BACKGROUND

[0001] A fluid ejection die in a fluid cartridge or print bar may include a plurality of fluid ejection elements on a surface of a silicon substrate. By activating the fluid ejection elements, fluids may be printed on substrates. The fluid ejection die may include resistive elements used to cause fluid to be ejected from the fluid ejection die.

BRIEF DESCRIPTION OF THE DRAWINGS

[0002] The accompanying drawings illustrate various examples of the principles described herein and are a part of the specification. The illustrated examples are given merely for illustration, and do not limit the scope of the claims.

[0003] Fig. 1 is an elevation cross-sectional diagram of a fluid flow structure, according to one example of the principles described herein.

[0004] Fig. 2 is an elevation cross-sectional diagram of a fluid flow structure, according to another example of the principles described herein.

[0005] Fig. 3 is an elevation cross-sectional diagram of a fluid flow structure, according to still another example of the principles described herein.

[0000] Fig, 4 is an elevation cross-sectional diagram of a fluid flow structure, according to yet another example of the principles described herein.

[0007] Fig. 5 is a block diagram of a fluid cartridge including a fluid flow structure, according to one example of the principles described herein. [0008] Fig. 6 is a block diagram of a fluid cartridge including a fluid flow structure, according to another example of the principles described herein.

[0009] Fig. 7 is a block diagram of a printing device including a number of fluid flow structures in a substrate wide print bar, according to one example of the principles described herein.

[0010] Fig. 8 is a block diagram of a print bar including a number of fluid flow structures, according to one example of the principles described herein.

[0011] Figs. 9A through 9E depict a method of manufacturing a fluid flow structure, according to one example of the principles described herein,

[0012] Throughout the drawings, identical reference numbers designate similar, but not necessarily identical, elements. The figures are not necessarily to scale, and the size of some parts may be exaggerated to more clearly illustrate the example shown. Moreover the drawings provide examples and/or implementations consistent with the description; however, the description is not limited to the examples and/or implementations provided in the drawings.

DETAILED DESCRIPTION

[0013] As mentioned above, the fluid ejection die may include resistive elements used to cause fluid to be ejected from the fluid ejection die. In some examples, trie fluid may include particles suspended in the fluid that may tend to move out cf suspension and collect in certain areas within the fluid ejection die as sediment. In one example, this sedimentation of particles may be corrected by including a number of fluid recirculation pumps to the fluid ejection die. In one example, the fluid recirculation pumps may be pump devices used to reduce or eliminate, for example, pigment settling within an ink by recirculating the ink through the firing chambers of the fluid ejection die and a number of bypass fluidic paths.

[0014] However, addition of the fluid recirculation pumps along with the fluid ejection resistors may cause an undesirable amount of waste heat to accumulate within the fluid, the fluid ejection die, and other portions of the overall fluid ejection device. This increase in waste heat may cause thermal defects in the ejection of the fluid from the fluid ejection die.

[0015] Examples described herein provide a fluid ejection device. The fluid ejection device may include a fluid ejection die embedded in a moldable material, a number of fluid recirculation pumps within the fluid ejection die to recirculate fluid within a number of firing chambers of the fluid ejection die, and a number of heat exchangers thermally coupled to a fluid channel side of the fluid ejection die. The fluid ejection device may further include a number of cooling channels defined in the moldable material thermally coupled to the heat exchangers. The heat exchangers may include a wire, a bind ribbon, a heat pipe, a lead frame, a loop heat exchanger, or combinations thereof. The fluid recirculated by the fluid recirculation pumps within the firing chambers of the fluid ejection die is present within the cooling channels. In another example, the cooling channels convey a cooling fluid. The cooling fluid functioning to transfer heat from the heat exchangers.

[0016] The heat exchangers may be embedded within the moldable material, and exposed to the cooling channels. Further, the heat exchangers at least partially protrude from the moldable material.

