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June 2000

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Subject:
From:
"Stephen R. Gregory" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Tue, 27 Jun 2000 13:43:00 EDT
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In a message dated 06/27/2000 10:08:37 AM Central Daylight Time,
[log in to unmask] writes:

<< <Rod Serling voice over>

 That must be of the few board related experiences you have missed, Steve.
;-)

 I believe what you are referring to is what I call "via plugging", which we
have done at our fabrication suppliers. This is a thermal epoxy applied after
HASL by silkscreening thermal epoxy soldermask. We normally do this only on
the "solder" side of the panel.

 Our vendors create the necessary artwork to do this from the drill chart,
and plug only the vias (typically 0.010" dia PTH's with 0.025" pads). This is
done because the "tenting" of the via with LPI mask would not be reliable,
and because the LPI "plugs" might rupture in the thermal excursion of HASL,
entrapping HASL flux or other nasty stuff.

 The cost is just a few dollars per panel, so on a unit basis, should be
slight.

 <back to "normal" comm mode>


 regards,

 Jerry Cupples
 Interphase Corporation
 Dallas, TX USA >>

Hi Jerry and all,

I didn't explain things enough. This board uses dry-film solder mask, and has
only the vias open that are used for ICT testing. We've been building these
boards in the past by masking the vias off just prior to wave solder to
prevent the cleaning issues that would happen because some of the vias are
beneath the LCCC's.

This has been a pain in the butt, but not so bad because there weren't that
many vias to worry about. But now they want to expand ICT coverage, and
instead of selectively going into the soldermask layer of the gerber and
opening the additional test vias that they need, they want to do a global
change and relieve ALL vias from the soldermask!
There's a number of different assemblies that they want to do this to, and I
was told that it would be too much work to edit each and every gerber to
accomodate the expanded test coverage on each assembly.

I told them that I had a real concern with the cleaning issues that will
arise from this, as well as being able to get good via fill. I've had trouble
in the past getting good via fill during wave solder on boards using a dry
film solder mask.

I've read a few posts over the past months that a half-filled via is worse
than no-fill or full-fill.

So what I was asking was; can the fab vendor fill the vias during the HASL
process? If they can, is it expensive?

-Steve Gregory-

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