The partial least squares calibration technique was used for calibration of a simple XRF instrument designed for simultaneous determination of the thickness and composition of Sn-Pb layers deposited on printed boards. The design of the instrument and the software used was presented. The root mean square errors of crossvalidtion for the determination of coating thickness and Sn content were 0.44 mm and 2.8% within the ranges 3-10 mm and 55-70% Sn, respectively.