JP2024055801A - Method for manufacturing a droplet ejection device - Google Patents

Abstract

A simplified method for manufacturing a printhead is provided, comprising a printhead unit (1) including a nozzle layer (16) defining a number of nozzles (50) and actuators (32) for generating pressure waves in a liquid in respective pressure chambers (20) respectively connected to the nozzles, the method comprising the steps of providing an anti-wetting layer (49) on the nozzle layer, dicing the printhead units from a common wafer by a dicing machine, providing a cover (2) on the printhead unit and adhering the cover to the nozzle layer, the cover having openings (6) overlapping the nozzles, the dicing machine locally removing the anti-wetting layer from the nozzle layer where the cover is adhered to the nozzle layer, thereby manufacturing the simplified printhead. [Selected Figure]

Description

The present invention relates to a method for manufacturing an inkjet printhead, and to such a printhead.

Inkjet printheads are known, for example, from US 10391768. Such printheads generally comprise a printhead unit having a nozzle layer defining a number of nozzles and a membrane layer carrying actuators on the membrane for generating pressure waves in liquid in respective pressure chambers respectively connected to the nozzles. By actuating the actuators, droplets of fluid can be ejected from the nozzles onto a print medium to form an image. The nozzle layer is provided with an anti-wetting layer, which prevents or reduces wetting of the fluid over the entire surface of the nozzle layer facing the print medium. This prevents ink from accumulating on said surface and adversely affecting the ejection of droplets from the nozzles. Such anti-wetting layers are known, for example, from US 9956777, US 9833996, US 80833645. Furthermore, a cover can be provided on top of the printhead unit, which cover is glued to the nozzle layer. The cover comprises openings overlapping the nozzles. The cover prevents the ejected fluid from penetrating into the printhead unit. A similar cover is known from NL 2022897. As described in US 10,391,768, the printhead units may be formed by dicing the wafer with a dicing machine to separate individual printhead units from the wafer.

The object of the present invention is to provide a simplified method for manufacturing a printhead.

According to the present invention there is provided a method for manufacturing a printhead as claimed in claim 1 and a printhead as claimed in claim 8.
The printhead comprises a nozzle layer defining a plurality of nozzles, and a membrane layer carrying actuators on the membrane for generating pressure waves in liquid in respective pressure chambers each communicating with the nozzles. The method comprises the steps of:
- providing an anti-wetting layer on the nozzle layer,
- dicing the printhead units from the common wafer by a dicing machine;
- Providing a cover over the printhead unit and adhering the cover to the nozzle layer, the cover having openings overlying the nozzles.
The method is characterized by a step in which a dicing device locally removes an anti-wetting layer from the nozzle layer where the cover is to be bonded to the nozzle layer.

Generally, the anti-wetting layer itself is not suitable for adhering a cover thereto, since the bond between the anti-wetting layer and most adhesives is generally weak. It has been found by the inventors that in the step of dicing the printhead units from the wafer, the anti-wetting layer can be partially removed using a dicing machine. This partial removal can be performed before or after dicing the printhead units separated from the wafer. Preferably, in the step of dicing is defined herein as while the wafer is mounted on, in and/or on the dicing machine. The dicing machine cuts the wafer to separate the printhead units, while only making shallow cuts where the anti-wetting layer is to be removed. In this way, adhesive-free areas are formed in the nozzle layer, suitable for adhesive adhesion. The cover can then be easily and reliably adhered to the nozzle layer without one or more additional processing steps specifically for removing the anti-wetting layer. In this way, the manufacturing method is simplified. Thus, the object of the present invention is achieved.

More specific optional features of the invention are set out in the dependent claims.

In one embodiment, the dicing machine applies a dicing cut to the nozzle layer, the dicing cut having a depth greater than the thickness of the anti-wetting layer and less than the thickness of the nozzle layer. The dicing machine applies a cut that locally removes the anti-wetting layer, but does not cut through the entire thickness of the nozzle layer. Preferably, the nozzle layer is considered to include the anti-wetting layer such that the thickness of the former includes the thickness of the latter. Preferably, the depth of the dicing cut is comparable, similar, and/or equal to the thickness of the anti-wetting layer measured perpendicular to the plane of the nozzle layer.