[0017] Examples described herein also provide a print bar. The print bar may include a number of fluid ejection devices. Each of the fluid ejection devices may include a fluid ejection die embedded in a moldable material, a number of fluid recirculation pumps within the fluid ejection die to recirculate fluid within a number of firing chambers of the fluid ejection die, a number of heat exchangers at least partially embedded within the moldable material and thermally coupled to a fluid channel side of the fluid ejection die of the fluid ejection die, and a number of cooling channels defined in the moldable matenal thermally coupled to the heat exchangers.

[0018] The print bar may further include a controller to control ejection of the fluid from the fluid ejection die, and control the fluid recirculation pumps. Λ recirculation reservoir may also be included for recirculating a cooling fluid through the cooling channels. The controller controls the recirculation reservoir. The recirculation reservoir may include a heat exchange device to transfer heat from the cooling fluid, in one example, the cooling fluid is the same as the fluid recirculated within the firing chambers of the fluid ejection die. In another example, the cooling fluid I» different than the fluid recirculated within the firing chambers of the fluid ejection die.

[0019] Examples described herein also provide a fluid flow structure. The fluid flow structure may include a die sliver compression molded into a molding, a fluid feed hole extending through the die sliver from a first exterior surface to a second exterior surface, a fluid channel fluidically coupled to the first exterior surface, and a number of heat exchangers at least partially molded into the molding and thermally coupled to the first exterior surface of the fluid ejection die. The fluid flow structure may further include a number of cooling channels defined in the moldable material thermally coupled to the heat exchangers. In one example, the heat exchangers may include a loop heat exchanger. In this example, the loop heat exchanger may at least partially protrude from the moldable material.

[0020] As used in the present specification and in the appended claims, the term "a number of or similar language is meant to be understood broadly as any positive number comprising 1 to infinity; zero not being a number, but the absence of a number.

[0021] In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the present systems and methods. It will be apparent, however, to one skilled in the art that the present apparatus, systems, and methods may be practiced without these specific details. Reference in the specification to "an example ^1' or similar language means that a particular feature, structure, or characteristic described in connection with that example is included as described, but may or may not be included in other examples.

[0022] Turning now to the figures, Fig. 1 is an elevation cross-sectional diagram of a fluid flow structure {100). according to one example of the principles described herein. A fluid flow structure (100) including those depicted throughout the figures may be any structure through which fluid flows, in one example, the fluid flow structures (100, 200, 300, 400, collectively referred to herein as 100) in, far example, Figs. 1 through 4 may include a number of fluid ejection dies (101). The fluid ejection dies (101) may be used in, for example, printing fluids onto a substrate. Further, in one example the fluid flow structures

(100) may include fluid ejection dies (101) including, for example, a number of fluid firing chambers, a number of resistors for heating and firing the fluid from the firing chambers, a number of fluid feed holes, a number of fluid

passageways, and other elements that assist in the ejection of fluid from the fluid flow structures (100, 20G. 300, 400). In still another example, the fluid flow structures (100, 200. 300, 400) may include fluid ejection dies (101) that are thermal fluid-jet dies, piezoelectric fluid-jet dies, other types of fluid-jet dies, or combinations thereof.

[0023] in one example, the fluid flow structure (100, 200, 300, 400) includes a number of sliver die (101) compression molded into a moldable matenal (102). A sliver die (101 ) includes a thin silicon, glass, or other substrate having a thickness on the order of approximately 650 micrometers (μιη) or less, and a ratio of length to width (UW) of at least three. In one example, the fluid flow structure (100) may include at feast one fluid ejection die (101)

compression molded into a monolithic body of plastic, epoxy mold compound (EMC), or other moldable material (102). For example, a print bar including the fluid flow structure (100, 200, 300, 400) may include multiple fluid ejection dies

(101) molded into an elongated, singular molded body. The molding of the fluid ejection dies (101) within the moldable material (102) enables the use of smaller dies by offloading the fluid delivery channels such as fluid feed holes and fluid delivery slots from the fluid ejection die (101) to the molded body (102) of the fluid flow structure (100, 200, 300, 400). In this manner, the molded body (102) effectively grows the size of each fluid ejection die (101 ), which, in turn, improves fan-out of the fluid ejection die (101) for making external fluid connections and for attaching the fluid ejection dies (101) to other structures.

