Hi Tim,

Yes, we have tried that approach ....we even have made some of our designs like
that at your facility.... the olnly issue there is the additional standoff,
especially that close to the BGA pads and less than 0.025" SMT ...that
definitely affects the solder print resolution/process....let me know if you can
think of any other 'relatively inexpensive' way of doing this....

Marcelo

        -----Original Message-----
        From:   Tim Snodgrass [SMTP:[log in to unmask]]
        Sent:   Thursday, October 22, 1998 6:12 PM
        To:     TechNet E-Mail Forum.; Chan, Marcelo
        Subject:        Re: [TN] Plugged/tented vias

        Marcelo

        We have used a two step soldermask process to tent vias. First we put a
layer of dryfilm down and print it
        with via image. Then coat the board with liquid soldermask. Then print
that image. This produces a part
        with tinted via's and liquid photoimageable to ensure that there is no
entrapment in the via holes. If you
        have any questions contact me off line.
        Regards,
        Tim Snodgrass
        Young Electronics
        818 407-4024

        Chan, Marcelo wrote:

        > We have tried different approaches to tenting/plugging vias for BGA
and some
        > backplane applications using LPI and screened SM with limited
success...PWB
        > vendors claim they could do it, but we are still looking for some one
who could
        > do this on 100% of the vias with no pin holes and it has to be done on
both
        > sides to prevent entrapment of cleaning solutions...the via sizes that
we have
        > in mind can have a finished hole diameter as large as 22 and as small
as 13
        > mils...Can someone share their 'hands-on' experiences on this issue
with me
        > through Technet or even off-line?
        > Thanks
        >
        > Marcelo Chan
        > Lead Engineer - Advanced Manufacturing Technology
        > Electronics Systems Sector, Harris Corp., FL
        >
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