder, operating as it does with a greater margin below melting poiint, but requires a higher temperature to make the joint. \$\endgroup\$ – Neil_UK Jan 18 '17 at 10:38
  • \$\begingroup\$ @Neil_UK The limiting temperature of the wire is probably well over 1000degC. The copper is the limiting factor. The wire is similar to what you get in an old fashioned meter movement. \$\endgroup\$ – Dirk Bruere Jan 18 '17 at 10:40
  • \$\begingroup\$ @Neil_UK Operating temperature will be below 85degC \$\endgroup\$ – Dirk Bruere Jan 18 '17 at 10:55
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While there are lots of solders available, none of what you seem to be looking at are remotely suitable - they'll solder copper just fine, but platinum is a different matter. You need to start looking specifically at platinum solders. Since the melting point of copper (1085 C) is an obvious limit to your process, you should be aware that only the softest platinum solders melt below this temperature. While it's true that only local heating of the copper is necessary, this isn't much help due to a) the high thermal conductivity of copper, and b) the fact that you'll be heating with a torch or something like it.

Frankly, I'd suggest you look into spot welding or something similar.

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I think you can braze (silver solder) platinum wire just fine with regular white flux as used on steels and some non-ferrous metals, using a propane or MAPP torch. It melts at about 800°C so cherry red. Much stronger than soft solder.

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