1. GLAST LAT ProjectLadder wirebonds break - MRB 03 Dec 2004 L. Latronico1 Ladder Wirebonds break MRB Meeting – 3 december 2004

2. GLAST LAT ProjectLadder wirebonds break - MRB 03 Dec 2004 L. Latronico2 Description and reference documentation Description –3 different ladders belonging to 2 tower A trays showed signal strips interrupted at half their length –this could be inferred from noise measurements (compatible with half strip capacitance) and CR hitmap occupancy –trays could not be inspected as they were already assembled into tower A Root cause –from comparison with measurements taken during acceptance test at G&A and after thermal cycle we could identify thermal cycle as the origin of the break Reference NCR List –INFN/PI_318 (Tray Heavy 020) –INFN/PI_319 (Tray Bottom 003)

3. GLAST LAT ProjectLadder wirebonds break - MRB 03 Dec 2004 L. Latronico3 Acceptance tests at G&A Findings –top plots: noise profiles show no disconnected or interrupted channels –bottom plots: CR hitmaps are uniformly efficient Reference documentation –Bottom 03 tested on 11/26/2004 ( EGSE session GA-alpha-105) –Heavy 020 front tested on 11/24/2004 (EGSE session GA-alpha-89) Bottom 03 Heavy 20 Front

4. GLAST LAT ProjectLadder wirebonds break - MRB 03 Dec 2004 L. Latronico4 Post thermal cycle tests Performed on stack of trays for bottom03 (11/28 - EGSE session INFN/PI-beta-15): –Noise profile shows a group of channels with lower noise. these channels were not detected as threshold for disconnected channels is ENC strip < 500 e - and they are just about above that threshold –CR hitmaps shows a less than 100% efficient region correspondingly Heavy 20 Front was not tested before tower assembly for a mistake: –After a standard flow-chart thermal cycle (4 cycles) a HV short was found on ladder 0 of back side (signal bonds touching ladder edge - NCR INFN/PI-303) –The tray was immediately brought to G&A (11/29) for repair without testing front side –The repaired back side was tested OK at G&A –The tray came back to INFN (11/29) and went to a second thermal cycle (2 cycles) but only the repaired side (back) was tested afterwards (11/30), in parallel to the start of tower assembly, and assuming that the front side had been tested before Bottom 03

5. GLAST LAT ProjectLadder wirebonds break - MRB 03 Dec 2004 L. Latronico5 Tower A findings Bottom 03Heavy 20 Front Mid 82 Back Tower 1 st test (11/26/2004 - INFN/PI-gamma-9) clearly revealed the problem – Mid 82 shown for reference as a good layer

6. GLAST LAT ProjectLadder wirebonds break - MRB 03 Dec 2004 L. Latronico6 Offline analysis confirm the problem 2D scatter plot X0 vs Y0: dead channels are inefficient all along strip length broken wire bonds along ladder are efficient for part of strip length 1D CR hitmap Y0 (Bottom 03) ~30 strips half dead ~ some strips broken at ¼ length? 1D CR hitmap X0 Few dead channels

7. GLAST LAT ProjectLadder wirebonds break - MRB 03 Dec 2004 L. Latronico7 Offline analysis confirm the problem 2D scatter plot X4 vs Y4: Break again at half strip length 1D CR hitmap Y4 (Heavy 20 Front) ~1.5 ladders half dead 1D CR hitmap X4 Few dead channels

8. GLAST LAT ProjectLadder wirebonds break - MRB 03 Dec 2004 L. Latronico8 Offline analysis from tower 0 Went back to tower 0 data –The only tray showing interrupted strips had very few live channels (NCR INFN/PI-92) –The problem was there already

9. GLAST LAT ProjectLadder wirebonds break - MRB 03 Dec 2004 L. Latronico9 Conclusions and Proposed dispositions Conclusions –Wirebonds connecting different SSDs inside a ladder broke in 4 ladders attached to 3 different trays of stiff type (heavy and bottom) –Break tend to appear at the centre of tray –Root cause is very likely the same effect that broke wirebonds between strips and FE and led us to remove encapsulation –We cannot remove encapsulation on ladders Proposed dispositions (for both NCRs) –use trays as they are for tower A: there was no availability of spare trays of heavy or bottom type, therefore trays were assembled into tower A to keep up with the schedule –Review temperature ranges for thermal cycles and thermal- vacuum tests: Proposed range is -20C - +50C Qualification program on tower0 trays

10. GLAST LAT ProjectLadder wirebonds break - MRB 03 Dec 2004 L. Latronico10 Tower A first 100 events Despite this issue, Tower A was assembled and test in a week and it’s a good tower!