Mechanical Strain
Mechanical forces originating from mismatched thermal expansion coefficients between metal alloy frames and encapsulation molding compounds alter sensor die geometry. Leadframe stress induces strain fields in piezoresistive and capacitive sensing elements, shifting zero-point offsets and sensitivity factors. The phenomenon governs long-term parameter stability in surface-mount IC packaged sensors.
Strain magnitude depends on copper alloy selection, die attach pad geometry, and molding compound curing cycles. Boundary limits occur where physical plastic deformation of the frame permanent alters die attachment alignment.
Package Expansion
Temperature changes cause differential expansion between the metal leadframe and surrounding epoxy mold compound. Forces transmit through the die attach layer directly into the active silicon substrate. Piezoresistive bridge elements record strain as apparent pressure or acceleration signals.
Asymmetric leadframe design creates directional stress vectors that distort planar sensor geometry across thermal cycles.
Stress Relaxation
Epoxy curing induces residual compressive forces across the silicon die.
Compensation Boundary
Factory calibration compensates for predictable thermal strain patterns via multi-order polynomial equations. Unpredictable stress relaxation over time causes post-calibration zero-drift in high-precision sensor packages. Package design guidelines recommend stress-isolation slots and low-modulus die attach materials to decouple mechanical forces.
Verification routines quantify residual stress by measuring offset shifts before and after thermal shock exposure.
