Dear Ingemar,

Are you sure it is PbCO3? Did you made a chemical analysis?
What you describe sounds to me as recrystallization of colophony
residues on the board.
In my former life I also made that misinterpretation until my teacher
Klein Wassink
put me on the right direction. In his book there is a picture of it
(page 218, 2nd edition).

Regards,
Peer Langeveld
Consultant Soft Soldering Processes
5502 VH 8 The Netherlands

2006/8/31, Ingemar Hernefjord (KC/EMW) <[log in to unmask]>:
>
> 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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