Internal Bandgap Voltage Error Reduction in High Gradient Layouts
Internal bandgap voltage errors in high gradient layouts are reduced by common-centroid matching, thermal isolation trenching, and package stress mitigation.
Mold Compound Creep
Polymer Deformation
Viscoelastic materials used for integrated circuit encapsulation undergo slow, time-dependent plastic deformation when subjected to continuous mechanical stress. The occurrence of mold compound creep leads to a gradual shift in the baseline package stress exerted on the silicon die, which can affect the long-term stability of precision analog sensors.
Sensor Drift
This gradual shift in stress modifies the electrical characteristics of the underlying silicon through the piezo-junction and piezoresistive effects. In high-resolution pressure or temperature sensors, this is observed as a slow drift in the calibrated output over hundreds of operating hours. The change is irreversible once the polymer chains have rearranged.
Environmental Stress
Elevated temperatures and high humidity accelerate the rate of creep by increasing the mobility of the polymer chains. When moisture is absorbed into the mold compound, it acts as a plasticizer, which lowers the glass transition temperature of the material. This makes the package much more susceptible to deformation under the internal stresses generated during PCB mounting.
Design engineers select high-grade epoxy compounds with low moisture absorption to mitigate these effects.
Testing Methodology
Long-term stability is evaluated using high-temperature operating life tests and temperature cycling. Drift is monitored at regular intervals during the tests to confirm that the sensor output remains within the specified lifetime accuracy limits. These tests are conducted over thousands of hours to simulate years of field operation.