Through-Hole Optical Measurement with Telecentric Imaging
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Solution Overview
Problem
Current methods for measuring geometric parameters of small features, such as through holes in substrates, are limited by the small depth of field of optical lenses, leading to distorted images and require destructive or slow processes, making it difficult to inspect thousands of features quickly and non-destructively.
Innovation Solution
A system and method using a camera with a telecentric lens and collimated lighting to capture images of through holes, allowing for non-destructive, automated measurement of geometric parameters like clear aperture size, independent of depth, with a depth of field greater than the substrate thickness, enabling rapid inspection of hundreds to thousands of holes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If high optical magnification objective lenses are used to resolve small features, then measurement precision is improved, but depth of field becomes too small to measure features at different depths
Solution Approach 1:
The patent changes the optical parameters by using a telecentric lens with a long working distance and large depth of field instead of a high magnification objective lens. This parameter change allows the system to maintain adequate measurement precision for sub-100-micron features while achieving a depth of field greater than the substrate thickness, enabling measurement of features at different depths without refocusing.
2Measurement precision
If conventional microscopy methods are used to acquire depth or shape information, then measurement capability is improved, but the process becomes destructive and slow
Solution Approach 1:
The patent replaces destructive mechanical or electron microscopy methods with a non-destructive optical measurement system using telecentric lens imaging. The system captures images of through-holes in transmission mode and uses image processing to extract geometric parameters including depth information, achieving both measurement capability and high productivity by inspecting hundreds to thousands of holes quickly without damage.
Solution Approach 2:
The patent creates an optical copy (image) of the through-hole geometry by capturing transmission images through the substrate. The image processing system then extracts geometric parameters from these optical copies, eliminating the need for physical sectioning or destructive electron microscopy while maintaining measurement accuracy and enabling rapid inspection.
3Ease of operation
If microscope objective lenses are used at distances other than their conjugate points, then flexibility in measurement positioning is improved, but image quality deteriorates due to aberration
Solution Approach 1:
The patent changes the optical system parameters by using a telecentric lens designed with a long working distance and large depth of field. This allows the substrate to be positioned at any height within the depth of field range without causing significant aberration, providing both positioning flexibility and maintaining image quality for accurate measurement.
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 rapid, non-destructive measurement of geometric parameters across various hole profiles without adjustments, providing accurate and high-resolution images of micron-sized features, overcoming the limitations of conventional microscopy techniques.
Implementation Method 1
positioning a camera comprising an image sensor and a lens having a depth of field greater than the thickness of the substrate at a measuring station
Implementation Method 2
The method includes illuminating the select sub-volume
Data Source
AI summary
A method of measuring geometric parameters of through holes in a thin substrate includes acquiring images of select sub-volumes of the substrate using an optical system having a field of depth greater than a thickness of the substrate. The acquired images are processed to determine the desired geometric parameters.