Thanks, Dee.  You, and several other members of this group, have been very
helpful.

The formula for calculating the anti-pad is the same in both IPC-D-275 and
its replacement, 222x - Clearance area (diameter) =  Max hole diameter + 2B
(Standard Fabrication Allowance) + A (Electrical Clearance).  The difference
appears to be that the 2221's Minimum Standard Fabrication Allowance table
has dropped maximum board size from consideration.  I'm glad to see that but
am now concerned about the spread (0.15 mm from A to B and only 0.05 from B
to C).  Interesting, to say the least.  I also find it interesting that the
Standard Fabrication Allowance is doubled when calculating for anti-pads and
not when calculating for pads.  Thus, for a Level A design, the tolerance is
+/- 0.4 mm for an anti-pad and +/- 0.2 mm for a pad, regardless of whether
it is an external, internal, or a nonfunctional pad on the plane.  See the
dilemma?

I tell you something else that it does not cover (very well, at least) - the
clearance width between the pad and the surrounding plane for a thermal
relief (the space across which the web segments span).  The Clearance Area
in Planes figure gives a space of 0.25 mm (0.010") minimum for a
Nonfunctional Land but no mention is given for a thermal relief.  What do
you think about that?

As Tim indicated, I have just about beat this horse to death.  It's
frustrating to see these discrepancies and try to point them out, just to
have the officials from IPC continue to defend what is printed (or not
printed, as the case may be).

Ray

----- Original Message -----
From: Dee Stover <[log in to unmask]>
To: <[log in to unmask]>
Sent: Friday, September 24, 1999 6:57 AM
Subject: Re: [DC] IPC Specs - Errors?


> Ray,
>
> I am looking at the section Tim specified and the very next page goes into
> "foil web size" and clearance area (diameter) in the plane.  Since we are
> talking antipads I think this is the information you want.
>
> This uses the Table 9-1 of IPC-2221 (which you now have)
>
> Clearance area (diameter) =  Max hole diameter + 2B
>
> B= fabrication allowance per Table 9-1 of IPC-2221
>
> If you need more I will see what I can do.
>
> Dee Stover  [log in to unmask]
> Design Drafting Technician
> National Optical Astronomy Observatory
> 950 N Cherry Ave
> Tucson, AZ 85719
> 520-318-8489
> FAX 520-318-8303
>
>
>
>
> At 02:56 PM 9/23/1999 -0700, you wrote:
> >Thanks, Tim.  I have (what I think) to be the correct information from
> >Paulo.  Your reference to Table 9-1, Feature Location Tolerances, is not
the
> >same as the Standard Fabrication Allowance, which is what I was looking
for.
> >The Standard Fabrication Allowance is to be included in the formula for
> >calculating the Minimum Land Size of pads and the clearance space around
> >holes in the plane, not the Feature Location Tolerance.
> >
> >Ray
> >
> >----- Original Message -----
> >From: <Tim Easterling> <[log in to unmask]>
> >To: <[log in to unmask]>
> >Sent: Thursday, September 23, 1999 2:02 PM
> >Subject: Re: [DC] IPC Specs - Errors?
> >
> >
> >> The information you are looking for is in IPC-2222
> >> page 17 section 9.1.3 Clearance Area in Planes and
> >> table 9-1 which provides feature location tolerances
> >> for technology levels A,B,C.
> >>
> >>
> >>
> >>
> >> Tim Easterling
> >> Cadd Manager Commercial Engineering
> >> SCI Systems Inc.
> >> 8600 S. Memorial Parkway MS 200
> >> Huntsville, Al. 35802
> >> (256)882-4426 (ph)
> >> (256)882-4700 x4426 (voicemail)
> >> (256)882-4304 (fx)
> >> ----------------------------------------------
> >> Can you tell me on what page of IPC-2221/2222 the fabrication allowance
> >> appears on?  I do not have a copy, yet, but the people I have asked to
> >check
> >> say it is not in there.  I have IPC-D-275, which has it in Table 5-10
on
> >> page 64.
> >>
> >> ----- Original Message -----
> >> From: Gary Ferrari <[log in to unmask]>
> >> To: <[log in to unmask]>
> >> Sent: Wednesday, September 22, 1999 6:43 PM
> >> Subject: Re: [DC] IPC Specs - Errors?
> >>
> >>
> >> > Ray,
> >> >
> >> > The IPC-2221/2222 makes quite a few improvements over the IPC-D-275,
> >> > especially in the standard fabrication allowance. I would suggest
that
> >you
> >> > obtain a copy and evaluate these differences against your
experiences.
> >Any
> >> > comments would be welcomed.
> >> >
> >> > Additionally, IPC standards committees are not closed to the public.
> >They
> >> > welcme all comments and data submitted for review. I suggest if you
have
> >> data
> >> > that supports your concerns, that you submit them to the committee
for
> >> > evaluation. The committee has scheduled a meeting at IPC Works in
> >> Minneapolis
> >> > on October 25th. I am sure they would like to meet with you and/or
> >discuss
> >> > your findings.
> >> >
> >> > Regards,
> >> >
> >> > Gary Ferrari
> >> > Executive Director
> >> > IPC Designers Council
> >> > 80-350-9300
> >> >
> >>
> >
> >
>