Printed electronics - Part 302-3: Equipment - Inkjet - Imaging-based measurement of drop direction

IEC 62899-302-3:2021(E) specifies in-flight imaging methods for the measurement of the direction of ink drops jetted from inkjet print-heads using drop watchers. It does not apply to holographic or other interference techniques, or to any method assessing deposited ink drops. It is specific to drop-on-demand type inkjet print-heads (used in printed electronics equipment).

General Information

Status
Published
Publication Date
20-Jan-2021
Technical Committee
Current Stage
PPUB - Publication issued
Completion Date
21-Jan-2021
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IEC 62899-302-3
Edition 1.0 2021-01
INTERNATIONAL
STANDARD
colour
inside
Printed electronics –
Part 302-3: Equipment – Inkjet – Imaging-based measurement of drop direction
IEC 62899-302-3:2021-01(en)
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---------------------- Page: 2 ----------------------
IEC 62899-302-3
Edition 1.0 2021-01
INTERNATIONAL
STANDARD
colour
inside
Printed electronics –
Part 302-3: Equipment – Inkjet – Imaging-based measurement of drop direction
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 19.080; 37.100.10 ISBN 978-2-8322-9286-0

Warning! Make sure that you obtained this publication from an authorized distributor.

® Registered trademark of the International Electrotechnical Commission
---------------------- Page: 3 ----------------------
– 2 – IEC 62899-302-3:2021 © IEC 2021
CONTENTS

FOREWORD ........................................................................................................................... 3

INTRODUCTION ..................................................................................................................... 5

1 Scope .............................................................................................................................. 6

2 Normative references ...................................................................................................... 6

3 Terms and definitions ...................................................................................................... 6

4 Measurement methods .................................................................................................... 7

4.1 General ................................................................................................................... 7

4.2 Process for projected angle using one double flash drop watcher (method 1) .......... 7

4.3 Process for projected angle using one single flash drop watcher (method 2) ........... 8

4.4 Process for projected angle using one strobe flash drop watcher (method 3) .......... 8

4.5 Process for trajectory angles using two double flash drop watchers (method 4)

............................................................................................................................... 8

4.6 Process for trajectory angles using two single flash drop watchers (method 5)

............................................................................................................................... 8

4.7 Process for trajectory angles using two strobe flash drop watchers (method 6) ....... 8

Annex A (informative) Determination of jetted drop direction .................................................. 9

A.1 Imaging-based measurements of jetted drop direction ............................................ 9

A.2 Formulae used for imaging results from the measurements ................................... 13

A.2.1 Formulae for projected angle using one double flash drop watcher

(method 1) ..................................................................................................... 13

A.2.2 Formulae for projected angle using one single flash drop watcher

(method 2) ..................................................................................................... 13

A.2.3 Formulae for projected angle using one strobe drop watcher (method 3) ....... 13

A.2.4 Formulae for trajectory angles using two double flash drop watchers

(method 4) ..................................................................................................... 14

A.2.5 Formulae for measured trajectory angles using two single flash drop

watchers (method 5) ...................................................................................... 15

A.2.6 Formulae for measured trajectory angles using two strobe flash drop

watchers (method 6) ...................................................................................... 17

A.3 Recording ............................................................................................................. 18

Bibliography .......................................................................................................................... 20

Figure A.1 – Schematic representation of jetted drop positions below a jetting nozzle

(0) for double flash (1-2), single flash (1-2ʹ) and strobe flash (1ʺ-2ʺ) at different delays ......... 10

Figure A.2 – Schematic representation of a) the projected angle δ in 2-D and b) the

trajectory angles θ and ψ in 3-D ............................................................................................ 11

Figure A.3 – Example of two orthogonally-mounted in-flight imaging drop watchers .............. 12

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IEC 62899-302-3:2021 © IEC 2021 – 3 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
PRINTED ELECTRONICS –
Part 302-3: Equipment – Inkjet –
Imaging-based measurement of drop direction
FOREWORD

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International Standard IEC 62899-302-3 has been prepared by IEC technical committee 119:

Printed Electronics.
The text of this International Standard is based on the following documents:
FDIS Report on voting
119/332/FDIS 119/344/RVD

Full information on the voting for the approval of this International Standard can be found in

the report on voting indicated in the above table.

