Abstract:
In one example, a molded printhead includes a printhead die embedded in a molding and an external electrical contact electrically connected to the printhead die and exposed outside the molding to connect to circuitry external to the printhead. The molding has a channel therein through which fluid may pass to the back part of the die. The front part of the die is exposed outside the molding and the back part of the die is covered by the molding except at the channel and the thickness of the molding varies from a lesser thickness around the die to a greater thickness away from the die.

Description:
BACKGROUND 
       [0001]    Conventional inkjet printheads require fluidic fan-out from microscopic ink dispensing chambers to macroscopic ink supply channels. 
     
    
     
       DRAWINGS 
         [0002]      FIG. 1  is a block diagram illustrating an inkjet printer implementing one example of a new molded print bar. 
           [0003]      FIGS. 2 and 3  are perspective front and back views, respectively, illustrating one example of a molded print bar such as might be used in the printer shown in  FIG. 1 . 
           [0004]      FIGS. 4 and 5  are section views taken along the lines  4 - 4  and  5 - 5 , respectively, in  FIG. 2 . 
           [0005]      FIG. 6  is a detail from  FIG. 5 . 
           [0006]      FIGS. 7-9  are details from  FIG. 2 . 
           [0007]      FIGS. 10-17  illustrate one example process for making a molded print bar such as the print bar shown in  FIG. 2 . 
           [0008]      FIG. 18  is a flow diagram of the process illustrated in  FIGS. 10-17 . 
           [0009]      FIG. 19  illustrates an ink cartridge implementing one example of a new molded printhead assembly. 
           [0010]      FIGS. 20 and 21  are perspective front and back views, respectively, of the printhead assembly in the ink cartridge shown in  FIG. 19 . 
           [0011]      FIG. 22  is a front side detail from  FIG. 20 . 
           [0012]      FIG. 23  is a back side detail from  FIG. 21 . 
           [0013]      FIG. 24  is a section taken along the line  24 - 24  in  FIG. 20 . 
           [0014]      FIG. 25  is a detail from  FIG. 24 . 
       
    
    