[0024] The fluid ejection device (100) of Fig. 1 may include at least one fluid ejection die (101) such as, for example, a sliver die embedded in the moldable material (102). A number of fluid feed holes (104) may be defined within and extending through the fluid ejection die (101) from a first exterior surface (106) to a second exterior surface (107) in order to allow the fluid to be brought from the back side of the fluid ejection die (101) tc be ejected from the front side. Thus, a fluid channel (108) is defined in the fluid ejection die (101) and fluidically coupled between the ftrst exterior surface (106) and the second exterior surface (107).

[0025] A number of heat exchangers (105) may be at least partially molded into the molding material (102). The heat exchangers (105) may be any passive heat exchange device that transfers heat generated by the fluid ejection die (101) to a fluid medium such as air or a liquid coolant. The heat exchangers

(105) may be a wire such as a copper wire, a bond ribbon, a heat pipe, a lead frame, other types of heat exchangers, or combinations thereof.

[00 26] The heat exchangers (105) are thermally coupled to the first exterior surface (106) of the fluid ejection die (101). The first exterior surface

(106) of the fluid ejection die (101) may be referred to as a fluid channel side of the fluid ejection die (101). in this manner, the heat exchangers (105) are able to draw heat generated by, for example, a number of resistors for heating and firing the fluid from the firing chambers included within the fluid ejection die (101).

[0027] Further, the heat exchangers (105) are able to draw heat generated by a number of fluid recirculation pumps within the fluid ejection die (101 ). In one example, the fluid recirculation pumps may be any device used to reduce or eliminate, for example, pigment settling within an ejectable fluid such as an ink by recirculating the ejectable fluid through the firing chambers of the fluid ejection die (101) and a number of by-pass fiuidic paths. The fluid recirculation pumps move the ejectable fluid such as the ink through the fluid ejection die (101). in one example, the fluid recirculation pumps may be micro- resistors that create bubbles within the fluid ejection die (101) that force the ejectable fluid through the firing chambers and by-pass fiuidic paths of the fluid ejection die (101). In another example, the fluid recirculation pumps may be piezoelectrically activated membranes that change the shape of a piezoelectric material when an electric field is applied, and force the ejectable fluid through the firing chambers and by-pass fiuidic paths of the fluid ejection die (101). Actuation of the fluid recirculation pumps and the firing chamber resistors increases the amount of waste heat generated within the fluid ejection die (101), The heat exchangers (105) are used to draw that heat from the fluid ejection die (101).

[0028] Fig. 2 is an elevation cross-sectional diagram of a fluid flow structure (200), according io another example of the principles described herein. Those elements similarly numbered in Fig. 2 relative to Fig. 1 are described above in connection with Fig, 1 and other portions herein. A number of fluid firing chambers (204) and associated firing resistors (201) are depicted within the fluid ejection die (101) of Fig. 2. The example fluid flow structure (200) of Fig. 2 further includes a number of micro-fluid recirculation pumps (202) as described herein. The micro-fluid recirculation pumps (202) may be located within a fluid passageway within the fluid ejection die (101).

[0029] The fluid flow structure (200) of Fig. 2 further includes a number of cooling channels (203) defined within the moldab!e material (102). The cooling channels (203) may be thermally coupled to the heat exchangers (105) in order to draw heat from the fluid ejection die (101) via the heat exchangers (1G5). The moldable material (102) such as an EMC may have a thermal conductivity (i.e., rate at which heat passes through a material) of approximately 2 to 3 watts per square meter of surface area for a temperature gradient of one ke!vin for every meter thickness (W/mK). Further, in an example where the moldable material {102} has a filler material such as aluminum oxide (Aid), its thermal conductivity may be approximately 5 W/mK. In contrast, copper (Cu) and gold (Au) have a thermal conductivity of approximately 410 W/mK and 310 W/mK, respectively. Further, silicon (Si) of which the fluid ejection dies (101) may be made of have a thermal conductivity of approximately 148 W/mK. Thus, in order to make the heat exchangers (105) embedded in the moldable material more effective in dissipating heat, at least a portion of the heat exchangers (105) may be exposed to the cooling channels (203).

