Patent Application
20240424788
Printer ink used in inkjet printers can be acidic or alkaline or a strong solvent which can cause cumulative damage and limit operating lifespan of printheads and other components of these machines. The printhead itself often has multiple components, including integrated circuit dies, microelectromechanical system (MEMS) dies, piezoelectric transducers, a head mount with internal chambers for ink, nozzles, etc. The various components are made of various construction materials (e.g., processed integrated circuit dies, processed microelectromechanical dies, plastics, metals) and assembly materials (e.g., a bonding material (e.g., solder, glue, adhesive, epoxy, etc.), fasteners, etc.), each of which imposes constraints on what can be done to protect the components from degradation resulting from exposure to printer ink, and perhaps other acid or alkaline or strong solvent liquids (e.g., during manufacture, cleaning or refurbishing). For example, solvent inks may also have detrimental effects on epoxy interfaces or on the epoxy/glues themselves. Therefore, there is an ongoing need in the art for improvements in component protection and operating lifespan of printheads and other components of inkjet printers, which may also benefit further components of further machines.
Printheads having protective coatings and methods for using the same are described. In some embodiments, the inkjet printhead or member thereof, includes a component having at least one internal cavity for printer ink, the at least one internal cavity accessible during materials processing; a protective coating on the component and on a surface of the at least one internal cavity, the protective coating comprising a film of HfO2, ZrO2, TiO2, or a chemically resistant oxide or nitride as a conformal layer; and the film having a thickness in a range that avoids formation of pinholes, thin spots and nodule growth.
Other aspects and advantages of the embodiments will become apparent from the following detailed description taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the described embodiments.
The described embodiments and the advantages thereof may best be understood by reference to the following description taken in conjunction with the accompanying drawings. These drawings in no way limit any changes in form and detail that may be made to the described embodiments by one skilled in the art without departing from the spirit and scope of the described embodiments.
Various embodiments are described herein for materials processes, films, materials, coatings, components, machines, and more specifically a protective coating and/or an internal protective coating for a printhead for an inkjet printer, and variations thereof from which further embodiments are understood. Embodiments disclosed herein show improvements in multiple technologies, including film, coating, materials processing, and inkjet printer technology. Embodiments disclosed herein present a technological solution to the technological problem of how to protect, reduce damage and improve operating lifespan of inkjet printer printheads and other components subjected to inkjet printer ink or other acid or alkaline liquids. Description of research goals, findings and technology, starting below, is followed by description of the drawings, in order to convey to the reader various aspects, principles, advantages, and practical ways to make and use the various embodiments.
Among the coatings described herein are Advanced Coatings—IPC (Internal Protective Coating) and NWC (Non-Wetting Coating). The following description includes the use and deposition of HfO2 (i.e., hafnia) coating and rationale(s) for choosing such a film, and alternatives to HfO2, including ZrO2, TiO2, Ta2O5, SiCN, and various nitrides (described further below). There is description of method and application of coatings with higher-order assemblies (MEMS (microelectromechanical system)/IP (inkjet printhead)/HM), integration of NWC, including optimization of IPC for NWC adhesion, density, robustness, and optimization of NWC for inkjet, both method and application. In some embodiments, the coatings are deposited using atomic layer deposition (ALD). In some other embodiments, other types of deposition are used (e.g., chemical vapor deposition (CVD) and plasma-enhanced (PE)-CVD)).
Inkjet printheads can be fabricated using known micromachining techniques to produce highly precise and repeatable devices in large arrays. One of the best materials to create such accurate structures is silicon. It has excellent mechanical properties, and does not typically exhibit mechanical hysteresis at operating temperatures below 400° C. Silicon is highly resistant to attack by most acids. It can, however, be dissolved in solutions of sufficiently high-pH or in the presence of hydrofluoric acid (HF). Although it is not typical to jet HF, alkaline inks are quite common, and as such often exhibit attack of the silicon structure composing micromachined printheads. For this reason, it is desirable to protect any surfaces that would be wetted by these inks from such chemical attack, especially from alkaline chemistries.
