Laser Via Drilling Sensing for Precise PCB Metal Sublayer Exposure
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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, especially when transitioning between sublayers.
Innovation Solution
A method and system that utilize electromagnetic radiation with wavelengths higher than the work-function of the metal layer to emit free electrons, measuring the quantity or intensity of electrically charged particles to detect exposure or disappearance of the metal layer, and adjusting drilling parameters in real-time to prevent further damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If laser drilling continues after metal sublayer exposure to ensure complete removal, then manufacturing precision is improved, but the metal sublayer may be thinned or punctured causing electrical disconnect
Solution Approach 1:
The system employs real-time feedback by detecting free electrons emitted from the metal sublayer during laser drilling. When the metal sublayer is fully exposed, the detection system identifies the sudden increase in free electron signal, automatically stopping the laser drilling process. This feedback mechanism prevents over-drilling that would thin or puncture the metal sublayer, thereby maintaining electrical connectivity while ensuring complete metal removal.
Solution Approach 2:
The system performs preliminary detection of the metal sublayer's presence and characteristics before completing the drilling process. By using free electron detection to identify when the metal sublayer is fully exposed, the system takes preliminary action to stop drilling before damage occurs, preventing the harmful effect of metal sublayer thinning or puncturing.
2Reliability
If laser drilling stops immediately upon metal sublayer exposure to prevent damage, then reliability is improved, but the metal sublayer may not be fully exposed causing electrical disconnect
Solution Approach 1:
The system continuously monitors free electron emission during laser drilling and provides real-time feedback on metal sublayer exposure status. The feedback signal increases as the metal sublayer is exposed and reaches a maximum when fully exposed, enabling precise determination of the stopping point that ensures complete metal removal while preventing damage.
Solution Approach 2:
The system replaces traditional mechanical depth measurement methods with a physical detection method based on free electron emission. This substitution allows for more accurate and real-time detection of metal sublayer exposure completeness, enabling the system to determine the precise moment when complete exposure is achieved without mechanical contact or estimation.
3Device complexity
If traditional depth control methods are used without real-time feedback, then device complexity is reduced, but manufacturing precision deteriorates due to inability to detect metal sublayer exposure status
Solution Approach 1:
The system introduces real-time feedback by detecting free electrons emitted from the metal sublayer during laser drilling. The detection system monitors the metal sublayer's exposure status continuously, providing feedback signals that enable precise control of the drilling process. This feedback mechanism achieves high manufacturing precision while maintaining relatively simple device architecture.
Solution Approach 2:
The metal sublayer itself serves as the detection target by emitting free electrons when exposed to laser radiation. The system utilizes the metal sublayer's own physical property (electron emission) to provide detection signals, eliminating the need for complex external sensing mechanisms and achieving self-service detection that simplifies the overall device complexity.
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 real-time feedback and control of the drilling process, ensuring complete exposure of the metal sublayer without thinning or puncturing, thereby maintaining signal integrity and preventing electrical disconnect.
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.