REG NASA-LLIS-0388-1995 Lessons Learned - Galileo Command Data Subsystem Memory Devices (Leadless Chip Carriers) Rework Problems.pdf

1、Lessons Learned Entry: 0388Lesson Info:a71 Lesson Number: 0388a71 Lesson Date: 1995-03-09a71 Submitting Organization: JPLa71 Submitted by: J. LangmaierSubject: Galileo Command Data Subsystem Memory Devices (Leadless Chip Carriers) Rework Problems Abstract: When large strips of conformal coating were

2、 removed from Galileo CDS boards, the process caused the coating to expand and stress the solder joints. The recommendations provide cautions on modification of existing procedures to include methods and processes which have not been proven and qualified.Description of Driving Event: The Galileo Com

3、mand Data Subsystem tests uncovered a “read disturb“ problem of the memory chips which required extensive rework of the flight boards. Due to the extensive rework and short schedule, the conformal coating was removed in large strips rather than in small areas. The flight memory boards were submerged

4、 in an alcohol bath, the conformal coating removed, and the failed parts replaced. Subsequently it was discovered that the parts adjacent to those replaced exhibited some fractures in the solder joints. The combination of the prolonged alcohol bath and the subsequent heating of the conformal coating

5、 around and under adjacent parts caused the coating to expand and stress the solder joints. Lack of experience with leadless chip carriers was a contributing factor in this event.Additional Keyword(s): RepairLesson(s) Learned: The modification of existing procedures to include methods and processes

6、which have not been proven and qualified, especially when applied to new technology, greatly increases program risk.Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Recommendation(s): 1. Use of existing procedures, particularly in the materials and fa

7、brication areas, should be carefully reviewed and followed.2. Extensions or modifications to standard procedures beyond their planned use should be carefully evaluated before use in a new application.3. Utilization of laboratory areas of expertise and standard documentation should be maximized by al

8、l designers of subsystems and modules. This is especially beneficial in the areas of packaging, materials and processes.4. New technology applications should be carefully reviewed.Evidence of Recurrence Control Effectiveness: N/ADocuments Related to Lesson: N/AMission Directorate(s): N/AAdditional K

9、ey Phrase(s): a71 Parts Materials & ProcessesAdditional Info: Approval Info: a71 Approval Date: 1987-09-04a71 Approval Name: Carol Dumaina71 Approval Organization: 125-204a71 Approval Phone Number: 818-354-8242Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-