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April 2000

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Subject:
From:
Ian McMillan <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Wed, 26 Apr 2000 12:51:00 -0700
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text/plain (76 lines)
Jack-

We would drill the vias at 13.5 for a 25.0 mil pad, not 18.0.
I really don't like to see the drilled hole to non-common conductor go
below 9.0 mils, prefer 10.0 min.

There is a cost associated with reducing the drill size below 13.5, tool
costs and drill time increase due to reduced stack heights.


At 10:18 4/26/2000 -0700, you wrote:
>Sorry for the cross-post, but I couldn't decide if this was more of a
>fabrication issue or a design issue.
>
>We typically remove unused pads from inner layers. (please don't change the
>subject to warn me against removing inner-layer pads, that's not the issue I
>need help with right now)
>I am being asked to use the extra routing space that has been freed up by
>the pads being removed. I have heard of this before but never tried it, and
>frankly I'm a little worried about it.
>
>Somewhere I heard that the gap between traces to the drilled hole should be
>something like 11-15mils, but that hardly makes sense from what we are
>already doing. A 13mil via hole in a 25mil pad is probably drilled with an
>18mil drill bit, right? If we were already using a 4mil clearance to the
>25mil pads, then removing the pad still only leaves 7mils to the edge of the
>drilled hole right? (sorry for all the numbers in one sentence)
>
>So how much extra routing space is there? I say virtually none. I can't
>remember where I heard that drill to route should be 11-15mils, has that
>become tighter these days?
>
>Anyway, that brings up another question. Maybe we can use smaller pads on
>inner layers? That's yet another thing I've never tried....  Is there a rule
>of thumb for that or am I just asking for trouble?
>
>Any responses will be greatly appreciated
>
>Jack
>
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Ian A. McMillan

Engineer
Herco Technology
Ph# 858-679-2800 ext. 107
Fax# 858-679-7565

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