1、Lessons Learned Entry: 0592Lesson Info:a71 Lesson Number: 0592a71 Lesson Date: 1998-06-17a71 Submitting Organization: LERCa71 Submitted by: Joseph A. GacekSubject: Conformal Coating as Moisture Protection of Electronic Circuitry in Micro Gravity Description of Driving Event: The Microgravity Smolder
2、ing Combustion protoflight unit was flown on the STS69 shuttle mission. Resulting flight data indicated anomalous readings from two thermocouples. Both channels had noticeable noise, and readings, which were higher than anticipated for the condition. Since the igniter algorithm uses this information
3、 to initiate igniter shut-off the igniter was shut off prior to establishing desired conditions in the foam for smoldering completion.Lesson(s) Learned: Post flight testing determined that water, resulting from moisture produced during the smoldering process, provide an apparent electrical coupling
4、between pins 9 and10 of the integrated circuit responsible for temperature compensation. The condition was repeated in the laboratory, producing the same results as those encountered in flight. Water on the card connector contacts likewise produced similar results.Increasing thickness of conformal c
5、oating on the circuit board to twice that originally used verified water no longer caused the coupling problem between the integrated circuit pins 9 and 10. Additionally, circuit board and chamber connectors were sealed with RTV to prevent water incursion.Conformal coating nominally used as a contam
6、ination and flammability barrier does not necessarily provide an effective electrical barrier. The need for electrical isolation should be considered in the selection of the conformal coating material and method of application, especially in humid applications.Recommendation(s): Provided by IHSNot f
7、or ResaleNo reproduction or networking permitted without license from IHS-,-,-Where condensation is anticipated in an experiment conducted in micro-gravity, it is imperative that sufficient encapsulation of electronic circuitry is used to prevent incursion of water into the electrical components. Ad
8、ditionally, tests should be performed to verify that moisture does not introduce detrimental coupling between, or within electronic components.Evidence of Recurrence Control Effectiveness: The re-flight on STS-77 with the additional conformal coating and added encapsulation produced expected tempera
9、ture values, and provided nominal test information.Documents Related to Lesson: N/AMission Directorate(s): N/AAdditional Key Phrase(s): a71 Parts Materials & ProcessesAdditional Info: Approval Info: a71 Approval Date: 1998-06-18a71 Approval Name: Joseph A. Gaceka71 Approval Organization: 501-4a71 Approval Phone Number: 216-433-5912Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-
