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Abstract

Two simple low-cost thick-film force sensor designs are optimised, characterised and tested in this work, combining calculations of sensor element and joint stresses, joint strength characterisation and measurement of complete sensors. All sensors are based on standard hybrid substrates. Our results show that a single sensor geometry cannot cover such a wide range of forces in an optimal way. For small forces (100 mN to ca. 2 N), simple cantilever force sensors are an excellent solution, achieving reasonable precision with a very simple design and compatibility with an SMD (surface mount device) assembly process with solder or conductive glue. Characterisation of solder joint strength shows that such joints can reliably withstand the bending moments resulting form the loading of the cantilever sensor up to ca. 2 N. Above this force, both solder joint and cantilever strength become critical in the cantilever design. Therefore, a 3-point or 4-point bending beam geometry must be selected, thereby extending the force range to ca. 100 N.

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