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Patent Searching and Data


Title:
INKJET PRINT HEAD WITH CONTAMINATION ROBUSTNESS
Document Type and Number:
WIPO Patent Application WO/2021/008700
Kind Code:
A1
Abstract:
The inkjet print head comprises a nozzle layer (4) with a plurality of nozzles (8) as well as a feed layer (6) comprising a plurality of feed ducts (20a, 20b) for feeding ink to the nozzles. The feed layer comprises a filter sublayer (32) forming filters (34) extending across the feed ducts (20a, 20b). The print head may be an electrohydrodynamic print head with electrodes (14) for accelerating the ink towards a target.

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Inventors:
GALLIKER PATRICK (CH)
Application Number:
PCT/EP2019/069221
Publication Date:
January 21, 2021
Filing Date:
July 17, 2019
Export Citation:
Click for automatic bibliography generation   Help
Assignee:
SCRONA AG (CH)
International Classes:
B41J2/06; B41J2/14; B41J2/16; B41J2/175; B41J2/18
Foreign References:
JP2005254666A2005-09-22
US20110261117A12011-10-27
US20040075722A12004-04-22
US20090309933A12009-12-17
US20110205319A12011-08-25
US20030016272A12003-01-23
JP2007237478A2007-09-20
US20130242012A12013-09-19
US20160082731A12016-03-24
US9073321B12015-07-07
US20050117005A12005-06-02
US20070229608A12007-10-04
US20140152747A12014-06-05
US20180009223A12018-01-11
US20160059359A12016-03-03
Attorney, Agent or Firm:
E. BLUM & CO. AG (CH)
Download PDF:
Claims:
Claims

1. An inkjet print head comprising

a nozzle layer (4) comprising a plurality of nozzles (8), and a feed layer (6) comprising a plurality of feed ducts (20a, 20b) extending through said feed layer (6) and communicating with said nozzles (8),

wherein said print head (6) comprises a filter sublayer (32) forming filters (34) extending across said feed ducts (20a, 20b).

2. The print head of claim 1 wherein said filter sublayer (32) comprises a dielectric layer (34b).

3. The print head of any of the preceding claims wherein said filter sublayer (32) comprises a metal layer (34a).

4. The print head of claim 3 further comprising electrically conductive filter connect leads (46a - 46c; 46d) connecting said metal layer (34a) to at least one electric filter terminal (44) of said print head.

5. The print head of any of the preceding claims wherein each filter (34) comprises a section of said filter sublayer (32) with a plurality of openings (36) therein.

6. The print head of claim 5 wherein a diameter of the openings (36) of a given filter (34) is smaller than an inner diameter of the nozzle (8) connected to the filter (34).

7. The print head of any of the claims 5 or 6 wherein a diameter of the openings (36) of a given filter (34) is at least five times smaller than a diameter of the feed duct (20a, 20b) at said filter (34).

8. The print head of any of the claims 5 to 7 wherein at least some (36a) of said openings (36) extend to a wall of the feed duct (20a, 20b) a given filter (34) is located in.

9. The print head of claim 8 wherein the openings (36a) extending to the wall of the feed duct (20a, 20b) are elongated.

10. The print head of any of the preceding claims wherein said feed layer (6) further comprises a bottommost sublayer (6a), wherein said feed ducts (20a, 20b) extend through said bottommost sublayer (6a) and wherein said bottommost sublayer (6a) is arranged between said nozzle layer (4) and said filter sublayer (32).

11. The print head of any of the preceding claims wherein said feed ducts (20a, 20b) comprise

- via sections (20a) extending transver sally, in particular perpendicularly, through at least part of said feed layer (6) and

- at least one interconnect section (20b) extending along said feed layer (6), wherein each interconnect section (20b) interconnects several of said via sections (20a).

12. The print head of claim 11 wherein said filters (34) are arranged between said interconnect section(s) (20b) and said nozzle layer (4), and in particular wherein said filters (34) extend across said via sections (20a).

13. The print head of any of the preceding claims comprising at least one ink input terminal (72) and at least one ink output terminal (76), wherein said feed ducts (20a, 20b) comprise

a connection duct (74) between said ink input terminal (72) and said ink output terminal (76), and

branch ducts (78) forking off from said connection duct (74) to at least part of said nozzles (8),

and in particular wherein said print head comprises a plurality of parallel connection ducts (74).

14. The print head of claim 13 wherein at least part of said filters (34) are arranged along said branch ducts (78).

15. The print head of any of the claims 11 or 12 and of any of the claims 13 or 14 wherein said connection duct (74) is formed at least in part by said interconnect section(s) (20a) and said branch ducts (78) are formed at least in part by said via sections (20a). 16. The print head of any of the claims 13 to 15 wherein said input terminal (72) is connected to a first end (80a) of said connection duct (74), and said output terminal (76) is connected to a second end (80b) of said connection duct (74).

17. The print head of any of the preceding claims wherein said filter sublayer (32) has a thickness smaller than 100 pm.

18. The print head of any of the preceding claims wherein said print head is an electrohydrodynamic print head comprising nozzle electrodes (14) at said nozzles (8).

19. The print head of any of the preceding claims wherein said filter sublayer (32) is part of said feed layer (6).

20. The print head of any of the preceding claims further compris ing

- electrical vias (26) extending through at least part of said feed layer (6), and in particular wherein said print head comprises at least one electrical via (26) for each of a majority of said nozzles (8), in particular for all of the nozzles (8),

- horizontal electrical tracks (60) arranged in or on said feed layer (6) and being connected to said electrical vias (26).

