Abstract:
An inkjet printhead which includes a substrate having a plurality of individual ink ejection chambers defined by a barrier layer formed on a first surface of said substrate and having an ink ejection element formed on the first surface of said substrate in each of said ink ejection chambers, said ink ejection elements electrically connected to electrodes on said substrate. The printhead further includes a nozzle member constructed of a first material having a predetermined thickness and having a plurality of nozzles formed therein, said nozzle member overlaying and affixed to said barrier layer such that said nozzles align with said ink ejection chambers and said ink ejection elements, said nozzle member including openings aligned with and exposing the electrodes on said substrate and a flexible circuit constructed of a second material and having electrical traces formed thereon, said flexible circuit overlying and affixed to said nozzle member such that a first opening therein exposes said plurality of nozzles, said flexible circuit including second openings therein for exposing the electrical traces bonded to the electrodes, said second openings on said flexible circuit aligned with said nozzle member openings; and an encapsulant in the openings of said nozzle member and the second openings of said flexible circuit for protecting said electrical traces and electrodes.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application relates to the subject matter disclosed in the following U.S. Patent Application and U.S. Patents: 
     U.S. Pat. No. 6,359,463, entitled “Multi-Drop Merge on Media Printing System;” 
     U.S. Pat. No. 6,234,613, entitled “Apparatus for Generating Small Volume, High Velocity Ink Droplets in an Inkjet Printer;” 
     U.S. Pat. No. 5,852,460, entitled “Inkjet Print Cartridge Design to Decrease Deformation of the Printhead When Adhesively Sealing the Printhead to the Print Cartridge.” 
     U.S. Pat. No. 5,736,998, entitled “Inkjet Cartridge Design for Facilitating the Adhesive Sealing of a Printhead to an Ink Reservoir;” 
     U.S. Pat. No. 5,450,113, entitled “Adhesive Seal for an Inkjet Printhead;” 
     U.S. Patent Application Ser. No. 09/302,837, filed Apr. 30, 1999, entitled “Inkjet Print Cartridge Design to Decrease Ink Shorts Due to Ink Penetration of the Printhead;” 
     U.S. Pat. No. 6,244,696, entitled “Inkjet Print Cartridge Design for Decreasing Ink Shorts By Using an Elevated Substrate Support Surface to Increase Adhesive Sealing of the Printhead from Ink Penetration;” 
     U.S. Pat. No. 5,442,384, entitled “Integrated Nozzle Member and TAB Circuit for Inkjet Printhead;” 
     U.S. Pat. No. 5,278,584, entitled “Ink Delivery System for an Inkjet Printhead;”and 
     U.S. Pat. No. 5,291,226, entitled “Nozzle Member Including Ink Flow Channels.” 
     The above patents are assigned to the present assignee and are incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention generally relates to inkjet printers and, more particularly, to the printhead portion of an inkjet print cartridge. 
     BACKGROUND OF THE INVENTION 
     Inkjet printers have gained wide acceptance. These printers are described by W. J. Lloyd and H. T. Taub in “Ink Jet Devices,” Chapter 13 of  Output Hardcopy Devices  (Ed. R. C. Durbeck and S. Sherr, San Diego: Academic Press, 1988) and U.S. Pat. Nos. 4,490,728 and 4,313,684. Inkjet printers produce high quality print, are compact and portable, and print quickly and quietly because only ink strikes the paper. 
     An inkjet printer forms a printed image by printing a pattern of individual dots at particular locations of an array defined for the printing medium. The locations are conveniently visualized as being small dots in a rectilinear array. The locations are sometimes “dot locations”, “dot positions”, or pixels”. Thus, the printing operation can be viewed as the filling of a pattern of dot locations with dots of ink. 
     Inkjet printers print dots by ejecting very small drops of ink onto the print medium and typically include a movable carriage that supports one or more printheads each having ink ejecting nozzles. The carriage traverses over the surface of the print medium, and the nozzles are controlled to eject drops of ink at appropriate times pursuant to command of a microcomputer or other controller, wherein the timing of the application of the ink drops is intended to correspond to the pattern of pixels of the image being printed. 
