My two cents, I would agree with Cyrus, there, to my knowledge, is no use
for the
fiducials after placement is done, the only reason to go with either
one fiducial under the part or two fiducials on a diagonal, (as far as I
know)
would be to increase the speed at which the machine could align and place
the parts.
Now I may be wrong on the speed thing maybe the latest machines are now as
fast either way now.
Robert M. Wolfe
PCB Design Engineer, C.I.D.
IPC Certified Interconnect Designer
Lucent Technologies
InterNetworking Systems Division
866 North Main St Ext.
Wallingford, CT 06492
Ph: 203-284-4176
Fax: 203-265-2094
[log in to unmask]
-----Original Message-----
From: Cyrus Ringle [mailto:[log in to unmask]]
Sent: Friday, January 26, 2001 3:44 PM
To: [log in to unmask]
Subject: Re: [DC] DC IPC Design rules for Fiducial clearances
David Cary wrote about local fiducials:
This doesn't interfere with most routing, but isn't visible after parts are
placed, so it's impossible to check placement automatically.
Just curious what placement you are checking for? We place them under
components
because the Pick-n-place machines need them to locate the position to place
a
fine pitch component. After it is placed visual inspection is done with
machines to confirm the correct parts have been placed by scanning for
component
markings with color imaging vision equipment. This helps to also determine
if
parts are really skewed but the local area fiducials are never used after
that
to determine fine pitch component locations. I am a designer and am
familiar
with our vendors processes and this is what I understand them to be but hay
I
could be wrong...
Cyrus Ringle CID
IPC Certified Interconnect Designer
CAD Engineer
Inter-Tel, Inc. http://www.inter-tel.com
7300 W. Boston St.
Chandler, AZ 85226
(480) 961-2263
mailto:[log in to unmask]
President of the Greater Phoenix Designers Council
David Cary <[log in to unmask]> on 01/26/2001 01:05:48 PM
Please respond to "DesignerCouncil E-Mail Forum." <[log in to unmask]>;
Please respond to David Cary <[log in to unmask]>
To: [log in to unmask]
cc: (bcc: Cyrus Ringle/Inter-Tel)
Subject: Re: [DC] DC IPC Design rules for Fiducial clearances
Dear designers,
All the information one could want about "global" fiducials are in
The SMEMA Fiducial Mark Standard 3.1
http://www.ipc.org/html/smema3.1.pdf
http://www.smema.org/
Protel fiducials
http://www.protel.com/earticles/maskexpan.htm
Hollomon p. 291 recommends a "BMW-style" fiducial over the simple round dot,
but
notes that some vision systems will not recognize anything but the round
dot.
I put one of these "bow-tie" fiducials on my board, but I'm pretty sure no
one
uses it for alignment purposes -- we just use it to check for over-etch or
under-etch.
That SMEMA standard seems a little vague about local fiducials. The SMEMA
standard mentions putting extra local fiducials centered underneath
fine-pitch
components (less than 0.05 inch pin pitch). This doesn't interfere with most
routing, but isn't visible after parts are placed, so it's impossible to
check
placement automatically. But I've seen many more boards have a fiducial next
to
the part, near pin 1, and another next to the diagonal opposite corner. They
are
visible after parts are placed, but a little more difficult to route traces
around them. These boards seem to conflict with the above SMEMA standard --
has
a improved "best practices" come out ? How old is the above document ? (I'm
annoyed when documents leave out important metadata like the publication
date).
--
David Cary
Charlene Dwyer <[log in to unmask]> on 2001-01-25 05:01:15 PM wondered:
...
Hi! Does anyone know of the standards for board
fiducials?
...
-Charlene Dwyer Lee
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