I want to connect 316 stainless steel wire to a printed circuit board.
I understand that I cannot solder the stainless steel wire to the
circuit board so I am wondering if there is another way to connect the
wire to the board. I am thinking about using a receiving pocket and
treating the wire as a "pin." Do you have any other suggestions?
Thanks,
James
I have tinned stainless steel with silver solder and some nasty flux but
that kind of solder needs to be really hot (just about red hot) so doing it
after plastic is in contact with the wire is likely to be troublesome. You
can then solder to the silver solder using ordinary soft solder. Often
silver solder contains cadmium, especially the stuff that melts at a lower
temperature than red-hot. This cadmium would be a RoHS problem in some
countries and probably isn't good for you either.
Once I worked at a place where one of the guys had an unlabelled jar of some
kind of grey goo that was a very fancy solder paste (nearly all flux and
almost no solder, and a very fine consistency). That stuff would solder
stainless but the process was slow and not easy.
For mass production, I suggest you investigate spot-welding the stainless
steel to some ordinary mild steel. Both stainless and mild steel can be
spot welded very easily due to the poor electrical conductivity and poor
thermal conductivity. You could spot-weld on a tab of ordinary steel that
is already tinned with soft solder in the place where it needs to be, or
you could spot weld a stainless steel spade terminal onto the stainless
wire. I have seen something like this on the end of the element in
electric hotplates and irons and water heaters.
I think that the key to reliable spot welding is very high contact pressure
and very high current, many many thousands of amps. You can find a lot of
home made spot welding devices on the internet but most of these have
insufficient current, and therefore would not work if the electrodes were
pressed together with a proper amount of pressure. They make these things
sort-of work (sometimes) by not pressing hard on the electrodes, so then
the contact resistance is higher and the heating is then usually enough to
weld even with a low current, sometimes. I think that this is not very
reliable though, because it relies on the poor contact between the metal
being just poor enough to get hot, but not too poor where the current would
be reduced. Therefore I would start by trying out a professional spot
welding machine, and only improvise if necessary and with great caution.
You might also find that it is possible to TIG-weld something onto the end
of the wire. This might be especially easy if you can make your terminal
in the form of a tube that slips over the stainles wire, where it would
only be necessary to melt the end of the tube and the wire inside it, with
a very short burst of current. This could be done before the heat has a
chance to spread to the plastic. Ask on sci.engr.joining.welding, they
might have some ideas.
Chris