[0030] In one example, the cooling channel (203) may transport a cooling fluid therein to assist in drawing the heat away from the fluid ejection die (101 ). In one example, the cooling fluid may be air passing through the cooling channels (203). In another example, the fluid introduced to the fluid ejection die (101) via the fluid channel (108) and ejected by the fluid firing chambers (204) and associated firing resistors (201) of the fluid ejection die (101) is present within the cooling channels (203) and is used as a heat transfer medium.

[0031] In still another example, a coating fluid other than air or the ejected fluid may be used as the heat transfer medium within the cooling channels (203). In this example, a coolant may be provided 'which flows through the cooling channels (203) and around the heat exchangers (105) to prevent the fluid ejection die (101) from overheating. The coolant transfers the heat produced by the firing resistors (201) and fluid recirculation pumps (202) within the fluid ejection die (101) to other portions of the fluid flow structure (200) or exterior to the fluid flow stn.ict.ure in order to dissipate the heat. In this example, the coolant may keep its phase and remain as a liquid or gas, or may undergo a phase transition, with the latent, heat adding to the cooling efficiency. When a phase transition within the coolant takes place, the coolant may be used to achieve below-ambient temperatures as a refrigerant.

[0032] Fig. 3 is an elevation cross-sectional diagram of a fluid flow structure (300), according to still another example of the principles described herein. Those elements similarly numbered in Fig. 3 relative to Figs. 1 and 2 are described above in connection with Figs. 1 and 2 and other portions herein. The example of Fig. 3 includes a nozzle plate (301) through which the fluid ejection die (101) ejects the fluid. The nozzle plate (301) may include a number of nozzles (302) defined in the nozzle plate (301). Any number of nozzles (302) may be included within the nozzle plate (301). and, in one example, each firing chamber (204) includes a corresponding nozzle (302) defined in the nozzle plate (301).

[0033] Fig. 4 is an elevation cross-sectional diagram of a fluid flow structure (400), according to yet another example of the principles described herein. Those elements similarly numbered in Fig. 4 relative to Figs. 1 through 3 are described above in connection with Figs. 1 through 3 and ether portions herein. The example of Fig. 4 may further include a number of loop heat exchangers (405). These loop heat exchangers (405) may be coupled to the fluid ejection die (101) via a connection pad (406), may be coupled directly to the fluid ejection die (101), or may be at least partially embedded within the fluid ejection die (101). As depicted in Fig. 4. the loop heat exchangers (405) may protrude from a surface of the molding material (102). In this manner, heat within the fluid ejection die (101) created by the firing resistors (201 ) and fluid recirculation pumps (20?.) may be drawn away from the fluid ejection die (101) to, far example, ambient air.

[0034] In one example, the loop heat exchangers (405) may extend vertically through moldable material (102) to contact a cooling channel (203) or a metal block to remove waste heat within the fluid ejection die (101). In another example, the loop heat exchangers (405) may extend horizontally, vertically, or a combination thereof through moldable material (102) to an exterior of the moldable material (102). The loop heat exchangers (405) of Fig. 4 may be incorporated into any example fluid flow structure (100) described herein.

