Hi Donald,

Today's PnP equip is much more stable than some of the older stuff. We
have not had to use local fiducials yet.

I recommend three fiducials per side, two at the corners of one end and
one on one of the corners at the other end. That prevents someone from
inadvertently inserting the board 180 degrees out of phase.

Ditto on Graham's feelings about having to use thru-holes as fiducials!

Charlie B.

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Donald Kyle
Sent: Wednesday, September 13, 2006 8:15 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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