Background

[0001] Printhead dies in an inkjet pen or print bar may include tiny channels that carry fluid, such as ink, to the ejection chambers, ink may be distributed from the snk supply to the die channels through passages in a structure that supports the printnead die(s) on the pen or print bar. It may he desirable to shrink the size of each printhead die, for example to reduce the cost of the die and, accordingly, to reduce the cost of the pen or print bar. The use of smaller dies, however, may require changes to the larger structures that support the dies, including the passages that distribute ink to the dses.

Brief Description of the Drawings

[0002] The detailed description section references the drawings, wherein;

Figures 1 -5 illustrate an Inkjet print bar implementing an example of a fluid ejection apparatus; Figures 6-12 illustrate an example of a method for making a fluid ejection apparatus;

Figures 13-1 ? illustrate another example of a method for making a fluid ejection apparatus; and

Figures 18-22 illustrate another example of a method for making a fluid ejection apparatus,

ail irt whsch various embodiments may be implemented.

[0003] Examples are shown in the drawings and described in detail below. The drawings are not necessarily to scale, and various features and views of the drawings may be shown exaggerated in scale or in schematic for clarity and/or conciseness. The same part numbers ^, may designate the same or similar parts throughout the drawings .

Detailed Description

[0004] Inkjet printers that utilize a substrate wide print bar assembly have been developed to help increase printing speeds and reduce printing costs . Conventional substrate wide print bar assemblies include multiple parts that carry printing fluid from the printing fluid supplies to the small printhead dies from which the printing fluid is ejected on to the paper or other print substrate . While reducing the size and spacing of the printhead dses continues to be important for reducing cost, channeling printing fluid from the larger supply components to ever smaller, more tightly spaced dies requires complex flow structures and fabrication processes that cart actually increase [0005] Described herein are various implementations of a fluid ejection structure enabling the use of smaller printhead dies and more compact die circuitry to help reduce coat in substrate wide inkjet printers, A printhead structure implementing one example of the new fluid ejection structure may include multiple printhead dies glued or otherwise mounted in openings in a printed circuit board such that drop ejectors of first surfaces of the printhead dies are exposed at a first surface of the printed circuit board . The structure may include plunge -cut fluid feed slot through which fluid may Mow to respective ones of the printhead dies, the plunge-cut fluid feed slot extending through a second surface, opposite the first surface, of the printed circuit board end into a second surface, opposite the first surface, of the printhead dies Conductive pathways in the printed circuit board may connect to electrical terminals on the dies. The printed circuit hoard in effect grows the size of each printhead die for making fluid and electrical connections and for attaching the printhead dies to other structures , thus enabling the use of smaller dies. The ease with which printed circuit boards can be fabricated and processed may also help simplify the fabrication of page wide print bars and other printhead structures as new, composite structures with built-in printing fluid channels, eliminating the difficulties of forming the printing fluid channels in a substrate.

[0006] In various implementations, the fluid ejection structure may not be limited to print bars or other types of printhead structures for inklet printing. but may be implemented in other devices and for other fluid flow applications. Thus, in one example, the fluid ejection structure may include a micro device embedded in a printed circuit board having fluid feed slots and channels therein through which fluid may flow to the micro device The micro device, for example, coufd be an electronic device, a mechanical device, or a

microelectromechanical system (MEMS) device. The fluid flow, tor example, could he a cooiing fluid flow into of ooto the micro device or fluid flow into a printhead am or other fluid dispensing micro device.

[0007] As used herein, a "printed circuit board" means a non- conductive substrate with conductive pathways for mechanically supporting and electrically connecting: to an electronic device and may comprise a stack of a plurality of layers such as, for example, prepreg layers and metal layers (printed circuit board is sometimes abbreviated "PCS"), a "micro device" means a device, such as a printhead die, etc., having one or more exterior dimensions less than or equal to 30mm; "thin" means a thickness less than or equal to 650pm; a "sliver" means a thin micro device having a ratio of length to width (L/W) of at least three; a " printhead and a "printhead die" mean that part of an inKyet printer or other snkjef type dispenser that dispenses fluid from one or more openings. A printhead includes one or more printhead dies. " printhead " and "printhead die" are not limited to printing with ink and other printing fluids but also include Inkjet type dispensing: of other fluids and/or for uses other than printing.

