Barrier Material
Protective potting compounds isolate sensitive electronic circuits and micro-electromechanical systems from environmental moisture, dust or chemical contaminants. For high-reliability sensors, polymeric encapsulants are formulated to provide high dielectric strength and structural support. This protective barrier must prevent the ingress of water while minimizing mechanical stress on the enclosed transducer by utilizing soft elastomer formulations that can absorb mechanical strains and thermal shock.
Moisture Permeation
No synthetic resin is completely impermeable to atmospheric moisture over long operating lives. High-density silicones or epoxies act as polymeric encapsulants that slow down the diffusion rate, delaying the arrival of water molecules at the sensor surface. This moisture ingress can cause corrosion of wire bonds or shift the parasitic capacitance of the circuit.
Stress Interaction
The mismatch in the coefficient of thermal expansion between the potting resin and the substrate creates thermal stress. During thermal cycling, polymeric encapsulants expand and contract, which can apply force to fragile silicon dies or microelectronic tracks. This mechanical strain can lead to shifts in the sensor output.
Material Qualification
Laboratories evaluate these protective resins by testing their adhesion strength and moisture absorption rates under highly accelerated stress test conditions. Formulators measure the glass transition temperature of the polymer to ensure that it remains outside the specified operating temperature range of the instrument. Selecting a material with the correct elasticity and thermal properties is essential for long-term stability in harsh field environments.
