Prepared by: Joe Cullinan
Subject: Encapsulation of wire bonds between the TMCM and SSD Ladders on Heavy Converter Tower Trays
INFN: Sandro Brez
GSFC: Tracy Shepherd, Fred Gross
SLAC: Darren Marsh,
An MRB was held
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
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,