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Connecting Stainless Steel Electrodes to a PCB

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
 
J

John Larkin

Jan 1, 1970
0
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

Phoenix or Weidmuller barrier strip?

John
 
J

John Popelish

Jan 1, 1970
0
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?

If you silver solder coat the end of the wire, then it can
be soldered with ordinary soft solder. I use tiny stainless
steel 'aircraft' type cable as glove heating elements and
connect it this way. I have also used crimp terminals to
connect to it. But it is stranded, not solid conductor.
 
E

Ecnerwal

Jan 1, 1970
0
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

Choose the correct flux, and your understanding becomes wrong. You WILL
need to clean carefully, as any flux that will flux stainless will be
highly corrosive - but you could possibly flux the wire and tin it, then
clean, then use a milder flux for connecting the tinned wire to the
board.

For soft soldering stainless at the high-volt lab, as best I recall, we
used Eutetic Castolin 157, or perhaps it was 157A or 157B, back in the
1980s.

In the AgEng metalworking lab, for stainless steel sink soldering, we
used 95-5 solder and plain old acid (Zinc dichloride?) flux, with more
attention paid to physical cleaning preparation as follows. Put on a
glove, dip a hunk of scotchbrite in flux, scrub the wire for mechanical
removal of as much oxide as possible (leaving a coating of flux on the
part).

However, depending on the mechanical stresses involved (if any), you
might do better to solder down a screw-type terminal strip.
 
R

Rich Grise

Jan 1, 1970
0
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?

Are you saying that you're unable to make solder stick to the 316, or
is it more like you're not allowed to solder directly to the board?

You could "tin" the end of the SS wire with some acid flux and silver
solder, clean it, and solder should stick to it.

If you're not _allowed_ to solder it to the board, I'd look into some
kind of crimp connector.

Good Luck!
Rich
 
S

Spehro Pefhany

Jan 1, 1970
0
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

Maybe you could plate or tin the wire (eg. with stainless solder) and
then it would be solderable.


Best regards,
Spehro Pefhany
 
Are you saying that you're unable to make solder stick to the 316, or
is it more like you're not allowed to solder directly to the board?

You could "tin" the end of the SS wire with some acid flux and silver
solder, clean it, and solder should stick to it.

If you're not _allowed_ to solder it to the board, I'd look into some
kind of crimp connector.

Good Luck!
Rich

I am allowed to attach the stainless to the board any way I can. I
didn't realize that "tinning" was an option. I am molding these
electrodes into a piece of plastic and then I need to attach the board
on top of the encased electrodes. I am unfamiliar with the acid flux-
silver solder technique. Will I still be able to tin when the
stainless is in plastic.

Thanks,
James
 
K

Kevin G. Rhoads

Jan 1, 1970
0
I am allowed to attach the stainless to the board any way I can. I
didn't realize that "tinning" was an option. I am molding these
electrodes into a piece of plastic and then I need to attach the board
on top of the encased electrodes. I am unfamiliar with the acid flux-
silver solder technique. Will I still be able to tin when the
stainless is in plastic.

What makes stainless a soldering nightmare is what makes it stainless,
a hard adherent Chromium-oxide &/or nickel-oxide based surface layer.

If you disrupt that layer with an agressive flux and make metal to metal
contact with a tinning layer that is solderable then soldering to the
tinned layer is no problem. However, do not depend upon such for mechanical
strength.

Since the disruption of the passivating layer is chemical (e.g., agressive
flux) so long as the plastic you use can take normal soldering temps, for
perhaps longer than soldering usually takes, since even an agressive flux
can take time on stainless, then no problem.

As for purely mechanical connections, while doable, they can suffer the
same issues as connecting aluminum wiring to things. For the same reasons,
the surface oxide layer spontaneously grows when exposed to atmosphere.
So something that connects now is not necessarily going to stay connected
unless the mechanical bonding is tight and avoids any motion, even temperature
induced creeps.

The same kinds of connections used to connect aluminum wiring to copper
will probably be OK for stainless.

Me, I'd tin. All your problems are up front, and you can deal with them
then. Tin and lead oxides are semiconducting and soft and readily displaceable.
They don't cause the kinds of problems that stainless or aluminum surface
films (hard, dureable, adherent and INSULATING) do.

But, it is your nickle, so your call. (Pun is accidental)
 
R

Rich Grise

Jan 1, 1970
0
I am allowed to attach the stainless to the board any way I can. I
didn't realize that "tinning" was an option. I am molding these
electrodes into a piece of plastic and then I need to attach the board
on top of the encased electrodes. I am unfamiliar with the acid flux-
silver solder technique. Will I still be able to tin when the
stainless is in plastic.

According to some other responders, with the right flux, you won't even
need silver solder - someone mentioned another alloy, which sounds like
they have more experience in these things.

Obviously, you can't tin _through_ the plastic, but if you're worried
about the pin heating up and melting the plastic housing, that depends
on a lot of other factors.

Can you draw a picture or something of what you're actually trying to
accomplish? i.e., what's the end result you're looking for?

Thanks,
Rich
 
C

Chris Jones

Jan 1, 1970
0
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
 
W

whit3rd

Jan 1, 1970
0
I want to connect 316 stainless steel wire to a printed circuit board.


Direct soldering is a mediocre idea, because the stiff 316 wire
will just crack the tin/lead and work its way loose if any stress is
applied.
It also won't crimp well (soft crimp lugs won't deform the SS wire, so
the crimp can rotate and come loose).

But, you can splice the stainless to a stranded-copper-wire pigtail,
then
solder or crimp-lug-and-bolt the copper. Lap the stainless with
the copper wire, wrap the pair with a short length of fine copper
wire, apply Nokorode or other acid flux (the stuff recommended
for stainless) and solder. Wash off any remaining flux.

Hard solder (silver solder) is preferred for this, of course, but it
requires at least a propane torch (better with acetylene/air). It can
be tricky to keep from melting the copper. Small quantities of
silver solder are jewelry-making supplies at art stores.
 
B

Barry Lennox

Jan 1, 1970
0
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

There's a few options.

Soldering is quite easy with the correct flux, I have used a Lonco
product with good results. I think it's "431" I recall reading the
MSDS and it's not that toxic, it's a clear yellowish liquid with a
sweet smell. It must be washed off with hot water after soldering.

Spot weld it to copper wire.

Secure them into a screw-down terminal board.

Barry
 
B

Barry Lennox

Jan 1, 1970
0
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?

Also take a look at this page :

http://www.azom.com/details.asp?ArticleID=1178#_Soft_Soldering
 
E

Ecnerwal

Jan 1, 1970
0
If you go with soldering tinned stainless to the board (certainly the
cheapest and simplest option) it's probably worthwhile to try the
following non-standard pain-in-the-behind method of mechanically
connecting the wire (which is stiff, and could tear pads off if
"mechanically" held in by solder, if subject to any force).

For each wire, drill two holes perhaps 1 cm apart with pads (a
connecting trace that's free of soldermask is optional, but could only
help). Tin the wire further than that (plain old low-temp solder is fine
with the right flux). Put wire through the board, bend once at 90
degrees, bend again at 90 degrees to match the spacing between holes,
and insert the tip in the second hole - pull tight to board. Bend the
tip over on the top of the board, and bend the body down flat against
the top of the board, so it's completely and solidly held in place by
bends. Then solder it.
 
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