Oil Cavity Volumetric Expansion Mitigation in Piezoresistive Transducers
Minimizing fluid volume below five microliters and matching diaphragm spring rate eliminates thermal zero shift in isolated piezoresistive pressure cells.
Fused Silica Filler
Inorganic Compound
A high-purity crystalline powder is added to polymer encapsulants to reduce their coefficient of thermal expansion. Incorporating fused silica filler into the potting compound protects delicate electronic circuits from mechanical stress during thermal cycling. This addition improves the physical stability of the sensor housing and protects integrated wire bonds.
Thermal Expansion
Potting resins and silicon chips expand at different rates when heated, which can cause micro-cracks or bond wire detachment. Adding the filler lowers the expansion rate of the resin, bringing it closer to the expansion rate of the metal and silicon components. This closer match reduces the shear stresses at the material interfaces, ensuring the sensor can survive thousands of thermal cycles.
Viscosity Control
The concentration of the powder in the resin must be carefully controlled to maintain the proper flow characteristics during the pouring process. If the mixture is too thick, it will not fill all the gaps around the sensing element, leaving air pockets that can fail under high pressure. On the other hand, if it is too thin, the filler can settle to the bottom, causing uneven mechanical properties.
Signal Stability
By minimizing the mechanical stresses that the potting compound exerts on the sensing chip, the filler helps prevent sensor drift. Stress on the chip can alter its electrical resistance, causing a false pressure reading that cannot be easily calibrated out. Consequently, using this composite material ensures that the long-term accuracy of the transmitter remains within its specified limits in challenging industrial environments, reducing the need for frequent manual re-zeroing.