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March 1999

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Subject:
From:
Andrew Buonviri <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Wed, 24 Mar 1999 08:23:48 -0500
Content-Type:
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text/plain (34 lines)
I read through the archives a bit, but didn't see a whole lot on the issue
of putting microvias inside BGA pads.

There were one or two positive emails on the subject, but I didn't see
anyone mention any concerns. Have many people used this configuration in
designs, and have any problems arisen?

We are using 50 mil pitch BGAs, anywhere from 25mm to 35mm in size, some
solid grid, some with balls in an outer ring only, both plastic and
ceramic. The vias will probably be 6 mil diameter laser-drilled, and will
go only to layer 2. So the volume of the hole is pretty negligible, right?
Will it get filled with solder during reflow, and displace the air that was
in there? Or will the solder paste fill it during solder screening?

Could there be any additional problems caused by the vias-in-pad if the
boards see thermal cycling from -40 to 71 C?

Finally, has anyone used via-in-pad with column grid arrays?

Thanks,
AndyB

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