2013 12-05-sirris-materials-workshop-printed-electronics-cosemans-seronveaux

Inks and their application in Printed Electronics Results of a European Research project for SME Associations (CLIP)

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Printed Electronics

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A wide range of (possible) applications

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Solar Cells

Food Sensors

Automotive sensors

RFID tags

EL Packaging

Presenter

Presentation Notes

Using a set of printing methods to create an electrical devices on various substrates.

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Printed Electronics

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A wide range of (possible) applications


Displays

Lightning (OLED)

Medical Sensors

Batteries

Presenter

Presentation Notes

Using a set of printing methods to create an electrical devices on various substrates.

Printed Electronics Manufacturing

Requirements Conversion of printed ink to a conductive track High Performance Cost efficient Flexible Large area / thin tracks / large area + thin tracks Various substrate (glass, paper, ceramic, plastics) Thermal compatibility with substrate and materials Defined interface formation between stacked materials Compatible with industry standard practices

Materials & Technology

Ink formulation Printing Drying Sintering Device

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Technology for Printed Electronics

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Conventional printing

Offset

Gravure

Screen

Flexo

Digital Printing

Inkjet

Aerosol Jet

Thermal transfer

magnetography



Presenter

Presentation Notes

Conventional printing always needs the creation of a master before printing can be done.

Technology for Printed Electronics


Conventional printing

Offset

Gravure

Screen

Flexo

Digital Printing

Inkjet

Aerosol Jet

Thermal transfer

magnetography



Which technology will dominate?

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Depends on market and applications




Inkjet (piëzo) Aerosol Jet Flexo Screen

Resolution ~30 µm ~10 µm ~80µm 40 - 100 µm

Throughput 0,01-0,5 m2/s 10 m2/s 2-3 m2/s

Single pass layer thickness < 500 nm 25 nm -10 µm 3 - 10 µm 50 - 100 µm

Particle size Nano Nano (micro) Nano & micro Nano & Micro

Conductive ink materials

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Research focus on graphene based inks


Conductive Material

Ink Type / Printing process

Advantage Disadvantage

Silver Flake Predominantly Screen printing

Cost effective for many applications

thick films, surface roughness, difficult to photocure

Silver Nanoparticles

Predominantly Inkjet, Aerosol jet printing

Thin films, flexibility, high conductivity, low T sintering

High cost

Copper Nanoparticles

Predominantly Inkjet, Aerosol jet printing

Same as Ag NP, but slightly lower cost

Can oxidise and lose conductivity

Polymers (PEDOT, PANI) All

Transparent, flexible, water resistant

Lower conductivity then metal based inks



Drivers

Silver flake inks for screen printing will continue to dominate with largest market share (low cost)

Increasing share for inkjet, AJP and nanoparticle inks. Delicate or irregular shaped objects Low temperature sintering required to

print onto cheap flexible substrates (polymer film, paper)

Alternative needed for sputtered

transparent ITO due to cost, supply and performance issues

Barriers

Cost Nanoparticles significantly more

expensive Ink development is time consuming and

expensive Total in-use cost needs to be considered

rather than a price comparison of inks

Technical Long term stability High resolution printing Curing

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Market




2012 market size*: $2.86 billion, dominated by silver flake inks 2018 forecast*: $3.36 billion, of which $735 million is based on nano Ag and Cu

* Adapted from IDTECHEX report: Conductive Ink Markets, 2012

Presenter

Presentation Notes

DRIVERS Silver flake inks for screen printing will continue to dominate with largest market share Mature technology, competitive pricing, sufficient technical performance for most applications However, PV is biggest market, and move towards ultra thin crystalline silicon PV may require the use of inkjet printing with nanoparticle base inks� Other emerging opportunities which require printing onto delicate or irregular shaped objects will also drive a move towards inkjet , AJP and nanoparticle inks� The ability to print onto cheap flexible substrates (polymer film, paper) requires low temperature sintering which is also driving a move towards nanoparticle inks� For transparent conductive films (TCF) there is an overwhelming requirement for an alternative to sputtered ITO due to cost, supply and performance issues Silver nanowire / nanofiber inks can be formulated into inks and printed to form TCFs with technically superior conductive properties to ITO films for use in touch panels, solid state lighting and PV applications BARRIERS Cost Nanoparticle silver is significantly more expensive that silver flake However with market uptake and economies of scale nanoparticle inks will become more cost competitive Total in-use cost needs to be considered rather than a price comparison of inks Technical Long term stability of nanoparticle inks is a key concern for large scale commercial uptake High resolution printing e.g. 10 microns required for transistor applications Value chain integration including optimization of conductive ink formulations for specific printing processes and products

CLIP:Conductive Low Cost Ink Project

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Objectives Development, formulation, and feasibility of low cost inks

