Interconnection & Double Layer for Flexible Electronic Circuit with Instant Inkjet Circuits

Tung Ta1, Masaaki Fukumoto2, Koya Narumi1, Shigeki Shino3,Yoshihiro Kawahara1, Tohru Asami1

1Asami & Kawahara Lab - The University of Tokyo2Microsoft Research

3Mitsubishi Paper Mills Limited

Background

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Digital Fabrication - Shape Forming Tools

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Laser Cutter3D Printer

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Digital Fabrication - Shape Forming Tools

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Laser Cutter3D Printer

How to make those objects rich feature?

Let’s make it Electronic!

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Instant Inkjet Circuits• Rapid prototyping with Conductive Printing

• Instant Inkjet Circuits [Best Paper at UbiComp ‘13]Sintering-free Silver Ink + Special Coated Paper + Inkjet Printer

BreadBoard Instant Inkjet Circuits610/16/2015 UbiComp ‘15

Instant Inkjet Circuits

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• A rapid prototyping tool for printing circuits– At low-cost

• < a few hundred dollars

– Off-the-shelf

• Using a home inkjet printer and ink available in the market

– Fast

• < a few minutes

Instant Inkjet Circuits

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RFIDPCB

Touch Sensor

Capacitive Sensor

Figure 8. Operating pr inciple of an inter-digitated capacitivesensor.

Figure 9. A plush toy instrumented with an instant inkjet pr inted ca-pacitive sensor r ibbon.

can be readily integrated with flat, curved or even flexiblesurfaces. Theprinted sensor electrode can beused to detect aslight change of permittivity near its surface; this signal canbe easily read by off-the-shelf microcontrollers such as Ar-duino. In our prototype, we attached the sensing ribbon tothe inside of the skin of a stuffed toy, see Figure 9. Sincethe capacitance of each strip can be read independently us-ing multiple microcontroller I/O pins, it is possible to detectthe exact touch location, causing the toy to react differentlydepending on the how the user touches it during interactions.

Capacitive sensing for liquid level detection

Figure 10 shows another example application based on aribbon-shaped inter-digitated sensing sticker. A laminate-coated sensor strip isattached to theinsideof adrinking glass.The flexibility of the ribbon allows it to fit to the curved sur-face of the glass. Its capacitance is measured using an Ar-duino nano and the Arudino CapSense Library. The graphin Figure 10 shows a very good correlation between mea-sured capacitance and liquid level, and for comparison theprinted sensor is much more accurate than the RFID-basedsystem presented in [3]. Since the sensor ribbon is insulatedby a laminate coating, it will not contaminate the liquid in theglass (or vice-versa). The manufacturing cost of one sensorribbon is no more than a few cents while the Arduino-basedcapacitance reader costs a few tens of dollars.

Printed Antennas

An antenna is an electronic component that converts electri-cal energy into electromagnetic radiation in the form of radiowaves and vice-versa. The simplest antennas consist of onlyan arrangement of metallic conductors, and in this case theconductivity, permittivity and shapeof theantennahasahugebearing on its performance.

0"

0.5"

1"

1.5"

2"

0" 50" 100"

Figure 10. A laminate-coated inter-digitated capacitive r ibbon is at-tached inside a dr inking glass. The r ibbon is connected to the digitalI /O of Arduino nano in order to measure the capacitance which is pro-por tional to the liquid level

Figure 11. University logo is modified as915MHz UHF band antenna. RFID chip isattached using conductive epoxy.

15#

20#

25#

30#

35#

50# 75# 100#125#

Power&(dBm)&

Range&(cm)&

Minimum&Power&Level&to&Read&Tag&

Figure 12. Per formanceof custom pr inted RFIDtag.

A 915MHz band dipoleantennawasdesigned based on auni-versity logo using the CST Studio microwave simulator. Thedimensions of the antenna are such that it fitsonto astandardsized business card. The antenna impedance was matchedto that of a standard RFID chip to support direct attachmentto the antenna terminals using conductive epoxy. Figure 11shows thefinal antenna design, which isacombination of theuniversity logo and a functional UHF folded dipole antenna.Figure 12 showstheperformance of theassembled RFID tag,which was comparable to that of a commercial low-profileUHF RFID tags. This result demonstrates that our instantinkjet printing process is suitable for prototyping RF struc-tures such as antennas.