21. The print head of claim 20 wherein said filters (34) are arranged below at least part of said horizontal electrical tracks (60).

22. The print head of any of the preceding claims wherein said feed layer (6) comprises a plurality of sublayers and wherein said nozzle layer (4) has a smaller horizontal extension than at least part of the sublayers of said feed layer (6).

23. A method for manufacturing the print head of any of the preceding claims comprising the steps of

a) manufacturing said nozzle layer (4) with said nozzles (8), b) manufacturing said feed layer (6),

c) forming said feed ducts (20a, 20b) in said feed layer (6), d) forming said filters (34). 24. The method of claim 23 comprising the steps of

applying said filter sublayer (32) onto a sublayer (90) of said feed layer (6),

structuring said filter sublayer (32) to create openings (36) therein, and, subsequently,

opening at least part said feed ducts (20a, 20b) in said sublayer (90).

25. The method of claim 24 further comprising the step of opening said feed ducts (20a, 20b) in said sublayer (90) by introducing an etching agent through said filters (34).

26. The method of any of the claims 24 or 25 comprising the step of forming the feed ducts (20a, 20b) in said sublayer (90) by laser-induced etching.

27. The method of claim 26 further comprising the steps of first laser-irradiating the sublayer (90) at irradiated locations (92), then forming said filters (34) over at least some of the irradiated locations (92),

then etching the sublayer (90) through the filters (34) at at least some of the irradiated locations (92) for forming the ducts therein.

28. Use of the print head of any of the claims 1 to 22 for electrohydrodynamic printing.

29. A printer comprising the print head (2) of any of the claims 1 to

22.

30. The printer of claim 29 with a print head (2) of any of the claims 13 to 16 further comprising an ink circulation pump (70) connected to said ink input terminal (72) and said ink output terminal (76) and adapted to circulate ink through said connection duct (74).

31. The printer of any of the claims 29 or 30 further comprising a temperature controller (81) thermally connected to said feed ducts (20a, 20b, 74).

Description:
Inkjet print head with contamination robustness

Technical Field

The invention relates to an inkjet print head. This is a print head structured to deposit droplets or jets of a liquid (the ink) onto a target. It comprises a nozzle layer having a plurality of nozzles and a feed layer forming feed ducts to the nozzles.

The invention also relates to a printer with such a print head and to a method for manufacturing such a print head.

Background Art

US 2018/0009223 describes an electrohydrodynamic print head having a nozzle layer comprising a plurality of nozzles. It is based on a silicon structure where the nozzles are arranged on one side, and feed ducts extend through a feed layer on the other side.

Disclosure of the Invention

The problem to be solved by the present invention is to provide a print head and method for manufacturing such a print head with improved reliability.

This problem is solved by the print head of claim 1.

Accordingly, the invention relates to an inkjet print head comprising at least the following elements:

- A nozzle layer: The nozzle layer comprises a plurality of nozzles for ejecting the ink onto the substrate.

- A feed layer: The feed layer comprises a plurality of feed ducts extending through it. The feed ducts communicate with the nozzles. They can be used to feed ink to the nozzles.

According to the invention, the print head comprises a filter sublayer forming filters extending across the feed ducts. The filters prevent at least the larger solid particles from reaching the potentially fine nozzles and clogging them. The invention is based on the understanding that clogging can occur at the nozzle as a result of agglomerated ink material or otherwise larger than usual solid material contents arriving at the nozzle exit.

The filter sublayer may comprise a metal layer, which allows making it electrically conductive, e.g. for electrically contacting the ink and setting it onto a defined potential.

The filter sublayer may comprise a dielectric layer.

The filter sublayer may also comprise the combination of at least one metal layer and at least one dielectric layer, e.g. for providing a thin metal layer with improved stability.

Advantageously, the filter sublayer may comprise electrically conductive leads, in the following called“electrically conductive filter connect leads”, which connect the metal parts of the filter sublayer to an electric filter terminal of the print head. This allows to apply a defined potential to the filters.

In a particularly advantageous embodiment, the print head is an electrohydrodynamic print head comprising nozzle electrodes at the nozzles. The nozzle electrodes are positioned to accelerate the ink from the nozzles onto the target.

Each filter may be formed by a section of the filter sublayer with a plurality of openings therein for letting the ink pass through the filters. By using a plurality of openings, clogging of a single opening -will not block the whole filter.

Advantageously, the diameter of the openings of a given filter is smaller than the inner diameter of the nozzle connected, by means of a feed duct, to the filter, such that any particle passing the filter can also pass the nozzle.

In one embodiment, at least some of the openings of a given filter extend to the wall of the feed duct the filter is located in. This expedites the passage of a fluid, in particular if the wall of the feed duct is easily wetted by the fluid.

The feed lines may comprise the following sections:

- Via sections extending transversally, in particular perpendicularly, through at least part of the feed layer: They transport the ink in vertical direction.

- At least one interconnect section extending along said feed layer: Each interconnect section interconnects several of the via sections.

In this case, the filters are best arranged between the interconnect sections and the nozzle layer. In particular, they can extend across the via sections.

The print head may comprise electrical feeds. In particular, it may comprise: - Electrical vias extending through at least part of the feed layer: These vias can be used to conduct electricity in vertical direction. In particular, the print head may comprise at least one electrical via for each of a majority of said nozzles in order to customize currents and/or voltages at each nozzle.

- Horizontal electrical tracks arranged in or on the feed layer and being connected to the electrical vias. They can be used to feed electricity to the electrical vias.

