Abstract:
An apparatus is provided, the apparatus including a printhead die, a base coupled to the printhead die, a flexible circuit mounted on the base and electrically connected to the printhead, and an adhesive sandwiched between the base and the flexible circuit. The base defines a trench with a sidewall having scallops formed therein. The adhesive is disposed in the trench to secure the flexible circuit to the base.

Description:
BACKGROUND 
     An inkjet printing system may include a printhead, an ink supply which supplies liquid ink to the printhead, and an electronic controller which controls the printhead. The printhead ejects drops of ink through a plurality of nozzles or orifices and toward a print medium, such as a sheet of paper, so as to print onto the print medium. Typically, the orifices are arranged in one or more columns or arrays such that properly sequenced ejection of ink from the orifices causes characters or other images to be printed upon the print medium as the printhead and the print medium are moved relative to each other. The printhead may be connected to the electrical controller via a flex circuit, which may be secured to a base that carries the printhead. Typically, the flex circuit is secured to the base via an adhesive that may be sandwiched between the flex circuit and the base. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram illustrating an inkjet printing system according to an embodiment of the invention. 
         FIG. 2  is a perspective view illustrating an inkjet print cartridge according to an embodiment of the invention. 
         FIG. 3  is an exploded perspective view showing the inkjet print cartridge of  FIG. 2 . 
         FIG. 4  is a plan view showing a print cartridge base configured to receive a flex circuit according to an embodiment of the invention. 
         FIG. 5  is an enlarged fragmentary perspective view showing an example sealing zone of a print cartridge base. 
         FIG. 6  is an enlarged fragmentary perspective view showing another example sealing zone of a print cartridge base. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  illustrates an inkjet printing system  10  including a fluid ejection system employing a fluid ejection device, such as printhead assembly  12 , and a fluid supply, such as ink supply assembly  14 . In the illustrated example, inkjet printing system  10  also includes a mounting assembly  16 , a media transport assembly  18 , and an electronic controller  20 . 
     Printhead assembly  12 , as one example of a fluid ejection device, is formed according to an example of the present invention and ejects drops of printing fluid, such as black and colored inks, via a plurality of ejection elements  13 . While the following description refers to the ejection of ink from printhead assembly  12 , it is understood that other liquids, fluids, or flowable materials may be ejected from printhead assembly  12 . 
     In one example, the drops are directed toward a medium, such as print media  19 , so as to print onto print media  19 . Typically, nozzles  13  are arranged in columns or arrays such that properly sequenced ejection of ink from the nozzles causes, in one example, characters, symbols, and/or other graphics or images to be printed upon print media  19  as printhead assembly  12  and print media  19  are moved relative to each other. 
     Print media  19  includes, for example, paper, card stock, envelopes, labels, transparent film, cardboard, rigid panels, and the like. In one example, print media  19  is a continuous form or continuous web print media  19 . As such, print media  19  may include a continuous roll of unprinted paper. 
     Ink supply assembly  14 , as one example of a fluid supply, supplies ink to printhead assembly  12  and includes a reservoir  15  for storing ink. As such, ink flows from reservoir  15  to printhead assembly  12 . In some examples, ink supply assembly  14  and printhead assembly  12  may form a recirculating ink delivery system. As such, ink may flow back to reservoir  15  from printhead assembly  12 . Printhead assembly  12  and ink supply assembly  14  may be housed together in a print cartridge or pen, as identified by dashed line  30 . In some examples, the ink supply assembly may be separate from the printhead assembly, and may supply ink to the printhead assembly through an interface connection, such as a supply tube (not shown). 
     Mounting assembly  16  positions printhead assembly  12  relative to media transport assembly  18 , and media transport assembly  18  positions print media  19  relative to printhead assembly  12 . As such, a print zone  17  within which printhead assembly  12  deposits ink drops is defined in an area between printhead assembly  12  and print media  19 . During printing, print media  19  is advanced through print zone  17  by media transport assembly  18 . 
     Printhead assembly  12  may take the form of a scanning-type printhead assembly, where mounting assembly  16  moves printhead assembly  12  relative to media transport assembly  18  and print media  19  during printing of a swath on print media  19 . 
