R&D on substrates for CMS tracker hybrids G. Blanchot 07/NOV/2011G. Blanchot - R&D on substrates for CMS tracker hybrids1

Outline 07/NOV/2011G. Blanchot - R&D on substrates for CMS tracker hybrids2  Tracker modules options.  Tracker upgrade  Double sided strip modules  Hybrid strip pixel modules  Pixel – Pixel modules  Double sided strip modules: hybrid circuits  Hybrid and HDI technologies  Hybrid constraints  CBC front-end ASIC  Sensor interface  R&D plans  Prototype hybrid  Schematic: 8 CBCs and Sensor.  A draft layout example.  Beyond a prototype: interconnection of hybrids.  Conclusions

Upgrade of the CMS Tracker 07/NOV/2011G. Blanchot - R&D on substrates for CMS tracker hybrids3  The LHC upgrade for higher luminosity drives the upgrade of the detectors.  A new CMS tracker is required:  New tracking topology  New sensors  New implementation of the front-end electronics.  The tracker is built with modules:  Barrel Modules  Double sided pixel modules (technical challenge)  Hybrid Pixel-Strips modules (see Sandro’s talk)  Regular double sided strip modules (this talk).  Endcap Modules  Every module is made of:  A sensor: strip lines or pixelated strip lines.  Front-end electronics: reads out the signals from the sensors.  Power and interface electronics.

HYBRID Double Sided Strip Module Topology 07/NOV/2011G. Blanchot - R&D on substrates for CMS tracker hybrids4  Parameters (per side) Double sided, 50mm strip detector, 1024 strips (128x8), 90u pitch. 8*256 inputs CBC ASICs on top side of hybrid. Collects 1024 inputs from top, 1024 inputs from bottom. 1 Concentrator ASIC  Common blocks (per module, not shown here) 1 DC-DC converter to power the hybrids. 1 Charge Pump to power the optical link. 1 GBT interface. 1 Optical Link module. EDMS CMS-TK-DF-0008 v.1 / EDMS Id Today’s estimation is: 4416 modules for the barrel modules for the endcap. 2x1024 STRIPS HYBRID COOLING & SUPPORTING STRUCTURE CBC 2x1024 STRIPS

Hybrid Pixel - Strip Module Topology 07/NOV/2011G. Blanchot - R&D on substrates for CMS tracker hybrids5  Parameters Top side: 25 mm strips. Bottom side: pixelated strip, bonded to pixel ASIC. Hybrids: simplified CBC collects pixel data and combines it with strips data. EDMS CMS-TK-DF-0008 v.1 / EDMS Id Sandro’s talk 10 cm 2.5 cm Z  Pixelated Sensor Cooling and support Strip Sensor

Double Sided Pixelated Strip Module Topology 07/NOV/2011G. Blanchot - R&D on substrates for CMS tracker hybrids6  Parameters Double sided, 25 mm pixelated strip detector. Pixel ASICs bump bonded to sensor and to hybrid, in a four sides abutment configuration. Manufacturing, powering and cooling challenges. This configuration introduces several technological challenges. Substrate … … One substrate instead of two

Double Sided Strip Module: Hybrid Topology 07/NOV/2011G. Blanchot - R&D on substrates for CMS tracker hybrids7 2x1024 STRIPS Concen- trator GBT CBC DC-DCOptical Link Charge Pump Power Data  Front-end circuit assemblies must have the minimum required area  CBC connection to strips requires high density layout.  CBC connection to concentrator requires several impedance matched pairs + single ended lines (bus), high density layout required.  The two CBC sides share a common optical module and power converter.  Options are:  U shaped single hybrid.  Frame shaped hybrid.  Two HDI hybrids plus one transverse service circuit.  This last option poses the problem of interconnecting the HDI substrates with the service circuit without connectors. 100 mm mm 20 mm 112 mm

Advantages of the C4’d CBC 07/NOV/2011G. Blanchot - R&D on substrates for CMS tracker hybrids8  Flip chip ASICs have several advantages compared with their wire bonded counterparts:  Having bumps under the ASIC allows getting rid of bond pads at the chip periphery:  The die area is significantly reduced  No dead space required around the chips for wire bonding  Chips can be abuted on all sides on the substrate  Power connections with less inductive parasitics:  The current is brought to the ASIC straight through a bump and not through an inductive bind wire.  The connection is less resistive too.  This is particularly important for the charge pump performance in the CBC.  Wire bonds are sensitive to noise pickup  The CBC ump bonding helps reducing the length of the sensor wirebonds, hence reducing the E field coupling on them.  The assembled hybrids are fully connected  It enables the testing of hybrids before they are assembled on modules and wired to a sensor.  All this results in smaller board area, and a less mass and better performing front-end system.

