Silicon Sensor Die Packaging Stress Decay Mechanics
Packaging stress decay in silicon sensor dies causes continuous zero-point drift that requires thermal preconditioning bakes to stabilize long-term offset accuracy.
Thermal Preconditioning Bake
Outgassing Management
Heating components before they are final assembled or calibrated helps to remove volatile substances from the materials. The thermal preconditioning bake ensures that moisture and trapped gases are driven out of the polymers and adhesives used in the sensor package. This step prevents the buildup of internal pressure or the contamination of sensitive surfaces during the life of the device.
Moisture Removal
Water molecules trapped within the plastic can cause swelling and internal stress that lead to measurement errors. By holding the parts at a high temperature for several hours, these molecules are released and the material reaches a dry state. This is especially important for sensors that operate in vacuum or high purity environments.
Residual Stress
Heat allows for the relaxation of the internal tensions. Without this bake, the parts might warp. Providing a controlled environment for this settling ensures that the final assembly is as stable as possible from the start.
Process Sequence
Placement of the bake within the manufacturing flow is essential for achieving the best results. It usually occurs after the initial assembly but before the final calibration to ensure that any changes in the material are captured during the zeroing process. Verification involves measuring the mass of the parts before and after the bake to confirm that the volatiles have been removed and that the material properties have stabilized.