Abstract:
In one example, a printhead includes: a printhead die having a front face along which fluid may be dispensed from the die, the die molded into a monolithic molding having a channel therein through which fluid may pass directly to a back part of the die, the front face of the die exposed outside the molding and the back part of the die covered by the molding except at the channel; an electrical contact exposed outside the molding to connect to circuitry external to the printhead; a printed circuit board molded into the molding, the printed circuit board having an exposed front face co-planar with and surrounding the exposed front face of the die and a conductor electrically connected to the contact; and an electrical connection between the die and the printed circuit board conductor fully encapsulated in the molding.

Description:
BACKGROUND 
       [0001]    Conventional inkjet printheads require fluidic fan-out from microscopic ink ejection chambers to macroscopic ink supply channels. 
     
    
     
       DRAWINGS 
         [0002]      FIG. 1  is a block diagram illustrating an inkjet printer with a media wide print bar implementing one example of a new molded printhead. 
           [0003]      FIGS. 2 and 3  are back-side and front-side perspective views, respectively, illustrating one example of a molded print bar with multiple printheads such as might be used in the printer shown in  FIG. 1 . 
           [0004]      FIG. 4  is a section view taken along the line  4 - 4  in  FIG. 2 . 
           [0005]      FIG. 5  is a section view taken along the line  5 - 5  in  FIG. 2 . 
           [0006]      FIG. 6  is a detail view from  FIG. 3 . 
           [0007]      FIGS. 7-11  illustrate one example process for making a print bar such as the print bar shown in  FIGS. 2-6 . 
           [0008]      FIG. 12  is a flow diagram of the process illustrated in  FIGS. 7-11 . 
       
    
    
