Offline capacitive system measures thickness of electrically conductive film

Precision sensor manufacturer Micro-Epsilon has extended its capaNCDT range of high precision capacitive measurement systems with a new high-precision system for fast, offline thickness measurement of very thin electrically conductive film such as that used in production of batteries.

A particular challenge of measuring thin conductive films or foils, like copper and aluminium in bare and coated forms, is that it is easily torn or crumpled when handled; especially when it is ‘wafer’ thin at only around 10 micron thick. Traditional methods of measurement for quality assurance involve removing a sample from the production roll and using a contact micrometer to measure the thickness. The tight tolerances and variability from operator to operator make performing this measurement difficult.

The capaNCDT TFG6220 thickness measurement system solves the handling issue through an innovative use of a vacuum bed and patented calibration of twin capacitive sensors measuring ‘through’ the vacuum bed to the foil. The TFG6220 consists of a measuring bracket including two capacitive sensors, a capaNCDT controller and a specially developed vacuum bed. Automatic smoothing of the measuring object (foil) is achieved using an externally connected vacuum pump (not supplied). In this way, measurements can be performed with the greatest possible precision with single micrometer precision.

The thickness is calculated by the resulting offset between the two sensors, including the bed. A permanently installed capacitive sensor in the upper area of the measuring bracket measures the distance to the measuring object. The vacuum bed provides a referencing surface over which the object to be measured is sucked in and clamped by means of an applied vacuum. The capacitive sensor in the lower area measures on the measuring insert and compensates for the mechanical offset of the contact surface.

The capaNCDT TFG6220 is used for quality inspection in the form of offline random samples. The system is pre-assembled ready for operation and enables a quick start. The system measures film thicknesses of <1mm at a resolution of 10nm and with a high repeatability of 1µm. An integrated measuring insert enables simple calibration before thickness measurements are carried out. The system also provides a web interface for intuitive setup and display of measured values, with no software installation required.