Isolating Micro-Machined Die Packaging Stress during Automated Thermal Calibration
Automated thermal calibration must isolate packaging thermo-mechanical stress shifts from intrinsic silicon sensor signals using real-time compensation.
Stress Bridge Extraction
Parameter Identification
Digital signal processing techniques isolate the mechanical influence of the package from the sensor output. This stress bridge extraction uses specialized resistor layouts to measure the deformation of the silicon surface. It allows the system to compensate for errors caused by mounting or encapsulation.
Four Resistors
Four resistive elements are typically arranged in a Wheatstone bridge configuration to maximize sensitivity to surface strain. Two resistors are oriented to increase in value under tension while the other two decrease. The resulting differential voltage provides a measure of the package-induced load without requiring an external force gauge.
Logic Compensation
Algorithms use the measured strain value to adjust the primary sensor signal in real time. Because the package stress changes with temperature and aging, the stress bridge extraction must run continuously during the life of the device. This active correction maintains the accuracy of the transducer even when the external housing warps or settles.
Calibration Verification
Calibration involves applying a known mechanical load to the package while monitoring the output of the internal bridge. The relationship between the applied force and the extracted voltage shift is characterized across the full operating range. A successful stress bridge extraction routine reduces the sensitivity to board-level assembly stresses by an order of magnitude.