We plug from the bottom side only. If the bottom side is plugged, no 
     flux can get to the top when spray fluxed. No reliability problems 
     have been found.
     
     I would be more worried about HASL flux and bare copper in the via 
     than about wave soldering, which uses considerably less aggressive 
     flus.


______________________________ Reply Separator _________________________________
Subject: Re: Tented vias???
Author:  [log in to unmask] at internet
Date:    12/5/96 5:46 AM


Gary,
     
We at GenRad have all our VIA's Plugged & tented for just this reason, however 
we are do note probe on the through VIA's, but to add extra bottom side Test 
Pads for ICT.
     
This does cause 1 or 2 problems at the design stage, but gives great benifits 
for out Test department, who get much better throughput, & much more reliable 
results.
     
  ________________________________________________________________________
 | [log in to unmask]         David Tandy. EDA Specialist.   GenRad ADS. | 
 | Tel: (+44) 161 491 9191     Orion Business Park, Bird Hall Lane,       | 
 | Fax: (+44) 161 491 9106     Stockport, Cheshire, SK3 0XG, England.     | 
 |________________________________________________________________________|
     
     
> Colleagues:
>
> Our in house SMT assembly facility has asked that we tent our vias on top and 
> bottom sides to aid in solder bridge reduction.  If bottom tenting is not
> possible becaues vias may double as test points, they ask that we still tent 
> the top (component) side.  They use a no clean process.
>
> I am concerned that contaminants will be trapped in vias tented only on one 
> side and cause premature failure down the road.  Normal via size is .012.
> What are your thoughts on tented vias???  One side?  Both sides?  Not tented 
> ever?  Why???  What other problems may we encounter?
>
> Thanks in advance for your opinions. 
>
>
> gary ...
>
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