Abstract:
A method for bonding a polymer layer to an outlet plate for an inkjet print head has been developed that enables the polymer layer to be attached to the outlet plate with little or no bowing of the polymer layer. The method includes aligning recesses in a bonding plate with channels in an outlet plate, interposing a polymer layer between the bonding plate and the outlet plate, and pressing the bonding plate against the polymer layer to bond the polymer layer to the outlet plate.

Description:
TECHNICAL FIELD 
     This disclosure relates generally to inkjet ejectors that eject ink from a print head onto an image receiving surface and, more particularly, to print heads having inkjet ejectors comprised of multiple layers. 
     BACKGROUND 
     Drop on demand inkjet technology has been employed in commercial products such as printers, plotters, and facsimile machines. Generally, an inkjet image is formed by the selective activation of inkjets within a print head to eject ink onto an ink receiving member. For example, an ink receiving member rotates opposite a print head assembly as the inkjets in the print head are selectively activated. The ink receiving member may be an intermediate image member, such as an image drum or belt, or a print medium, such as paper. An image formed on an intermediate image member is subsequently transferred to a print medium, such as a sheet of paper. 
       FIGS. 5A and 5B  illustrate one example of a single inkjet ejector  10  that is suitable for use in an inkjet array of a print head. The inkjet ejector  10  has a body  48  that is coupled to an ink manifold  12  through which ink is delivered to multiple inkjet bodies. The body also includes an ink drop-forming orifice or nozzle  14  through which ink is ejected. In general, the inkjet print head includes an array of closely spaced inkjet ejectors  10  that eject drops of ink onto an image receiving member (not shown), such as a sheet of paper or an intermediate member. 
     Ink flows from the manifold to nozzle in a continuous path. Ink leaves the manifold  12  and travels through a port  16 , an inlet  18 , and a pressure chamber opening  20  into the body  22 , which is sometimes called an ink pressure chamber. Ink pressure chamber  22  is bounded on one side by a flexible diaphragm  30 . A piezoelectric transducer  32  is secured to diaphragm  30  by any suitable technique and overlays ink pressure chamber  22 . Metal film layers  34 , to which an electronic transducer driver  36  can be electrically connected, can be positioned on either side of piezoelectric transducer  32 . 
     Ejection of an ink droplet is commenced with a firing signal. The firing signal is applied across metal film layers  34  to excite the piezoelectric transducer  32 , which causes the transducer to bend. Because the transducer is rigidly secured to the diaphragm  30 , the diaphragm  30  deforms to urge ink from the ink pressure chamber  22  through the outlet port  24 , outlet channel  28 , and nozzle  14 . The expelled ink forms a drop of ink that lands onto an image receiving member. Refill of ink pressure chamber  22  following the ejection of an ink drop is augmented by reverse bending of piezoelectric transducer  32  and the concomitant movement of diaphragm  30  that draws ink from manifold  12  into pressure chamber  22 . 
     To facilitate manufacture of an inkjet array print head, an array of inkjet ejectors  10  can be formed from multiple laminated plates or sheets. These sheets are configured with a plurality of pressure chambers, outlets, and apertures and then stacked in a superimposed relationship. Referring once again to  FIGS. 5A and 5B  for construction of a single inkjet ejector, these sheets or plates include a diaphragm plate  40 , an inkjet body plate  42 , an inlet plate  46 , an outlet plate  54 , and an aperture plate  56 . The piezoelectric-transducer  32  is bonded to diaphragm  30 , which is a region of the diaphragm plate  40  that overlies ink pressure chamber  22 . In previously known inkjet ejectors, these plates are metal plates that are brazed to one another with gold. 