One ideal protective layer (IPC) would have the following properties:
Atomic Layer Deposition (ALD), and similar related approaches, are a set of deposition techniques that exhibit many of the above desirable characteristics. They can be used to deposit several chemically resistant ceramic materials, in thin and dense layers that are highly conformal, and can be performed at temperatures that are compatible with the piezo-inkjet materials set. Given that there are many materials to consider, it is desirable to choose from among these materials for one that is superior. Prior investigations were performed by ceramicists to understand which materials might be highly resistant to chemical attack.
For example, K. Komeya and K. Nishida, Boshoku Gijutsu, 35, 646655 (1986) [in Japanese] divides a graph of radius of positive ion versus electric charge of positive ion, showing elements from the periodic table, into three regions:
“Hot corrosion of Al2O3 and SiC ceramics by KCl—NaCl molten salt”, Takaaki NAGAOKA,3 Ken'ichiro KITA and Naoki KONDO, technical report in Journal of the Ceramic Society of Japan 123 [8] 685-689 2015, discusses hot corrosion tests of alumina and carbon silicate ceramics.
In research for present embodiments, it was determined that, for materials more alkaline-resistant than SiO2 and depositable in thin layers, candidates include ZrO2, TiO2, and Ta2O5. With an ionic radius of 0.83 Å, and ionic charge of +4, HfO2 is also an excellent candidate for films deposited through ALD.
There are many possible flows, and one embodiment of process flow (with variations) includes a wafer construction with:
In research for embodiments disclosed herein, candidate oxide films were evaluated, including:
Nitride films are also good candidates likely requiring plasma-enhanced deposition. These include but are not limited to:
One example embodiment (with variations) includes:
Higher order assemblies are discussed below. The micromachined silicon structure described above does not typically contain all the necessary functions for creating a printhead. For this reason, it is common to combine the micromachined inkjet wafer with other micromachined wafer strata that may include ink distribution, temperature measurement/control, fluidic and electrical interfaces, among other functions. These inkjet and other functional strata may be attached to one another through various means including bonding with metallic (e.g., solder) or organic attachment/structural materials (e.g., glue, adhesive, epoxy, etc.). These materials may also be susceptible to attack by inks and other functional fluids. For this reason, it is desirable to have an IPC coating which may be applied after bonding of various strata. It is also desirable that the IPC coating be generally compatible with these additional materials, for example to:
Additional Functional Layers (AFL) include, in various embodiments:
Characteristics of polymers are considered below, with impact on IPC and overall process. Polymers tend to degrade with heat more easily than many other suitable materials, with the possible exception of solders, which have intentionally low melting points, and which some embodiments exclude from pre-IPC construction. One piezoelectric actuator material (e.g., PZT, etc.) has been shown to degrade in performance at temperatures in excess of 280° C., especially in the presence of electric/magnetic fields. The temperature at which polymers degrade (e.g., shrink, expand, slump, reflow, embrittle, or crack) determines the upper temperatures at which some embodiments subsequently deposit an IPC or NWC film. One embodiment utilizes SU-8 (EPON photo-epoxy) in a MEMS die construction. SU-8 has glass transition temperature of 230° C., but does not change shape significantly at this temperature because of extensive cross-linking. Above this temperature, and especially approaching 270° C., larger shape changes or shrinkage will occur, which can put stress on other layers, and cause performance/reliability issues. For these reasons, one ALD deposition technique is attractive, as it can be deposited with high quality at temperatures<250° C., preferably at 230° C. or below. In a further embodiment, another process that can deposit at or below these temperatures, with good density/uniformity/conformality would be attractive. ALD seems to be uniquely capable of achieving all the objectives, but other approaches could be worth investigating and/or developing. In some other embodiments, different precursors that allow use of a lower temperature are used. In some additional embodiments, plasma-enhancement of a reactant or reactants is used.
