Polymer Die Attach Viscoelastic Relaxation Dynamics in Precision MEMS Accelerometers
Viscoelastic relaxation in polymer die attach causes time-dependent strain transfer to MEMS proof masses, driving long-term zero-g offset drift.
Stress Transfer
Force Transmission
The mechanical transmission of forces from an outer protective package to an internal sensitive silicon die occurs through intervening adhesive and substrate layers. In sensor assemblies, stress transfer determines how much of the external mounting strain reaches the active sensing element. High transmission can lead to unwanted offset shifts and mechanical failures.
Package Interface
Transducers measuring pressure or acceleration must be isolated from the expansion and contraction of their outer housings. Reducing the stress transfer requires the use of compliant adhesives with a low shear modulus. If the adhesive layer is too thin or too stiff, it transmits a larger fraction of the package-level deformation to the silicon die.
Sensor Drift
Micro-sensor calibration relies on the long-term stability of the mechanical interface. Over time, changes in the stress transfer due to adhesive aging or moisture absorption cause the sensor output to drift. Minimizing this effect is a primary goal in the design of high-accuracy MEMS packages destined for automotive and aerospace environments, where temperature extremes and mechanical vibrations are continuously present.
Verification Metric
Finite element analysis modeling estimates the strain distribution across the bonded assembly. Engineers verify the actual stress transfer by measuring the sensor’s zero-point output before and after applying a controlled mechanical load to the package housing.