     In some known thermal inkjet print heads, the aperture plate may be a polymer layer in which apertures are formed using laser ablation. The advantages of using a polymer layer include low cost and the ability to taper or otherwise shape the apertures. Using a polymer layer also presents challenges to print head design. In the present art, the outlet plate is generally manufactured from a metal layer, such as stainless steel. The metal layer is etched with openings that fluidly couple the apertures in the polymer aperture plate to a pressure chamber in a body layer once the print head assembly is completed. An adhesive is used to bond the polymer aperture plate to the outlet plate. The adhesive bond is formed with heat and pressure once the two plates are positioned adjacent to one another. Since the apertures in the polymer aperture plate are smaller than the openings in the outlet plate, solid portions of the polymer aperture plate extend over the openings in the outlet plate. The attendant lack of support for these portions as the metallic outlet plate is pressed against the polymer aperture plate produces uneven pressure on the polymer aperture plate and causes the polymer aperture plate to warp. While an ideal print head is usually configured to eject ink droplets perpendicularly to the aperture plate&#39;s surface, the warped apertures may eject droplets at different angles, reducing print quality. 
     The lack of flatness in the aperture plate arising from the application of uneven pressure to polymer layers is known to the art. U.S. Pat. No. 5,467,115 discloses the cutting of extra trenches in the silicon die mounting material to produce unsupported areas of the aperture plate that are symmetrical with regard to the apertures in the polymer aperture layer. These symmetrical unsupported areas help reduce errors in apertures caused by the polymer layer warping. While this method tries to reduce the negative effects caused by warped nozzles, it does not address the underlying problem that the polymer aperture plate is being warped during the print head fabrication process. Additionally, existing thermal inkjet print heads in which the above described compensation method addresses effects at the ends of the plates and not the effects at each aperture. A print head fabrication method for making print heads with flat polymer aperture plates benefits the print head fabrication field. 
     SUMMARY 
     A method for forming a polymer aperture plate has been developed that enables the polymer aperture plate to be attached in alignment with outlets in an outlet plate more precisely and to maintain the flatness of the aperture plate. The flatness of the aperture plate is important to avoid print quality defects due to misdirection of the ejected droplets. The method includes aligning recesses in a bonding plate with channels in an outlet plate, interposing a polymer layer between the bonding plate and the outlet plate, and pressing the bonding plate against the polymer layer to bond the polymer layer to the outlet plate. The outlet plate may be a metal plate or other rigid or semi-rigid plate that helps the polymer aperture plate to exhibit sufficient rigidity that the polymer aperture plate adheres to the outlet plate without bowing or other dimensional displacement that adversely impacts the jetting of ink droplets from the apertures in the polymer aperture plate. Likewise, a bonding plate exhibits similar rigidity to apply sufficient pressure for bonding without adverse dimensional displacement. 
     The method produces inkjet print heads that can take advantage of the economy of polymer layers. The inkjet print head includes a body layer in which a plurality of pressure chambers is configured, an outlet plate configured with a plurality of channels, and a polymer layer having apertures that are aligned with the channels in the outlet plate, the polymer layer deviating no more than about 1.5 μm on either side of a straight line across an opening in a channel in the outlet plate. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing aspects and other features of fabricating a polymer aperture plate and how the polymer aperture plate is attached to a rigid inkjet stack are explained in the following description, taken in connection with the accompanying drawings. 
         FIG. 1  depicts a flat polymer aperture layer bonded directly to an outlet plate. 
         FIG. 2  is a flow diagram of the process used to bond a polymer layer to an outlet plate. 
         FIG. 3  is a flow diagram of tacking and bonding processes used to tack or bond two or more material layers together. 
         FIG. 4A  depicts a bonding plate being used to bond a polymer layer directly to an outlet plate. 
         FIG. 4B  depicts a bonding plate being used to bond a polymer layer to an outlet plate with a separate layer of adhesive. 
         FIG. 4C  depicts a polymer layer spanning a channel etched into the outlet plate. 
         FIG. 5A  is a schematic side-cross-sectional view of a prior art embodiment of an inkjet. 
         FIG. 5B  is a schematic view of the prior art embodiment of the inkjet of  FIG. 5A . 