In one embodiment, multiple parallel dicing cuts are applied to locally remove the anti-wetting layer. The dicing cuts generally have a relatively small width so that multiple printhead units can be placed closely together on the wafer. To reduce processing time, the same dicing machine is used to remove the anti-wetting layer, which requires multiple adjacent passes of the dicing machine across the nozzle layer. Each dicing cut is preferably applied as a straight line. Each straight line contacts such that the anti-wetting layer is completely removed in the area through which the line extends.

In one embodiment, the adhesive is on the dicing cut. The adhesive is attached or applied directly to the dicing cut or by first placing the adhesive on the cover. The areas where the anti-wetting layer has been locally removed are covered with adhesive. The adhesive may be applied first on the nozzle layer or may be provided on the cover to be attached to the printhead unit. The adhesive is preferably applied with a thickness such that the adhesive extends at least to or beyond the level of the anti-wetting coating.

In one embodiment, the cover is adhered to the area of the dicing cuts by an adhesive. The adhesive is provided between the cover and the area where the anti-wetting layer has been removed, thereby securing the cover to the nozzle layer.

In an embodiment, the anti-wetting layer is locally removed along the periphery of the nozzle layer. The area from which the anti-wetting layer has been removed extends around the remainder of the anti-wetting layer, preferably as an endless loop. This area surrounds the remaining anti-wetting material, at least when viewed perpendicular to the plane of the nozzle layer. The area extends inwardly from the outer edge of the nozzle layer to a predetermined distance from said edge. The area preferably overlaps the cover.

In one embodiment, the printhead units are formed from a silicon wafer by a photolithography process. Multiple printhead units are formed on a single wafer, for example by applying the methods described in US 10,391,768, particularly with respect to Figures 2 to 15 of US 10,391,768.

The invention further relates to a printhead unit comprising a nozzle layer defining a number of nozzles, an anti-wetting layer covering the nozzle layer, a membrane layer carrying actuators on the membrane for generating pressure waves in liquid in respective pressure chambers respectively connected to the nozzles, and a cover bonded to the nozzle layer, the area of the nozzle layer being provided around its periphery with a number of dicing cuts with localized removal of the anti-wetting layer, the cover being bonded to said dicing cuts by means of an adhesive. The printhead may be formed by the method described above. Preferably, the nozzle layer is formed of silicon.

In one embodiment, the cover includes a peripheral wall that surrounds the printhead unit and a top wall that includes an opening that overlaps the nozzle. The top wall extends parallel to the plane of the nozzle layer, while the peripheral wall extends at an angle thereto to surround the side of the printhead unit.

Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the present invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the present invention will become apparent to those skilled in the art from this detailed description.

The present invention will be more fully understood from the detailed description given herein below and the accompanying drawings, which are given by way of example only and therefore are not intended to be limiting of the invention.

FIG. 1 is a cross-sectional view of a droplet ejection device according to one embodiment of the present invention.

FIG. 2 is a wafer containing a number of printhead units which make up the droplet ejection device shown in FIG.

3 is a cross-sectional view of the droplet ejection device of FIG. 1 after dicing of the printhead units from the wafer of FIG.

FIG. 4 is a cross-sectional view of the droplet ejection device of FIG. 3 after localized dicing of the anti-wetting layer.

FIG. 5 is a cross-sectional view of the droplet ejection device of FIG. 3 with adhesive applied to the diced area of the nozzle layer.

FIG. 6 is a cross-sectional view of the droplet ejection device of FIG. 3 after adhering a cover to the nozzle layer.

7 is a bottom view of the nozzle layer of the droplet ejection device of FIG.

8 is a bottom view of another embodiment of the nozzle layer of the droplet ejection device of FIG.

