Abstract:
A circuit interconnect generally comprises an electrical connection pad, a shape memory material, and a flowable conductor. The electrical connection pad has an upper surface, a portion of which is covered by the shape memory material. The flowable conductor extends through the shape memory material and is electrically coupled to the electrical connection pad. The shape memory material has a first configuration at a first temperature and a second configuration at a second temperature. In the instance of the second temperature being greater than the first, the shape memory material has a first configuration that is substantially planar and a second configuration that is cupped.

Description:
BACKGROUND 
       [0001]    Drop on demand ink jet technology is widely used in the printing industry. Various types of technology may be used to implement drop on demand ink jet printing. One of the more common technologies utilizes printheads with piezoelectric ink jets. 
         [0002]    Piezoelectric ink jet printheads typically include a flexible diaphragm, contained within a jetstack body, and an array of transducers, i.e., piezoelectric elements, attached to the diaphragm. When a voltage is applied to a transducer, typically through electrical connection with an electrode electrically coupled to a voltage source, the transducer bends or deflects, causing the diaphragm to flex which expels a quantity of ink from a chamber through a nozzle. The flexing further draws ink into the chamber from a main ink reservoir through an opening to replace the expelled ink. 
         [0003]    The electrode, described above, typically protrudes as a pad electrode from a flexible printed circuit and is typically electrically connected to the transducer via a conductive material such as a silver epoxy. An adhesive standoff layer operates to contain the conductive material atop the transducer and enables attachment/adhesion between the flexible printed circuit and the transducer. As the adhesive layer is cured the pad electrode of the flexible printed circuit is drawn towards the transducer compressing the conductive material and causing it to flow to any open area on the transducers upper surface. Under ideal circumstances, the compressed conductive material provides a broad contact surface for the pad electrode ensuring an optimal electrical connection between the electrode and the transducer. However, in the real world, ideal circumstances are not always present. 
       SUMMARY 
       [0004]    A circuit interconnect generally comprises an electrical connection pad, a shape memory material, and a flowable conductor. The electrical connection pad has an upper surface, a portion of which is covered by the shape memory material. The flowable conductor extends through the shape memory material and is electrically coupled to the electrical connection pad. The shape memory material has a first configuration at a first temperature and a second configuration at a second temperature. In the instance of the second temperature being greater than the first, the shape memory material has a first configuration that is substantially planar and a second configuration that is cupped. 
         [0005]    The circuit interconnect may additionally incorporate a corresponding first and second configuration of the flowable conductor. The first configuration presents the flowable conductor in an arcuate configuration atop the substantially planar configuration of the shape memory material and the second configuration presents the flowable conductor in a balled configuration that is partially contained by the cup configuration of the shape memory material. The portion of the flowable conductor not contained by the cup configuration extends in an arcuate presentation above the rim of the cup shape. Further, the circuit interconnect may include a standoff adhesive layer, the flowable conductor may comprise a silver epoxy, the electrical connection pad may comprise a piezoelectric ink jet printhead transducer, the balled configuration of the flowable conductor may also be configured as a flex-circuit electrical contact, and the balled configuration of the flowable conductor may be of a higher aspect ratio than the arcuate configuration of the flowable conductor. 
         [0006]    An interconnect system of the present disclosure generally comprises a transducer, a flex-circuit and a conductor. The flex-circuit is secured to the transducer and incorporates an electrically conductive pad. The conductor is partially contained by a cup-shaped memory material but extends through the cup-shaped memory material to establish electrical communication between the transducer and the conductive pad of the flex-circuit. The interconnect system may additionally include a transducer that comprises a piezoelectric ink jet printhead transducer, a conductor that is a flowable conductor capable of conforming to the cup-shaped shape memory material, a cup-shaped shape memory material that is formed by heating a substantially planar configuration of the material, and a conductor that is a high aspect ratio conductor. 
         [0007]    A method of the present disclosure generally comprises securing a shape memory material atop an electrical connection pad, depositing a flowable conductor atop and through the shape memory material to electrically couple the flowable conductor to the electrical connection pad, and heating the shape memory material to form a cup configuration where a portion of the flowable conductor is contained by the cup configuration and wherein a portion of the flowable conductor extends above the cup configuration to present a flex-circuit pad bondable contact. The method may further comprise heating the shape memory material from a substantially planar configuration to form the cup configuration. 
