Sensitivity Metric
Proportional scaling factors used in surface spectroscopy convert raw signal intensities into quantitative chemical concentrations. This scaling coefficient, known as the relative sensitivity factor, accounts for the differences in ionization and detection efficiency of different chemical elements. It ensures that the spectroscopic output accurately reflects the elemental ratios present within the tested sample.
Composition Calculation
Quantifying the surface composition during depth profiling of metal finishes depends on dividing each element’s raw peak area by its specific factor. For example, calculating the ratio of phosphorus to nickel in an electroless nickel phosphorus alloy requires applying the relative sensitivity factor for each element to the measured photoelectron peaks. Incorrect factors can lead to an overestimation of the phosphorus concentration, which could hide a potentially brittle coating.
This calculation is a fundamental step in preventing black pad failures, as it allows engineers to accurately identify the chemical limits of the alloy deposit before the assembly is sent to the reflow line.
Calibration Standard
Establishing these factors involves measuring known reference materials under identical spectroscopic and vacuum conditions. While standard values are provided by instrument manufacturers, optimizing them for specific printed circuit board materials requires running local calibration standards. This process ensures that the quantitative data gathered from surface finishes remains accurate and reliable over long-term production monitoring.
