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March 1997

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Subject:
From:
"Larry Morse" <[log in to unmask]>
Date:
Wed, 12 Mar 1997 09:17:16 -0800
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On Mar 11, 1997 Darrel Daigle wrote:

Hello Technetters,
I am having a slight problem with the amount of solder on fiducials. This
is 
causing optical recognition problems during the pick and place.
Any suggestions, maybe an alternative surface finish.


Darrel:

Many of the older binary based fiducial recognition vision systems that saw
in only black or white have the same problem you describe.   The solder
"bump" produced by a HASL finish will reflect the light source in random
directions causing the vision system to "see" it in a location other than
the correct one.  The newer 256 gray-scale vision systems are far less
prone to this type of error, but that may not help you if you have the
older stuff.  Masking over the fiducial with LPI (liquid photo-imagable
solder mask) has been suggested, or use most other solder masks, for that
matter.  That's a good option, IF you vision system can read through the
mask.  Many of the older binary systems can't.  Another option is to
specify that the fiducial marks be left as bare copper.  This will produce
a nice planar, unglaring surface that nearly all fiducial cameras will read
nicely.  This requires an extra masking step during PCB fabrication, but
the cost should be minimal, if any.

Hope this helps,

Larry Morse
Celwave RF
[log in to unmask]

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