[0008] Figures 1-5 illustrate an example of a fluid ejection apparatus 100 to which printhead dies are embedded in a printed circuit board with plunge-cut fluid feed slots. In this example, fluid ejection apparatus 100 may he configured as an elongated print bar such as might be used in a single pass substrate wide printer . Referring first to Figures 1 and 2. pnntheods 102 may be embedded in an elongated primed circuit board 104 and arranged generally end to end m rows 106 in a staggered configuration m which the prifitheads 102 in each row overlap another phnthead 102 in that row.

Although four rows 106 of staggered printheads 102 are shown, for priming four different colors tor example, other suitable configurations may be possible . Figures 3-5 are detailed views of one of the die slivers 102 shown in Figure 2

[0009] Referring now to Figures 1 -5, in the example shown, each printhead 102 may include a single printhead die sliver 108 with two rows of election chambers 1 10 and corresponding drop ejectors 112 through which printing fluid may be ejected from chambers 1 10. A fluid feed slot/channel 1 14 m printed circuit board 104 may supply printing fluid to each printhead die slsver 108. Other suitabie configurations for each printhead 102 may he possible. For example, more or fewer printhead die slivers 108 may be used with more or fewer ejection chambers 1 10 and fluid feed slots 114 or larger dies (not slivers) may bo used.

[0010] Printing fluid may flow into each ejection chamber 1 10 from a manifold 1 16 extending lengthwise along each die sliver 108 between the two rows of ejection chambers 1 10. Printing fluid may feed into manifold 1 16 through multiple ports 118 that are connected to a printing fluid feed slot/channel 1 14 at die surface 120. The idealized representation of a printhead die 108 m Figures 1 -5 depicts three layers 12.2, 124, 125 for convenience only to clearly show ejection chambers 110, drop ejectors 112, manifold 1 16, and ports 1 1 8 An actual inkjet printhead die sliver 108 may be a typically complex integrated circuit (IC) structure formed on a silicon substrate 122 with layers and elements not shown in Figures 1 -5 For example, a thermal ejector element or a piezoelectric ejector element formed (not shown) on substrate 122 at each ejection chamber 11D may bo actuated to eject drops or streams of ^' ink or other printing fluid from drop ejectors 1 12 Conductors 128 covered by a protective iayer 1 30 and attached to electrical terminals 132 on substrate 122 carry electrical signals to ejector and/or other elements of printhead die sliver 108.

[0011] Figures 6-1 1 illustrate one example method for making a printhead structure 100 such as the one shown in Figures 1 -5. Figure 1 2 Is a flow diagram of the method illustrated In Figures 6- 1 1 . Although a process for making a printhead structure 100 with printhead dies 108 is shown, the method may be used to form other fluid ejection structures using other micro devices. Also, while only one printhead structure 100 ss shown , the method may be used to simultaneously fabricate multiple printhead structures 100. Indeed, one of the advantages of embedding dies 108 in a printed circuit board 104 is the ease with which a print circuit board 104 may be made to different sizes to accommodate individual , group or wafer level fabrication.

[0012] Referring first to Figure 6, in preparation for receiving a micro device (such as, e g , a printhead die), an opening 134 is sawn or otherwise termed in a first printed circuit board layer set 104a of a printed circuit board and conductors 1 28 exposed inside the opening 134, in Figure 7, a patterned die attach film or other suitable adhesive 138 is applied to printed circuit board 104 and a PET (polyethylene terephthafate) film, high-temperature tape, or other suitable barrier 138 applied over die attach film 136 (operation 1202 of figure 1 2) Barrier 130 spanning opening 134 forms a cavity for receiving a printhead die 102 (operation 1204 of Figure 1 2} such that a first surface, the top Side, of the die 102 faces the barrier 138 and a second surface, the hack side, of tne die 102 faces away from the barrier 13-8, as shown in Figure 8.

