Jim and Franklin,
I agree there is a difference between tenting and plugging. My perception
of "tenting" is using dryfilm soldermask that really produces a "tent".
Not many products require that now with the advent of Liquid Photoimageable
Soldermask (LPI).
I'm not sure I completely agree with Franklin's statement, "Plugging is
best
performed on both sides...". If you ,mean plugging each side at different
holes,
then I agree. If you mean the "same" hole, then I'd caution against that
approach.
"Plugging" is what most fabricators do. "Plugging" from both sides could
trap solutions or moisture (as you've eluded to) but additionally any
trapped air
would expel causing "volcanoeing" of the plugs. (features that look like
volcanoes
caused from the air inside expanding and escaping out one <or both> sides)
Some fabricators are able to apply "pre-plugs" (before soldermask
application
and final finish) that produce a fairly "filled via" which can have fairly
good results.
It's best to discuss with your fabricator what your expectations are on the
finished
product. Then let them determine what's the best way to process the PCB to
achieve
your requirements. (Surface finish selection will have some input into the
fabricators
soldermask plugging decisions. Also, make sure you check with your assembler
on
which plugging combinations they have had success with based on component
density and pitch.)
Jim..also plugging can easily be accomplished for today's via sizes. (<18
mils FHS)
Hope this helps some.
David Hoover
http://home.earthlink.net/~dhoovy
----- Original Message -----
From: "Franklin D Asbell" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Monday, November 17, 2003 2:32 PM
Subject: Re: [TN] tented over vias
> Don't confuse "tenting" with "plugging". Solder mask tented vias may not
> necessarily "close" the via opening. Tenting really means the pads are
> tented...solder mask may fill the hole, but only smaller ones.
>
> Plugging is a better process for vias under components. Plugging is best
> performed on both sides; however, the process your board shop uses needs
to
> be exact...otherwise, moisture, contaminates, etc may become entrapped
> causing a major mess during assembly...
>
> As for the sodler mask, Enthone, Coates, are probably the most common and
> they will do the job quite nice...
>
> Franklin
>
> ---------------------------------------------------
----- Original Message -----
From: "Marsico, James" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Monday, November 17, 2003 12:41 PM
Subject: [TN] tented over vias
> Hello, Technet...
> A quick question (or two, maybe three)... We're designing a small
> double-sided SMT PWB which is somewhat dense. The designer has to place
> plated through vias under some of the small chip components. Our only
> option is to tent over these vias with solder mask. My question is what's
> the best S.M. for this application and what's the max size hole it can be
> used on. Is it best to tent over both sides of the via or just one?
> Thanks for your help,
>
> Jim Marsico
> Senior Engineer
> Production Engineering
> EDO Electronics Systems Group
> [log in to unmask] <mailto:[log in to unmask]>
> 631-595-5879
>
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