In this case, the filters are advantageously arranged below (i.e. on the nozzle-side of) at least part of the horizontal electrical tracks. This allows to standardize the filters in an earlier manufacturing step while using individualization of the horizontal electrical tracks in a later manufacturing step.

The invention also relates to an embodiment where the print head comprises at least one ink input terminal and at least one ink output terminal. These terminals may e.g. be arranged at the top side of the print head.

In this case, the feed ducts may comprise:

- A connection duct between the ink input terminal and the ink output terminal; and

- Branch ducts forking off from the connection duct to at least part of the nozzles. Advantageously, each branch duct leads to one nozzle.

This design allows to circulate the ink between the input and output terminals, thereby continuously or periodically refreshing the ink in at least part of the feed ducts.

In this case, at least part of the filters are advantageously arranged in the branch ducts for blocking particles there.

The connection duct may be formed at least in part by the interconnect section(s) and the branch ducts may be formed at least in part by the via sections.

The invention also relates to a printer comprising such a print head.

In another aspect, the invention relates to a method for manufacturing such a print head. The method comprises the steps of

a) Manufacturing the nozzle layer with the nozzles: This step can e.g. be carried out in a semiconductor foundry.

b) Manufacturing the feed layer: This step can be carried out sepa rately from step a) or in combination with step a).

c) Forming the feed ducts in said feed layer.

d) Forming the filters, e.g. by applying a uniform layer to the feed layer or a sublayer thereof and subsequently structuring it.

The orders of these steps is arbitrary. In one embodiment, the method may comprise the following steps:

- Applying the filter sublayer onto a sublayer of said feed layer.

- Structuring the filter sublayer for creating openings therein: These openings form the passageways of the filters where the ink passes through them. Subsequently:

- Opening at least part said feed ducts in the sublayer through the feed layer.

This allows to easily create of the filters.

The method may further comprise the step of opening the feed ducts in said sublayer by introducing an etching agent through the filters, i.e. the openings in the filters are used to introduce the etching agent into the sublayer behind them.

Advantageously, the method comprises the step of forming the feed ducts in the sublayer by laser-induced etching. This method allows to generate deep ducts in the sublayer and, optionally, to easily customize their locations.

The etching may take place through the filters. In other words, the method may further comprise the steps of:

- First laser-irradiating the sublayer: This defines the irradiated regions where the subsequent etching can take place anisotropically, i.e. where the etch rate is faster in one direction than in another. Here, the etch rate is faster in direction of the laser irradiation as compared to perpendicular to such laser irradiation direction.

- Then forming said filters over at least some of the irradiated locations: At this point, the sublayer is not yet etched, which makes the creation of the filters easier.

- Then etching the sublayer through the filters at at least some of the irradiated locations for forming the ducts therein. The feed layer may additionally be covered at least partly by a masking layer, e.g. by a photoresist, which can be removed again once the sublayer has been etched. Masking prevents etching of the sublayer at locations where the sublayer is not yet masked by the filter.

The invention also relates to a printer, and it also relates to the use of the print head for electrohydrodynamic printing.

Brief Description of the Drawings The invention will be better understood and objects other than those set forth above will become apparent when consideration is given to the following detailed description thereof. This description makes reference to the annexed drawings, wherein:

Fig. 1 is a sectional view of a first embodiment of a print head,

Fig. 2 is a sectional view along line II-II of Fig. 1 ,

Fig. 3 is a sectional view along line III-III of Fig. 1,

Fig. 4 is a sectional view along line IV-IV of Fig. 1,

Fig. 5 is a sectional view of a second embodiment of a print head, Fig. 6 is a sectional view along line VI-VI of Fig. 5,

Fig. 7 is a top view of an example of a filter including a sectional view illustrating the wetting process,

Fig. 8 is a sectional view of part of a filter,

Fig. 9 is a sectional view of a second embodiment of a print head, Fig. 10 is a sectional view along line X-X of Fig. 9,

Fig. 11 is a sectional view along line XI-XI of Fig. 9,

Fig. 12 is a sectional view along line XII-XII of Fig. 9,

Fig. 13 is a schematic view of a printer illustrating a first variant for connecting the print head to a voltage source and ink circulation pump,

Fig. 14 is a schematic view of a printer illustrating a second variant for connecting the print head to a voltage source and ink circulation pump,

Fig. 15 is a sectional view of a first interconnect layer of another embodiment of the print head with a first set of interconnect sections,

Fig. 16 is a sectional view of second interconnect layer of the embodiment of Fig. 15,

Fig. 17 shows a first step of a manufacturing process,

Fig. 18 shows a second step of a manufacturing process,

Fig. 19 shows a third step of a manufacturing process.

Modes for Carrying Out the Invention

Definitions

A dielectric is a material having an electrical conductivity of 10 ~ 6

S/m or less. Laser-induced etching of the feed duct is a method where a laser beam is used to modify the structure of the feed layer such that it becomes more susceptible to an etching agent than unexposed regions. Thereafter, the etching agent is used to open the feed ducts, in which case the feed ducts can have almost vertical walls along the direction the laser irradiation took place.

Terms such as above, below, top, bottom are to be understood such that the nozzle layer defines the bottom part of the print head and the feed layer is arranged above the nozzle layer.

Horizontal designates the directions parallel to the planes of the nozzle and feed layers. Vertical designates the direction perpendicular to the planes of the nozzle and feed layers.