     The typical inkjet printhead (i.e., the silicon substrate, structures built on the substrate, and connections to the substrate) uses liquid ink (i.e., dissolved colorants or pigments dispersed in a solvent). It has an array of precisely formed nozzles attached to a printhead substrate that incorporates an array of ejection chambers which receive liquid ink from the ink reservoir. Each chamber has a thin-film ink ejection element, known as a inkjet ejection chamber ink ejection element, located opposite the nozzle so ink can collect between it and the nozzle. The ejection of ink droplets is typically under the control of a microprocessor, the signals of which are conveyed by electrical traces to the ink ejection element elements. When electric printing pulses heat the inkjet ejection chamber ink ejection element, a small portion of the ink next to it vaporizes and ejects a drop of ink from the printhead. Properly arranged nozzles form a dot matrix pattern. Properly sequencing the operation of each nozzle causes characters or images to be printed upon the paper as the printhead moves past the paper. 
     The ink cartridge containing the nozzles is moved repeatedly across the width of the medium to be printed upon. At each of a designated number of increments of this movement across the medium, each of the nozzles is caused either to eject ink or to refrain from ejecting ink according to the program output of the controlling microprocessor. Each completed movement across the medium can print a swath approximately as wide as the number of nozzles arranged in a column of the ink cartridge multiplied times the distance between nozzle centers. After each such completed movement or swath the medium is moved forward the width of the swath, and the ink cartridge begins the next swath. By proper selection and timing of the signals, the desired print is obtained on the medium. 
     In U.S. Pat. No. 5,442,384, entitled “Integrated Nozzle Member and TAB Circuit for Inkjet Printhead,” a novel nozzle member for an inkjet print cartridge and method of forming the nozzle member are disclosed. A flexible circuit tape having conductive traces formed thereon has formed in it nozzles or orifices by Excimer laser ablation. The resulting flexible circuit having nozzles and conductive traces may then have mounted on it a substrate containing heating elements associated with each of the nozzles. The conductive traces formed on the back surface of the flexible circuit are then connected to the electrodes on the substrate and provide energization signals for the heating elements. A barrier layer, which may be a separate layer or formed in the nozzle member itself, includes ejection chambers, surrounding each orifice, and ink flow channels which provide fluid communication between a ink reservoir and the ejection chambers. 
     In U.S. Pat. No. 5,648,805, entitled “Adhesive Seal for an inkjet Printhead,” a procedure for sealing an integrated nozzle and flexible or tape circuit to a print cartridge is disclosed. A nozzle member containing an array of nozzles has a substrate, having heater elements formed thereon, affixed to a back surface of the flexible circuit. Each orifice in the flexible circuit is associated with a single heating element formed on the substrate. The back surface of the flexible circuit extends beyond the outer edges of the substrate. Ink is supplied from an ink reservoir to the nozzles by a fluid channel within a barrier layer between the flexible circuit and the substrate. In either embodiment, the flexible circuit is adhesively sealed with respect to the print cartridge body by forming an ink seal, circumscribing the substrate, between the back surface of the flexible circuit and the body. This method and structure of providing a seal directly between a flexible circuit and an ink reservoir body has many advantages. Also, in U.S. Pat. No. 5,736,998, entitled “Inkjet Cartridge Design for Facilitating the Adhesive Sealing of a Printhead to an Ink Reservoir,” and U.S. Pat. No. 5,852,460, entitled “Inkjet Print Cartridge Design to Decrease Deformation of the Printhead When Adhesively Sealing The Printhead to the Print Cartridge;” improved headland designs are disclosed which alleviate some of the above-mentioned problems. 
