Hello Matt,

Fiducials are visual alignment marks used by placement machines to locate the board 
and fine pitch components.
I've seen these in the form of hashes '#' or simple 1mm dia copper pads (no hole) with 
a 3mm dia clearance in the solder mask.
It's important that there are no other visible features within the 3mm clearance area.
Thes things must be easily recognised by 'machine vision'.
I usually place 2 'global' fiducials at opposite corners of the board (if it's large 
enough - small boards are usually loaded in multiples on a pallett, which would then 
have the global fiducials itself), and 2 'local' fiducials on the diagonals of the 
'fine-pitch' parts.
The larger boards often require 2 loading tooling holes for alignment as well, (NPTH 
controlled hole tolerance).
There are 'cleverer' placement machines that can recognise the actual component land 
patterns, but not all assembly shops would have these. Talk to the assembly house, 
they would usually be only too glad to help you to provide them with their preferred 
requirements.
(just a tiny part of DfM)

regards,

Phil.

-----Original Message-----
From: Matt Daggett [mailto:[EMAIL PROTECTED]]
Sent: Monday, 14 October 2002 11:59 PM
To: Protel EDA Forum
Subject: [PEDA] Fiducials


 I just sent off parts + boards for our first needed outsourced assembly and
the assembly house is requesting that I...

"remember to add fiducials to your design.  All high precision placement
machines must have visual targets as part of the design."

Can someone give a brief explanation of what these are and what I need to do
in Protel to satisfy their requirements.

thanks,

matt


`````````````````````````````````````````````````````
      Matt Daggett
      MCNC - Signal Electronics Division
      3021 Cornwallis Road
      Research Triangle Park, NC 27709
      voice: 919-248-9278 fax: 919-248-1455
      http://www.mcnc.org/wireless/
,,


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