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Drilling Holes of Accurate Depth

IP.com Disclosure Number: IPCOM000109382D
Original Publication Date: 1992-Aug-01
Included in the Prior Art Database: 2005-Mar-24
Document File: 1 page(s) / 30K

Publishing Venue

IBM

Related People

Storz, W: AUTHOR

Abstract

For drilling holes of accurate depth into a circuit board, it is important to know when the drill touches the board's copper layer. With modern drilling machines, using a rotor with an air bearing, there is no electrical contact between drill and stator, so that contact sensing of drill and Cu layer is impossible, as there is no conductive path between stator and Cu layer. (Image Omitted)

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Drilling Holes of Accurate Depth

       For drilling holes of accurate depth into a circuit
board, it is important to know when the drill touches the board's
copper layer.  With modern drilling machines, using a rotor with an
air bearing, there is no electrical contact between drill and stator,
so that contact sensing of drill and Cu layer is impossible, as there
is no conductive path between stator and Cu layer.

                            (Image Omitted)

      The proposed method uses the capacitance of about 3000 pF
between the stator and rotor of the drilling machine.  As long as the
downward moving drill does not touch the Cu layer, the electric
circuit between Cu layer, control unit, stator and rotor is open.
When the drill touches the Cu layer, the circuit is closed via
control unit Cu and the capacitance of the air bearing.  A pulse is
generated and, starting from that drill position, holes of the
desired depth are drilled into the circuit board.  Thus, this method
takes account of the thickness of the board and the position of its
surface relative to the drilling machine.