         [0008]    The above summary is not intended to describe each embodiment or every implementation. A more complete understanding will become apparent and appreciated by referring to the following detailed description and claims in conjunction with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIGS. 1-2  are cross-sections depicting the formation of a transducer interconnect for piezoelectric ink jet printheads according to standard practices. 
           [0010]      FIGS. 3-4  are cross-sections depicting the formation of a transducer interconnect for piezoelectric ink jet printheads according to standard practices and the limitations associated therewith. 
           [0011]      FIGS. 5-8  are cross-sections depicting the formation of a high-aspect ratio transducer interconnect for piezoelectric ink jet printheads according to various embodiments. 
           [0012]      FIG. 9  is a flowchart diagramming the process for manufacturing a high-aspect ratio transducer interconnect for piezoelectric ink jet printheads according to various embodiments 
       
    
    
       [0013]    The figures are not necessarily to scale. Like numbers used in the figures refer to like components. However, it will be understood that the use of a number to refer to a component in a given figure is not intended to limit the component in another figure labeled with the same number. 
       DETAILED DESCRIPTION 
       [0014]    In the manufacture of piezoelectric ink jet printheads, transducers  20  are typically secured to the jetstack body  22  of the printhead, see  FIG. 1 . The transducers  20  are typically piezoelectric elements comprising PZT (lead zirconate titanate). After the transducer  20  attachment to the jetstack body  22 , a patterned standoff layer  24  (for example, a 1 mil adhesive) is applied to the edges of each of the transducers  20  leaving a central opening to expose a large portion of the upper surface  26  of each transducer  20 . Next, a drop of a flowable conductor  28  (for example, a silver epoxy) is dispensed into each central opening and establishes an electrically conductive contact with the upper surface  26  of the transducer  20 . Pad electrodes (not shown) of a flexible printed circuit (flex-circuit)  30  are then aligned with the central openings to position the pad electrode directly over the drop of flowable conductor  28 . Upon subjecting the afore-described configuration to a curing temperature, see  FIG. 2 , the flex-circuit  30  and pad electrodes are drawn downward towards the underlying transducer  20  causing the drop of flowable conductor  28  to compress and spread across the open, upper surface  26  of the transducer  20  creating a transducer electrical contact. Note that the standoff layer  24  is intended to contain the spreading conductor  28  to the desired location atop the transducer  20 . With the pad electrode touching the transducer electrical contact, electrical communication between the pad electrode/flex-circuit  30  and the transducer  20  is established. The electrical communication is maintained by the adherence of the flex-circuit  30  to the underlying transducer  20  via the cured, adhesive standoff layer  24 . 
         [0015]    While the manufacturing process described above is an accepted practice, it is not without its limitations. One area of consideration is the dispensation of the flowable conductor. Referring now to  FIGS. 3-4 , the volume of conductor  28  dispensed can vary and this variation tends to increase with increased volume. Too little conductor  28  volume can result in electrical opens due to poor adhesion and reduced contact area between the pad electrodes of the flex-circuit  30  and the transducers  20 . Too much conductor volume can result in overflow creating shorts between adjacent transducers  20 . Moreover, as ink jet printhead nozzle density increases, more and more transducers  20  are placed within a defined space, the decreased dimension/spacing between transducers  20  causes an increased occurrence of the described opens and shorts. 
         [0016]    In view of the above, embodiments of the present disclosure are presented with reference to  FIGS. 5-9  and describe a system  10  and method  100  for a high aspect ratio circuit interconnect that is appropriate for use with, for example, transducers in piezoelectric ink jet printheads. However, the system and method are equally applicable to any application that utilizes an electrical connection pad from which electrical coupling is to be established. 
         [0017]    Referring now to  FIG. 5 , the system  10  is established with an electrical connection pad, in this instance, a transducer  20  secured to a jetstack body  22 . A full height (for example, 1 mil) adhesive, standoff layer  24  is applied to the outer edges of the transducer  20 . According to one embodiment, the transducer  20  is a piezoelectric element comprised of PZT (lead zirconate titanate). 
