1. MIL-HDBK-217 contains, as a part of the reliability equations, factors for various parts classes. The factors for microcircuits are *Low=0.25, **Medium=1.0, ***High=2.0, and ****Unknown=10.0. Therefore medium grade parts could be said to be 4 times more likely to fail than low risk parts, etc.

2. Qualification of MIL passive EEE parts to exponential failure rates is granted and maintained at a specific level (S, R, P or M) based upon periodic life testing of sample parts used to represent a range of styles/values/ratings. Once the manufacturer has been granted qualification at a given failure rate level, all product manufactured from that line within the range of values qualified is considered to have this same failure rate level regardless of whether the manufacturer marks the parts with a higher (worse) failure rate level in order to fulfill user-specific marking or purchase requirements. Therefore, there is no advantage (either reliability or cost) to ordering a higher (worse) failure rate level part (e.g., "P" level parts for a Level 2 program) when the supplier is qualified to a lower (better) failure rate level (e.g., "R" or "S" level). Exponential failure rate levels are assigned as follows:
       "M" = 1.0% failures/1000 hours
       "P" = 0.1% failures/1000 hours
       "R" = 0.01% failures/1000 hours
       "S" = 0.001% failures/1000 hours

3. Weibull refers to the 100% accelerated life test performed on solid tantalum capacitors in order to establish "lot-specific" failure rate levels. Through this testing failure rate levels are assigned as follows:
       Weibull "B" = 0.1% failures/1000 hours
       Weibull "C" = 0.01% failures/1000 hours
       Weibull "D" = 0.001% failures/1000 hours

4. For passive EEE parts, Class S refers to specifications that are specifically written for space grade or extremely high reliability applications. Examples include MIL-PRF-123 for ceramic capacitors and MIL-PRF-87217 for metallized film capacitors. Class "T" for passive EEE parts generally refers to an established reliability level product that is available with space application relevant requirements and testing in addition to the MIL established reliability requirements.

5. The requirements defined in MIL-PRF-38535 for Class "T" active EEE parts are sufficiently vague to consider them to be of a generally "high" risk for NASA applications. Per MIL-PRF-38535E Amendment 5 paragraph 3.4.8, "Class T for active EEE parts is not for use in NASA manned, satellite, or launch vehicle programs without written permission from the applicable NASA Project Office (i.e., cognizant EEE parts authority)."

6. "S" Source Control Drawings (SCDs) are those customer-owned drawings that require full compliance to all of the Military specification processing requirements for a Space Quality Device, without the JAN marking (e.g., Microcircuits: compliance to MIL-STD-883 Methods 5004 and 5005 for a Class "S" device; Hybrids: compliance to MIL-PRF-38534 Class K, etc.).

7. For most spaceflight applications radiation effects are critical factors to consider for mission assurance. This EEE Parts Risk Matrix does not address radiation sensitivity of EEE parts. Always consult a radiation specialist for guidance especially for active EEE parts.

8. For more details on parts considered by NEPAG to be suitable for spaceflight applications, consult the NASA Parts Selection List (NPSL) at: http://nepp.nasa.gov/npsl

9. ESA has gone to a single Level system based on ESA SCC Level B, so that new product will only be available as SCC Level B. ESA SCC Level C products (previously listed as Medium Risk - Level 2) may remain available for previously manufactured product while stocks last.

Acronyms:
975 = MIL-STD-975 (canceled in 1998)
COTS  = Commercial-Off-The-Shelf
DSCC = Defense Supply Center Columbus
ESA = European Space Agency
JAXA = Japan Aerospace Exploration Agency (formerly known as NASDA)
MIL = United States Military Specification System
NPSL = NASA Parts Selection List
QML = Qualified Manufacturers List
QPL = Qualified Products List