In some embodiments, there is a need to remove IPC from the electrical connection areas of the jetting die for products that have electrical connection to the outside established via flex circuit and/or one or more methods, including, for example, flex, wire bonding, and soldering. This may not be the case in some embodiments with electrical connection established via wire bonding as it may be possible to bond through a thin coating due to mechanical impacts. This is similar to bonding Au wire bond to an Al bond pad, which has a thin AlO passivation layer. In some embodiments, this layer is broken up by scrubbing action at the bond, often with ultrasonic energy applied to the bond head. Some embodiments have one or both of two different electrical routing metallization schemes that have Au (gold) as the final coating because of its ability to establish reliable connections. Other metals (e.g., Pd, Pt, Nb, others) are possible. In some flex circuit embodiments, because there is soldering on to pads on the device, there is a restriction of the amount of Au on the pads because Au will dissolve into the solder melt, in turn causing the solder to become embrittled upon cooling, which will cause electrical connection reliability issues. However, if one process adds Au on the pads and another process removes all the Au on the pads, solder will not wet to the pad in some further process(es). This situation imposes constraints on both the amount of Au added on pads, and the amount of Au once added that is subsequently removed from pads, for example when removing IPC in electrical connection regions. These considerations are true for other interface materials besides Au as well.
In one embodiment, a process deposits IPC film(s) after the plumbing of the jetting die is open to the outside (through nozzles or ink fill ports), i.e., internal cavity (ies) are exposed for materials processing, which allows coating of all ink-contacted surfaces with IPC. Internal cavities being open/exposed for processing currently precludes utilization of wet chemistry to remove the IPC, as this would then remove IPC from the internal cavities where such coating is desired to remain in place. On the other hand, photopolymerizable films combined with efficient dry stripping is contemplated.
In one embodiment, IPC films (e.g., ALD oxides) are difficult to remove through selective chemical means, including in dry/plasma etching approaches. Inclusion of chlorine-containing etch species may make this easier. One method is to utilize ion milling with argon (i.e., Ar), which is a somewhat selective process. Unfortunately, selectivity is biased in the wrong direction, therefore Au is relatively more easily removed as compared to the ALD oxides. Polymers are not readily removed by this process. The ALD oxides are typically 30-50 nm in thickness, in one embodiment, and the selectivity of hafnia (i.e., HfO2) to Au removal is about 3:1. That is, argon ion milling removes Au three times as easily as it removes HfO2. Therefore, one embodiment with a 30-50 nm ALD oxide coating, including coating over electrical contact regions, has about 150 nm extra Au on pads (e.g., electrical contacts in this context) that can be removed (assuming 100% over-etch in argon ion milling), while leaving sufficient Au to ensure solderability of the pad. In this approach, a process thickens the Au layer in regions where the Au will be exposed to ion milling, and not in areas that are to remain covered by polymer passivation (Au is relatively expensive). This process has been demonstrated in one manufacturing environment.
The following description includes discussion around coating over plastic and what should occur in order to achieve success with the IPC, including example process steps. Plastic materials are attractive in printhead construction for several reasons, primary of which is that at the level of dimensional accuracy required for plumbing external to the Si die (e.g., headmount), molding allows relatively inexpensive implementation. Polymeric materials can vary in coefficient of thermal expansion (CTE) in the range of 15-75 ppm/C. Si, by comparison, has a CTE of 3 ppm/° C. Transfer molding of thermoset materials (e.g., EMC, CTE=10-12 ppm/° C.), used extensively in the semiconductor packaging application, is well-established and includes materials that are suitable for inkjet printhead construction. In one embodiment, SU-8 (CTE=55-60 ppm/° C.) is a plastic material used in the construction of printheads. Multiple Si strata, the headmount, and other elements exposed to ink are bonded together using ink-compatible epoxies (i.e., an example, glue, adhesive, etc.). If all Si parts are coated with IPC, they will be protected from, i.e., not be subject to, chemical attack. That means that the plastic elements become the weak link of any construction, in terms of such chemical attack. The ability to deposit IPC (e.g., HfO2 bulk CTE=6.0 ppm/° C.) on the printhead construction at stages beyond the jetting die wafer-level is attractive for increasing the chemical resistance of the printhead. In various embodiments, IPC materials are brittle ceramics, which are typically stronger in compression than tension, but will fail with excessive loading. Given the above, being able to establish the chemically protective function of IPC at the lowest temperature possible is fundamental to achieving a reliable construction with an assortment of materials. ALD, e.g., using HfO2 as described in various embodiments herein, allows creation of sufficient film density, uniformity, conformality, adhesion, and chemical-resistance for the inkjet application.