This document has been drafted in accordance with the ISO/IEC Directives, Part 2.

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– 4 – IEC 62899-302-3:2021 © IEC 2021

A list of all parts in the IEC 62899 series, published under the general title Printed electronics,

can be found on the IEC website.

The committee has decided that the contents of this document will remain unchanged until the

stability date indicated on the IEC website under "http://webstore.iec.ch" in the data related to

the specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.

IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates that it

contains colours which are considered to be useful for the correct understanding of its

contents. Users should therefore print this document using a colour printer.
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IEC 62899-302-3:2021 © IEC 2021 – 5 –
INTRODUCTION

Establishing the jetted drop direction under specific operating conditions of inks and inkjet

print-heads is significant for accurate drop placement during the manufacture of printed

electronics. Manufacturers that include such print-heads in their equipment should know the

angular spread of ink drop directions because this influences the achievable spatial resolution

of the printed material, and in particular whether any neighbouring conducting tracks could be

connected by stray materials, which would affect the printed electronics' product performance.

This document defines the methods for in-flight imaging measurement of jetted drop direction

from drop-on-demand type inkjet print-heads to be used in printed electronics equipment.

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– 6 – IEC 62899-302-3:2021 © IEC 2021
PRINTED ELECTRONICS –
Part 302-3: Equipment – Inkjet –
Imaging-based measurement of drop direction
1 Scope

This part of IEC 62899 specifies in-flight imaging methods for the measurement of the

direction of ink drops jetted from inkjet print-heads using drop watchers. It does not apply to

holographic or other interference techniques, or to any method assessing deposited ink drops.

It is specific to drop-on-demand type inkjet print-heads (used in printed electronics

equipment).
2 Normative references

The following documents are referred to in the text in such a way that some or all of their

content constitutes requirements of this document. For dated references, only the edition

cited applies. For undated references, the latest edition of the referenced document (including

any amendments) applies.

IEC 62899-302-1, Printed electronics – Equipment – Inkjet – Imaging based measurement of

jetting speed
3 Terms and definitions

For the purposes of this document, the terms and definitions given in IEC 62899-302-1 and

the following apply.

ISO and IEC maintain terminological databases for use in standardization at the following

addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
3.1
inkjet nozzle plane
flat outer surface of the inkjet print-head nozzle plate

Note 1 to entry: The inkjet nozzle plane is defined for a drop-on-demand multi-nozzle print-head, or as otherwise

specified by the print-head manufacturer or inkjet equipment integrator and stated in the measurement results.

3.2
nozzle row direction
line in the inkjet nozzle plane passing through a row of nozzle exit centres

Note 1 to entry: Typically along the length of the inkjet nozzle plane, or as otherwise specified by the print-head

manufacturer or inkjet equipment integrator and stated in the measurement results.

3.3
reference direction
normal angle (90°) to the inkjet nozzle plate

Note 1 to entry: Or as otherwise specified by the print-head manufacturer or inkjet equipment integrator and

stated in the measurement results.
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IEC 62899-302-3:2021 © IEC 2021 – 7 –
3.4
measurement region

3-D space closest to the inkjet nozzle plane used for imaging of the jetted drops

3.5
drop trajectory
direction of drop travel in 3-D in the measurement region

Note 1 to entry: It can be measured with two drop watchers mounted with a wide angle between them

simultaneously imaging jetted drops.
3.6
trajectory angles, pl.
two orthogonal angles necessary to define the drop trajectory

Note 1 to entry: The polar angle is relative to the reference direction; the azimuthal angle is relative to a specific

direction within the nozzle plane, often assumed to be the nozzle row direction.
3.7
projected angle
angle of the drop trajectory in the 2-D image plane of a single drop watcher

