Abstract:
A method of making a fluid channel in a printhead structure includes positioning a printhead die on a carrier; compression molding the die into a molded printhead structure; compression molding a first segment of a fluid channel into the molded printhead structure simultaneously with compression molding the die; and materially ablating a second segment of the fluid channel to couple the channel with a fluid feed hole in the die.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of U.S. application Ser. No. 14/770,425, filed Aug. 25, 2015, which is itself a 35 U.S.C. 371 national stage filing of international application S.N. PCT/US2013/052512, filed Jul. 29, 2013, which is itself a continuation-in-part of each of: PCT/US2013/048214, filed Jun. 27, 2013; PCT/US2013/033865, filed Mar. 26, 2013; PCT/US2013/033046, filed Mar. 20, 2013; PCT/US2013/028216, filed Feb. 28, 2013; and PCT/US2013/028207, filed Feb. 28, 2013, each of which is incorporated herein by reference in its entirety. 
     
    
     BACKGROUND 
       [0002]    A printhead die in an inkjet pen or print bar includes a plurality of fluid ejection elements on a surface of a silicon substrate. Fluid flows to the ejection elements through a fluid delivery slot formed in the substrate between opposing substrate surfaces. While fluid delivery slots adequately deliver fluid to fluid ejection elements, there are some disadvantages with such slots. From a cost perspective, for example, fluid delivery slots occupy valuable silicon real estate and add significant slot processing costs. In addition, lower printhead die costs are achieved in part through shrinking the die size. A smaller die size results in a tightening of the slot pitch and/or slot width in the silicon substrate. However, shrinking the die and the slot pitch increases the inkjet pen costs associated with integrating the small die into the pen during assembly. From a structural perspective, removing material from the substrate to form an ink delivery slot weakens the printhead die. Thus, when a single printhead die has multiple slots (e.g., to provide different colors in a multicolor printhead die, or to improve print quality and speed in a single color printhead die), the printhead die becomes increasingly fragile with the addition of each slot. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0003]    The present embodiments will now be described, by way of example, with reference to the accompanying drawings, in which: 
           [0004]      FIG. 1  is an elevation section view illustrating one example of a compression molded fluid flow structure implemented as a printhead structure; 
           [0005]      FIG. 2  is a block diagram illustrating an example system implementing a compression molded fluid flow structure such as the printhead structure of  FIG. 1 ; 
           [0006]      FIG. 3  is a block diagram illustrating an inkjet printer implementing one example of a fluid flow structure in a substrate wide print bar; 
           [0007]      FIGS. 4-6  illustrate an inkjet print bar implementing one example of a compression molded fluid flow structure as a printhead structure suitable for use in a printer; 
           [0008]      FIGS. 7-10  illustrate an example method for making a compression molded printhead fluid flow structure having a fluid channel formed by processes that include both compression molding and material ablation; 
           [0009]      FIG. 11  is a flow diagram of the example method for making a compression molded printhead fluid flow structure illustrated in  FIGS. 7-10 ; 
           [0010]      FIGS. 12-14  illustrate examples of mold tops that have varying topographical designs that can be used in a compression molding process to create differently shaped fluid channels. 
       
    
    
       [0011]    Throughout the drawings, identical reference numbers designate similar, but not necessarily identical, elements. 
       DETAILED DESCRIPTION 
     Overview 
       [0012]    Reducing the cost of conventional inkjet printhead dies has been achieved in the past through shrinking the die size and reducing wafer costs. The die size depends significantly on the pitch of fluid delivery slots that deliver ink from a reservoir on one side of the die to fluid ejection elements on another side of the die. Therefore, prior methods used to shrink the die size have mostly involved reducing the slot pitch and size through a silicon slotting process that can include, for example, laser machining, anisotropic wet etching, dry etching, combinations thereof, and so on. Unfortunately, the silicon slotting process itself adds considerable cost to the printhead die. In addition, successful reductions in slot pitch are increasingly met with diminishing returns, as the costs associated with integrating the shrinking die (resulting from the tighter slot pitch) with an inkjet pen have become excessive. 