         [0018]    Subsequently, per  FIGS. 6A and 6B , a second patterned adhesive standoff layer  32  is applied to the top surface  26  of the transducer  20 . Standoff layer  32  is approximately half the thickness/height of standoff layer  24  and is positioned to the center of transducer  20  in a circular configuration presenting an open center  33 . Standoff layer  32  provides support and adhesion for a patterned shape memory polymer layer  34  positioned atop standoff layer  32  in a planar, widened circular configuration, see  FIG. 6B , that maintains open center  33  providing a path to the top surface  26  of the underlying transducer  20 . It should be noted that the shape memory polymer has been manufactured to a desired pattern, length, width and depth prior to being applied to the standoff layer  32 . The desired shape memory polymer may be manufactured via any suitable means including, but not limited to, being punched out with a die and/or laser cut. 
         [0019]    Referring now to  FIG. 7 , a drop of flowable conductor  28  (for example, silver epoxy), is placed atop the shape memory polymer layer  34 , wherein the drop of conductor  28  flows through open center  33  to contact transducer  20  and flows outward to the outer edges of the circularly-configured shape memory layer  34  thereby presenting the flowable conductor  28  in an arcuate configuration atop the shape memory layer  34 . A notably less amount of flowable conductor  28  is needed for the present configuration as compared to the configuration of  FIG. 1 . As such, overflow of the flowable conductor is not a significant concern. With the flowable conductor  29  deposited, the configuration of  FIG. 7  is subjected to a temperature increase, i.e., a curing temperature that may cure both the shape memory polymer layer  34  and the flowable conductor  28 . 
         [0020]    The heat activates the shape memory polymer layer  34  causing it to pull upward into a cup configuration, see  FIG. 8 . The flowable conductor  28  conforms to the cup configuration, while maintaining contact with the upper surface  26  of the transducer  20 , by presenting a balled configuration that is partially contained by the cup-shaped memory polymer layer  34 . The portion of conductor  28  not contained by the cup-shaped memory polymer layer  34  extends above the upper rim of the cup in an arcuate presentation thereby completing the configuration of system  10 . 
         [0021]    The balled conductor  28  of the system  10  presents a high aspect ratio electrical contact i.e., a smaller volume dispensed during manufacture to conserve conductor and to prevent conductor overflow, yet a taller structure to make adequate electrical contact. Furthermore, the balled conductor  28  is in a configuration that will conform to the electrode pads of the flex-circuit  30  during the bonding/adhesion process of securing flex-circuit  30  to the transducer  20  through use of adhesive standoff layer  24 . It should be noted that while  FIGS. 5-8  illustrate a single transducer configuration for clarity, the same configuration may be applied to a plurality of transducers as appropriate to the specific ink jet printhead configuration in which the transducer is used. Further, the application of system  10  need not be limited to printers but can easily be extended to any application utilizing interconnect circuitry such as flexible printed circuits, ribbon cable, etc. 
         [0022]      FIG. 9  is a flowchart illustrating a method  100  for creating a high aspect ratio contact suitable for bonding with a flex-circuit according to various embodiments. Initially, a full height, first adhesive standoff layer is applied to the edges of a transducer,  102 . A half-height, second standoff adhesive layer is applied in a circular configuration atop the transducer while maintaining a central opening,  104 . A shape memory polymer layer is applied atop the second standoff adhesive in a circular configuration, maintaining the central opening, and extending outwards toward the first adhesive standoff layer,  106 . A flowable conductor is dispensed to the central opening where it flows down to the transducer and outward to the edge of the shape memory polymer layer,  108 . The transducer with the two standoff layers, shape memory polymer and flowable conductor are submitted to an increase in temperature whereby the heat activates the shape memory polymer to form a cup configuration and the flowable conductor to present a cup-conforming ball configuration,  110 , suitable for contacting and conforming to a flex-circuit. 
         [0023]    Systems, devices or methods disclosed herein may include one or more of the features structures, methods, or combination thereof described herein. For example, a device or method may be implemented to include one or more of the features and/or processes above. It is intended that such device or method need not include all of the features and/or processes described herein, but may be implemented to include selected features and/or processes that provide useful structures and/or functionality. 
         [0024]    Various modifications and additions can be made to the disclosed embodiments discussed above. Accordingly, the scope of the present disclosure should not be limited by the particular embodiments described above, but should be defined only by the claims set forth below and equivalents thereof.