Barry,

The following approach has worked for us: 

1) Group the vias to be covered under a separate drill tool and flag 
   them as tented vias with a note on the part drawing. 
   
2) Designed the solder mask to provide coverage for the vias that 
   require tenting, leaving other vias open. 
   
3) Design the solder mask so that the vias are tented from the 
   board side that prevents interference with assembly operations. 

4) Lastly, specify dryfilm solder mask. It has been our experience 
   that liquid photoimageable solder masks are not as reliable in 
   holding the tent as dryfilm masks are, or that in oder to make 
   LPIs reliable extra process coating steps are required.

Best regards,

Luis Rivera
CompuRoute, Inc.
Dallas, TX
luisr@croute
(214) 340-0543


> Date: 11 Oct 96 13:20:56 -0400
> From: Barry Darnell <[log in to unmask]>
> Sender: [log in to unmask]
> To: [log in to unmask]
> Subject: PLUGGED VIAS
> 
> I have run into a problem with a board that has vias in smt pads.  We 
> need all of the vias plugged, and I am told that solder mask is the best 
> way to do that.  This is to ensure that a good vacuum is maintained for 
> our ATE equipment.  That is the problem.  I can not have a via covered 
> with solder mask on top of an smt pad.  The board house I am using says 
> this is difficult for them because they have to determine which vias are 
> plugged and which are not.  Anyone out there with any suggestions?
> 
> Thanks,
> 
>     Barry Darnell
> (864)627-8800 Ext. 231
> [log in to unmask]
> CD Electronics, Inc.
> Printed Circuit Board Designer
> 
 

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