X-Ray Fluorescence Analysis:  The Ideal Method for Quality Control in Electroplating (Part 2)

X-Ray Fluorescence Analysis: The Ideal Method for Quality Control in Electroplating (Part 2)

The modern XRF systems line the FISCHERSCOPE XUL or XULM are typically small and can be installed and used near production, shipping or receiving areas, as well as in a laboratory. Helmut Fischer Group also offers portable handheld-XRF systems.

Besides the x-ray source, the main component of the X-ray measuring system is the detector. The quality of the detector determines which measuring tasks can be solved with a single device. Fischer offers three different types of detectors.

The proportional counter is a gas-filled tube. It is a tried-and-tested detector for simple measuring tasks, well suited for measuring thicker layers with small measuring spots. If the emissions from the sample are well separated, that is if the elements of interest differ strongly (i.e., tin coating on a copper substrate), then the proportional counter will do a very good job.

If the sample is complicated – with many elements or heavily overlapping emissions (adjacent atomic numbers) – then silcon detectors are preferred or even necessary. Here Fischer offers models with a silicon PIN diode (Si-PIN) or with a silicon drift detector (SDD). Both have a better energy resolution than the proportional counter which provides much better peak-to-background (single-to-noise) response. The PIN is a mid-range detector. While it can be used for both material analysis and layer thickness measurement, it requires longer measuring times for small measuring spots. The SDD is the most modern semiconductor detector with excellent resolution and best detection limits. Its strength lies in measuring very thin coatings on the nanometer scale and in material analysis in the per mil range.

Analysis of the Metallic Content of Plating Solutions

In order to apply coatings at a well-defined plating rate and with a well-defined composition, electro-plating companies must monitor and control the formulation of their plating baths very closely. For example, the metallic coatings (like AuCuCd, AuCuIn, RhRu or others) especially popular in the jewelry industry must be applied absolutely homogeneously over the entire surface to ensure an even color finish.

All the Fischer XRF instruments can be easily outfitted for analyzing plating solutions by mounting the optional solution analysis cell (see Figure 3). First, the specialized cell is filled with the solution to be analyzed, then it is covered with a thin but robust Mylar foil and sealed with a plastic ring – all part of the solution analysis kit. Different cells with different base materials are available. Choosing the correct material can considerably improve the measurement performance. Matrix effects (Cl, SO4, CN) in the solution can be corrected via the absorption of fluorescence radiation of the cell’s base material (e.g. Mo or Ni).

Compared with other methods, XRF (x-ray fluorescence) analysis of such solutions is straightforward: sample preparation is quick, and the only consumables required are small pieces of plastic foil, as opposed to other analytical methods where gases (Ar) or purified water are used.

Setup of the solution analysis cell. First, it is filled with the solution, then covered by a Mylar foil and sealed with a plastic ring
Setup of the solution analysis cell. First, it is filled with the solution, then covered by a Mylar foil and sealed with a plastic ring

This way using XRF analysis to monitor the plating bath is a quick and effective way to determine the concentrations of ions and chemicals in the solution. Plating bath analysis can be carried out directly in the production process without specially qualified personnel present. As accurate measurement results are available within seconds, the reaction time when bath solution deviates is minimized. Furthermore, solution analysis cells can be re-used resulting in no additional operating costs.

Conclusion

XRF analysis with Fischer devices offers plating companies significant benefits. By effectively managing both coating thickness of components and plating bath analysis through XRF analysis, plating companies will be able to enhance their product quality and process and cost control and to meet the needs of their manufacturers and end-users. As samples no longer have to be sent to a lab to be analyzed, there are significant time and cost savings so that an Fischer XRF measuring system can pay for itself after a short time.

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