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Gold standard
Monday, 18 April 2016 00:00

XRF measurement solutions for thin gold and palladium coatings on PCB’s

As the electronics industry makes use of ever thinner coatings, manufacturers increase their demands on measuring technologies to provide reliable parameters for product monitoring.  One example is the Au/Pd/Ni/Cu printed circuit board system with coating thicknesses for gold and palladium of just a few nm. For monitoring the quality of these coating systems, X-ray fluorescence instruments have established themselves as the measurement method of choice.

The thinner the coatings, the more important it becomes to select a suitable detector. Table 1 shows a comparison of results from FISCHERSCOPE X-RAY instruments fitted with a proportional counter tube, PIN diode and silicon drift detector (SDD), respectively.

As illustrated in Table 1 below, the SDD’s significantly superior repeatability precision allows for the reliable measurement of even very thin gold and palladium coatings.

The trueness is also better for instruments with SDD because the high energy resolution of the usable signal is less susceptible to influence from the background or adjacent fluorescence lines.

Proper handling of the fluorescence signal generated by the substrate material is also more important with thinner coatings. While a general subtraction of the background signal does improve the repeatability precision, it can also introduce errors into the results.  The evaluation software WinF therefore explicitly allows the composition of the substrate material to be taken into account with every measurement.

The FISCHERSCOPE X-RAY XDL with proportional counter tube, XDAL with PIN detector, or  XDV- SDD with SDD detector are all available from Fischer Instrumentation (GB) Ltd.

Table 1: Various types of detectors and their corresponding achievable standard deviations and variation coefficients