IPC-SM-840 Rev C (that has just been published) has some additional suggestions and pros/cons regarding plugging vias. Although I do not agree with all of the conclusions states but it might give you some additional information. P.S. You can pick up a copy of this new spec. at your local IPC store. [log in to unmask] ______________________________ Reply Separator _________________________________ Subject: Tenting via holes Author: [log in to unmask] at corp Date: 12/7/95 11:06 AM We have been tenting via holes (dia. .014-.020) with dry film solder resist per IPC-SM-840, type B, Class 3, for the following reasons: - increases usable area for silkscreening - eliminates solder fill inspection in the via-hole, thus enabling vias to be placed under components On the down side, tenting does introduce the risk of contaminating the plated-through via hole if the hole does not get fully tented. Our PWB fabrication vendors are showing an increasing reluctance to use this type of solder mask coating, claiming that it is expensive, wasteful panel-wise, and has adhesion problems. In order to get the dry film to adhere better, they are forced to do another process (oxide treatment). They would rather use a liquid photo-imagable (LPI) coating conforming to the same spec, since the process takes less time, with less waste of material, better adhesion, and finer pattern definition. Unfortunately, LPI coatings don't tent vias reliably under normal processing. My question: What material and processing can tent via holes (dia. .014-.020) in a reliable and cost-effective way?