Hi Jeff,
        The vias immediately adjacent to BGA pads should be plugged with
solder mask.  Savvy board shop are smart enough to perform this operation
last so no chemicals need to be washed off the bare board and out of the
plugged vias.  Provided your SMT and Wave process does not introduce flux
into the vias; the only "chemical" that might get trapped is the dirty water
from the wash (for OA fluxes).

        The via plugging near BGA pads on the BGA side really helps drive
down the DPMO numbers for BGA soldering defects.  Rework will really prefer
the plugged vias as well.  It is common for the solder mask web to come off
during rework BGA pad prep.  The via plug helps hold down the webbing, and
prevents solder robbing down vias, as well as ball to ball bridging.

        However, in the end, you have to decide for yourself how much this
extra effort is worth.

Ryan G.

> -----Original Message-----
> From: Jeff Hempton [SMTP:[log in to unmask]]
> Sent: Tuesday, March 14, 2000 8:28 AM
> To:   [log in to unmask]
> Subject:      [TN] ASSY & FAB: vias: To plug or not to plug
>
>      Hi Technetters,
>        We are researching moving away from plugging our vias with solder
>      mask (problems and reliability issues) and plugging with solder thru
>      the wave solder process.
>      I have read all of the archives, and printed a major novels worth
>      (thanx for past info group, those archives are a wealth!!) bit one
>      item is still missing I hope you can respond with info on:
>
>      ASSY: Do you have problems with, or design guidelines that address,
>      the solder filled vias under components, or is this even an issue?
>
>      FAB: How do most of your customers address this?
>
>      Please, deluge me with your wisdoms, responses and help on this
> issue.
>      Thanx in advance group.
>
>      Jeff Hempton, Sr. SMD Mfg. Engineer
>      United Technology Electronic Controls
>      e-mail:   [log in to unmask]
>
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