     Flexible circuit leads are bonded to pads or electrodes on the outer edges of the substrate. To enable this bonding, a window is created in the flexible circuit to allow a bonder thermode to apply force and temperature to the flexible circuit leads that are resting on the bond pads. After the leads have been bonded, an encapsulant is dispensed across the window to protect the exposed bond pad region from intrusion of ink or contamination. 
     By providing the nozzles in the flexible circuit itself, the shortcomings of conventional electroformed nozzle members are overcome. This integrated nozzle and tab circuit design is superior to the nozzle members for inkjet printheads formed of nickel and fabricated by lithographic electroforming processes. 
     In U.S. Pat. No. 5,450,114, entitled “Adhesive Seal for an Inkjet Printhead,” a procedure for sealing an integrated nozzle and tab circuit to a print cartridge is disclosed. See also U.S. Pat. No. 5,736,958, entitled “Inkjet Cartridge Design for Facilitating the Adhesive Sealing of a Printhead to an Ink Reservoir.” 
     However, the above designs did not address the problem of “dimples” being formed in the nozzle member caused by bending of the nozzle member due to the stresses created by the adhesive process of sealing the nozzle member to the print cartridge. This dimpling of the nozzle member creates nozzles which are skewed causing trajectory errors for the ejected ink droplets from the nozzles. When the TAB head assembly is scanned across a recording medium the ink trajectory errors will affect the location of printed dots and thus affect the quality of printing. 
     In a typical edge-feed inkjet printhead assembly  14  the flexible circuit  18  serves as both an nozzle member  16  and as a carrier of the conductor traces  36 . There are several fundamental problems with this design approach. First, the conductor traces  36  must be protected with a cover layer  38  to prevent electrical shorting and corrosion and it is difficult to design a cover layer  38  and an adhesive  90  that is resistant to a wide range of inks and also has good adhesion to both the print cartridge  10  body and the flexible circuit  18  material. Second, most head-to-body adhesives de-laminate from the flexible circuit over time. When this occurs, inks can readily penetrate the cover layer adhesive and cause electrical shorting and corrosion. Third, on edge-feed print cartridges, there is an unprotected region between the edge of the cover layer and the substrate. Here, the conductor traces are susceptible to shorting and corrosion if ink penetrates between the structural adhesive and the flexible circuit. This gap is necessary because of the cover layer placement tolerances in manufacturing. The nozzle member material, thickness, and manufacturing processes cannot be optimized independently from that of the flexible circuit, even though each has very different functional requirements. 
     Accordingly, it would be advantageous to have an improved printhead design which reduces dimpling of the nozzle member and ink penetration and shorting of the substrate electrodes and flexible circuit leads. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention an inkjet printhead includes a substrate having a plurality of individual ink ejection chambers defined by a barrier layer formed on a first surface of said substrate and having an ink ejection element formed on the first surface of said substrate in each of said ink ejection chambers, said ink ejection elements electrically connected to electrodes on said substrate. The printhead further includes a nozzle member constructed of a first material having a predetermined thickness and having a plurality of nozzles formed therein, said nozzle member overlaying and affixed to said barrier layer such that said nozzles align with said ink ejection chambers and said ink ejection elements, said nozzle member including openings aligned with and exposing the electrodes on said substrate and a flexible circuit constructed of a second material and having electrical traces formed thereon, said flexible circuit overlying and affixed to said nozzle member such that a first opening therein exposes said plurality of nozzles, said flexible circuit including second openings therein for exposing the electrical traces bonded to the electrodes, said second openings on said flexible circuit aligned with said nozzle member openings; and an encapsulant in the openings of said nozzle member and the second openings of said flexible circuit for protecting said electrical traces and electrodes. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of an inkjet print cartridge. 
     FIG. 2 is a plan view of the front surface of a printhead assembly removed from a print cartridge. 
     FIG. 3 is a highly simplified perspective view of the back surface of the printhead assembly of FIG. 2 with a silicon substrate mounted thereon and the conductive leads attached to the substrate. 
