[log in to unmask] wrote:
> 
> 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 ...
> 
> ***************************************************************************
> * TechNet mail list is provided as a service by IPC using SmartList v3.05 *
> ***************************************************************************
> * To unsubscribe from this list at any time, send a message to:           *
> * [log in to unmask] with <subject: unsubscribe> and no text.        *
> ***************************************************************************
> * If you are having a problem with the IPC TechNet forum please contact   *
> * Dmitriy Sklyar at 847-509-9700 ext. 311 or email at [log in to unmask]      *
> ***************************************************************************
I have some experience with board-suppliers having difficulties with Hot
Air Solder Levelling of boards which are tented on one side, probably
because the tenting makes it impossible to blow air through the via's.
One of our suppliers doesn't have this problem (I don't know how they do
it), but on these boards tenting on the topside results in some
"tin-bubbles" on the bottomside via-lands after wave soldering. I think
this has to do with air or flux-vapors that are entrapped between solder
wave and the solder resist. 
Leaving the via's open, or tenting them on both sides, saves you from
these troubles (but I'm sure that there are more thing to take into
account !). I hope this helps.

Daan Terstegge
[log in to unmask]

***************************************************************************
* TechNet mail list is provided as a service by IPC using SmartList v3.05 *
***************************************************************************
* To unsubscribe from this list at any time, send a message to:           *
* [log in to unmask] with <subject: unsubscribe> and no text.        *
***************************************************************************
* If you are having a problem with the IPC TechNet forum please contact   *
* Dmitriy Sklyar at 847-509-9700 ext. 311 or email at [log in to unmask]      *
***************************************************************************