SSL 20 June 2018 Evaluation of COTS Diodes for Long Term High Reliability Applications James Loman June 20, 2018 Prepared by: Prepared for: Space Systems/Loral, LLC NASA Electronics Parts and Packaging Program 3825 Fabian Way 2018 Electronics Technology Workshop Palo Alto, CA 94303-4604 USA
Overview 1. We determined it is technically feasible and practical to use some limited commercial parts on large GEO spacecraft with 15 year life 2. We showed the critical risks can be reasonably retired 3. We now have our highest volume EEE part- a diode- as COTS 4. We found a high barrier to entry which limits opportunities for existing GEO programs 5. New design, small satellites at LEO represent better opportunities for use of COTS -2 20 June 2018
EEE Parts Overview- Large SSL Geo Spacecraft 200K EEE Parts per Large Spacecraft -3 20 June 2018
Diode Project Project Objective: Use a commercial alternative for the most used Hi-rel diodes without impacting performance and reliability – Must be equivalent form, fit, function, reliability, performance – Must be drop-in replacement (no tray level redesign) Part types usage – Use 16,000 pieces of the most common diode per S/C- replaced half of these – Second most common type- 8000 per spacecraft – Many other opportunities to replace diodes elsewhere, but the return on investment is less and may not be worthwhile as a design change – COTS parts orders of magnitude less expensive The simplest parts with the most savings and the least impact -4 20 June 2018
Selected Commercial Diodes Selection criteria utilized – High Volume Commercial Process Control benefits – Same or similar electrical characteristics as current flight diodes – Drop-in replacement package only (no re-design) – Automotive grade preferred = qualification and compliance to AEC Q101 standard Hi-rel COTS Mfg. Grade V rated I rated Package Fit Type TYPE Automotive 75 V 250 mA Fits ok for all 1 A applications Most Commercial 75 V 250 mA OK for some 2 B Used applications Diode Automotive 200 V 2 A Fits ok for all 3 B 2 nd applications Most Commercial 150 V 2 A Fits ok for all 4 C Used applications -5 20 June 2018
COTS Vendor Information Amount of info & quality of correspondence varied from vendor to vendor. The goal was to obtain reliability & quality info, qualification & screening process description, product change handling, and other details usually available from Hi-rel vendors Vendors A & B would only communicate through local sales office – Provided general standard answers about their processes but no specific details Vendor C was forthcoming – Provided details about engineering evaluations, summary of environmental testing for the part & estimated failure rate value In conclusion, communication is possible with COTS vendors, but we need to rely on our own evaluation data -6 20 June 2018
Diodes DC Electrical Parameter Test Results Testing performed on each type: – DC tests at ambient, hot (125 or150 deg C) & cold: (-65°C) on ~250 pieces/ type – Tests were a combination of vendor data sheet tests and Hi-rel tests (where different conditions apply) Testing results summary – No part failed any parameter, except One part tested out of spec during initial test, but tested in-spec after rad testing, so likely it was a bad measurement – Measured values were well within limits – The data compared quite well to the observed Hi-rel data – Some parameters had dual modes indicating mixing of two wafer lots – not a major concern -7 20 June 2018
DC Electrical Testing Results Summary All diodes performed within their respective Data Sheet limits. Compared to Hi-rel parts, the commercial diodes had tighter distributions and equal or better values for most parameters – Breakdown voltage: higher and standard deviation ~1/3 of Hi-rel parts – Forward voltage: similar to Hi-rel – Leakage current: much lower (>10x less), tighter distribution – A few obvious outliers existed, however all parts well within spec – Forward voltage & leakage notably better at Hot Temp (+125°C) COTS diodes data shows equivalent or better performance than the Hi-rel parts -8 20 June 2018
Materials Outgassing Test The diode encapsulation materials were separated and outgassing tested. All 4 types tested passed outgassing measurements with large margin. Max Total Mass Loss (TML) was 0.267% <<1.0% specification All four types had Vacuum Condensable Materials (VCM) << 0.1% specification (typical 0.000%) -9 20 June 2018