     Electronic controller  20  communicates with printhead assembly  12 , mounting assembly  16 , and media transport assembly  18 . Electronic controller  20  receives data  21  from a host system, such as a computer, and includes memory for temporarily storing data  21 . Typically, data  21  is sent to inkjet printing system  10  along an electronic, infrared, optical or other information transfer path. Data  21  represents, for example, a document and/or file to be printed. As such, data  21  forms a print job for inkjet printing system  10  and includes one or more print job commands and/or command parameters. 
     Electronic controller  20  typically provides control of printhead assembly  12  including timing control for ejection of ink drops by ejection elements  13 . As such, electronic controller  20  defines a pattern of ejected ink drops which form characters, symbols, and/or other graphics or images on print media  19 . Timing control and, therefore, the pattern of ejected ink drops, is determined by the print job commands and/or command parameters. In one example, logic and drive circuitry forming a portion of electronic controller  20  is located on printhead assembly  12 . In another example, logic and drive circuitry forming a portion of electronic controller  20  is located off printhead assembly  12 . 
     Although not shown in  FIG. 1 , inkjet printing system  10  may include a printhead servicing assembly, such as a priming assembly, or the like. As will be described further below, printing device  10  is configured to reduce leakage during priming to enhance effectiveness of priming and to reduce cross-contamination. 
     Turning now to  FIG. 2 , an example print cartridge is shown at  30 , the print cartridge including a printhead assembly  12  and a printing fluid supply in the form of ink supply assembly  14 . The printhead assembly and ink supply cartridge may be coupled or joined together to form print cartridge  30 . Print cartridge  30  thus may include a body or housing  32  which supports printhead assembly  12  and contains reservoir  15  ( FIG. 1 ) of ink supply assembly  14 . As such, reservoir  15  communicates with printhead assembly  12  to supply ink to printhead assembly  12 . In other examples, body  32  may receive fluid from a remote fluid supply. 
     As shown in  FIG. 2 , housing  32  also supports an electrical circuit  40 , which facilitates communication of electrical signals between electronic controller  20  ( FIG. 1 ) and printhead assembly  12  for controlling and/or monitoring operation of printhead assembly  12 . Electrical circuit  40  includes a plurality of electrical contacts  42  and a plurality of conductive paths  44 , which extend between and provide electrical connection between electrical contacts  42  and printhead assembly  12 . Electrical contacts  42  provide points for electrical connection with print cartridge  30  and, more specifically, with printhead assembly  12 . As such, electrical contacts  42  facilitate communication of power, ground, and/or data signals to printhead assembly  12 . In some examples, electrical circuit  40  may be supported by print cartridge  30  such that electrical contacts  42  are provided along a side  34  of housing  32  of print cartridge  30 . 
     Electrical circuit  40  may be a flexible electrical circuit. As such, conductive paths  44  may be formed in one or more layers of a flexible base material  46 . Base material  46  may include, for example, a polyimide or other flexible polymer material (e.g., polyester, poly-methyl-methacrylate) and conductive paths  44  may be formed of copper, gold, or other conductive material. 
     Printhead assembly  12  is a modular printhead assembly formed of separate components including a base  50 , one or more substrates  60  ( FIG. 3 ), and one or more printhead die  70 . Base  50  and substrates  60  mate with each other and are configured such that base  50  and substrates  60  provide mechanical support for and accommodate fluidic routing to printhead die  70 . 
     In the present example, housing  32  includes isolated internal chambers (collectively referred to as reservoir  15 ) for supplying distinct fluids to the printheads. A first color of ink thus may be supplied to one printhead, while a second distinct color of ink may be supplied to another printhead. In some examples, plural colors may be supplied to a single printhead. For purposes of this disclosure, with reference to inks, the term “color” includes black inks. 
     Referring now to  FIGS. 2 and 3 , base  50  has a first side surface  52  and a second side surface  54 , which is opposite first side surface  52 . In one example, base  50  is supported by housing  32 . More specifically, first side surface  52  of base  50  is secured to or mounted on a side  36  of housing  32 . Fluid outlets  38  (in fluid communication with the internal chambers of reservoir  15  ( FIG. 1 )) are provided on side  36  of housing  32 . Base  50  is mounted on side  36  of housing  32  so as to accommodate fluidic coupling with housing  32  and/or communicate with fluid outlets  38 . 
