1、Best Practices Entry: Best Practice Info:a71 Committee Approval Date: 2000-04-18a71 Center Point of Contact: GSFCa71 Submitted by: Wil HarkinsSubject: Electrical, Electronic, and Electromechnical (EEE) Parts Screening Practice: Implement a 100% nondestructive screening test on EEE parts prior to ass
2、embly, which would prevent early-life failures (generally referred to as infant mortality).Programs that Certify Usage: This practice has been used on all Goddard Space Flight Center (GSFC) flight programs.Center to Contact for Information: GSFCImplementation Method: This Lesson Learned is based on
3、Reliability Practice number PT-TE-1401, from NASA Technical Memorandum 4322A, Reliability Preferred Practices for Design and Test.Benefit:EEE Parts Screening provides a lower rework cost during manufacturing and lower incident of component failures during flight.Implementation Method:Screening for e
4、ach part can be established as follows:Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-a71 Refer to NASAs compilation of screening criteria for use with various EEE part types. An example may be found in Appendix C of the GSFC Preferred Parts List.a7
5、1 If Class S parts are purchased, the screening tests shown in Table 1 have already been conducted. When Class S parts are not available, the screens of Table 1 should be used.a71 Failure criteria during screening should specify Percent Defectives Allowable (PDA) and allowable parameter drift. Typic
6、al PDA criterion is 5%.A sample listing of failure mechanisms, the associated distribution of failures, and related screening tests are provided in Table 2.refer to D descriptionProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-D Table 1. 100% Parts Sc
7、reening Matrixrefer to D descriptionD Table 2. Failure Mechanisms/Screening MethodsTechnical Rationale:Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-The EEE parts manufacturing is controlled by military specification requirements covering a variety
8、 of areas such as: starting materials, process controls, electrical or electromechanical performance characteristics, and periodic inspections of some characteristics of finished product. Despite these requirements, defects that cause early-life failures can be randomly built into a product. The scr
9、eening tests are designed to be destructive to parts with particular defects but nondestructive to good parts.As an example, integrated circuits such as CMOS are highly susceptible to electrical performance failures caused by ionic contamination on the die surface. The contamination can be introduce
10、d by any of several uncontrollable avenues during manufacture and cannot be ruled out as an occurrence in any given lot of parts. To avoid early-life failures at higher assembly levels, the lot of parts is subjected to a 100% static burn-in. The burn-in is designed to drive contamination into the di
11、e areas where it will interfere with proper circuit operation and cause electrical failures before parts are installed on boards.References:1. NASA GSFC Preferred Parts List (NPPL) 18/19.2. Seidl, Raymond H., Garry, William J., “Pi Factors Revisited,“ Proceedings of the Annual Reliability and Mainta
12、inability Symposium, 1990.Impact of Non-Practice: Without screening, there could be latent failure mechanisms that could cause flight delays and/or failures. For example, two circuits on the Solar Maximum Mission (SMM) spacecraft failed. The failed parts were analyzed upon return from the repair mis
13、sion and found to contain defects that would have been revealed through screening. In one case, the microcircuit had a metallization flaw; in the second, the CMOS microcircuit had contamination on the die. In another example, screening tests performed on microcircuits resulted in an 85% failure rate
14、 Subsequent failure analysis revealed that improper parts had been used.Related Practices: N/AAdditional Info: Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Approval Info: a71 Approval Date: 2000-04-18a71 Approval Name: Eric Raynora71 Approval Organization: QSa71 Approval Phone Number: 202-358-4738Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-