Development of optimized inks for screen, flexo, inkjet and aerosol jet printing

Optimization of inks for large area printing with high resolution, <50 microns

Prepare demonstrators


Specific guidelines for the inks

Viscosity Surface Tension

Particle size

Complex composition of nanoparticles and chemicals

Nanoparticles Solvents Binders Additives

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Ink formulation




Presenter

Presentation Notes

Viscosity Viscosity should be between 10-20 cP at operating temperature. Surface Tension Surface tension should be between 28 and 48 dynes/cm Filtering In general, a filter is used to remove any large aggregates or particles. In general, the particles in the fluid should be 1/100 the size of the nozzle. Nanoparticles Functional ingredient for conductivity Solvents Impact on surface tension and viscosity Binders Matrix for cross-linking nanoparticles Additives preventing agglomeration

Multimodal Ag inks


40 nm/6 nm/ <1nm Improve particle packing improved sintering and conductivity Less material Lower cost





Filtering Filtering of the inks

necessary if small nozzle cartridges are used

Nano-particles tend to agglomerate Wide variety of filters available

Materials: PP,PES,PTFE,Nylon6,… Different µ-structures Ink dependent

Cellulose PVDF PC PES



Inkjet

High resolution Different printheads

Fujifilm, Xaar, Konica, Ricoh,... 1 pL to 80 pL

Planar substrates Line and area printing

AJP

Very high resolution Wide ink viscosity range Local laser sintering

Non-planar substrates possible Line printing

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Printing




Digital printing - print at wish High quality

Low cost Small waste

Non contact/sensitive substrates No masking

Flexible & Scalable


High speed No clogging Low resolution

Limited fluids All fluids



Inkjet technology

Continuous Drop on Demand

Thermal Piezoelectric Acoustic Electrostatic

Non contact AJP technology AJP Technology description

1 2

3

4

1 – Nitrogen input

2 – Mist created (1-5µm droplet)

3 – Sheath gas input

4 - Printing and Deposition





Substrates Type of substrate depends on application

Papers: good printability, good adhesion, solvents are absorbed quickly by the paper, fast drying but porosity of paper can have a negative effect on conductivity.

Plastics: good printability, longer drying and curing time, adhesion can be a problem. No interference from substrate (no porosity). If curing and sintering are good optimal conductivity

Pretreatment can enhance adhesion



Untreated substrate Treated substrate

Curing: Drying and Sintering Depending on substrates and used materials

Thermal heating Standard practice / conventional approach - Silver Uniformity Wide area of practice Substrate limiting the maximum temperature Long residence time -> inert atmosphere Not usable for Cu (oxidation)

UV Curing

Wide area of processing Standard practice Lower intensity, continuous output




Drying and Sintering Depending on substrates and used materials

Broadband flash High power densities / wide area of processing Less substrate limited and curing times short Adjustable spectrum / tunable pulse lengths High capital cost for some systems

Laser

High Power densities Exposure area smaller / Fixed wavelength but targeted wavelength to match ink requirements / uniform across the beam

/ Spatial selectivity - targeted Cost / rastering




Printing results

Trimodal CLIP-ink Commercial Reference


Reference

Sheet Resistance after sintering 150°C Low temperature better conductivity Sheet Resistance

Multimodal better conductivity


Inkjet demonstrator Chipless RFID tag

4-bit chipless RFID tags successfully demonstrated using the final trimodal ink on PEL paper and Kapton polyimide respectively.

Higher performance than reference ink thanks to its higher conductivity at lower sintering temperature

Sintering Temperature

CLIP trimodal ink Reference

200 °C 7.85E+6 S/m 5.66E+6 S/m

39% higher





AJP and inkjet demonstrator Humidity sensor

Printing of primary circuitry MCU Gluing by KTH Overprinting

Rest of component programming and placing

Hybrid Integration of printed electronics and silicon electronics by AJP-printed interconnections.





AJP printed demonstrator LED application

3D printing by AJP of conductive tracks for LED application.





Conclusions

Inkjet technology is mature and available for conductive printing Upscaling is possible to R2R with increasing printing speed Bottleneck is the ink-development to fit the requirements Cost reduction related to Cu-inks was limited because nanoparticle

production was driving factor but improving Sintering of Cu-based inks needs alternative for thermal sintering At low sintering temperatures

Multimodal Ag-based inks show lower resistance Less ink necessary for comparable conductivity as monomodal inks


Conclusions

Aerosol technology is dedicated for the future. Direct printing on 3D substrate is easily done with AJP Due the “Aerosol” dynamic deposition, inks are easily printable AJP is very suitable for ink development.

Large range of viscosity Size particle from nano to micro

AJP is equipped with Laser sintering. Curing by laser allow us to print and cure the deposition on low melting temperature substrates.

The printing is dedicated for line printing (10µm to 100µm) not for large area printing (even in case of scaling up according to industrial requirement).


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[email protected]

Patrick Cosemans – Senior Project Engineer Smart Coating Application Lab

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