Richard remember that tented vias provide a greater soldermask dam between
land pads and those solder stealing vias. You want a minimum of 12 mils
soldermask dam between a typical IC land pad and a typical (usually test)
via.

Dorothy Lush

> ----------
> From:         Richard Todd[SMTP:[log in to unmask]]
> Reply To:     TechNet E-Mail Forum.
> Sent:         Thursday, August 16, 2001 10:16 AM
> To:   [log in to unmask]
> Subject:      Tenting of vias
>
> 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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