[0013] In Figure 8, PCB conductors 128 are bonded to phnihead die terminals 132 (operation 1206 of Figure 12) and die attach adhesive 136 is flowed into the gaps around printhead die 102 (operation 1208 of Figure 12). Die attach adhesive 136 forms the g!ue that holds pnntneao die 102 in the opening 134. Die attach adhesive 136 also seals the embedded die 1 02 in the opening 134. Accordingly, although any suitable adhesive may be used for die attach 136, including die attach films commercially available for

semiconductor fabrication, the adhesive should resist the corrosive effect, if any, of the Ink or other printing fluids.

[0014] In one example for bonding and fiowmg, solder or conductive adhesive is applied to one or both conductors 128 and terminals 1 32 before assembly and the structure heated after assembly to reflow the solder to bond conductors 128 and terminals 132 and to flow (or wick) adhesive 13$ into the gaps around printhead die 102 as shown in Figure 8.

[0015] In Figure 9. a second primed circuit board layer set 104b ts coupled to the first printed circuit board layer set 104b (operation 1210 of Figure 12). As shown, the second printed circuit board layer set 104b covers the second surface, the back side, of the d-e 102 second surface, opposite the first surface, of the printhead die 102. Printhead structure 100 is then released from barrier 138, as shown in Figure 10 (operation 1212 of Figure 12}

£001 $ ] In Figure 10, a fluid feed slot 1 14 is plunge-cut through the second printed circuit board layer set 104b and into the second surface of the dse 102 _: as shown (operation 1214 of Figure 12). in at least some

implementations, forming fluid feed slot 1 14 after the die 102 is coupled io the printed circuit board 104a/104b may provide a more mechanically robust structure into which fluid feed slot 1 14 may be formed as compared to forming fluid feed slot 1 14 into a die without a printed circuit board 104a/ 104b, which may result in fewer cracks during the formation of the fluid feed slot 1 14. In addition, handling of the die 102 may be facilitated fcy coupling the die 102 to the larger footprint printed circuit hoard 104a/104o .

[0017] Figures 13-17 and 18-22 illustrate other examples m which electrical connections between the printed circuit board 104 and the die 102 {operation 1206 of Figure 1 1 ) may be made after the printhead dies 102 are embedded in printed circuit board 14 to conductors 128 exposed on the exterior of printed circuit board 104 adjacent to the opening 134. For example. In various implementations, electrical connections between the printed circuit hoard 104 and the die 102 {operation 1206 of F igure 1 1 ) may he performed after die attach adhesive 136 is flowed into the pans around printhead die 102 (operation 1208 of Figure 1 2} or after the second printed circuit board layer set 104 b is coupled to the first printed circuit board layer set 104b (operation 1210 of Figure 1 2). In some implementations, electrical connections between the primed circuit board 104 and the die 102 (operation 1206 of Figure 1 1 ) may be performed after fluid feed slot 1 14 is plunge-cut through the second printed circuit board layer set 1040 and into the second surface of the die 102. as shown (operation 1214 of Figure 12).

[0018] As shown in Figure 13. a barrier 1 38 spanning the opening 134 m the first printed circuit hoard layer set 1 Q4a may form a cavity for receiving a printhead die 102 such thai a first surface, the top side, of the die 102 faces the harrier 138 and a second surface, the back side, of the die 102 faces away from the bamer 138 , in this example, the first printed circuit board layer set 104a may be a pre-impregnated ("pre- preg") with an epoxy resin or other scmabie adhesive. The assembly may then be heated to flow pre-preg adhesive 136 into the gaps around printhead die 102 to couple printhead die 102 in the opening 1 34,

[0019] In Figure 14 , a second printed circuit board layer set 104b is coupled to the first printed circuit board layer set 104b. As shown, the second printed circuit board layer set 104b covers the second surface, the back Side, of the die 102 second surface, opposite the first surface, of the printhead die 102. Printhead structure 100 is then released from barrier 1 38 , as shown in Figure 1 5

[0020] in Figure 16, wires 142 are bonded to conductors 120 on the printed circuit board I04a/l 04b and the connections encapsulated in an encepso!ant material 144.

