Patent Document

CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application is a continuation application claiming priority under 35 USC §120 from co-pending U.S. patent application Ser. No. 14/418,433 filed on Jun. 29, 2015 by Rivas et al. and entitled FLUID EJECTION ASSEMBLY WITH CONTROLLED ADHESIVE BOND which was an application filed under 35 USC §371 claiming priority from PCT/US2012/056115 filed on Sep. 19, 2012, the full disclosures both of which are hereby incorporated by reference. 
     
    
     BACKGROUND 
       [0002]    Fluid ejection devices, such as printheads in inkjet printers, provide drop-on-demand ejection of fluid drops. Inkjet printers produce images by ejecting ink drops through a plurality of nozzles onto a print medium, such as a sheet of paper. The nozzles are typically arranged in one or more arrays, such that properly sequenced ejection of ink drops from the nozzles causes characters or other images to be printed on the print medium as the printhead and the print medium move relative to each other. In a specific example, a thermal inkjet printhead ejects drops from a nozzle by passing electrical current through a heating element to generate heat and vaporize a small portion of the fluid within an ink ejection chamber. In another example, a piezoelectric inkjet printhead uses a piezoelectric material actuator to generate pressure pulses in an ink ejection chamber that force ink drops out of a nozzle. 
         [0003]    Prior to the ejection of ink drops from a nozzle, ink may travel from an ink reservoir to the ink ejection chamber through an ink feed slot that connects the chamber to the ink reservoir. Often, the ink feed slot is formed in a silicon substrate that is bonded to a body of the ink reservoir. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0004]    The present embodiments will now be described, by way of example, with reference to the accompanying drawings, in which: 
           [0005]      FIG. 1  illustrates an inkjet printing system  100  suitable for incorporating a fluid ejection assembly with a controlled adhesive bond as disclosed herein, according to an embodiment; 
           [0006]      FIG. 2  shows an example of an inkjet printhead assembly implemented as an inkjet cartridge/pen, according to an embodiment; 
           [0007]      FIG. 3  shows a cross-sectional view of a portion of a fluid ejection/printhead assembly, according to an embodiment; 
           [0008]      FIG. 4  shows an enlarged cross-sectional view of one adhesive bond that bonds a substrate rib with a carrier rib, according to an embodiment; 
           [0009]      FIG. 5  shows an enlarged cross-sectional view of another adhesive bond that bonds a substrate rib with a carrier rib, according to an embodiment; and 
           [0010]      FIG. 6  shows a flowchart of an example method of fabricating a controlled adhesive bond in a fluid ejection/printhead assembly, according to an embodiment. 
       
    
    
     DETAILED DESCRIPTION 
     Overview 
       [0011]    As noted above, inkjet printheads often have at least one ink feed slot formed in a silicon substrate that provides fluid communication between an ink ejection chamber and an ink reservoir. The substrate is disposed between the ink ejection chamber and the ink reservoir body, or substrate carrier, and is adhered to the substrate carrier such that ink feed slots in the substrate correspond with fluid pathways in the carrier. Because the width of the ink feed slots can be on the micron scale, small obstructions may adversely affect the ink flow from the ink reservoir to the ink chamber. Such obstructions can also trap air or other gases within the ink chamber, resulting in an inadequate ink supply to the printhead nozzles. Air in the ink chamber can be generated during the ink ejection process in a number of ways. For example, the heating of ink can lead to the formation of air bubbles because heated fluid has a lower solubility for dissolved air. In addition, bubbles can form in an ink chamber either from ejecting an ink drop or from ingesting an air bubble during refill of the chamber. 
         [0012]    A printhead can be designed with a passive air management system that buoyantly conveys the air bubbles away from the ink ejection chamber, through the ink feed slot, and into a safe air storage location within the body of the ink reservoir (i.e., substrate carrier). In general, such a system comprises increasingly wider fluid pathways that extend from the ink ejection chamber to the safe air storage location. Thus, the geometric shapes and relative cross-sectional widths of the ink feed slots and fluid passageways help to manage air bubbles in the printhead. However, small obstructions in the ink feed slot and/or fluid pathways of the substrate carrier can trap the air bubbles, impeding their natural buoyant conveyance. One common obstruction often found in an ink feed slot is the adhesive employed to bond the substrate to the carrier. An ongoing challenge with the fabrication of printheads is an adhesive “squish” or “bulge” into the ink feed channel that can occur when the printhead die/substrate is attached to the substrate carrier. If the adhesive bulges far enough into the width of the ink feed slot, it can obstruct the ink flow and inhibit the passive air management of the printhead, eventually leading to nozzle starvation and print defects. 
