XRF is a standard elemental-analysis technique with a broad range of applications. In addition to compositional analysis of samples, XRF can be used in specialized applications, such as measuring the thickness of layers or coatings on samples.

In XRF, x-rays are directed from a source onto a sample, penetrating the sample surface at a depth that depends on the material. This allows the instrument to interrogate beyond the surface composition to deeper into the sample. The x-rays eject electrons from the inner electron shells of the sample’s atoms. When other electrons make a quantum transition from an outer shell to fill the hole left by the ejected electrons, x-rays of a wavelength corresponding to each element are emitted. These are detected, and the strength of the fluorescence signal from each component reveals the relative concentration of each element in the sample.

For thickness analyzers, additional software routines make use of appropriate standards or models to determine the thickness of layers deposited on a substrate. For instance, if the sample is known to be a coating of zinc on steel, the instrument can calculate the mass density of the zinc coating from the intensity of the zinc’s XRF signal. Using the known value of the density of zinc, this can be converted into a measurement of thickness. Depending on the sophistication of the modeling software, and proper development of standards and methods, XRF thickness analyzers can measure multiple layers of complex multielement coatings on a sample.

The primary applications are for electronics and metals. Electronics components, wire coatings and even entire circuit boards can be analyzed with these instruments. In addition to direct measurements of component contact thickness that may affect performance, XRF composition information can guarantee that the right materials are being used (e.g., lead-free solder for ROHS compliance). Metals can be analyzed for plating thickness and other coatings, with applications ranging from steel to gold-plated jewelry. Other applications involve semiconductor wafers, paint and powder coatings, and photovoltaics.

Rather than specific instrument solutions, most major XRF vendors offer software allowing their instruments to be used as thickness analyzers. Oxford Instruments is the leading vendor, with products including the X-Strata and MAXXI lines. Hitachi High-Technologies also has a broad product line of XRF coating-thickness gauges. Bruker provides thickness-measurement software for its M-series of XRF instruments. Its M2 Blizzard is designed for thickness and composition measurements of printed circuit boards. EDAX (AMETEK) recently released the XLNCE series. Other significant vendors include Fischer Technology, HORIBA, Rigaku and Skyray. Cianflone’s thickness analyzers are based on WD- rather than ED-XRF. PANalytical (Spectris) offers a WD-XRF instrument for automated analysis of semiconductor wafers.

XRF Thickness Analyzers at a Glance:

Leading Suppliers

• Oxford Instruments

• Hitachi High-Technologies

• Bruker

Largest Markets

• Electronics

• Metals

• Coatings

Instrument Cost

• $30,000–$120,000