X-ray Solder Thickness Calibration via Logarithmic Intensity
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Solution Overview
Problem
Conventional X-ray inspection methods for electronic devices face inaccuracies in measuring solder thickness due to non-linear interactions with multiple absorbing materials, and existing approximation methods are time-consuming and lack a theoretical basis.
Innovation Solution
A method for calibrating a transmissive energy imaging system by varying the thickness of a second absorbing material while keeping the first absorbing material fixed, using multiple pairs of image data to determine fitting constants that allow for precise calculation of the first absorbing material's thickness through logarithmic transformations of foreground and background intensities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional X-ray inspection methods are used to measure solder thickness, then the measurement can be obtained, but the accuracy is reduced due to non-linear interactions with multiple absorbing materials
Solution Approach 1:
The patent changes the parameter representation from direct gray-scale values to logarithmic transformations of intensity ratios. By taking the logarithm of the ratio between foreground (solder + absorber) and background (absorber only) intensities, the non-linear interaction becomes linearizable, enabling accurate thickness measurement through simple subtraction of material contribution terms.
Solution Approach 2:
The patent introduces an intermediary calibration process using known thickness standards to determine material-specific coefficients. These coefficients serve as mediators that translate the complex non-linear X-ray interactions into linear relationships that can be used for accurate measurement of unknown samples.
2Measurement precision
If approximation methods with look-up tables are used to estimate solder thickness, then thickness estimation is possible, but the process becomes time-consuming
Solution Approach 1:
The patent replaces the mechanical lookup table approach with a direct mathematical calculation method. Instead of storing pre-computed values in a lookup table and performing time-consuming searches, the invention uses a closed-form mathematical equation that directly computes thickness from measured intensities, eliminating the need for extensive database searches.
Solution Approach 2:
The patent inverts the traditional approach by deriving a direct calculation formula from first principles rather than building lookup tables from experimental data. This inversion allows for real-time calculation without requiring extensive pre-computed databases, significantly improving measurement speed while maintaining accuracy.
3Loss of information
If complete characterization of solder and shading materials is attempted from limited gray scale calibration measurements, then all material parameters can be obtained, but the process becomes highly complex and generally not possible
Solution Approach 1:
The patent extracts only the necessary information for thickness measurement rather than attempting complete material characterization. By focusing specifically on the solder thickness parameter and using background measurements to account for absorber materials, the method extracts the essential information needed without requiring full characterization of all materials in the path.
Solution Approach 2:
The patent performs partial characterization by measuring only what is necessary for the primary goal (solder thickness). Instead of attempting to characterize all materials completely, the method uses background measurements to effectively subtract out the absorber material contributions, performing just enough characterization to achieve the measurement objective.
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 a quick and precise way to measure the thickness of the first absorbing material, reducing errors and eliminating the need for extensive databases, enabling rapid and accurate characterization of solder joints in electronic devices.
Implementation Method 1
an incident transmissive energy having an incident intensity is transmitted through the first and second absorbing materials
Implementation Method 2
The images or pictures formed represent the X-ray shadow cast by an object being inspected when it is illuminated by a beam of X-rays
Data Source
AI summary
A method for measuring the thickness of a first absorbing material in the presence of a second absorbing material is provided. The method comprises the steps as follow. The thickness (tS) of the first absorbing material is fixed and the thickness of the second absorbing material is varied to obtain a calibration standard. The intensity of the transmissive energy passing through the calibration standard is detected by acquiring multiple pairs of image data comprising a foreground value (logn(Ic+s)) and a background value (logn(Ic)). The thickness (tSi) of the first absorbing material is changed and the above steps are repeated to obtain sets of image data. A fitting constant Id is determined to describe each set of the intensity data asμsαtS=logn(Ic+Id)-logn(Ic+s+Id).A best fit of the proportional constantμsαis determined to further calculate an unknown thickness of the first absorbing material (ts′) through the equationts′=αμs[ln(Ic′+Id)-ln(Ic+s′+Id)].