1. ECAL SLAB Interconnect by FFC: Intro
The use of a short FFC (Flat Flexible Cable) to make the interconnections between the Slab component PCBs looks a promising way ahead. The following slides discuss:
The general interconnect problem
The way in which FFCs could be used
The initial design work
The investigations and assessment work needed
A programme for the work
Some initial costing
DIF-ASU-ASU_Interconnect.ppt
Maurice Goodrick & Bart Hommels , University of Cambridge

2. ECAL SLAB Interconnect
DAQ Architecture - Overall view
~150 VFE ASICs on each side of SLAB
LDA
SLAB
DIF
ODR
LDA
SLAB
DIF
SLAB
DIF
LDA
SLAB
DIF
SLAB
DIF
LDA
SLAB
DIF
DIF-ASU-ASU_Interconnect.ppt
Maurice Goodrick & Bart Hommels , University of Cambridge

3. ECAL SLAB Interconnect
DIF – ASU – ASU -,,,- Terminator
6 or 7 ASUs on each side of a SLAB
DIF
ASU[0]
ASU[6]
Term
Termination of LVDS lines & loop back R/O Token
7 or 8 interconnections
- each of many ways
?? Integrate on all ASUs as option
DIF-ASU-ASU_Interconnect.ppt
Maurice Goodrick & Bart Hommels , University of Cambridge

4. ECAL SLAB Interconnect
Interconnections
6 or 7 ASUs on each side of a SLAB
DIF
ASU[0]
ASU[6]
Term
7 or 8 interconnections
- each of many ways
34 plus power at the last count
DIF-ASU-ASU_Interconnect.ppt
Maurice Goodrick & Bart Hommels , University of Cambridge

5. ECAL SLAB Interconnect
6 or 7 ASUs on each side of a SLAB
DIF
ASU[0]
ASU[6]
Term
- But each extra row needs >= 8 extra signals !!
7 or 8 interconnections
- each of many ways
Multiple rows make sense
34 plus power at the last count
DIF-ASU-ASU_Interconnect.ppt
Maurice Goodrick & Bart Hommels , University of Cambridge

6. ECAL SLAB Interconnect – Why Multi-Rows?
Silicon Wafer options:
6x6 cm wafers
6x9 cm wafers or
DIF-ASU-ASU_Interconnect.ppt
Maurice Goodrick & Bart Hommels , University of Cambridge

7. ECAL SLAB Interconnect – Why Multi-Rows?
Where the VFEs go: 3 row solution
6x6 cm wafers
6x9 cm wafers
VFEs in middle row
each serve 2 wafers
- is this good??
DIF-ASU-ASU_Interconnect.ppt
Maurice Goodrick & Bart Hommels , University of Cambridge

8. ECAL SLAB Interconnect – Why Multi-Rows?
Where the VFEs go: 6 row solution
6x6 cm wafers
6x9 cm wafers
This avoids any VFE-sharing problem
DIF-ASU-ASU_Interconnect.ppt
Maurice Goodrick & Bart Hommels , University of Cambridge

9. ECAL SLAB Interconnect – Why Multi-Rows?
How to read them out – single trace
3 rows of VFEs
6 rows of VFEs
Per ASU: L ~ 850mm, C ~ 85pF
Per ASU: L ~ 900mm, C ~ 90pF
Per Slab of 7 ASUs:
L ~ 6m, C ~ 600pF
Per Slab of 7 ASUs:
L ~ 6.3m, C ~ 630pF
Do these look BIG ?? - we’ll look at that later
DIF-ASU-ASU_Interconnect.ppt
Maurice Goodrick & Bart Hommels , University of Cambridge

10. ECAL SLAB Interconnect – Why Multi-Rows?
How to read them out – multiple trace
3 rows of VFEs, 3 traces
6 rows of VFEs, 6 traces
Per ASU: L = 240mm, C ~ 24pF
Per ASU: L = 240mm, C ~ 24pF
Per Slab of 7 ASUs:
Per trace: L ~ 1.7m, C ~ 170pF
Per Slab of 7 ASUs:
Per trace: L ~ 1.7m, C ~ 170pF
How much difference will this make?
DIF-ASU-ASU_Interconnect.ppt
Maurice Goodrick & Bart Hommels , University of Cambridge