Note 1 to entry: The projected angle does not correspond to the polar angle of the drop trajectory unless the

azimuthal angle is 0° or 180°.
3.8
reference speed
speed of the drop along the reference direction
3.9
projected speed
speed of the drop along the projected angle
3.10
absolute speed
speed of the drop along the drop trajectory
4 Measurement methods
4.1 General

The jetted drop direction shall be determined by using one of the following methods, unless

there is an agreement between the user and the supplier. In that case the method is fully

reported with the measurement results.

All equipment engaged in the trajectory measurement shall have a carefully calibrated

geometry.

The image plane shall be aligned in a precisely orthogonal direction to the inkjet nozzle plane

before the start of the measurement.
4.2 Process for projected angle using one double flash drop watcher (method 1)

1) Establish reliable jetting from the nozzle under study in the image measurement region.

2) Record the images and analyse the drop image position changes for the chosen double

flash delay.
3) Report the projected angle, using the formula provided in A.2.1.
4) Report the conditions as indicated in Clause A.3.
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– 8 – IEC 62899-302-3:2021 © IEC 2021
4.3 Process for projected angle using one single flash drop watcher (method 2)

1) Establish reliable jetting from the nozzle under study in the image measurement region.

2) Record a single flash image of a jetted drop and of the nozzle under study and analyse the

drop and nozzle exit image positions. Alternatively, record two single flash images of two

separate drops jetted at different times from the nozzle under study, and analyse the

single flash drop image positions.
3) Report the projected angle, using the appropriate formula specified in A.2.2.
4) Report the conditions as indicated in Clause A.3.
4.4 Process for projected angle using one strobe flash drop watcher (method 3)

1) Establish reliable jetting from the nozzle under study in the image measurement region.

2) Record a strobe flash image, at a chosen flash delay time, of the nozzle under study and

the superposed drops, and analyse the image positions of the nozzle exit centre and the

superposed drops. Alternatively, record two strobe flash images, at two different delay

times, of two separate drops from the same nozzle, and analyse the change of the single

flash image positions.
3) Report the projected angle, using the appropriate formula specified in A.2.3.
4) Report the conditions as indicated in Clause A.3.

4.5 Process for trajectory angles using two double flash drop watchers (method 4)

1) Establish reliable jetting from the nozzle under study in the image measurement region,

with the image planes of the two double flash drop watchers having a wide angle between

them aligned with a common axis along the reference direction.

2) Record double flash images of the same drop in each drop watcher for the chosen double

flash delay times and analyse the drop image positions in each double flash drop watcher.

3) Report the trajectory angles, using the appropriate formula specified in A.2.4.

4) Report the conditions as indicated in Clause A.3.

4.6 Process for trajectory angles using two single flash drop watchers (method 5)

1) Establish reliable jetting from the nozzle under study in the image measurement region,

with the image planes of the two single flash drop watchers having a wide angle between

them aligned with a common axis along the reference direction.

2) Record single flash images of the same drop and nozzle exit at a chosen delay time in

each drop watcher and analyse the image positions of the drop and nozzle exit centre in

each single flash drop watcher. Alternatively, record images, at chosen delay times in

each single flash drop watcher, of separate drops jetted from the nozzle under study, and

analyse the single flash drop image positions in each drop watcher.

3) Report the trajectory angles, using the appropriate formula specified in A.2.5.

4) Report the conditions as indicated in Clause A.3.

4.7 Process for trajectory angles using two strobe flash drop watchers (method 6)

1) Establish reliable jetting from the nozzle under study in the image measurement region,

with the image planes of the two strobe flash drop watchers having a wide angle between

them aligned with a common axis along the reference direction.

