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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