       [0009]    The same part numbers designate the same or similar parts throughout the figures. The figures are not necessarily to scale. The relative size of some parts is exaggerated to more clearly illustrate the example shown. 
       DESCRIPTION 
       [0010]    Conventional inkjet printheads require fluidic fan-out from microscopic ink ejection chambers to macroscopic ink supply channels. Hewlett-Packard Company has developed new, molded inkjet printheads that break the connection between the size of the die needed for the ejection chambers and the spacing needed for fluidic fan-out, enabling the use of tiny printhead die “slivers” such as those described in international patent application numbers PCT/US2013/046065, filed Jun. 17, 2013 titled Printhead Die, and PCT/US2013/028216, filed Feb. 28, 2013 title Molded Print Bar, each of which is incorporated herein by reference in its entirety. Although this new approach has many advantages, one challenge is making robust electrical connections between the printhead dies and external wiring that withstand ink and mechanical stresses while not interfering with low cost capping and servicing. 
         [0011]    To help meet this challenge, a new molded printhead has been developed in which, for one example configuration, the electrical connections are moved to the back of the printhead die and embedded in the molding. This configuration allows mechanically robust connections that are largely protected from exposure to ink and, because there are no electrical connections along the front face of the die, the printhead can be made flat and thus minimize protruding structures that might interfere with printhead-to-paper spacing and/or capping and servicing. In one example implementation, described in detail below, a page wide molded print bar includes multiple printheads with bond wires buried in the molding. The electrical connections are routed from the back of each printhead die through a printed circuit board embedded in the molding to enable a continuous planar surface across the front face of the print bar where the ejection orifices are exposed to dispense printing fluid. 
         [0012]    Examples of the new printhead are not limited to page wide print bars, but may be implemented in other structures or assemblies. As used in this document, a “printhead” and a “printhead die” mean that part of an inkjet printer or other inkjet type dispenser that dispenses fluid from one or more openings, and a die “sliver” means a printhead die with a ratio of length to width of  50  or more. A printhead includes one or more printhead dies. “Printhead” and “printhead die” are not limited to printing with ink and other printing fluids but also include inkjet type dispensing of other fluids and/or for uses other than printing. The examples shown in the Figures and described herein illustrate but do not limit the invention, which is defined in the Claims following this Description. 
         [0013]      FIG. 1  is a block diagram illustrating an inkjet printer  10  with a media wide print bar  12  implementing one example of a molded printhead  14 . Referring to  FIG. 1 , printer  10  includes a print bar  12  spanning the width of a print media  16 , flow regulators  18  associated with print bar  12 , a media transport mechanism  20 , ink or other printing fluid supplies  22 , and a printer controller  24 . Controller  24  represents the programming, processor(s) and associated memory(ies), and the electronic circuitry and components needed to control the operative elements of a printer  10 . Print bar  12  includes an arrangement of one or more molded printheads  14  for dispensing printing fluid on to a sheet or continuous web of paper or other print media  16 . Print bar  12  in  FIG. 1  includes one or more printheads  14  embedded in a molding  26  spanning print media  16 . The electrical connections  28  between printhead(s)  14  and the contacts  30  to external circuits are routed from the back of each printhead  14  and buried in molding  26  to allow a single uninterrupted planar surface along the front face  32  of printhead(s)  14 . 
         [0014]      FIGS. 2 and 3  are back-side and front-side perspective views, respectively, illustrating one example of a molded print bar  12  with multiple printheads  14  such as might be used in printer  10  shown in  FIG. 1 .  FIGS. 4 and 5  are section views taken along the lines  4 - 4  and  5 - 5  in  FIG. 2 .  FIG. 6  is a detail from  FIG. 3 . Referring to  FIGS. 2-6 , print bar  12  includes multiple printheads  14  embedded in a monolithic molding  26  and arranged in a row lengthwise across the print bar in a staggered configuration in which each printhead overlaps an adjacent printhead. Although ten printheads  14  are shown in a staggered configuration, more or fewer printheads  14  may be used and/or in a different configuration. Examples are not limited to a media wide print print bar. Examples could also be implemented in a scanning type inkjet pen or printhead assembly with fewer molded printheads, or even a single molded printhead. 
         [0015]    Each printhead  14  includes printhead dies  34  embedded in molding  26  and channels  35  formed in molding  26  to carry printing fluid directly to corresponding printhead dies  34 . Although four dies  34  arranged parallel to one another laterally across molding  26  are shown, for printing four different ink colors for example, more or fewer printhead dies  34  and/or in other configurations are possible. As noted above, the development of the new, molded inkjet printheads has enabled the use of tiny printhead die “slivers” such as those described in international patent application no. PCT/US2013/046065, filed Jun. 17, 2003 and titled Printhead Die. The molded printhead structures and electrical interconnections described herein are particularly well suited to the implementation of such tiny die slivers  34  in printheads  14 . 
