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From [log in to unmask] Wed Dec 4 17: |
05:44 1996 |
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Gary:
Typically the boards are HASL and then the via tents are applied to
one side. With this process there is no solder buildup in the hole.
Ron Yanuszewski
______________________________ Reply Separator _________________________________
Subject: Re: Tented vias???
Author: [log in to unmask] at !INTERNET
Date: 12/4/96 5:34 PM
[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 ...
>
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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
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