Molded die slivers with exposed front and back surfaces | Patent Number 11292257US 11292257 B2
This is a continuation of U.S. application Ser. No. 16/110,346, filed Aug. 23, 2018, which is a continuation of U.S. application Ser. No. 15/646,163, filed Jul. 11, 2017, which is a continuation of U.S. Pat. No. 9,724,920, having a national entry date of Aug. 24, 2015, which is a national stage application under 35 U.S.C. § 371 of International Application No. PCT/US2014/030945, filed Mar. 18, 2014, which claims priority to each of International Application Nos. PCT/US2013/033046, filed Mar. 20, 2013, PCT/US2013/046065, filed Jun. 17, 2013, PCT/US2013/048214, filed Jun. 27, 2013, PCT/US2013/052505, filed Jul. 29, 2013, PCT/US2013/052512, filed Jul. 29, 2013, and PCT/US2013/068529, filed Nov. 5, 2013, all of the above hereby incorporated by reference in their entirety.
Inkjet pens and print bars can include one or more printhead dies, each having a plurality of fluid ejection elements on a surface of a silicon substrate. Fluid typically flows to the ejection elements through one or more fluid delivery slots formed in the substrate between opposing substrate surfaces. While such slots effectively deliver fluid to the fluid ejection elements, there are some disadvantages associated with their use. From a cost perspective, for example, fluid delivery slots occupy valuable silicon real estate and add significant slot processing cost. Lower printhead die costs can be achieved in part through shrinking the die size. However, a smaller die size results in a tighter slot pitch and/or slot width in the silicon substrate, which adds excessive assembly costs associated with integrating the smaller die into the inkjet pen. In addition, removing material from the substrate to form an ink delivery slot structurally weakens the printhead die. Thus, when a single printhead die has multiple slots (e.g., to improve print quality and speed in a single color printhead die, or to provide different colors in a multicolor printhead die), the printhead die becomes increasingly fragile with the addition of each slot.
Examples are described below, with reference to the accompanying drawings, in which:
Throughout the drawings, identical reference numbers designate similar, but not necessarily identical, elements.
Reducing the cost of 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 formed through the silicon substrate 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, as die sizes have decreased, the costs and complexities associated with integrating the smaller dies into an inkjet pen or print bar have begun to exceed the savings gained from the smaller dies. Furthermore, as die sizes have decreased, the removal of die material to form ink delivery slots has had an increasingly adverse impact on die strength, which can increase die failure rates.
Recent developments in molded fluid flow structures, including molded inkjet printheads and molded inkjet print bars, have done away with the use of fluid delivery slots in the die substrate. Examples of the molded fluid flow structures and processes for making such structures are disclosed in international patent application numbers PCT/US2013/046065, filed Jun. 17, 2013, titled Printhead Die, and PCT/US2013/033046, filed Mar. 20, 2013, titled Molding A Fluid Flow Structure, each of which is incorporated herein by reference in its entirety.
These molded fluid flow structures (e.g., molded inkjet printheads) enable the use of tiny printhead die “slivers”. A die sliver includes a thin silicon, glass or other substrate (i.e., having a thickness on the order of 650 μm or less) with a ratio of length to width (L/W) of at least three. Molded fluid flow structures, such as a molded inkjet printhead, do not have fluid slots formed through the die sliver substrate. Instead, each die sliver is molded into a monolithic molded body that provides fluidic fan-out through fluid channels formed into the molding at the back surface of the die sliver. Thus, a molded printhead structure avoids significant costs otherwise associated with prior die slotting processes and the related assembly of slotted dies into manifold features of inkjet pens and print bars.