Feed ducts are ducts guiding ink through the feed layer. Feed ducts may include via sections that extend transversally, in particular vertically, through one or more sublayers of the feed layer and provide ink transport in vertical direction. Feed ducts may also include interconnect sections that extend horizontally through the print head and provide ink transport in horizontal direction. Typically, interconnect sections interconnect several via sections in a next lower sublayer of the print head.

Feed lines are electrically conductive leads (tracks) guiding electric current through the feed layer. Feed lines may include electrical vias that extend transversally, in particular vertically, through one or more sublayers of the feed layer and provide current (voltage) transport in vertical direction. Feed lines may also include horizontal electrical tracks that extend horizontally through or along the feed layer and provide current (voltage) transport in horizontal direction.

First Embodiment

Figs. 1 - 4 show a first embodiment of a print head 2.

Print head 2 comprises a plurality of structured layers. In particular, print head 2 comprises a nozzle layer 4 and a feed layer 6, with nozzle layer 4 being arranged, by definition, below feed layer 6.

Nozzle layer 4 forms a plurality of nozzles 8. Each nozzle 8 has a spout 10 arranged in a recess 12 and a nozzle electrode 14. Nozzle electrode 14 is arranged at a lower level than spout 10 in order to electrohydrodynamically extract ink from spout 10 and accelerate it towards a target located below print head 1.

Nozzle electrode 14 is advantageously arranged, at least in part, around recess 12 and may be annular. Nozzle layer 4 comprises a plurality of sublayers. In the present embodiment, these include:

- A first sublayer 4a forming a bottom section of the recesses 12.

- A second sublayer 4b located above first sublayer 4a and forming a middle section of the recesses 12.

- A third sublayer 4c located above second sublayer 4b and forming a top section of the recesses 12 as well as forming the spouts 10.

- A fourth sublayer 4d arranged above third sublayer 4c and forming a plate carrying the spouts 10 at the center of their respective recesses 12.

The sublayers 4a - 4d are advantageously dielectric layers, such as layers of silicon dioxide or glass.

The nozzle electrodes 14 are located between first and second sublayer 4a, 4b.

From each nozzle electrode 14, an electrically conducting via 16 extends upwards through nozzle layer 4 to feed layer 6.

Each spout 10 forms a channel 18 extending between a bottom-side opening of the spout and feed layer 6.

Nozzle layer 4 may have the same structure at a majority of all nozzles 8 or even at all of them. It may e.g. be mass-produced at a semiconductor foundry using known anisotropic etching and lithographic patterning technologies.

A shielding electrode 19 may be arranged at a level below the nozzle electrodes 14. Shielding electrode 19 reduces crosstalk between neighboring nozzle electrodes 14 and/or allows controlling the field between the printing head and the target below it in more controlled manner.

Shielding electrode 19 may be located at the bottom of first sublayer 4a. If there is no shielding electrode 19, sublayer 4a may be dispensed with.

Advantageously, shielding electrode 19 is the bottommost electrode in the print head, although the shielding electrode 19 may be covered at its bottom by additional layer, e.g. a dielectric layer for protecting it from electrical breakdowns and in case such dielectric layer consist of low surface-energy material, it may also guide as a non-wetting layer, i.e. a layer that is not readily wetted by the ink.

Shielding electrode 19 is advantageously a continuous conducting layer surrounding a plurality of the nozzles 8 with openings at the locations below the nozzles 8.

Advantageously, all of shielding electrode 19 is interconnected to be at the same electric potential. Feed layer 6 comprises several sublayers 6a - 6e arranged on top of each other. The sublayers 6a - 6e are advantageously dielectric layers, such as layers of S1O2 or glass. Some or all of them may also consist of a photo-pattemable polymer, such as an epoxy-based polymer.

A plurality of feed ducts 20a, 20b extend through feed layer 6 for feeding ink to the nozzles 8 for feeding ink to the nozzles 8.

In the shown embodiment, the feed ducts comprise via sections 20a extending perpendicularly upward from one of the nozzles 8 through the bottommost sublayer(s). In the embodiment of Fig. 1, they extend through the sublayers 6a, 6b,

6c. The via sections 20a are formed by openings in these layers. The sublayers forming via sections 20a are also called“via sublayers”.

In the present example, the feed ducts further comprise at least one interconnect section 20b extending horizontally and interconnecting a plurality of the via sections 20a.

In the embodiment shown, there is one interconnect section 20b formed by a cavity in sublayer 6d as best shown in Fig. 2. Sublayer 6d is also called an“interconnect sublayer”.

The feed ducts 20a, 20b connect the nozzles 8 to one or more ink terminals of the print head. One such ink terminal 21 is shown as an example in Fig.

1. The ink terminal(s) 21 can in turn be connected to one or more either ink reservoirs 22, directly or by means of ducts 24 as schematically illustrated in Fig. 1.

In the example of Fig. 1, the ink terminal(s) 21 is/are formed in sublayer 6e above sublayer 6d. However, feed layer 6 may comprise further duct sections and sublayers as described for some of the later embodiments.

Several first electric vias 26 extend through at least part of feed layer 6. They form at least part of a system of electrically conductive tracks and con nect one or more first voltage terminals 28 (shown later, in Fig. 13, 14) of feed layer 6 to at least part of the nozzle electrodes 14 and/or to other electrodes in the print head. For this purpose, the first electric vias 26 of feed layer 6 are connected at their bottom end to the top ends of the electric vias 16 of nozzle layer 4.

The first voltage terminal(s) 28 is/are connected to a voltage supply 30, which is adapted to generate voltage pulses that control the ejection of ink from the nozzles 8.

Feed layer 6 further comprises a filter sublayer 32 forming a plurality of filters 34.