         [0013]    Embodiments of the present disclosure provide a fluid ejection device and fabrication methods that enable a controlled adhesive bond between a substrate and a substrate carrier (i.e., the ink reservoir body). The controlled adhesive bond comprises a concavely tapering adhesive profile that narrows in the middle as the adhesive bond extends away from bonding locations on both the substrate and carrier surfaces. Adhesive contact footprints formed at the adhesive bonding locations on the substrate and carrier surfaces have widths that do not exceed, respectively, the widths of the substrate and carrier bonding surfaces themselves. Thus, the width of the adhesive bond at any point of the bond, does not exceed the width of either the substrate bonding surface or the carrier bonding surface. The adhesive bond profile, controlled in this manner, eliminates any bulging out at the middle area of the adhesive bond into the ink feed slots. In addition, the controlled adhesive bond profile eliminates any protrusion of the adhesive bond into the ink feed slots from the adhesive contact footprints at both the substrate bonding surface and the carrier bonding surface. Accordingly, the controlled adhesive bond profile eliminates adhesive bond obstructions in the ink feed slots and facilitates the passive air management within the printhead. 
         [0014]    Methods of achieving the controlled adhesive bond profile comprise making the adhesive-to-substrate contact angles, and adhesive-to-carrier contact angles, hydrophilic. That is, the contact angles of the adhesive to both the substrate and carrier surfaces are made to be less than 90 degrees. The desired hydrophilic contact angles can be achieved by controlling the adhesive formulation, the substrate surface, and the carrier surface. 
         [0015]    In one embodiment, a fluid ejection assembly includes a substrate with substrate ribs that define an ink feed slot extending from a top side to a bottom side of the substrate. The assembly further includes a substrate carrier having carrier ribs that define a fluid passageway to provide ink to the ink feed slot. The assembly also includes a concavely tapered adhesive bond to adhere a substrate rib surface to a carrier rib surface without protruding into the ink feed slot or the fluid passageway. 
         [0016]    In another embodiment, a fluid ejection assembly includes a printhead bonded to a fluid distribution manifold. The bond forms a fluid pathway extending from a fluid chamber on the printhead through the manifold. The assembly also includes a concavely tapered adhesive bond between the printhead and the manifold that does not protrude into the fluid pathway. 
         [0017]    In another embodiment, a method of fabricating a controlled adhesive bond in a fluid ejection assembly includes fabricating a printhead substrate comprising substrate ribs defining ink feed slots. The method further includes fabricating a substrate carrier comprising carrier ribs defining fluid passageways. The method also includes depositing an adhesive on bonding surfaces of the carrier ribs, and bringing the substrate ribs into proximity with respective carrier ribs such that the deposited adhesive contacts bonding surfaces of the substrate ribs. The method includes forming hydrophilic contact angles of less than 90 degrees where the adhesive contacts the bonding surfaces. The hydrophilic contact angles are formed such that the adhesive forms a concavely tapered adhesive bond profile that does not protrude into the ink feed slots or fluid passageways. 
