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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