1、Best Practices Entry: Best Practice Info:a71 Committee Approval Date: 2000-04-17a71 Center Point of Contact: GRCa71 Submitted by: Wil HarkinsSubject: Thermal Cycling Practice: As a minimum, run eight thermal cycles over the approximate temperature range for hardware that cycles in flight over ranges
2、 greater than 20oC. The last three thermal cycles should be failure free.Programs that Certify Usage: This practice has been used on ATLAS, CENTAUR, Space Electronic Rocket Tests (SERTs) 1 and 2, Communication Technology Satellite (CTS), GOES, COBE, NOAA, LANDSAT, Solar Maximum Mission.Center to Con
3、tact for Information: GRCImplementation Method: This Lesson Learned is based on Reliability Practice number PT-TE-1402, from NASA Technical Memorandum 4322A, Reliability Preferred Practices for Design and Test.Benefit:Demonstrates readiness of the hardware to operate in the intended cyclic environme
4、nt. Precipitates defects from design or manufacturing processes that could result in flight failures.Implementation Method:Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-As part of ATP, run at least eight thermal cycles over the temperature range ex
5、perienced by the hardware during storage, shipping, launch, flight, and reentry. The maximum and minimum temperatures anticipated should be exceeded by 10 degrees C. The last three thermal cycles should be failure-free.Equipment must stabilize at these limits before cycling to the opposing limit. Eq
6、uipment generally should be operated within the anticipated thermal range rather than at the thermal limits.Thermal cycling should be conducted in a vacuum if the test item is designed to operate in a vacuum.Technical Rationale:Thermal cycle modeling has shown that the general form of the thermal cy
7、cling test math model is given by Equation (1).refer to D descriptionD: Where:a71 TE = Test Effectivenessa71 F = Fraction of total failures that can be recipitated by a thermal cyclea71 Pd= Probability of detectiona71 lO= Failure rate at TOa71 N = Number of thermal cyclesa71 K = A constanta71 DT = T
8、 - TOa71 T = Operating temperature for la71 TO= Operating temperature for lOFig. 1 shows that the failures available are the sum of three parts:1. Failures detected by thermal cycle tests2. Undetected failures3. Failures not precipitatedProvided by IHSNot for ResaleNo reproduction or networking perm
9、itted without license from IHS-,-,-refer to D descriptionD Figure 1: General Form of TC Test Model For single temperature range of 50oC, the test effectiveness equation reduces to Equation (2).refer to D descriptionD Figure 2 shows a plot of Equation (2) based on a probability of detection, Pd, of 0
10、.9. The equation is based on values of lOand K that were found by solving two simultaneous equations.Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-refer to D descriptionD Figure 2. Test Effectiveness Plot for lT = 50oC Printed circuit boards (PCBs)
11、 are especially prone to solder joint cracking. The design is required to minimize the mechanical forces, as generated by thermal mismatch of materials or vibration, in the solder joints.References:1. GDCD BNZ 69-007, Curssell, G. M., “Atlas and Centaur Component Acceptance Test Plan,“ 1984.2. NASA
12、TMX-53731, Van Orden, R. E., “Mounting of Components to Printed Wiring Boards,“ 1968.3. Laube, R. B., “Space Vehicle Thermal Cycling Test Parameters,“ Proceeding of the Institute of Environmental Sciences, 1983.4. Nelson, C. E., “System Level Reliability Thermal Cycling,“ Proceeding of the Institute
13、 of Environment Sciences, 1983.Impact of Non-Practice: Design and manufacturing defects that could have been detected during ground testing manifest themselves during flight.Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Related Practices: N/AAdditional Info: Approval Info: a71 Approval Date: 2000-04-17a71 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-,-,-