11. ECAL SLAB Interconnect – Why Multi-Rows?
How much difference will this make?
Multi Row is aesthetically much more pleasing 
- but what material advantages does it offer?
Clock and Control Lines: LVDS, controlled impedance
length of each C&C trace reduced below 1/NROWS:
less signal degradation
far cleaner routing – no need for stubs
Read-Out Lines: low voltage swing CMOS
data load is shared between the rows, so lower rate needed
length (and hence capacitance) of each R-O trace reduced below 1/NROWS
power for R/O reduced in same ratio
DIF-ASU-ASU_Interconnect.ppt
Maurice Goodrick & Bart Hommels , University of Cambridge

12. ECAL SLAB Interconnect – Why Multi-Rows?
How much difference will this make?
Read-Out Rates and Power
# Rows R-O Rate/Row R-O Power/Row R-O Power Total Trace Length
(Mb/s) (mW) (mW) (m)
The power savings may not be important compared to the power budget of a complete Slab
But achieving data rates of several Mbits/sec over complex traces of several metres length will be difficult
DIF-ASU-ASU_Interconnect.ppt
Maurice Goodrick & Bart Hommels , University of Cambridge

13. ECAL SLAB Interconnect
The existing plan is to use conductive adhesive to make these interconnections.
… but:
power pads need to be large – say 3 pads of 1cm width
only 3 signal pads per cm
gives 45 pads for signals – this is barely enough for a
2 row scheme – and there are good reasons to favour a
3 or even 6 row solution
will large pads upset signal transmission properties?
will the connections deteriorate with time?
will the mechanical joint be good enough?
if the joint is not to be mechanical, is the rigidity a
problem?
the lap joint with clean pads on the step will make PCB
more expensive (unless already needed on ASU)
re-work will be difficult
DIF-ASU-ASU_Interconnect.ppt
Maurice Goodrick & Bart Hommels , University of Cambridge

14. ECAL SLAB Interconnect
We have been looking at alternative forms of interconnect.
The most interesting is the use of a Kapton-backed Flat Flexible Cable (FFC)
The FFC would be soldered onto pads on the ASU (/DIF/Term) PCB
If the overall thickness of the ASU were reduced by ~50um, connections could be on the top of the PCB – avoiding the difficult step on the edge.
DIF-ASU-ASU_Interconnect.ppt
Maurice Goodrick & Bart Hommels , University of Cambridge

15. ECAL SLAB Interconnect – using FFCs
DIF-ASU-ASU_Interconnect.ppt
Maurice Goodrick & Bart Hommels , University of Cambridge

16. ECAL SLAB Interconnect – using FFCs
DIF-ASU-ASU_Interconnect.ppt
Maurice Goodrick & Bart Hommels , University of Cambridge

17. ECAL SLAB Interconnect – FFC Detail
Optional Pre-form
to reduce
inter-ASU
forces
Alignment
notches
DIF-ASU-ASU_Interconnect.ppt
Maurice Goodrick & Bart Hommels , University of Cambridge

18. ECAL SLAB Interconnect – FFC Section
Optional Pre-form
DIF-ASU-ASU_Interconnect.ppt
Maurice Goodrick & Bart Hommels , University of Cambridge

19. ECAL SLAB Interconnect: + Mechanical connect
FFC
ASU
ASU
Glue
Good mechanical joint
… but hard to rework
DIF-ASU-ASU_Interconnect.ppt
Maurice Goodrick & Bart Hommels , University of Cambridge

20. ECAL SLAB Interconnect – PCB Footprint
DIF-ASU-ASU_Interconnect.ppt
Maurice Goodrick & Bart Hommels , University of Cambridge