     FIG. 4 is a side elevational view in cross-section taken along line A—A in FIG. 3 illustrating the attachment of conductive leads to electrodes on the silicon substrate for an integrated flexible circuit and nozzle member. 
     FIG. 5 is a perspective view of the headland area of the inkjet print cartridge of FIG. 1 with the printhead assembly removed. 
     FIG. 6 is a schematic cross-sectional view taken along line B—B of FIG. 1 showing the printhead assembly and the print cartridge body. 
     FIG. 7 is a schematic perspective view of a decoupled flexible circuit and nozzle member and the headland area of a print cartridge body. 
     FIG. 8 is a schematic cross-sectional view taken along line B—B of FIG. 1 showing a decoupled printhead assembly and the print cartridge body. 
     FIG. 9 is a side elevational view in cross-section illustrating the attachment of conductive leads to electrodes on the silicon substrate for a decoupled flexible circuit and nozzle member. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIG. 1, reference numeral  10  generally indicates an inkjet print cartridge incorporating a printhead according to one embodiment of the present invention. The inkjet print cartridge  10  includes an internal ink reservoir (not shown) and a printhead formed using Tape Automated Bonding (TAB). The printhead or TAB head assembly  14  includes a nozzle member  16  comprising two parallel columns of offset holes or nozzles  17  formed in a flexible polymer flexible circuit  18  by, for example, laser ablation. The flexible circuit  18  provides for the routing of conductive traces  36  which are connected at one end to electrodes on a substrate and on the other end to contact pads  20 . The print cartridge  10  is designed to be installed in a printer so that the contact pads  20  on the front surface of the flexible circuit  18 , contact printer electrodes providing externally generated energization signals to the printhead. 
     FIG. 2 shows a front view of a TAB head assembly  14  removed from a print cartridge  10 . TAB head assembly  14  has affixed to the back of the flexible circuit  18  a silicon substrate  28  containing a plurality of individually energizable ink ejection elements. Each ink ejection element is located generally behind a single orifice  17  and acts as an ohmic heater when selectively energized by one or more pulses applied sequentially or simultaneously to one or more of the contact pads  20 . 
     Flexible circuit leads  37  are bonded to pads or electrodes  40  on the outer edges of the substrate  28 . To enable this bonding, a windows  22 ,  24  which extend through the flexible circuit  18  are created in the flexible circuit  18  to allow a bonder thermode to apply force and temperature to the flexible circuit leads  37  that are resting on the bond pads  40 . The windows  22 ,  24  in the TAB head assembly  14  are chemically milled in the flexible circuit  18 . Earlier during intermediate assembly of the TAB head assembly  14  after the leads  37  have been bonded to the bond pads  40 , an encapsulant  34  is dispensed across the windows  22 ,  24  from the top to protect the exposed bond pad region from intrusion of ink or contamination. 
     The portion of the windows  22 ,  24  which are off the substrate extend back approximately to the location on the flexible circuit  18  where the laminated cover layer  38  of the flexible circuit  18  terminates. Thus, the openings in windows  22 ,  24  must be large enough to be open near the end of the cover layer  38  so that the leads  37  without any cover layer  38  are fully encapsulated by adhesive  90  and encapsulant  34 . For additional details on intermediate assembly, see U.S. Pat. No. 5,442,384, entitled “Integrated Nozzle Member and TAB Circuit for Inkjet Printhead;” and U.S. Pat. No. 5,278,584 to Keefe, et al., entitled “Ink Delivery System for an Inkjet Printhead;” which are herein incorporated by reference. 
     The nozzles  17  and conductive traces  36  may be of any size, number, and pattern, and the various figures are designed to simply and clearly show the features of the invention. The relative dimensions of the various features have been greatly adjusted for the sake of clarity. 
