Area Scan Camera Inspection System for PCB Height Measurement
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Solution Overview
Problem
Existing inspection systems for analyzing defects in printed circuit boards and semiconductor wafers face limitations in image quality and accuracy due to limited optical sensor line length, requiring multiple passes and complex setups, and often produce inaccurate height measurements due to blurring and reflectance issues.
Innovation Solution
An inspection system utilizing a projection device with a spectrometer to split white light into spectral components and project a multichromatic light beam at an angle of incidence, combined with an area scan camera and a dispersive or diffractive element in the detection unit, which allows for precise height information calculation from the spatial distribution of saturation values and improved color determination using a grayscale chip.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a line scan camera with limited optical sensor line length is used, then the device complexity is reduced, but the productivity decreases due to requiring multiple passes to capture the entire product surface
Solution Approach 1:
The patent transitions from a line scan camera (1D detection) to an area scan camera (2D detection), adding a spatial dimension to the detection capability. This allows the entire product surface to be captured in a single pass, eliminating the need for multiple scanning passes and significantly improving productivity while maintaining manageable device complexity through the use of standard area scan camera technology.
2Measurement precision
If multiple illumination devices with different colors are used to achieve reliable defect analysis, then the measurement precision is improved, but the device complexity increases
Solution Approach 1:
The patent employs a single white light source that serves multiple functions: it provides full-spectrum illumination for defect detection, enables spectral analysis through the spectrometer, and allows height measurement through chromatic dispersion. This multi-functional approach achieves the same measurement precision as multiple colored light sources would provide, but with significantly reduced device complexity by using one illumination device instead of multiple specialized sources.
Solution Approach 2:
The patent changes the parameter of light from fixed wavelength (as in colored LED sources) to variable wavelength (white light containing all visible wavelengths). This parameter change allows a single light source to provide the spectral information that would otherwise require multiple monochromatic sources, achieving comprehensive defect analysis with improved precision while maintaining simple illumination system architecture.
3Measurement precision
If the angle of incidence is increased to improve height measurement resolution, then the measurement precision is improved, but the object-generated harmful factors increase due to enhanced reflectance variations
Solution Approach 1:
The patent introduces a spectrometer as an intermediary device between the product and the detector. The spectrometer disperses the reflected light into its spectral components, allowing the system to capture wavelength information that encodes height data. This intermediary enables the use of higher angles of incidence to improve resolution while compensating for reflectance variations through spectral analysis, as the spectrometer can distinguish between intensity variations caused by angle and those caused by surface properties.
Solution Approach 2:
The patent changes the detection parameter from simple intensity measurement to spectral distribution measurement. By analyzing the spectral composition of reflected light rather than just its intensity, the system can extract height information even at higher angles of incidence where reflectance variations would normally interfere. The spectral parameters provide additional information dimensions that separate the height signal from the reflectance noise.
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 reliable and accurate defect analysis with improved resolution and precision in height measurement, allowing for simultaneous capture of high-quality analysis images and topography in a single scan, reducing the need for multiple passes and complex setups.
Implementation Method 1
a spectrometer member configured to split white light into its spectral components and project a multichromatic light beam thus formed from monochromatic light beams
Implementation Method 2
the detection unit has a dispersive or diffractive element disposed in the detection plane in the objective or between the objective and the product
Implementation Method 3
the detection unit has a dispersive or diffractive element disposed in the detection plane
Data Source
AI summary
The invention relates to an inspection system (26) for analyzing defects in a product, the inspection system (26) comprising a projection device (32), an optical detection device (28) and a processing device, the projection device having at least one spectrometer member configured to split white light into its spectral components and project a multichromatic light beam (37) thus formed from monochromatic light beams onto a product, a detection unit (29) comprising an area scan camera (27) and an objective (28) being configured to detect the light beam (37) reflected on the product in a detection plane (46) perpendicular, preferably orthogonal, to a product surface (38) of the product. The detection unit has a dispersive or diffractive element (31) disposed in the detection plane in the objective or between the objective and the product, the reflected light beam being projectable onto an image plane (49) of the area scan camera, the processing device being configured to derive a height information of the product surface from a spatial distribution of saturation values of the reflected light beam in the image plane, a position of the optical detection unit relative to the product and the angle of incidence β.