Connecting Thin Wires for Thermopile: Tips & Tricks

[0xDEADBEEF]

I have to connect very thin wires d<40\mathrm{\mu m} of different metals multiple times to make a thermopile. Due to the geometry, the cost of the wire and personal nerves I do not have too many tries. The wires are insulated, and in the end the whole thermopile should also be electrically insulated, but I'll do that with varnish if there are no other suggestions.
So what are my options, and what is the best way to bond these wires? If it is soldering, what are the tricks of the trade? I tried that today and the wires oxidize like hell and collect burned resin/insulation. Removing the insulation with a scalpel is pretty much impossible without ripping them.
I am working in a well funded lab. Technology can be bought...

 

[dlgoff]

What type of metals? Most thermocouples I've worked with I've just soldered. Are you using an iron? You should try to minimize the time you apply heat to keep the insulation from melting. If you need to remove the resins you can use http://en.wikipedia.org/wiki/1,1,1-Trichloroethane" . There are probably other solvents you could use.

 

[MATLABdude]

I'd use a wirebonder. Check with your local microfab. You may also be able to use mems-exchange.org to find a facility somewhere reasonably close (or not) that can do it for you.

 

[Proton Soup]

geez, taht's small. we used hot tweezers to strip wire without nicking it, but that's hair-thin, ain't it?

 

[0xDEADBEEF]

The wire materials are not yet clear, but the usual thermocouple types with letters on the wikipedia page are good candidates. Actually it is thinner than most hairs, and the thinnest copper wire we have is sticking to anything it comes in contact with, because
of the low weight.
From what I have read some wire bonders only seem to work with gold, and I don't know how much choice you have with the thickness. But I'll check out what I can find.

 

[berkeman]

I don't know much about thermopiles, but can you just hold them in contact with compression? Or do you need the metals to mix for some reason at the junctions?

If compression would work, you could layer them up with the tips resting on each other in a channel arrangement of some sort (non-conducting), and then apply some compression clamp to the whole stack...

 

[Averagesupernova]

Solderability of course depends on the type of metal. The thermocouples I've had experience with did not solder well.

 

[MATLABdude]

The wire materials are not yet clear, but the usual thermocouple types with letters on the wikipedia page are good candidates. Actually it is thinner than most hairs, and the thinnest copper wire we have is sticking to anything it comes in contact with, because
of the low weight.
From what I have read some wire bonders only seem to work with gold, and I don't know how much choice you have with the thickness. But I'll check out what I can find.

Do a Google search for copper wire bonding. Additionally, what's wrong with gold or aluminum?

 

[0xDEADBEEF]

Do a Google search for copper wire bonding. Additionally, what's wrong with gold or aluminum?

Gold is one of my favored options, but the wire has not been delivered yet. I was hoping for something that I can train now with less expensive wires, which I can later use with the specialized wires. I think I'll try spot welding or abusing a wire bonder with the wrong materials.