Outline

Prototype flex hybrid and module designs for the ATLAS Inner Detector Upgrade

Ashley Greenall

The University of Liverpool

On behalf of the ATLAS Tracker Silicon Strip Upgrade Stave Programme

Topical Workshop on Electronics for Particle Physics Paris, September 21-25, 2009 1

2

Outline

Introduction to the Stave (2009) concept Geometry and components

Stave flex hybrid, first steps Build considerations - preparing for mass production Prototype flex, a test vehicle for the 0.25µm ABCN-25 ASIC

Electrical performance (using untested ABCN-25) Short strip module demonstrator using ATLAS07 large area sensor (10cm x 10cm)

Bridged Hybrid Hybrid directly glued onto sensor

Summary

First stave module, a substrate-less and connector-less module Module concept and flex build

Current substrate-less hybrids Substrate-less stave hybrids and industrialisation Stave Readout architecture A first look at module integration onto a stave

Conclusions

Topical Workshop on Electronics for Particle Physics Paris, September 21-25, 2009

Stave 2009 – Geometry and components


~ 1.2m (1200mm)

Bus cable

HybridsCarbon honeycomb

Carbon fiberfacing

Readout IC’s

P-type 4 segment crystals (10cm x 10cm) ABCN-25 readout ASIC

40 per module 960 per stave (>120k channels)

Kapton hybrid Auxiliary BCC asic (digital I/O) Serial Power protection

Embedded bus cable End of stave card Stave mechanical core

Coolant tube structure

3

Single flex Module with 2 x flex

120mm

Sensor

12 modules/side of stave

Stave flex hybrid – Build considerations


Hybrid layout is driven by minimising material Keep the area small! Engage ASIC and sensor designers to achieve this.

Eventually we will want to source in excess of 10000 pieces (for Barrel short-strip layers) Yield and reliability has to be taken into account from the outset Don’t push the limits on design rules (pertinent to feature size) Repeatability becomes problematic for non-standard capability – limits vendor choice

Manufacturability, feedback from UK (flex) manufacturers: Keep to standard 100µm track and gap routing to maintain yield Identified via lands (for plated-through holes) as critical, need to be >300µm

Ref: CMS had many problems with micro-vias (had to increase to 320µm to recover yield/stability) Settled on 375µm via lands with 150µm laser drilled holes

Kapton carrier (dielectric) should be no thinner than 50µm – handling issues during manufacture

Will be a staged design First stage – very cautious, new ASICs and sensors to be evaluated THIS IS WHERE WE ARE

Flex build is electrically ‘robust’ – maximal power planes and supply decoupling Second more aggressive stage – comes much later,

Reduction in hybrid mass (removal of non-critical passives, power plane reduction etc.)

S

M: Master (Legacy mode)

Mm: Master (Legacy mode + MCC I/O)

S: Slave

Common Bus serving 20 x ABCN-25

Primary Data O/P

Redundant Data O/P

MCC I/O (Data + Token)

Connector

Consists of 2 columns of ABCN-25s with a services connector

Readout Architecture is made up of

Single TTC Bus (BCOClk, Com, L1, DataClk)

Power Control Bus for serial powering circuitry

Auxiliary Analogue Supply routed to front-end of ABCN-25s

Alternatively make use onboard regulator for the front-end

Common Digital Supply provided for ABCN-25s

Legacy data paths at top and bottom of each column (maintains compatibility with existing DAQ)

Bi-directional data paths within columns can be exercised

Data & Token I/O for 2 leading ABCN-25s for use with an upgraded DAQ (if desired)

Column 0 Column 1

Prototype flex topology


S

S

S

S

S

S

S

Mm

M

S

S

S

S

S

S

S

S

Mm

M

ASIC – Sensor Detail

<16° bond angle


Dialogue with designers

4.1mm

Se

nso

r b

on

d p

ad

s

Front-end Decoupling Capacitor

Early dialogue with ASIC and sensor designers lead to modifications to increase manufacturability and reduce mass...

Wire bond pad locations and ASIC size/placement fixed to allow for direct ASIC-to-sensor wire bonding

Pitch adaptors are no longer requiredLess mass and wire bonds

ASIC bond pads re-located:Inter-chip communication now provided by

wire bonds and not traces on the flex.Front-end decoupling capacitor positioned

for shortest bond length.

