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August 2011

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Subject:
From:
Gerry Gagnon <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Gerry Gagnon <[log in to unmask]>
Date:
Thu, 4 Aug 2011 11:42:17 -0400
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Hi Brian,

 

You have me beat by only a few years......

 

Since we are talking about surface finish we are talking about outerlayer surfaces.

Tin is typically used as the outerlayer etch resist (it used to be gold in my day) and the etchants are typically ammoniacal. I do not know for sure but I don't think there are any other potential sources of tin further downstream in outerlayer processes after etch. I could be wrong though.

 

Thanks for the copper foil memory.... I seem to remember that Gould used a zinc treatment which upon conversion with copper formed the thin brass layer. I remember rejecting sheets of "discolored" foil on the treated side and was told by Gould to bake the foil. Voila, the brass color returned. Although the bond strength was fine, I think this treatment died out because the newer developments in foil treatment were so much superior in other ways.

 

 

Gerry



----------------------------------------
> Date: Thu, 4 Aug 2011 18:16:43 +0300
> From: [log in to unmask]
> Subject: Re: [TN] Removing SnCl2
> To: [log in to unmask]
>
> Logically, I would expect no Sn on a bare ENIG board. Where would it
> come from? The only answer I can offer is from the copper treatment.
> When I was half my present age (~1970), I seem to remember Gould (?)
> offered a copper treated with brass; I thought this had died a natural
> death (peel strength?) but has someone resurrected it??? If so, then
> using a chloride etchant would be a natural source.
>
> Brian
>
> On 04/08/2011 15:22, Don McFarland wrote:
> > Sn(iv) would make more sense because this stuff seems impervious to anything we've thrown at it.
> >
> > We have traced it back and found that this residue is visually present on the bare ENIG pcb. We have the sem, edx ad ftir tests being done on the bare board to compare residual signature to post-assembly residues. The interesting this was our FTIR only showed FR-4, but nothing else. Should ftir detect these Sn residues if present and adequate sample captured? I am wondering if this is a laminate curing issue and not a contamination issue, since our data points arent seeing the chemistry.
> >
> > The SEM/edx found minute flakes of Sn that appear to attach to Cu contaminate found on bare pcb. These embedded flakes are only visible at 1000x and are small at that...just a bit out of the allowed mag for fod inspection.
> >
> >
> >
> > Sent from my iPhone
> >
> > On Aug 3, 2011, at 4:24 PM, R Sedlak<[log in to unmask]> wrote:
> >
> >> Don: I think I qualify as a "real Chemist", or at least I have a lot of people fooled...
> >> Actually, SnCl2 is easy to remove, but it is highly unlikely your deposit is SnCl2, but is much more likely to be SnCl4 (Stannic Chloride) which is rather more difficult to remove...
> >> I would recommend either a Caustic cleaner, preferably with some chelate, if your substrate can tolerate that.
> >> If not, probably the only other cleaner which will remove Stannic Chloride is a dip in an Ammonium Bifluoride solution, say, 5-10%. Stannic salts are highly insoluble, and hydrolyze easily to Stannic oxide, which needs either strong alkali, or HF to remove.
> >> Wish I had better news.
> >> Rudy Sedlak
> >> RD Chemical Company
> >>
> >> --- On Wed, 8/3/11, Don McFarland<[log in to unmask]> wrote:
> >>
> >> From: Don McFarland<[log in to unmask]>
> >> Subject: [TN] Removing SnCl2
> >> To: [log in to unmask]
> >> Date: Wednesday, August 3, 2011, 10:49 AM
> >>
> >> Any ideas on methods to remove a tin chloride residue that was found on a FR-4 substrate after wave solder. We have done some good homework to find the source, but we are looking for good and proven methods to remove the residues from affected assemblies.
> >>
> >> Any input is welcome.
> >>
> >> Regards,
> >>
> >> Don McFarland
> >>
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