     
    
    
     DETAILED DESCRIPTION 
     For a general understanding of the environment for the system and method disclosed herein as well as the details for the system and method, reference is made to the drawings. In the drawings, like reference numerals have been used throughout to designate like elements. As used herein, the word “printer” encompasses any apparatus that performs a print outputting function for any purpose, such as a digital copier, bookmaking machine, facsimile machine, a multi-function machine, etc. Devices of this type can also be used in bioassays, masking for lithography, printing electronic components such as printed organic electronics, and for making 3D models among other applications. The word “ink” can refer to wax-based inks known in the art but can refer also to any fluid that can be driven from the jets including water-based solutions, solvents and solvent based solutions, and UV curable polymers. The word “polymer” encompasses any one of a broad range of carbon-based compounds formed from long-chain molecules including thermoset polyimides, thermoplastics, resins, polycarbonates, and related compounds known to the art. The word “metal” may encompass either single metallic elements including, but not limited to, copper, aluminum, or titanium, or metallic alloys including, but not limited to, stainless steel or aluminum-manganese alloys. A “transducer” as used herein is a component that reacts to an electrical signal by generating a moving force that acts on an adjacent surface or substance. The moving force may push against or retract the adjacent surface or substance. 
       FIG. 1  depicts a combination  100  of a flat polymer aperture plate  112  bonded to an outlet plate  116 . The outlet plate has outlet channels  120  that extend through the plate. The polymer aperture plate  112  has nozzles  124  that have been formed through the layer. The polymer aperture plate is substantially flat along its length including the portions that overlie channel openings  120  in the outlet plate  116 . Each nozzle  124  corresponds to an outlet channel  120 . The nozzles and channels enable ink to flow through the outlet plate  116  and to be ejected from the nozzle  124  as a droplet in direction  140 . 
     An example process capable of producing the bonded polymer layer and outlet plate of  FIG. 1  is depicted in  FIG. 2 . The process  200  of  FIG. 2  is an embodiment that uses an adhesive material to bond the polymer layer to the outlet plate. The adhesive material is first tacked to the polymer layer (block  204 ) and then bonded to the polymer layer (block  208 ). The tacking process of block  204  aligns the adhesive material with the polymer layer, and the bonding process of block  208  laminates the two layers together. Then the polymer layer with the bonded adhesive is tacked to the outlet plate with the adhesive material placed between the polymer layer and the outlet plate (block  212 ). The tacking process aligns the polymer layer with the outlet plate. The tacked outlet plate and polymer layer are then bonded together (block  216 ). The bonding process hermetically seals the polymer layer and outlet plate together to produce an outlet plate and polymer layer combination that is at least 25 mm in length. 
     A flow diagram that describes an example of a process for tacking the polymer layer and adhesive material ( FIG. 2  block  204 ) is depicted in  FIG. 3 . The tacking process begins by cleaning a fixture, two bonding plates, and the outlet plate in a detergent spray wash and ultrasonic wash cycle to clean larger contaminants from their surfaces (block  304 ). The fixture and two bonding plates are then exposed to a plasma cleaner to remove thin-film contamination and leave their surfaces exposed (block  308 ). The first bonding plate is then aligned and placed above the fixture (block  312 ). The fixture is a superstructure providing a base with a plurality of pins extending vertically from the base. The pins are arranged to align with tooling holes formed through various plates used in the tacking process. The first bonding plate is placed on the fixture with the fixture pins extending through tooling holes formed through the first bonding plate. The first bonding plate preferably has a uniformly flat surface except for the tooling holes and is preferably made from a metal such as stainless steel. 
     The tacking process continues by placing the two target layers above the first bonding plate (block  316 ). In this instance, the target layers are the polymer layer and the adhesive material. The polymer layer is placed above the first bonding plate with a release agent coating on the polymer layer facing the first bonding plate. The release agent coating may be a fluoropolymer material and the release agent prevents the polymer layer from adhering to the first bonding plate during the tacking process. The polymer layer has tooling holes that accept the fixture pins and align the polymer layer with the first bonding plate. The adhesive is then placed above the polymer. Suitable adhesive materials include double sided adhesive tapes having thermoset or thermoplastic adhesives on opposite sides of a thermoset or thermoplastic polymer core. Alternatively, the adhesive material can be a thermoplastic or thermoset adhesive. The adhesive material is positioned using thermal tape capable of withstanding the temperatures of the tacking process. The thermal tape is applied to the edge of the adhesive, leaving the portions of the adhesive that contact the output plate in the process of  FIG. 2  exposed. 
