The solder pot technique usually works OK on Litz wire. Also known as magnet
wire or self fluxing wire if you want to extend your search terms, but your
man hasn't given complete advice.
It has to be done with a very hot pot and low tin content solder
[also usually single stranded wire, not flex.]
The low tin content [30/70 or 40/60] is necessary to prevent the copper
wire necking in or even completely dissolving at the high (like 270-300 C)
temps necessary to get a good burn on the insulation, also cuts the drossing
down a bit.
Regards
Mike Fenner
Indium Corporation
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-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Stephen Gregory
Sent: 30 January 2006 16:28
To: [log in to unmask]
Subject: [TN] Prepping Stranded Litz wire for soldering...
Mornin' All!
I hope you all had a good weekend! We finally got some rain here, it was
only a half inch, but it was better than nothing...
My question has to do with Litz wire. We're building an assembly that has an
inductor that we bond to the core, then hand solder the two stranded Litz
wires to surface mount pads on the board. You can see some photos here:
http://www.stevezeva.homestead.com/files/Coil_Solder_Joints.jpg
http://www.stevezeva.homestead.com/files/Coil_Solder_Joints_2.jpg
The solder joint appearance hasn't pleased the source inspector, he's been
rejecting these. We've been having a hell of a time getting decent looking
joints because of the residue from the insulation on these wires.
The manufacturer of the part says all they do to prep the ends of the wires
is dip them in a solder pot to melt the insulation and tin the ends. But
that doesn't get all the insulation off. Residue from the melted insulation
winds-up migrating up through the joint when we're trying to solder them to
the pads on the board. You'll see voids, and non-wetting on some of the
strands. That's what the source inspector is rejecting them for.
In the photos, those are just about the best we could get. I know they look
really excessive. In one photo you can see where the source inspector was
rejecting for "strand separation".
I'm looking for some suggestions on how best to prep the ends of this wire
so that we can solder it to this board.
I was thinking about crimping some sort of small diameter copper tubing over
the ends (after it was tinned as best as we could), then forming a "foot" to
solder to the pad?
Is there a better way to prep this wire? I did a search and found that there
are all kinds of different suggestions for prepping this wire, from using a
blow torch, to paint remover, to dipping it in molten aspirin...yes that's
right, molten aspirin!
I've asked for a sample of the stranded wire from the inductor manufacturer
and I'll be doing some experimentation on it.
All I know is that I'm getting a headache over this wire....
Stephen Gregory
Senior Process Engineer
LaBarge Incorporated
Tulsa, OK 74146
(918) 459-2285
(918) 459-2350 FAX
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