Characterization of coatings in the nano range

As coatings become thinner, the difficulty in determining their physical properties increases. The limits of previously tried and tested surface engineering techniques are encountered and results become unreliable. Available from ZwickRoell is an efficient solution to this problem in the form of a tester developed specifically for characterizing mechanical surface properties in the micro and nano ranges.

The thinner the electroplated coating, the more difficult it is for manufacturers to reach definitive conclusions regarding its physical properties. A typical example is the assessment of thin gold-cobalt layers on plug connectors, electrical contacts and edge connectors for printed circuit boards. In this case the layer thickness is nowadays only 600 to 800 nanometers. The usual way of determining Vickers hardness is to press a diamond pyramid indenter into the surface and measure the remaining hardness indentation optically. A definitive result is obtained if the indentation depth is equal to a maximum of one-tenth of the depth of the coating being measured. Applying this criterion to thin gold coatings produces indentation depths of only 60 nanometers. At this thickness the long-established Vickers test to ASTM B488-01 has reached its limits.

Leading supplier of galvanic precious metal electrolytes Umicore Galvanotechnik therefore uses ZwickRoell's 'Universal Nanonmechanical Tester' (UNAT) for hardness determination. This enables precise determination of indentation depths in the nano range in accordance with EN ISO 14577 ('Instrumented indentation test for hardness and materials parameters'); the measured values are converted to Vickers hardness by software for comparison purposes. UNAT was specifically designed for characterization of mechanical surface properties in the micro and nano ranges up to a maximum force of 2N. What makes this solution special is the use of two completely independent measuring-heads for the measurement of normal and of lateral force-displacement curves, with resolution in the nanometer range. This allows this instrument to be used as a tensile testing instrument and profilometer as well as for hardness, wear and scratch tests.