B5.3 - Polymer Based Packaging of Silicon Pressure Sensors in the Oral Cavity

SENSOR+TEST Conferences 2011
2011-06-07 - 2011-06-09
Proceedings SENSOR 2011
B5 - Sensor-Packaging
I. Stöhr, R. Werthschützky - Technische Universität Darmstadt (Germany)
303 - 308


In this paper we describe a novel polymer based packaging of silicon pressure sensors for use in the oral cavity. The sensors are part of a wireless sensor system for measuring the spatially resolved pressure of the tongue against the hard palate. To minimize the disturbance of the patient during measurement one key requirement is a minimal thickness of the measuring system. For this and other reasons commercially available packaged sensors are not suitable for this application.

Therefore a novel packaging based on the smallest commercially available piezoresistive absolute pressure sensors (SM 5108 from Silicon Microstructures) is designed.

To comply with requirements for mounting the sensors in an upper plate made of thermoplast, we choose a two-stage packaging. First stage of the packaging is the protection of the 25 um Al bond wires. We achieve this by applying a hard (shore D 80) UV-curing epoxy resin (Panacol- Elosol, Vitralit 1605) around the sensor an under the bond wires. This step spares the sensors membrane, so mainly offset is influenced.

In this state the sensors are mounted in the custom-built upper plate. The second and final step of packaging is done with a soft and biocompatible material to allow for a good pressure transmission and to assure a smooth surface. For this packaging step usability of many biocompatible polymers was investigated. Best suited from its technical specifications and from usability in the packaging process is a soft (shore A 55) UV-curing acrylic urethane (Dymax, Ultra Light-Weld 1165-M).

The sensors are tested for offset, sensitivity, nonlinearity and hysteresis error prior to and after packaging. Due to later deployment of the sensors in the oral cavity, the resistance to moisture is also investigated.