         [0016]    In the example shown, the electrical conductors  36  that connect each printhead die  34  to external circuits are routed through a printed circuit board (PCB)  38 . A printed circuit board is also commonly referred to as a printed circuit assembly (a “PCA”). An inkjet printhead die  34  is a typically complex integrated circuit (IC) structure  39  formed on a silicon substrate  41 . Conductors  36  in PCB  38  carry electrical signals to ejector and/or other elements of each printhead die  34 . As shown in  FIG. 5 , PCB conductors  36  are connected to circuitry in each printhead die  34  through bond wires  40 . Although only a single bond wire  40  is visible in the section view of  FIG. 5 , multiple bond wires  40  connect each printhead die  34  to multiple PCB conductors  36 . 
         [0017]    Each bond wire  40  is connected to bond pads or other suitable terminals  42 ,  44  at the back part  46 ,  48  of printhead dies  34  and PCB  38 , respectively, and then buried in molding  26 . (Bond wires  40  and bond pads  42 ,  44  are also shown in the fabrication sequence views of  FIGS. 8 and 9 .) Molding  26  fully encapsulates bond pads  42 ,  44  and bond wires  40 . “Back” part in this context means away from the front face  50  of print bar  12  so that the electrical connections can be fully encapsulated in molding  26 . This configuration allows the front faces  32 ,  52 ,  54  of dies  34 , molding  26 , and PCB  38 , respectively, to form a single uninterrupted planar surface/face  50  along ink ejection orifices  56  at the face  32  of each die  34 , as best seen in the section view of  FIG. 4 . 
         [0018]    Although other conductor routing configurations are possible, a printed circuit board provides a relatively inexpensive and highly adaptable platform for conductor routing in molded printheads. Similarly, while other configurations may be used to connect the printhead dies to the PCB conductors, bond wire assembly tooling is readily available and easily adapted to the fabrication of printheads  14  and print bar  12 . For printhead dies  34  in which the internal electronic circuitry is formed primarily away from the back of the dies, through-silicon vias (TSV)  58  are formed in each die  34  to connect bond pads  42  at the back of the die  34  to the internal circuitry, as shown in  FIG. 5 . TSVs are not needed for die configurations that have internal circuitry already at the back of the die. 
         [0019]    One example process for making a print bar  12  will now be described with reference to  FIGS. 7-11 .  FIG. 12  is a flow diagram of the process illustrated in  FIGS. 7-11 . Referring first to  FIG. 7 , printhead dies  34  are placed on a carrier  60  with a thermal tape or other suitable releasable adhesive (step  102  in  FIG. 12 ). In the example shown, an application specific integrated circuit (ASIC) chip  62  is also placed on carrier  60 . Then, as shown in  FIGS. 8 and 9 , PCB  38  is placed on carrier  60  with openings  64  surrounding printhead dies  34  and opening  66  surrounding ASIC  62  (step  104  in  FIG. 12 ). Conductors in PCB  38  are then wire bonded or otherwise electrically connected to dies  34  and ASIC  62  (step  106  in  FIG. 12 ). Surface mounted devices (SMDs)  68  may be included with PCB  38  as necessary or desirable for each print bar  12 . One of the advantages of a molded print bar  12  with PCB conductor routing is the ease with which other components, such as ASIC  62  and SMDs  68 , may be incorporated into the print bar. 
         [0020]      FIG. 10  is a plan view showing the lay-out of multiple in-process print bars from  FIG. 8  on a carrier panel  60 . PCBs  38  and printhead dies  34  on panel  60  are overmolded with an epoxy mold compound or other suitable moldable material  26  (step  108  in  FIG. 12 ), as shown in  FIG. 11 , and then individual print bar strips are separated (step  110  in  FIG. 12 ) and released from carrier  60  (step  112  in  FIG. 12 ) to form individual print bars  12  shown in  FIGS. 2-6 . The molded structure may be separated into strips and the strips released from carrier  60  or the molded structure may be released from carrier  60  and then separated into strips. Any suitable molding technique may be used including, for example, transfer molding and compression molding. Channels  35  in molding  26  formed during overmolding may extend through to expose printhead dies  34 . Alternatively, channels  35  formed during overmolding may extend only partially through molding  26  and powder blasted or otherwise opened to expose printhead dies  34  in a separate processing step. 
         [0021]    Overmolding printhead dies  34  and PCB  38  placed face-down on carrier  60  produces a continuous planar surface across the front face  50  of each print bar  12  where ejection orifices  56  are exposed to dispense printing fluid. As best seen in  FIG. 6 , print bar face  50  is a composite of die faces  32 , PCB face  52  and the face  54  of molding  26  surrounding dies  34  and PCB  38 . If necessary or desirable to the particular implementation of print bar  12 , the rear face  70  of molding  26  may be molded flat as well to make a completely flat print bar  12  (except at channels  35 , of course). The use of a single adhesive, molding  26 , to both hold the printhead dies  34  apart and encapsulate the electrical connections not only simplifies the printhead structure but also helps reduce material costs as well as fabrication process costs. In addition, an electrical RDL (redistribution layer) is unnecessary, an inexpensive PCB  38  performs the RDL function, and only a single level of electrical interconnect is used to connect each die  34  to PCB  38 , to further simplify the structure and reduce fabrication costs. 
         [0022]    “A” and “an” as used in the Claims means one or more. 
         [0023]    As noted at the beginning of this Description, the examples shown in the figures and described above illustrate but do not limit the invention. Other examples are possible. Therefore, the foregoing description should not be construed to limit the scope of the invention, which is defined in the following claims.