We currently use small (25um diameter) Nichrome wire as micro electrodes which we use to record the weak electrical signals produced by single brain cells. We have considerable problems however in joining this wire to a suitable connector which can then be plugged into a preamp. The connection doesn't need to be mechancally strong but does need to be electrically sound. The Nichrome wire we use is coated in Formvar insulation and this is also causing problems because it is difficult to remove the insulation without damaging the wire. The wire could be joined either directly to the pins on a connector or to a PCB track.

It seems as though resistance welding is a promising method. I have done a few quick tests with a current limited power supply and a piece of copper wire and it works occasionally although i have to strip the insulation off first and usually the wire just breaks. Can anyone provide any advice regarding electrode material, shape and size, suitable current and voltages, whether i will be able to spot weld through the insulation or not and any other details that come to mind? Thanks

-- Noah Russell (noah.russell@nimr.mrc.ac.uk), June 28, 2004

Answers

The insulation will have to be removed prior to the weld, or possibly during the weld, using the heat generated at the work piece. This has successfully been done by many manufactures of similar type products, including but not limited to brain nerve stimulation for epilepsy patients. The typical application uses a true d.c. power supply, that can produce extreme stable waveforms at currents as low as 5 Amps for 10 micro seconds, and weld heads that can operate with very fast follow up, in the 20 - 50 gram range. Kurt Tolliver - Unitek Miyachi Corp. kurt(@)unitekmiyachi.com

-- Kurt Tolliver (kurt(@)unitekmiyachi.com), June 28, 2004.