Quantitative Depth Profiling Procedures for Multi-Layer Circuit Board Surface Finishes
Quantitative depth profiling via AES or XPS accurately measures sub-nanometer interfacial oxidation and phosphorus enrichment to prevent joint failures.
Shirley Background Subtraction
Background Analysis
Iterative mathematical correction applied to surface spectra removes the contributions of inelastically scattered electrons from the measured photoemission peaks. This processing method, known as Shirley background subtraction, assumes that the background intensity at any point is proportional to the integrated peak area at higher kinetic energies. It yields a clean and well-defined peak shape that is suitable for quantitative elemental analysis.
Peak Integration
Isolating the true signal from the background noise allows for precise calculation of the area under the curve for each element. During the evaluation of thin gold or palladium finishes, Shirley background subtraction is applied to separate the core-level peaks from the broad scattering baseline. By performing this step, analysts can determine the thickness and oxidation state of the surface layers with greater precision.
Signal Resolution
Comparing this subtraction method to linear or Tougaard models reveals that it is particularly effective for transition metals with high background steps. However, if the energy range for the subtraction is chosen incorrectly, it can distort the resulting peak area and lead to errors in calculating composition. Utilizing a consistent set of energy boundaries during the subtraction process minimizes these calculation errors and ensures reliable data across different test runs.
This mathematical consistency is highly valuable when comparing surface finish quality across different production lots, as it prevents false variations caused by manual adjustments of the data analysis parameters.