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August 2006

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Subject:
From:
R Sedlak <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, R Sedlak <[log in to unmask]>
Date:
Thu, 31 Aug 2006 05:28:02 -0700
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Ingemar:
  If you have PbCO3, you truly have a problem, this dissolves rapidly in few things, and my best suggestion, ignoring effects on the substrate, would be dilute Nitric acid.  This seems a bit extreme, but you need something acidic to dissolve this stuff, and many/most common acids will form insoluble salts with Lead, Nitric is one of the few that will not.
  Worse, the surface left behind will likely re-oxidize more rapidly than it did originally.
  RA flux is probably not acidic enough to dissolve the PbCO3, and mixing it with ethanol would probably slow dissolution.

  Good luck.
  Rudy Sedlak
  RD Chemical Company

"Ingemar Hernefjord (KC/EMW)" <[log in to unmask]> wrote:

We got lots of such growth on CBGA balls recently. After
soldering/cleaning: nada. After one week in stock: signs of growth.
After one month: unacceptable crystals. Now, being insoluble in water
and many solvents, some specialists advise you to mix an RA with
ethanol, heat this mixture and dip the part until the crystals vanish.
My question to TN is whether there is alternative methods? Some accept
PbCO3 growth as being harmless, but this is not our intention, because
loose particles are semiconducting and can create leakage current paths.

Brian's book "Cleaning and Contamination of Electronics and Assemblies"
mention there are five groups of white residues, but, oddly enough, lead
carbonate is not included. The chemistry world of soldering residues is
so complicated, that I have to ask you for help.

Thanks in advance
Ingemar Hernefjord
Ericsson Microwave Systems

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