DIN standard for the measurement of the thickness of polymer layers

From motion sensors to smartphones – many everyday products increasingly contain parts which are made of polymer materials. Their dimensions can be deter-mined optically or tactically – however, with systematic deviations which are observed when measuring the thickness of transparent materials by means of optical measuring methods, and also in the stylus measurement of coatings on hard substrates. In tactile methods, the main influencing factors are the probing force and the tip radius. With viscous materials whose mechanical properties are timedependent, also different scanning speeds affect the level of the systematic deviations.

PTB has therefore, in cooperation with other European national metrology in-stitutes, developed a method for correcting these systematic errors, which has been standardized in DIN 32567. In this standard, the main influencing factors are shown for tactile and optical measurements, and methods for the estimation, correction and reduction of systematic errors are described. In optical measuring instruments, the main influencing factors are the effective numerical aperture of the optical system used, the position of the reflection plane in volume-scattering materials, and the phase shift at boundary surfaces upon reflection. The standard describes, for white light microscopes and fo-cusing instruments, methods for deter-mining these values and the correction of systematic errors on the basis of new calibration standards.

The research took place within the international MeProVisc project (Dynamic mechanical properties and long-term deformation behaviour of viscous materials) within the European Metrology Research Programme EMRP. Result of the project is a comparison of creep measurements with the dynamic instrumented indentation for viscous materials. The standardization of these methods is planned in part 5 of the nanoindentation standard ISO 14577. In addition, international standardization is planned in the field relating to ISO/TC213.