6

Vias

Flex build details4 layer build designed to qualify components i.e. ASICs and sensors and to prove signalling quality as fast as possible

Layer 1 & 2: SignalLayer3: Analogue and Digital PowerLayer4: Common Ground

Flex manufactured by Stevenage Circuits Ltd UK100µm track and gap375µm via lands with 150µm laser drilled holes50µm Kapton (polyimide) dielectrics

Digital Power

Analogue Power

Common Ground

Component Layer

Solder Resist (25µm)5µm Cu foil carrier + Ni/Au plating (5µm)Bond ply (50µm)Cu (18µm)Kapton (50µm)

Predicted build thickness is ~260µm, actual is ~280µm(uncertainty arises due to plating of outer layers)


Digital Bus

Hybrid Stuffed with Passives and 6 x ABCN-25s

Inter-chip bondingNeighbouring ABCN-25s wire bonded

7.5mm 7.5mm2.1mm

Flex Weight ≤2g (unpopulated)

Fully populated hybrid

24mm

8Topical Workshop on Electronics for Particle Physics Paris, September 21-25, 2009

Hybrid realisation

100

mm

Distributed decoupling capacitors adjacent to the ASICs for power supply decoupling - capacitance increases whilst inductance reduces (improves high frequency decoupling)

Sensor HV filter with guard ring

Transmission of fast LVDS signals (expected to be 160MHz for next generation ASICs), need to account Use of thin dielectrics for flex build, results in a high capacitance (~25pF on a 100m trace) further loading the bus Bus loading (up to 20 ASICs max)

Trace impedance set by width, thickness of dielectric and dielectric constant. Hybrid topology makes use of embedded edge-strip geometry for LVDS transmission. For proposed build using 100µm track and gap with 50µm dielectrics, ZDIFF ~ 71Ω.

But this does not take into account asic receiver loading (see plot below). 20 ASICs on bus reduces impedance to <50Ω.

Trace Impedance, Zdiff as function of 10 & 20 ASIC loading

0

10

20

30

40

50

60

70

80

1 2 3 4 5 6 7 8 9 10 11 12

Asic drops

Imp

edan

ce (

Oh

ms)

10 ASICs

20 ASICs

Unloaded Bus Loaded Bus

80Mbs PRBS

43Ω end termination

(2ns/div, 50mV/div)

160Mbs PRBS

43Ω end termination

(2ns/div, 50mV/div)

Electrical Performance – Signal Propagation


Eye diagrams for 20 ASIC Loading

•Hybrid tested at both 40MHz and 80MHz data rates (maximum that ABCN-25 operates at)•All 4 data paths from hybrid work - confirming ABCN-25 bi-directional I/O functions correctly

40MHz data readout

Gain: 105mV/fC

Input Noise: ≤400e ENC

Threshold variation:5.5mV before trimming, 1mV after trimming

Noise Occupancy

Electrical Performance – Hybrid results


80MHz data readout

After trimming

ASICs and hybrids working extremely well with high yield

Channel threshold spread

Channel threshold spread

ENC vs ChannelENC vs Channel

ENC vs Channel

Occupancy vs Channel

ATLAS Tracker Upgrade Week, 23rd-27th Feb 09

Short-strip module demonstrator with 10x10cm sensor


Overview

Al plate with machined bridge legs and cooling pipe (10°C glycol + water)

Sensor glued directly to fixture 2 layers of 75µm thick kapton

between Al plate and sensor HV connection through tab to

backplane Al plate referenced to ground of hybrid First hybrid bridged with 1mm thick Al

2mm air gap between hybrid and sensor

Second hybrid directly glued to sensor

Objective

Test the functionality of the ABCN-25 in a 20 ASIC hybrid bonded to a full size ATLAS07 sensorUsing untested ASICs

Check the noise performance and occupancyStability at low threshold of 0.5fC


First tests – Bridged hybrid


Bridge grounded to plate Thermal grease applied to cooling

points Hybrid operating at 40°C i.e. 30° above

coolant temperature (coolant at 10°C) Peak currents >4A during readout Token passing non-functioning between

chips 5 and 6 (damaged bond pad) All chips work BUT only able to

readout 15 chips at a time

Noise Slope

• Able to join 2.5cm segments of sensor to single ABCN-25 e.g. 2.5cm, 5cm and 7cm strip lengths

• Also have bare hybrid plus 1cm silicon strip measurement

• Sensor design provides 1pF/cm load

2.5cm

5cm

7.5cm


Preliminary Noise slope


With separate analogue/digital power

With analogue regulator

Bare Hybrid

400-450 e- 400-450 e-

1 pF 525 e-

2.5 pF 605 e- 575 e-

5 pF 986 e- 952 e-

7.5 pF 1364 e- 1313 e-

Noise prediction from ASIC designers with no detector leakage

Measured noise is slightly higher than that expected from simulation – especially above 2.5pF load


Bridged Hybrid Electrical Performance


Module tested with front-end regulator enabledSingle Digital power feed to all ASICs

Input Noise is as expected at ~600e-

Open circuit channels are due to wire-bonding problems Al plate hybrid is mounted on is not rigid enough – makes it difficult to bond

