Abstract
The ability to measure conductive coatings applied to electronic packages has improved significantly. Beta Backscatter replaced microscopic cross-sectioning in most applications because of it's ability to resolve thinner coatings than possible with micro-sectioning. In the last ten years, x-ray fluorescence (XRF) coating measurement systems have replaced beta backscatter systems because of XRF's lower random error and because of it's abilities for material discrimination and measurement of several layers on very small areas. While the ability to measure coatings has improved, the potential sources of error have changed. It is interesting that an XRF instrument may produce acceptable results on it's calibration standards and not produce accurate results on the samples being measured. This paper will discuss the sources of error involved with measurement of coatings on electronic packages and present methods for eliminating their effects on measurement.

Scope
This paper will cover the measurement of gold, nickel, and tin-lead solder on copper, phosphor bronze, kovar (glass sealing alloys), and printed circuit board substrates. It will begin with a discussion of accuracy and precision, and end with a measurement assurance procedure. Specific adjustment procedures should be found in the appropriate instrument instruction manual.