VELO Upgrade Modules

Introduction

The upgraded VELO will be composed of 52 modules placed along the beam axis divided into two retractable halves. The modules will each be equipped with 4 silicon hybrid pixel tiles, each read out by 3 VeloPix ASICs. The VELO upgrade modules will have their detector assemblies and electronics mounted onto a cooling substrate which is composed of thin silicon plates with embedded micro-channels that allow the circulation of liquid CO2. This technique was selected due to the excellent thermal efficiency, the absence of thermal expansion mismatch to the silicon ASICs and sensors, radiation hardness of CO2 and very low contribution to the material budget. The front-end hybrid hosts the VeloPix ASICs and a GBTx ASIC for controls and communication. The hybrid is linked to the opto-and-power board (OPB) by 60 cm electrical data tapes running at 5 Gb/s. The tapes are vacuum compatible and radiation hard and required to have enough flexibility to allow the VELO to retract during LHC beam injection.

The Modules will be made at 2 collaboration sites: Nikhef (Netherlands) and University of Manchester (UK). Meetings are held every Tuesday at 16:00 (CET) to follow up on the development of module construction. The Work Package has gone through Engineering Design Review and Production Readiness Review.

Assembly sequence

In the following, the assembly sequence is shown together with images of both sides of a module after each assembly step.

Bare Module

The construction of a module starts by assembling a so-called Bare Module, which comprises an Aluminium foot, two carbon fibre legs, a cable clamp, a carbon fibre mid-plate and a micro-channel substrate with cooling pipes and connector.

Module with tiles

In the second step of the assembly, the 4 tiles (each consisting of a silicon sensor and 3 ASICs bump-bonded to it) are attached either side of the substrate with a thermally conductive glue (Stycast 2850FT and catalyst 23LV).

Module with hybrids

In the third step of the assembly, the 4 front-end hybrids and the 2 GBTx hybrids are attached either side of the substrate with a flexible glue (Loctite 5145).

Module with hybrid cables

Once the hybrid boards have been glued to the module, the front-end hybrids are wire-bonded to the ASICs. Afterwards, the HV, interconnect and data cables are connected. The HV cables are also glued with Araldite 2020 to the substrate and wire-bonded to the back of the silicon sensor.

Fully assembled Module

Finally, the LV harness is attached to the module.

Manchester setup

A collection of photos and CAD models of the setups and equipment used at Manchester for the module production.

Bare Module jig

Stages

Tiles are positioned to the desired X,Y position using motorised stages that can move horizontally, vertically and can rotate. A camera is used to locate the tiles precisely.

Turnplate

The turnplate is used to hold the bare module firmly during the positioning of the tiles.

Transfer plates

The transfer plates are used to pick up the tiles and hybrids after they have been accurately positioned.

Wire-bonding jig

Vacuum tank setup

Nikhef setup

Nomenclature

The nomenclature of the tiles is according to the following 3 possibilities:

• C(onnector) and N(oconnector) face of the module,
• L(ong) and S(hort) side of the substrate,
• I(n) and O(ut) with respect to the beam.

Therefore, the four tiles are labelled as:

• CLI and CSO on the connector side of the module,
• NLO and NSI on the non-connector side of the module.

The figure below shows the tiles and their chips. The 3 ASICs bump-bonded to the silicon sensors are shown as grey rectangles and their name is given as well. The red labels show the name of the link(s) in each corresponding ASIC: each chip has 1, 2 or 4 links, depending on its position w.r.t the beam.

Manuals and checklists

The assembly procedures at Nikhef and Manchester are described in details in the following documents:

• Manchester module construction manual v3 (June 23rd, 2019) can be found here .
• Manchester checklists are available here .

• Nikhef module construction manual v0.0 can be found here  (on cernbox) and the gitlab repository can be found here . 
• Nikhef checklists (on gitlab) can be found here . 
• In both cases the most recent build can be downloaded from the links at the bottom of the gitlab page.

• Instructions on how to run the electrical tests with the new FSM can be found here 

Reviews, Workshops and important meetings

• 2011, CERN, LHCb Upgrade Mini-workshop on VELO 
• 2012, CERN, VELO pixel module0 face to face meeting 
• 2012, Santiago de Compostela, LHCb VELO Upgrade mini workshop 
• 2013, Nikhef, VELO Upgrade Technology Review 
• 2015, Manchester, LHCb VELO Upgrade mini workshop 
• 2015, Nikhef, LHCb VELO Upgrade mini workshop 
• 2015, Liverpool, LHCb VELO Upgrade Mechanics mini workshop 
• 2015, Oxford, LHCb VELO Microchannel substrate EDR and Mechanics meeting 
• 2016, Liverpool, LHCb VELO Upgrade sensor PRR 
• 2017, CERN, LHCb VELO Upgrade Review 
• 2017, CERN, VELO mini component review 
• 2017, Manchester, VELO Upgrade Mechanical Module EDR 
• 2018, CERN, PRR of VELO FRont-End electronics 
• 2018, Nikhef, VELO Upgrade Module PRR 
• 2019, Nikhef, VELO Module Production Site Specific Review Nikhef 
• 2019, Manchester, VELO Module Production Site Specific Review Manchester