Time domain reflectometry

Wimmer et al. did not suggest the use of inkjet printing theirwork on time domain reflectrometry for sensing interaction[21], but we have successfully implemented this techniqueusing an inkjet printed transmission line, see Figure 13. Weused a Hilbert curve as the basis of the stripline pair whichmakes up the transmission line. This is a fractal space-fillingcurve that gives a fairly good mapping between 1D and 2Dspace that preserves locality, which means that the patternoffers consistent touch resolution in the x and y directions.

DISCUSSION

Additional practical issues

Throughout the course of this work we have been pleasantlysurprised how well the inkjet process has worked. Of course,anumber of issueshavecometo light. Asalready mentioned,

Moisture Sensor

Instant Inkjet Circuits• Only Single Layered Circuits

• Difficult to route complex circuits

LED Matrix

Tunable Coil9

Hide Wiring10/16/2015 UbiComp ‘15

Instant Inkjet Circuits• Only Single Layered Circuits

• Difficult to route complex circuits

LED Matrix

Tunable Coil10

Hide Wiring

Needs • Double and Multilayered Circuits• Interconnection between layers

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Related Works

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Related Works

Stapler

Electro-plate

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Conductive Adhesive

[Kisiel, et al., 2002]

Laser Cutter

[Falat, et al., 2011]

Rivet

[Anderson, et al., 2014]10/16/2015 UbiComp ‘15

Related Works

13

Conductive Adhesive

Laser Cutter Stapler Rivet

Footprint Small Small Large Large

Positioning Flexible Flexible Not Flexible Flexible

Energy Medium Huge Low Low

Time Long Long Short Medium

Durability Stable Stable Not Stable Not Stable

Danger Low High Low Low

Needs• Small Footprint• Flexible Positioning• Low Power Consumption

• Short Time• Durable• Not Dangerous

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Proposal

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Proposal – Idea

• Use double sided paper• Via hole to make interconnection• Drill Bits – Hole Punchers – Felting Needles

• Diameter: 0.2mm ～ 1mm• Drill hole• Fill silver ink

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Proposal – How Does It Work?

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Paper LayerResin Coated

Layer

Micro-porousLayer

Structure of Double Sided Paper

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Coating develops silver particle to bulk metal

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Paper LayerResin Coated

Layer

Micro-porousLayer

Structure of Double Sided PaperWith Via-Hole

Proposal – How Does It Work?

No coating layer inside the hole

Is it? NO

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Paper LayerResin Coated

Layer

Micro-porousLayer

Structure of Double Sided PaperWith Via-Hole

Proposal – How Does It Work?

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Paper LayerResin Coated

Layer

Micro-porousLayer

Material Entanglement

Structure of Double Sided PaperWith Via-Hole

Proposal – How Does It Work?Sintering-free

Immediately Conductive

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Experiment

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Experiment – Preparation

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Hole Opener

Drill Bit Hole Puncher Felting Needle

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Experiment – Preparation

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Substrate & Silver Nanoparticle Ink

From Mitsubishi Paper Mills• Double Side Photo paper• Silver Ink NBSIJ-MU01

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Experiment – Preparation

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Environment

• Environment vs. Conductivity

• Temperature: 20ºC

• Humidity: 20% ~ 30%

• Humidifier: create 100% humidity box

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Experiment – Conduction

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How to fill silver ink? – 3 options

• AgIC silver ink brush

• Epson Inkjet Printer• Open source driver Gutenprint

(widely applicable)• Control overprinting• “Print Density” (1 – 8)

• Print Density > 2• dirty sample• Use Print Density 1 & 2

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Experiment – Conduction

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Sample

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Experiment – Conduction

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Sample Processing

1

2

4, 5, 6

3

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Experiment – Conduction

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Parameters

Parameter Value

Hole OpenerDrill Bits – Hole Punchers

Felting Needles

EnvironmentT = 20ºC, H = 20% ~ 30%,

Humidifier

Ink fillingAgIC Brush/“Print Density = 1”/

“Print Density = 2”

