Creating a sensible derating system

Derating is the intentional reduction of applied stress on a component in order to assure reliability. A series of derating guides have been issued by the U.S. military services as well as other groups. Each guide, by itself, is not complete. Entries in guides are typically "rules of thumb" such as "derate at 70% of maximum power up to 70 degC and then derate linearly to zero by 100 degC". This rule may work for most of the cases of a certain component in a common design practice. Derating guidelines should also work for the balance of the remaining applications. The remaining cases represent the challenge and probably need supplemental notes, explanations or active design team involvement with the reliability engineer. A good derating system will also include recommended derating factor information supplemented, in some cases, by additional comments or figures which describe practical limits. The additional cautions and/or supplemental notes could help for the more difficult cases. Lastly, alternate component types should be suggested when required. Placing these derating guides into your own company will help to develop reliability thinking at the design level