Low Mass Alice Pixel Bus Rui de Oliveira TE/MPE/EM 6/9/20161Rui de Oliveira Alice worshop

Alice Pixel Aluminium Bus Existing BUS description –Material budget –Staircase shaping –Aluminum vacuum deposition –Creating micro-vias –Patterning aluminum –Aluminum plating and bonding –Testing –Production info Possible evolutions –Reducing amount of metals –Cooling element Conclusions 6/9/20162Rui de Oliveira Alice worshop

ladder Pixel_chip Pilot & Optical link Extender carrier bus TOP VIEW OF ALICE PIXEL DETECTOR ONE SECTOR Image:INFN(Padova) 6/9/20163Rui de Oliveira Alice worshop

1 2 READOUT CHIP PIXEL DETECTOR Aluminium Polyimide CARBON FIBER SUPPORT 1 GND 50µ 2 VDD 50µ 3 SIG 1 10µ 4 SIG 2 10µ 5 SIG 3+ SMD pad 10µ Glue COOLING TUBE SMD COMPONENTS PIXEL BUS CROSS SECTION 6/9/20164Rui de Oliveira Alice worshop

Aluminium bus Size : 160 mm x 16 mm Working support: Thick Cu (300 μm) Chemically removed at the end of the production 6/9/20165Rui de Oliveira Alice worshop

Material budget MaterialRadiation length [cm] Density [gr/cc] Resistivity [uohms*cm] Aluminium Copper Beryllium Gold Glass epoxy 19.4 Polyimide 29.0 Copper is close to 6.5 times more transparent than aluminium And aluminium has only 1.6 times the resistivity of copper Polyimide is 1.5 times better than glass epoxy. 6/9/20166Rui de Oliveira Alice worshop

Staircase shape PIXEL BUS MCM Signals1 VDD GND Pixel readout chip Pixel detector Signals2 Signals3 GND VDD Signals1 Signals3 Signals2 6/9/20167Rui de Oliveira Alice worshop

Aluminum Vacuum deposition -10 μm aluminum deposition with sputtering assisted with a DC magnetron -Pre-cleaning with oxygen and argon plasma -0.1μm Cr adhesion layer Problems -Thick aluminum  High temp process  degassing during deposition -High degassing  nodules in deposition  bad chemical etching -Aluminum thickness uniformity Improvements -Put the degassing under control -Improve the surface treatment before deposition (sandblast) -Target position during deposition (uniformity) 6/9/20168Rui de Oliveira Alice worshop

Al on Al deposition Al on polyimide Backed Prismatic & columnar deposition Al on Polyimide/epoxy Backed Al on polyimide/epoxy Backed Nodules: 3μm big nodules (10μm) 6/9/20169Rui de Oliveira Alice worshop

 vias – Process Al Cu Dielectric Glue Cooper Etching Dielectric Etching Anisotropic Glue Etching Metallization Copper etching Al deposition 6/9/ Rui de Oliveira Alice worshop

aluminium tracks layer n-1 Glue Deposited aluminium Polyimide aluminium tracks layer n-1 Glue Polyimide cavity no cavity Glue removed chemically Glue removed by sand blasting Glue removal 6/9/201611Rui de Oliveira Alice worshop

Aluminum etching In order to etch precise aluminum tracks on thick deposited aluminum and glued foil layers we have tried: - Different types of resist (liquid, solid) - Different ways for resist deposition (spraying, dipping, laminating, spinning) - Different chemicals to etch the aluminum (phosphoric acid, ferric perchloride, KoH, NaOH etc…) Some examples 6/9/201612Rui de Oliveira Alice worshop

Bad solutions to etch Vacuum deposited aluminum Direct phosphoric acid etching - micro delamination - bad edges quality Direct ferric perchloride etching - over etchings and parts not etched Phosphoric etching with no resist baking - resist delamination before the end of the process - residues of aluminum 6/9/201613Rui de Oliveira Alice worshop

Phosphoric acid etching - solid resist (140deg baking) - 45 min etching - nitric acid pre-cleaning (before resist lamination) Ferric perchloride etching - solid resist -15 sec etching - nitric acid activation during process Good solutions for aluminum etching 10 μm vacuum deposited aluminium 15 μm aluminium foil glued 6/9/201614Rui de Oliveira Alice worshop

Vertical lines Analogue power Analogue ground Bonding and plating 400µ digital power Digital ground Pixel readout chip Pixel detector 6/9/201615Rui de Oliveira Alice worshop

Bonding Close up view LadderBonding Copper bus (initial tests) Plating defect 10umAl + 0.1umZinc + 10umNi + 0.1umAu With sand blast pre-treatment 6/9/201616Rui de Oliveira Alice worshop

Testing Flying probe tester speedy 580 -Thinner testable pitch : 150um -Existing Bus just below this value  Creation of test boards -For future productions no problems for direct test 6/9/201617Rui de Oliveira Alice worshop

104 right left bus produced 70% average yield Last batches up to 85% yield 14 months to build all the buses Main problems : –epoxy glue degassing –Testability –NI/Au plating for perfect bonding Last production numbers 6/9/201618Rui de Oliveira Alice worshop

- Reduce chip consumption to reduce Bus Power layers ( 2x 50um  2x 30um) - Reduce signal line thickness ( 3x 10um  3 x 5um) - Remove NI/Au Plating and Tin/lead soldering (all connections with AL bonding) - Remove metal in the cooling element Possible actions to reduce the Material budget 6/9/201619Rui de Oliveira Alice worshop

NEW possible cooling structure 1 2 READOUT CHIP PIXEL DETECTOR CARBON FIBER SUPPORT COOLING TUBE SMD COMP SMD COMP With new cooling structureExisting structure 6/9/201620Rui de Oliveira Alice worshop

0.5mm copper glued to Kapton or epoxy or carbon Copper etch Epoxy fill Copper etch Kapton or epoxy or carbon covering -No metals -Thinner skins -Full area cooling -Less sensitive to fluid pressure NEW possible cooling structure details 6/9/201621Rui de Oliveira Alice worshop

Thin Al layers Remove Ni, Au, Sn and Pb Remove Stainless-steel from cooling Conclusions: Possible actions to reduce the material budget 6/9/201622Rui de Oliveira Alice worshop