         [0013]    A compression molded fluid flow structure enables the use of smaller printhead dies and a simplified method of forming fluid delivery channels/slots to deliver ink from a reservoir on one side of a printhead die to fluid ejection elements on another side of the die. The fluid flow structure includes one or more printhead dies compression molded into a monolithic body of plastic, epoxy mold compound, or other moldable material. For example, a print bar implementing the fluid flow structure includes multiple printhead dies molded into an elongated, singular molded body. The molding enables the use of smaller dies by offloading the fluid delivery channels (i.e., the ink delivery slots) from the die to the molded body of the structure. Thus, the molded body effectively grows the size of each die which improves opportunities for making external fluid connections and for attaching the dies to other structures. 
         [0014]    At the wafer or panel level, a segment of a fluid delivery channel or slot is formed into the fluid flow structure at the back of each printhead die during a compression molding process in which the die is compression molded into the fluid flow structure. The fluid delivery channel is subsequently completed using a material ablation process, such as powder blasting, that removes remaining channel material and fluidically couples the channel to the printhead die. The compression molding process provides an overall cost reduction when forming fluid delivery channels compared to traditional silicon slotting processes. The first, compression molded segment of the fluid delivery channel formed during the compression molding process, serves as a self-aligning mask that is used in the subsequent material ablation process to complete the channel. The compression molding process enables added flexibility in the molded channel/slot shape, its length, and its sidewall profile, through changes in the topographical design of the top mold chase. 
         [0015]    The described fluid flow structure is not limited to print bars or other types of printhead structures for inkjet printing, but may be implemented in other devices and for other fluid flow applications. Thus, in one example, the molded structure includes a micro device embedded in a molding having a channel or other path for fluid to flow directly into or onto the device. The micro device, for example, could be an electronic device, a mechanical device, or a microelectromechanical system (MEMS) device. The fluid flow, for example, could be a cooling fluid flow into or onto the micro device or fluid flow into a printhead die or other fluid dispensing micro device. These and other examples shown in the figures and described below illustrate but do not limit the invention, which is defined in the Claims following this Description. 
         [0016]    As used in this document, a “micro device” means a device having one or more exterior dimensions less than or equal to 30 mm; “thin” means a thickness less than or equal to 650 μm; a “sliver” means a thin micro device having a ratio of length to width (L/W) of at least three; a “printhead structure” and a “printhead die” mean that part of an inkjet printer or other inkjet type dispenser that dispenses fluid from one or more openings. A printhead structure includes one or more printhead dies. “Printhead structure” and “printhead die” are not limited to printing with ink and other printing fluids but also include inkjet type dispensing of other fluids for uses other than or in addition to printing. 
       Illustrative Embodiments 
       [0017]      FIG. 1  is an elevation section view illustrating one example of a compression molded fluid flow structure  100  implemented as a printhead structure  100  that is suitable for use in a print bar of an inkjet printer. The printhead structure  100  includes a micro device  102  compression molded into a monolithic body  104  of plastic or other moldable material. A molded body  104  may also be referred to herein as a molding  104 . In general, a micro device  102  could be, for example, an electronic device, a mechanical device, or a microelectromechanical system (MEMS) device. In the present printhead structure  100  of  FIG. 1 , micro device  102  is implemented as a printhead die  102 . Printhead die  102  includes a silicon die substrate  106  comprising a thin silicon sliver on the order of 100 microns in thickness. The thin silicon sliver substrate  106  includes fluid feed holes  108  dry etched or otherwise formed therein to enable fluid flow through the substrate  106  from a first exterior surface  110  to a second exterior surface  112 . The silicon substrate  106  further includes a silicon cap  114  (i.e., a cap over the silicon substrate  106 ) adjacent to and covering the first exterior surface  110 . The silicon cap  114  is on the order of 30 microns in thickness and can be formed of silicon or some other suitable material such as a polymer layer, a thick metal layer, or a thick dielectric layer. In one implementation, for example, a polymer film can be laminated onto the thin silicon sliver to cover the silicon substrate  106  so an epoxy mold compound will not enter the fluid feed holes  108  during a compression molding process. 
         [0018]    Formed on the second exterior surface  112  of substrate  106  are one or more layers  116  that define a fluidic architecture that facilitates the ejection of fluid drops from the printhead structure  100 . The fluidic architecture defined by layers  116  generally includes ejection chambers  118  having corresponding orifices  120 , a manifold (not shown), and other fluidic channels and structures. The layer(s)  116  can include, for example, a chamber layer formed on the substrate  106  and a separately formed orifice layer over the chamber layer, or, they can include a monolithic layer that combines both the chamber and orifice layers. Layer(s)  116  are typically formed of an SU8 epoxy or some other polyimide material. 