       Illustrative Embodiments 
       [0018]      FIG. 1  illustrates an inkjet printing system  100  suitable for incorporating a fluid ejection assembly with a controlled adhesive bond as disclosed herein, according to an embodiment. In this embodiment, the fluid ejection assembly is implemented with a fluid drop jetting printhead  114  bonded to a substrate carrier with a controlled adhesive bond. Inkjet printing system  100  includes a fluid ejection assembly implemented as an inkjet printhead assembly  102 , an ink supply assembly  104 , a mounting assembly  106 , a media transport assembly  108 , an electronic controller  110 , and at least one power supply  112  that provides power to the various electrical components of inkjet printing system  100 . Inkjet printhead assembly  102  includes at least one fluid ejection device  114  or printhead  114  with a controlled adhesive bond, that ejects drops of ink through a plurality of orifices or nozzles  116  toward a print medium  118  so as to print onto print medium  118 . Print medium  118  comprises any type of suitable sheet material, such as paper, card stock, transparencies, Mylar, and the like. Typically, nozzles  116  are arranged in one or more columns or arrays such that properly sequenced ejection of ink from nozzles  116  causes characters, symbols, and/or other graphics or images to be printed onto print medium  118  as inkjet printhead assembly  102  and print medium  118  are moved relative to each other. 
         [0019]    Ink supply assembly  104  supplies fluid ink to printhead assembly  102  and includes a reservoir  120  for storing ink. Ink flows from reservoir  120  to inkjet printhead assembly  102 . Ink supply assembly  104  and inkjet printhead assembly  102  can form either a one-way ink delivery system or a recirculating ink delivery system. In a one-way ink delivery system, substantially all of the ink supplied to inkjet printhead assembly  102  is consumed during printing. In a recirculating ink delivery system, however, only a portion of the ink supplied to printhead assembly  102  is consumed during printing. Ink not consumed during printing is returned to ink supply assembly  104 . 
         [0020]    In one example implementation, inkjet printhead assembly  102  and ink supply assembly  104  are housed together in an inkjet cartridge or pen.  FIG. 2  shows an example of an inkjet printhead assembly  102  implemented as an inkjet cartridge/pen  102 , according to an embodiment. The inkjet cartridge/pen  102  includes a body  200 , a printhead  114  (i.e., fluid ejection device), and electrical contacts  202 . Individual ejection elements (e.g., thermal resistors, piezo membranes) within the printhead  114  are energized by electrical signals provided at contacts  202  to eject droplets of fluid ink from selected nozzles  116 . The fluid can be any suitable fluid used in a printing process, such as various printable fluids, inks, pre-treatment compositions, fixers, and the like. In some examples, the fluid can be a fluid other than a printing fluid. The inkjet cartridge  102  may contain its own fluid supply within the cartridge body  200 , or it may receive fluid from an external supply such as a fluid reservoir  120  connected to the cartridge  102  through a tube, for example. In either case, as discussed below, a printhead assembly  102  such as an inkjet cartridge  102  comprises a printhead substrate bonded to a substrate carrier that comprises a fluid distribution manifold with fluid pathways providing fluid communication between the printhead and the fluid reservoir. Inkjet cartridges  102  containing their own fluid supplies are generally disposable once the fluid supply is depleted. 
         [0021]    Referring again to  FIG. 1 , mounting assembly  106  positions inkjet printhead assembly  102  relative to media transport assembly  108 , and media transport assembly  108  positions print medium  118  relative to inkjet printhead assembly  102 . Thus, a print zone  122  is defined adjacent to nozzles  116  in an area between inkjet printhead assembly  102  and print medium  118 . In one embodiment, inkjet printhead assembly  102  is a scanning type printhead assembly. In a scanning type printhead assembly, mounting assembly  106  includes a carriage for moving inkjet printhead assembly  102  relative to media transport assembly  108  to scan print medium  118 . In another embodiment, inkjet printhead assembly  102  is a non-scanning type printhead assembly. In a non-scanning printhead assembly, mounting assembly  106  fixes inkjet printhead assembly  102  at a prescribed position relative to media transport assembly  108 . Thus, media transport assembly  108  positions print medium  118  relative to inkjet printhead assembly  102 . 
         [0022]    Electronic controller  110  typically includes a processor, firmware, and other printer electronics for communicating with and controlling inkjet printhead assembly  102 , mounting assembly  106 , and media transport assembly  108 . Electronic controller  110  receives data  124  from a host system, such as a computer, and includes memory for temporarily storing data  124 . Typically, data  124  is sent to inkjet printing system  100  along an electronic, infrared, optical, or other information transfer path. Data  124  represents, for example, a document and/or file to be printed. As such, data  124  forms a print job for inkjet printing system  100  and includes one or more print job commands and/or command parameters. 