Further, on the embodiments that include coating over glue (e.g., to encapsulate the glue) or other bonding material, one main objective for IPC in this context is to coat at low temperature so as to avoid degradation of the glue, but with sufficient film performance. The printhead materials should be chosen such as to find the right balance of CTE, adhesion, and elastic modulus at full-cure (near zero remaining outgassing). Testing has confirmed coating over SU-8 films using various embodiments of this approach with excellent success. This has the implication that, provided a process includes selection of appropriate glues (e.g., DELO-OB787 w/CTE=38 ppm/C @50° C., 72 ppm/° C. @ 150° C.), with sufficient adhesion, and the right cure schedule, a process can coat IPC over a variety of printhead construction materials while maintaining chemical resistance.
A lower electrode 150 and an adhesion layer 160 form the foundation of a lower electrode stack, which has a buffer PZT layer 148 on the adhesion layer 160. An epitaxial growth layer 146 physically contacting the buffer PZT layer 148, an adhesion layer 144 and an upper electrode 142 are upper layers in the structure depicted in the drawing. To the other side of the adhesion layer 160 (i.e., downward in the drawing), a deflection membrane 162 defines surfaces for the body 164A, 164B to adhere, and defines a surface of the cavity 168. Further surfaces of the cavity are defined by portions of the body 164A, 164B, which is made of a base wafer that defines an ink channel 167 and a pumping chamber 168 in one embodiment. A nozzle plate 166A, 166B adhered to the body 164A, 164B has an aperture 171, such that the structure defines a nozzle 170. Depending on viewpoint, the ink channel 167 and the pumping chamber 168 can each be considered, or can be considered in combination, as an internal cavity of the printhead 140. As such, the internal cavity and the nozzle 170 are intended to receive a protective coating. Surfaces of the internal cavity and the nozzle 170 are exposed through the nozzle 170, during materials processing, to receive a protective coating as described herein in various embodiments.
In some embodiments, there is a non-selective process in which no masking is used and ion milling can remove the entire coating from one external surface (or more) of a wafer and/or component. Such non-masking is used for cases in which the surfaces are not expected to be exposed to attack by fluid.
In an action 502, a component is provided for coating. For example, a component of an inkjet printhead, a printhead assembly or subassembly, or a component of an inkjet printer could be used. The component could be manufactured in-house, or sourced externally and brought in for further processing. In various embodiments, the component has at least one internal cavity that is accessible for processing. In various embodiments, the component is to be exposed to an acid or alkali liquid during usage of a machine. For example the liquid could be printer ink.
In an action 504, a film material is selected for a coating. In various embodiments described herein, the film material is HfO2, to be made as a conformal coating using atomic layer deposition.
In an action 506, a target thickness is selected for the film. In various embodiments described herein, the target thickness for a film of HfO2 is between 10 and 50 nm, between 20 and 40 nm, between 30 and 50 nm, or about 30 nm. The target thickness is selected to avoid formation of pinholes, thin spots and nodule growth. In some embodiments in which laser dicing is to be used, the thickness of HFO2 is maintained below 50 nm.
In an action 508, a temperature is selected for film deposition. In various embodiments described herein, the temperature is suitable for film deposition on thermoset and/or on glue (or other bonding material). In some embodiments, the selected temperature is in a range between 185° C. and 275° C., inclusive.
In an action 510, using atomic layer deposition, adjusted for the selected target thickness and selected temperature, a film of the selected film material is deposited as a conformal layer on the component, including on an internal cavity exposed for processing.
The method can be varied with additional actions, for example to deposit additional films (e.g., NWC coating) as described herein.
In an action 602, gold, thicker than a specified amount or in a specified thickness range, is added on electrical contact region(s) of a component. For example, in some embodiments, at least 200 nm of gold, or gold thicker than 200 nm (e.g., gold thicker than 300 nm), or gold in a range of 220-240 nm is added on top of a contact pad of a component. In some other embodiments, a lower amount of gold can be used. The amount of gold is specified as an amount that will leave some gold (enough for solder wetting, but not too much so that solder becomes embrittled) on the contact pad after ion milling with over etch removes HfO2 film or coating in a defined electrical contact region.
