Auto Focus Optics for High-Density Part Inspection
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Solution Overview
Problem
Existing focus systems fail to maintain focus during the inspection of high-density electronic parts due to limitations in maintaining focus for all trace orientations and features, especially when lines and traces become too small, leading to inaccurate measurements and loss of focus in high-density, high aspect ratio regions.
Innovation Solution
Projecting multiple patterns composed of geometric shapes onto the part at different wavelengths, vector angles, and vector directions, and analyzing slice measurements and known good reference shapes to calculate and adjust the distance between the part and lens optics, ensuring focus is maintained across the optical field of view.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single focus line is projected onto the part, then the focus measurement can be obtained, but the measurement becomes inaccurate when the line blurs due to out-of-focus surfaces
Solution Approach 1:
The patent divides the single focus line into multiple projected lines at different orientations (e.g., 0°, 45°, 90°, 135°). By segmenting the measurement into multiple directional components, the system ensures that at least some lines remain sharp and measurable even when surfaces are out of focus, thereby maintaining measurement accuracy and reliability.
Solution Approach 2:
The projected lines serve multiple functions: they act as both focus measurement indicators and orientation-independent reference features. The same set of projected lines is used to measure focus across different trace orientations, making the system universally applicable to high-density interconnect structures regardless of their spatial arrangement.
2Reliability
If the depth of focus is increased to maintain focus across different heights, then focus is maintained, but the measurement precision for fine lines deteriorates
Solution Approach 1:
The patent applies local quality by projecting lines at specific orientations that match the local trace orientations being measured. For each region of the part, the system selects and projects reference lines oriented to align with the dominant trace directions in that local area, ensuring optimal focus measurement precision for fine lines while maintaining adequate depth of focus coverage.
3Measurement precision
If multiple projected lines at different orientations are used, then focus measurement accuracy improves, but the device complexity increases
Solution Approach 1:
The patent uses simplified 2D projected line patterns as copies or representations of the 3D focus measurement requirements. Instead of using complex 3D measurement structures, the system projects simple 2D line patterns that, when analyzed across multiple orientations, provide comprehensive focus information. This copying approach reduces device complexity while maintaining measurement precision.
4Illumination intensity
If the focus line width is increased to improve signal intensity, then detection sensitivity improves, but the measurement precision for small features deteriorates
Solution Approach 1:
The patent employs dynamic adjustment of projection parameters, including line width and intensity, based on the specific measurement requirements. The system can adaptively modify the projected line characteristics to optimize the balance between signal intensity for detection sensitivity and line width for measurement precision, allowing the same system to effectively measure both large and fine 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
Enables accurate focus maintenance independent of feature and trace orientation, even in high-density parts, by using valid slice measurements and reference shape fitting to calculate focus heights, thereby improving focus accuracy and reducing measurement errors.
Implementation Method 1
a first pattern is projected onto the part... a second pattern is projected onto the part... The projected patterns are viewed with a focus camera... to calculate the distance between the part and lens optics
Data Source
AI summary
A method and apparatus to maintain image focus on parts such as wafers, circuit boards, or high-density substrates as the part is being inspected. Focus performance is independent of feature and trace orientation and density. This apparatus can be easily integrated into an inspection system and can maintain focus on parts with high aspect ratio structures and or low or non-reflective insulators. It enables the inspection of high-density fine line products requiring the use of high resolution, high numerical aperture (NA) imaging optics with small depths of focus (DOF) that must be kept in focus during the inspection.