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Spotfacing Technique for Improved Drill Registration

IP.com Disclosure Number: IPCOM000102334D
Original Publication Date: 1990-Nov-01
Included in the Prior Art Database: 2005-Mar-17
Document File: 3 page(s) / 82K

Publishing Venue

IBM

Related People

Burbank, DW: AUTHOR [+2]

Abstract

A spotfacing technique has been developed to use reference targets on the inner layers of printed circuit boards to determine offsets and check registration during the drilling process.

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Spotfacing Technique for Improved Drill Registration

       A spotfacing technique has been developed to use
reference targets on the inner layers of printed circuit boards to
determine offsets and check registration during the drilling process.

      Round reference targets are etched on the inner layers of
panels, as shown in Fig. 1.  Six sets of targets are used, each set
consisting of four round pads.  The sets are spaced around the card
so that compensation can be made for any shrinkage or growth of the
panel.  Skew and other registration problems can also be detected.

      The diameter of the targets is generally 0.006" to 0.012"
bigger than the diameter of the drill bits used for drilling through
the targets.  All internal layers have targets so that misalignment
can be checked between two planes.

      Removing the outer copper layer to expose the targets is done
by spotfacing after the panel has been pinned to the drill table.
The drill has z-axis control, and the depth control is set so that an
endmill removes the copper layer and goes slightly into the glass-
epoxy.  The surface finish of the exposed area is smooth enough so
that the reference targets on the inner layers are clearly visible.

      The targets are drilled in a certain sequence so that offsets
can be determined and inputted into the drill machine.  Two targets
of each set are drilled when drilling each side of the panel.  With
two targets per side, the drill operator gets one chance to make an
adjustment. Targets can easily be added if more chances for correct
adjustment are needed.

      This drill compensation technique can be divided into several
steps, which are shown in Fig. 2.  Spotfacing and drilling of the
targets is done in a certain s...