         [0019]    In addition to the fluidic architecture defined by layer(s)  116  on silicon substrate  106 , the printhead die  102  includes integrated circuitry formed on the substrate  106 . Integrated circuitry is formed using thin film layers and other elements not specifically shown in  FIG. 1 . For example, corresponding with each ejection chamber  118  is a thermal ejector element or a piezoelectric ejector element formed on the second exterior surface  112  of substrate  106 . The ejection elements are actuated to eject drops or streams of ink or other printing fluid from chambers  118  through orifices  120 . 
         [0020]    The printhead structure  100  also includes signal traces or other conductors  122  connected to printhead die  102  through electrical terminals  124  formed on substrate  106 . Conductors  122  can be formed on structure  100  in various ways. For example, conductors  122  can be formed in an insulating layer  126  as shown in  FIG. 1 , using a lamination or deposition process. Insulating layer  126  is typically a polymer material that provides physical support and insulation for conductors  122 . In other implementations, conductors  122  can be molded into the molded body  104  as shown below in  FIG. 6 , for example. 
         [0021]    A fluid channel  128  is formed through the molded body  104  and the thin silicon cap  114  to be fluidically coupled with the printhead die substrate  106  at the exterior surface  110 . A first segment of the channel  128  is formed during the compression molding process that molds the printhead die  102  into the printhead structure  100 . The remainder of the channel  128  is formed through a material ablation process that removes channel material using the first channel segment as a self-aligning mask. The fluid channel  128  provides a pathway through the molded body and thin silicon cap  114  that enables fluid to flow directly onto the silicon substrate  106  at exterior surface  110 , and into the silicon substrate  106  through the fluid feed holes  108 , and then into chambers  118 . As discussed in further detail below, the fluid channel  128  is formed into the molded body  104  in part using a compression molding process that enables the formation of a variety of different channel shapes whose profiles each reflect the inverse shape of whatever mold chase topography is being used during the molding process. 
         [0022]      FIG. 2  is a block diagram illustrating a system  200  implementing a compression molded fluid flow structure  100  such as the printhead structure  100  shown in  FIG. 1 . System  200  includes a fluid source  202  operatively connected to a fluid mover  204  configured to move fluid to a fluid channel  128  formed in fluid flow structure  100  by compression molding and material ablation processes. A fluid source  202  might include, for example, the atmosphere as a source of air to cool an electronic micro device  102  or a printing fluid supply for a printhead die  102 . Fluid mover  204  represents a pump, a fan, gravity or any other suitable mechanism for moving fluid from source  202  to flow structure  100 . 
         [0023]      FIG. 3  is a block diagram illustrating an inkjet printer  300  implementing one example of a fluid flow structure  100  in a substrate wide print bar  302 . Printer  300  includes print bar  302  spanning the width of a print substrate  304 , flow regulators  306  associated with print bar  302 , a substrate transport mechanism  308 , ink or other printing fluid supplies  310 , and a printer controller  312 . Controller  312  represents the programming, processor(s) and associated memories, and the electronic circuitry and components that control the operative elements of a printer  300 . Print bar  302  includes an arrangement of printhead dies  102  for dispensing printing fluid onto a sheet or continuous web of paper or other print substrate  304 . Each printhead die  102  receives printing fluid through a flow path that extends from supplies  310  into and through flow regulators  306 , and then through compression molded fluid channels  128  within print bar  302 . 
         [0024]      FIGS. 4-6  illustrate an inkjet print bar  302  implementing one example of a compression molded fluid flow structure  100  as a printhead structure  100  suitable for use in printer  300  of  FIG. 3 . Referring to the plan view of  FIG. 4 , printhead dies  102  are embedded in an elongated, monolithic molding  104  and arranged generally end to end in rows  400 . The printhead dies  102  are arranged in a staggered configuration in which the dies in each row overlap another printhead die in that same row. In this configuration, each row  400  of printhead dies  102  receives printing fluid from a different compression molded fluid channel  128  (illustrated with dashed lines in  FIG. 4 ). Although four fluid channels  128  feeding four rows  400  of staggered printhead dies  102  are shown (e.g., for printing four different colors), other suitable configurations are possible.  FIG. 5  illustrates a perspective section view of the inkjet print bar  302  taken along line  5 - 5  in  FIG. 4 , and  FIG. 6  illustrates a section view of the inkjet print bar  302  also taken along line  5 - 5  in  FIG. 4 . The section view of  FIG. 6  shows various details of a printhead structure  100  as discussed above regarding  FIG. 1 . 