         [0023]    In one example implementation, electronic controller  110  controls inkjet printhead assembly  102  for ejection of ink drops from nozzles  116 . Thus, controller  110  defines a pattern of ejected ink drops that form characters, symbols, and/or other graphics or images on print medium  118 . The pattern of ejected ink drops is determined by the print job commands and/or command parameters from data  124 . 
         [0024]    In one implementation, inkjet printhead assembly  102  includes one fluid ejection device/printhead  114 . In another implementation, inkjet printhead assembly  102  is a wide-array or multi-head printhead assembly. In one example of a wide-array printhead assembly, the inkjet printhead assembly  102  includes a conveyance such as a print bar that carries multiple printheads  114 , provides electrical communication between the printheads  114  and electronic controller  110 , and provides fluidic communication between the printheads  114  and the ink supply assembly  104 . 
         [0025]    In one example implementation, inkjet printing system  100  is a drop-on-demand thermal bubble inkjet printing system where the fluid ejection device  114  is a thermal inkjet (TIJ) fluid ejection device/printhead  114 . The TIJ printhead  114  implements a thermal resistor heating element as an ejection element in an ink chamber to vaporize ink and create bubbles that force ink or other fluid drops out of a nozzle  116 . In another example implementation, inkjet printing system  100  is a drop-on-demand piezo inkjet printing system where the fluid ejection device  114  is a piezoelectric inkjet printhead that employs a piezoelectric material actuator to generate pressure pulses to force ink drops out of nozzles  116 . 
         [0026]      FIG. 3  shows a cross-sectional view of a portion of a fluid ejection/printhead assembly  102 , taken along the line A-A of  FIG. 2 . Printhead assembly  102  generally includes a printhead  114  bonded to a fluid distribution manifold  300 . The fluid distribution manifold  300  is sometimes referred to as a chiclet or a printhead substrate carrier, but in this description it will primarily be referred to as a substrate carrier  300 . Printhead  114  includes a printhead substrate  302  comprising a silicon die. Elongated ink feed slots  304  are formed between substrate ribs  305  of the substrate  302 . The elongated ink feed slots  304  extend into the plane of  FIG. 3 . The ink feed slots  304  are in fluid communication at the top side of the substrate  302  with fluid/ink chambers  306  formed in a fluidics or chamber layer  308  disposed on the top side of the substrate  302 . Each fluid/ink chamber  306  comprises a thermal resistor heating element  310  that acts as an ejection element within the respective chamber  306  to vaporize ink or other fluids, creating bubbles that force fluid drops out of a corresponding nozzle  116 . Resistor  310  can be formed within a thin film stack applied on the top side of substrate  302 . A thin film stack generally includes a metal layer forming the resistor  310  (e.g., tantalum-aluminum (TaAl), tungsten silicon-nitride (WSiN)), a passivation layer (e.g., silicon carbide (SiC) and silicon nitride (SiN)), and a cavitation layer (e.g., tantalum (Ta)). A top hat layer  312 , also referred to as the orifice plate or nozzle layer  312 , is disposed on top of the chamber layer  308  and has nozzles  116  formed therein that each correspond with a respective chamber  306  and resistor  310 . Thus, individual fluid drop generators  314  are formed by corresponding chambers  306 , resistors  310 , and nozzles  116 . The chamber layer  308  and nozzle layer  312  can be formed, for example, of a polymeric material such as SU8 commonly used in the fabrication of microfluidics and MEMS devices. In one implementation, the nozzle layer  312  and chamber layer  308  are formed together such that they comprise a single structure. 
