Hi Ed,

Fiducials which are reversed with a laminate centre surrounded by copper
or tinned copper seem to be favoured by some but I suppose a lot depends
on the type of camera system used. Just a possibly heretical thought; if
you are getting consistent pwb's, you could try turning off the fiducial
system once you have corrected the programme for the first pwb. This
could speed up the process no end. 

Provided the fabricator is using a good pin registration system for
imaging, the main source of variation is in the step and repeat pattern
used on the production panel. If each step is identified by a number,
the batch can be divided into sets which come from the same step
position on the panel. The variation within each set should be much
smaller than the variation across all the sets. This should eliminate
the need to use fiducial correction for each pwb but only on the first
one from each set. Even then the total variation in the pwb's could be
much less than you may be getting from the fiducial correction system
hence you may be better off without it.

I think fiducials are a great idea but we seem to be overdependent on
them as a belt and braces or substitute for consistent manufacture and
good tooling.

Good Luck
Paul Gould

>A few weeks ago, there was considerable discussion about fiducial 
>recognition problems on various pieces of equipment and some of the 
>corrective action that could be taken by the board manufacturer and by 
>changes in vision system settings.  In my opinion, since we manufacture 15,
>000bds/day, I am not going to have someone sit with an eraser and polish 
>fiducials.  I need to correct the problem.  
>
>I have seen references to the IPC archive of issues discussed on Technet.  
>How do I retrieve copies of these discussions so I can find out what was 
>the final solution?  I would also be interested in a quick re-cap if anyone 
>would care to spend the time
>
>Thanks
>Ed Holton
>[log in to unmask] 

-- 
Paul Gould

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