In the embodiment of Figs. 1 - 4, the filters 34 extend across the via sections 20a. They may, however, also extend across other parts of the feed ducts. Each filter 34 comprises a plurality of openings 36.

The diameter of the openings 36 is advantageously smaller that the inner diameter of the nozzles 8, i.e. the diameter of the channels 18 of the nozzles, such that any particles that pass a filter 34 can also pass the nozzles 16.

The filters 34 are formed by suitably structuring filter sublayer 32.

Filter sublayer 34 is located between two of the sublayers of feed layer 6. In the embodiment of Figs. 1 - 4, filter sublayer 34 is located between bot tommost sublayer 6a and the next sublayer 6b.

As can be seen from Fig. 4, filter sublayer 34 also forms first horizontal electrical tracks 38, which may be connected to electrical vias 40 (the position of which is shown in dotted lines in Fig. 1),

The electrical vias 40 can be connected to one or more of the electrodes of nozzle layer 4. In the embodiment of Figs. 1 - 4, they extend through sublayer 6a and nozzle layer 4 down to shielding electrode 19.

Feed layer 6 can be used for customizing the function of the nozzles 8, e.g. for disabling some of them by design.

In the embodiment of Figs. 1 - 4, only a subset of the nozzles 8 is connected to the ink terminal(s) 21 via the feed ducts 20. Namely, the nozzle at position A is not connected to a feed duct 20 because the via section 20a is missing at this position.

This allows structuring the print head by means of a proper design of feed layer 6 even though nozzle layer 4 has an identical design for each or for a majority of the nozzles 8.

Another way to customize the print head by design is through suita bly wiring the nozzle electrodes 14 to the voltage terminal(s). For example, a nozzle that is not required in a customized print head may be left without a wired nozzle electrode in which case the nozzle is filled with ink but no ink is ever ejected from it.

In the embodiment of Fig. 1, the electrical vias 26 from the nozzle electrodes 14 are connected to second horizontal electrical tracks 42 between sublayers 6b and 6c, which connect them to one or more voltage terminals 28 of the print head. The electrical tracks 42 can be customized to meet a print head’s needs. However, in the case of the present embodiment all nozzles connected to the same horizontal electrical tracks cannot be operated individually anymore but are either activated all together or none of them at all.

The filters 34 may also be electrically connected to an electric filter terminal 44 (Fig. 1) of the print head in order to apply them to a desired electrical potential. In the embodiment of Fig. 1 , this is achieved by providing filter connect leads 46a, 46b, which comprise a first part 46a extending along the inner wall of via section 20a and a second part 46b extending through the topmost layers, e.g. layers 6d and 6e, of the print head, to a third set of horizontal electrical tracks 46c at the top of topmost layer 6e.

Techniques for manufacturing the various embodiments of print head 2 are described in more detail in a separate section below.

Second Embodiment

Figs. 5 and 6 show a second embodiment of a print head.

Here, the filters 34 are electrically interconnected by filter connect leads 46d formed by horizontal electrical tracks. The filter connect leads 46d may e.g. be manufactured from filter sublayer 32 by suitably structuring said sublayer. This obviates the need for interconnecting them at a higher level and allows to reduce the number of sublayers of feed layer 6.

Filter Design

In the first and second embodiment, the openings 36 in the filters 34 form a regular two-dimensional array.

Fig. 7 shows a preferred design of the filters 34, which may be combined with any of the embodiments of the print head. Here, at least part of the openings 36, namely the openings 36a in Fig. 7, extend to the wall 52 of the feed duct (via section) 20a. As described above, this expedites the passage of the ink through the filter because there is no discontinuity for the wettable surface at the wall region.

Hence, liquid wetting progresses downwards into the feed duct 20a and then fills the feed duct 24a from bottom to top.

This is illustrated in inset X of Fig. 7, where reference number 54 denotes the ink. As can be seen, an at least partially wettable wall 52 draws the ink down through the openings 36a that extend to wall 52.

Once that ink 54 has passed through the openings 36a and filled the via section 20a below filter 34, ink may also pass through the central openings 36b that do not contact wall 52.

The openings 36a extending to wall 52 are advantageously elongate for allowing more ink to pass and to improve the likelihood of forming the interface with the wall 52 because alignment between the openings 36a and wall 52 is less critical. Advantageously, the central openings 36b are not elongate, e.g. round, in order to improve mechanical stability.

However, other combinations of shapes for the openings 36a, 36b may be used, too. For example, the outer openings 36a may also be circular or comprise a combination of slit-shaped and circular openings.

The diameter of the openings 36, 36a, 36b is typically much smaller than via section 20a (or any other feed duct the filter 34 may be located in). In particular, the diameter of the openings 36, 36a, 36b is at least five times smaller than the diameter of the feed duct at filter 34.

For an elongate opening, the“diameter” is defined as the maximum width of the opening perpendicular to its longitudinal extension.

As mentioned, the filters 34 advantageously comprise at least one metal layer, which allows to apply a voltage to them, thereby better defining the potential of the ink in respect to the electrodes of the nozzle layer 4.

However, and as shown in Fig. 8, the filters 34 may also be a combination of at least one metal layer 34a and at least one dielectric layer 34b.

Filter sublayer 32 is advantageously thin, having a thickness of e.g. less than 100 pm.

Advantageously, the filters 34 are of, or comprise, a noble metal, such a platinum or gold.

In yet another embodiment, the filters 34 are of a dielectric material, e.g. when the electrical potential of the ink is defined in different manner.