     Because the adhesive should not adhere to the bonding plates used in the tacking and bonding processes, a release agent covers the exposed surface of the adhesive material (block  320 ). The release agent is applied above the adhesive, typically as a thin sheet of a fluoropolymer, such as polytetrafluoroethylene (block  324 ). The release agent prevents the adhesive from tacking to a second bonding plate, which is placed above the adhesive and polymer layer in alignment with the fixture pins (block  328 ). The second bonding plate may be identical in form to the first bonding plate and provides a uniform upper surface for the tacking process. Another layer of release agent, preferably a thin polyimide film, such as Upilex (formed from biphenyl tetracarboxylic dianhydride monomers), is applied above the second bonding plate (block  332 ). A pad is placed over the release agent coating of the second bonding plate (block  336 ). The pad allows for an even transfer of pressure to the target layers during the tacking process. In the embodiment of  FIG. 3 , this pad is made of a flexible material capable of withstanding the pressure and temperature of the tacking process, such as silicone rubber, and is 6.35 mm thick. A layer of the same release agent coating the second bonding plate is applied over the upper surface of the pad (block  340 ). 
     The assembly formed in blocks  312 - 340  is placed in a heated pressure chamber in order to tack the polymer layer to the adhesive (block  344 ). Pressure is applied vertically through the pad, second bonding plate, polymer layer, adhesive, first bonding plate, and the fixture. The combination of heat and pressure causes the adhesive to tack to the polymer layer. In the example embodiment of  FIG. 3 , the tacking is complete after 3 minutes of exposure to a temperature of 250° C. at a pressure of 150 psi (block  348 ). The polymer layer with tacked adhesive is extracted from the fixture assembly (block  352 ). The release agent coatings on the exposed surfaces of the polymer layer and adhesive material allow the bonding plates to be removed without distorting the polymer layer and adhesive. The thermal tape used in the tacking process may be removed as the tacked adhesive material remains aligned with the polymer layer. The layer of release agent between the second bonding plate and the pad allows the pad to be removed as well. The fixture, bonding plates, and pad may be reused in another tacking process. 
     The flow diagram of  FIG. 3  also describes an example of a process for permanently bonding the tacked adhesive to the polymer layer ( FIG. 2  block  208 ). The process begins with the fixture and bonding plates being washed (block  304 ) and plasma cleaned (block  308 ) in the same manner described above in order to remove contaminants. The fixture, bonding plates, and pad used for the tacking process may also be used in the bonding process. 
     The bonding process of  FIG. 3  continues with the first bonding plate being aligned and placed above the fixture with the fixture pins passing through tooling holes formed in the first bonding plate surface (block  312 ). The target is then placed above the first bonding pad (block  316 ). In this case, the target is the tacked polymer layer and adhesive material. The polymer layer is aligned with the first bonding plate and is placed above the plate with the fixture pins extending through tooling holes in the polymer layer. The polymer layer&#39;s thin coating of release agent prevents the polymer layer from adhering to the first bonding plate during the bonding process. The adhesive material already has a release agent layer applied to its exposed surface, obviating the need for application of release agent (block  320 ). The second bonding plate is placed above the adhesive material with the fixture pins passing through tooling holes formed in the second bonding plate surface (block  328 ). As with the tacking process, a thin layer of release agent is applied to the second bonding plate (block  332 ), a pad is placed above the second bonding plate (block  336 ), and a thin layer of release agent is applied to pad&#39;s upper surface (block  340 ). 