     Base  50  is secured to or mounted on housing  32  so as to provide a fluid-tight seal with housing  32 . For example, first side surface  52  of base  50  may be secured to or mounted on side  36  of housing  32  by use of an adhesive  80  provided between base  50  and housing  32 . Other connection methods providing a fluid-tight seal between base  50  and housing  32  may also be used. 
     In one example, base  50  further includes ramped surfaces  56 . Ramped surfaces  56  are provided on opposite ends of second side surface  54  of base  50  and aid in preventing crashes between printhead assembly  12  and print media  19  ( FIG. 1 ) as printhead assembly  12  and print media  19  are moved relative to each other during printing. 
     Base  50  defines one or more pockets  58  into which one or more substrates  60  are fit. Pockets  58  are open at least to second side surface  54  of base  50 , and are sized and configured to receive and support substrates  60 . Although base  50  is illustrated and described herein as having two pockets  581 ,  582 , each receiving and supporting one substrate  601 ,  602 , it is within the scope of the present invention for base  50  to have any number of pockets  58 , each receiving and supporting one or more substrates  60 . 
     As indicated in  FIG. 3 , substrates  60  each have a first side surface  62 , and a second side surface  64 , which is opposite first side surface  62 . Substrates  60  are fit or received within respective pockets  58  of base  50 . More specifically, substrates  60  are fit or received within pockets  581 ,  582  such that second side surface  64  of each substrate  601 ,  602  is adjacent second side surface  54  of base  50 . As such, pockets  581 ,  582  position substrates  601 ,  602  relative to housing  32 , and position substrates  601 ,  602  for supporting printhead dies  701 ,  702 . In some examples, pockets  58  and/or substrates  60  include features (e.g., datum pads and/or lockout features) to ensure correct orientation and retention (e.g., press fit) of substrates  60  within pockets  58 . 
     Substrates  601 ,  602  may be formed of a plastic, ceramic, glass, or other suitable material. When substrates  601 ,  602  are formed of a plastic material, filler materials such as glass, carbon fibers, minerals, or other suitable filler materials may also be used. In addition, substrates  601 ,  602  may be formed by a number of methods such as injection molding, pressing, machining, or etching depending on the substrate material. 
     Substrates  601 ,  602  are secured or mounted within pockets  581 ,  582  so as to provide a fluid-tight seal with base  50 . For example, first side surface  62  of each substrate  601 ,  602  may be secured or mounted within a corresponding pocket  581 ,  582  by use of an adhesive  82  provided between substrates  601 ,  602  and base  50 . Other connection methods providing a fluid-tight seal between substrates  60  and base  50  also may be used. 
     An area or footprint of each substrate  601 ,  602  may be approximately the same as an area or footprint of a respective printhead die  701 ,  702  to provide support for the respective printhead die  701 ,  702 . More specifically, a length and a width of second side surface  64  of each substrate  601 ,  602  approximates (or is substantially equal to) a length and a width of a respective printhead die  701 ,  702 . In addition, substrates  601 ,  602  have fluid passages  66  formed therethrough. Fluid passages  66  communicate with first side surface  62  and second side surface  64  of substrates  601 ,  602  and provide fluidic routing for printhead dies  701 ,  702 . 
     In one example, each printhead die  701 ,  702  includes a thin-film structure formed on a die substrate. The die substrates are formed, for example, of silicon, glass, or a stable polymer, and the thin-film structure includes a conductive layer and one or more passivation or insulation layers. 
     Each printhead die  701 ,  702  defines a one or more fluid slots (not shown), which communicate printing fluid from printing fluid supply  14  to ejection elements  13  ( FIG. 1 ) formed on the printhead die. The ejection elements, in turn, eject fluid through nozzles of corresponding nozzle arrays  72 . Each nozzle array  72  may be associated with a different printing fluid, according to the particular printing parameters desired. Although nozzle arrays  72  are shown as each including a single column of nozzles, each nozzle array may include one, two or more columns of nozzles fed by a single fluid slot. Other nozzle configurations also are possible. 
