Opportunities and challenges of printed force sensors on 3D substrates

The demand for printed sensors is constantly growing over the last few years. Of special importance for various industrial applications are force sensors. They measure stress or bending along one or more axis. Conventional sensors need a time consuming gluing process to mount the sensor onto the substrate. The force sensors from binder are printed directly onto the component where measuring is needed.
For three dimensional or structured substrates pad printing is used. The challenge of this printing process is to apply a defined electrical resistor with high precision and reproducibility. The resistance can be adapted to typical conventional sensor values of 350 or 1kΩ. A typical line width is 80- 100 µm and a layer thickness of 8-15 µm. Normally a full bridge design is printed in order to compensate for thermal drifts. Different designs allow the customer to measure bending of the substrate, stress along an axis or torque. Typical K factors are between 2- 4 depending on the composition of the printing paste.
To connect the sensor with the analysis unit a great variety of connection methods can be applied. A simple solution is conductive glue. Sensors on a copper basis can also be connected via a low temperature soldering process.