XRF coating thickness measurement

In electroplating, electronics and connector manufacturing, coating thickness and composition determine product quality and durability. X-ray fluorescence (XRF) measures single and multi-layer coatings without destroying the sample, with high repeatability and no contact with the part.

The range covers different scales: from large PCB boards and enclosures, through complex-shaped parts, to micro-areas of IC pins and wafers, where suitable optics and precise positioning are required.

What XRF actually measures

The XRF spectrum is used to determine the coating mass per unit area. Converting this to thickness requires the layer’s density to be known. The result also depends on a correctly defined layer structure (for example Au/Ni on copper, Sn or Ag on copper, Zn or ZnNi on steel, Au/Pd/Ni on PCBs) and on calibration with standards representative of the layers and substrate. The method is described in ISO 3497 and ASTM B568.

Limitations worth knowing

• Each layer system has a measurement range. At excessive thickness, the signal becomes less sensitive to further changes, so the result is no longer reliable.
• Similar coating and substrate compositions can limit or prevent layer separation. Very thin coatings and light elements also require checking the capabilities of the specific configuration.
• XRF is used mainly for metallic coatings and selected nonmetallic systems. For typical paint or lacquer on metal, a magnetic or eddy-current gauge is usually selected according to the substrate. An XRF analyzer should not be assumed to replace such a gauge.

How to choose an analyzer

Our main coating-thickness model is the EDX 2000A — an automatic micro-area analyzer with a FAST-SDD detector, X/Y/Z motion, dual-laser positioning and a programmable stage for multi-point measurement. Consider another model for specific requirements:

• Smallest measuring spot — the collimator or optics define the measuring area; micro-areas of IC pins and wafers need positioning as in the EDXThick800.
• Part size and shape — complex shapes and edges (EDX-T30 with 3D motion), large boards and enclosures (EDX-PCB).
• Number of measurements — multi-point programs and an automatic stage shorten inspection series.
• Additional tasks — if you also need to screen for RoHS-restricted elements, measure light elements or check plating-bath composition, include those requirements when selecting the model and analytical program.

What to prepare for an enquiry

The layer structure and substrate, expected thickness range, smallest measuring area, part dimensions, number of measurements per shift and any standards or customer requirements. Representative samples and standards help establish whether the selected configuration meets the measurement needs.

Recommended techniques and instruments

• EDX 2000A — our main coating-thickness analyzer: automatic micro-area measurement, a FAST-SDD detector for multilayer coatings and multi-point measurement on a programmable stage.
• XRF spectrometers — benchtop coating-thickness analyzers, including EDX-T30 and EDXThick800 for micro-areas.
• Thick800A — automatic multi-point measurement and XY-stage positioning; also plating-bath composition analysis with a suitable configuration.
• EDX-PCB — large travel range for big PCB boards, enclosures and wafers.
• XRF accessories — preparing reference samples and bulk materials.