Dynamic Structured Light for 3D Circuit Board Inspection
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Solution Overview
Problem
Current circuit board inspection systems using white light phased profilometry face limitations such as triangulation shadows, fixed structured light patterns, and inflexibility in measurement range and light intensity, which hinder accurate and efficient 3D height imaging, especially with miniaturized components and varied reflectivities.
Innovation Solution
A system employing multiple cameras with digital structured light projectors that adjust the structured light pattern's frequency, orientation, and intensity in real-time, and mask areas causing multipath reflections, allowing for improved dynamic range and reduced noise in height image acquisition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If white light phased profilometry is used for 3D height imaging, then height measurement capability is provided, but triangulation shadows and measurement errors occur on areas with large edge slopes
Solution Approach 1:
The patent divides the illumination task into multiple segments by using multiple pattern projection sources positioned at different locations. Each source illuminates the circuit board from a different angle, ensuring that areas shadowed by one source are illuminated by another. This segmentation of illumination sources eliminates triangulation shadows and enables complete coverage of height features with large edge slopes.
Solution Approach 2:
The patent transitions from single-angle illumination to multi-angle illumination by adding spatial dimensionality to the illumination geometry. Multiple pattern projection sources are arranged in a spatial configuration that provides illumination from different directions, allowing the system to capture height information from multiple perspectives and eliminate shadowing effects.
2Measurement precision
If multiple pattern projection sources are used to eliminate triangulation shadows, then complete height image coverage is achieved, but image acquisition time increases due to sequential acquisition requirements
Solution Approach 1:
The patent employs periodic modulation of multiple pattern projection sources, where sources are activated in a sequential but synchronized manner. Each source projects its pattern during a specific time interval, and the camera captures the composite illumination pattern during these periodic intervals. This periodic action allows multiple sources to contribute to a single image acquisition cycle, maintaining speed while achieving complete coverage.
Solution Approach 2:
The patent merges the illumination patterns from multiple pattern projection sources into a single composite illumination pattern that is captured by the camera in one image acquisition cycle. The controller coordinates the timing and intensity of each source so that their combined effect provides complete area coverage without requiring sequential image captures, thus reducing total acquisition time.
3Device complexity
If fixed structured light patterns are used, then system simplicity is maintained, but adaptability to varied reflectivities and measurement ranges is limited
Solution Approach 1:
The patent introduces dynamic control of the structured light pattern characteristics, allowing the system to adapt to different measurement conditions. The controller can modify parameters such as pattern frequency, orientation, and intensity in real-time based on the specific requirements of the circuit board being inspected. This dynamic adjustability enables the system to handle varied reflectivities and measurement ranges while maintaining a relatively simple hardware configuration.
Solution Approach 2:
The patent utilizes parameter changes in the structured light pattern to enhance adaptability. By varying parameters such as spatial frequency, temporal frequency, and intensity distribution of the projected patterns, the system can optimize illumination for different surface reflectivities and height ranges. This parameter modulation allows a single flexible system to replace multiple fixed systems.
4Device complexity
If uniform light intensity is used across the field of view, then illumination simplicity is maintained, but areas with different reflectivities produce noisy height images
Solution Approach 1:
The patent implements local quality control by applying different light intensities to different regions of the field of view based on the local reflectivity characteristics of the circuit board. The controller analyzes the reflectivity distribution and adjusts the illumination intensity locally, providing enhanced illumination to dark areas and reduced illumination to bright areas. This local adaptation minimizes noise in the height images while maintaining overall system simplicity.
Solution Approach 2:
The patent incorporates feedback mechanisms where the system monitors the reflected light intensity from different areas and uses this information to adjust the illumination pattern in real-time. The controller receives feedback about reflectivity variations and dynamically modifies the light intensity distribution to achieve optimal signal-to-noise ratio across the entire field of view, thereby reducing height image 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
Enhances the accuracy and speed of 3D topology sensing on circuit boards by reducing noise and errors, accommodating varied reflectivities and component heights, and enabling in-process inspection without the need for mechanical changes or multiple image acquisition cycles.
Implementation Method 1
A laser illuminates a spatial light modulator that is programmed to form an intensity pattern that corresponds to a sinusoidal pattern
Implementation Method 2
The use of multiple cameras can be extended to more than two cameras... Each of the sources projects a structured pattern onto the circuit board from different incident angles
Data Source
AI summary
A system for sensing a three-dimensional topology of a circuit board is provided. An illumination source generates patterned illumination from a first point of view. At least one camera acquires an image of the patterned illumination from a second point of view. A controller is coupled to the source, and to the at least one camera. The controller generates a height topology of the circuit board based on images acquired from first and second image detectors of the patterned illumination. The characteristics of the pattern illumination are modified based on knowledge of the circuit board to enhance the dynamic range of the sensor and to reject image defects caused by multipath reflections.