The present invention is described with reference to the accompanying drawings, in which the same reference numerals are used throughout the several views to identify the same or similar elements.

Figure 1 shows a single droplet ejection device 10, which is one of several ejection devices having the same design and integrated into a printhead unit in the form of a typical MEMS chip that can be used, for example, in an inkjet printhead. The printhead unit contains a large number of these droplet ejection devices 10 arranged side by side. The MEMS chip, and therefore the ejection device 10, has a layer structure including as main layers a distribution layer 12, a membrane layer 14 and a nozzle layer 16.

The distribution layer 12 is a single layer of silicon having a relatively large thickness of at least 400 microns. In the present embodiment, the thickness is 400 microns. The distribution layer 12 defines ink supply lines 18 through which liquid ink is supplied from an ink reservoir 19 to pressure chambers 20 formed on the underside of the membrane layer 14. The ink reservoir 19, which is only shown diagrammatically in FIG. 1, is common to several ejection devices and is formed separately from the distribution layer 12, on the upper side of the distribution layer, i.e. opposite the membrane layer 14. This has the advantage that the distribution layer 12 is not weakened by cavities forming a reservoir.

The membrane layer 14 is obtained from an SOI wafer having an insulator layer 22 and silicon layers 24 and 26 formed on either side thereof. In this embodiment, the final membrane layer 14 may have a thickness of about 75 microns. The pressure chambers 20 are formed in the bottom silicon layer 26. The top silicon layer 24 and the insulator layer 22 form a continuous flexible membrane 30 of uniform thickness that extends over the entire area of the MEMS chip and is penetrated by openings 28 only at the locations of the ink supply lines 18 to connect the ink supply lines to the pressure chambers 20. A piezoelectric actuator 32 is formed on the upper side of the membrane 30 over the portion covering the pressure chambers 20. The actuator 32 is housed in an actuator chamber 34 formed on the lower side of the distribution layer 12.

An electrically insulating silicon oxide layer 36 insulates the actuator 32 and its electrodes from the silicon layer 24 and carries electrical leads 38 positioned to contact the upper and lower electrodes of the actuator 32. The leads 38 are exposed and accessible at contact areas 40 where the distribution layer 12 has been removed.

The nozzle layer 16 is obtained from a double SOI wafer and has a top silicon layer 42 and a thin silicon layer 44 interposed between two insulator layers 46 and 48. In this embodiment, the final nozzle layer can have a thickness of about 125 microns. The nozzle 50 is formed in the two insulator layers 46 and 48 and the silicon layer 44 interposed therebetween, so that the thicknesses of these three layers define the length of the nozzle. The top silicon layer 42 of the nozzle layer 16 defines a feedthrough 52 that connects the pressure chamber 20 to the nozzle 50, the cross section of which is significantly larger than that of the nozzle 50. The nozzle layer 16 is coated with an anti-wetting (also called non-wetting) layer 49. In FIG. 1, the anti-wetting layer 49 is applied as a coating on the insulator layer 48. The material of the anti-wetting layer 49 is selected corresponding to the fluid or ink to be applied, so that the wetting of said fluid on the anti-wetting layer 49 is small. The adhesive force between the anti-wetting layer 49 and the fluid ensures that the contact angle between the fluid droplet and the anti-wetting layer 49 is relatively large (e.g., greater than 90°). This prevents the fluid from seeping onto the anti-wetting layer 49 and adversely affecting the ejection of the droplet from the nozzle 50.

It will be appreciated that the MEMS chip droplet ejection device 10 is arranged such that its nozzles 50 define a nozzle array, for example consisting of one, two or more parallel nozzle lines, with a uniform nozzle spacing that determines the spatial resolution of the printhead. Within the contact area 40, each of the leads 38 can be contacted, for example via bumps 54, so that an energizing signal in the form of a voltage pulse can be applied to each actuator 32 individually. When a voltage is applied to the electrodes of the actuators 32, the piezoelectric material of the actuators is deformed in a bending mode, thereby deflecting the membrane 30 and thus changing the volume of the pressure chamber 20. Typically, a voltage pulse is applied to the actuator, causing a deformation that increases the volume of the pressure chamber 20, resulting in ink being sucked from the supply line 18. If the voltage pulse is then lowered or changed to a pulse of the opposite polarity, the volume of the pressure chamber 20 will suddenly decrease, thereby generating an acoustic pressure wave that propagates through the pressure chamber 20 and through the feedthrough 52 to the nozzle 50, resulting in the ejection of a droplet of ink from the nozzle 50.