     FIG. 3 shows a highly simplified view of the back surface of a TAB head assembly  14 . The back surface of the flexible circuit  18  includes conductive traces  36  formed thereon using a conventional photolithographic etching and/or plating process. The silicon die or substrate  28  is mounted to the back of the flexible circuit  18  with the ink ejection chambers  32  aligned with the nozzles or orifices  17 . The conductive traces  36  are terminated by leads  37  that are bonded to bond pads or electrodes  40  on the substrate  28  and on the other end by contact pads  20  as discussed above. Also shown is one edge of the barrier layer  30  containing ejection chambers  32  formed on the substrate  28 . Shown along the edge of the barrier layer  30  are the entrances to the ejection chambers  32  which receive ink from an internal ink reservoir within the print cartridge  10 . 
     FIG. 4 shows a side view cross-section taken along line A—A in FIG. 3 illustrating the connection of the leads  37  of the conductive traces  36  to the electrodes  40  formed on the substrate  28 . A portion  42  of the barrier layer  30  is used to insulate the conductive traces  36  from the substrate  28 . Also shown is the flexible circuit  18 , the barrier layer  30 , the windows  22  and  24  and the entrances to the ink ejection chambers  32 . Also shown is the encapsulant  34  that is dispensed into the windows  22 ,  24  after bonding of the leads  37  to the bond pads  40  to insulate the leads  37  and conductive traces  36 . Droplets of ink  100  are shown being ejected from nozzles  17  associated with each of the ink ejection chambers  32 . 
     FIG. 5 shows the headland area  50  of the print cartridge body  12  of FIG. 1 in a perspective view and with the TAB head assembly  14  removed to reveal the headland design used in providing a seal between the TAB head assembly  14  and the body  12  of the print cartridge  10 . Shown are an inner raised wall  54 , an adhesive support surface  53  on the inner raised wall, openings  55  in the inner raised wall  54 , a substrate support surface  58 , a flat top surface  59  and a gutter  61 . Also shown are adhesive ridges  57  and the area  56  on the substrate support surface  58  between the adhesive ridges  57 . Adhesive  90  is dispensed along the adhesive support surface  53  of inner raised wall  54  and across substrate support surface  58  in the wall openings  55  of the inner raised wall  54  and adjacent to and suspended off adhesive ridges  57 . 
     As the TAB head assembly  14  is pressed down onto the headland  50 , the adhesive  90  is squished down. The adhesive squishes through the wall openings  55  in the inner raised wall to encapsulate the traces leading to electrodes on the substrate. The adhesive  90  also squishes both inwardly and upwardly through the windows  22 ,  24  and flush with the bottom surface of the encapsulant and partially encapsulates the exposed leads  37 . 
     This seal formed by the adhesive  90  circumscribing the substrate  28  allows ink to flow around the sides of the substrate  28  to the ejection chambers  32  formed in the barrier layer  30 , but prevents ink from seeping out from under the TAB head assembly  14 . Thus, this adhesive seal  90  provides a strong mechanical coupling of the TAB head assembly  14  to the print cartridge  10 , a fluidic seal and flexible circuit trace  36  encapsulation. 
     FIG. 6 is a cross-sectional view taken along line B—B of FIG. 1 showing ink ejection chambers  32 , ink ejection elements  70 , and nozzles  17  after the barrier layer  30  and substrate  28  are secured to the back of the flexible circuit  18  at location  84  and the flexible circuit is secured to the body of the print cartridge  10  by adhesive  90 . A side edge of the substrate  28  is shown as  86 . In operation, ink flows from reservoir  12  around the side edge  86  of the substrate  28 , and into ink ejection chamber  32 , as shown by the arrow  88 . Upon energization of the ink ejection element  70 , a thin layer of the adjacent ink is superheated, causing a droplet of ink  100  to be ejected through the orifice  17 . The ink ejection chamber  32  is then refilled with ink by capillary action. Also shown is a portion of the adhesive seal  90 , applied to the inner raised wall  54  surrounding the substrate  28 . 
