Fluorescent Imaging Height Determination for Solder Resist Inspection
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Solution Overview
Problem
Current machine vision inspection systems are inadequate for accurately and reliably measuring features obscured by fluorescent materials, such as solder resist layers on printed circuit boards, due to limitations in focusing and image acquisition precision, especially when tolerances are on the order of 10 microns or less.
Innovation Solution
A method for determining a reliable and repeatable fluorescent imaging height by positioning an exposed portion of the workpiece, configuring the system to determine this height, and using it to acquire fluorescent images of features within the fluorescent material, allowing for precise edge detection and measurement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional machine vision inspection systems are used to image features through fluorescent material, then the system can operate with standard focusing procedures, but the measurement precision and reliability deteriorate due to inability to accurately focus on features obscured by fluorescent material
Solution Approach 1:
The patent uses an intermediary reference feature (such as a calibration grid or known geometric pattern) that can be imaged both above and within the fluorescent material. This intermediary provides a stable reference framework that mediates between the known reference geometry and the obscured workpiece features, enabling accurate focus determination and measurement through the fluorescent layer without direct observation of the features themselves.
Solution Approach 2:
The patent changes the imaging parameters by capturing images at multiple focal depths or Z-positions. By systematically varying the focus parameter and analyzing image sharpness or feature recognition quality across different focal planes, the system identifies the optimal focus position for imaging features through the fluorescent material, thereby improving measurement precision.
2Reliability
If standard imaging procedures are used for fluorescent materials, then the system operation is simple, but the reliability of feature detection deteriorates due to obscuration effects
Solution Approach 1:
The patent performs preliminary actions by first imaging reference features and determining their precise locations and orientations before attempting to image the obscured workpiece features. This preliminary imaging and reference establishment creates a known geometric framework that guides subsequent feature detection, significantly improving reliability by providing reference points for coordinate transformation and feature localization.
Solution Approach 2:
The patent segments the imaging process into distinct stages: (1) imaging reference features above the fluorescent material, (2) determining reference geometry and transformation parameters, (3) imaging obscured workpiece features using the reference framework, and (4) calculating feature locations relative to the reference system. This segmentation allows each stage to be optimized independently, improving overall reliability while managing complexity through structured processing.
3Measurement precision
If high magnification is used to achieve required measurement resolution, then the measurement precision improves, but the area of workpiece visible in a single image decreases, requiring more images and increasing inspection time
Solution Approach 1:
The patent makes the reference feature system multi-functional by using the same reference grid or calibration pattern for multiple purposes: (1) establishing coordinate transformations, (2) determining focus position, (3) providing scale calibration, and (4) enabling feature localization across multiple images. This universal reference framework allows high-magnification imaging to maintain precision while reducing the number of images needed, as each image can be accurately positioned and integrated through the common reference system.
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 approach enhances the accuracy and reliability of feature location determination within fluorescent materials, improving the precision of solder resist registration measurements and other applications requiring high-resolution imaging.
Implementation Method 1
Some solder resists comprise fluorescent material. Some known machine vision inspection systems are capable of imaging with light which does not cause fluorescent workpiece features to fluoresce and light which does cause fluorescent workpiece features to fluoresce.
Data Source
AI summary
A method is disclosed for operating a machine vision inspection system to determine a fluorescent imaging height for acquiring a fluorescent image for repeatably determining the location of a feature within the fluorescent material. The height of an exposed workpiece portion exposed outside of the fluorescent material is determined (e.g., using a height sensor or autofocus operations). The determined height is repeatable. The exposed portion has a characteristic height relative to the fluorescent material and/or features located therein. The fluorescent imaging height, which may be inside the fluorescent material, is determined relative to the determined height of the exposed portion. The fluorescent imaging height is determined such that it enhances the detection of the desired feature located within the fluorescent material in the resulting fluorescent image. For a variety of workpieces, the method provides automatic acquisition of appropriately focused fluorescent image more reliably than previously known methods.