[0035] Fig. 5 is a block diagram of a fluid cartridge (500) including a fluid flow structure (100, 200, 300, 400, collectively referred to herein as 100).

according to one example of the principles described herein. The fluid flow structure (100) depicted in Fig. 5 may be any of those fluid flow structures described in Figs. 1 through 4 and throughout the remainder of this disclosure, or combinations thereof. The fluid cartridge (500) may include a fluid reservoir (502). a fluid flow structure (100). and a cartridge controller (501 ). The fluid reservoir (502) may include the fluid used by the fluid flow structure (100) as an ejection fluid during, for example, a printing process. The fluid may be any fluid that may be ejected by the fluid flow structure (100) and its associated fluid ejection dies (101 ). In one example, the fluid may be an ink, a water-based ultraviolet (UV) ink, pharmaceutical fluids, and 3D printing materials, among other fluids.

[0036} The cartridge controller (501 ) represents the programming, processor(s), and associated memories, along with other electronic circuitry and components that control the operative elements of the fluid cartridge (500) including, for example, the resistors (201) and the fluid recirculation pumps (202). The cartridge controller (501) may control the amount and timing of fluid provided to the fluid flow structure {100) by the fluid reservoir (502).

[0037] Fig. 6 is a block diagram of a fluid cartridge (600) including a fluid flow structure (100) according to another example of the principles described herein. Those elements similarly numbered in Fig. 6 relative to Fig. 5 are described above in connection with Fig. 5 and other portions herein. The fluid cartridge (600) may further include a recirculation reservoir (601). The recirculation reservoir (601) recirculates a cooling fluid through the cooling channels (203) within the fluid flow structure (100). in one example, the controller may control the recirculation reservoir (601).

[0038] Further, in one example, the recirculation reservoir (601 ) may include a heat exchange device (602) to transfer heat from the cooling fluid within the recirculation reservoir (601). The heat exchange device (602) may be any passive heat exchanger that transfers the heat within the cooling fluid of the recirculation reservoir (601). In one example, the heat exchange device (602) dissipates the heat into ambient air surrounding the recirculation reservoir (601).

[00 39] in one example, the cooling fluid may be the same as the fluid recirculated within the firing chambers (204) of the fluid ejection die (101). In this example, the fluid reservoir (502) and the recirculation reservoir (601 ) may be fluidically coupled such that the fluid within the fluid reservoir (502) is cooled as it is introduced into the recirculation reservoir (601). Further, in this example, the recirculation reservoir (601) may pump the fluid within the fluid reservoir (502) into the cooling channels (203).

[0040] In another example, the cooling fluid may be different than the fluid recirculated within the firing chambers (204) of the fluid ejection die (101). In this example, the fluid reservoir (502) and the recirculation reservoir (601) may be fluidically isolated from one another such that the fluid within the fluid reservoir (502) is introduced to the fluid ejection die (101) via the fluid channel (106). and the cooling fluid within the recirculation reservoir (601 ) is introduced into the cooling channels (203) via different channels. As described herein, the cooling fluid or coolant may be any fluid that transfers the heat produced by the resistors (201 ) and fluid recirculation pumps (202) within the fluid ejection die (101 ) to other portions of the fluid flow structure (100) or exterior to the fluid flow structure in order to dissipate the heat, in this example, the coolant may keep its phase and remain as a liquid or gee, or may undergo a phase transition, with the latent heat adding to the cooling efficiency. When a phase transition within the coolant takes place, the coolant may be used to achieve below-ambient temperatures as a refrigerant.

[0041] Fig. 7 is a block diagram of a printing device (700) including a number of fluid flow structures (100) in a substrate wide print bar (704), according to one example of the principles described herein. The printing device (700) may include a print bar (704) spanning the width of a print substrate (706). a number of flow regulators (703) associated with the print bar (704), a substrate transport mechanism (707), printing fluid supplies (702) such as a fluid reservoir (502). and a controller (701). The controller (701) represents the programming, processor(s). and associated memories, along with other electronic circuitry and components that control the operative elements of the printing device (700). The print bar (704) may include an arrangement of fluid ejection dies (101) for dispensing fluid onto a sheet or continuous web of paper or other print substrate (706). Each fluid ejection die (101) receives fluid through a flow path that extend from the fluid supplies (702) into and through the flow regulators (703), and through a number of transfer molded fluid channels (108) defined in the print bar (704).

