Surface Finishing Tutorial

#223 Plating Thickness Measurement by Eddy Current

Category : Electroplating

January 8, 2016

(1)Measurement principle

When you apply a high-frequency current to the coiled probe and place the probe against the plating surface, a high-frequency eddy current will be generated in the plating surface area. Determine the plating thickness by measuring this eddy current.

(2)Operation

	1.	Prepare a substrate in the same shape as the plating sample as well as a standard sample with the known thickness.
	2.	The surface roughness of the substrate must be same as that of a plating sample.
	3.	Place the probe on the substrate. Then, set the thickness indicator scale to zero (zero calibration).
	4.	Next, set the standard sample onto the substrate. Place the probe and calibrate the indicator scale according to the standard sample thickness (sensitivity calibration).
	5.	Repeat steps 3 and 4 three times (these steps are referred to as calibration). After improving the reproducibility, start the measurement.

(3)Operational precaution

	1.	Note that a high-frequency eddy current fluctuates considerably according to plating/basis metal properties, including electric conductivity, thickness, shape, and surface conditions.
	2.	Without a sufficient difference in electric conductivity between the substrate and plating, the measurement fails or accuracy is significantly reduced.
	3.	Perform a calibration at every measurement. The item used for calibration must be made of the same materials, in the same shape, and have the same surface conditions as the measurement sample. The calibration will not be accurate if the shape of the sample, such as plate and round bar, is different, even if they are made of the same materials.
	4.	Factors that could affect the measurement accuracy include the following: plating thickness, magnetic property of basis metal, shape/thickness of basis metal, surface roughness, and edge effect.

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