Factors driving circuit reliability

Reliability depends on these factors:

1. Components: quality, tolerances, failure rate (λ), the number of parts (system failure rate is the sum of part rates for a series system; fewer parts means higher reliability) and derating.
2. Operating environment: temperature (failure rate roughly doubles for every 10 degrees C rise), humidity, vibration, shock, dust, corrosion, radiation.
3. Electrical stress: voltage, current and power overload, transients, ESD, EMI, power supply quality.
4. Design quality: simple design, worst-case tolerance analysis, protection circuits, redundancy, thermal management and good layout.
5. Manufacturing: soldering quality, assembly process, testing, burn-in and quality control.
6. Software and firmware: bugs, robustness (for microprocessor systems).
7. Maintenance and use: preventive maintenance, correct use and operator errors.

Reliability is quantified as R(t) = e^(-λt), with MTBF = 1/λ.