In Figure 1, the anti-wetting layer 49 is not present locally around the nozzle layer 16. The anti-wetting layer 49 is removed up to or beyond the insulator layer 48 which extends a predetermined distance inward from the edge of the nozzle layer 16. Adhesive 8 is provided in the areas where the anti-wetting layer 49 has been removed.
Adhesive 8 bonds cover 2 to nozzle layer 16. Preferably, adhesive 8 is applied around the entire periphery of nozzle layer 16 such that a fluid-tight seal is formed between nozzle layer 16 and cover 2. This prevents fluid from entering droplet ejection device 10 and adversely affecting its operation and/or lifespan.

The cover 2 is formed as an endless peripheral wall 5 surrounding the droplet ejection devices 10 of the printhead unit. A top wall 5 is provided on the peripheral wall. The top wall 5 extends parallel to the nozzle layer 16. The top wall 5 is provided with an opening 6. The opening 6 is large enough so that all the nozzles 50 of the printhead unit are not blocked by the top wall 5. Preferably, the top wall 5 at least partially overlaps the adhesive 8 and therefore does not extend substantially inward beyond the diced area of the anti-wetting layer 49. If the top wall 5 extends partially over the adhesive 8, a meniscus of the adhesive 8 can be formed at the side edges of the top wall 5, which improves the liquid-tightness of the bond between the adhesive 8 and the top wall 5.

The droplet ejection device 10 of FIG. 1 has the advantage that a larger number of MEMS chips can be manufactured from a single wafer (70 in FIG. 2) of a given diameter. Furthermore, the compact design allows for close packing of individual devices 10 within a chip, resulting in high nozzle density and therefore spatial resolution of the printhead. Another advantage of the vertical placement of the restrictor 56 is that the length and cross-sectional area of the restrictor can be controlled with high precision using well-established lithography techniques.

As shown in FIG. 1, the distribution layer 12 is connected to the membrane layer 14 by a bonding layer 62. Similarly, the membrane layer 14 is connected to the nozzle layer 16 by a bonding layer 64. Because the bonding layers 62 and 64 are layers of adhesive, their physical properties are difficult to control. However, in the design proposed here, the bonding layers are positioned such that their properties do not significantly affect any of the critical parameters of the design.

Figure 2 shows a silicon wafer 70 having a number of printhead units 1 formed thereon. One side or surface of the wafer 70 is coated with an anti-wetting layer, for example using spin coating, sputtering, chemical vapor deposition, or other suitable technique. The anti-wetting layer 49 may be provided on the nozzle layer 16 at any point during the lithographic manufacturing process of the printhead units 1. Preferably, the anti-wetting layer 49 covers the entire surface of the wafer 70 except for the nozzles 50.

In a top view, each printhead unit 1 is a rectangular MEMS chip embedded in a wafer 70. Each printhead unit 1 includes a number of droplet ejection devices 10, as shown in FIG. 1. In the process shown in FIG. 2, the printhead units 1 are cut from the wafer 70 by dicing the wafer 70 along dicing lines 72. The dicing cuts are made across the wafer 70 in two perpendicular directions, thereby separating the printhead units 1 from the wafer 70. The dicing is preferably performed by a dicing device such as a dicing saw commonly applied in semiconductor dicing.