Noise Occupancy at 1fC is <10-6

Shows a very regular uniform profile across all channelsClearly shows the 5 ASICs we are unable to readout

Noise Occupancy

ENC vs Channel



Directly Glued Hybrid on to Sensor


p- bulk p-spray/stop

Passivation

Hybrid

Kapton (75 m)

Kapton (150 m)Copper (75 m)

Glue(~20 m)

Hybrid was not designed to be glued directly to sensor Vias go right through the flex circuit – results in a perforated ground plane No shielding of the digital bus is provided

Copper shield added between hybrid and sensor Insulated from hybrid and sensor Can be referenced to hybrid ground if desired

Hybrid operates at 24°C during readout (compare with the bridged hybrid of 40°C)

Glue was only applied on passivated regions of sensor, maintaining a clearance of 5mm from the guard-rings.


Glued Hybrid Electrical Performance


With the screen connectedTo either module ground or HVretChannels towards the edges of the ASICs

have elevated noiseInput noise is ~650e-

With the screen floatingNoise profile is flatInput noise is ≤600e-

Performance is comparable to Bridged Hybrid

Shield Connected Shield Open Circuit


ENC vs Channel ENC vs Channel


Glued Hybrid Electrical Performance – Low Threshold Stability


Scurves at 0.5fC threshold show no instability with 2.5cm sensor strips bonded

Scurve distortion is due to wire-bonding (see next slide)


Wire-Bonding Problems


• Identified that glued hybrid is 400µm off centre w.r.t. sensor

• Results in increased bond-angle from ASIC to chip

• Bonds at chip-edges are at 12-21° angle• Anything >16° is at risk of shorting to

neighbouring bond pads on ABCN-25• This is what we see on the noise plots

• Problem with bonding of front-end ground pads • Wire bonds are orthogonal to pad

• Pad is too narrow for the bond foot• Adhesion of bonds is not so good

• Revised layout of flex will correct for this


Prototype flex/module Summary


First batch of flexes arrived towards the end of last year – 36 totalYield of 89% was achievedShould increase to ≥98% during production run (achieved by process tuning)Yield enhancement is part of the design stage – high yield translates into a reliable

object

Hybrid performs as expected – untested ASICsHybrids have been successfully used at 4 different sitesWire-bonded at 2 sites with no problems

For the module, bridged and glued hybrids have similar electrical performanceBoth stable at 0.5fC thresholdNoise is higher than predicted from simulation

No show stoppers identified for Stave hybrid


Stave Module Concept


•Flex circuit is designed at the outset for direct gluing to the sensor•Core of the circuit (trace routing, component placement remains as prototype) – it works•But will have to revise the flex build to take into account additional shield layer

•Sensor provides mechanical support and thermal management

•Prior to gluing the flex circuit to the sensor the flex is not rigid•Need to stuff with passives/ASICs and then test before gluing on to the sensor

Furthermore

•Have to take into account integration of the module on to a stave

•Stave design calls for a connector-less system•All connectivity is made by wire-bonds to/from a bus cable•Bus cable is a single-layer design – results in connections at opposing ends of flex

•Would like to maintain maximum flexibility for stave module – especially true for powering•Default powering is serial •But power/protection board has provision for auxiliary plug-in boards (for DC-DC, etc/)

•Also start looking at industrialisation of flexes•Component stuffing and testing

Sensor


Stave Module Layout


Flex is a 4+1 layer build (4 electrical + shield layer)

Layer 1 Signal Layer 2-3 Signal/Power Layer 4 Non-split Ground Layer 5 Shield (single-point contact with option

to connect to module ‘ground’ or leave open)

Inner layer Cu thickness is 18µm Top layer is 5µm Cu with Ni/Au plating Shield is 5µm Cu Kapton dielectric thickness is 50µm

Total build thickness is ~300µm

Power/Protection Board

‘M’ Shunt Regulation Control Circuit

Digital I/O - BCC

97.6mm

5mm

6.2mm

6.2mm

5mm

24mm

TTC & Data Bus

Serial Power, Control & Sensor Bias

Sensor HV Filter Circuit +Power In/Out to flex

AB

CN

-25

fle

x

AB

CN

-25

fle

x

Stave 2009 – Readout Architecture


Module 1 Module 2 Module 12

TTC

Data

PwrIn

PwrOut

TTC (L1, Command and 40MHz clock) is broadcast as multi-drop LVDS to all modules 24 drops in total with ac-coupled receivers Non-balanced data transmission

2 data output links per module, 1 per flex Point-to-point LVDS Up to 160Mbs data rate AC-coupled, non-balanced data transmission