     In a typical inkjet printhead assembly the flexible circuit  18  serves both as the nozzle member  16  and as the carrier of the conductor traces  36 . There are several fundamental problems with this design approach. First, the nozzle member  16  material, thickness and manufacturing processes cannot be optimized independently from that of the flexible circuit  18 , even though each has very different functional requirements. Second, the conductor traces  36  must be protected with a cover layer  38  to prevent electrical shorting and corrosion. Third, it is difficult to design a cover layer  38  and an adhesive  90  that is resistant to a wide range of inks while also having good adhesion to both the print cartridge  10  body and flexible circuit  18  material. Fourth, most printhead-to-headland adhesives de-laminate from the flexible circuit  18  over time. When this occurs, inks can readily penetrate the cover layer  38  and adhesive  90  to cause electrical shorting and corrosion. Fifth, as shown in FIG. 4, in edge-feed print cartridges there is an unprotected region between the end of the cover layer  38  and the substrate  28 . Here, the conductor traces  36  are susceptible to shorting and corrosion if ink penetrates between the structural adhesive  90  and the flexible circuit  18 . 
     More importantly, prior printhead designs have not addressed the problem of dimples being created in nozzle member  16  and flexible circuit  18  of TAB head assembly  14  by the bending or deformation of the nozzle member  16  and flexible circuit  18  due to the stresses created by the adhesive process of sealing the nozzle member  16  to the headland  50  of the print cartridge  10 . This dimpling of the nozzle member  16  creates nozzles  17  which are skewed causing trajectory errors for the ejected ink droplets from the nozzles. Also, the nozzle member  16  is susceptible to wiper induced ruffles around the nozzle  17  exits which adversely affect drop ejection performance and thus print quality. 
     In addition, the flexible circuit  18  thickness has to be matched to the other printhead parameters such as the dimensions of the ink ejection chamber  32 , ink ejection element  70 , barrier layer  30  thickness, nozzle diameters, as well as the ink formulation. Simply reducing the above dimensions reduces the volume of the ejected drops, but creates ink drops with a low ejection velocity. A standard two mil (50.8 micron) flexible circuit  18  creates a long nozzle when the dimensions are decreased to obtain low drop volumes. Consequently, drops are ejected at a velocity which is too low. Accordingly, a one mil flexible circuit  18  needs to be used in order to obtain sufficient drop ejection velocity. However, a one mil flexible circuit being one-half as thick and has less stiffness than a two mil flexible circuit. Therefore, dimpling and bending of the flexible circuit  18  and wiper induced ruffles around the exit of nozzles  17  is increased. Moreover, matching flexible circuit thickness to nozzle length limits design freedom because the thickness independent of the thickness of the flexible circuit and nozzle member have different functional requirements. Accordingly, it would be advantageous to adjust the nozzle member  16  thickness independent of the thickness of the flexible circuit  18 . 
     By decoupling the nozzle member from the flexible circuit there is freedom to use a thin stiff material for the nozzle member  16  and a thicker flexible material for the flexible circuit  18 . As discussed above, thin nozzle members are needed with very low drop volume print cartridges to achieve drop velocities comparable to higher drop volume print cartridges. If the drop velocity is too low, image quality will be degraded. 
     FIGS. 7,  8  and  9  illustrate the decoupled nozzle member-flexible circuit printhead assembly  14  of the present invention. Referring to FIG. 7, the present invention is a de-coupled printhead assembly  14  wherein the nozzle member  16  has the ablated nozzles  17  and the flexible circuit  18 ′ carries the conductive traces  36 . Accordingly, the nozzle member  16  and the flexible circuit  18 ′ may be made of different materials based on the individual functional requirements of the flexible circuit and nozzle member. Suitable materials for the nozzle member  16  and flexible circuit  18 ′ include teflon, polyimide, polymethylmethacrylate, polycarbonate, polyester, polyimide polyethylene-terephthalate or mixtures thereof. In a preferred embodiment of the present invention, the de-coupled the flexible circuit  18 ′ can be made of a flexible material such as Kapton™ while the nozzle member  16  can be constructed of a stiffer, more ink resistant material such as Upilex™ polyimide. Upilex has better dimensional retention over life and is less susceptible to dimpling and wiper induced ruffles around the nozzle  17  exits which adversely affect drop ejection performance and thus print quality. 
