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In XRF coating measurement, an x-ray photon is emitted from the target of an x-ray tube. This photon travels through a collimator and strikes the sample, ejecting low valence level electrons from the atoms in the sample. Higher valence level electrons must change energy levels to fill the space vacated by the ejected electrons. The energy carried by these electrons at their higher valence level is then cast off in the form of secondary fluorescence or characteristic x-rays.
The energies of these x-rays are characteristic to the materials they are emitted from, hence their name. These characteristic x-rays are quite useful in performing qualitative and quantitative analysis of the nature of coatings.
A calibration curve defining the relationship between the count rate within the region of interest of the coating material and the thickness or composition of the coating is developed by allowing the instrument to sample and store count rates from samples of known thickness and composition.
So, an XRF coating thickness measurement system actually counts the number of atoms of a given material within the unit of area defined by the collimator down to a saturation depth which varies according to the material. Thickness can be calculated if the density of the coating and the calibration standards is known, or if the calibration standards have the same density as the coating.
Abstract
Accuracy and Precision
Principle of Measurement
Gold and Nickel Measurements on Copper
Gold and Nickel Measurements on Phosphor Bronze
Gold and Nickel Measurements on Kovar and Other Glass-Sealing Alloys
Gold and Nickel Measurements on FR-4 Circuit Board Substrates
Tin-Lead Solder on Copper, FR-4 Circuit Board Substrates, and Kovar
Tin-Lead Solder on Phosphor Bronze
Adjustments for Part Geometry
Measurement Assurance
Conclusion
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