Coatings on Electrical Contacts: Simple Measurement using the X-ray Fluorescence Method

Coatings on Electrical Contacts: Simple Measurement using the X-ray Fluorescence Method

Due to its wide range of applications, numerous technologies exist for contact manufacture in the area of electrical connections. These technologies are ultimately intended to optimise important parameters such as electrical resistance or mechanical stress ability for the respective application. For this purpose, metallic base materials with one or several metallic coatings are normally used as contact materials. The thickness of these coatings is important for contact characterisation. Coating thickness measurement is therefore essential for the process and for quality control in the production of electrical contacts.

Table 1: Combinations of base materials and coating systems frequently used for contact systems can lead to a very large number of measurements. WinFTM® Version 6 software helps to reduce this number. The coating systems shown in the table are only a few of the systems used in normal practice.
Table 1: Combinations of base materials and coating systems frequently used for contact systems can lead to a very large number of measurements. WinFTM® Version 6 software helps to reduce this number. The coating systems shown in the table are only a few of the systems used in normal practice.

Table 1 shows several examples of frequently used base materials and coatings for electrical connections. The possible combinations result in numerous coating systems, including multiple coatings, which require measurement. For correct determination of the coating thickness by X-ray fluorescence analysis, the coating structure and base material must be known. This generally involves numerous measurements. The management and calibration sometimes required for these measurements is time-consuming and quickly leads to confusing and error-prone structures. The number of necessary measurements can now be reduced considerably with WinFTM® Version 6 evaluation software.

The IOBC method (Independent of Base Composition) simplifies the procedure. With this method, the coating thickness can be measured correctly regardless of the base material composition. The simplification of the procedure increases the accuracy of measurement. A changed base material is correctly taken into account automatically by the software.

Table 2: Standard less measuring results of the coating system Au/Ni/CuSn6 und Au/Ni/CuZn36 obtained with the XDLM®-C4 with a measuring time of 10 seconds and a collimator of 0.3 x 0.05 mm
Table 2: Standard less measuring results of the coating system Au/Ni/CuSn6 und Au/Ni/CuZn36 obtained with the XDLM®-C4 with a measuring time of 10 seconds and a collimator of 0.3 x 0.05 mm.

These options offered by WinFTM® V 6 are best illustrated on the basis of specific examples. The first example is the Au/Ni/Base system. Various Cu alloys and Fe alloys are used as base materials. For classic evaluation, the software for every Au/Ni contact of the respective base material to be measured must be known (measured). By measuring with the IOBC method, all contacts can now be measured in one operation. The comparison of a coating system (films of a known thickness) on CuSn6 and CuZn36 shows that the base material has virtually no influence on the measured coating thickness. In addition, the results obtained standard less are highly satisfactory in terms of the accuracy and repeatability of the Au and Ni coatings. Even when measuring standard free.

Table 3: Comparison of different Sn/Ni coatings on the base materials CuSn6 und CuZn36. Measurement was standard less with the XDLM®-C4 with a measuring time of 10 seconds and a collimator of 0.3 x 0.05 mm.
Table 3: Comparison of different Sn/Ni coatings on the base materials CuSn6 und CuZn36. Measurement was standard less with the XDLM®-C4 with a measuring time of 10 seconds and a collimator of 0.3 x 0.05 mm.

There is one limitation of the IOBC method for coatings that contain elements which are also present in the base material, for example Cu/CuZn. A defined base material must be used in this case. Sn coatings are an important exception to this rule: Since the element Sn has two widely separated measurable components in the x-ray fluorescence spectrum (Sn-K and Sn-L lines), where both lines from the coating can be seen, but only the Sn-K lines of the base material, with their high energy, contribute to the spectrum. Therefore Sn coatings on Sn-containing base materials can also be measured using the IOBC method. Table 3 shows a comparison of different Sn coatings on CuSn6 and CuZn36. The influence of the base material on the measured Sn coating thickness is also negligible in this case.

Conclusion

The numerous measurements required for contact systems due to the large number of employed coating systems and base materials can be reduced substantially with WinFTM® V6 software. This greatly reduces time and effort and minimises the potential risk of errors.

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