GLAST LAT ProjectHV-short risk evaluation from bubbles cut - 12 Nov, 2004 L. Latronico1 from ANNEX 02 to NCR/FM/INFN/RM2/ cm/tile 4.24 m/layer ~34 m total length of tower0 preventive cut Preventive Cuts (Pcut) Procedure originally thought to prevent delaminations in TVAC only performed on 8 tower0 trays on W-side (8layers)

GLAST LAT ProjectHV-short risk evaluation from bubbles cut - 12 Nov, 2004 L. Latronico2 Small ( 1mm) using an edged scalpel Insulation test (OL) with an ohm-meter between tray and shield plane Used for tower0 trays and # TowerA trays Estimate of total bubble-cut for tower0 = 17layers x 2bubbles x 2mm <~ 7cm Bubble Cuts (Bcut) Procedure

GLAST LAT ProjectHV-short risk evaluation from bubbles cut - 12 Nov, 2004 L. Latronico3 Tower Position Tray S/N Tray typeWPcutBcut (side)HV Short (side)layers Comments 18001TOPSand-Blasted (SB)NFAIL TVAC Y17No Si 17048MIDSBNY(T/B) X16-X17No Si 16047MIDSBNFAIL TVAC Y15-Y16No Si 15004MIDHand-Blasted (HS)YY(T/B) X14-X15No Si 14017MIDHSYY Y13-Y14No Si 13012MIDHSYY(T)Y(B) X12-X13HV-short on bottom 12011MIDHSYY(T/B)Y(B) Y11-Y12HV short on bottom 11008MIDHSYY(T/B)Y(B) X10-X11HV short on bottom 10006MIDHSYY(T)Y(B) Y9-Y10HV short on bottom 9046MIDSBNY(T)N X8-X9OK 8007MIDHSYY(B)N Y7-Y8OK 7010MIDHSYY(B)N X6-X7OK 6009HEAVYHSYY(T/B)N Y5-Y675 disc. ch. 5008HEAVYHSYY(T/B)N X4-X5183 disc. ch. 4035HEAVYSBNY(B)N Y3-Y4249 disc. ch. 3011HEAVYSBNY(T)N X2-X31319 disc. ch. 2023LIGHT NY(T/B)N Y1-Y2OK 1015LIGHT NY(B)N X0-X121 disc. ch. 0002BOTTOM NY(T)N Y0OK Tower0 trays summary chart

GLAST LAT ProjectHV-short risk evaluation from bubbles cut - 12 Nov, 2004 L. Latronico4 0 short on shield lines 4 HV short on trays Pcut and Hand-Sanded W 23 layers OK on HV line (6 Pcut, 15 Bcut) 27 layers OK on shield line (8 Pcut, 17 Bcut)  all shorts due to W whiskers generated from tiles hand-sanding which entered long, deep Pcuts – such whiskers were actually observed on towerA:  NO Pcuts  W tiles are etched and primed, therefore very flat, clean and whiskers-free  Bcuts are superficial (see procedure) Let’s calculate anyway a conservative HV-short probability: a HV short would cause 1 ladder loss (on tower0 trays with HV-short we disconnected HV resistors on MCM boards for all 4 ladders to avoid current flow) Conclusions – risk assessment Prob(1ladder-loss/Bcut) = 4 / 34 m x 2mm = , i.e. 1ladder-loss every 4250 Bcut or 1 ladder with HV-short every 2150 ladders (assuming 1 Bcut every 2 ladders)

GLAST LAT ProjectHV-short risk evaluation from bubbles cut - 12 Nov, 2004 L. Latronico5 Conclusions – schedule constraints type TrayI D Bcut - bottomBcut - topMCM pocket B003NA10ready B004NA6,10,11 H0126,10,116,7,15ready H0107,10,116,7,10,11ready H0206,7,11,12 ready H00610,116,7,9,10,11ready H00510,1111ready H0377 small H018 11,15small L01377,11,12,16small L01377,11,12,16small L004106,10small M042 II test article typeTrayID Bcut - bottom Bcut - top MCM pocket M small M ,12,10,14,15ready M05167,10small M077 assembled M063 ready M050 assembled M053 7assembled M0666,107,11ready M079 assembled M0647,8,127,12ready M0817,10,14,15 ready M0802,7,1511,10ready M small M062106,7,9,10,1small M00211 ready T0026,10NANCR List of available trays 3 trays without Bcut and MCM pocket deep enough to hold MCM  GA flow will be slowed until new trays are available without Bcut