Parameter Stability
Electrical characteristics of active transistors mounted on printed circuit assemblies must remain constant to ensure correct circuit operation over time. This slow change in the gate voltage required to activate a semiconductor channel, known as threshold voltage drift, occurs due to the trapping of charges at the gate oxide interface during operation. It alters the switching behavior of the transistor and can cause timing errors in digital circuits.
Circuit designers must select devices with minimal drift to guarantee long-term system reliability.
Stress Influence
High operating temperatures and elevated voltage stresses accelerate the trapping of carriers within the dielectric layers of the transistor. This degradation is further exacerbated by the presence of moisture or chemical contaminants from the printed circuit board assembly process. When the threshold voltage shifts beyond a specific design limit, the system fails to recognize digital high or low signals correctly.
Designing adequate thermal heat sinks and ensuring thorough board cleaning reduce the impact of this degradation.
Testing Assessment
Parametric measurements of the circuit board before and after extended stress tests are used to quantify the level of gate voltage change. This testing confirms that the component parameters remain within the acceptable margins specified by the system design. Devices with shift values exceeding the drift budget are replaced to prevent early failure.
