Grating Projection Inspection for PCB Device Extraction
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Solution Overview
Problem
Existing methods for inspecting measurement objects on printed circuit boards using two-dimensional images are challenging due to sensitivity to color and illumination, difficulty in distinguishing objects from noise, and limitations in extracting devices with small fillets, especially when noise is present or when the device's dimension changes.
Innovation Solution
A method involving the generation of shape and shadow maps by projecting grating pattern light onto the substrate, acquiring height and visibility information, and comparing these maps with templates to extract device information such as size, position, and rotation, which is less sensitive to color and illumination and not affected by noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If two-dimensional image capturing is used to set up measurement object region, then the inspection process is simple, but the measurement precision deteriorates due to sensitivity to color and illumination changes
Solution Approach 1:
The patent transitions from two-dimensional image capturing to three-dimensional shape measurement by projecting grating patterns and analyzing height information. This dimensional change eliminates sensitivity to color and illumination variations, as the measurement is based on geometric shape rather than optical properties.
2Ease of manufacture
If two-dimensional image is used for device extraction, then the method is straightforward, but the measurement precision deteriorates when device dimensions change or noise is present
Solution Approach 1:
The patent uses three-dimensional height information from grating projection to distinguish devices from noise and pad regions. The height dimension provides additional discrimination capability that is insensitive to color changes, illumination variations, and device dimensional changes.
3Ease of manufacture
If fillet portion of two dimensional image is used for device extraction, then the extraction method is simple, but the measurement precision deteriorates when fillet is small
Solution Approach 1:
The patent replaces two-dimensional fillet-based extraction with three-dimensional height information. The height data from grating projection provides robust device boundaries even when fillets are small or absent, as it captures the actual physical shape of the device.
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 method effectively discriminates devices regardless of color, illumination, or noise, and can accurately extract device information even when the device's height exceeds the measurement range, enhancing inspection reliability and precision.
Implementation Method 1
acquiring height information of each pixel by projecting grating pattern light onto the substrate through a projecting section
Implementation Method 2
acquiring visibility information of each pixel of the substrate through N-number of images captured by a camera when the grating pattern light is reflected by the substrate
Data Source
AI summary
An inspection method for inspecting a device mounted on a substrate, includes generating a shape template of the device, acquiring height information of each pixel by projecting grating pattern light onto the substrate through a projecting section, generating a contrast map corresponding to the height information of each pixel, and comparing the contrast map with the shape template. Thus, a measurement object may be exactly extracted.