Material Property
Mathematical distributions of relaxation times that describe the time-dependent mechanical behavior of polymers used in sensor packaging define how stress relaxes over time. The viscoelastic relaxation spectrum of an adhesive determines the long-term drift characteristics of mounted sensing elements, such as silicon strain gauges or optical fiber coils. This profile is critical for predicting how mounting stress changes after assembly and thermal cycling.
Stress Migration
Internal mechanical stress from assembly or thermal expansion decays at different rates depending on the polymer’s molecular weight and cross-linking density. This relaxation causes the zero-point calibration of the sensor to drift over time as the physical forces acting on the sensing element change. Characterizing this spectrum allows engineers to predict the long-term stability of the sensor.
Experimental Analysis
Measuring this behavior requires dynamic mechanical analysis where polymer samples are subjected to oscillating stress at different frequencies and temperatures. The resulting storage and loss modulus data are used to construct a master curve that defines the relaxation times of the material. This characterization is performed during the design phase to select the most stable potting compounds.
Thermal Conditioning
Pre-baking the sensor assemblies at elevated temperatures accelerates the relaxation process to stabilize the mechanical structure before final calibration.
