Adhesive Test Program

Transcription

1 Adhesive Test Program Claudia Gemme / INFN - Genova Adhesives needed to assembly a module Status of each adhesive To do list C. Gemme University and INFN / Genova Pixel week, Cern, Dec 6th 2001

2 Module parameters to be assessed Flex-sensor interface Different candidates Different gluing patterns and methods Potting: Different candidates different methods MS adhesive: 3 candidates Modules: 2 bump types C-C 2 2

3 Glue Joints on Modules At least 5 adhesives are needed during module assembly: Flex on test support frame; MCC on Flex; Pigtail to Flex; Flex to module: Under the MCC; Under the Pigtail; Under the FE s wire bonds; Module to Carbon-Carbon support. Wire bonds potting. General comments: No stress on bumps during thermal cycles (or other fragile points as flex traces, wire bonds...). Experience in some labs with thermal cycles with hot/dummy modules. 3 3

4 Requirements: allow wire bonding flex/frame; Flex on support frame maintain properties up to ~200 0 C (flex glued on frame before SMD mounting). Experience: Only Bonn has experience on this topic: suggested high temperature epoxy. Some experience now in Oklahoma for flex V3: chip tacking adhesive. To do list: Is the Flex flat enough for probing? Needed some pins during gluing for a better alignment? Experience needed with flex V3. 4 4

5 MCC on Flex Requirements: radiation hard; quantity small enough not to wet the wire bonds pads; electrically conductive; thermally conductive (?, how many mw?); no mechanical requirements; no requirement on curing temperature/time or pot life. Experience: Mipot: Epotec H20 in the centre + Epotec H70 outside the ground pad; Bonn: E-SOLDER 3025 Silver epoxy. 5 5

6 Pigtail to Flex Requirements: radiation hard; quantity small enough not to wet the wire bonds pads; no requirements on electrical and thermal conductivity; requirement on curing temperature: if the pigtail attached after the flexmodule assembly, T curing <60 0 C; mechanical requirements: through the pigtail possible stresses on the module (at least it will be permanently bent, ). This effect has to be studied combined with the glue used to attach the flex on the module (4b). Peel strength constraint? Experience: Bonn: Pyralux LF 0300 Epoxy Prepreg foil (high temperature required). To do list: Quantify the strength on the module when the pigtail is bent. Verify possible damage on bumps (AMS-Genova, IZM-Bonn). Pigtail has to fixed by clamp to the module/stave support during module test. 6 6

7 Flex to bare module Main Requirements: keep the flex attached to the sensor: quantity enough to handle the module when attaching it to the stave; support the stresses coming from the pig tail; quantity small enough to reduce coupling flex-module and minimize CTE mismatch; uniformity (glue/not glue) under flex wire bonding pads; no glue on the sensor alignment marks; electrically not conductive; radiation hard; curing temperature < T curing <60 0 C; short curing time (if possible). Minor Requirements: No glue in the guard ring region (? sensor tests and experience seem to show no difference); thermally conductive under the MCC (?); pot life > 1 hour (more modules with the same glue ); applied on the flex or the sensor by a dispenser (automatic and reproducible way). 7 7

8 Deposition methods: Flex to bare module LBNL Genova Bonn Candidates: LBNL: Eccobond 45 Genoa: Eccobond 45, silicon DC 734, Epotek353 Bonn: DC SE4445 under the MCC, DC 3140 or 3145 and a primer ASEOL under the pigtail, 9 small dots per side between the flex and the FE s (DC 3140 or 3145) 8 8

9 Flex to bare module To do list: define a standard and reproducible procedure for glue deposition using glasses, dummy flex. verify mechanical stress coming from handling when: attaching pigtail and bending it; mounting on the stave (vacuum holder). thermal cycles in real conditions: C-C support and final MS adhesive; dummy chain modules; real flex; glue on module deposited with a standard procedure. Effects on bumps can be monitored with dummy chain modules (PCB). Effects on flex (line ruptures) or wire bonding (detachments) can be monitored only through hot modules. Wire bonds uniformity: test with nitrogen flow to verify the wb s quality, x-ray, pull-up test. 9 9

10 Can we avoid wire bonds potting? Main Requirements: radiation hard; Wire bonds Potting quantity small enough not to wet the zone for the vacuum holder; Experience: Genova: silicon DC 734 (too fluid). Some experience with optical fibre. LBNL: Bonn: silicon?? First trials. No firm conclusions yet. Comments: This adhesive can be chosen after the other ones. Problems with weak wire bonds (if any) during deposition and thermal cycles

