The 'Film-inspect' sensor, developed by the Fraunhofer Institute for Physical Measurement Techniques IPM in cooperation with plasma system specialist Plasma Electronic, uses infrared measurement technology to detect thin coatings with a thickness of less than 10 nm to 200 nm inline. Plasma coatings are applied to plastic packaging, for example, to protect food. Here, a diffusion-tight layer - made of silicon oxide (SiOx) or aluminum oxide (AlOx), for example - protects products such as coffee or nuts from harmful external influences or loss of aroma. However, comparable thin films are also used in completely different areas - for example in pharmaceutical products, in household appliances, in fuel cells or on vehicle parts. They can be used to optimize wettability, adhesion properties or surface chemistry, or to protect against corrosion.

The sensor developed by Fraunhofer IPM enables process-integrated 100% inspection of individual parts in the production cycle - even for three-dimensionally shaped, complex surfaces such as those typically used for packaging. The researchers use the infrared optical properties of the coatings for quality control: the chemical bond between atoms can be resonantly excited by infrared light of the appropriate wavelength. The coating thickness can be determined from the intensity of the reflected light. The choice of wavelength depends on the coating material and can be configured to suit the specific material. The compact sensor is only around 20 × 40 × 80 mm3 in size and can therefore be easily integrated into the production line. Several sensors can be coupled in production processes and communicate with the system control via Profinet and OPC-UA. A USB interface and evaluation software are available for simpler applications with individual sensors.

An array of eight sensors was successfully integrated and tested in a plasma coating system at project partner Plasma Electronic. In addition to the application shown there in a batch process, Film-Inspect can also be used in continuous processes. It is also possible to monitor a roll-to-roll coating system.

The research and development work was carried out as part of the 'O-Kuba - Optical process control for ultra-thin barrier coatings' project. O-Kuba is funded by the Baden-Württemberg Ministry of Economic Affairs, Labor and Tourism as part of the Invest BW - Innovation II funding program.