You need to be careful about putting local fiducials under some of these
"low profile" large PQFP's if you are using HASL finish.
We have had several occasions where the fiducial was higher than the smt
pads. The part would then teeter-totter on the fiducial, leaving one side
up in the air and not making contact with the pads.

For some strange reason, the boards don't work very well under those
conditions.  ; > )

I have found that for .020" and greater pitch parts, the board fiducials
are sufficient for accurate placement with the equipment we are using. Most
of our boards are about 7" x 7" so we are not dealing with large boards.

Good luck.

Charlie B.




Comwave Engineering <[log in to unmask]> on 08/17/98 09:53:26 AM

Please respond to "TechNet E-Mail Forum." <[log in to unmask]>; Please respond
      to Comwave Engineering <[log in to unmask]>

To:   [log in to unmask]
cc:    (bcc: Charles Barker/US/I-O INC)
Subject:  [TN] Fine Pitch




The IPC document IPC-SM-782 states that a fine pitch component must have
local fiducials added at the component level.  I would like to know what
deteremines "Fine Pitch".  Is it anything that is 25 Mil pitch and
below, or is it anything below 25 Mil pitch...what is the true
definition of "Fine Pitch"?

Thank you

Kevin Harding
E-mail: [log in to unmask]

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