Hi Ingemar! I'll assume that your CBGA has a 90Pb10Sn solderball which
would account for a large enough source of Pb to allow for the formation of
PbCO3. What is puzzling is that Sn preferentially oxidizes before Pb which
I would think would inhibit the formation of PbCO3 (e.g. competing surface
species growth reactions). What type of environment is the CBGA exposed
too? I can't image your stock room being an environment to promote the
growth of PbCO3. What are the CBGAs stored in? Have you conducted an FTIR
test to see if there is a flux residue film on the CBGA solderballs after
cleaning? Oh, do you have any of your usual cool photos of the PbCO3 that
Steve can post?

Dave Hillman
Rockwell Collins
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             "Ingemar
             Hernefjord
             (KC/EMW)"                                                  To
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             Sent by: TechNet
             <[log in to unmask]>                                     Subject
                                       [TN] PbCO3

             08/31/2006 03:20
             AM


             Please respond to
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             ; Please respond
                    to
                 "Ingemar
                Hernefjord
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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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