In prior molded inkjet printhead designs, fluid channels formed into the molded body enable printing fluid to flow to the back surface of each die sliver. Fluid/ink feed holes (IFH's) formed through the die sliver from its back surface to its front surface enable the fluid to flow through the sliver to fluid drop ejection chambers on the front surface, where it is ejected from the molded printhead through nozzles. Processes for forming the fluid channels into the molded body, and the ink feed holes into the die sliver, are considerably less costly and complex than the die slotting and assembly processes associated with prior printhead designs. However, these processes do present some added costs and complications. For example, in one fabrication process, a cutting saw is used to plunge cut through the molded body to form the fluid channels in the molded printhead die, as described in international patent application number PCT/US2013/048214, filed Jun. 27, 2013, titled Molded Fluid Flow Structure with Saw Cut Channel, which is incorporated herein by reference in its entirety. In other examples, the fluid channels can be formed in the molded body through compression molding and transfer molding processes such as those described, respectively, in international patent application numbers PCT/US2013/052512, filed Jul. 29, 2013 titled Fluid Structure with Compression Molded Fluid Channel, and PCT/US2013/052505, filed Jul. 29, 2013 titled Transfer Molded Fluid Flow Structure, each of which is incorporated herein by reference in its entirety. Thus, while there are a number of processes available to form the fluid channels in the molded body, each one contributes a measure of cost and complexity to the fabrication of the molded inkjet printheads.
In an effort to further reduce the cost and complexity of molded inkjet printheads, examples described herein include a “thinned”, molded printhead die that includes one or more die slivers embedded into a molded body. The molded printhead die is thinned, or ground down, from its back side to remove a portion of the molded body at the back surface of the molded printhead die. Because the molded printhead die is thinned down all the way to the surface of the die sliver (or die slivers) embedded in the molding, there are no fluid channels formed into the molded body to direct fluid to the back surface of the die sliver, as in prior molded inkjet printhead designs. Instead, both the front and back surfaces of each die sliver are flush with the molding material in which the die sliver is embedded. Thinning the molded printhead die in this manner opens up the previously formed fluid/ink feed holes (IFH's) in each die sliver from its back surface to enable fluid to flow from the back surface of the die sliver to fluid ejection chambers on the front surface of the die sliver.
In one example, a printhead includes a die sliver molded into a molding. The die sliver includes a front surface that is flush with the molding and exposed outside the molding to dispense fluid. The die sliver also includes a back surface that is flush with the molding and exposed outside the molding to receive fluid. The die sliver has edges that contact the molding to form a joint between the die sliver and the molding.
In another example, a print bar includes multiple thinned, molded printhead dies embedded in a molding material. The molded printhead dies are arranged generally end to end along the length of a printed circuit board (PCB) in a staggered configuration in which one or more of the dies overlaps an adjacent one or more of the dies. Each molded printhead die comprises a die sliver having a front surface and a back surface exposed outside of the molding. The back surface is to receive fluid and the front surface is to dispense fluid that flows from the back surface to the front surface through fluid feed holes in the die sliver.
In another example, a print cartridge includes a housing to contain a printing fluid and a thinned, molded printhead die. The thinned, molded printhead die comprises a die sliver embedded in a molding. The die sliver has edges forming a joint with the molding, and a front surface and back surface are exposed outside of the molding. The back surface is to receive fluid and the front surface is to dispense fluid that is to flow from the back surface to the front surface through fluid feed holes in the die sliver.
As used in this document, a “printhead” and a “printhead die” mean the part of an inkjet printer or other inkjet type dispenser that can dispense fluid from one or more nozzle openings. A printhead includes one or more printhead dies, and a printhead die includes one or more die slivers. A die “sliver” means a thin substrate (e.g., silicon or glass) having a thickness on the order of 200 μm and a ratio of length to width (L/W) of at least three. A printhead and printhead die are not limited to dispensing ink and other printing fluids, but instead may also dispense other fluids for uses other than printing.
