Hi Phil
You need fiducials if you are doing automated SMT - some pick and place
machines use tooling pins but most use fiducials.  Same deal with screen
printers, some of the semi-auto machines don't require them but for
automatic processing you should have them.

My preference is:
 - three fiducials, close to the board corners, and mirrored on the
bottom side (if there are parts there too).  This pattern makes
mis-loading the board foolproof, it won't run if you rotate it 180
degrees or flip it.
 - component fiducials are required if you think you may not get the
required accuracy without them.  We don't use them, our largest board is
12" by 10" and our smallest pitch is 20 thou.  For a bigger board they
are likely more necessary.

Hope this helps.


regards,

Graham Collins
Process Engineer,
L-3 Communications Electronic Systems Inc.
Halifax
(902) 873-2000 ext 6215

>>> [log in to unmask] 05/11/06 11:18AM >>>
My disclaimer... I'm a neophyte at SMT and need some education.

Fiducials;
At what point do I need fiducials on my boards?

Is there a specific pitch or device size that will require fiducials?

Is there a "Cliff's Notes" for this?

Thermal Stitching;
We have an SMT power transistor that has about 16 thermal stitch holes
located directly under the device.  The adjacent pad area is taken up
by
heat sink.  Is this "industry standard"?

Short of reading all the IPC standards... zzzzzzzz... oh sorry, I
dozed
off there, is there a good source for coming up to speed on SMT and
board layout good standards?

Thanks in advance,

Phil Nutting

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