Minutes of MRB held
PN: TMCM LAT-DS-00898/899 Flight
Subject: NCR 00237/00226
Debonding/lifting of flex on Italian side.
Die Encapsulation (Hysol FP4450) separation wire bonding region of Pitch
Adaptor. (SN 775 & 11378)
Attendees: Persis Drell INFN: Luca Latronico
Dick Horn Ronaldo Bellazzini
Tom Himel NASA: Jim Lohr
Ref: Work order 545 – 33 Flight TMCM’s to INFN hand carried
GSFC report: Exam of GLAST LAT MCM SN 775 Failed Bond Wires,
Authors: Diane Kolos & Bruno Munoz.
This MRB was held to review the issue of wire bonding
separation under the Hysol FP4450 black encapsulant and flex debonding on the
Italian side of the TMCM’s identified on NCR’s 00226 & 00237, with
assessment of risk for the 33 flight TMCM’s hand carried to INFN by Persis
Work Order 545 identifies the following 33 TMCM’s hand carried to INFN:
QTY 30 LAT-DS-00898. SN: 342, 388, 432, 457, 469, 477, 478, 481, 540, 622, 697, 735, 777, 816, 861, 862, 904, 933, 966, 998, 11233, 11234, 11292, 11336, 11345, 11347, 11419, 11438, 11459, 11480.
QTY 3 LAT-DS-00899. SN: 1010, 1040, 1063.
Understanding that the failure of bond wires appears to be the result of the disbond of the Hysol encapsulant FP4450, from the board surface, caused by flexure of the PWB due to the long, narrow geometry and potential mismatch of CTE between the 1 mil aluminum wires, the 8-layer polyamide PWB and the FP4450 black encapsulant, possibly exasperated due to excessive handling and thermal cycle temperature, a decision was made regarding usage of these 33 TMCM’s to bond TMCM’s into trays @ INFN.
An investigation continues to search for cause of the most serious encapsulation disbond issue, with an ongoing effort to “fix” internal manufacturing process issues @ Teledyne, documented on several NCR’s for flex debonding, conformal coating wicking & insufficient application of conformal coating.
Regarding the most serious issue as being the broken wire
bonds under the Hysol FP4450 encapsulant, the NASA team which reviewed this
Flex lifting/debonding rework effort is underway @ SLAC for the 24 TMCM’s identified as having this issue. Root cause has not yet been identified. SLAC & Teledyne are in close communication reviewing process variation for possible casue(s). Once root cause has been determined and corrected, additional inspection steps will be implemented by SLAC Source Inspector & Teledyne QA to assure no flight TMCM’s shipped has this issue.
The 33 flight TMCM’s listed above will be utilized in Tower B, with a decision not to use any suspect TMCM’s for Tower 1 at this time.