Referring generally to
Each die sliver 102 has a front surface 108 that opposes its back surface 106. Through a molding process in which the die slivers 102 are molded into the molding material 104, the front surfaces 108 are flush with and remain exposed outside of the molding material 104, enabling each die sliver 102 (and printhead die 100) to dispense fluid. Each die sliver 102 includes a silicon die substrate 110 comprising a thin silicon sliver that includes fluid feed holes 112 dry etched or otherwise formed therein to enable fluid flow through the substrate 110 from a first substrate surface 114 to a second substrate surface 116. In addition to removing the molding material 104 from the back surfaces 106 of die slivers 102, the process used to thin the molded printhead die 100 (e.g., a grinding process) may also remove a thin silicon cap layer (not shown) covering up the fluid feed holes 112 to enable fluid at the back surfaces 106 to enter and flow through the fluid feed holes 112 to the front surfaces 108.
Formed on the second substrate surface 116 are one or more layers 118 that define a fluidic architecture that facilitates the ejection of fluid drops from the molded printhead die 100. The fluidic architecture defined by layer(s) 118 generally includes ejection chambers 120 having corresponding orifices 122, a manifold (not shown), and other fluidic channels and structures. The layer(s) 118 can include, for example, a chamber layer formed on the substrate 110, and a separately formed orifice layer over the chamber layer. In other examples, layer(s) 118 can include a single monolithic layer that combines the chamber and orifice layers. The fluidic architecture layer 118 is typically formed of an SU8 epoxy or some other polyimide material, and can be formed using various processes including a spin coating process and a lamination process.
In addition to a fluidic architecture defined by layer(s) 118 on silicon substrate 110, each die sliver 102 includes integrated circuitry formed on the substrate 110 using thin film layers and elements (not shown). For example, corresponding with each ejection chamber 120 is an ejection element, such as a thermal resistor ejection element or a piezoelectric ejection element, formed on the second surface 116 of substrate 110. The ejection elements are actuated to eject drops or streams of ink or other printing fluid from chambers 120 through orifices 122. Thus, each chamber 120 and corresponding orifice 122 and ejection element generally make up a fluid drop generator formed on the second surface 116 of substrate 110. Ejection elements on each die sliver 102 are connected to bond pads 124 or other suitable electrical terminals on the die sliver 102, directly or through substrate 110. In general, wire bonds connect the die sliver bond pads 124 to a printed circuit board, and the printed circuit board is connected through signal traces in a flex circuit 922 (
The molding process, generally shown in
After the compression molding process, the carrier 300 is released from the thermal tape 302, and the tape is removed from the molded printhead die 100, as shown in
The molding process and the thinning process leave the die slivers 102 embedded within the molding material 104 such that the edges 126 or sides of the die slivers 102 comprise the amount of surface area that forms a joint or connection with the molding 104. In some examples, in order to make the joints between the die sliver 102 and the molding 104 more robust, a joint enhancement feature is incorporated at the edges 126 of the die sliver 102. The joint enhancement feature generally increases the amount of surface area contact between the die sliver 102 and the molding material 104 to improve the connection and reduce the possibility that the die sliver 102 could come loose from the molding material 104.
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While specific examples of joint enhancement features are shown and discussed herein with respect to the silicon substrate 110 and fluidics layer 118 at the edges 126 of die sliver 102, the shapes and configurations of such features are not limited in this respect. Rather, joint enhancement features made at the edges 126 of die sliver 102 generally can take on numerous other shapes and configurations including, for example, grooves, cuts, notches, channels, tapers, indentations, bumps, combinations thereof, and so on.
As shown in
As noted above, thinned, molded printhead dies 100 are suitable for use in, for example, a print cartridge and/or print bar of an inkjet printing device.
Print cartridge 902 is fluidically connected to ink supply 910 through an ink port 918, and is electrically connected to controller 914 through electrical contacts 920. Contacts 920 are formed in a flex circuit 922 affixed to the housing 916. Signal traces (not shown) embedded within flex circuit 922 connect contacts 920 to corresponding contacts (not shown) on printhead die 100. Ink ejection orifices 122 (not shown in
In some examples, a print cartridge comprises a printhead die that includes a die sliver molded into a molding. The die sliver includes a front surface exposed outside the molding to dispense fluid, and a back surface exposed outside the molding and flush with the molding to receive fluid. Edges of the die sliver contact the molding to form a joint between the die sliver and the molding.