Don,
The size of the anti-pad should not be so large that it allows slivers
of copper 5 mils or less between anti-pads.  These slivers can break loose
and cause shorts.  Go with 0.029 over the nominal hole size.

Have not had a board shop question vias that were not thermally isolated.
My EE's (like I own them) prefer not to thermally isolate vias.


---------------------------
John Laur
Rockwell Automation
Allen-Bradley Co Inc.                 
1201 South Second Street
Milwaukee, WI 53204
+1 414 382 2162 (fax)
+1 414 382 2393 (phone)

[log in to unmask]
---------------------------

> From [log in to unmask] Tue Sep 17 09:36:47 1996
> Resent-Date: Tue, 17 Sep 1996 09:23:51 -0700
> Old-Return-Path: <[log in to unmask]>
> From: "Walker, Don" <[log in to unmask]>
> To: [log in to unmask]
> Subject: Re[2]: Design (fwd)
> Resent-From: [log in to unmask]
> 
> 
> 
> With thermal connections you can visually tell to which plane a via
> is connected... don't hardly seem worth it, does it.
> 
> Actually, I think the biggest reason we used thermal connections on
> vias originally was because the CAD systems were so limited in the
> kind of pad stacks which could be defined, especially with regard to
> vias.  Prior to CAD systems 99% of the boards designed were only 2 layer.
> 
> I had been considering switching to direct connection (I'd have to convince
> the engineers that it really is OK... sometimes it like talking to children).
> What differences have you noticed?  Performance should be very marginally
> better.  Board shop processes should be the same.  Do the board shops call
> and ask about them?
> 
> In this same vein -- We have traditionaly used anti-pads which are larger
> than the positive pads on the outer layers.  I have thought about switching
> to an anti-pad just large enough to clear the hole barrel + std clearance.
> Any comments/advise?
> 
> [log in to unmask]
> Don Walker
> 
> 
> > This discussion brings up another point....
> >
> > Does it make sense to use thermal connections on vias?
> > Thermals were originally used on thru hole comps to increase
> > solderability of the leads, but now that is not necessary for SMT.
> > Is there any reason to use them for vias?
> > I've been using direct connection to the inner planes.
> >
> > Tom Kavendek
> > Lucent Technologies
> > Murray Hill, N.J.
> > [log in to unmask]
> 
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