Metal Sublayer Sensing In Multi-Layer Workpiece Hole Drilling

A system comprising:

• a source of electromagnetic radiation configured to transmit a measurement pulse in open air to a workpiece, the pulse having at least one wavelength with higher energy than a work-function of a metal layer of the workpiece, and giving rise to electrically charged molecules deriving from free electrons that were emitted by the metal layer in the workpiece, the quantity of free electrons emitted being dependent on the extent of exposure of the metal of the workpiece;
• an anode;
• a resettable electric charge sensor (ECS), operably connected to the anode;
• a control unit, operably connected to the ECS, and configured to:
• receive, from the ECS, at least one value indicative of the quantity of at least part of charged molecules received at the anode since ECS activation,
• determine, from the at least one value, a second value indicative of the quantity of charged molecules received at the anode that were derivative of emitted electrons responsive to the measurement pulse;
• wherein the control unit is further configured to perform at least one of:
• compare at least part of said second value or at least one combination of at least part of said second value to at least one threshold, or calculate an envelope of at least part of said second value or of at least part of said at least one combination, said at least one control unit being further configured to perform at least one of:
• identify at least one of:
• exposure or disappearance of said at least one metal layer at least partly based on outcome of said compare to said at least one threshold,
• identify at least one of:
• exposure or disappearance of said at least one metal layer at least partly based on said calculated envelope, control drilling at least partly based on outcome of said compare to said at least one threshold, or
• control drilling at least partly based on said calculated envelope.

A system comprising:

• a source of electromagnetic radiation directed in open air to at least one metal layer in a workpiece, the electromagnetic radiation having at least one wavelength with higher energy than a work-function of the at least one metal layer;
• an anode, the anode having a voltage sufficient to impose an electric field that accelerates at least part of electrically charged molecules deriving from free electrons that were emitted by at least one metal layer in the workpiece due to the photoelectric effect, thereby causing at least part of said electrically charged molecules to arrive at the anode;
• at least one control unit configured to receive at least one value indicative of quantity or intensity of at least part of said electrically charged molecules, wherein said at least one control unit is further configured to perform at least one of:
• compare at least part of said at least one value or at least one combination of at least part of said at least one value to at least one threshold, or
• calculate an envelope of at least part of said at least one value or of at least part of said at least one combination,
• said at least one control unit being further configured to perform at least one of:
• identify at least one of:
• exposure or disappearance of said at least one metal layer at least partly based on outcome of said compare to said at least one threshold,
• identify at least one of:
• exposure or disappearance of said at least one metal layer at least partly based on said calculated envelope,
• control drilling at least partly based on outcome of said compare to said at least one threshold, or control drilling at least partly based on said calculated envelope.