[0042] Pig. 8 is a block diagram of a print bar (704) including a number of fluid flow structures (100), according to one example of the principles described herein. Thus, Fig. 8 illustrates the print bar (704) implementing one example of the transfer molded fluid flow structures (100) as a printhead structure suitable for use in the printer (700) of Fig. 7. Referring to the plan view of Fig. 8, the fluid ejection dies (101 ) are embedded in an elongated, monolithic molding (102) and arranged end to end in a number of rows (800). The fluid ejection dies (101) are arranged in a staggered configuration in which the fluid ejection dies (101 ) in each row (800) overlap another fluid ejection die 102 in that seme row (800). In this arrangement, each row (800) of fluid ejection dies (101) receives fluid from a different transfer molded fluid channel (108) as illustrated with dashed lines in Fig. 8. Although four fluid channels (108) feeding four rows (800) of staggered fluid ejection dies (101) is shown for us In. for example, printing four different colors such as cyan, magenta, yellow, and black, other suitable configurations are possible.

[00 43] Figs. ΘΑ through ΘΕ depict a method of manufacturing a fluid flow structure (100). according to one example of the principles described herein. Those elements similarly numbered in Figs. ΘΑ through 9E relative to Figs. 1 through 8 are described above in connection with Figs, 1 through 8 and other portions herein. The method may include adhering a thermal release tape (901) or other adhesive to a carrier (900) as depicted in Figs. ΘΑ.

[00 44] In Fig. ΘΒ. a preprocessed fluid ejection die (101) is coupled to the thermal release tape (901). A number of heat exchangers (105) may be formed on the first side (106) of the fluid ejection die (101 ). In Fig. 9C. the entirety of the fluid flow structure (100) as depicted in Fig. 9B may be compression overmolded with the moldable material (102).

[00 45] In Fig. 9D, the fluid channel (108) and a number of cooling

channels (203) are formed in the moldable material (102). The fluid channel (108) and cooling channels (203) may be formed through a cutting process, laser ablation processes, or other material removal processes. At Fig. 9E, the thermal release tape (901) and carrier (900) are removed exposing the nozzle plate (301) and the coplanar surface of the moldable material (102).

[0046] Aspects of the present system and method are described herein with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems) and computer program products according to examples of the principles described herein. Each block of the flowchart illustrations and block diagrams, and combinations of blocks in the flowchart illustrations and block diagrams, may be implemented by computer usable program code. The computer usable program code may be provided to a processor of a genera! purpose computer, special purpose computer, or other programmable data processing apparatus to produce a machine, such that the computer usable program code, when executed via, for example, the printer controller (701) of the printing device (700), the cartridge controller (501) of the fluid cartndge (500. 600), or other programmable data processing apparatus, or combinations thereof implement the functions or acts specified in the flowchart and/or block diagram block or blocks. In one example, the computer usable program code may be embodied within a computer readable storage medium; the computer readable storage medium being part of the computer program product. In one example, the computer readable storage medium is a non-transitory computer readable medium.

[0047] The specification and figures describe a fluid ejection device. The fluid ejection device may include a fluid ejection die embedded in a moldable material, a number of fluid recirculation pumps within the fluid ejection die to recirculate fluid within a number of firing chambers of the fluid ejection die. and a number of heat exchangers thermally coupled to a fluid channel side of the fluid ejection die. This fluid ejection device reduces or eliminates pigment settling and decap when printing high solid electable fluids such as inks which may otherwise prevent proper printing at start up. Micro-recirculation of the fluid within the fluid ejection die solves the pigment settling and decap issues, and the heat exchangers and cooling channels reduce or eliminate thermal defects during printing caused by waste heat generated by the micro-fluid recirculation pumps.

[0048] The preceding description has been presented to illustrate and describe examples of the principles described. This description is not intended to be exhaustive or to limit these principles to any precise form disclosed. Many modifications and variations are possible in light of the above teaching.