     Printhead dies  701 ,  702  may be joined with or mounted on flexible circuit  40  such that printhead dies  701 ,  702  and electrical circuit  40  are supported by substrates  601 ,  602 , respectively, and base  50 . In some examples, a portion of flexible circuit  40  extends beneath or underlies a printheads dies  701 ,  702 , facilitating connection between flexible circuit  40  and printhead dies  701 ,  702 . Flexible circuit  40  bends and wraps around and is supported by side  34  of housing  32  of print cartridge  30 . Flexible circuit  40  is coupled to or retained along a side or sides of housing  32  so as to not interfere with printing. In some examples, a printed circuit assembly, or “PCA”, (not shown) may be rigidly mounted to housing  32 , and flexible circuit  40  may be soldered to the PCA. Contact Pads  42  thus may be included on the PCA, rather than on flexible circuit. In such a configuration, the PCA may be rigidly affixed to side  34  of housing  32  using screws, swage posts, or other structure. 
     Flexible circuit  40  may have various configurations. For example, flexible circuit  40  may have openings underlying printhead dies  701 ,  702  to provide for communication of printing fluids into the printheads. In some examples, flexible circuit  40  may define a separate opening underlying each printhead die  701 ,  702 . In other configurations, the flexible circuit may define a single opening, underlying portions of multiple printhead dies. In still other configurations, flexible circuit  40  may not extend completely about and on all sides of the printhead dies. 
     Printhead dies  701 ,  702  are secured to or mounted on substrates  601  and  602  so as to provide a fluid-tight seal between substrates  601 ,  602  and base  50 . For example, printhead dies  70  may be secured to (or mounted on) second side surface  64  of substrates  601 ,  602  by use of an adhesive  84  provided between printhead dies  701 ,  702  and substrates  601 ,  602 . Similarly, flexible circuit  40  is secured to or mounted on second side surface  54  of base  50  by use of an adhesive  86  provided between flexible circuit  40  and base  50 , and may be generally planar so as to accommodate flat placement of flexible circuit  40  thereon. Second side surface  54  thus also may be referred to as a flex-mounting surface. In one example, a heat-staked attach layer  88  may be interposed between flexible circuit  40  and base  50 . Other connection methods providing a fluid-tight seal between printhead dies  70  and substrates  60 , and between flexible circuit  40  and base  50  also may be used. 
       FIG. 4  is a plan view of printhead assembly  12 , with portions fragmented and/or omitted for purposes of illustration. As indicated, base  50  defines pockets  581 ,  582 , each of which receives a substrate  601 ,  602  that provide fluidic routing for corresponding printheads  701 ,  702  ( FIG. 3 ). Although the present example references two printheads, one or more printheads may be employed, and may be arranged in any of a variety of different printhead configurations. 
     As indicated above, flexible electrical circuit  40  may be secured to base  50  via an adhesive  86  (shown in fragment in  FIG. 4 ). Adhesive  86  may be a layer or bead of solidified adhesive paste sandwiched between flexible circuit  40  and flex-mounting surface  54  of base  50 . As will be explained further below, the adhesive bead extends at least partially about a perimeter of pockets  581 ,  582 , and correspondingly, about substrates  601 ,  602  (received in such pockets) and printhead dies  701 .  702  (mounted on the substrates). In the illustrated example, adhesive  86  extends continuously about both printhead dies  701 ,  702 , collectively, while being sandwiched between base  50  and flexible circuit  40 . 
     Adhesive  86  may have sufficiently low viscosity, prior to curing or solidification, such that the adhesive may flow into or gaps or voids in flex-mounting surface  54 , as well as into gaps or voids in an exterior surface of flexible circuit  40 . In addition, adhesive  86  may accommodate surface irregularities or non-flatness associated with flex-mounting surface  54 . As a result, upon curing or other solidification, adhesive  86  may form a hermetic seal between flex-mounting surface  54  and the opposing portion of flexible circuit  40 . The seal formed by adhesive  86  between flex-mounting surface  54  (of base  50 ) and flexible circuit  40  inhibits airflow or fluid flow between flexible circuit  40  and base  50 . Consequently, priming may be enhanced and cross-contamination of different fluids between printhead dies  701 ,  702  may be reduced. 
