3.4.3. Random failure#

The reliability.space approach for EEE items provides models for reliability predictions for the EEE components which are used in space applications. The conventional component types refer to the components which are defined in the EPPL list [BR_EEE_9] and the PCB as expressed in Annex A : example of mission profiles for space applications.

The reliability.space approach covering the random failures for EEE items is described in this part of the handbook. This methodology is based on the FIDES methodology, 2009 version.

Following the observations from the TEC QQD Study - Reliability Prediction Data Sources and Methodologies for space applications, it is adapted to the specificities of the space applications.

Note 1

A 2021 version of FIDES have been issued including some of the updates proposed here. So far, the analysis presented in this handbook shall be applied to the 2009 version, but in order to prepare the future, when anticipations could be made for a future applicability of the 2021 version, information is provided.

Note 2

It is recommended to read this section carefully before modelling the reliability of the different component families (from Section 3.4.3.5.1). But within these individual sections, the full process is clearly described again within each section, with links to common features (Section 3.4.3.2 and Section 3.4.3.4).

The FIDES approach consists in putting a special attention on the following aspects:

  • Technologies: FIDES considers the instrinsic aspect of the EEE components and their integration into equipment;

  • Process: it translates the idea that all practices from the development of the equipment to its use in operation are important for the overall reliability, it refers to the equipment and not to the EEE components;

  • Use: it is also important to take into account the constraints linked to the use of the equipment into the satellite.

The part stress method is based on a general equation and calculation of physical stresses depending on external constraints. Some additional considerations and factors are adjoined in order to consider:

  • the mission profile of the equipment for the different use phases

  • the quality of EEE components linked to their manufacturing

  • the quality and technical control over reliability in the product life cycle

The reliability.space approach is performed by considering each of these three aspects. However, some modifications and adaptations have been made in order to reflect the specificities of space applications. The main changes performed in the reliability.space approach are the following:

  • adaptation of a mission profile as defined in Section 3.4.3.2 with some specificities of the space applications such as thermal management by conduction, cyclic variations of temperature, level of humidity and vibrations in space;

  • use of the reliability models built for each technology of EEE components based on the Physics of Failure with some adaptations described in Section 3.4.3.5 each component model; the preferred use is the part stress method as described in the section.

  • consideration of the process during the phases of development, integration into the equipment, integration into the satellite and operations by evaluating a process factor as defined in Section 3.4.3.3.1.

  • use of acceleration factors as described in Section 3.4.3.2.12 to Vibration stress by considering the duration of each phase \(t_{text{phase}}\) according to the total life duration of the satellite

  • recommendation of default values for some of the factors defining the induced factor \(\Pi_{\text{induced}\_i}\) as described in Section 3.4.3.2.17, such as the influence of the usage environment \(\Pi_{\text{application}\_i}\) and the influence of the policy for over-stresses \(\Pi_{\text{ruggedising}}\);

  • improvement and adaptation of values for some of the factors defining the part manufacturing factor \(\Pi_{\text{PM}}\) as described in Section 3.4.3.4 such as the manufacturer quality assurance \(\text{QA}_{\text{manufacturer}}\), the results and severity of tests factor \(\text{RA}_{\text{component}}\) and the experience factor \(\epsilon\).

General model for all families

In the following, the general model for conventional components is described, forming the basis for the models provided in Section 3.4.3.5:

Equation

(3.4.1)#\[\lambda = \lambda_{\text{Physical}}{\cdot \Pi}_{\text{PM}} \cdot \Pi_{\text{Process}} \cdot \Pi_{\text{LF}}\]

for RF/HF components:

Equation

(3.4.2)#\[\lambda = \lambda_{\text{Physical}} \cdot \Pi_{\text{PM}} \cdot \Pi_{\text{Process}} \cdot \Pi_{\text{ProcessRFHF}} \cdot \Pi_{\text{LF}}\]

and for ASIC components:

Equation

(3.4.3)#\[\lambda = \lambda_{\text{Physical}} \cdot \Pi_{\text{PM}} \cdot \Pi_{\text{Process}} \cdot \Pi_{\text{ProcessASIC}} \cdot \Pi_{\text{LF}}\]

and for Hybrids & MCM components:

Equation

(3.4.4)#\[\lambda_{\text{HM}} = \sum_{\mu\text{-components}}(\lambda_{\mu\text{-components}}\cdot \Pi_{PM_{\mu\text{-components}}})\cdot\Pi_{\text{Process HM}} \cdot \Pi_{\text{Process}} + (\lambda_{\text{wiring}} + \lambda_{\text{case + substrate}} + \lambda_{\text{external connections}}) \cdot \Pi_{\text{Process HM}}\cdot\Pi_{\text{Process}}\]

With:

  • \(\lambda\) as the estimated reliability prediction;

  • \(\lambda_{\text{physical}}\) as the physical contribution of reliability prediction;

  • \(\Pi_{\text{PM}}\) as the part manufacturing factor described in Section 3.4.3.4

  • \(\Pi_{\text{Process}}\) as the process related factor described in Section 3.4.3.3.3

  • \(\Pi_{\text{ProcessRFHF}}\) as the process related factor for HF/RF components described in Section 3.4.3.3.5;

  • \(\Pi_{\text{ProcessASIC}}\) as the process related factor for ASIC components described in Section 3.4.3.3.6;

  • \(\Pi_{\text{LF}}\) as the lead-free process factor described hereafter.