Any SMT needs fiducials.  I recommend placing is a standard location to
a tooling hole in the pallet for ease of P&P programming.  2mm size is
fairly standard with a .400 keep out - finished like the PCB or covered
with mask if you vision system can resolve.  Dense devices will need
local alignment fidicuials if the distance from the global targets is
large.  I also see a bad panel marker being placed to allow the fab
house to black out a matrix when a PCB in the pallet array is not to be
placed.

Jeffrey Bush
Director, Quality Assurance and Technical Support
VERMONT CIRCUITS INCORPORATED 
           76 Technology Drive - POB 1890 
              Brattleboro, Vermont 05302
                Voice - 802.257.4571 ext 21
                    Fax - 802.257.0011
                       <http://www.vtcircuits.com/> 
                           

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Phil Nutting
Sent: Thursday, May 11, 2006 10:18 AM
To: [log in to unmask]
Subject: [TN] Use of Fiducials & thermal stitching

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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