1.Derating

The stress experienced by the component during use is lower than its rated value, in order to delay the degradation of its parameters and improve the reliability of use. It is usually expressed in terms of stress ratio and ambient temperature.

2.Rating

The component can use a large value of stress.

3.stress

Electrical, thermal, and mechanical loads that affect component failure rates.

4.stress ratio

The ratio of component working stress to rated stress. The stress ratio is also called the derating factor.

5. Division of derating levels

Components usually have a better derating range. Within this range, the reduction of the component's working stress has a significant improvement in the reduction of its failure rate, and the design of the equipment is easy to implement without having to pay a large price in terms of equipment weight, volume, and cost.

The derating level shall be comprehensively weighed according to factors such as equipment reliability requirements, design maturity, maintenance costs and easiness, safety requirements, and restrictions on equipment weight and size. Three derating levels are recommended within the better derating range.

a. Grade Ⅰ derating Grade Ⅰ derating is a large derating, which greatly improves the reliability of component use. Larger deratings beyond this usually result in limited improvements to component reliability and may be difficult to achieve with device design.

Class Ⅰ derating is applicable to the following situations: equipment failure will cause personal injury or serious damage to equipment and support facilities; have high reliability requirements for equipment, and adopt new technology and new process design; due to cost and technical reasons, The equipment cannot or cannot be repaired after the equipment fails; the system has severe restrictions on the size and weight of the equipment.

b. Grade Ⅱ derating Grade Ⅱ derating is a medium derating, which significantly improves the reliability of component use. Class II derating is easier to implement than Class I derating. Cause damage to equipment and support facilities; have high reliability requirements, and use some special designs;

Need to pay higher maintenance costs.

c. Class III derating Class III derating is a smaller derating, which has a greater relative benefit to the reliability improvement of component use, but the absolute effect of reliability improvement is not as good as that of class I and class II derating. Ⅲ level derating is easier to achieve in design.

Class III derating is applicable to the following situations: equipment failure will not cause personal injury or damage to the facility; equipment adopts mature standard design; faulty equipment can be quickly and economically repaired; limit.

6.Recommended derating levels for different applications

According to Article 4.1, the recommended derating levels for different applications are shown in Table 1.

Table 1 Limits of derating

Derating can effectively improve the reliability of the use of components, but derating is limited. In general, the greater the derating beyond the better range, the lower the relative benefits of improved component reliability, see Appendix A (Reference). However, the weight, volume and cost of equipment will increase rapidly. Sometimes excessive derating will change the normal characteristics of components, and even components that meet the functional requirements of equipment or circuits may not be found; excessive derating may also introduce new failure mechanisms of components, or lead to the number of components Unnecessary increase, as a result, the reliability of the equipment will be reduced.

7. Adjustment of derating amount

The amount of derating recommended in this standard should not be absolute. Derating is the result of a comprehensive analysis of multiple factors. The derating value specified in this standard takes into account the feasibility of the design and design constraints consistent with reliability requirements. In actual use, due to the limitation of the conditions, some derating values are allowed to be changed, that is, a derating parameter can be adjusted with another parameter comprehensively, but the derating level should not be changed easily (such as changing from Ⅰ to Ⅱ Derating). In some cases, the choice of a derating value exceeding the requirements of this standard may be reasonable, but it should also be made on the basis of careful weighing. It should also be noted that small deviations from the derating values specified in this standard usually do not have a large effect on the expected failure rates of the components.

8. Determining the working basis of the derating value The working basis of the derating value can be divided into the following three cases, which should be paid attention to in the application: (1) Analysis of a large number of use data, and the stress and component of components Have a good understanding of the reliability relationship (type A in Table 2); (2) the data for analysis is limited or the structure is more complicated. But have a certain understanding of the relationship between the stress and reliability of the components (type B in Table 2);

(3) As the technology is newer or is limited by the combination method in the device where the device is located, no derating application data is available for reference. However, their structures and materials have been studied, and derating engineering judgments have been made (Class C in Table 2).

9. Quality level of components

The components of suitable quality grade must be selected according to the product reliability requirements. Derating compensation cannot be used to solve the problem of using low-quality components.

Appendix: List of Component Derating Guidelines