In another embodiment the filters 34 consist at least partly of a material that has low wettability by the ink, e.g. Teflon or a similar material. Preferably the material of low wettability at least faces upwards such that large particles do not stick to the filter and clog it.

Third Embodiment

Figs. 9 - 12 show a third embodiment of a print head.

This embodiment illustrates the customization of the print head by means of customizing the electrical feed lines in feed layer 6.

Here, the electrical vias 26 from the nozzle electrodes 14 reach to a level higher than the filters 34, where they are connected to horizontal electrical tracks 60 at a wiring layer 66. The horizontal electrical tracks 60 are also arranged at a level higher than at least part of the interconnect sections 20b of the feed ducts. While the layers below the horizontal electrical tracks 60 can be the same for a large number of print heads, the horizontal electrical tracks 60 can be individualized in order to adapt a print head to a specific application. This allows to manufacture the layers below the horizontal electrical tracks 60, i.e. below wiring layer 66, using mass-production techniques that are generally not well-adapted to design changes.

In the embodiment of Figs. 9 - 12, the filter connect leads 46d (Fig. 12) are again formed by horizontal electrical tracks made from structures of the filter sublayer 32. These tracks connect to filter connect vias 46e, which extend upwards from filter sublayer 32.

Further, and as shown in Fig. 12, filter sublayer 32 may also form horizontal electrical tracks 62 connecting the via sections 40 from shielding layer 19 to further electrical vias 64, which extend upwards from filter sublayer 32.

In the shown embodiment, the vias 26, 46e, and 64 go upwards to wiring layer 66 located above the interconnect ducts 20b.

As shown in Fig. 10, wiring layer 66 forms the horizontal electrical tracks 60 connected to the electrical vias 26 from the nozzle electrodes 14. These tracks 60 may be customized to the needs of a specific print head. For example, where a nozzle is not to be used, such as the nozzle at location A in Fig. 9, its electrical via 26 may remain unconnected.

The horizontal electrical tracks 60 can be connected to a plurality of nozzle electrode terminals of the print head that allow e.g. to operate a corresponding number subsets of the nozzles 8 independently.

Wiring layer 66 may also form horizontal electrical tracks 68 connecting the filter connect vias 46e to the electric filter terminal.

Finally, wiring layer 66 may also fomi horizontal electrical tracks 70 connecting the vias 64 from shielding electrode 19 to an electrical shielding terminal of the print head.

As can be seen form Figs. 9 - 12, the number of vias 40, 64 for connecting shielding electrode 19 to the electrical shielding terminal of print head 2 is smaller than in the previous embodiments. Since shielding electrode 19 is one large, continuous electrode, it can still be maintained at the same potential everywhere.

Usually, such vias 40, 64 are provided at regular intervals, such that e.g. there is one via in each window of 0.5 x 0.5 mm 2 , which allows dicing larger wafers containing the print head structure into smaller ones and provides for a certain degree of redundancy in each diced print head. This technique of thinning out the vias 40, 64 connected to shielding electrode 19 to less than one via per nozzle, in particular to less than 1 via per 16 nozzles, provides more room of other electrical wiring needs.

Similarly, there are less electrical vias 46e than nozzles, i.e. the electrical vias 46e connected to the filters 34 can be thinned out, too, because the horizontal electrical tracks 46ed are used to wire several filters together at the level of filter sublayer 32. In other words, there are advantageously less electrical vias 46e than there are nozzles 8, in particular less than 1 electrical via 46e per 16 nozzles. Again, this provides more room of other wiring needs, in particular at the level of wiring layer 66.

Not only electrical vias but also feed ducts 20a, 20b can be thinned out at the level of the wiring layer 66. Here, interconnect sections 20b are formed on sublayer 6c, wherein several via sections 20a along a row are interconnected. All interconnected via sections 20a can be guided to the topmost sublayer 6f to a single ink terminal 21.

Ink Circulation

As mentioned, print head 2 can be designed to support ink circulation. Recirculation in the form presented below improves the filtering properties by removing particles stuck at the filter through sheer forces introduced by the lateral flow.

A first embodiment of a printer using such a print head 2 is illustrated in Fig. 13. It comprises an ink circulation pump 70, which is adapted to pump ink from ink reservoir 22 to an ink input terminal 72 of print head 2, from where it passes through a connection duct 74 of the feed ducts. The ink not ejected by the nozzles 8 is returned through an ink output terminal 76 and fed back to ink reservoir 22.

In more general terms, the printer comprises a print head 2 and an ink circulation pump 70 connected to ink input terminal 72 and ink output terminal 76. Ink circulation pump 70 is adapted to pump ink through connection duct 74.

Fig. 13 schematically shows the geometry of the feed ducts of print head 2. The feed ducts comprise:

- The connection duct 74: It extends between ink input terminal 72 and ink output terminal 76. It may e.g. be formed at least in part by one or more of the interconnect sections 20b shown in the embodiments herein. There may be several such connection ducts 74. - Branch ducts 78 forking off from connection duct 74 to at least part of the nozzles 8. They may e.g. be formed at least in part by the via sections 20a shown in the embodiments herein.

The filters 34 are advantageously arranged in the branch ducts 78, which typically have smaller cross section than the connection duct(s) 74.

To avoid stagnant regions of ink in connection duct 74, input terminal 72 is advantageously connected to a first end 80a of connection duct 74, and output terminal 76 is connected to a second end 80b of connection duct 74. First end 80a is advantageously opposite second end 80b.