Figure 3 shows the result of the process carried out in Figure 2, i.e. the individual printhead units 1. The entire bottom surface of the printhead units 1 is formed by an anti-wetting layer 49. It will be understood that the dicing process of Figure 2 may be carried out before or after the processes shown in Figures 3 to 6 below. The processes of Figures 3 to 6 are illustrated only with respect to the individual printhead units 1 for illustrative purposes only. The process of locally dicing the anti-wetting layer 49 of Figures 3 to 4 is carried out while the wafer 70 is mounted in a dicing machine, but may be carried out before or after the process of separating the individual printhead units 1, as shown in Figure 2. The same may apply mutatis mutandis to the processes of Figures 5 and/or 6.

In the process shown in FIG. 4, a dicing device is applied to locally remove the anti-wetting layer 49 along the edge of the nozzle layer 16. The anti-wetting layer 49 is diced at least to the depth of the anti-wetting layer 49 itself. The anti-wetting layer 49 typically has a thickness of about 5-10 nm, in which case the dicing cuts are applied, for example, to a depth of at least 100% of said thickness. In case of irregularities in the thickness of the anti-wetting layer 49, the dicing cuts 74 are selected to cut down to the nozzle layer 16 at all locations where the dicing cuts 74 are locally applied to remove the anti-wetting coating 49. The dicing cuts 74 are shown in an enlarged cross section in FIG. 4. The dicing cuts 74 are preferably applied as parallel lines in order to perform the removal process quickly. An example of a suitable pattern of the dicing cuts 74 is shown in FIG. 7. FIG. 7 shows the underside of the printhead unit 1 after partial removal of the anti-wetting layer 49 by dicing. The dicing cuts 74 are applied along the entire circumference of the nozzle layer 16 such that the anti-wetting coating 49 is completely removed up to a predetermined distance from the end of the nozzle layer 16. FIG. 7 shows that the dicing cuts 74 are applied in two perpendicular directions. Parallel to the long sides, horizontal dicing cuts 74H are applied on both sides of the nozzle layer 16. Similarly, vertical dicing cuts 74V removed portions of the anti-wetting layer 49 along the short sides of the nozzle layer 16. The horizontal and vertical directions are the directions of the long and short sides of the nozzle layer 16, respectively. As shown in the enlarged view of FIG. 4, the dicing cuts 73 can leave a relatively irregular surface with ridges or grooves. This increases the effective area for applying adhesive and improves adhesion.

Figure 8 shows a different embodiment of the dicing cuts 174. The dicing cuts 174 are applied in an intermittent pattern along at least the long side along the perimeter of the anti-wetting layer 49. The horizontal dicing cuts 174H are applied as narrow cuts that are many times smaller than the length of the horizontal side. As a result, islands 49I of anti-wetting material remain between the dicing cuts 174H. Thus, a pattern of islands 49I and dicing cuts 174H is formed. Preferably, the pattern is such that a liquid-tight seal can be formed, although different fluid-opening patterns can be applied. In Figure 8, the vertical dicing cuts 174V are similar to Figure 7, but they may also be formed as intermittent dicing cuts 174H. The adhesive 8 contacts the dicing cuts 174H, 174V, and preferably does not contact the islands 49I.

Figure 5 shows the process of applying adhesive 8 after the wetting prevention layer 49 has been diced away. The adhesive 8 is applied onto the dicing cut 74 from the outer edge of the nozzle layer 16 to the outer edge of the wetting prevention layer 49. The adhesive 8 is applied in an endless loop around the remaining wetting prevention layer 49, similar to the dicing cut 74.

FIG. 6 illustrates the process of adhering the cover 2 to the nozzle layer 16. The top wall 5 of the cover 2 is placed on the adhesive 8 such that the perimeter of the cover 2 extends around the perimeter of the printhead unit 1. The cover 2 is positioned such that the nozzles 50 are not interfered with by the top wall 5. The top wall 5 and adhesive 8 form an endless perimeter seal around the anti-wetting layer 49 to prevent fluid ingress into the droplet ejection device 10, thereby improving the life and/or performance of the printhead.

