Printed circuit board fluid flow structure and method for making a printed circuit board fluid flow structure

In one example, a fluid flow structure includes a micro device embedded in a printed circuit board (PCB). Fluid may flow to the micro device through a channel in the PCB and a PCB conductor is connected to a conductor on the embedded micro device.

BACKGROUND

Each printhead die in an inkjet pen or print bar includes tiny channels that carry ink to the ejection chambers. Ink is distributed from the ink supply to the die channels through passages in a structure that supports the printhead die(s) on the pen or print bar. It may be 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, can require changes to the larger structures that support the dies, including the passages that distribute ink to the dies.

The same part numbers designate the same or similar parts throughout the figures. The figures are not necessarily to scale. The relative size of some parts is exaggerated to more clearly illustrate the example shown.

DESCRIPTION

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 dies 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 can actually increase cost.

A new fluid flow structure has been developed to enable the use of smaller printhead dies and more compact die circuitry to help reduce cost in substrate wide inkjet printers. A printhead structure implementing one example of the new flow structure includes multiple printhead dies glued or otherwise mounted in openings in a printed circuit board. Each opening forms a channel through which printing fluid may flow directly to a respective die. Conductive pathways in the printed circuit board connect to electrical terminals on the dies. The printed circuit board in effect grows the size of each die for making fluid and electrical connections and for attaching the dies to other structures, thus enabling the use of smaller dies. The ease with which printed circuit boards can be fabricated and processed also helps simply 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 silicon substrate.

The new 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 new structure includes a micro device embedded in a printed circuit board having a channel therein through which fluid may flow to the micro 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.

As used in this document, a “printed circuit board” means a non-conductive substrate with conductive pathways for mechanically supporting and electrically connecting to an electronic device (printed circuit board is sometimes abbreviated “PCB”); 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” 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 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.

FIGS. 1-5illustrate one example of a new inkjet printhead structure10in which printhead dies are embedded in a printed circuit board with fluid flow channels. In this example, printhead structure10is configured as an elongated print bar such as might be used in a single pass substrate wide printer. Referring first toFIGS. 1 and 2, printheads12are embedded in an elongated printed circuit board14and arranged generally end to end in rows16in a staggered configuration in which the printheads12in each row overlap another printhead12in that row. Although four rows16of staggered printheads12are shown, for printing four different colors for example, other suitable configurations are possible.FIGS. 3-5are detail views of one of the die slivers12shown inFIG. 2. Referring now toFIGS. 1-5, in the example shown, each printhead12includes a single printhead die sliver18with two rows of ejection chambers20and corresponding orifices22through which printing fluid is ejected from chambers20. A channel24in printed circuit board14supplies printing fluid to each printhead die sliver18. Other suitable configurations for each printhead12are possible. For example, more or fewer printhead die slivers18may be used with more or fewer ejection chambers20and channels24or larger dies18(not slivers) may be used.

Printing fluid flows into each ejection chamber20from a manifold26extending lengthwise along each die sliver18between the two rows of ejection chambers20. Printing fluid feeds into manifold26through multiple ports28that are connected to a printing fluid supply channel24at die surface30. The idealized representation of a printhead die18inFIGS. 1-5depicts three layers32,34,36for convenience only to clearly show ejection chambers20, orifices22, manifold26, and ports28. An actual inkjet printhead die sliver18is a typically complex integrated circuit (IC) structure formed on a silicon substrate32with layers and elements not shown inFIGS. 1-5. For example, a thermal ejector element or a piezoelectric ejector element formed (not shown) on substrate32at each ejection chamber20is actuated to eject drops or streams of ink or other printing fluid from orifices22. Conductors38covered by a protective layer40and attached to electrical terminals42on substrate32carry electrical signals to ejector and/or other elements of printhead die sliver18.

