Layer thickness measurement
In addition to hardness and adhesive strength, layer thickness is a crucial factor for the quality of a coating. Deviations can lead to coating breakdown, which in the worst case can result in the failure of a component. Layer thickness measurement assists during monitoring for the required characteristics and makes visible irregularities, deviations from the nominal values and possible deficiencies in the coating.
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For what is layer thickness measurement used?
Layer thickness measurement is used for quality assurance in many industrial and technical applications and is a key method for determining the thickness of coatings and layers on various materials. This measurement is crucial for ensuring that the coatings provide the desired protection or functionality, whether corrosion resistance, protection against wear or optical quality. These methods can measure single coatings as well as multiple coating systems and cover layer thicknesses in the micrometre to nanometre range.
Quality Analysis – the right partner for layer thickness measurement
At Quality Analysis, we use state-of-the-art methods to analyse coatings and measure layer thicknesses down to the nanometre range. The high-resolution ZEISS Supra 40 field-emission scanning electron microscope can be used to assess coating structures in a plan view and layer systems in cross-section. Using our ZEISS Crossbeam 350 focused ion beam system, it is possible to examine delicate and extremely thin coating systems (nanometre range) and depict them at high resolution, completely free of artefacts and without the application of heat.
- Destructive and non-destructive methods for layer thickness measurement using the ZEISS Supra 40 SEM
- State-of-the art FIB-SEM microscopy using the ZEISS Crossbeam 350
- Both systems are equipped with EDX for undertaking an elemental analysis
Destructive and non-destructive methods
The methods for layer thickness measurement can be divided into two main categories: destructive methods and non-destructive methods. Both approaches have their advantages and disadvantages and are used depending on the application and measuring accuracy required.
Non-destructive methods measure layer thickness without damaging the sample and are ideal for regular quality control and real-time monitoring in production. The measurement is usually undertaken using external probes or sensors that act on the surface without direct physical degradation. These methods are often faster and less invasive, but may have limitations in terms of the layer thickness or substrate types they can measure.
Destructive methods, on the other hand, require physical alteration or destruction of the sample to measure the layer thickness. This action may involve cutting, grinding or milling the sample to make visible a cross-section. These methods often offer greater accuracy and permit detailed measurements, however they are only suitable if sample destruction is acceptable or where precise and detailed information is required in research applications.
Which methods are used for layer thickness measurement?
The test methods used are varied, which is why only a small selection of the methods relevant in practice is presented here.
Optical methods
Optical methods such as laser scanning microscopy or white-light interferometry utilise the characteristics of light to determine the thickness of layers. These methods are particularly suitable for very thin layers in the nanometre range, such as those found in the semiconductor industry or in optical coatings. Optical methods are often used for coatings on glass or ceramics.
Microscopic methods
Microscopic methods, such as the analysis of cross-sections under a light microscope or a scanning electron microscope permit the direct determination of the layer thickness. These methods offer high precision and are mainly used in research and development for analysing layered structures. They are suitable for a wide range of layer thicknesses from 1 µm to several millimetres, depending on the preparation method.
Energy-dispersive X-ray spectroscopy (EDX)
Energy-dispersive X-ray spectroscopy (EDX) is often used together with scanning electron microscopy (SEM) to determine the chemical composition of materials. With EDX, X-rays are generated when atoms in the layer are excited by electron beams. These X-rays help to determine the layer thickness and chemical composition, especially of very thin layers in the µm range. EDX is particularly useful in electronics manufacturing and material research.
X-ray fluorescence analysis
X-ray fluorescence analysis (XRF) measures the layer thickness by analysing X-rays emitted by the atoms in the layer when they are excited by external X-rays. This method is particularly suitable for measuring metallic multiple coating systems, such as those used in electronics manufacturing and in electroplating processes. XRF can determine layer thicknesses from a few nanometres to around 100 µm.
Magnetoinductive method
The magnetoinductive method is used to measure non-magnetic layers on ferromagnetic substrates. This method uses a probe to generate a magnetic field that is disrupted by the layer. The magnitude of this disruption depends on the thickness of the layer, which makes it possible to determine precisely the layer thickness. This method is often used in the automotive sector and in the construction industry to measure the thickness of paints, layers of plastic and electroplating on steel. It is suitable for layer thicknesses from 1 µm to around 1 mm and is compliant with standards such as DIN EN ISO 2178 and ASTM B499.
Eddy current method
In the eddy current method, a coil is supplied with a high-frequency alternating current to produce small electrical currents, known as eddy currents, in an electrically conductive material such as metal. A non-conductive layer, such as paint or an anodised coating, influences the eddy currents making it possible to measure the thickness of the non-conductive layer. This method is used for non-magnetic, electrically conductive substrates such as aluminium, particularly in aerospace and electronics manufacturing. It is suitable for layer thicknesses from 1 µm to around 500 µm and is compliant with standards such as DIN EN ISO 2360 and ASTM B244.
Applications for layer thickness measurement
Automotive
In the automotive industry, layer thickness measurement is an indispensable tool for the quality control of paint finishes, corrosion protection coatings and electroplating. Precise measurement ensures that the coatings are applied evenly and provide the required protection. This aspect is crucial for the durability of vehicle parts and meeting the high aesthetic and functional standards required in this sector.
Aerospace industry
In the aerospace industry, layer thickness measurement plays a decisive role in the safety and performance of aircraft and spacecraft. Coatings must be able to withstand extreme environmental conditions without significantly increasing weight. Accurate layer thickness measurement ensures that these coatings maintain the structural integrity and corrosion resistance of components under extreme conditions.
Plastics industry
In the plastics industry, layer thickness measurement is used both to check the thickness of coatings on plastic parts and to monitor the wall thickness of plastic products. This task is particularly important for packaging to ensure material efficiency and for functional coatings that offer special characteristics such as scratch resistance or conductivity. The measurement helps to ensure product quality and compliance with industrial standards.
Electronics manufacturing
Layer thickness measurement in microelectronics and semiconductors is used to check conductor tracks, layers of insulation and protective coatings on printed circuit boards. Precise measurements ensure the functionality and reliability of the electronic components. Consistent, precisely measured layer thickness is crucial for avoiding short circuits, optimising conductivity and maximising the service life of electronic components.
Lithium-ion batteries
With precise sectional images, different coatings and materials within the battery cells can be analysed. These images permit, among other things, the evaluation of layer thicknesses and the detection of signs of degradation.
In summary: layer thickness measurement
Layer thickness measurement acquires the thickness of coatings on various materials and plays a central role in quality control in numerous sectors. Different methods are available: non-destructive methods, which leave the sample unchanged, as well as destructive methods, which permit precise measurements by physically damaging the sample.