     The assembly formed in blocks  312 - 340  is placed in a heated pressure chamber in order to bond the polymer layer to the adhesive (block  344 ). Pressure is applied vertically through the pad, second bonding plate, polymer layer, adhesive, first bonding plate, and the fixture. The combination of heat and pressure causes the adhesive to bond to the polymer layer. In the example embodiment of  FIG. 3 , the bonding is complete after 30 minutes of exposure to a temperature of 290° C. at a pressure of 350 psi (block  348 ). The polymer layer with bonded adhesive is extracted from the fixture assembly (block  352 ). The bonding process permanently laminates the adhesive to the polymer layer. The release agent coatings on the exposed surfaces of the polymer layer and adhesive material allow the bonding plates to be removed without distorting the polymer layer and adhesive. The layer of release agent coating the exposed adhesive surface may be removed after the bonded adhesive and polymer layer are extracted from the bonding plates. The layer of release agent between the second bonding plate and the pad enables the pad to be removed as well. The fixture, bonding plates, and pad may be reused in another bonding process. 
     A process of tacking the polymer layer with the bonded adhesive material to the outlet plate (block  211 ,  FIG. 2 ) may also be described with reference to  FIG. 3 . The tacking process of the polymer layer and the outlet plate is similar to the process used to tack the polymer layer and adhesive material that was described above. The process begins with the fixture and bonding plates being washed (block  304 ) and plasma cleaned (block  308 ) in the same manner described above in order to remove contaminants. The outlet plate, which is typically metallic, also undergoes the washing and plasma cleaning process of block  304  and  308 . The fixture, bonding plates, and pad used for tacking and bonding the polymer layer and adhesive material may also be used for tacking the polymer layer and outlet plate. 
     The bonding process of  FIG. 3  continues with the first bonding plate being aligned and placed above the fixture, with the fixture pins passing through tooling holes formed in the first bonding plate&#39;s surface (block  312 ). The target outlet plate and polymer layer are then placed above the first bonding pad (block  316 ). The outlet plate is placed above the first bonding pad with the fixture pins passing through tooling holes in the outlet plate to aligning it with the bonding plate. The polymer layer is placed above the outlet plate with the adhesive material facing the outlet plate. The polymer layer is aligned with the outlet plate using thermal tape capable of withstanding the temperatures of the tacking process. The exposed surface of the polymer layer already has a coating of release agent, obviating the need to apply more release agent (block  320 ). The second bonding plate is placed above the polymer layer with the fixture pins passing through tooling holes formed in the second bonding plate surface (block  328 ). As with the tacking and bonding processes discussed above, a thin layer of release agent is applied to the second bonding plate (block  332 ), a pad is placed above the second bonding plate (block  336 ), and a thin layer of release agent is applied to pad&#39;s upper surface (block  340 ). The assembly formed in blocks  312 - 340  is placed in a heated pressure chamber in order to tack the polymer layer to the outlet plate (block  344 ). Pressure is applied vertically through the pad, second bonding plate, polymer layer, adhesive, outlet plate, first bonding plate, and the fixture. The combination of heat and pressure causes the adhesive to tack to the surface of the outlet plate. In the example embodiment of  FIG. 3 , the tacking is complete after 3 minutes of exposure to a temperature of 250° C. at a pressure of 150 psi (block  348 ). 
     The tacked polymer layer and outlet plate combination is extracted from the fixture assembly (block  352 ). The release agent coating on the exposed surfaces of the polymer layer enables the second bonding plate to be removed without distorting the polymer layer and the outlet plate is removed from the first bonding plate. The thermal tape used in the tacking process may be removed as the tacked polymer layer remains in alignment with the outlet plate. The layer of release agent between the second bonding plate and the pad allows the pad to be removed as well. The fixture, bonding plates, and pad may be reused in another tacking process. 
     A process for bonded the polymer layer with bonded adhesive material that is tacked to the outlet plate (block  216 ,  FIG. 2 ) may also be described with reference to  FIG. 3 . The process begins with the fixture and bonding plates being washed (block  304 ) and plasma cleaned (block  308 ) in the same manner described above in order to remove contaminants. The fixture, bonding plates, and pad used for the tacking process may also be used in the bonding process. 
