Impossible to say without a full rundown of all your materials and
processes. However, if this happens with only one flux, I would suggest
you start looking at an incompatibility between some component in the
flux and the solder mask. What you ***may*** be seeing is the surface of
the mask being very slightly attacked, exposing fillers which would
normally be invisible.

Brian

Peter Lee wrote:
> Technet,
>
> I have a question on white residues formation at wave soldering. We have
> recently run experiments to test the performance of various halide-free
> water soluble fluxes (ORH0 under JSTD-004). The flux was applied through a
> spray fluxer and all PCAs were immediately washed after wave soldering in
> in-line cleaner, with DI water only.
>
> Surprisingly, we've identified several PCAs built with flux A from one
> vendor exhibiting white residues at various T/H leads on the boards. See
> images below.
>
> http://members.shaw.ca/ppwlee1/Images/White_residues1.JPG
> http://members.shaw.ca/ppwlee1/Images/White_residues2.JPG
>
> What could be the cause and forming mechanism of the residues? What causes
> it to become (sometimes) insoluble in water? In general what approach can be
> taken to minimize or prevent formation of white residues?
>
>
> Rgds,
> Peter
>
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