Capacitive Sensor for Contactless Inspection of Conductive Structures
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Solution Overview
Problem
Existing methods for inspecting electrically conductive structures on or in substrates, such as display backplanes and printed circuits, are limited in their ability to detect cracks or short circuits non-destructively and efficiently, especially for small or floating structures, as they often require direct contact or are not capable of measuring electrical properties effectively.
Innovation Solution
A capacitive, contactless inspection device using a three-dimensionally designed capacitive sensor with vertically offset sensor electrodes, which allows for the detection of electrically conductive structures without direct signal application, enabling the measurement of their spatial extent and height profile by calculating the distance between the sensor and the structure based on capacitive coupling differences.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional needle testing is used to inspect electrically conductive structures, then electrical functionality can be tested, but the method causes mechanical wear on needles, requires precise alignment and defined pressure, and is only partially efficient for inline inspections
Solution Approach 1:
The patent replaces the mechanical needle-based contact system with a capacitive sensor system that uses electrical fields to detect conductive structures. The capacitive sensor establishes a location-dependent capacitance between the substrate surface and the sensor, eliminating mechanical contact, wear, and alignment requirements while maintaining electrical functionality testing capability.
Solution Approach 2:
The patent introduces capacitance as an intermediary measurement mechanism. Instead of direct mechanical contact with needles, the system uses capacitive coupling between the sensor and the conductive structures on the substrate. This intermediary approach allows electrical property detection without physical contact, solving the problems of mechanical wear and alignment complexity.
2Manufacturing precision
If optical inspection is used to verify lateral geometry of structures, then material inspection is possible, but no information about electrical properties or proper functionality is obtained
Solution Approach 1:
The capacitive sensor system performs multiple functions: it can verify the lateral geometry of structures through capacitive coupling variations and simultaneously detect electrical properties and functionality. By measuring location-dependent capacitance, the system obtains both geometric and electrical information in a single inspection process, eliminating the need for separate optical inspection.
3Reliability
If conventional non-contact capacitive inspection is used to scan substrate surface, then voltage and capacitance changes can be detected, but very small, electrically unconnected, i.e., floating, structures cannot be inspected
Solution Approach 1:
The patent applies local quality by using multiple capacitive sensors positioned at different locations and orientations on the substrate. This array of sensors creates localized measurement zones that can detect floating structures through their individual capacitive signatures, enabling inspection of small, electrically unconnected structures that a single sensor would miss.
Solution Approach 2:
The patent segments the inspection system into multiple capacitive sensors distributed across the substrate surface. This segmentation allows each sensor to independently detect local capacitance changes, including those from small floating structures, and the combined data provides comprehensive coverage that overcomes the limitations of single-sensor approaches.
4Reliability
If capacitive coupling via substrate is used for measurement, then electrical inspection is improved, but the coupling area of the substrate must be significantly larger than the coupling area to the sensor
Solution Approach 1:
The patent transitions from two-dimensional planar capacitive coupling to three-dimensional capacitive sensing by positioning sensors at elevated positions above the substrate. This vertical dimension allows the sensor to establish capacitive coupling with underlying conductive structures through the substrate thickness, enabling detection without requiring large lateral coupling areas and improving signal differentiation for small structures.
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
This solution enables reliable, non-destructive inspection of electrically conductive structures, including those that are small or floating, by determining the presence and spatial extent of conductive structures without physical contact, improving efficiency and accuracy in detecting cracks and short circuits.
Implementation Method 1
a location-dependent capacitance is established between the substrate surface and the sensor. Voltage and capacitance changes can then be detected at this capacitive coupling.
Implementation Method 2
For corresponding measurements, the substrates must be supplied with signals. In the case of capacitive surface scanning, the signal supply to the substrate can also be capacitively excited via an electrically conductive contact surface.
Data Source
Figure 1A~1B
Figure 2A~2C
Figure 3
AI summary
The present invention relates to an apparatus and a method for the simple and reliable capacitive contactless and non-destructive inspection of electrically conductive structures (3) which are produced on or in a substrate (1) or are produced such that said structures are floating in a substrate (1). The invention uses a capacitive sensor (11) having at least two sensor electrode surfaces (9) which are arranged at different constant distances from one another parallel to a surface of the substrate (1) and are arranged beside one another relative to the surface of the substrate (1).