REG NASA-LLIS-0924--2000 Lessons Learned Tin Whiskers Cause Electrical Shorts.pdf

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1、Lessons Learned Entry: 0924Lesson Info:a71 Lesson Number: 0924a71 Lesson Date: 2000-11-16a71 Submitting Organization: JPLa71 Submitted by: C. Bodie, D. Oberhettinger, J. BrusseSubject: Tin Whiskers Cause Electrical Shorts Abstract: Although the phenomenon of tin whisker formation is well known, spac

2、ecraft are still suffering failures from them. When tin plating is used on mechanical, electrical or electromechanical components, continuous process monitoring (especially of suppliers) must occur to assure that tin whisker growth is addressed including control of the type and amount of impurities

3、added to plating baths and compliance is maintained.Description of Driving Event: During the period May-July 1998, one or more of the redundant spacecraft control processors (SCPs) failed in each of three commercial communications satellites. This resulted in one of the satellites being removed from

4、 service. Three SCP failures were attributed to intermittent or continuous short circuits caused by the growth of conductive filaments, known as “tin whiskers,“ from the tin-plated surface of an electronic assembly or its cover. Although well known in the past, these recent failures have reminded th

5、e space community of the potential risks associated with the use of pure tin-plated finishes on electronic components and assemblies. While pure tin protective coatings are favored by the electronics industry because of their material properties and cost, they are susceptible to the spontaneous grow

6、th of single crystal structures - tin whiskers. Growth occurs with pure tin plating, regardless of the presence of an applied electric field, moisture, or an atmosphere. It may begin soon after plating or may take years to initiate. Tin whiskers are capable of causing electrical failures ranging fro

7、m parametric deviations to catastrophic short circuits. “Bright“ pure tin plating has been found to be particularly susceptible to whisker growth, and the U.S. military has discouraged its use.Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-refer to

8、D descriptionDSimulation of Whisker Growth (courtesy of GSFC)refer to D descriptionDReference(s):1. NASA Goddard Space Flight Center Tin Whiskers Information Page, http:/nepp.NASA.gov/whisker/index.html.2. “Tin Plating, Whisker Growth,“ GIDEP Alert No. AAN-U-00-11, January 4, 2000.3. Military specif

9、ication MIL-T-10727, Tin Plating: Electrodeposited or Hot-Dipped, For Ferrous and Nonferrous Metals (cancelled February 7, 1997) - refer to ASTM B545-1997, Standard Specification for Electrodeposited Coatings of Tin.Lesson(s) Learned: 1. Although the tin whisker phenomenon has been documented for de

10、cades and is reasonably well understood, it remains a reliability hazard that warrants continuous attention to vendor and in-house tin plating processes.2. Tin whiskers may grow spontaneously to more than 4 mm in length. The filaments can Provided by IHSNot for ResaleNo reproduction or networking pe

11、rmitted without license from IHS-,-,-typically carry 25-50 mA of current, or 1 amp for a short period. (Reference #1)Recommendation(s): 1. The recommendations documented in the previous military specification MIL-T-10727 and the current industry specification ASTM B545, such as controlling the type

12、and amount of impurities intentionally added to the plating bath, should be implemented to prevent or minimize the occurrence of tin whiskers.2. When tin plating is used on mechanical, electrical or electromechanical components, continuous process monitoring (especially of suppliers) must occur to a

13、ssure that tin whisker growth is addressed and compliance maintained.Additional Key Words: Latent Failure, Material Properties, Sneak CircuitEvidence of Recurrence Control Effectiveness: This lesson will be evaluated for possible corrective action and practices may be modified as appropriate.Documen

14、ts Related to Lesson: N/AMission Directorate(s): a71 Exploration Systemsa71 Sciencea71 Space Operationsa71 Aeronautics ResearchAdditional Key Phrase(s): a71 Hardwarea71 Parts Materials & Processesa71 Payloadsa71 Safety & Mission Assurancea71 SpacecraftAdditional Info: Provided by IHSNot for ResaleNo

15、 reproduction or networking permitted without license from IHS-,-,-Approval Info: a71 Approval Date: 2001-03-5a71 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-,-,-