Development Plan 07/NOV/2011G. Blanchot - R&D on substrates for CMS tracker hybrids9 2x1024 STRIPS Concen- trator GBT CBC DC-DCOptical Link Charge Pump Power Data  Step 1: One CBC, wire bonded to small sensor, interface to test connector only. Exercise HDI layout and CBC assembly onto substrate. No major difficulties expected.  Step 2: Eight CBCs, wire bonded to full sensor, interface to test connector only (no concentrator yet). Exercise HDI layout and CBC flip chip assembly on a large substrate. R&D on this topic ongoing now.  Step 3: Full module.

Hybrid technologies 07/09/2011G. Blanchot - CMS Tk Phase II Electronics10 CBC flip chips with 350 μm and 250 μm have been investigated. The use of any of both options discards any standard PCB technology. The 350 μm pitch option would in principle enable a less constrained hybrid technology, however it resulted in many more layers and lots of microvias to connect the CBCs with the sensors. Therefore we went back to a more dense CBC at 250 μm pitch. Dense HDI substrates from Endicott (CoreEZ) enable 25um traces width & spacing and 50u vias with a ring of 25um only, up to 12 layers. Endicott now proposes the CoreEZ subtsrate with a LCP core: features of CoreEZ are preserved but LCP leads to lighter substrate, but number of layers is limited to 6. Alternate suppliers are being looked for. AttributeStandard (Epoxy Glass or Polyimide) HDI: Dense (Particle Filled Epoxy) HDI: LCP (liquid crystal polymer) HDI: PTFE (PTFE) Line width75 microns25 microns37.5 microns25 microns Line space75 microns25 microns37.5 microns33 microns Via typemechanicallaserLaserlaser Via diameter200 microns50 microns Stacked viasBuild up only In 2010 Capture pad diameter 400 microns100 microns110 microns Surface finishE-less Ni / I Au, ENEPIG Same Solder maskyes no Thickness<1mm mm0.5mm Layers10124, 6 in 1 st article11 From Endicott presentation at ACES 2011.

Alternatives to substrates 20/10/2011G. Blanchot - Module Interconnection Discussion11  Rui Oliveira (CERN) recommended the HIGHTEC company in Switzerland for hybrids HiCoFlex technology 30 um vias 15 um traces Very thin (low mass) Very flexible Can be embedded in other boards. Might be a solution for PS-Pt modules where top-bottom links will be needed. Can be an alternative to Endicott.

CBC at 250 um pitch 07/NOV/2011G. Blanchot - R&D on substrates for CMS tracker hybrids12  CBC 250um (not final release) 728 pins flip chip, 250 μm pitch. 254 input pads in 6 rows. Routable in top/bot layers with 25 um pitch tracks. Top side: input/output pads. Ground pins dominate. TRG + CLK + 4*DATA lvds pairs per chip. (2 * 28) + 2 = 58 single ended lines per CBC for communication between CBCs. Lots of lines to/from concentrator: 4 pair * 8 CBC = 32 SLVS pairs 2 stub coincidence pairs * 8 CBC = 16 single ended lines (160 MHz). TRG & CLK pair = 2 LVDS pairs. I2C lines port Power/gnd. GND Inputs Point of Load DCDC LDO outputs Strip inputs Clock & Trigger Inter-chip data lines I2C PortSLVS Outputs Single ended outputs

250um pitch CBC connection to sensor 07/09/2011G. Blanchot - CMS Tk Phase II Electronics13 Sensor wirebonding: 25um traces enable straight connection to bond fingers.  Sensor bond fingers can be in-line or staggered In both cases, the wirebond pads are very close of the sensor edge. Traces escape all in same direction with need of vias. Traces can still go through 2 adjacent vias without turn arounds.  Sensor bond fingers are present at same locations on the bottom side: The connection is possible through the CBC pin escapes via array from the 3 last rows. The 3 top rows are associated to the top side sensor. No need for extra layers neither blind vias. Rows 1, 2, 3: top sensor, straight connection.Rows 4, 5, 6: bottom sensor, straight connection through pin escapes.