     The bonding process continues with the first bonding plate being aligned and placed above the fixture with the fixture pins passing through tooling holes formed in the first bonding plate&#39;s surface (block  312 ). The target is then placed above the first bonding pad (block  316 ). In this case, the target is the tacked outlet plate and polymer layer. The outlet plate is aligned with the first bonding plate and is placed above the first bonding plate with the fixture pins extending through tooling holes in the outlet plate. The polymer layer faces up from the outlet plate. The polymer layer already has a release agent layer applied to its exposed surface, obviating the need for application of release agent (block  320 ). The second bonding plate is placed above the polymer layer with the fixture pins passing through tooling holes formed in the second bonding plate&#39;s surface (block  328 ). As with the tacking process, a thin layer of release agent is applied to the second bonding plate (block  332 ), a pad is placed above the second bonding plate (block  336 ), and a thin layer of release agent is applied to pad&#39;s upper surface (block  340 ). 
     The assembly formed in blocks  312 - 340  is placed in a heated pressure chamber in order to bond the outlet plate to the polymer layer (block  344 ). Pressure is applied vertically through the pad, second bonding plate, polymer layer, adhesive, outlet plate, first bonding plate, and the fixture. The combination of heat and pressure causes the adhesive to bond to the outlet plate. In the example embodiment of  FIG. 3 , the bonding is complete after 30 minutes of exposure to a temperature of 290° C. at a pressure of 350 psi (block  348 ). The bonded outlet plate and polymer layer combination is extracted from the fixture assembly (block  352 ). The bonding process forms a hermetic seal between the polymer layer and outlet plate. The layer of release agent between the second bonding plate and the pad allows the pad to be removed as well. The fixture, bonding plates, and pad may be reused in another bonding process. 
     The processes disclosed in  FIG. 2  and  FIG. 3  are merely illustrative of possible embodiments for tacking and bonding the polymer layer, adhesive, and outlet plate, and alternative processes are envisioned. A possible alternative process could tack and bond the adhesive material to the outlet plate before tacking and bonding to the polymer layer. In another alternative process, the polymer layer may be formed from a thermoset compound or another form of polymer that is self-adhering. These materials may adhere directly to an outlet plate, and this allows for the process of  FIG. 2  to begin at block  212  by tacking the polymer layer directly to the outlet plate. Another possible embodiment could use polymers that do not require a separate tacking process to align the polymer layer with the outlet plate. These alternatives only require a bonding process, and not a tacking process. Some examples of adhesives that do not require a tacking operation are dispensed liquid adhesives or transfer film adhesives. Active optomechanical alignment of the adhesives and plates may used for one or all of the alignments rather than the tooling pin and slot alignment described above. 
     Two possible assemblies of the process depicted in  FIG. 2  are depicted in  FIG. 4A  and  FIG. 4B .  FIG. 4A  depicts one assembly of layers for bonding the polymer layer  412  to the outlet plate  416  while the polymer layer remains flat. In this embodiment, a rigid plate called a bonding plate  404  is etched or otherwise formed to match the patterns placed in the outlet plate. Thus, recesses in the bonding plate match the channels contained in the outlet plate. In one embodiment the bonding plate may be built from outlet plates. Both the outlet plate and bonding plate may be formed from stainless steel, but could be made from other metals, ceramics, glass, or plastics. The bonding plate is then positioned to align the bonding blank recesses with the outlet plate channels. The outlet plate in  FIG. 4A  is shown in a cross-sectional view through the channels in the outlet plate. 
     Referring again to  FIG. 4A , the polymer layer is placed between the bonding plate and the outlet plate in the final position in which the polymer layer is bonded to the outlet plate. The polymer layer may be formed from a polyimide material or other polymers including polyetherether ketone, polysulfone, polyester, polyethersulfone, polyimideamide, polyamide, polyethylenenaphthalene, etc. The polymer layer can be a self-adhesive thermoplastic or have a thin layer of adhesive deposited on the side of the polymer layer that is placed in contact with the outlet plate. Pressure and heat are applied to the bonding plate, polymer layer, and outlet assembly  400  in order to bond the polymer layer to the outlet plate. In one embodiment having a thin thermoplastic adhesive layer, a pressure of 350 psi is applied at 290° C. for 30 minutes. During the bonding process, the bonding plate places pressure against all of the same portions of the polymer layer that the outlet plate on the opposite of the polymer layer does. This support prevents the bonding plate from warping or deforming the polymer layer portions  420  that span channels in the outlet plate, leaving the polymer layer substantially flat after the bonding is completed. 
