Introduction

The traditional galvanic layers give more and more way in PCB production to immersion coating. It is especially important, since the usual leaded solder will be substituted for no Pb containing materials as immersion Sn or Ag. The measurement of these layers with X-ray Fluorescence Spectrometry becomes complicated because of their extreme thinness. The new instrument generation with high-resolution detectors possesses better sensitivity and increase measurement accuracy and repeatability

Measuring conditions

Two Compact 5 instruments with micro focus glass window x-ray tube were compared:

Two test samples with exposition time 1 minutes and 2 minutes respectively and three PCB cards with an immersion Ag coating were measured. The measuring time was 60 second.

Measurement results

Figure 1 shows the example x-ray spectra of measured samples

Fig. 1. Spectra of an immersion Ag coating on Cu:
            A - measured with proportional counter;
            B – measured with PIN diode

The measurement repeatability was calculated from 10 measurements per sample. The results are present in the follow table.

Measurement of immersion Ag coating

Comparison table.

Conclusion

The measurements on two ComPact 5 instruments shows the significant better peak-to-background ratio and accordingly the higher sensibility to very thin layers of immersion Ag coating for instrument with PIN diode. The measurement repitibility is by PIN diode nearly two times better as by proportional counter.