Retired following 44 years in component engineering
Introduction
The EEE Components used in space shall meet the specific mission radiation requirements. The radiation requirements shall be met regardless the quality level (industrial level COTS or space level or military level), regardless of the subject packages (hermetic or nonhermetic).
One of the leading documents in this domain was issued by ESA:
ECSS-Q-ST-60-15C Space Product Assurance - Radiation Hardness Assurance - EEE Components
The above document is referenced also in the following leading ESA EEE Components related documents:
ECSS-Q-ST-60C Rev.2 Space Product Assurance - Electrical, Electronic and Electromechanical (EEE) Components
ECSS-Q-ST-60-13C Space Product Assurance - Commercial Electrical, Electronic and Electromechanical (EEE) Components
This article deals with some problematic wording in ESA ECSS-Q-ST-60-15C. The used wording may confuse the user.
Problematic Wording in ESA ECSS-Q-ST-60-15C
Following are observations regarding difficulties to understand the wording of requirements expected to be met:
Wording in para. 5.1 ESA ECSS-Q-ST-60-15C:
5.1.t For geostationary orbit, RVT on flight lot shall be performed if flight model part diffusion lot number is different from tested part diffusion lot number and tested parts date code is 4 years older than flight model part date code.
5.1.u For other orbits, the criteria for performing RVT on flight lot, if not defined by the customer, shall be defined by the supplier and submitted to customer for approval.
NOTE : It is part of hardness assurance to perform RVT on flight lot based on the following criteria: age of available test data, part type and technology, and RDM.
Observations:
The subject is the yes/no Radiation Verification Tests (RVT) performance for a given flight lot. Technically speaking, as far as schedule is concerned and moneywise there is no doubt that this is a critical issue in any project.
However, it is difficult to understand the ESA criteria for the RVT performance as a function of orbits (GEO etc.). Any orbit/mission radiation requirements shall be defined and met. What could be the logics to define the above criteria for RVT performance as function of the relevant orbit?
Following the ESA wording foe GEO, one should conclude that both conditions (part diffusion lot number and part date code) shall be considered.
The use of the word "and" implies that any GEO project is built exclusively with space level components!!! That assumption does not correlate with the reality.
Only space level components meet wafer traceability requirements. One can expect to receive information about the above mentioned "part diffusion lot number" only for those components.
The term "part diffusion lot number" is exclusively attributed to space level components. However, there are two subgroups of the space level parts: Radiation Hardened and not Radiation Hardened.
The term "radhard" deserves some attention for the sake of the users. The term does not always cover all the radiation aspects, that the term "RVT" covers (e.g. TID, NTID, SEE). Consequently, the user is not automatically released from any RVT.
Even if one considers applicability of only TID RVT of radhard components, it seems that further confusing wording can be found in other documents.
Are those radhard components really tested lot by lot by the component manufacturer, releasing the users of any TID RVT performance?
Following are ESA requirements from the component manufacturers:
Para. 5.3.3 ESCC5000 (discrete semiconductors) and ESCC 9000 (ICs):
During procurement:
– If specified in the Detail Specification and required in the Purchase Order, components shall be produced from a wafer lot which has been subjected to and successfully completed Total Dose Radiation Testing in accordance with Para. 8.4 to the required total dose level.
Another use of "and" leads to the conclusion that RVT has to be explicitly required in the Purchase Order!?
Para. 2.9 ESCC Detail Specification No. 5201/004 Issue 6 BASED ON TYPE 2N3700:
TOTAL DOSE RADIATION TESTING
All lots shall be irradiated in accordance with ESCC Basic Specification No. 22900, low dose rate (window 2: 36 to 360 RAD/h).
Be aware that This detail specification specify RVT as required above in the ESCC5000.
All lots. No need to be ordered? Does those requirements correlate?
MIL-PRF-38535K APPENDIX J states:
J.3.10.5 Group E inspection. When applicable, group E inspection shall include RHA tests on each wafer lot.
All lots shall be tested (RVT).
The above is worth to be clarified.
Wording in ESA ECSS-Q-ST-60-15C:
5.1.f TID test data used to assess TIDS shall comply with the following rules to be acceptable:
3. tested parts are manufactured with technology identical to the technology of flight parts: same process, same diffusion mask, and same wafer fabrication facility, and
4. test bias conditions are worse or equivalent to the application.
5.2.f TNID data used to assess TNIDS shall satisfy the following criteria to be acceptable:
2. Tested parts are manufactured with technology identical to the technology of flight parts: same process, same diffusion mask, and same wafer fabrication facility.
5.3.f SEE test data shall meet the following criteria to be acceptable:
2. Tested parts are manufactured with technology identical to the technology of flight parts: same process and same diffusion mask.
3. Test conditions are worse or equivalent to the application.
The word "and" sums conditions to be fulfilled for finding acceptable test data to try to avoid actual RVT performance.
The requirements themselves are OK. However, I question their practicality and applicability to all EEE Components leverls. The "and" only makes the things more questionable.
Does it look achievable to find test data (usually public ones) containing full information about "same process, same diffusion mask, and same wafer fabrication facility....".
It is understood that the ESA document covers all EEE components. It seems that maybe only space level are covered.
Who (user) is supposed to be able to access all the above mentioned information?
What about COTS?
Conclusion
There is ample space for pragmatism.
Never be afraid of what you really feel.
The author, Dan Friedlander, graduated Engineering School/Tel Aviv University with a degree in physics (1965-1969). He has 44 years of experience in Component Engineering at MBT/Israeli Aerospace Industries (1969 to 2013), as Head of Components Engineering. As such, he was responsible for all aspects of EEE components – including policymaking, standardization at corporate level, approval, etc. – for military and space applications. Now retired, Friedlander is an industry consultancy (2013 to present). For further details on his experience, visit his LinkedIn page.
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