While specific embodiments of the present invention have been illustrated and described herein, those skilled in the art will recognize that various alternative and/or equivalent embodiments exist. It should be understood that the exemplary embodiment or exemplary embodiments are merely illustrative and are not intended to be limiting in any way in scope, applicability, or configuration. Rather, the foregoing summary and detailed description are intended to provide one skilled in the art with a convenient road map for implementing at least one exemplary embodiment, and it will be understood that various changes can be made in the function and arrangement of elements described in the exemplary embodiment without departing from the scope as set forth in the appended claims and their legal equivalents. In general, this application is intended to cover any adaptations or variations of the specific embodiments discussed herein.

It will also be understood that, as used herein, the terms "comprise," "comprising," "include," "including," "contain," "containing," "have," "having," and variations thereof are intended to be understood in an inclusive (i.e., non-exclusive) sense such that the methods, methods, devices, apparatus, or systems described herein are not limited to those features or portions or elements or steps described, but may include other elements, features, portions, or steps not expressly recited or inherent to such methods, methods, articles, or apparatus. Furthermore, the terms "a" and "an," as used herein, are intended to be understood to mean one or more, unless expressly stated otherwise. Furthermore, terms such as "first," "second," "third," and the like, are used merely as labels and are not intended to impose numerical requirements on their subject matter or to establish a certain ranking of importance of their subject matter.

The invention being thus described, it will be apparent that the same may be varied in many ways. Such variations are not to be regarded as departing from the spirit and scope of the invention, and it is intended that all such variations which would be obvious to one skilled in the art be included within the scope of the following claims.

Claims (10)

1. A method of manufacturing a printhead comprising a printhead unit (1) comprising a nozzle layer (16) defining a plurality of nozzles (50) and actuators (32) for generating pressure waves in liquid in respective pressure chambers (20) respectively connected to said nozzles (50), comprising:
- providing an anti-wetting layer (49) on said nozzle layer (16);
- dicing said printhead units (1) from a common wafer (70) by a dicing machine;
providing a cover (2) over the print head unit (1) and adhering the cover (2) to the nozzle layer (16), the cover (2) having openings (6) overlapping the nozzles (50);
13. A method for manufacturing a printhead, characterized by a step in which the dicing device locally removes the anti-wetting layer (49) from the nozzle layer (16) where the cover (2) is bonded to the nozzle layer (16). The method of claim 1, wherein the dicing device applies dicing cuts (74, 174) to the nozzle layer (16), the dicing cuts (74, 174) having a depth greater than a thickness of the anti-wetting layer (49) and less than a thickness of the nozzle layer (16). The method of claim 2, in which multiple parallel dicing cuts (74H, 74V; 174H, 174V) are applied to locally remove the anti-wetting layer (49). The method of claim 3, wherein adhesive (8) is on the dicing cuts (74H, 74V; 174H, 174V). The method of claim 4, wherein the cover (2) is adhered to the areas of the dicing cuts (74H, 74V; 174H, 174V) by the adhesive (8). A method according to any one of claims 1 to 5, in which the anti-wetting layer is locally removed along the periphery of the nozzle layer (16). A method according to any one of claims 1 to 6, wherein the print head unit (1) is formed from a silicon wafer (70) by a photolithography process. A print head comprising a print head unit (1) having a nozzle layer (16) defining a plurality of nozzles (50), a wetting prevention layer (49) covering the nozzle layer (16), and an actuator (32) for generating pressure waves in liquid in each pressure chamber (20) connected to each of the nozzles (50), and a cover (2) bonded to the nozzle layer (16), characterized in that an area of the nozzle layer (16) has a plurality of dicing cuts (74, 174) around its periphery in which the wetting prevention layer (49) is locally removed, and the cover (2) is bonded to the dicing cuts (74, 174) by an adhesive (8). The printhead of claim 8, wherein the nozzle layer (16) is formed of silicon. The print head according to claim 9 or 10, wherein the cover (2) comprises a peripheral wall (4) surrounding the print head unit (1) and a top wall (5) including an opening (6) that overlaps with the nozzle (50).

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