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Innovative Packaging Methods for Ultra-Thin Monolithic Sensors in Ladder Construction

This paper explores advanced packaging methods for ultra-thin monolithic active pixel sensors (MAPS) and their integration into ladder structures for particle detection applications. Highlighting the PLUME and SERVIETTE projects, it discusses the use of standard flexible PCBs, thermal management strategies, and innovative materials. The research emphasizes the ongoing efforts in high-resistivity substrate integration, sensor efficiency, and the potential for radiation-hard designs. Future prospects include further miniaturization and enhanced performance for high-energy physics applications.

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Innovative Packaging Methods for Ultra-Thin Monolithic Sensors in Ladder Construction

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  1. Novel packaging methods for ultra-thin monolithic sensors ladders construction Wojciech Dulinski1 on behalf of PLUME, SERVIETTE and PLUMETTE Collaboration 1IPHC/IN2P3 Strasbourg, France 5University of Bristol, UK 6DESY, Hamburg, Germany 7University of Oxford, UK 2IMEC, Leuven, Belgium 3CMST, University of Gent, Belgium 4IFK, Goethe University, Frankfurt/M, Germany 8CERN, Geneva • Outline • Short status of MAPS development at IPHC • PLUME: the lightweight ladder based on standard flex PCB • Embedding in plastics projects (two different process approach) • Conclusions and prospects

  2. R.T. Monolithic Active Pixel Sensor: effective use of a thin epitaxial layer (10 – 20 µm) for MIP tracking past present Industrial availability of high resistivity substrate (epi) in a standard CMOS process Fast and more efficient charge collection  should be radiation tolerant

  3. Present status of MAPS: just one example of mature design • Binary sparsified readout sensor for EUDET beam telescope: > 2 cm2 active area, 0.7 Mpixel tracker • Medium speed readout (100 µm integration 10 kFrame/s) • Spatial resolution < 4 µm for a pitch of 18.4 µm • Efficiency for MIP > 99.5 % • Fake hit rate < 10-6 • Radiation hardness > 1013 n/cm2 (high resistivity epi substrate) • Easy to use, “off-shell” product: used already in several application • Recent newcomer : Ultimate sensor for STAR Microvertex upgrade (~4 cm2) • Radiation hardness: >1014 n/cm2 attainable? Mimosa 26

  4. One of the main feature of MAPS Can be very thin (~25 µm of silicon in total) and still fully efficient! Problem: how to handle, interconnect and at the end built a low mass ladder with such a thin device?

  5. PLUME concept: double-sided ladder (ILC compatible) • 2x6 Mimosa26 sensors • Standard flex PCB: kapton + Cu (two layers) • SiC foam for spacer between layers

  6. Expected PLUME material budget: only air flow cooling!

  7. Current status of PLUME prototype: single sided flex

  8. PLUME thermal study: M26 parameters • “Rolling shutter”, column parallel processing: only processed pixel row dissipate power! • Total 730 mW (1/3 for pixel, discri and digital) • 250 mW/cm2(160 mW/cm2 for STAR Ultimate) • 1.1 µW/pixel (5-10 µW/pixel for time continuous shaping ~1 µs) • Power dissipation distributed unevenly: hot spots!

  9. PLUME thermal study: simulations Hot spots with temperature of above 100 °C!

  10. PLUME thermal study: results

  11. Effects of temperature distribution on electrical parameters: S-curve of Mimosa 26 on PLUME ladder

  12. Add heat-spread layer? The best would be based on CVD diamond! Or carbon fibers, excellent also for mechanics…

  13. SERVIETTE: use of UTCP by IMEC… • Stands for : • ULTRA THIN FILM CHIP PACKAGING • In short : • Off-the-shelf die • Thinned down to ± 20-30 µm • Packaged between two polyimide foils • Metallisation : fan-out • Circuit contact through vias Polyimide 2 • Result : • Flexible package • Thin : 50-70 mm • Embeddable in commercial flexible PCB Polyimide 1 - Partner restricted PTW Oct. 2010 - HUMAN++

  14. UTCP flow: overview • Polyimide on rigid carrier with release layer (KCl) • Dispense/spin of BCB • Chip thinning • Placement (face up) of IC 60 mm • Photo definable polyimide spinning (20µm)) • Opening vias using lithography • Cleaning of contact pads • Metallization: TiW (50nm) + Cu(1µm) • Electroplating : Cu (5µm) • Lithography to pattern metal • Encapsulation polyimide spinning • Release from carrier

  15. First results: Mimosa18 mechanical grade sample Submitted for fabrication more thana year ago, very slow progress since…

  16. PLUMETTE: “standard” PCB process for chip embedding in plastic foils (R. de Oliveira, CERN) • Gluing between two kapton foils • Opening vias using lithography • Single module: intermediate tests • Metallization: Al (5-10 µm) • Lithography to pattern metal • Complete ladder assembling, laser cut along sensor edges • Gluing of another kapton foil for deposition of second metal layer 16

  17. PLUMETTE: details of 1st, “redistribution” metal layer If too difficult for PCB-standard lithography (too small feature size), this post-processing step can be provided by CMOS foundry (discussion with AMS, 5th metal in 0.35 µm process)

  18. PLUMETTE: details of 4 metal layer flex Impedance of readout lines (last metal, 100 µm width, 100 µm gap) as a function of kapton thickness: 100 Ωfor 60 µm thick kapton (last layer)

  19. Future techniques: stitching (“one die per wafer”) Maximum length of monolithic ladder (8’ wafer): 10 –15 cm

  20. Bonding pads On going work and future plans: use of Vertical Integration Process (3D Electronics) Sensor comprised of several active silicon layers: sensor, analog processing, digital processing, memory, optoelectronics layer… Total thickness of this stack is still ~50 µm! 20 µm 3-tiers, heterogeneous CMOS, ultra-thin and edgeless MAPS - Possible decrease of power per pixel (by order of magnitude): see Yavuz Degerli talk from FEE-2009 - Elimination of some “hot spots”

  21. Conclusions • Ultra thin packaging technology seems to be interesting option for ultra light sensor ladders construction • It is the must, if one wants to take full profit from MAPS tracking performances (front-end mechanics is as important as front-end electronics) Outlook • Double-sided PLUME ladder by autumn 2011, followed by beam tests • Delivery of working Mimosa18 sensors embedded at IMEC: June/July ? • Delivery of single Mimosa26 embedded at CERN in June, full PLUME compatible ladder (six M26) in September/October • Stitching exercise next year?

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