Microstructural Effect Limitations in the Analysis of SnAg, SnBi and SnIn Lead-free Solders by Wavelength Dispersion X-Ray Spectrometry

This article describes the effects of microstructures in an analysis of lead-free solders, namely SnAg, SnBi and SnIn, using X-ray fluorescence spectrometry ( XRF ). The size of the microstructures in the samples and calibration materials has a strong impact on the calibration accuracy and results. A comparison of the microstructure size and critical thickness values demonstrated the importance of the former parameter in terms of the analyzed volume of the specimen. The re-melting and casting in an induction furnace at developed conditions were determined to be a way to obtain samples with fine-grained microstructures. Calibration with re-melted reference materials yielded more accurate calibration curves than calibration using the materials in their original state. Re-melting of the samples resulted in improvements in the XRF results in comparison to the reference values. This improvement is especially important in case of alloying elements with concentrations that determine the recognition of a specific solder grade.