2) Record strobe flash images of the superposed drops and nozzle under study at a chosen

strobe flash delay time and analyse the image positions of the nozzle exit centre and

superposed drops in each strobe flash drop watcher. Alternatively, record strobe flash

images, at two different delay times, of separate drops jetted from the nozzle under study,

and analyse the superposed drop image positions in each strobe flash drop watcher.

3) Report the trajectory angles, using the appropriate formula specified in A.2.6.

4) Report the conditions as indicated in Clause A.3.
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IEC 62899-302-3:2021 © IEC 2021 – 9 –
Annexe A
(informative)
Determination of jetted drop direction
A.1 Imaging-based measurements of jetted drop direction

The jetted drop direction should be determined from drop image position measurements for at

least two different points in three-dimensional space. While IEC 62899-302-1 determines 2-D

components of drop velocity it does not explicitly consider imaging-based measurement of the

spatial components necessary to specify the jetted drop direction (or velocity) in 3-D space.

This document also uses just two different points to define the jetted drop direction, by

assuming a straight-line motion and the absence of electrical and gravitational effects on

jetted drops. All the drop watcher types are assumed to provide a flat 2-D image plane in this

document, with the camera image plane aligned orthogonally to the inkjet nozzle plane. This

alignment can be checked using reliably jetted drops with different delays spanning the region

of interest in the camera image plane. Drop trajectories for drop-on-demand printed ink drops

studied using multiple flashes, high-speed photography and orthogonally mounted drop

watchers showed straight line motion holds in the absence of sideways aerodynamic and

significant electric field effects. The effects of gravity as compared with air drag forces acting

on near-vertically jetted drop-on-demand inkjet drops are usually negligible.

In-flight imaging measurement methods are not based on the final printed drop position or any

other print quality (PQ) assessment methods applied to inkjet-printed electronics products. By

contrast, the measurement of printed drop positions on a fixed substrate defines final 3-D

locations at the expense of accurate knowledge of in-flight drop directions, and importantly

does not accurately determine the drop trajectory close to the nozzles, i.e. where jetted drops

are fully formed and furthest from their final printed positions.

Drop watchers provide the direct means of observing the region of interest for free-flying

jetted drops, although practical considerations can prevent the imaging of the nozzle exit. The

extent of the region of interest will depend upon these practical limits and the flash delay

times chosen, together with drop speed and the drop formation process, which in turn depend

on the ink properties and the particular inkjet print-head technology. Drop travel (throw)

distances from the jetting nozzle to the printed substrates are typically less than 1 mm;

completion of the drop formation process to give near-spherical droplets can require 100 µm

travel from the nozzle. The region of interest for the measurement of jetted drop direction

would be around 100 µm to 300 µm from the nozzle, but not near a substrate.

In-flight determination of the jetted drop direction relies on double flash drop watchers or

single flash drop watchers or strobe flash drop watchers taking one or more images of a

single drop or of different drops (and possibly the nozzle exit). Only methods such as that

using two double flash drop watchers can provide a direct measurement of the drop trajectory

for a single drop. Single flash drop watchers provide a projected angle based on image

positions for different drops (or possibly one and the nozzle exit), at two different single flash

delays. Strobe flash drop watchers provide an inherently representative average measured

image position for a number of superposed drops and a projected angle based on inherently

representative average measured image positions for two sets of superposed drops (or

possibly one set and the nozzle exit) at different strobe flash delays. This hierarchy of

methods should be associated with increasing uncertainties in the quoted projected angle and

in the quoted trajectory angles. The method used should always be reported, whether based

on this document or under an alternative user-supplier agreement.
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– 10 – IEC 62899-302-3:2021 © IEC 2021

Figure A.1 depicts the positions (1 and 2) of a jetted drop at two different locations (hence the

flash delay times) in the region of interest near the inkjet nozzle 0 for the double flash

measurement method; positions (1 and 2’) of different jetted drops at two different locations

(and flash delay times) in the region of interest near the inkjet nozzle 0 for the single flash

measurement method; and the image of superposed nozzle position 0″ and of the centroids of

the superposed jetted drop images 1″ and 2″ at two different locations (and flash delay times)

for the strobe measurement methods. Figure A.1 can represent 2-D (x, y) projections or 3-D

locations in space for drop images.