       [0015]    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 
       [0016]    Conventional inkjet printheads require fluidic fan-out from microscopic ink dispensing 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 dispensing 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. It may be desirable in some printing applications to utilize an ASIC (application specific integrated circuit) in a print bar for high speed input/output between the printer controller and the print bar as well as to perform some logic functions. A conventional integrated circuit packaging process in which the ASIC is flip chip bonded to a molded die package to form a POP (package on package) package does not work well for a molded print bar since there is no UBM (under bump metallization) on the back part of the molding. 
         [0017]    Accordingly, a new molded print bar has been developed in which the thickness of the molding varies to accommodate the use of an ASIC in the print bar. The variable thickness molding allows integrating the ASIC into the molding without increasing the thickness of the print bar in the area of the printhead die slivers. A printed circuit board embedded in the molding may be used to connect the ASIC(s) to the printhead dies and to circuitry external to the print bar, and thus avoid the need to form UBM or other wiring in the molding. 
         [0018]    Examples of the new variable thickness molding are not limited to print bars or to the use of ASICs, but may be implemented in other printhead structures or assemblies and with other electronic devices. 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. 
         [0019]    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, and a die “sliver” means a printhead die with a ratio of length to width of  50  or more. A printhead includes a single printhead die or multiple printhead dies. “Printhead” and “printhead die” are not limited to printing with ink but also include inkjet type dispensing of other fluids and/or for uses other than printing. 
         [0020]      FIG. 1  is a block diagram illustrating an inkjet printer  10  implementing one example of a molded print bar  12 . Referring to  FIG. 1 , printer  10  includes a print bar  12  with an arrangement of printheads  14  spanning the width of a print media  16 , flow regulators  18  associated with print bar  12 , a print 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 printheads  14  each with a single printhead die or multiple printhead dies embedded in a molding  26  for dispensing printing fluid on to a sheet or continuous web of paper or other print media  16 . Print bar  12  also includes an ASIC or other non-printhead die electronic device  28  embedded in molding  26 . As described in detail below with reference to  FIGS. 4-9 , the thickness of molding  26  varies to accommodate ASIC  28  at a thicker part  30  while still maintaining a uniform, thinner part  32  in the print zone spanning the length of printheads  14 . 
         [0021]      FIGS. 2 and 3  are perspective front and back views, respectively, illustrating one example of a molded print bar  12  such as might be used in printer  10  shown in  FIG. 1 .  FIGS. 4-9  are section and detail views from  FIG. 2 . (In  FIG. 7 , the protective coverings on the wire bonds are omitted to show the underlying connections. In  FIG. 8 , the encapsulant covering the wire bonds is shown and in  FIG. 9  the protective cap covering the encapsulant is shown.) Referring to  FIGS. 2-9 , print bar  12  includes multiple printheads  14  embedded in a monolithic molding  26  and arranged in a row lengthwise along 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 bar. Examples might also be implemented in a scanning type inkjet pen or in a printhead assembly with fewer molded printheads, or even in a single molded printhead. 
         [0022]    Each printhead  14  includes printhead dies  34  embedded in molding  26  and channels  36  formed in molding  26  to carry printing fluid directly to corresponding printhead dies  34 . In the example shown, as best seen in  FIG. 4 , channels  36  carry printing fluid directly to inlets  38  at the back part of each die  34 . Although four dies  34  arranged parallel to one another laterally across molding  26  are shown for each printhead  14 , 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 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 . 
         [0023]    In the example shown, as best seen in the detail of  FIG. 6 , the electrical conductors  40  that connect each printhead die  34  to external circuits are routed through a printed circuit board (PCB)  42 . A printed circuit board is also commonly referred to as a printed circuit assembly (a “PCA”). Referring specifically to  FIG. 6 , an inkjet printhead die  34  is a typically complex integrated circuit (IC) structure  44  formed on a silicon substrate  46 . PCB conductors  40  carry electrical signals to ejector and/or other elements in the IC part  44  of each die  34 . In the example shown, PCB conductors  40  are connected to circuitry in each printhead die  34  through bond wires  48 . Each bond wire  48  is connected to bond pads or other suitable terminals  50 ,  52  at the front part of printhead dies  34  and PCB  42 , respectively. Thus, PCB conductors  42  connect printhead dies  34  to exposed contacts  54  for connection to circuits external to print bar  12 . 
         [0024]    Although other conductor routing configurations are possible, a PCB provides a relatively inexpensive and highly adaptable platform for conductor routing in molded printheads. Similarly, while connectors other than bond wires may be used, bond wire assembly tooling is readily available and easily adapted to the fabrication of printheads  14  and print bar  12 . Bond wires  48  may be covered by an epoxy or other suitable protective material  56  as shown in  FIGS. 5 and 8 . A flat cap  58  may be added as shown in  FIG. 9  to form a more flat, lower profile protective covering on bond wires  48 . Also, in the example shown, the exposed front part of printhead dies  34  is co-planar with the adjacent surfaces of molding  26  and PCB  42  to present an uninterrupted planar surface  60  surrounding the fluid dispensing orifices  62  in each die  34 . (Encapsulant  56  and cap  58  are omitted from  FIG. 7  and cap  58  is omitted from  FIG. 8  to more clearly show the underlying structures.) 
