Peter,

Use the type that your equipments' vision system prefers. Just for info we
use diamonds (well, 1mm squares turned at 45 deg. actually). Something else
to bear in mind is surface finish and contrast with the surrounding
background. If using HASL make sure your PCB supplier can give a relatively
flat finish. If excessively applied you end up with a 'domed' effect and the
vision system may have difficulty with that as the greyscale values will
vary as the illumination is reflected all over the place (I've had no end of
trouble with this!). Also leave a nice big clearance in your resist if you
can. In the end, give your equipment as much chance as possible to recognise
the marks, whatever the preferred shape.

From what you say you are somewhat hamstrung by what your customer has
designed in. Try to exert some influence on their designers if you can. It
works wonders in the longer run.

Best regards,




===== Original Message from [log in to unmask] at 28/11/01 11:23
>Hot on the heels of the smelly paste saga (some of the new ones that you
>turned up are great - we haven't come off the ceiling yet).
>
>Fiducials - just a quick survey (and Bob you may already have posted
>something similar so apologies if the answer is staring me in the face).  We
>don't use them - yet - as most stuff here is hand placed but as we venture
>into the twilight zone of automated production I am starting to take an
>interest in them.  Up to now they were just pretty little signs that we
>thought were ancient runic inscriptions from the days of the early Viking
>coastal raids - Ericsson the Mobile and Nokia the Trendy being just two
>names that have come forward.
>
>Question is - what is the most popular - I would have said that crosses were
>the most common but I looked back over several boards from different places
>and found circles and the occasional butterfly were more common than I
>thought.
>
>As the machine we have in mind (yes its an old one) doesn't like crosses we
>would prefer circles but we mostly have to smile sweetly and say thank you
>for whatever we get.  So what does everyone else use? And given the chance,
>would you use a different shape?
>
>regards
>
>Peter Allgood
>
>Allgood Technology Ltd, 1 Horton Court, Hortonwood 50, Telford, TF1 7GY
>Tel and Fax 01952 677145    Web: www.allgoodsmt.com

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