MRB Minutes


Prepared by:  Joe Cullinan


Date:  16 November 2004


Subject:  Encapsulation of wire bonds between the TMCM and SSD Ladders on Heavy Converter Tower Trays


Subsystem:  Tracker



INFN:  Sandro Brez


GSFC:  Tracy Shepherd, Fred Gross


SLAC:  Darren Marsh, Joe Cullinan, Lowell Klaisner, Dick Horn, Dave Rich, Persis Drell, Robert Johnson



An MRB was held 16 November 2004 to discuss proposed solutions to the observed wire bond failures in 4 heavy converter trays following thermal cycling testing.  The purpose of this MRB was to review the problem, potential causes, and proposed corrective actions.


Robert Johnson presented the details of the wire bond failure (presentation attached).  The wire bond failure is attributed to physical movement of the wire encapsulant (NuSil 2502) during thermal cycling.  This failure has only been observed on heavy converter trays.


Corrective actions proposed included using a different silicone or epoxy encapsulant, spraying the wires with a thin silicone conformal coating, or eliminating encapsulant on heavy converter trays. 


Fred Gross proposed evaluating the use of a polyurethane conformal coating, such as Urelane, in this application.  Currently GLAST PWBs are conformally coated with polyurethanes.  Polyurethanes do not require a primer for good bonding, cure at room temperature, offer desirable combination of strength and flexibility that may not be achieved with either a silicone or epoxy, and can be dispensed with the same equipment currently used.  


Potential risks discussed included handling damage, contamination-induced electrical shorting and oxidation/corrosion of exposed wires. 





The MRB concluded to proceed with building heavy converter trays without wire encapsulation for Tower A and B.  In parallel, Tracker team shall submit a plan for testing and developing a new wire encapsulation process for the remaining heavy converter trays.  ECD for this plan is 12/3/04.


Action Items: 


1.  Review flowdown of heat pipe requirements and procurement specifications from SLAC to Lockheed Martin to verify requirements are correctly documented in Lockheed Martin manufacturing and test plans.


Actionee:  LAT Mechanical Subsystems


ECD: 28 May 2004


2.  Perform schedule and cost impact if CCHPs are unusable and must be scrapped.


Actionee:  Aaron Avallon (Lockheed Martin)


ECD:  21 May 2004


3.  SLAC to review Lockheed Martin Acceptance Test Procedures for Variable Conductance Heat Pipes (VCHPs) to verify documented test requirements are correct.


Actionee:  Joe Cullinan


ECD:  21 May 2004


4. SLAC to witness reproof pressure testing of CCHPs at Lockheed Martin with GSFC QA representative


Actionee:  Joe Cullinan, Tracy Shepherd


ECD:  As determined by Lockheed Martin test schedule




Attachment:  MRB slide presentation, 5/11/04