Rieger Metallveredlung Blog – Layer thickness measurement - An essential quality factor

Explanation of a protective layer

25.01.2022 - Blog

Layer thickness measurement

An essential quality factor

The most frequently specified criterion for the quality of the galvanic layers is the layer thickness. Therefore, the measurement of the layer thickness is an essential quality factor.

But before we go into these, it must first be clear what a layer actually is.

A layer is the volume of a solid material enclosed by the two interfaces between the gaseous, liquid or solid environment and the layer, as well as the interface between the layer and the substrate (= carrier or base material). The layer thickness is defined as the distance between the two interfaces.

The layer thickness measurement methods can be divided into destructive and non-destructive methods. The application of the layer thickness measurement method also depends on the layer to be measured and the base material.

1. Non-destructive methods

The eddy current process is used for anodised layers (anodized layers on aluminium). This is a non-destructive measuring method. The eddy currents generated in the base material by a high-frequency coil current change the impedance of the coil. The change in impedance, which depends on the distance between the probe and the base material, is used to measure the layer thickness. X-ray fluorescence analysis (also known as X-ray) is used as a non-destructive testing method for the applied layers of copper, nickel, chrome and tin. The method is based on the fact that the atoms in a material sample are excited by the primary X-rays to emit secondary X-rays. The resulting characteristic fluorescence radiation has an intensity that differs from the layer thickness and is used to determine the layer thickness.

2. Destructive Procedures

When determining the layer thickness with the help of a section, the test piece is cut perpendicularly to the layer. The layer is then directly measured optically using a microscope. This is a destructive and very time consuming and costly process.