         [0027]    Printhead substrate  302  is bonded at the surface of its bottom side to the underlying substrate carrier  300  (i.e., fluid distribution manifold) by an adhesive bond  316 . More specifically, in one implementation each substrate rib  305  is bonded to a corresponding carrier rib  318  of substrate carrier  300 . The ink feed slots  304  are in fluid communication at the bottom side of the substrate  302  with the fluid passageways  320  formed by carrier ribs  318  of substrate carrier  300 . Thus, the ink feed slots  304  provide fluid communication between the fluid/ink chambers  306  on the top side of substrate  302  and the fluid passageways  320  at the bottom side of substrate  302 . The variously slanted fluid passageways  320  in the substrate carrier  300 , in turn, provide fluid communication with a fluid/ink reservoir such as reservoir  120  ( FIG. 1 ). The fluid passageways  320  and ink feed slots  304  together, conduct fluid/ink from a reservoir  120  toward the fluid/ink chambers  306  where it can be ejected through nozzles  116 , as generally indicated by solid direction arrows  322 . Additionally, the physical orientation of the printhead assembly  102  during its use is with the substrate carrier  300  situated above the substrate  302  (i.e., with nozzles  116  facing downward toward print media), which enables the buoyant conveyance of air bubbles away from chambers  306  in a manner indicated by the dashed direction arrows  324 . Thus, the printhead assembly  102  provides a passive air management system in which air bubbles travel away from chambers  306  through the ink feed slots  304  and fluid passageways  320 . 
         [0028]    The adhesive bond  316  facilitates the buoyant conveyance of air bubbles away from the fluid/ink chambers  306  by its recessed profile. The adhesive bond  316  is controlled such that its profile does not protrude into the ink feed slots  304  and fluid passageways  320 , and therefore does not hinder the conveyance of air bubbles away from chambers  306 . By contrast, prior adhesive bonds are generally not controlled and hinder the conveyance of air bubbles away from chambers  306  because they protrude and/or bulge out to some extent into the ink feed slots  304  and fluid passageways  320 . 
         [0029]      FIG. 4  shows an enlarged cross-sectional view of one adhesive bond  316  that bonds a substrate rib  305  with a carrier rib  318 , according to an embodiment. It is noted that the contours of the adhesive bond profile, as well as the relative widths of the adhesive bond profile to one another and to the widths of the substrate rib  305  and carrier rib  318 , are not to scale and may be exaggerated for the purpose of illustration. The controlled adhesive bond  316  comprises a profile that tapers away from the adhesive contact points ( 400 ,  402 ) in a concave manner. Thus, the concavely tapering adhesive bond profile narrows toward the mid-section of the adhesive bond  316  as the bond extends away from both its substrate contact point  400  and its carrier contact point  402 . Each adhesive contact point ( 400 ,  402 ) forms an “adhesive footprint” having an associated width. As shown in  FIG. 4 , in one implementation the width, W 1 , of the substrate adhesive footprint/contact  400 , is less than or does not exceed the width, W 2 , of the bonding surface of the substrate rib  305 . Also shown in  FIG. 4 , in one implementation the width, W 3 , of the carrier adhesive footprint/contact  402 , is less than or does not exceed the width, W 4 , of the bonding surface of the carrier rib  318 . In one implementation, the width, W 5 , of the mid-section of the adhesive bond  316  does not exceed either of the widths, W 1  or W 3 , of the adhesive footprints/contacts ( 400 ,  402 ). Thus, the controlled adhesive bond  316  does not bulge or protrude out into the ink feed slots  304  and fluid passageways  320  at its mid-section, its adhesive footprints/contacts ( 400 ,  402 ), or at any other point of its concavely tapered profile. 
         [0030]      FIG. 5  shows an enlarged cross-sectional view of another adhesive bond  316  that bonds a substrate rib  305  with a carrier rib  318 , according to an embodiment. As in the  FIG. 4  example, the controlled adhesive bond  316  shown in  FIG. 5  comprises a profile that tapers away from the adhesive contact points ( 400 ,  402 ) in a concave manner such that the adhesive bond profile narrows toward the mid-section of the adhesive bond  316  as the bond extends away from both its substrate contact point  400  and its carrier contact point  402 . As shown in  FIG. 5 , in one implementation, while the width, W 1 , of the substrate adhesive footprint/contact  400  does not exceed the width, W 2 , of the bonding surface of the substrate rib  305  (i.e., as discussed above regarding  FIG. 4 ), in some cases the width, W 1 , can exceed the width of the bonding surface of the carrier rib  318 . In general, while the width of an adhesive footprint/contact ( 400 ,  402 ) does not exceed the width of the surface to which it is bonded, it may exceed the width of the surface to which the opposite adhesive footprint/contact ( 400 ,  402 ) is bonded. This may in part, depend at least upon the relative widths of the bonding surfaces available on the substrate rib  305  and the carrier rib  318 . In any case, as noted above with regard to  FIG. 4 , the controlled adhesive bond  316  does not bulge or protrude out into the ink feed slots  304  and fluid passageways  320  at its mid-section, its adhesive footprints/contacts ( 400 ,  402 ), or at any other point of its concavely tapered profile. 
