additive manufacture of interconnects event/4. thomas.pdf · 2011. 3. 25. · tooling cost ©2011...

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…


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


Screen Printing


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…


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…


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


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


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


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


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


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


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


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


Photolithographic PatterningApply Catalyst


Photolithographic PatterningBake


Photolithographic PatterningExpose Through Mask


Photolithographic PatterningDevelop Catalyst


Photolithographic PatterningGrow Copper on Catalyst By Electroless

Plating


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


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

additive manufacture of interconnects event/4. thomas.pdf · 2011. 3. 25. · tooling cost ©2011...

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