The connection duct 74 (or any other part of the ink circulation system) may be in connection to a heat source (in particular an active heating device) / heat sink (in particular an active cooling device), e.g. a Peltier element, in order to bring it to a controlled temperature. Such temperature can be passed to the circulating ink, particularly if the connection duct 74 is made at least partially of a material with good thermal conductivity, e.g. from a metal or from a ceramic like Aluminum Nitride or Boron Nitride. In this way the ink and print head can be brought to a controlled temperature such that optimal flow conditions are achieved.

In other words, the printer may comprise a temperature controller 81, such as an active heat source or heat sink, thermally connected to the feed ducts.

In particular, temperature controller 81 may be thermally connected to connection duct 74.

For a larger print head 2, there may be several ink input terminals 72 and ink output terminals 76, as shown in Fig. 14, with smaller stretches of connection ducts 74 between them. This allows pumping the liquid along the channels with a lower pressure.

In this case, an adaptor 82 with adaptor ducts 84a, 84b may be provided for connecting pump 70 and reservoir 22 to the ink input and output terminals 72, 76.

Again, the adaptor 82 may be in connection to a temperature controller 81, such as a heat source / heat sink, e.g. a Peltier element, in order to bring it to a controlled temperature and eventually to bring such temperature also the print head through recirculation of ink through the temperature-controlled adapter 82.

Figs. 13 and 14 also show the voltage supply 30, which is connected to the voltage terminals 28, 24 and any other voltage terminals of print head 2 for feeding the control voltages to the various electrodes and/or filters.

Here, the lowest layer can be regarded as the combination of nozzle layer 4 and the lowest sublayer 6a of the feed layer, and this combined layer is smaller in its horizontal extension than at least some of the sublayers of the feed layer above the lowest sublayer 6a. This allows a fan-out electrical wiring to be implemented, i.e. where the voltage terminals are located beyond the circumference of nozzle layer. This is only possible though if the all sublayers 6b, 6c... of the feed layer 6 beyond the lowest one are manufactured after dicing of the wafer into chips, hence a large portion of the manufacturing process cannot take place on a wafer-level.

Alternatively, only the topmost sublayers of the feed layer 6 may be formed with a larger horizontal extension than the nozzle layer, particularly those sublayers that need to carry electrical wiring, e.g. the wiring layer introduced in Fig.

9. In this case all sublayers of the feed layer 6 having equal size as the nozzle layer can still be manufactured on a wafer-scale.

In other, more general terms, nozzle layer 4 has a smaller horizontal extension (in at least one direction) than at least part of the sublayers of feed layer 6.

Figs. 15 and 16 show a horizontal section through an embodiment of a print head of a type similar to the one of Fig. 14 but adapted to carry at least two different types of ink.

A first ink reservoir 22 and a first pump 70 are provided for the first ink, and a second ink reservoir 22’ and a second pump 70’ are provided for the second pump.

Fig. 16 shows a sectional view of adaptor 82. As can be seen, it al- tematingly has adaptor ducts 84a, 84b for the first ink and 84a’, 84b’ for the second ink. They are connected to ink input terminals 72, 72’ and ink output terminals 76,

76’, respectively.

The connection ducts 74 for the first ink and 74’ for the second ink are shown in Fig. 15. As can be seen, they extend parallel to each other but are offset in respect to each other along their longitudinal direction.

Manufacturing techniques

As mentioned, manufacturing the print head may comprise at least the following three steps:

a) Manufacturing nozzle layer 4 with the nozzles 8. b) Manufacturing feed layer 6.

c) Forming the feed ducts 20a, 20b for the ink and the feed lines 26, 46, 60, 68, 70 for the electrical connections in feed layer 6.

d) Forming the filters 34.

The order of these steps may vary.

In one embodiment, nozzle layer 4 may be manufactured first. Next, after completing nozzle layer 4 at least in part, advantageously fully, at least part of feed layer 6 is applied by adding sublayers to the top side of nozzle layer 4.

Alternatively, feed layer 6 may be manufactured separately from nozzle layer 6 and the two can then be mounted to each other.

In yet another embodiment, part of feed layer 6 may be grown onto nozzle layer 4 by adding sublayers and another part may be manufactured separately and then bonded to the print head.

Figs. 17 - 19 illustrate an advantageous method for manufacturing the filters 34 and the via sections 20a below them using laser-induced etching.

It is assumed that the filters 34 are to be formed on a sublayer 90 of feed layer 6. For the embodiments shown herein, sublayer 90 is advantageously bottommost layer 6a of feed layer 6.

The method includes the following steps:

A) First, sublayer 90 is irradiated at certain locations 92 by means of laser light, as shown in Fig. 17.

B) Next, filter sublayer 32 is applied, e.g. by sputtering, and then structured, e.g. using photolithography and etching techniques, preferably by dry etching techniques that achieve anisotropic etch profiles. In this way, structures as shown in Figs. 4, 6, or 12 may e.g. be formed. In particular, the filters 34 are formed. Advantageously, the filters 34 are located to cover the surface of at least some of the irradiated locations 92 as shown in Fig. 18.

C) Next, sublayer 90 is wet-etched through the filters 34 e.g. by hydrofluoric acid. The etching agent is passed through the openings 36 of the filter 34. It is understood that the irradiated regions etch much faster than the non-irradiated regions. Hence, as soon as the etching agent reaches the region below the filter where material was previously irradiated, the etching process will strongly accelerate along the irradiation direction. In this way, the anisotropic ducts, namely the via sections 20a, are formed in sublayer 92 as shown in Fig. 19. The width of the ducts can be installed by controlling the etching duration.