         [0025]    Referring now specifically to  FIGS. 2 ,  3 ,  5  and  6 , print bar  12  includes two non-printhead die electronic devices  28  embedded in molding  26  at the back part of print bar  12 . In the example shown, as best seen in  FIG. 6 , devices  28  are mounted to the back surface of PCB  42  and connected directly to PCB conductors  40  with solder balls  63 . Thus devices  28  are denoted in in  FIGS. 5 and 6  as surface mounted devices (SMDs)  28 . Although other mounting techniques are possible for devices  28 , surface mounting is desirable to facilitate molding. Electronic devices  28  that might be integrated into an inkjet print bar  12  include, for example, ASICs, EEPROMs, voltage regulators, and passive signal conditioning devices. 
         [0026]    The thickness of molding  26  varies to accommodate SMDs  28  at a thicker part  30  while still maintaining a uniform, thinner part  32  in the print zone spanning the length of printheads  14 . That is to say, the profile of molding  26  defines a narrower part  32  along die slivers  34  and a broader part  30  at SMDs  28 . While two SMDs  28  are shown in  FIGS. 2 and 3 , more or fewer devices  28  are possible and/or with other mounting techniques. Also, while devices  28  are positioned at the back of print bar  12  in this example, to allow a substantially flat front print bar surface, it may be desirable in some applications to position devices  28  at the front of print bar  12  or at both the front and back of print bar  12 . It is expected that devices  28  will usually be positioned at one end of the print bar to help maintain a uniform, thinner part  32  of molding  26  in the print zone covering the area of fluid dispensing orifices  62 . 
         [0027]    One example process for making a print bar  12  will now be described with reference to  FIGS. 10-17  and the flow diagram of  FIG. 18 . Referring first to  FIG. 10 , a PCB  42  pre-populated with SMDs  28  is placed on a carrier  64  with a thermal tape or other suitable releasable adhesive (step  102  in  FIG. 18 ). Then, as shown in  FIGS. 11 and 12 , printhead dies slivers  34  are placed face down on carrier  64  inside openings  66  in PCB  42  (step  104  in  FIG. 18 ). It is expected that multiple print bars will be laid out and molded together on a carrier wafer or panel  64  and singulated into individual print bars after molding. However, only a portion of a carrier panel  64  with part of one print bar in-process is shown in  FIGS. 10-12 . 
         [0028]    Referring to  FIG. 13 , the print bar carrier assembly  68  is loaded into the top chase  70  of a molding tool  72  (step  106  in  FIG. 18 ). The bottom chase  74  may be lined with a release film  76  if necessary or desirable to facilitate the subsequent release of the part from the molding tool. In  FIG. 14 , an epoxy or other suitable mold compound  78  is dispensed into bottom chase  74  (step  108  in  FIG. 18 ) and, in  FIG. 15 , chases  72  and  74  are brought together as indicated by arrows  77  to form the in-process print bar assembly  79  shown in  FIG. 16  (step  110  in  FIG. 18 ). In  FIG. 16 , the in-process molded print bar assembly  79  is removed from molding tool  72  and channels  36  cut or otherwise formed in molding  26 , as indicated generally by saw  81  and arrows  83  in  FIG. 16  (steps  112  and  114  in  FIG. 18 ) The in-process structure is released from carrier  64  in  FIG. 17  (step  116  in  FIG. 18 ). The printhead die slivers are connected to the PCB conductors to form print bar  12 , for example by wire bonding as shown in  FIG. 6  (step  118  in  FIG. 18 ). 
         [0029]    The order of execution of the steps in  FIG. 18  may differ from that shown. For example, it may be desirable in some fabrication sequences to place the printhead dies on the carrier before placing the PCB on the carrier. Also, it may be desirable in some implementations to perform two or more steps concurrently. For example, it may be possible in some fabrication sequences to form the channels in step  114  concurrently with molding the parts in step  110 . 
         [0030]      FIG. 19  illustrates an ink cartridge  80  implementing one example of a new molded printhead assembly  82 .  FIGS. 20 and 21  are perspective front and back views, respectively, of the printhead assembly  82  in the ink cartridge  80  shown in  FIG. 19 .  FIGS. 22-25  are detail and section views from  FIGS. 19-21 . Referring first to  FIG. 19 , ink cartridge  80  includes a molded printhead assembly  82  supported by a cartridge housing  84 . Cartridge  80  is fluidically connected to an ink supply through an ink port  86  and electrically connected to a controller or other external circuitry through electrical contacts  88 . Contacts  88  are formed in a so-called “flex circuit”  90  affixed to housing  32 . Tiny wires (not shown) embedded in flex circuit  90 , often referred to as traces or signal traces, connect contacts  88  to corresponding contacts  54  on printhead assembly  82 . The front face of printhead assembly  82  is exposed through an opening  92  in flex circuit  90  along the bottom of cartridge housing  84 . 
         [0031]    Referring now also to  FIGS. 20-25 , printhead assembly  82  includes multiple printheads  14  each with printhead die slivers  34  embedded in a monolithic molding  26 . Channels  36  formed in molding  26  carry printing fluid directly to the back part of corresponding printhead dies  34 . As in the print bar example described above, PCB conductors  40  connect ejector and/or other elements in the IC part  44  of each die  34  to external contacts  54 . In this example, however, the wire bonds connecting each die  34  to PCB conductors  40  are at the back part of the dies  34  and buried in molding  26 . Also in this example, SMDs  28  are connected to PCB conductors with bond wires  48 . As best seen in  FIGS. 23 and 25 , each bond wire  48  is buried in molding  26 . “Back” part in this context means away from the front face of printhead assembly  82  so that the electrical connections can be fully encapsulated in molding  26 . This configuration allows the front faces of dies  34 , molding  26 , and PCB  42  to form a single uninterrupted planar surface across the front face  94  of printhead assembly  82  in the printing area of printheads  14 . 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. 
         [0032]    “A” and “an” as used in the Claims means one or more. 
         [0033]    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.