     Referring to FIG. 7, the flexible circuit  18 ′ is aligned and positioned with respect to de-coupled nozzle member  16  so that the opening  26  in the flex circuit is aligned with the array of nozzles  17  in the nozzle member  16  and so that the windows  22 ,  24  in the flex circuit  18 ′ are aligned with the windows  23 ,  25  in the nozzle member. The nozzle member  16  and the flexible circuit  18 ′ may be joined together with an adhesive  44  (shown in FIGS. 8 and 9) or by heat staking. In this decoupled printhead assembly, the active conductor traces  36  are still on the bottom side of the flexible circuit  18 ′, but conductor traces  36  are protected by the nozzle member  16  which is attached to the bottom side of the flexible circuit  18 ′. Accordingly, the cover layer  38  covering the conductive traces  36  may be eliminated. Also shown in FIG. 7 is a highly schematic drawing of the headland area of the print cartridge body  12 . 
     FIG. 8 is a schematic cross-sectional view taken along line B—B of FIG. 1 showing a decoupled printhead assembly  14  and the print cartridge body  12 . FIG. 9 is a side elevational view in cross-section illustrating the attachment of conductive leads  37  to electrodes  40  on the silicon substrate  28  in the window  22 ,  24  in the flexible circuit  18 ′ and the window  23 ,  25  in the nozzle member  16 . 
     Referring to FIG. 8, the substrate  28  is aligned and positioned with respect to the back surface of the de-coupled nozzle member  16  so as to align the ink ejection chambers  32  formed in the barrier layer  30  and the ink ejection elements  70  formed on the substrate  28  with the nozzles  17  formed in the decoupled nozzle member  16 . Referring to FIG. 9, this alignment step also inherently aligns the electrodes  40  on the substrate  28  with the leads  37  of the conductive traces  36  on flexible circuit  18 ′ which has been previously affixed to the nozzle member  16 . The top surface  84  of the barrier layer  30  is then affixed to the back surface of the decoupled nozzle member  16  by heat bonding or an adhesive. The conductive traces  36  are then bonded to the electrodes  40  and the encapsulant  34  is dispensed into the windows  22 ,  24  and  23 ,  25  as shown in FIG.  9 . The printhead assembly  14  is then attached to the headland area  50  of the print cartridge body  12  as discussed above. 
     Referring to FIG. 9, the unprotected region between the end of the cover layer  38  and the substrate  28  (see FIG. 4) is eliminated. With the de-coupled printhead assembly  14  of the present invention, the nozzle member  16  and adhesive  44  act as the protective layer. However, unlike the cover layer  38 , the nozzle member  16  does not terminate near the end of the substrate  28 , but is continuous across the entire headland area  50 , thus providing a barrier between the ink and the conductor traces  36  which now are located above the nozzle member  16 . 
     By eliminating the cover layer  38 , the substrate  28  is exposed to fewer thermal stresses during manufacturing. During manufacturing of the print cartridge constructed as in FIGS. 2-4, the protective cover layer  38  is applied after substrate  28  attachment to the flexible circuit  18 . With the present invention, the flexible circuit  18 ′ and the nozzle member  16  are joined prior to substrate  28  attachment and the need for a multi-layer protective cover layer  38  and its associated thermal curing are eliminated. 
     The foregoing has described the principles, preferred embodiments and modes of operation of the present invention. However, the invention should not be construed as being limited to the particular embodiments discussed. As an example, the above-described inventions can be used in conjunction with inkjet printers that are not of the thermal type. Thus, the above-described embodiments should be regarded as illustrative rather than restrictive, and it should be appreciated that variations may be made in those embodiments by workers skilled in the art without departing from the scope of the present invention as defined by the following claims.