Suitable laser-etching techniques are known to the skilled person. For example, the techniques described by US2016059359 may be used.

The filter sublayer 32 may be additionally covered by a patterned photoresist or similar masking layer 93, in order to prevent open areas of the sublayer 90 to be etched which are not covered by the etched filter sublayer 32.

If the via sections 20a in a sublayer 92 are to be customized, the following techniques may e.g. be used: - Only the locations where via sections 20a are to be formed are irradiated, and then all of the irradiated locations are etched.

- All locations for potential ducts are irradiated, as shown in Fig. 17. Then some of the locations are masked by covering them with a continuous section 94 of filter sublayer 32 and/or by masking layer 93. Then, etching is performed. This process leaves the masked location 92 non-etched and has the advantage that the laser irradiation can be the same for all print heads and customization can take place at a later time by masking.

As mentioned, at least some of the sublayers of feed layer 6 and/or of nozzle layer 4 may be of S1O2 or glass. This material is particularly advantageous when using laser-induced etching for manufacturing the ducts in the sublayers.

At least one of the sublayers of feed layer 6 may be a structured photoresist film, e.g. by structuring a dry photoresist film or a spin-coated photoresist film. The photoresist may e.g. be US8 or any other epoxy-based material.

In order words, a photoresist film is structured by irradiation and subsequent selective material removal.

In a particularly advantageous embodiment, at least some of the conducting feed lines, in particular the horizontal electrical tracks in wiring layer 66 (Fig. 10), are manufactured using a printing process, where the conductive material for the feed lines is deposited from a printing head onto a dielectric sublayer of the feed layer 6. This allows customizing the tracks easily. In particular, electrohydrodynamic printing can be used for this purpose.

A suitable printing process is e.g. described in US 2018/0009223. It may also involve print heads manufactured according to this invention.

A suitable printing ink for printing such electrically conducting feed lines is e.g. a silver or gold nanoparticle ink, where silver or gold nanoparticles are dispersed in a higher alkane, for example. After printing, the structure is tempered at 100 °C for 10 minutes in order to anneal the silver nanoparticles into conductive tracks.

In this embodiment, crossing, non-contacting feed lines may be formed at a single level by printing insulating patches at the locations where the feed lines intersect. To print the insulating patches, an ink with dispersed dielectric nanoparticles may be used, e.g. with dispersed S1O2 or AI2O3 particles. The ink may also be of polymeric nature and be cured with TJV light, for example. Curing is best exercised directly after printing. The insulating patches may be further annealed together with the deposited conductive material of the conductive feed lines. Most preferably, this method of manufacturing is used to redistribute the feed lines of extraction electrodes on the upper sublayers of the feed layer 6, e.g. after dicing of the wafer into print head dies.

Printing may also be employed to fill electrical vias with metal or to form voltage terminals in the form of electrical bumps, wherein such electrical bumps have a large aspect ratio (the aspect ratio being the ratio between average height and average width of the structure), advantageously above 1 , so they can enhance physical contact to a voltage supply or be used for soldering. Electrical bumps may be formed in geometries and with materials well-known to those skilled in the art.

Notes

The filters 34 can all be interconnected by means of the filter con nect leads to a common potential. This is particularly expedient if the feed ducts are all interconnected, i.e. if the print head is designed to carry one ink only.

However, in particular if the feed ducts form separate manyfolds for a two or more inks, such as in the embodiment of Figs. 15 and 16, the filters in the different manyfolds may be connected to different electrical filter terminals. This allows to enable or disable printing nozzles by controlling the electrical potential of the ink as well as of the nozzle electrodes, separately. Any nozzles where the ink (filter) potential is the same as the nozzle electrode potential will not print.

It should be noted that in case one or more inks at times are supposed to be at different electrical potential, the adapter 82 is preferably not made completely from metal or another electrically conductive species. Otherwise, current can flow through the liquid, and in some cases, this may even lead to nonreversible electrochemical reactions at the metal. In this case, it is advisable to at least form insulating portions between the parts of the adapter carrying the ink at different electrical potential or to form it from an electrically non-conductive material altogether. In case adapter 82 is also used for temperature control, such non-conductive material is preferably a ceramic such as Aluminum Nitride or Boron Nitride. Otherwise, it can also consist of other dielectric materials such as glass.

In the shown embodiments, the filters 34 are arranged on the bottommost sublayer 6a. At least this bottommost sublayer 6a is arranged between nozzle layer 4 and filter sublayer 32. Filter sublayer 32 may, however, also be arranged on one of the higher sublayers of feed layer 6.

In the embodiments above, filter sublayer 32 is part of feed layer 6, e.g. arranged at the top or bottom of feed layer 6 or, advantageously, between two of the sublayers of feed layer 6. Alternatively, filter sublayer 32 may e.g. be located be tween feed layer 6 and nozzle layer 4 or it may form part of nozzle layer 4.

Nozzle layer 4 is advantageously arranged adjacent to feed layer 6.

Advantageously, the present print head is an electrohydrodynamic print head with nozzle electrodes to generate electric fields directly acting on the ink for accelerating the ink towards the target.

The present invention may, however, also be used in another type of inkjet print head, such as (a) a thermal inkjet where heaters are provided for vaporizing ink and generating pressure pulses to accelerate the ink, or such as (b) a piezoelectric print head where a piezoelectric elements are used for generating pressure pulses to accelerate the ink.

While there are shown and described presently preferred embodiments of the invention, it is to be distinctly understood that the invention is not limited thereto but may be otherwise variously embodied and practiced within the scope of the following claims.