     In one example, adhesive  86  has a viscosity at room temperature of less than or equal to about 200,000 centipoise (cp). The adhesive material may, for example, be an epoxy paste (which may not need mixing, but which may utilize a curing process step). Adhesive  86  may be Bisphenol A thermosetting epoxy. Other types of adhesive may be used. 
     Adhesive  86  may be placed between flex-mounting surface  54  and flexible circuit  40  in various manners. For example, the adhesive may be initially deposited upon flexible circuit  40 , and flexible circuit  40  then may be pressed against base  50 , bringing adhesive  86  into contact with flex-mounting surface  54 . In another example, adhesive  86  may be initially deposited on flex-mounting surface  54 , and flexible circuit  40  may be pressed into contact with the paste on flex-mounting surface  54 . 
     Adhesive  86  may be applied by various techniques, including but not limited to, robot needle dispensing, showerhead dispensing, manual needle dispensing, silk screening, or patterned preforms. With patterned preforms, the adhesive material may be in a non-paste state upon both sides of the preform, and the preform may be treated, such as with the application of heat, so as to cause the adhesive material on the preform or backing to change to a paste state. Once in the paste state, the adhesive paste material on the preform may be pressed into contact with either flex-mounting surface  54  or flexible circuit  40  prior to being joined to the other of flex-mounting surface  54  or flexible circuit  40 . 
     As also noted above, because adhesive  86  has low viscosity, the adhesive will flow into gaps or voids in flex-mounting surface  54 . Accordingly, flex-mounting surface  54  may be contoured with surface features that enhance adhesion of adhesive  86 .  FIG. 4  illustrates an example surface feature in the form of a rail  90 , the rail defining a pattern that extends continuously about both of substrates  601 ,  602  (corresponding to the positions of printhead dies  701 ,  702 ). In particular, rail  90  includes a closed loop  92  extending continuously about both substrates, and a segment  94  extending between the substrates  601 ,  602  and interconnecting opposite sides of loop  92 . Additional segments, such as intermediate segment  96 , also may be employed to ensure that the pattern surrounds each substrate in close proximity to the substrate. 
     Flex-mounting surface  54  may further define a trench  98  on one or both sides of rail  90 . Rail  90  thus may serve as a sidewall of the trench (with flexible circuit support features  106  defining an opposite sidewall of the trench. Trench  98  typically forms a continuous path around the printhead dies, and may form an independent continuous path around each printhead die. Adhesive  86  thus may be applied onto rail  90  and/or into trench  98  (between sidewalls of trench  98 ) to form a continuous seal around the printhead dies, and potentially, between the printhead dies to isolate the printhead dies from one another. However, in some examples, trench  98  may form a less than continuous path around the printhead dies. 
     Upon application of adhesive  86  (and/or upon corresponding placement of flexible circuit  40  on flex-mounting surface  54 ), excess adhesive may flow into trench  98 . Trench  98  generally limits or contains the extent to which excess adhesive  86  may migrate prior to partial or complete solidification. Trench  98  further provides flexible circuit  40  with a greater degree of flatness or levelness. In particular, adhesive  86  (prior to solidification) is directly deposited onto rail  90  of flex-mounting surface  54  so as to contact and seal against flexible circuit  40 . As flexible circuit  40  and flex-mounting surface  54  are pressed against one another (prior to curing or solidification of the adhesive), trenches  98  serve to contain excess adhesive displaced from rail  90 . Trenches  98  thus enable a greater volume of the adhesive  86  to be applied without a corresponding unevenness of flexible circuit  40  being created. Flexible circuit  40  may have a greater degree of parallelism with flex-mounting surface  54 . As a result, adhesive displaced from the top of rail  90  to the sides of rail  90  and into the adjacent trenches  98  may enhance subsequent sealing against flexible circuit  40  during priming and may permit printhead assembly to be positioned closer to media during printing. 
     Flex-mounting surface  54  also may define side channels  102  and/or end channels  104 . Channels  102 ,  104  extend from trenches  98  on one or both sides of rail  90 . Channels  102 ,  104  serve to vent air from the trenches  98 . Channels  102 ,  104  help to prevent a breach of the adhesive  86 , which could lead to a leak between die pockets or die pockets and atmosphere during priming of the print head. 
