IEC 62380 Reliability Prediction
The following are paraphrased key concepts of the IEC 62380 electronic reliability prediction standard. International Electrotechnical Commission
IEC 62380 models take into account the influence of the environment as a significant factor in the predicted reliability. The thermal cycling seen by components during the variety of "mission profiles" undergone by the equipment, replace the difficult to evaluate environment factor of other standards. These models support permanent working, on/off cycling and dormant applications.
Failure rate related to component soldering/mounting is included in component failure rate.
The reliability data contained in the IEC 62380 handbook is taken from field data concerning electronic equipment operating in these environments:
- Ground; stationary; weather protected (equipment for stationary use on the ground in weather protected locations, operating permanently or otherwise).
- Ground; stationary; non-weather protected (equipment for stationary use on the ground in non-weather protected locations).
- Airborne, Inhabited, Cargo (equipment used in a aircraft, benign conditions).
- Ground; non stationary; moderate (equipment for non-stationary use on the ground in moderate conditions of use).
IEC 62380 does not support parts count only approach, because mission profiles are needed to calculate credible failure rate results.
For the vast majority electronic components, the wear-out period is very far out from the periods of use or lifetime. However, there are cases where the occurrence of wear-out failures should be taken into account:
- Wear-out mechanisms may give rise to systematic failures after too short a period of time; electro-migration in active components is an example.
- Wear-out period is not far into the future. This is called life expectancy, and is subject to influencing factors. Relays, aluminum capacitors (with non-solid electrolyte), laser diodes, optocouplers, power transistors in cyclic operation, connectors and switches and keyboards are examples.
It is important to ensure that the life expectancy given by the handbook is consistent with the intended use.
Non-intrinsic failures due to electrical overloads
The reliability of the components used in equipment located "at the heart" of a system, is significantly better than that of the components located at the periphery (connected to the external environment). This difference is due to residual overloads, since the equipment is assumed adequately protected.
A utilization factor is included to take into account non-intrinsic residual failures due to the electrical environment of active components.
Integrated circuit production date influence
The reliability growth of components since the 1990's has slowed, unlike that of the 1970's and the 1980's. Particularly true for integrated circuits, this can be attributed to many factors to the credit of the manufacturers. However, the integration density for integrated circuits continues to grow at the same rate as in the past, at constant reliability figure. Taking into account MOORE's law, it is necessary to know the manufacturing year to calculate the failure rate of integrated circuits.
A mission profile has to be decomposed in several working phases, on the basis of a typical year of use. The following phases can be used:
On/off working phases with various average outside temperatures the equipment is exposed to.
Permanent-working phases with various average outside temperature changes the equipment is exposed to.
Storage or dormant phases mode with various average outside temperature changes the equipment is exposed to.
The time quantity, is the number of calendar hours of the installed equipment, including working as well as storage or dormant hours.
Mission profile parameters:
- Average outside ambient temperature surrounding the equipment, during a phase of the mission profile
- Average ambient temperature of the printed circuit board (PCB) near the components during a phase of the mission profile
- Annual ratio of times for the PCB, in permanent working mode, and at the temperature
- Total annual ratio of time for the PCB, in permanent working mode
- Total annual ratio of time for the PCB, in non working or storage/dormant modes
- Annual number of thermal cycles seen by the components of the PCB, corresponding to the phase of the mission profile with an average temperature change
- Average change of the thermal variation seen by the components of the PCB, corresponding to a phase of the mission profile
For a storage or permanent working phase, the average of the difference between maximal and minimal temperatures per cycle experienced by the equipment on the considered phase is used. If this value is below 3°C, it is assumed that the temperature change = 0.
For majority of the applications, a day is corresponding to one cycle, and temperature change?is corresponding to the annual daily mean of the daylight / night temperature difference seen by the equipment.
A daily temperature variation is always superimposed to a permanent working phase according to the environment of the equipment. For an on/off working this daily variation is also applied on the equipment. However, only the greater temperature variation has to be taken into account, because the highest one has the main effect on the reliability of the device packages and on the mounting process.