Calculating Burn in Duration to Attenuate Non Linear Sensor Aging
Calculate sensor burn-in time by dividing equivalent operating hours at the infant drift inflection point by the temperature-derived Arrhenius acceleration factor.
Secondary Cross Linking
Polymer Network
Post cure chemical reactions in polymeric encapsulation materials alter the structural density and mechanical stiffness of thermosetting resins over extended operational periods. During thermal exposure in field operations, secondary cross linking drives the formation of additional covalent bonds between unreacted polymer chains within die attach epoxies and potting compounds. Continuous reaction increases glass transition temperature and volumetric shrinkage of sensor packaging materials.
The scope of this chemical process applies to cured thermoset polymers subjected to elevated operational or ambient temperatures.
Kinetic Reaction
Initial curing cycles leave residual reactive functional groups trapped within the vitrified polymer matrix due to steric hindrance and reduced molecular mobility. During sustained thermal exposure, secondary cross linking resumes as thermal energy increases polymer chain mobility, allowing remaining unreacted monomer groups to combine. Continuous polymerization increases resin density and induces volumetric shrinkage, generating localized compressive stresses on embedded silicon sensor dies.
Strain gauge and piezoresistive bridge outputs shift in response to this evolving mechanical pressure, manifesting as zero offset drift over operational time. Differential scanning calorimetry monitors reaction kinetics by measuring exotherm energy released during elevated temperature exposure. Controlling thermal cure schedules during assembly minimizes the concentration of unreacted species that drive long term polymer structural evolution.
Mechanical Stiffness
Increases in cross link density elevate the elastic modulus of encapsulation epoxies, altering transducer mechanical resonance and damping properties. Glass transition temperature shifts caused by continuous network formation change the thermal expansion coefficient across normal operational temperature ranges. Altered physical properties transmit ambient thermal expansion stresses directly to sensitive transducer elements, causing sensitivity drift.
Reaction Ceiling
Chemical network formation terminates once all available functional groups react or when operating temperatures remain below the threshold required to mobilize polymer chains. Beyond this chemical completion point, secondary cross linking stops and packaging mechanical properties stabilize.