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January 2006

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Subject:
From:
Guy Ramsey <[log in to unmask]>
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Date:
Mon, 30 Jan 2006 11:57:01 -0500
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It sounds like the component mfg is not controlling the process very well.
The varnish will burn off and leave a nicely tinned wire if, the solder pot
is hot enough and if the dwell time is long enough. It can take several
seconds.
Do you have a solder fountain? A little scrubbing / rinsing action might
help. We didn't have one but I bet it would help a lot.

-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Stephen Gregory
Sent: Monday, January 30, 2006 11:28 AM
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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