FIGS. 6-10illustrate one example process for making a printhead structure10such as the one shown inFIGS. 1-5.FIG. 11is a flow diagram of the process illustrated inFIGS. 6-10. Although a process for making a printhead structure10with printhead dies18is shown, the process may be used to form other fluid flow structures using other micro devices. Also, while only one printhead structure10is shown, the process may be used to simultaneously fabricate multiple printhead structures10. Indeed, one of the advantages of embedding dies18in a printed circuit board14with channels24is the ease with which a print circuit board14may be made to different sizes to accommodate individual, group or wafer level fabrication.

Referring first toFIG. 6, in preparation for receiving a printhead die, a slot44is sawn or otherwise formed in printed circuit board14and conductors38exposed inside slot44(steps100and102inFIG. 11). InFIG. 7, a patterned die attach film or other suitable adhesive46is applied to printed circuit board14and a PET (polyethylene terephthalate) film or other suitable barrier50applied over die attach film46(steps104and106inFIG. 11). Barrier50spanning slot48forms a cavity52for receiving printhead die18(step108inFIG. 11) and provides a mounting surface for attaching the in-process structure54shown inFIG. 8to a wafer chuck56as shown inFIG. 9(step110inFIG. 11).

InFIG. 9, PCB conductors38are bonded to printhead die terminals42(step112inFIG. 11) and die attach adhesive46is flowed into the gaps around printhead die18(step114inFIG. 11). Die attach adhesive46forms the glue that holds printhead die18in slot44. Die attach adhesive46also seals the embedded die18in channel24. Accordingly, although any suitable adhesive may be used for die attach46, 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 in channel24.

In one example for bonding and flowing, solder or conductive adhesive is applied to one or both conductors38and terminals42before assembly (FIG. 8) and the structure heated after assembly (FIG. 9) to reflow the solder to bond conductors38and terminals42and to flow (or wick) adhesive46into the gaps around printhead die18as shown inFIG. 9. Printhead structure10is then released from chuck56and barrier50removed as shown inFIG. 10(steps116and118inFIG. 11).

FIGS. 12-17illustrate another example process for making a printhead structure10.FIG. 18is a flow diagram of the process illustrated inFIGS. 12-17. In this example, the electrical connections are made after the printhead dies are embedded in printed circuit board14to conductors38exposed on the exterior of PCB14adjacent to slot44. Referring toFIG. 12, in preparation for receiving a printhead die, a slot44is sawn or otherwise formed in printed circuit board14with conductors38exposed along the exterior surface of PCB14outside slot44(step120inFIG. 18). In this example, a printed circuit board14pre-impregnated (“pre-preg”) with an epoxy resin or other suitable adhesive is used with a high temperature tape50to seal printhead die18in slot44. A pre-preg tape50may be used as an alternative to or in addition to a pre-preg PCB14. As shown inFIG. 13, tape50applied to printed circuit board14forms a cavity52for receiving printhead die18(steps122and124inFIG. 18) and provides a mounting surface for attaching the in-process structure54shown inFIG. 14to a wafer chuck56as shown inFIG. 15(step126inFIG. 18).

A PCB flow structure10enables the use of long, narrow and very thin printhead dies18. For example, a 100 μm thick printhead die18that is about 26 mm long and 500 μm wide can be embedded in a 1 mm thick printed circuit board14to replace a conventional 500 μm thick silicon printhead die. Not only is it cheaper and easier to form channels24in a printed circuit board compared to forming the feed channels in a silicon substrate, but it is also cheaper and easier to form printing fluid ports28in a thinner die18. For example, ports28in a 100 μm thick printhead die18may be formed by dry etching and other suitable micromachining techniques not practical for thicker substrates. Micromachining a high density array of through ports28in a thin silicon, glass or other substrate32rather than forming conventional slots leaves a stronger substrate while still providing adequate printing fluid flow.

As noted at the beginning of this Description, the examples shown in the figures and described above illustrate but do not limit the invention. Other examples are possible. Therefore, the foregoing description should not be construed to limit the scope of the invention, which is defined in the following claims.