Test & measurement
MEASUREMENT OF THIN LAYERS F ROM 1 µm
The interferoMETER IMS5200-TH from Micro- Epsilon enables thickness measurement of extremely thin layers from 1 to 100 µm. With extremely high resolution and measuring rate, dynamic measurements can be ensured with high precision.
Multi-peak thickness measurement is used when several layers are present. Up to five layers can be measured simultaneously, for example, to calculate the distance between a glass and the carrier plate in display glass production (i.e. air gap). Interference at different interfaces produces several reflection signals (peaks) in the signal, from which the thickness of individual layers can be determined. Based on the measurement, the controller outputs up to five thickness values. These are obtained with a high measurement stability regardless of the layer’s position within the transparent object.
CHECKING THE COATING OF BEVERAGE CARTONS
re-reference themselves. For example, distance profiles of moving measurement targets can be generated with high precision and reliability. Unlike white light interferometers,
conventional interferometers use highly coherent, monochromatic light in which the waves are in phase. They can only measure relatively and require a preset reference. This method is tedious and costs the user valuable time and resources. With white light interferometers from Micro- Epsilon, distances and thicknesses can be measured absolutely and with the highest precision. This measuring method also makes it easy to measure fast-moving objects, which opens up a wide range of applications for inline inspection such as distance, multi-peak or thickness measurements of different measuring objects. The user achieves maximum signal stability for industrial processes, semiconductor production, machine building and laboratory testing.
Another example where maximum precision is required is in the monitoring of coating thickness in the packaging industry. Here, the white light interferometer tests the coating process of beverage cartons, which are made up of several thin layers of paper fibre, plastic and aluminium. To ensure that the carton remains tight, hygienic and durable, the layer thicknesses must be uniform.
The interferoMETER IMS5200-TH checks this uniformity by emitting broadband light onto the surface and evaluating the reflected signals of each individual layer and the associated layer boundaries. By evaluating the position of various interference peaks using the multi-peak function, the thickness of each individual layer can be precisely determined.
White light interferometry is perfectly suited to this application as it is non-contact and non-destructive. Several layers can be detected simultaneously over large surface areas. This allows defective areas, uneven layers or air pockets in beverage cartons to be detected at an
early stage. White light interferometers enable inline quality control, which avoids rejects and increases the quality of the end product.
MONITORING THE COATING THICKNESS OF METALS
Another application in which the measuring principle of white light interferometry is used is inspecting the coating thickness of metals. This is important because layers of varnish protect components from corrosion, improve their appearance and increase their mechanical resistance. In the automotive, construction and household appliance industries in particular, it is crucial that varnishes are not applied too thinly (insufficient protection) or too thickly (waste of material, optical defects).
The interferoMETER IMS5200-TH enables non-destructive measurement of the varnish layer thickness during the coating process. It emits broadband light onto the coated metal surface, creating reflections both on the coated surface and at the interface with the metal. The interferometer measures the interference between the reflections on the varnish surface and the underlying metal layer. The exact varnish thickness is determined from the distance between the signals, which works even with very thin transparent layers. This allows the varnish density to be checked inline and non-destructively to ensure consistent coating quality.
This method offers considerable advantages over other measuring methods: it is non-contact, highly precise and allows multi-layered varnish structures to be analysed. White light interferometry is suitable for both random checks and for inline quality monitoring in the production process, for example, when coating car bodies or testing metallic construction profiles.
AIR GAP MEASUREMENT OF GLASS MASKS AND WAFERS One of the many applications of the interferoMETER IMS5200-TH is measuring the air gap of glass wafers and masks in semiconductor production. Here, the polychromatic light is directed vertically onto the glass and wafer. Part of the light is reflected on the underside of the glass, another part on the wafer. Between them is an air gap with a thickness of several µm. The two light beams overlap and create an interference pattern that depends on the slit size. This enables non-contact detection of whether the wafer is correctly positioned or whether the optimum distance between the mask and wafer for the process is being maintained. With this measuring method, the company significantly increases the quality of products in the semiconductor industry.
Micro-Epsilon
www.micro-epsilon.co.uk Instrumentation Monthly June 2026 45
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