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Additive Manufacture of Interconnects
Steve Thomas
Conductive Inkjet Technology Ltd.
© 2011 Conductive Inkjet Technology Ltd CONFIDENTIAL
Importance Of Interconnects
• All electronic devices have
one thing in common:
– Need to get charge carriers
in and out of the device
• Interconnects usually
overlooked
– Organic semiconductors
need lots of development
but metals are already
understood
– Solution exists…
© 2011 Conductive Inkjet Technology Ltd CONFIDENTIAL
Traditional Production Methods
Copper Clad Board Apply Resist
Expose Resist
Develop Resist Etch Copper Strip Resist
Labour and equipment intensive.
Wasteful of copper – Reprocessing etch solution expensive
Tooling Cost
© 2011 Conductive Inkjet Technology Ltd CONFIDENTIAL
Screen Printing
© 2011 Conductive Inkjet Technology Ltd CONFIDENTIAL
Screen Printing
© 2011 Conductive Inkjet Technology Ltd CONFIDENTIAL
Screen Printing
© 2011 Conductive Inkjet Technology Ltd CONFIDENTIAL
Screen Printing
© 2011 Conductive Inkjet Technology Ltd CONFIDENTIAL
Why Move Away?• Etching metals wasteful, equipment and labour
intensive
– Expensive (especially for sputtered metals)
• Printed Silver
– Expensive material
– Good conductivity requires high temperatures
– Problems with soldering
• Both methods require tooling and high up-front costs
– Not good for high mix applications
• Additive and Digital would be nice…
© 2011 Conductive Inkjet Technology Ltd CONFIDENTIAL
Print and Plate
• Useful if we can separate the printability
from the conductivity
– Print something with poor conductivity but
good print reliability
– Enhance the conductivity once the pattern
has been defined
• Example: Electroplating of silver in seed
layer
– Good conductivity
– But requires advanced plating system or
fully linked pattern
• Use chemistry rather than electricity…
© 2011 Conductive Inkjet Technology Ltd CONFIDENTIAL
Electroless Copper Plating
• Reduction of copper 2+ ions out of solution without the need to apply an electric current
• Requires 3 main ingredients
– Source of copper ions – Copper Sulphate/Chloride
– Chelating agent to stabilise copper – EDTA/Quadrol
– Reducing agent
• Need a method of control so that the copper only reduces where and when we want it to
© 2011 Conductive Inkjet Technology Ltd CONFIDENTIAL
Electroless Copper Plating
Catalytic Reduction of Metal Ions in Solution
HCHO + 30H- HCOO- + 2H20 + 2e-Au, Pt, Ni
Cu2+ + 2e- Cu0
Autocatalytic!
2HCHO + 40H- 2HCOO- + 2H20 + H2 + 2e-Cu
Reaction continues after catalyst is completely covered
© 2011 Conductive Inkjet Technology Ltd CONFIDENTIAL
Catalyst Ink Formulation
Inkjet printing catalyst allows easy patterning of metal and leads to an additive process
� Catalytic metal species
� Binder/thickener
� Solvent
� Humectants
� Surfactant
• Requires drying to remove solvent
• Relatively slow process
• Image quality can deteriorate
• Catalyst prone to chemical attack
© 2011 Conductive Inkjet Technology Ltd CONFIDENTIAL
UV Cure
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
200 250 300 350 400
Wavelength (nm)
OD
2-Benzyle-2-(dimethylamino)-1-[4-(4-morpholinyl) phenyl]-1-butanone
Photoinitiator Materials used to kick off a free-radical polymerisation after exposure to UV light
Very rapid transition between non-volatile liquid and insoluble solid
© 2011 Conductive Inkjet Technology Ltd CONFIDENTIAL
Microstructural Control
• Microstructural control + Phases of differing solubility
– Provides good access to plating solution
– Good adhesion to metal and substrate
A B
C
• Pure UV cure has hard glassy surface and seals catalyst away from plating solution
• Blending different phases and carefully controlling curing/drying can lead to carefully controlled microstructure
© 2011 Conductive Inkjet Technology Ltd CONFIDENTIAL
Reel to Reel Manufacture
• Inkjet suitable for reel
to reel
• Reel to reel plating
– Fluidic bearings
– No moving parts
– Improved reliability
• Cost of manufacture
– Continuous
– Reduced labour
© 2011 Conductive Inkjet Technology Ltd CONFIDENTIAL
Typical Properties
• Line Width
– Typical 220 µm and above
• Conductivity
– Typical sheet resistance 20 mΩ/□ to
100 mΩ/□
• Production Speed
– Print ~ 20 m/min
– Plate ~ 2 – 12 m/min
• Solderable
– Assembly using conventional SMT
process and low temp solder
© 2011 Conductive Inkjet Technology Ltd CONFIDENTIAL
Finer Features
• Device structures such as TFT
arrays, memory or display
elements require much finer
features
• Micron scale
• Not really practical by current
printing technology
• UV Cure nature of ink makes it
ideal to modify for
photolithographic patterning!200 µm
© 2011 Conductive Inkjet Technology Ltd CONFIDENTIAL
Photolithographic PatterningApply Catalyst
© 2011 Conductive Inkjet Technology Ltd CONFIDENTIAL
Photolithographic PatterningBake
© 2011 Conductive Inkjet Technology Ltd CONFIDENTIAL
Photolithographic PatterningExpose Through Mask
© 2011 Conductive Inkjet Technology Ltd CONFIDENTIAL
Photolithographic PatterningDevelop Catalyst
© 2011 Conductive Inkjet Technology Ltd CONFIDENTIAL
Photolithographic PatterningGrow Copper on Catalyst By Electroless
Plating
© 2011 Conductive Inkjet Technology Ltd CONFIDENTIAL
Advantages• Micron scale features
– Typically down to 3 µm
• Less wasteful of metal than sputter and etch
• Ideal for fine metal features on transparent substrates
– ITO Replacement
– Displays, Photovoltaics, Lighting, Transistors, Touch Screens
© 2011 Conductive Inkjet Technology Ltd CONFIDENTIAL
Summary
• In many applications Print and Plate method is a
more economical solution for interconnect
metallisation
• Inkjet printing allows interconnects to be produced
digitally and reel to reel with modest feature size
• Photolithographic patterning allows micron sized
features for device applications and potential ITO
replacement