The direction of jetting is either defined using the change in the image position between the

centre of the nozzle exit (0 or 0ʺ) compared to the centroid position (1 or 1″) of a drop at later

times or, as more usual for regions of interest without the nozzle visible, by using the change

in the centroid positions (i.e. 1 and 2, or 1 and 2’, or 1″ and 2″). Some drop image positions (1″

and 2″) have exaggerated extent compared with the other positions, representing the multiple

drops superposed in strobe flash images; likewise nozzle exit image position (0ʺ) can shift

during strobe flash imaging. Lines between the nozzle image positions 0 (or 0″) and drop

positions 2′ (or 2″) are shown to emphasize the additional inherent inaccuracies of single flash

measurement methods. The lowest inaccuracies in the measurement of the trajectory angles

are expected when using the double flash measurement method for single drops based on

centroid positions 1 and 2, provided their separation is sufficient.

Figure A.1 – Schematic representation of jetted drop positions below a jetting nozzle (0)

for double flash (1-2), single flash (1-2ʹ) and strobe flash (1ʺ-2ʺ) at different delays

With two drop watchers aligned with a common x-axis and a wide angle χ (typically 90°)

between the image planes, the trajectory angles (and the absolute speed) for a jetted drop

can be determined. When there is only one drop watcher, only the projected angle (and the

projected speed) for a jetted drop can be obtained.

Polar angle θ is measured relative to the reference direction (x-axis); azimuthal angle ψ is

measured relative to a specific direction within the nozzle plane, often assumed to be along

the nozzle row direction. A representation of these jetted drop angles in Figure A.2 shows: a),

the projected angle δ in 2-D corresponding to a double flash drop watcher (1 and 2), the

nozzle exit and other drop images at different delays for a single flash (0, 1 and 2′) or a strobe

flash (0″, 1″ and 2″) drop watcher; b), the trajectory angles θ and ψ in 3-D as measured by two

orthogonal (wide angle χ = ψ + ψ = 90°) or non-orthogonal drop watcher systems A and B for

A B

the double flash scenario. Equivalent schematic representations for trajectory angles θ and ψ

found with orthogonal or non-orthogonal single flash or strobe flash drop watcher systems A

---------------------- Page: 12 ----------------------
IEC 62899-302-3:2021 © IEC 2021 – 11 –

and B are not given here. They can be obtained from Figure A.2b) after appropriate

substitutions for the coordinate labels (′ or ″), respectively, following the notation already

shown in Figure A.1.
a) The projected angle δ in 2-D
b) The trajectory angles θ and ψ in 3-D
Figure A.2 – Schematic representation of a) the projected angle δ in 2-D and b)
the trajectory angles θ and ψ in 3-D
---------------------- Page: 13 ----------------------
– 12 – IEC 62899-302-3:2021 © IEC 2021
Figure A.3 – Example of two orthogonally-mounted in-flight imaging drop watchers

When determining the trajectory angles of the jetted drop direction for a specific inkjet nozzle,

it is preferable that the very same drop is measured by the drop watcher(s) involved, to avoid

the additional direction uncertainties which will arise from any jetted drop-to-drop variations,

as depicted in Figure A.1.

An example of two orthogonally mounted in-flight imaging drop watchers is shown in

Figure A.3. Orthogonally-mounted drop watchers provide image planes at 90° and have the

downwards reference direction in common with each other; alternatively, these two drop

watchers should have their image planes at a wide non-zero angle with respect to the

common downwards direction.

The use of two drop watchers simultaneously imaging drops, jetted from a specific nozzle, in

two different 2-D planes allows a more accurate measurement of jetted drop speed than

possible with a single drop watcher, although for a small polar trajectory angle the difference

between the speeds is very small: the absolute speed exceeds the projected s
...

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