Metal Sublayer Sensing in PCB Hole Drilling Feedback Control
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Solution Overview
Problem
Drilling via in multi-layer workpieces poses challenges in accurately stopping the laser energy once the target metal sublayer is fully exposed, risking electrical disconnect or metal breakdown if not managed properly.
Innovation Solution
A method and system that utilize electromagnetic radiation with wavelengths higher than the work-function of the metal layer to detect the exposure or disappearance of the metal layer during drilling, allowing for real-time feedback and control of the drilling process to prevent further thinning or puncturing of the metal sublayer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If laser drilling continues after metal sublayer exposure to ensure complete penetration, then drilling reliability is improved, but metal sublayer thickness is reduced causing electrical disconnect or signal integrity loss
Solution Approach 1:
The patent employs real-time feedback by detecting process radiation emitted from the workpiece during laser drilling. The detection system monitors radiation intensity at multiple temporally sequential times, and when the radiation intensity exceeds a threshold for a predetermined number of consecutive times, the system determines that the metal sublayer has been fully exposed and automatically adjusts or stops the laser drilling process. This feedback mechanism resolves the contradiction by enabling reliable complete penetration while precisely controlling metal sublayer thickness to prevent electrical disconnect or signal integrity loss.
2Productivity
If laser intensity is increased to improve drilling speed, then productivity is improved, but measurement precision of metal exposure detection is reduced
Solution Approach 1:
The patent uses periodic action by determining the radiation intensity at multiple temporally sequential times during the laser drilling process, rather than relying on a single measurement. The system checks whether the radiation intensity exceeds a threshold for a predetermined number of consecutive times before determining metal sublayer exposure. This periodic monitoring approach maintains measurement precision even when laser intensity is increased for higher productivity, as it filters out transient fluctuations and provides more reliable detection of the exposure state.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables accurate and controlled drilling by detecting the initial partial exposure and full exposure of the metal sublayer, preventing electrical disconnect and maintaining signal integrity, while adjusting laser intensity for finer spatial and depth granularity.
Implementation Method 1
directing toward at least one metal layer in said workpiece at location of said at least one hole electromagnetic radiation having at least one wavelength with higher energy than a work-function of said at least one metal layer, thereby causing said at least one metal layer to emit free electrons
Data Source
AI summary
Disclosed herein is a system for drilling in a multilayer printed circuit board. The system includes a source of electromagnetic radiation configured to transmit a measurement pulse in open air to a workpiece, an anode, a resettable electric charge sensor (ECS), operably connected to the anode, and a control unit, configured to receive at least one value indicative of the quantity of at least part of charged molecules received at the anode and determine 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.