2D Metrology for Solder Paste Inspection Using Multi-Wavelength Fluorescence
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Solution Overview
Problem
Current solder paste inspection (SPI) techniques face challenges in accurately inspecting the dimensions, geometry, and transparency variations of solder paste in Ball Attach modules due to roadmap changes, new paste materials, and substrate warpage, leading to data loss and mismatched patterns, with existing tools lacking 2D measurement capability and suffering from low throughput.
Innovation Solution
A multi-level fluorescence imaging technique using ultraviolet (UV) excitation wavelengths to selectively obtain images with optimized contrast for solder paste and solder resist openings, enabling high-accuracy 2D imaging and measurement of solder paste boundaries and offsets, which can be integrated with 3D commercial tools for enhanced inspection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multi-level fluorescence imaging technique is used, then measurement precision and inspection accuracy are improved, but device complexity increases
Solution Approach 1:
The imaging system segments the inspection task by using multiple excitation wavelengths (e.g., 365nm and 405nm UV) to separately illuminate different organic materials (solder paste flux and solder resist). Each wavelength excites specific materials to produce distinct fluorescence signals, allowing the system to separately image and analyze different components. This segmentation enables precise boundary detection between solder paste and solder resist openings by comparing images from different excitation sources.
Solution Approach 2:
The system changes the excitation wavelength parameter to differentiate between materials. By switching between multiple UV excitation wavelengths, the system exploits the different fluorescence characteristics of organic materials. This parameter change allows selective excitation and imaging of specific materials, improving measurement precision without requiring complex physical modifications to the imaging apparatus.
2Measurement precision
If 3D measurement tools are used for solder paste inspection, then inspection capability is improved, but throughput decreases due to slow scanning speed
Solution Approach 1:
The invention extracts the 2D imaging capability from the 3D measurement system by implementing a dedicated 2D camera system with multi-wavelength UV excitation. This separate 2D imaging subsystem operates independently and simultaneously with the 3D scanning process, providing fast 2D boundary detection without interfering with or slowing down the 3D measurement throughput. The extracted 2D imaging function addresses the throughput limitation by providing rapid inspection data in parallel.
Solution Approach 2:
The system adds a 2D imaging dimension to the existing 3D measurement capability. By implementing a separate 2D camera system that captures fluorescence images at multiple excitation wavelengths, the invention provides an additional dimensional perspective for inspection. This 2D dimension enables fast boundary detection and offset measurement that complements the 3D data, allowing simultaneous operation without throughput penalty.
3Ease of manufacture
If existing SPI tools are used, then inspection process is maintained, but measurement accuracy deteriorates due to lack of 2D measurement capability
Solution Approach 1:
The invention merges the new 2D fluorescence imaging system with existing 3D SPI tools to create an integrated inspection solution. The 2D camera system with multi-wavelength UV excitation is combined with the existing 3D scanning capability, allowing both 2D boundary detection and 3D dimensional measurement to operate together. This merging maintains continuity with existing inspection processes while adding enhanced 2D measurement accuracy for boundary and offset detection.
Solution Approach 2:
The imaging system is designed with multi-functionality to perform multiple inspection tasks simultaneously. The same 2D camera system with multi-wavelength excitation can detect solder paste boundaries, measure offsets, identify buried solder resist openings, and differentiate between various organic materials. This universal approach maintains ease of manufacture by using a single integrated system rather than requiring separate specialized tools for each measurement type.
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 provides fast and accurate 2D metrology for solder paste inspection, overcoming data loss and measurement inaccuracies, ensuring the quality of solder joints by clearly differentiating solder paste from solder resist openings and detecting buried boundaries, even with varying metal loadings and substrate warpage.
Implementation Method 1
irradiating a sample solder joint comprising an organic material, an organic and metal material enclosed by an irregular boundary, and a metal material enclosed by a regular boundary, with a first wavelength energy and detecting first fluorescence energy at a third wavelength; irradiating the sample with a second wavelength energy and detecting second fluorescence energy at a fourth wavelength
Data Source
AI summary
A method, apparatus and computer readable memory for solder paste inspection. A light source is configured to irradiate a sample solder joint comprising an organic material, an organic and metal material enclosed by an irregular boundary, and a metal material enclosed by a regular boundary. A first wavelength ultraviolet (UV) energy irradiates the sample to obtain first fluorescence energy, and a second wavelength UV energy irradiates the sample to obtain second fluorescence energy. A two-dimensional (2D) camera is configured to acquire a first image of the sample primarily from the first fluorescence energy and a second image of the sample primarily from the second fluorescence energy. Photo manipulation software is stored on at least one hardware processor, the photo manipulation software configured to overlay the first image and the second image to visually compare the boundary of the organic and metal material with the boundary of the metal material.