Fluorescing Plate for Microvia Inspection
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Solution Overview
Problem
Current automatic optical inspection (AOI) systems fail to effectively differentiate conductor pads from surrounding bulk material in microvias, particularly those with diameters 50 microns and below, leading to high rates of false positives and yield issues due to incomplete drilling, which can cause electrical failures in multilayered printed circuit boards and chip packaging.
Innovation Solution
The method employs fluorescence-based optical imaging techniques combined with selective coaxial illumination and multivariable off-axis illumination, using an integrated fluorescing plate with a CCD or EMCCD array to enhance resolution and differentiate the conductor pad from surrounding material, ensuring accurate detection of defects through comparative image analysis and transformation of back-reflected radiation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If standard AOI systems use conventional illumination and optical imaging techniques, then the system structure remains simple, but the system fails to differentiate conductor pads from surrounding bulk material in microvias 50 microns and below, resulting in high false positive rates
Solution Approach 1:
The patent introduces a fluorescing plate as an intermediary element between the light source and the microvia structure. This plate contains fluorescent materials that convert incident light to specific wavelengths, enabling selective excitation of the dielectric material in microvias. The intermediary transforms the illumination mechanism to achieve superior differentiation capability without requiring complete system redesign
Solution Approach 2:
The patent employs multiple illumination wavelengths (UV, blue, green, red) and filters to change the optical parameters of the inspection system. By varying the wavelength parameters and using corresponding fluorescent materials in the plate, the system achieves enhanced contrast and differentiation of conductor pads from surrounding bulk material, resolving the measurement precision limitation
2Measurement precision
If AOI systems use standard illumination techniques, then the illumination system remains simple, but the system cannot detect thin films of dielectric material as thin as 1 micron, leading to unacceptable false positive rates
Solution Approach 1:
The patent utilizes fluorescent color changes to enhance thin film detection. The fluorescing plate contains materials that emit specific wavelengths when excited, causing the dielectric thin films to appear with distinct color signatures different from the conductor pads and bulk material. This color differentiation mechanism enables detection of films as thin as 1 micron by transforming the detection from intensity-based to wavelength-based measurement
Solution Approach 2:
The fluorescing plate acts as an intermediary that converts broad-spectrum illumination into wavelength-specific excitation. The plate's fluorescent materials absorb incident light and re-emit at characteristic wavelengths, creating enhanced signal-to-noise ratio for thin film detection while maintaining a relatively simple illumination system
3Manufacturing precision
If AOI systems inspect microvias with diameters down to 10 microns, then the inspection coverage is comprehensive, but the system lacks the resolution and capability to differentiate features, resulting in yield issues
Solution Approach 1:
The patent changes the optical measurement parameters by using multiple illumination wavelengths and corresponding fluorescent emission wavelengths. This parameter transformation enables the detection system to resolve features in microvias as small as 10 microns by converting spatial resolution challenges into spectral resolution problems, which are more easily solved with modern detectors
Solution Approach 2:
The patent replaces conventional mechanical/optical resolution-based differentiation with fluorescence-based spectral differentiation. Instead of relying solely on physical resolution limits of the optical system, the invention uses the fluorescent emission characteristics to differentiate features, effectively bypassing the mechanical resolution constraints of standard AOI systems
4Productivity
If standard AOI systems are used for high-density chip packaging with 40,000 microvias per package, then the inspection throughput is maintained, but the false positive rate causes serious field failures
Solution Approach 1:
The patent maintains high inspection throughput by using rapid fluorescent excitation and detection, while simultaneously improving reliability through wavelength-based differentiation. The fluorescent plate enables quick excitation-response cycles that preserve productivity, while the spectral differentiation provides robust false positive reduction even in high-density packages with 40,000 microvias
Solution Approach 2:
The patent implements a feedback mechanism where multiple images taken with different illumination wavelengths are processed and compared. The system uses the fluorescent plate's wavelength-specific emission characteristics to provide feedback on dielectric material presence, enabling real-time differentiation and reducing false positives while maintaining high-speed inspection capability
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 significantly reduces false positives and negatives by providing a better signal-to-noise ratio and isolating defects, ensuring the quality of microvias, thus preventing electrical failures in high-density chip packaging.
Implementation Method 1
The present invention utilizes the fluorescent nature of polymers and the differentiating of this fluorescence from the bulk surrounding material
Implementation Method 2
transformation of back reflected radiation by means of an integrated fluorescing plate mounted to the surface of a CCD or EMCCD array
Implementation Method 3
selective coaxial illumination and multivariable off-axis illumination
Implementation Method 4
multivariable off-axis illumination and the use of comparative image analysis
Data Source
AI summary
Inspection of partially drilled microvias by fluorescence based optical imaging techniques, selective coaxial illumination and multivariable off-axis illumination and the use of comparative image analysis and the transformation of back reflected radiation by means of an integrated fluorescing plate mounted to the surface of a CCD or EMCCD array.