Assembly Deviation
High-temperature soldering processes generate mechanical stress in surface-mount components, leading to altered electrical characteristics. This thermal effect, known as reflow offset shift, modifies the zero-point calibration of precision sensors after they are mounted on a printed circuit board. The shift occurs due to the different rates of thermal contraction between the silicon die, the plastic packaging and the fiberglass board.
It is a common challenge in the production of high-precision accelerometers.
Stress Mechanism
As the solder cools and solidifies, it locks the sensor package into a strained state. The physical strain is transferred directly through the package leads to the silicon sensing element. This mechanical tension alters the piezo-resistive properties of the silicon, changing the sensor baseline.
Mitigation Strategy
Designers reduce this stress by using symmetrical pad layouts and keeping the sensors away from board edges or mounting holes. Thin, flexible printed circuit boards or slot cuts around the sensor also isolate the component from external board bending. These physical methods reduce the magnitude of the shift.
Calibration Restoration
Since the solder-induced shift is permanent, the factory calibration performed before assembly is no longer fully accurate. Post-assembly testing allows systems to measure the offset shift and store new calibration values in the microcontroller memory. This step restores the accuracy of the assembled device.