21. ECAL SLAB Interconnect – FFC advantages
Provides copious connections (3 x 36 easily fit)
plenty for Power Planes
would allow multi-row VFE organisation (3 or 6)
Solder joints well proven
Signal transmission likely to be less compromised
Rework possible
Mechanical junction would be independent: could still use glued lap joint, but non-conductive adhesives stronger and more reliable.
Also the machining of the step in the PCB is far simpler as there are no pads to damage.
DIF-ASU-ASU_Interconnect.ppt
Maurice Goodrick & Bart Hommels , University of Cambridge

22. ECAL SLAB Interconnect – FFC issues
How to solder:
Hot-Bar Soldering (Thermode) is usual technique
Laser Soldering
IR soldering
Force needed:
Hot-Bar soldering typically uses ~50N (10 lbf)
force a major issue when Si wafers on ASUs
vacuum chuck is a possible solution
DIF-ASU-ASU_Interconnect.ppt
Maurice Goodrick & Bart Hommels , University of Cambridge

23. ECAL SLAB Interconnect: Assembly Sequence
Attach FFCs on input edge of ASUs (leave other edge footprints empty)
Build ASU, testing with temporary connections to FFCs (ZIF connector or using custom jig)
Assemble Slab from ASUs, Terminator and DIF, soldering free ends of FFCs to neighbouring PCB
Alternatively (and now preferred):
Build ASU, testing with temporary connections to FFCs using custom jig
Assemble Slab from ASUs, Terminator and DIF, adding FFCs to join neighbouring PCBs
Much more difficult once wafers added!!
DIF-ASU-ASU_Interconnect.ppt
Maurice Goodrick & Bart Hommels , University of Cambridge

24. ECAL SLAB: FFC Programme Phase 1
Sample FFC tests using FFC-Test PCB
Have samples from Axon Cables
PCB design started
Get custom FFC
Hot-Bar soldering trials:
Oxford have machine we an use for trials
Unitek-Miyachi (Derby) will do half day of tests f.o.c., would then charge £650/day – preferred route?
Custom Thermode tool: £650
Laser Soldering:
Group at Univ. of Hull working on this – in contact
equipment likely to be expensive
IR: may turn out simplest – but unproven!!
Kapton pretty transparent at IR
Cambridge HEP have IR rework station that may be adequate for this stage. Upgrade planned.
DIF-ASU-ASU_Interconnect.ppt
Maurice Goodrick & Bart Hommels , University of Cambridge

25. ECAL SLAB: FFC Programme Phase 2
Phase 2 would aim to refine and equip for EUDET Prototype Assembly:
Re-iterate FFC design
Close collaboration with mechanical design and SLAB production
Establish what equipment/ service provider
Handling techniques and production jigs
Considerable tooling effort, e.g. vacuum chuck for Hot-Bar work
Rework techniques:
IR rework station ?
Pad levelling
Rework of any mechanical joints
Connnection Jig design and production for ASU testing
DIF-ASU-ASU_Interconnect.ppt
Maurice Goodrick & Bart Hommels , University of Cambridge

26. ECAL SLAB: FFC Programme Phase 1 Costs
Cost of FFC Programme Phase 1
FFC-Test PCB: £600
Custom FFC run: £350 - £550 for ~200 pieces
Hot-Bar soldering trials at Unitek (including custom Thermode tool): allow £1700
Laser Soldering: no indication as yet as to whether Hull would charge to carry out investigation.
IR: no major costs foreseen – a bit for tooling ?
DIF-ASU-ASU_Interconnect.ppt
Maurice Goodrick & Bart Hommels , University of Cambridge

27. ECAL SLAB Interconnect: FFC Conclusions
There are major advantages in using FFCs:
Removes major bottleneck in number of connections
Promises greater reliability
Rework likely to be easier
There are issues that need to be tackled:
Bonding force is the most serious
IR or Laser Soldering will minimise this
Vacuum chuck (or other) offer a solution
Phase 1 project looks promising:
Cost less than £3000 (within WP2.2 ??)
Good candidate companies and contacts
DIF-ASU-ASU_Interconnect.ppt
Maurice Goodrick & Bart Hommels , University of Cambridge