PCB Via Drilling Stop Control Using Photoelectron Sensing

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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 done correctly.

Innovation Solution

Implementing a method that uses 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, and adjusting drilling parameters in real-time to prevent further thinning or puncturing of the metal sublayer.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Length of stationary object

If laser energy is continued after metal sublayer is fully exposed, then drilling depth is increased, but metal sublayer integrity is compromised causing thinning or puncturing

Engineering Contradiction:

Improvedrilling depthVSAvoidmetal sublayer integrity

Core Design Contradiction:

Length of stationary objectVSReliability

Solution Approach 1:

The system employs real-time feedback by detecting free electrons emitted from the metal sublayer using electromagnetic radiation. When the metal sublayer is fully exposed, the detection system identifies the sudden increase in free electron emission and sends a stop signal to the laser, preventing over-drilling and maintaining metal sublayer integrity

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The system performs preliminary detection of the metal sublayer exposure status before continuing the drilling process. By detecting free electrons in advance, the system knows when to stop the laser energy application, preventing the harmful effect of metal sublayer thinning or puncturing

Inventive Principle:

Principle #10Preliminary action

2Reliability

If laser energy is stopped early, then metal sublayer integrity is preserved, but electrical disconnect occurs due to incomplete exposure

Engineering Contradiction:

Improvemetal sublayer integrityVSAvoidelectrical connection quality

Core Design Contradiction:

ReliabilityVSManufacturing precision

Solution Approach 1:

The real-time feedback system continuously monitors free electron emission during the drilling process. It ensures the laser continues until the metal sublayer is fully exposed (detected by characteristic electron emission pattern) and stops immediately after, achieving both complete exposure for electrical connection and prevention of over-drilling

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The system replaces traditional mechanical depth measurement methods with electromagnetic radiation detection of free electrons. This substitution enables precise, non-contact detection of metal sublayer exposure status, ensuring accurate timing for laser stop to achieve both complete exposure and integrity preservation

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Device complexity

If conventional drilling methods are used without real-time detection, then device complexity is reduced, but manufacturing precision deteriorates due to inability to accurately control drilling stop point

Engineering Contradiction:

Improvedrilling system complexityVSAvoiddrilling depth control precision

Core Design Contradiction:

Device complexityVSManufacturing precision

Solution Approach 1:

The system introduces real-time feedback detection of free electrons emitted during laser drilling. This feedback mechanism provides continuous information about metal sublayer exposure status, enabling precise control of the drilling stop point without requiring overly complex mechanical measurement systems

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The system uses free electron emission as an intermediary signal to indicate metal sublayer exposure status. This intermediary provides a clear, detectable signal that bridges the gap between the laser drilling process and the control system, enabling precise depth control without direct mechanical measurement

Inventive Principle:

Principle #24Intermediary (Mediator)

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 precise control of the drilling process, ensuring the metal sublayer is fully exposed without compromising its integrity, thereby maintaining signal integrity and preventing electrical or mechanical property degradation.

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

Methodology Applied

Scientific EffectPhotoelectric effect: Photoelectric Effect

Data Source

PatentUS10933490B2Metal sublayer sensing in multi-layer workpiece hole drilling

Publication Date: 2021.03.02 DRILLIANT LTD

AI summary

Disclosed herein is a method of drilling in a multilayer printed circuit board. The method includes drilling a one hole; directing electromagnetic radiation having at least one wavelength with higher energy than a work-function the metal layer toward the hole, and thus causing the metal layer to emit free electrons; and measuring the quantity or intensity of electrically charged particles derived from the emitted free electrons, to detect the extent of exposure or disappearance of the metal layer during drilling.