Sample Processing

6 Types of Processing

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Experiment – Conduction

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Measurement

• 4-probe tester: Tonga TH2821 LCR• Measure resistance

• Different processing typeDifferent measuring time

Evaluation

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Evaluation– Ink Filling

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Ink Filling vs. Resistance (Ω)

41.27%

1.19%8.73%

76.98%

6.75%

29.76%

93.65%

13.49%

39.68%

Density2 Density1 Brush

R≤1 R≤10 R≤100

756 samples Best with Print Density = 2

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Evaluation – Hole Opener

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Hole Opener vs. Resistance (Ω)

Resistance of Via hole immediately after printing with “Print Density = 2” (Ω)

Process

1

2

3

4

5

6

Drill 0.2mm

700

740K

10.5

32.78

1.2M

336K

Drill 0.5mm

27

230

1.27

1

137K

1.46

Drill0.8mm

12

300

1.33

14.2

17.8

273

Puncher 0.5mm

52

2.5K

53.34

110

150K

88.9

Puncher 1mm

17.4

18

6.68

67K

170K

190K

Felting Needle

0.6

0.62

0.56

1.3M

960K

930K

𝟏𝟎𝟎 < 𝐑 ≤ 𝟏𝐊𝟎 < 𝐑 ≤ 𝟏 𝟏 < 𝐑 ≤ 𝟏𝟎 𝟏𝟎 < 𝐑 ≤ 𝟏𝟎𝟎 𝟏𝐊 < 𝐑

32

Evaluation – Hole Opener

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Hole Opener vs. Resistance (Ω)

Felting Needle seems to be good!

Durability?

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Evaluation – Hole Opener

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Hole Opener vs. Resistance (Ω)

AfterInkFill

AfterSteam

1dayAfterSteam

2days 3days 5days

Process1 0.60Ω 0.60Ω 0.71Ω 0.76Ω 0.76Ω

Process2 0.62Ω 0.43Ω 0.42Ω 0.57Ω 0.45Ω 0.44Ω

Process3 0.56Ω 0.49Ω 0.55Ω 0.54Ω 0.49Ω 0.47Ω

0.00Ω

0.10Ω

0.20Ω

0.30Ω

0.40Ω

0.50Ω

0.60Ω

0.70Ω

0.80Ω

Resistan

ce(Ω)

FELTNEEDLE &PRINTDENSITY=2

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Evaluation – Via Hole Structure

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Drill bit

FeltingNeedle

Hole Puncher

Applications

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Applications

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LED Matrix Hiding Wire

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Applications

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Wireless Power Transmission Coil

Paper Speaker Coil

Demo at Gadget Show Plus - Room 3 @ 18:00 today

Future Works

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Future Works

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Handy Drill Pen Printer Integration

Improve misalignment between 2 sides

Conclusion

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Conclusion

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• Double sided circuits with silver nanoparticle ink• Via hole to connect layers• Via hole by drill bits, hole punchers, felting needles• Best result:

• Felting Needle• “Print Density” = 2• R < 1Ω right after printing

• Applications of double sided circuits• Drill Pen & Integrate to printer

Thank You!

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43

Experiment – Conduction

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How to open the hole?

Experiment – Measurement

Measurement Time

No Humidify(P1 & 4)

0h – Humidify (P2 & 5)

24h – Humidify (P3 & 6)

Immediately ◯ ◯ ◯

After humidifying ╳ ◯ ╳

1 day ◯ ◯ ◯

After humidifying ╳ ╳ ◯

2 days ◯ ◯ ◯

3 days ◯ ◯ ◯

5 days ◯ ◯ ◯

• 4-probe tester: Tonga TH2821 LCR• Measure resistance

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◯ : Measure ╳ : Skip, not measure

UbiComp '15 - Osaka, Japan

Digital Fabrication - Electronic Circuits Fab

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CircuitSticker LittleBits

CircuitScribe Bare Paint10/16/2015 UbiComp ‘15

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Experiment – Conduction

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Sample Processing

1

2

4, 5, 6

3