Default powering scheme is serial Flexes sat at differing voltage potentials (2.5V per flex, 60V total across a stave) Parallel (DC-DC) powering is also provided for

Independent parallel sensor biasing (12 x HVbias + return) Single NTC thermistor per flex for temperature monitoring

BufferControlChip provides digital I/O

Serial powering

Digital I/O

Sensor bias


How to make a substrate-less hybrid


Flex circuit composed of 2 components

1. Main active circuit (non-glued)

2. Sacrificial ends which are glued to FR4

Circuit sits flat on a rigid FR4 base

Drilled for vacuuming down

Sacrificial ends

Main circuit

I/O bond pads

Step 1

Step 2 Step 3

Final step, circuit + sensor removed

Sacrificial ends (retained)

Initiated a program to investigate working with substrate-less hybridsTry to learn as much as possible from the pixel community

Kindly sent jigs to show steps involved in their module construction (see below)Dialogue set up with both flex and circuit population companies.


Stave substrate-less hybrids and industrialisation


Flexi-rigid construction with flexes selectively glued to a FR4 Panel.8 flexes per panel.Panel is 300mm x 200mm.Matches up to auto-placement machine (passive stuffing geared for industry)Various hole detail shown are used for wire-bonding and module assembly jigs

Panel designed so that flexes can be electrically tested as 1 to 8 items (using legacy or future DAQ)

Active part of flex – not glued to FR4

Score line is used as guide for cutting out of flexes

Sacrificial ends of flex, cut off during flex removal (beyond score line)

DAQ Connector(s)

Power

Bond pads


Stave Integration – Bus Cable Detail


Bus Detail (100µm track & gap)Segmented Shield Detail

(showing break between adjacent modules) Continuous Shield

Serial Power Return (7mm width)

TTC multi-drop Busand Module Data

Power, Control & Sensor Bias

Plots courtesy of Carl Haber & Roy Wastie

1200mm

120mm

Bond Pads

Flexes are DC connected to their respective shield

Flexes are AC connected to the

shield

• Modules (sensor + flex) glued onto stave – embedded bus cable sits between stave core and module• Bus cable used to distribute services to module(s) – digital I/O, power, sensor bias etc. – connections made by wire-bonds• Cable build is single layer Cu Kapton + Al shield on top layer (2 flavours of shield, segmented and continuous to be evaluated)


Conclusions


For the ATLAS Inner Detector and the large number of circuits required, it is important to plan at the outset for manufacturability and reliability.

Dialogue should be set up during the design phase between ASIC, hybrid and sensor designers.This is also true for industrial partners

Hybrid operation has shown nothing untoward – performance is as expected!

Module demonstrator has also been shown to perform wellFirst time an ATLAS07 large area sensor has been bonded to full 20 x ABCN-25 readoutNoise is slightly higher than expectedBUT no show stoppers as yet identified

Have now migrated to ‘next generation’ hybrid designed for integration onto a stave.

Submission took place over the summer and flexes are due imminent.If no problems identified expect flex passive/ASIC stuffing and testing in the near future.

Furthermore module integration onto a stave structure is well understood – now awaiting modulesBus cables have been received and are ready for assembly on to a stave.


Backup


Sensor biasing and gluing


Concerns about gluing hybrid assembly directly to the sensorIs there a risk of damaging the sensor – especially the sensitive guard ring structure

Limited maximum sensor bias to 200VReduces the risk of micro-discharge

Before assembly sensor current is 0.8µAAfter gluing to Al fixture 0.8µAAfter wire-bonding of front-end of bridged hybrid 3.1µAAfter directly gluing of hybrid to sensor 2.9µAAfter wire-bonding of front-end of glued hybrid 3.0µA

Some slight damage occurred during the wire-bonding of the bridged hybrid to the sensor

Otherwise no effect observed due to gluing of hybrid to sensor

Before Irradiation, 20°C

2 Epolite glued miniature sensors were irradiated at CERN PS to 9.3×1014 neq cm-2. Before irradiation, W17-BZ3-P15 showed some breakdown above 950 V before gluing (blue circles). W31-BZ3-P9 goes to 1000V.

After irradiation, W17-BZ3-P15 shows breakdown above 1000 V. W31-BZ3-P9 goes to 1100 V. The currents are consistent with the expected fluence.

No measurable effects from the epoxy on the surface

After Irradiation, -25 C

24 GeV Proton Irradiation Results


Irradiated to 1.5×1015 p cm-2 at CERN (9.3×1014 neq cm-2)No measurable effect of glue relative to similar irradiations

Using fit of clustered charge, efficiency at 500 V near 100% at threshold of 1 fC for 1×1 cm2. Would expect 0.75 fC needed for 2.5 cm strips.


24 GeV Proton Irradiation Results (2)

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