A XRF calibration standard (or reference standard) is a reference material that is certified with known thickness and/or composition. When used in a calibration, the standards provide NIST traceability to the XRF calibration.

XRF calibrations can be sorted into two types: ones with and without calibration standards. As implied by the name, a standardless calibrations is a calibration built without any reference standards (calibration standards). While many XRFs can provide plating thickness measurements with a standardless calibration, this method is not traceable to any internationally recognizable national laboratories and is often less accurate than a calibration created with standards.

The inclusion of a calibration standard will not only improve the accuracy of the XRF measurements, but it can also used as a quality check on measurement instrument. You can be confidence that your XRF plating thickness readings are accurate to a known good value, and you can periodically read back the calibration standards to monitor the stability and performance of a XRF.

The calibration standard is what makes the reading mean something. An instrument calibrated against the wrong standard — wrong substrate, wrong element, wrong thickness range — will produce readings that are precise, repeatable, but wrong.

Bowman manufactures XRF calibration standards for all XRF instruments of regardless of brand and model through our ISO/IEC 17025 accredited laboratory. We can even recertify standards from any manufacturer, not just Bowman standards!

How to choose the right calibration standard

For the most accurate calibration, the standards used should replicate the plating structure for the part/sample being analyzed. There are three main consideration for determining which standard you need, and getting any of them wrong undermines the measurement:

• The coating or layer structure: A standard must replicate the layer structure you are measuring — the same coating over the same underlayer over the same substrate. If you are measuring gold over nickel over copper, you should not be using a gold over brass standard (Wrong layer structure and substrate.)
• The thickness range: the calibration standards’ thickness and compositional value should mimic your plating specification. Standards should cover your upper and lower limit of plating specification.
• The substrate (or base material): The substrate for your standards should be the same as the substrate on your product or samples. A mismatch in substrate can introduce factors that affect the accuracy of measurement. For example, using a Ni/SS304 standard to calibrate a Ni/Fe calibration will give erroneous Ni thickness readings, as the nickel content from the 304 substrate was not properly accounted for.

When calibration standard are required

Where a specification governs a plating process, using standard is not optional. Under IPC-4552 for ENIG coatings, demonstrating instrument capability requires a Type 1 gauge study run against a traceable reference standard whose value falls inside the specified range. A standardless Type 1 gage study only measures repeatability only — accuracy cannot be assessed at all.

IPC-4552B goes further than most specifications here: it names the traceability required, the layer construction, and the specific thickness combinations a standard must have for the copper thickness you run. See XRF calibration standards for IPC-4552B ENIG compliance.

Standards for any XRF instrument, not just ours

Bowman’s standards are manufactured for use on all XRF brands and models. Laboratories rarely run a single-vendor fleet, and a plating shop that bought its XRF instrument from one supplier a decade ago still needs traceable standards today. The measurement is only as good as the reference standard behind it, regardless of whose name is on the instrument.

Our standards are produced through Bowman’s ISO/IEC 17025 accredited laboratory and all calibration standards will come with certificate to support customer audits.

Common questions

How often should standards be recertified? What is the difference between a calibration standard and a check standard? What happens when a standard is scratched or contaminated? Those and others are answered on the XRF standards FAQ.