There have been numerous postings to this forum over plugging,
capping, and other means of sealing one or both sides of a PWB coated with
LPISM.  Many PWB vendors use processes where LPISM is applied over bare
copper, then surface finish (HASL, other immersion metallization, or OSP) is
applied.
        I don't know anyone who offers a 100% guarantee of the integrity of
the "seal" of the via holes.  If one side of a via has a pin-hole or crack,
and then is processed through acid cleaners, micro-etches, and aggressive
fluxes, will these chemicals be drawn in by capillary action, and not
effectively rinsed?  Would a subsequent "capping" operation further seal
these corrosives in place?  It only takes one failed via to cause a field
failure, or worse, an intermittent.  Is anyone else out there concerned
about this, or is it only one man's unease?

Thanks for your responses,

Greg Anderson
Advanced Manufacturing Engineer
GE Fanuc Automation, N.A.

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