XRF Inspection of Ag/Sn Solder Bumps Using L-Line Excitation
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Solution Overview
Problem
Conventional XRF techniques for inspecting Ag/Sn solder bumps in electronic circuits face inaccuracies due to high excitation energies causing penetration into lower layers, Compton scattering, and interference from atmospheric gases like argon, leading to flawed material analysis.
Innovation Solution
An XRF inspection system utilizing L-line excitation with lower energy X-rays and replacing atmospheric gas with inert gases like nitrogen or helium to eliminate interference, enabling precise analysis of Ag/Sn solder bumps by reducing background noise and penetration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If high energy X-rays (around 50KeV) are used for K-line excitation, then the fluorescent emission can be detected, but the excitation beam penetrates into lower layers and substrate causing inaccurate composition analysis
Solution Approach 1:
The patent changes the excitation energy parameter from high energy (50KeV for K-line) to low energy (around 10KeV for L-line) X-rays. This parameter change reduces beam penetration depth into the substrate while still enabling fluorescent emission detection, thereby improving composition analysis accuracy without the harmful penetration effect
Solution Approach 2:
The patent introduces an intermediary gas (nitrogen or helium) between the X-ray source and sample, and between the sample and detector. This intermediary serves multiple functions: it absorbs scattered X-rays to reduce background noise, and it prevents atmospheric gases from interfering with the measurement, thereby improving measurement precision
2Measurement precision
If high energy X-rays are used for inspection, then K-line fluorescent emission can be obtained, but Compton scattering occurs causing background noise and reduced measurement accuracy
Solution Approach 1:
The patent changes the excitation energy parameter from high energy (suitable for K-line) to low energy (suitable for L-line) X-rays. This parameter change shifts the interaction mechanism away from Compton scattering dominance, reducing background noise and improving fluorescent emission detection accuracy
Solution Approach 2:
The patent introduces an intermediary gas (nitrogen or helium) that absorbs Compton scattered X-rays, preventing them from reaching the detector. This reduces background noise caused by Compton scattering and improves the signal-to-noise ratio for fluorescent emission detection
3Ease of operation
If atmospheric gas is present during inspection, then the inspection process can proceed, but argon and other atmospheric gases cause interference with the fluorescent emission data
Solution Approach 1:
The patent replaces the atmospheric gas environment with an inert gas environment (nitrogen or helium). This inert atmosphere eliminates interference from argon and other atmospheric gases that would otherwise contaminate the fluorescent emission data, thereby improving measurement precision while maintaining ease of operation
Solution Approach 2:
The patent introduces an intermediary inert gas (nitrogen or helium) that fills the inspection chamber. This intermediary gas acts as a protective medium that prevents atmospheric gas interference while allowing the X-ray inspection process to proceed, thus maintaining ease of operation without sacrificing measurement precision
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
The system achieves accurate and precise determination of Ag/Sn solder bump composition and thickness with reduced interference, improving manufacturing quality control by minimizing errors from atmospheric gases and lower penetration.
Implementation Method 1
The interaction of the X-ray radiation with the elements in the bumps causes fluorescence, emitting secondary X-rays characteristic of the specific elements present in the region of the sample
Implementation Method 2
flowing a selected composition of inert gas... to thereby eliminate interference associated with scattering and fluorescence of components of atmospheric composition
Data Source
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AI summary
An XRF inspection system, and a respective method are presented. The system and method are directed at inspection of a sample. The system comprising at least one X-ray radiation source providing X-ray radiation of selected energy spectrum, an optical arrangement for focusing the X-ray radiation onto a selected inspection spot of the sample, and at least one detector configured for detection of radiation emitted from the sample and providing output data indicative of emission spectrum from the sample; wherein the output data comprises data indicative of L-line excitation fluorescent response of the sample.