Actually placing 3 is better as it prevents the PCB being placed only 1
way. Two placed diagonally across means the PCB can be rotated 180 & the
fiducials are still the same orientation, telling the reading device,
the PCB is inserted OK ( which it isn't ).

As a rule & as a PCB designer, best practice is to ensure the PCB is
done such that if 1 day someone else purchases the company & wants to
take that PCB into high volume, it is ready. Not doing so means it has
to be respun & room made (possibly) to fit in the extra fiducials ( and
we have all been there ). What a pain that becomes as it causes the
cctry to be moved, traces re-routed, etc.

But you have to be the judge of that ( that depends, as you earlier
warned us ).

Regards
TDK




-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Donald Kyle
Sent: Wednesday, September 13, 2006 7:05 AM
To: [log in to unmask]
Subject: [TN] Fiducials

Good morning

I have one of those It Depends questions regarding fiducials and
pick-n-place machines.

Per IPC-7351 and I'm sure other standards, a board at minimum should
have two fiducials on each end and each side.  Furthermore, if there
are fine pitch components there should be two fiducials for each fine
pitch component, sharing of fiducials is ok.

For assembly houses that place components at a billion a second I can
see the justification for the above requirements.

But lets say that your customer requires typically 5 to 10 boards per
run and those boards have fine pitch components.

It's not likely that they would be asking you to build them but maybe
you like to do prototypes and these quantities will fit somewhere in
your production area.

So my question to assembly houses is:

Can you live with fiducials placed every two inches across a board
such that any fine pitch component has two fiducials within two inches?

Is it possible to adjust the speed of pick-n-place machines to
accommodate for these parameters?

Thanks in advance


Donald Kyle C.I.D.+

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