Transcript ppt - GLAST at INFN-Pisa

Gamma-ray Large Area
Space Telescope
Procedure for MCM rework on tray
MID 070
See NCR INFN-PI 385 Major
Description of the nonconformance
• Description of nonconformance:
– All the 64 channels of one Front-end chip are always over
threshold.
• Relevant NCR:
– Refer to NCR 385 major.
• Impact (if no action is taken):
– 64 contiguous channels on one silicon layer are lost.
• Root cause:
– Very likely due to a resistor on the MCM board (R111) found
to be broken during the optical inspection.
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Preparation I
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MID 070 rework
Remove the handles from
the tray box.
Remove the top cover of
the tray box.
Remove the two covers
for the connector savers
on the box closeout in
correspondence of the
MCM to be reworked.
Remove the box closeout
in correspondence of the
MCM to be reworked.
 All the process shall take place in class 100.000 clean
room.
 Standard ESD procedures shall be observed at each
step of the rework process.
 Tray box shall be grounded through the ESD bonding
point.
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Preparation II
Approximate
location of the
broken resistor.
 The MCM is easily accessible for rework without removing the tray
from its box.
 This reduces the risk of damage to the tray itself induced by accidental
mishandling.
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Removal of the broken resistor
Location of the broken resistor
(R111) - a non flight MCM is
shown in the picture for reference.
Hole for PCB fixing
screw.
 Remove the conformal coating
over the resistor –
 Unsolder the resistor with an ESD soldering tool- during this step precautions
should be taken as to avoid accidental damage of silicon detectors induced by
soldering material.
Remove further residuals of conformal coating (if any) debonded during the
process.
 Clean the surface close to the location of the resistor with isopropanol.
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Installation of the new resistor
 Install the new resistor in place
 Close the tray box.
 Perform a comprehensive electrical test on both faces of the tray.
 Open the tray box again – as described before – and reinstall the top cover;
this leaves the MCM accessible from the outside minimizing the exposed area.
 Put the tray box in a vertical position .
 Encapsulate the new resistor using NUSIL CV15-2500 (already used for the
encapsulation of the wire bonds) and wait for the glue to cure with the tray box
still in a vertical position.
 Remove the top cover and close the box.
 Perform the final electrical test on both faces.
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