     According to one example embodiment, trench  98  has a width of between approximately 0.25 millimeters and approximately 2 millimeters (nominally about 0.4 millimeters) and a depth of between approximately 0.1 millimeters and approximately 2 millimeters (nominally about 0.4 millimeters). In other examples, trench  98  may have other widths or depths depending upon the desired amount of adhesive  86  that is to be used. 
     As indicated in  FIG. 4 , adhesive also will flow into adhesion-enhancing features, such as scallops  100 . Such adhesion-enhancing features, and particularly scallops  100 , add substantially to the shear surface of the rail  90  in contact with the adhesive, and thus may significantly improve adhesion of the flexible circuit  40  to base  50 . Accordingly, once cured, the adhesive will tend to lock the flexible circuit  40  in place on flex-mounting surface  54 . 
     Referring to  FIGS. 4 and 5 , it will be noted that scallops  100  may take the form of scalloped recesses formed in rail  90 . In the present example, rail  90  defines plural scalloped recesses  100  generally equidistantly positioned along linear runs of rail  90 , and in fluid communication with trench  98 . More particularly, scallops  100  may be formed along substantially the entire length of rail  90 , including along loop  92  and along segments  94 ,  96 . Scallops  100  may add substantially to the shear surface of the rail  90  that is in contact with the adhesive, and thus may significantly improve adhesion of the flexible circuit to base  50 . 
     Where rail  90  is formed with trenches  98  on opposite sides of the rail, scallops  100  similarly may be formed on opposite sides of the rail. Scallops on opposite sides of the rail may be offset from one another as shown to preserve structural integrity of the rail. Although not particularly shown, scallops  100  may additionally (or alternatively) be formed in cheeks  106 , or in other flexible circuit support features adjacent trench  98 . 
     In one example, scallops  100  are semi-spherical recesses formed in rail  90 . Semi-spherical recesses  100  may be formed in rail  90  to tangentially intersect an adjacent trench floor. In one particular example, semi-spherical recesses  100  each have a radius of approximately 0.5 millimeters, and are spaced from each other by approximately 2.7 millimeters along each side of rail  90 . Rail  90  may have a width of approximately 0.8 millimeters and a height of approximately 0.4 millimeters above the trench floor. In other examples, scallops  100  may have other shapes and/or dimensions. 
     As shown in  FIG. 4 , rail  90  (and trench  98 ) may include additional adhesion-enhancing features in areas where lift of flexible circuit  40  is a concern. Such adhesion-enhancing features may take the form of chicanes  110 , such as those shown in the corners of flex-mounting surface  54 . Because adhesive  86  follows rail  90  (and trench  98 ), the extra corner turns established by chicanes  110  effectively increase the amount of adhesive  86  in the corners of flex-mounting surface  54 . This, in turn, reduces the potential for detachment of flexible circuit  40  (which is secured to flex-mounting surface  54  via adhesive  86 ), and is accomplished without negative impact on the flatness of flexible circuit  40  on flex-mounting surface  54 . 
     In the present example, chicanes  110  are arranged so as not to impact height of base  50 . More particularly, referring to  FIG. 5 , rail  90  includes a transverse segment  112  that extends beyond a longitudinal segment  114 , before turning back toward longitudinal segment  114  via a return segment  116 . Return angle θ (defined between transverse rail portion  112  and return rail portion  116 ) typically is an acute angle, selected so as to minimize impact on the adhesive application procedure. In one particular example, return angle θ is approximately 45 degrees. In other examples, other return angles, and/or other chicane shapes may be used. 
     As shown in  FIGS. 5 and 6 , rail  90  may be employed with or without scallops  100 . Furthermore, chicanes  110  need not necessarily be employed in all four corners of flex-mounting surface  54 . Chicanes  110  may be employed in fewer than all four corners, or may be employed at other positions along loop  92 , segment  94  and/or intermediate segment  96 . Chicanes  110  thus may be positioned in various locations on flex-mounting surface  54 , where lift of flexible circuit  40  is a concern. 
     Although the present disclosure has been described with reference to examples, changes may be made in form and detail without departing from the spirit and scope of the subject matter. For example, although different examples may have been described as including one or more features providing one or more benefits, it is contemplated that the described features may be interchanged with one another or alternatively be combined with one another in the described examples or in other alternative examples.