     After the bonding process is complete, the bonding plate must be removed without damaging the polymer layer. To this end, the bonding plate may be covered with a layer of release agent  408  that prevents the bonding plate from adhering to the polymer layer during the bonding process. This release agent may be a low surface energy coating such as a fluoropolymer. Alternatively, the release agent may be applied to the polymer layer. In this case, the release agent may also be a low surface energy coating such as a fluoropolymer. 
       FIG. 4B  depicts another possible embodiment for bonding the polymer layer to the outlet plate. In this embodiment, an adhesive layer  424  is placed between the polymer layer  412  and the outlet plate  416 . This adhesive layer bonds the polymer plate to the outlet plate. Suitable film adhesive layers include double sided adhesive tapes having thermoset or thermoplastic adhesive layers on opposite sides of a thermoset or thermoplastic polymer core. Alternatively, the adhesive layer can be a thermoplastic or thermoset adhesive. In yet further alternatives, the adhesive may be dispensed liquid adhesive or a transfer film of liquid adhesive. As in  FIG. 3A , the bonding plate  104  and outlet plate  116  are aligned with the polymer plate  412  in between them. Pressure and heat are then applied to the bonding plate, polymer layer, adhesive, and outlet plate until the bonding is complete. Finally, as in  FIG. 4A , the bonding plate is removed from the polymer layer to leave a substantially planar polymer layer bonded to the outlet plate. 
       FIG. 4C  depicts the flatness of the polymer layer  412  spanning a single channel in the outlet plate  416  after the polymer layer has been bound to the outlet plate. The improved bonding process described above preserves the polymer layer&#39;s shape such that the maximum deviation  428  from a geometrically straight line across a channel opening in the outlet plate, represented by line  432  in  FIG. 4C , does not exceed 1.5 μm. 
     In each embodiment of  FIGS. 4A and 4B , the improved bonding process allows for print heads using longer polymer layers that are at least 20 mm in length. The outlet plate has channels in its surface that carry ink from the print head assembly to apertures formed in the polymer layer. In the embodiments depicted in  FIGS. 4A and 4B , the polymer layer is bonded to the outlet plate before apertures are formed in the polymer layer. After the bonding process is completed, one possible embodiment ablates apertures through the polymer layer using the outlet plate as an alignment feature to locate the apertures precisely. This process turns the polymer layers of  FIGS. 4A and 4B  into the final polymer aperture plate with apertures or nozzles extending through the polymer layer. Other possible embodiments form the apertures in the polymer layer before bonding the polymer layer to the outlet plate. In these embodiments, the apertures in the polymer layer are aligned with the channels in the outlet plate before the polymer aperture layer is bonded to the outlet plate. In the finished print head, ink flows from the outlet plate to the nozzles in the polymer aperture layer and leaves the print head as droplets. 
     In operation, aperture plates are prepared from polymer material bonded to an outlet plate configured with outlets. Apertures are laser ablated in the polymer layer from the outlet plate side to align the apertures precisely with the channels in the outlet plate. The outlet plate may then be attached to a partially constructed inkjet stack to provide outlet channels and apertures for pressure chambers in the inkjet stack. This bonding rigidly positions the apertures and outlet channels with the pressure chambers to form inkjet ejectors that are aligned more precisely even though the more flexible polymer material was used. 
     It will be appreciated that various of the above-disclosed and other features, and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. Various presently unforeseen or unanticipated alternatives, modifications, variations, or improvements therein may be subsequently made by those skilled in the art, which are also intended to be encompassed by the following claims.