1. Procedure for MCM rework on tray MID 070
Gamma-ray Large Area Space Telescope
Procedure for MCM rework on tray MID 070
See NCR INFN-PI 385 Major

2. 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.

3. Preparation I 1 2 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. 3 4 5
All the process shall take place in class 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.

4. 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.

5. 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.

6. 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 CV (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.