[0021] In Figure 17, a fluid feed slot 1 1 4 is plunge-cut through the second printed circuit board layer set 104b end into the second surface of the die 102 , as shown . [0022] Figures 18-22 show another example for electrically coupling printed circuit board 104a/104b with prsnthead die 102. As shown in Figure 18, a bamer 138 spanning the opening 1 34 m the fits; printed circuit board: layer set 104a may form a cavity tor receiving a printhead die 102 such that a first surface, the top side, of the die 102 faces the harrier 136 and a second surface, the back Side, of the die 102 faces away from the barrier 138. T he first printed Circuit board layer set 104a may be a pre-preg with an epoxy resin or other suitable adhesive. The assembly may then be heated to flow pre-preg adhesive 136 into the gaps around printhead die 102 to couple printhead die 102 in the opening 1 34, as shown .

[00233 In Figure 19, a second printed circuit board layer set 104b is coupled to the first printed circuit board layer set 104b. As shown, the second printed circuit board layer set 104b covers the second surface, the back side., of the die 102 second surface, opposite the first surface, of the printhead die 102. Printhead structure 1 00 is then released from barrier 1 38 , as shown in Figure 20.

[00243 In Figure 21 , a metal trace layer may be formed over the printed circuit board 104a/104b to electrically couple conductors 128 on the printed Circuit board 104a/104b with the electrical terminals 1 32 of the printhead die 102 As shown, the printhead die 102 may include a conductive via 146 to electrically interconnect conductors 128 with the electrical terminals 132. in various implementations, a protective layer 148 may be laminated or deposited over at least a portion of the structure 100. [0025] For the various implementations described herein, a printed circuit board fluid ejection apparatus 100 may enable the use of long, narrow and very thin printhead dies 102. for example, a 100μm thick printhead die 102 that is about 26mm long and 500μm wide can be embedded in a 1 mm thick printed circuit board 104 to replace a conventional 500pm thick silicon printhead die . Not only is it cheaper and easier to form plunge-cut ink slots 114 in 3 printed circuit board compared to forming feed channels/slots in a silicon substrate, but it is also cheaper and easier to form printing fluid ports 1 12 in a thinner die 102. For example, ports 1 12 in a 100μm thick printhead die 102 may be formed by dry etching and other suitable micromachining techniques not practical tor thicker substrates. Micromachining a high density array of through ports 1 12 in a thin silicon, glass or other substrate rather than forming conventional slots leaves a stronger substrate while stiff providing adequate printing fluid flow.

[0026] Various aspects of the illustrative embodiments are described herein using terms commonly employed by those skilled in the art to convey the substance of their work to others skilled in the art. it will be apparent to those skilled in the art that alternate embodiments may fee practiced with only some of the described aspects . For purposes of explanation , specific numbers, materials, and configurations are set forth in order to provide a thorough understanding of the illustrative embodiments, it will be apparent to one skilled tn the art that alternate embodiments may be practiced without the specific details. In other instances , well-known features are omitted or simplified In order not to obscure the illustrative embodiments. [0027] Although: certain embodiments have been illustrated and described herein, it will be appreciated by those of ordinary ski in the art that, a wide variety of alternate and/or equivalent embodiments or implementations calculated to achieve the same purposes may be substituted for the embodiments shown and described without departing from the scope of this disclosure. Those with skill in the art will readily appreciate that embodiments may he implemented In a wide variety o? ways. This application is intended to cover any adaptations or variations of the embodiments discussed herein. If is manifestly intended, therefore, that embodiments be limited only by the claims and the equivalents thereof.