Radiation Performance Pre- and post-radiation electrical performance measurements – All pass initial electrical limits per SSL SCD (JANS equivalent) – All pass electrical limits in the vendor datasheet – Standard radiation testing method to 300KRad – All diodes were tested and all passed the post-radiation test – Small parameter shifts were seen, but all were well within specification -10 20 June 2018
Constructional Analysis Constructional Analysis was performed on 5 pcs from each sample group (total 20 pcs) – External Characterization: (OK) Package photographs and dimensions – Dimensions were measured for each part per vendor datasheet. – All measurements were tabulated for each diode part serial number. Package weights were measured and tabulated Package, Lead and Lead plating materials were identified – Radiographic Characterization: (OK) Typical radiographs (3 axes), exposure parameters recorded – Internal Characterization (1 device per part number): Plastic encapsulant removal (OK) Photo-documented after removal of package Interconnect structures examined – Leads and/or Lead Frame: Dimensions, materials – Wire bonds: Wire size, material, and bond types -11 20 June 2018
Constructional Analysis – Internal Characterization (Continued): (Issues) Overall photograph of exposed die and leads (identified Sn) SEM photograph of die and leads Overall die dimensions Photographs of typical structures Die bond method and materials (identified Cu wire bonds or lead frame) Die metallization system/materials/thicknesses and etch method (unique structures) – Cross-Sectional Characterization (2 samples per part number): (OK) Sample 1 - Cross-section along the x-axis halfway through the device Sample 2 -- Cross-section along the y-axis halfway through the device Photographs of cross-sectioned parts Part construction/materials/joining methods External lead to package seals Leads / Lead Frame material/plating, thicknesses Typical diffusion structures/depths Isolation methods/structures -12 20 June 2018
Constructional Analysis- Example -13 20 June 2018
Constructional Analysis -14 20 June 2018
Diode Environmental/Qual Test Plan Three best fit qualification documents were compared for plastic/commercial parts: NASA, ESA and Automotive Council (in that order) – NASA PEM-INST-001, ECSS-Q-ST-60-13b, & AEC-Q101 – AEC tests all utilize a 77pcs sample size (3x consecutive lots) – Larger sample size needed to demonstrate equivalent reliability to space grade parts – Obviously “Not Applicable” tests excluded: Cavity parts only tests: hermeticity, wire bonded part tests, die shear, vibration/shock/constant acceleration -15 20 June 2018
Reliability Life Test Plan & Failure Rate Purpose: – Demonstrate that commercial diode has a failure rate comparable to the currently used space grade (Hi-rel) diode Approach: – Accelerated life testing was used to reduce test time using temperature and voltage as acceleration factors – This approach is well-established and accepted in both the space and commercial industries – To demonstrate failure rate (FR) of 1 FIT (failure in time, 1 FIT = 1 failure/10 9 hours) without accelerated testing – 1,000 devices would need to operate for 10 6 hours or 114 years Accelerated Testing Conditions: – Targeted FR = 0.85 FIT @ 67°C operating junction temperature – Test conditions are T A = 150°C, V R = 80% rated (HTRB test) – 538/0 pcs must be tested for 1,000 hrs OR 269/0 pcs for 2,000 hrs -16 20 June 2018
ROI Considerations Even Hi-rel diodes are a relatively low cost part Savings on a per-part basis may not overcome fixed costs involved unless the volumes are significant (thousands used) – Manufacturing assessment- determine fit, function, pure tin (Sn) assessment – Design assessment- will it work the same over temperature, revisit Worst Case Analysis? – Switching tests are needed for certain applications – Test in breadboard or EM- need to show that it works – Change drawings, bills of material and part numbers – Unit level testing – Brief customers & request contractual relief High barrier to entry for changing a part in exiting designs -17 20 June 2018
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