         [0025]      FIGS. 7-10  illustrate an example method for making a compression molded printhead fluid flow structure  100  having a fluid channel  128  formed by processes that include both compression molding and material ablation.  FIG. 11  is a flow diagram  1100  of the method illustrated in  FIGS. 7-10 . As shown in  FIG. 7  at part “A”, a printhead die  102  is attached to a carrier  160  using a thermal release tape  162  (step  1102  in  FIG. 11 ), forming die carrier assembly  163 . The printhead die  102  is placed with the orifice  120  side down onto the carrier  160 . The printhead die  102  is in a pre-processed state such that it already includes layer(s)  116  defining fluidic architectures (e.g., ejection chambers  118 , orifices  120 ), and electrical terminals  124  and ejection elements (not shown) formed on the thin sliver substrate  106 . Fluid feed holes  108  have also already been dry etched or otherwise formed in the sliver substrate  106 . 
         [0026]    Referring to  FIG. 7  at part “B”, the printhead die  102  is compression molded into a molded body  104  (step  1104  in  FIG. 11 ). In general, a compression molding process involves preheating a molding material such as plastic or an epoxy mold compound, and placing the material with the die  102  into a heated mold cavity such as the area inside the bottom mold  164 . The mold top  166  is brought down to close the mold, and heat and pressure force the molding material into all the areas within the cavity such that it forms a molding  104  that encapsulates the printhead die  102 . In addition to encapsulating the die  102 , the molding  104  takes on a shape whose contours follow the topography of the mold top  166 . In this example, the molding  104  forms a partial fluid channel  168  that makes up a first, compression molded segment  169  of the fluid channel  128  at the first exterior (backside) surface  110  of substrate  106 , as shown at  FIG. 7 , part “C”. 
         [0027]    Referring still to  FIG. 7 , parts “B” and “C”, it is apparent that during the compression molding process, the silicon cap  114  prevents molding material from entering into the fluid feed holes  108  in the sliver substrate  106 . In addition, the compression molding process leaves a residual layer  170  of molding material over the silicon cap  114 . Accordingly, as shown at part “C”, the partial fluid channel  168  (first compression molded channel segment  169 ) does not extend all the way to the ink feed holes  108 . Consequently, the fluid channel  128  is subsequently completed in a material ablation process as discussed below. As shown at part “C” of  FIG. 7 , the die carrier assembly  163  is removed from the bottom and top molds ( 164 ,  166 ), and the carrier  160  is released from the thermal tape  162  and the tape is removed from the die (step  1106  in  FIG. 11 ). 
         [0028]    As shown at part “D” of  FIG. 7 , a polymer insulating layer  126  is laminated onto the orifice  120  side of the printhead die  102 , and then patterned and cured (step  1108  in  FIG. 11 ). An SU8 firing chamber protection layer  172  is deposited over the fluidic architecture layer(s)  116 , as shown in  FIG. 7  at part “E” (step  1110  in  FIG. 11 ). At part “F”, as shown in  FIG. 7 , a metal layer (Cu/Au) is deposited onto the polymer insulating layer  126  and patterned into conductor traces  122  (step  1112  in  FIG. 11 ). A top polymer insulating layer  126  is then spin coated over the conductor traces  122 , and then patterned and cured as shown at part “G” of  FIG. 7  (step  1114  in  FIG. 11 ). At part “H” of  FIG. 7 , the firing chamber protect layer  166  is stripped off and a final cure of the polymer insulating layer  126  is performed (step  1116  in  FIG. 11 ). As shown at part “I” of  FIG. 7 , the residual layer  170  of molding material and the silicon cap  114  are removed over the area of the fluid feed holes  108  in the substrate  106 , forming the completed fluid channel  128  (step  1118  in  FIG. 11 ). In one example, a material ablation process is used to remove the residual layer  170  and silicon cap  114 . Thus, the completed fluid channel  128  includes a first, compression molded channel segment  169 , and a second segment that is a material ablated channel segment  174 . 