In an action 604, a conformal film, layer or coating of HfO2 is deposited on the component, using atomic layer deposition (see, e.g., method in
In an action 606, in some embodiments, selective removal regions are defined, for removing HfO2. For example, a mask, photoresist, physical masking, etc., is used to expose a portion of the HfO2 and shield the remainder of the HfO2 from removal. The selective removal regions should align with electrical contact regions of the component.
In an action 608, using argon ion milling with selected overetch, HfO2 is removed at selective removal regions, leaving sufficient gold at electrical contact region(s) for soldering with solder wetting and not solder embrittlement.
There are a number of example embodiments described herein.
Example 1 is an inkjet printhead or member thereof, comprising: a component having at least one internal cavity for printer ink, the at least one internal cavity accessible during materials processing; a protective coating on the component and on a surface of the at least one internal cavity, the protective coating comprising a film of HfO2, ZrO2, TiO2, or a chemically resistant oxide or nitride as a conformal layer; and the film having a thickness in a range that avoids formation of pinholes, thin spots and nodule growth.
Example 2 is the inkjet printhead, or member thereof, of example 1 that may optionally include that the thickness of the film of protective coating is between 10 nm and 50 nm, inclusive.
Example 3 is the inkjet printhead, or member thereof, of example 1 that may optionally include that the component includes at least one from a group consisting of: multiple members bonded together with a bonding material, a portion of thermoset, a MEMS (microelectromechanical system) die, a wafer having dies attached thereto, a carrier having dies attached thereto, and a flexible circuit board (FCB) having dies attached thereto.
Example 4 is the inkjet printhead, or member thereof, of example 3 that may optionally include that the bonding material comprises at least one selected from a group that comprises: glue, epoxy, adhesive, solder, and photoresist.
Example 5 is the inkjet printhead, or member thereof, of example 1 that may optionally include that the film of HfO2 has at least one aperture exposing a metallic surface of an electrical contact region of the component.
Example 6 is the inkjet printhead, or member thereof, of example 5 that may optionally include that the metallic surface comprises gold, platinum, iridium, or a noble metal.
Example 7 is the inkjet printhead, or member thereof, of example 1 that may optionally include a non-wetting coating (NWC) on the film of HfO2.
Example 8 is the inkjet printhead, or member thereof, of example 1 that may optionally include a non-wetting coating (NWC) on one from a group of various silanes with functional tail groups formed into a film on the film of HfO2 or a layer resulting from a treatment applied to the film of HfO2.
Example 9 is a product by process, comprising: an inkjet printhead or member thereof, as a component of an inkjet printer that is to be exposed to printer ink during usage of the inkjet printer; the component having a film of HfO2 deposited using atomic layer deposition (ALD) adjusted for a target thickness that avoids formation of pinholes, thin spots and nodule growth; and the atomic layer deposition depositing a portion of the film of HfO2 on an external surface of the component and a surface of at least one internal cavity of the component.
Example 10 is the product by process of example 9 that may optionally include that the target thickness for the film of HfO2 is between 10 nm and 50 nm, inclusive, and the film of HfO2 is deposited in a process temperature range between 185° C. and 275° C., inclusive.
Example 11 is the product by process of example 9 that may optionally include that the film of HfO2 has a plurality of apertures each exposing a contact region comprising a metallic surface, each of the plurality of apertures opened by using ion milling with overetching to remove a portion of the film of HfO2 and a portion of the metallic surface, leaving a remaining portion of the metallic surface in the exposed contact region of the component.
Example 12 is the product by process of example 9 that may optionally include that the metallic surface comprises gold, platinum, iridium, or a noble metal.
Example 13 is the product by process of example 9 that may optionally include that the component formed by assembling at least two members using at least one from a group consists of: glue, solder, die bonding to a wafer, die bonding to a carrier, and die bonding to a flexible circuit board (FCB).
Example 14 is an inkjet printhead or member thereof, comprising: a component having at least one internal cavity for printer ink, the at least one internal cavity accessible during materials processing; a protective coating on the component and on a surface of the at least one internal cavity, the protective coating comprising a film of HfO2 as a conformal layer; and the film of HfO2 having a thickness in a range that avoids formation of pinholes, thin spots and nodule growth, wherein the film of HfO2 has a plurality of apertures exposing a plurality of gold surfaces of electrical contact regions of the component.