11 Module to Carbon-Carbon support This is the most tested adhesive. Requirements: thermal conductivity > 0.2 W/mK; soft: shear modules < 50 N/mm 2 ; radiation hard; Electrically non conductive; curing at room temperature; adhesive confined within the chip; good wetting; not creeping after curing; allow module replacement without damaging the support

12 Module-support adhesive Status of the adhesive test program (first part): CGL7018 is the current baseline: 1 component thermal paste; its function is exclusively thermal ; the mechanical link of the module on the support relies on permanent UV tags; the long term reliability is unknown (it is a grease, only partially cured). Starting with a list of 15 candidates, after two selection steps we restricted the choice to the following two: Eccobond 45 (Emerson Cuming): 2 component epoxy (flexible mixture). SE 4445 (Dow Corning): 2 component silicon

13 Eccobond vs SE4445 Eccobond deposition possible with dispenser (similar to CGL) do not need tacks good applicability with simple masks (tricky on the stave?) removal is feasible only heating up to C (test on stave done in Genoa) stiffer (more stress on module) SE4445 To do list: Shear and creep tests on irradiated SE4445 (samples ready at CERN). Irradiate and repeat temperature cycles on samples already temperature cycled (Marco and Wolfgang). Equip a full stave with dummy Si heaters glued with the three adhesive candidates and perform an evaporative cooling test to get a final assessment of the different thermal performances (Marseille) Get more experience on SE4445 application. (done in Bonn, should also done in Genova, Bonn will send spheres..)

14 Conclusions to the MS adhesive program On the basis of the results available up to now we have two alternative options to CGL7018. We can decide to have three candidates or we can reduce them to two (baseline + backup). To have reproducibility is not easy and it s a long job (Marseille experience on CGL): each lab can not tune its own tools for each of the 3 adhesives. When do we have to decide???? Still to do: Radiation effects on SE4445 (when???); Verify effects on pixel noise/threshold if adhesive is not confined under the chip surface (relaxing this constraint would make easier to get reproducibility). Next slides refer to some measurements done in Genova (Apr 00)

15 Effects on glass of glue Dow Corning 734RTV and Epotek 353ND have been used on glass samples bumped on bad electronics, both glues are fluid. A minimal quantity is applied on two edges (parallel to columns), it enters in between chip and glass by capillary effect. Dow Corning enters <0.5mm, Epotek fills almost everything

16 Effects on electronics of glue Small amount of Araldit353 has been put on glass sample and on a single chip with FE_C (GE_C_7). In both cases glue is deposited at the EoC logic edge (the only accessible for the single chip once mounted on board). Glue enters as expected (~3-4 mm) EoC logic is here 16 16

17 Effects on electronics of glue 3150e 140e 5000e 290e 6500e 17 17

18 Threshold before and after 18 18

19 Noise before and after 19 19

20 How to go on Take a decision on module-c-c support adhesive (3 or less candidates). When???? Make a test program on flex module adhesive, using the new dummy modules to define pattern deposition and candidates as a function of the bump bonder (IZM,AMS). We need to verify during thermal cycles and module handling flex lines; bump connectivity; wire bonds connectivity. Quantify possible effects induced by the pigtail bending. I see no priority on other adhesives (MCC-flex, pigtail-flex, wb s potting). We have some experience: we need to collect it but coordinate efforts

21 Flex module adhesive: Towards next Pixel Week As a main requirement there is the possibility to have uniform wire bonds quality. This could be achieved putting no glues under the pads (then the flex could be no flat, other difficulty for the wb s) or putting a uniform amount of glue. This was an issue in Genova where we always used glue under the pads deposited manually. Now we have a automatic dispenser, reproducibility should improve. Check the wb s quality using: nitrogen flow (flow to be carefully tuned to individuate weak wire bonds but not to weaken the good ones); pull up test; x-rays ( available in Genova in few months)

22 Towards next Pixel Week Test with thermal cycles: setup dummy chain modules gluing on a C-C support with a final candidate adhesive; testing flex-module pattern glue; real flex; no wire bonds or potting. Monitoring: by probing dummy chip or monitoring signals through a board (Bonn/Genova- AMS in this case some wire bonds are needed to the board) to check bump connectivity; by probing flex to check line continuity

23 Pigtail stress on module: Quantify strength. Towards next Pixel Week First measurements can be done with old modules: attaching the pig tail and bending it, eventually performing thermal cycles. We can do measurement with the dummy modules already used before again: : attaching the pig tail and bending it, eventually performing thermal cycles