Bromine is added to epoxy-glass printed circuit board substrates to provide fire retardant characteristics. Bromine fluorescence, as shown in Figure 9, can add to gold fluorescence if the copper plane underneath is sufficiently thin (i.e., less than 700µin.) or unless the measurement is located on a small feature where a layer of copper does not exist in the area surrounding the feature (i.e., on a surface mount pad).

The best way to eliminate bromine interference is to use numerical filtering. If a problem is suspected, measure in the same place with an application (calibration) using numerical filtering to strip bromine and with an application not using the numerical filter. If a difference exists between the measurements, use the application with the numerical filter to measure the printed circuit boards.

Always place the circuit board so that the axis of the tab, gate array, or surface mount pad is perpendicular to the axis of the detector (i.e., pointing away from the operator).

If you do not have numerical filter available, it is possible to mask the bromine fluorescence with copper foil. Punch a small hole in the foil and use it to cover the circuit board area on the detector side.

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