A detailed study of variation in screen printed resistors on plastic

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https://doi.org/10.4224/23000708

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A detailed study of variation in screen printed resistors on plastic

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Information, data and drawings embodied in this document are strictly confidential and are supplied to the

team members of the Printable Electronics Consortium participating in this Project on the understanding that

they will be held confidentially and not disclosed to third parties without the prior written consent of the NRC

Executive Director responsible for the Printable Electronics Program.

A Detailed Study of Variation

in Screen Printed Resistors on

Plastic

Neil Graddage, Christophe Py, Heping Ding, James Lee, Ye Tao

Industrial Partners

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Smart Packaging for Pharmaceutical

Applications

This work has been performed as part of the Smart

Packaging for Pharmaceutical Applications project within

the Printed Electronics Program at NRC.

Project is led by Jones Packaging.

• Packaging design and production company.

• Specialists in pharmaceutical packaging.

Other partners in the project include

• Caledon Controls Ltd.

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3 IEEE Trans. on Components, Packaging and Manufacturing Technology, vol. 6 (3), pp. 335-345, 2016

Resistor based multiplexing

• The project aim is to print

smart drug packaging

• Monitor removal of medication

from a blister by the breaking of

a conductive trace

• Current solutions require one

connection for every blister.

• We wished to multiplex this

by use of resistors in series

with each blister.

• This technique is limited by

the variation of the printed

resistors.

R

₁

R

₂

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Screen Printing

• Common printing process

• Ink is displaced through a mesh

stencil

• Mesh is under tension in a frame

• Ink is drawn across the screen by a

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Screen Printed Resistors 1

• Comprehensive testing performed

to assess capabilities of screen

printing.

• Focused on variability rather than

absolute values.

• Electrodes were silver.

• DuPont 5025

• Resistors were carbon.

• DuPont 7082

• Printed resistors of width 0.25 and

0.5 mm.

• Printed a range of resistor lengths

between 0.1 and 20 mm.

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Screen Printed Resistors 2

• Resistors below 0.25 mm

were not reliable due to

limits of screen printing.

• Best case was nominally

0.5 mm wide resistors of

length over 1mm

• Average relative standard

deviation of 8%

• As low as 3.7% for > 1mm

long resistors within a set.

• Printed perpendicular to

squeegee print direction.

0.5 mm wide resistors perpendicular to print direction

0 2 4 6 8 10 12 14 16 18 0.1 0.15 0.2 0.25 0.5 1 1.3 2 3 4 4.5 6 20 Rela tiv e S tand ar d Dev iatio n [ % ] Track Length [mm]

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M=3 Demonstrator Production

– Relative Referencing

• Group resistors close together

• Design device with reference

resistor in centre.

• Measure ratio instead of absolute

values.

• Maximise multiplexing factor

• Increase robustness

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M=3 Demonstrator Printing

• Simulated volume production

• 119 samples printed

• Two batches

• Measured every sample using

interrogator

0 20 40 60 80 100 120 0.26 0.28 0.30 0.32 0.34

Pin 2 Pin 3 Pin 4 Pin 5 Pin 7 Pin 8 Pin 9 Pin 10 Pin 11

R a ti o o f Pi n s 2 -5 a n d 7 -1 1 W it h R e fe re n ce R e si st o r Sample Number Threshold = 0.32047 0 20 40 60 80 100 120 140 160 36 38 40 42 44 46 48 50 52 54 R e si st a n ce [ k  ] Time [min] Reference Resistance Linear Regression

• Initial yield of 85%

• 3 handling errors

• 4 electrode defects

• 10 resistor tolerance

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Causes of Variability 1

Misalignment

• Resistor variability could be caused by:

• misalignment;

• cross sectional profile variation;

• roughness (line edge and surface), and

• variations in ink resistivity.

• Misalignment

• Not a significant cause of variation.

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Causes of Variability 2

Roughness

• Line edge Roughness

• Measured planar area of

50 resistors.

• Variation appears random

and small.

• Does not correlate with

device functionality.

• Surface roughness

• Decreases through print

run.

• Correlates with decreasing

cross sectional area.

350 400 450 500 60 70 80 90 100 110 120 60 70 80 90 100 110 120 3200 3300 3400 3500 RA Al o n g R e si st o r L e n g th [ n m] C ro ss Se ct io n a l Are a [  m 2 ] Sample Number

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Causes of Variability 3

Cross Sectional Area and Resistivity Within a Print

• Cross sectional area slightly

increasing along print direction

• But resistance/ length decreases.

• Also periodic with length

• Why?

• Squeegee causing a gradient in ink

composition?

• Screen tension?

• Printing perpendicular to resistors

was incorrect.

0 5 10 15 20 25 30 19.5 21.0 22.5 24.0 2800 3000 3200 3400 3600 6.2 6.4 6.6 6.8 7.0 0 5 10 15 20 25 30 Printed First R e si st ivi ty [m  .m] Resistor Number Printed Last C ro ss Se ct io n a l Are a [  m 2 ] R e si st a n ce / L e n g th M  /m

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Causes of Variability 4

Cross Sectional Area and Resistivity During Batch

• Cross sectional area

decreases during print

run

• Resistance therefore

increases.

• But increase in resistivity

also observed.

• Ink evolving during

printing.

60 70 80 90 100 110 120 -10 -8 -6 -4 -2 0 2 4 6 8 10

D

e

vi

a

ti

o

n

F

ro

m

Me

a

n

[

%

]

Sample Number

Area

Resistance

Resistivity

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Causes of Variability 5

Ink Evolution

• Solvent evaporation causes ink

to evolve during printing

• Increases solid concentration

• Rheology change affects

transfer.

• However we would

expect the

rate of change to be consistent

.

• Note that the rate of change is

different in each batch.

• Also variability appears to

increase.

• Screen damage?

• Squeegee wear?

0 20 40 60 80 100 120 140 160 36 38 40 42 44 46 48 50 52 54 R e si st a n ce [ k  ] Time [min] Reference Resistance Linear Regression

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Summary

• Screen printed resistors are

capable of 3.7% relative

standard deviation.

• Devices should align with print

direction

• Ink evolution is the major

contributor to variability

• Resistance drift through batch

• Next Steps

• Design strategies to minimise

ink evolution

• Further examine screen and

squeegee wear.

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15

Thank you

Any Questions / Comments?

Neil Graddage

Research Associate, Printable Devices

Tel: 613-991-2786

neil.graddage@nrc-cnrc.gc.ca

www.nrc-cnrc.gc.ca

Thanks to the following for their assistance:

• Stephen Lang

• Terho Kololuoma

• John Weber