Proto Hybrid Schematic 07/NOV/2011G. Blanchot - R&D on substrates for CMS tracker hybrids14 To/From concentrator I2C Port Clock & Trig SE and SLVS Outputs

Hybrid prototype 07/NOV/2011G. Blanchot - R&D on substrates for CMS tracker hybrids15 20 mm 116 mm 32.4 mm The hybrid must be fitted with a test connector that extends the substrate to 116 mm. Top & base layers: routing layers. Two internal power and ground planes. Layout based on 25 μm space/width traces and 50 μm microvias over 100 μm pads. The layout also uses 300 μm vias for less demanding regions.

Top side CBC routing 07/NOV/2011G. Blanchot - R&D on substrates for CMS tracker hybrids16 The input pads are comfortably routed to the sensor edge (staggered bond pads) without vias. The inter-chip connections are easily routed too. Pin escapes to internal planes fit well with a 50 μm via.

Base side CBC routing 07/NOV/2011G. Blanchot - R&D on substrates for CMS tracker hybrids17 The input pads are comfortably routed to the sensor edge (staggered bond pads) from a single pin escape The inter-chip connections are easily routed too. Bus lines for output data lines.

Output lines 07/NOV/2011G. Blanchot - R&D on substrates for CMS tracker hybrids18 The output lines (single ended and SLVS) are routed with 25um tracks too. A wider pitch would force the addition of internal layers to reach the connector pins. SLVS pairs don’t have matched impedance here (draft layout). Matching the impedance will result in a spreading of the tracks.

And the whole thing… 07/NOV/2011G. Blanchot - R&D on substrates for CMS tracker hybrids19 Layout of an 8 CBCs hybrid using the Endicott HDI subtsrate constraints is feasible. The 25um width rule is possible on short track lengths. Bus connections will required larger pitch on the hybrid, b ut that should not pose a problem. Hybrid can end up very narrow. Note: diff pairs unmatched in this view. Impedance matching can spread the data lines over the board. This proposal has been discussed last Friday at Endicott, no showstoppers found.

Full module 07/NOV/2011G. Blanchot - R&D on substrates for CMS tracker hybrids20 2x1024 STRIPS Concen- trator GBT CBC DC-DCOptical Link Charge Pump Power Data 100 mm mm 20 mm 112 mm  The preferred configuration for a full module is a U shaped circuit, or eventually a square frame  Discussed with Endicott: it is manufacturable but…  Show stoppers could be:  Cost.  Flatness (impact on wire bonding of sensor).  Alternative implementations require the interconnection of substrates.

Wire bonding of substrates 07/NOV/2011G. Blanchot - R&D on substrates for CMS tracker hybrids21 2x1024 STRIPS Concen- trator GBT CBC Optical Link Charge Pump Power Data DC-DC 100 mm mm 20 mm 112 mm  The substrate has already 2x1024 wirebonds to be connected: we could add few more to interconnect the hybrids with a service board.  Drawbacks:  Wirebonds need to carry the full power of the hybrid.  Impedance matching from Concentrator to GBT might be difficult (High speed single ended lines).  Fragile.  But this technique is very well established in our community.

Stud bumping 07/NOV/2011G. Blanchot - R&D on substrates for CMS tracker hybrids22 2x1024 STRIPS GBT CBC DC-DCOptical Link Charge Pump Power Data 100 mm mm 20 mm 112 mm  Stud bumping is a well established technique for connection flip chips onto substrates.  Exploring if this technique can be used to connect a kapton with the subtsrates:  Reconstructed U shape or frame.  Better power delivery to substrates.  High density matrix.  Stud bumping on base side of the substrate to preserve board area for the concentrator chips.  Other techniques have been proposed by Endicott and will be investigated. Glue

Summary and next steps 07/NOV/2011G. Blanchot - R&D on substrates for CMS tracker hybrids23  Items that compose the module are still under development and subject to changes, but some critical parts are now converging: Sensor size and pitch CBC ASIC flip chip pitch and size Routability of dense hybrid regions.  The LCP core and CoreEZ are compatible with the 4 layers required for a hybrid prototype with 8 CBCs and full connection to a sensor. Margin to add 2 more layers if required. 25 um tracks and 50um microvias turned out to be fully compatible with our constraints  A draft layout has been proposed to Endicott. The layout need to be tuned of course, but no major difficulties have been found. We stay in close contact with Endicott to move a step forward. We continue to look for alternative suppliers.  Remaining issues: Interconnection techniques for a full module assembly need to be investigated. In last resort, wirebonding between boards will always be a fall back solution.