Our printed circuit board purchasing specification currently specifies
that, when required by design, the vias shall be tented with solder mask.
I am in the process of reviewing this specification for its continued
applicability and have some questions about the tenting of vias.  We are
currently in the process of switching from an ENIG process to an OSP-based
finish.  Our ENIG boards were not tented, should the OSP boards be tented
to reduce the possibility of oxidation occurring on the vias assuming that
most (if not all) of the OSP burns off during the reflow process?  I think
that the vias should be plugged prior to tenting to eliminate the
possibility of entrapped liquids or gases in the vias, any thoughts?  We
use a LPI solder mask (SMOBC process) and a dry film would not be
appropriate due to the fine pitch and small traces (4 on 4) on some of our
designs.  What is the best process for tenting with a LPI solder mask?
I guess that my primary question is do we need to tent the vias at all on
an OSP finished board?  We do not perform ICT testing so the vacuum issue
is not a concern.

I apologize for all of these questions, but as you can see I am fairly
confused.

Thank you in advance for any and all replies.

R. Todd
Dataram Corporation
Ivyland, PA

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