Tegehall,

Thanks for sharing. I have not ruled out the flux to cause these residues.
But what puzzled me is why elements of flux are not captured in EDX? I
expect to see some carbon - that is what I thought I should see in flux.

I also thought the water soluble flux would be soluble in DI water- that is
what my supplier claimed.

The only concern I have over this residue is that it is corrosive in
nature, otherwise it should be harmless like you said.

The residue only showed up after few days and only on some substrate. I am
in the process of simulating this effect by subjecting in different
temperature profile, storing in different environment, having the substrate
washed and unwashed. Please share if you have additional input you like me
to look at.

Thanks once again.



----------
> From: Tegehall Per-Erik <[log in to unmask]>
> To: [log in to unmask]
> Subject: Re: [TN] White Residue on solder joints
> Date: Wednesday, May 26, 1999 10:07 PM
>
> I have seen the type of flux residues you describe a number of times. In
> most cases, it has turned out to be a lead salt, for example lead
adipinate
> formed when adipic acid in the flux (an activator) react with lead oxide
on
> the surface to be soldered. My experience is that these salts are very
> difficult to dissolve whatever solvent you use. Since the residues are so
> difficult to dissolve, they are probably rather harmless for most
> applications (but I have no proof for that statement). However, if you
will
> conformally coat the assemblies, they may cause poor adhesion of the
> coating. What puzzle me is that you say it was manifested a few days
after
> aqueous wash. It should have been there immediately after cleaning.
>
> Per-Erik Tegehall
> IVF
> Sweden
>
> > ----------
> >
> > Has anyone ever come across white residues that looks like snow cap
> > covering the solder joints? The phenomenon only manifested  a few days
> > after Aqueous wash and EDX captured high lead and oxygen. The white
> > residues are so stubborn that they could not be dissolved in DI water
and
> > IPA. We use a water soluble paste and clean our assembly twice
> >
> > All inputs are welcome and appreciated.
> >
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