Hi Mitch, all
        We have used Details to build us proto type boards in the past,
and they do
        a fantastic job with quick turn boards (8 layers in 5 days).
        The down fall is when we turn the board loose to the production
vendor, they
        can not maintain the quality in production quantities. Hence the
larger pad for
        internal layers and increased manufacturing tolerances.(hole to
pad ratio)

        Regards,
        John Shaub
        Honeywell IAC Inc.

> John, Bob, and others interested,
>
> I've had this exact issue come up when I was designing a board. The
> issue of
> <0.0135" diameter vias was discussed with my fabrication house. There
> seems
> to be much more concern with the movement of the internal layers than
> the
> movement (misalignment) of the external layers. AND so it was
> explained to
> me that the fab house will look at the drill size to pad size of the
> internal
> layers with greater concern than that of the external layers.
>
> The formulas I was given were (and remember this is for SMALL vias
> sizes, I was
> going to use .0135" vias, possibly .010" ):
>
> External layer pads:  drill size + .012"= preferred MINIMUM size
> Internal layers    :  drill size + .015"= preferred MINIMUM size
> Internal antipads  :  drill size + .020"= preferred MINIMUM size
>
> And what I used for the .0135" vias were .030 outers/.033 internal
> pads. The
> fab house was comfortable with this and the boards worked great!
>
> If you need more information I would recommend you contact Terry
> Wright at
> Details, Inc in Anaheim, California (www.detailsinc.com) and he (or
> Anhil)
> would gladly discuss this with you.
>
> Hope this help,  :)
>
> Mitch Morey
> Cadence Design Supervisor
> Praegitzer Design
> San Diego, CA 92121
> Phone: (619)450-0994 x-17
> Pager: (619)982-7529
> Fax:   (619)450-0529
> EMAIL: [log in to unmask]
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