Example 15 is the inkjet printhead, or member thereof, of example 14 that may optionally include that the thickness of the film of HfO2 is between 10 nm and 50 nm, inclusive.
Example 16 is the inkjet printhead, or member thereof, of example 14 that may optionally include that the component includes at least one from a group consisting of: multiple members bonded together with a bonding material, a portion of thermoset, a MEMS (microelectromechanical system) die, a wafer having dies attached thereto, a carrier having dies attached thereto, and a flexible circuit board (FCB) having dies attached thereto.
Example 17 is the inkjet printhead, or member thereof, of example 16 that may optionally include that the bonding material comprises at least one selected from a group that comprises: glue, epoxy, adhesive, solder, and photoresist.
Example 18 is the inkjet printhead, or member thereof, of example 14 that may optionally include a non-wetting coating (NWC) on one from a group consisting of: the film of HfO2, an additional film on the film of HfO2, or a layer resulting from a treatment applied to the film of HfO2.
Detailed illustrative embodiments are disclosed herein. However, specific functional details disclosed herein are merely representative for purposes of describing embodiments. Embodiments may, however, be embodied in many alternate forms and should not be construed as limited to only the embodiments set forth herein. It should be appreciated that descriptions of direction and orientation are for convenience of interpretation, and the apparatus is not limited as to orientation with respect to gravity. In other words, the apparatus could be mounted upside down, right side up, diagonally, vertically, horizontally, etc., and the descriptions of direction and orientation are relative to portions of the apparatus itself, and not absolute.
It should be understood that although the terms first, second, etc. may be used herein to describe various steps or calculations, these steps or calculations should not be limited by these terms. These terms are only used to distinguish one step or calculation from another. For example, a first calculation could be termed a second calculation, and, similarly, a second step could be termed a first step, without departing from the scope of this disclosure. As used herein, the term “and/or” and the “/” symbol includes any and all combinations of one or more of the associated listed items.
As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises”, “comprising”, “includes”, and/or “including”, when used herein, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. Therefore, the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting.
It should also be noted that in some alternative implementations, the functions/acts noted may occur out of the order noted in the figures. For example, two figures shown in succession may in fact be executed substantially concurrently or may sometimes be executed in the reverse order, depending upon the functionality/acts involved.
Although the method operations were described in a specific order, it should be understood that other operations may be performed in between described operations, described operations may be adjusted so that they occur at slightly different times or the described operations may be distributed in a system which allows the occurrence of the processing operations at various intervals associated with the processing.
Various units, circuits, or other components may be described or claimed as “configured to” perform a task or tasks. In such contexts, the phrase “configured to” is used to connote structure by indicating that the units/circuits/components include structure (e.g., circuitry or mechanical features) that performs the task or tasks during operation. As such, the unit/circuit/component can be said to be configured to perform the task even when the specified unit/circuit/component is not currently operational (e.g., is not on). The units/circuits/components used with the “configured to” language include hardware—for example, circuits, memory storing program instructions executable to implement the operation, etc. Reciting that a unit/circuit/component is “configured to” perform one or more tasks is expressly intended not to invoke 35 U.S.C. 112, sixth paragraph, for that unit/circuit/component. Additionally, “configured to” can include generic structure (e.g., generic circuitry) that is manipulated by software and/or firmware (e.g., an FPGA or a general-purpose processor executing software) to operate in manner that is capable of performing the task(s) at issue. “Configured to” may also include adapting a manufacturing process (e.g., a semiconductor fabrication facility) to fabricate devices (e.g., integrated circuits or manufactured articles) that are adapted to implement or perform one or more tasks, or designing an article or apparatus to have certain features or capabilities.
The foregoing description, for the purpose of explanation, has been described with reference to specific embodiments. However, the illustrative discussions above are not intended to be exhaustive or to limit the invention to the precise forms disclosed. Many modifications and variations are possible in view of the above teachings. The embodiments were chosen and described in order to best explain the principles of the embodiments and its practical applications, to thereby enable others skilled in the art to best utilize the embodiments and various modifications as may be suited to the particular use contemplated. Accordingly, the present embodiments are to be considered as illustrative and not restrictive, and the invention is not to be limited to the details given herein, but may be modified within the scope and equivalents of the appended claims.