         [0029]      FIGS. 8-10  further illustrate the material removal (ablation) process step shown in part “I” of  FIG. 7 . There are various processes that can be used to remove material from the silicon cap  114  and the residual layer  170  of molding material that remains over the silicon cap  114 . These material ablation processes can include, for example, powder blasting, etching, lasering, milling, drilling, electrical discharge machining, and so on. Such processes often involve the use of a mask that prevents the removal of material in areas where material should not be removed. In the present case the first, compression molded channel segment  169  formed during the compression molding step at parts “B” and “C” of  FIG. 7 , serves as a self-aligning mask that guides the etchant or other abrasive substance  800  to remove material from the silicon cap  114  and residual layer  170  in areas that extend and complete the channel. The material ablation process forms a second, material ablated channel segment  174  that extends the first channel segment  169 , forming the completed fluid channel  128 . The completed fluid channel  128  provides a pathway through the molded body and through the thin silicon cap  114 , enabling fluid to flow directly onto the silicon substrate  106  at the exterior surface  110 , and into the silicon substrate  106  through the fluid feed holes  108 , and then into chambers  118 . 
         [0030]    As shown in  FIG. 8 , the etchant or other abrasive substance  800  is guided by the first channel segment  169  to remove by ablation, material at the closed end of the channel. The ablation process begins with removing the residual layer  170  of molding material that remains over the silicon cap  114  (step  1120  in  FIG. 11 ). Thus, the material ablation process shown in part “I” of  FIG. 7  first removes the residual layer  170  and exposes the silicon cap  114  to the etchant or other abrasive substance  800 , as shown in  FIG. 9 . The material ablation process then proceeds to remove material from the silicon cap  114  (step  1122  in  FIG. 11 ) in the channel area that extends the channel to the exterior surface  110  of the substrate  106 . Removing the residual layer  170  and silicon cap material forms a second (material ablated) channel segment  174  that completes the fluid channel  128  and opens up the fluid feed holes  108  to the channel  128  (step  1124  in  FIG. 11 ). Thus, the completed fluid channel  128  comprises a first segment that is a compression molded channel segment  169  and a second segment that is a material ablated channel segment  174 . 
         [0031]    As can be seen in the figures discussed above, the compression molding process can generate varying shapes within the fluid channel  128 . More specifically,  FIGS. 1, 5, and 6 , illustrate fluid channels  128  that have generally straight sidewalls that are parallel with one another, while  FIGS. 7-10  show fluid channels  128  whose sidewalls are straight, but tapered or divergent with respect to one another. Different fluid channel shapes can be generated during the compression molding process by using mold tops  166  that have varying topographical designs. In general, the resulting shape of the fluid channel  128  follows, inversely, the contours of the topography of the mold top  166  used in the compression molding process. 
         [0032]      FIGS. 12-14  illustrate several additional examples of mold tops  166  that have varying topographical designs that can be used in a compression molding process to create differently shaped fluid channels  128 . As shown in  FIG. 12 , the mold top  166  has contours that result in a fluid channel  128  with molded sidewalls, S 1  and S 2 , that mirror one another. The sidewalls, S 1  and S 2 , each have two generally straight sections, one section where the sidewalls are parallel with one another and one section where the sidewalls are tapered. In  FIG. 13 , the mold top  166  contours result in a fluid channel  128  with molded sidewalls, S 1  and S 2 , that each have two sections that are generally straight. Both sections of the sidewalls are tapered, and again, are mirror images as they taper away from each other. As shown in  FIG. 14 , a mold top  166  can also have curved (or other shaped) contours that generate curved side wall shapes within the fluid channel  128 . 
         [0033]    In general, the molded fluid channels  128  shown in the figures and discussed above, have channel sidewalls formed in various straight and/or curved configurations that are parallel and/or tapered and/or mirrored to one another. In most cases, it is beneficial to have the channel sidewalls diverge or taper away from one another as they recede or move away from the printhead sliver substrate  106 . This divergence provides the benefit of assisting air bubbles to move away from the orifices  120 , ejection chambers  118 , and fluid feed holes  108 , where they may otherwise hinder or prevent the flow of fluid during operation. Accordingly, the fluid channels  128  discussed and shown in the figures comprise side walls that are typically divergent, but that are at least parallel, as they recede from the sliver substrate  106 . However, the illustrated channel side wall shapes and configurations are not intended to be a limitation as to other shapes and configurations of side walls within fluid channels  128  that can be formed using a compression molding process. Rather, this disclosure contemplates that other compression molded fluid channels are possible that have side walls shaped in various other configurations not specifically illustrated or discussed.