         [0031]      FIG. 6  shows a flowchart of an example method  600  of fabricating a controlled adhesive bond in a fluid ejection/printhead assembly, according to an embodiment of the disclosure. Method  600  is associated with the embodiments discussed herein with respect to  FIGS. 1-5 , and details of the steps shown in method  500  may be found in the related discussion of such embodiments. Method  600  may include more than one implementation, and different implementations of method  600  may not employ every step presented in the flowchart. Therefore, while steps of method  600  are presented in a particular order in the flowchart, the order of their presentation is not intended to be a limitation as to the order in which the steps may actually be implemented, or as to whether all of the steps may be implemented. For example, one implementation of method  600  might be achieved through the performance of a number of initial steps, without performing one or more subsequent steps, while another implementation of method  600  might be achieved through the performance of all of the steps. 
         [0032]    Method  600  begins at block  602  with fabricating a printhead substrate comprising substrate ribs defining ink feed slots. The printhead substrate is typically fabricated from a silicon or glass wafer through standard micro-fabrication processes that are well-known to those skilled in the art such as electroforming, laser ablation, anisotropic etching, sputtering, dry etching, photolithography, casting, molding, stamping, and machining. The printhead substrate may also be further developed to include a fluidics and nozzle layer on a top side of the substrate. The method  600  continues at block  604  with fabricating a substrate carrier comprising carrier ribs defining fluid passageways. The substrate carrier is a fluid distribution manifold such as a plastic fluidic interposer, or chiclet. At block  606  of method  600 , an adhesive is deposited on bonding surfaces of the carrier ribs. Alternatively, or in addition, the adhesive can be deposited onto bonding surfaces of the substrate ribs. In one implementation, the deposition of the adhesive occurs by jetting the adhesive. Jetting the adhesive, rather than using another method such as needle deposition, provides advantages such as the ability to precisely control both the volume of the adhesive and the precise location of the adhesive on the bonding surfaces. 
         [0033]    The method  600  continues at block  608 , with bringing the substrate ribs into proximity with respective carrier ribs such that the deposited adhesive contacts both the substrate rib bonding surfaces and respective carrier rib bonding surfaces. Thus, a single volume of adhesive is disposed between each of the substrate rib and carrier rib surfaces. At block  610 , the method  600  includes forming hydrophilic contact angles of less than 90 degrees in the adhesive where it contacts the bonding surfaces of the substrate ribs and carrier ribs, such that the adhesive bond forms a concavely tapered profile between each substrate rib and carrier rib. As is known to those skilled in the art of theoretical wetting and contact angle science, following Young&#39;s equation, hydrophilic contact angles are achieved by engineering the interfacial energies of the carrier and substrate surfaces to air interfacial energy, the carrier and substrate surfaces to adhesive liquid interfacial energy, and the adhesive liquid to air interfacial energy. The bonding surface roughness will also inform the contact angle as per Wenzel&#39;s equation. Thus, the hydrophilic contact angles are achieved in various ways including, by controlling the adhesive formulation, and controlling the bonding surfaces of the substrate and carrier. For example, for epoxy adhesives, the liquid adhesive surface energy is controlled by the selection and proportions of the resin and activator chemical compounds in the adhesive. Additionally, the surface energy can modified with additives to the adhesive. The carrier surface energy is controlled by the selection of molded plastic and the roughness of the carrier surface. Additionally, the carrier surface may be coated to change the surface energy. The substrate surface energy is also controlled by the roughness of the bonding surface of the substrate ribs. The bonding surfaces of the substrate can be the silicon substrate itself, or they can have a thinfilm coating such as silicon oxide, silicon nitride or tantalum.

Technology Category: b