From: Kelly Kovalovsky, PCS Engineering
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Subject: polishing fiducials

I have seen where a 0.016" copper dot fiducial will take HASL such
that the solder is extremely domed. The dome will reflect light
depending on the solder skew and cause fiducial recognition problems.
One fix is to make a larger copper dot.

A better fix is to design the fiducial as a copper donut. Let the
optics look for the opening (the donut hole), which will always be
laminate material. The laminate will provide a consistent surface,
assuming you are not routing circuitry through the area on the
internal.

I know that the Panasonic equipment manuals offer a variety of
fiducial designs that work with their equipment.

IBM Microelectronics Division
1701 North Street IMAD:FKFE
Endicott, NY  13760-5553
*** Reply to note of 11/13/96 10:06