Multi-Phase Structured Light Height Mapping for Solder Paste Inspection
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Solution Overview
Problem
Existing height topology inspection systems face limitations in accurately measuring the height of small solder paste bricks on circuit boards due to phase wrap issues, which result in inaccuracies and increased costs from faulty board detection after fabrication.
Innovation Solution
A method employing multi-phase structured light with distinct fringe periods is used to project patterns onto the circuit board, allowing for relative sensor movement to acquire multiple images, generating a height map that leverages different fringe periods for precise and extended height measurement without additional hardware or exposure time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single fringe period is used for height measurement, then measurement precision is improved, but the effective height measurement range is limited due to phase wrap issues
Solution Approach 1:
The reticle is divided into multiple distinct regions, each generating a different fringe period. This segmentation allows simultaneous projection of multiple fringe periods onto the test surface, enabling the system to measure both small features with high precision and larger features within the extended height range without phase wrap errors
Solution Approach 2:
The invention transitions from using a single fringe period (one-dimensional measurement approach) to using multiple fringe periods with different spatial frequencies (multi-dimensional approach). This allows the system to resolve height ambiguities by combining information from different fringe periods, effectively extending the measurable height range while maintaining precision
2Manufacturing precision
If multiple fringe periods are projected simultaneously, then the effective height measurement range is extended, but system complexity increases
Solution Approach 1:
Multiple fringe periods are merged into a single reticle structure, allowing simultaneous projection through one optical path. This combining approach extends the measurement range while avoiding the complexity of multiple separate projection systems or sequential scanning mechanisms
Solution Approach 2:
The reticle is designed to serve multiple functions: it generates multiple distinct fringe periods from different regions, each contributing to different aspects of the height measurement. This multi-functionality allows a single component to achieve what would otherwise require multiple separate systems
3Device complexity
If traditional single-phase inspection is used, then device complexity is kept simple, but measurement accuracy deteriorates for small solder paste bricks
Solution Approach 1:
The reticle is segmented into multiple functional regions, each contributing a different fringe period. This segmentation enables the system to maintain simple single-shot acquisition while achieving high measurement accuracy through the combined information from multiple fringe periods, particularly for small solder paste features
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 expands the effective height measurement range without reducing resolution, overcoming phase wrap issues and enabling in-process inspection for improved accuracy and reduced costs by detecting solder paste placement errors before component placement.
Implementation Method 1
a first image of the feature is acquired while the patterned illumination is projected upon the feature. Relative movement is then generated between a sensor and the feature to cause relative displacement of a fraction of a field of view of a detector
Data Source
AI summary
A method for mapping height of a feature upon a test surface is provided. The method includes projecting patterned illumination upon the feature, the patterned illumination having a plurality of distinct fringe periods. A first image of the feature is acquired while the patterned illumination is projected upon the feature. Relative movement is then generated between a sensor and the feature to cause relative displacement of a fraction of a field of view of a detector, the fraction being equal to about an inverse of the number of distinct regions of a reticle generating the pattern. Then, a second image of the feature is acquired while the patterned illumination is projected upon the feature. The height map is generated based, at least, upon the first and second images.