- Posted by Susana Galdeano
- On December 5, 2020
Risk Considerations, parts and Manufacturer
The pre-procurement phase combines the EEE parts state-of-the-art analysis, risk analysis and component ownership cost optimization with regards to the mission requirements, design criticality and budget.
In order to achieve this, the project manager leading a multidisciplinary team must find the optimal balance between component information availability (traceability, materials, testing, previous use…) and minimum tests to perform, reaching an acceptable level of reliability covering the technical, schedule and costing constraints.
- Risk considerations
The use of COTS components in a high-reliability system depends on the results of detailed risk assessments, which should determine if the risk of using a certain commercial device is acceptable for the mission or application, leading to different approaches for the risk mitigation.
The consideration of acceptable risks for the project, as well as the budget limitation, will allow the optimization of the selection/evaluation/testing sequence and must be defined on a case-by-case basis. It aims to ensure the correct functionality of the selected COTS in critical applications, minimizing or preventing the loss or malfunction of the system due to a faulty part. The main requirements and risk considerations are described in the next paragraphs.
Anti-counterfeit measures must be implemented during the procurement and acceptance phases, from the use of validated sources that will be used for each procured lot to the correct use of detection methods with different grades of restrictions (External Visual Inspection, XRF inspection, Electrical measurements, Microscopy, Decapsulation, etc.…)
COTS components have a short manufacturing life cycle, so it is essential to evaluate the manufacturers’ processes for obsolescence notification.
The use of a powerful and permanently updated database allows keeping the Parts Lists/BOMs/DCLs dully alert by continuously monitoring for obsolescence detection.
A stocking plan or Long-Term Storage (LTS), studied case-by-case, can be considered in the pre-procurement phase as a possible solution to component obsolescence. Also, strategic procurement of large quantities is a good option to rule out issues like several lot validations, traceability, process change notifications, follow-up, and lot test representativeness.
Lot homogeneitya nd traceability
Each procured EEE part shall be traceable to a manufacturer trace code and shall be maintained through the entire supply chain. The procurement of a single trace code per delivery lot should be preferred.
If no evidence of lot homogeneity is available and the information obtained cannot provide enough confidence in the product homogeneity, it would be required to evaluate additional actions to increase the confidence of the validity of testing results.
To avoid the inherent risk of using pure tin in space applications (mainly due to tin whiskers growth), the following considerations must be taken into account:
- Lead finish identification at device selection step.
- Lead finish confirmation/verification, as part of the incoming inspection, either based on the device marking/lot received information, or through physical verification/material analysis (XRF) in case of doubt.
- Mitigation techniques at assembly/design level.
COTS are usually rated for industrial or commercial temperature ranges. Parts shall be selected in the highest available temperature range and not below -40ºC to +85ºC.
Depending on technology and family, EEE parts can be sensitive to radiation environments. Space parts are usually radiation tested, or at least there are a lot of data evaluating their behaviour. However, this practice is not usual in the commercial market. This means that it must be paid special attention to this matter and design a plan to test, foresee and mitigate the possible damage for radiation effects, ensuring that parts are fully operative in a radiation environment.
- Component manufacturer selection
The part manufacturer selection is one of the most important points of the part selection process and it is absolutely mandatory to select parts only from reliable manufacturers. The following order of preference applies to the manufacturer selection process for a project:
- Manufacturer qualified by space agencies (QPL/QML) or listed in space agencies PPL.
- Manufacturer qualified/certified by space/ military/automotive subcontractors.
- Manufacturer with an adequate quality system based on statistical process control (SPC).
- Manufacturer worldwide leader.
- Manufacturer with a willingness to cooperate and good responsiveness.
- Components selection (restricted and prohibited)
On one hand, some specific EEE parts and materials are prohibited for quality and reliability reasons, due to previous experiences, alerts and agencies recommendations.
On the other hand, for technical/reliability reasons or because the parts/families are produced in small quantities, there are some specific parts and families that are not authorized to be considered as a reliable commercial part option. In these cases, the equivalent high-reliability-grade part must be used.
Components standardization and components selection strategy
The wide variety of commercial components justifies the need for standardization. The use of COTS in critical applications will force to the project managers to apply cost/reliability/risk trade-offs between the procurement of COTS versus the high-reliability equivalent parts and what the project actually needs in order to get a minimum level of confidence. If there is not enough level of confidence in the quality and/or reliability data of the parts to be approved, on a case-by-case basis, additional lot validation activities shall be developed, which have to be included into the total ownership cost:
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