CPC H05K 3/0038 (2013.01) [B23K 26/032 (2013.01); B23K 26/0604 (2013.01); B23K 26/064 (2015.10); H05K 1/0269 (2013.01); H05K 2203/0207 (2013.01)] | 20 Claims |
1. A method of monitoring laser drilling of a workpiece, the method comprising:
a) transmitting, by a source of electromagnetic radiation, a measurement pulse in open air to the workpiece,
wherein the pulse has at least one wavelength with higher energy than a work-function of a metal layer in the workpiece,
and gives rise to electrically charged molecules deriving from interactions of air molecules with free electrons emitted by the metal layer in the workpiece, a quantity of the free electrons emitted being dependent on an extent of exposure of the metal of the workpiece;
b) receiving, by an anode, at least part of the electrically charged molecules;
c) accumulating, by a resettable electric charge sensor (ECS) operably connected to the anode, electric charge derivative of charged molecules received at the anode;
d) receiving, by a control unit, from the ECS, at least one value indicative of a quantity of at least part of charged molecules received at the anode since ECS activation;
e) determining, by the control unit, from the at least one value, a second value indicative of a quantity of charged molecules received at the anode since ECS activation that were derivative of electrons emitted responsive to the measurement pulse; and
f) performing at least one of a group consisting of:
i. identifying at least one of: exposure or disappearance of the metal layer in accordance with, at least, the second value, and
ii. controlling drilling in accordance with, at least, the second value.
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