Patent Grant
6959471
The present invention relates to droplet deposition apparatus, particularly inkjet printheads, components thereof and methods for manufacturing such components.
A particularly useful form of inkjet printer comprises a body of piezoelectric material with ink channels formed, for example, by disc cutting. Electrodes can be plated on the channel-facing surfaces of the piezoelectric material, enabling an electrical field to be applied to the piezoelectric “wall” defined between adjacent channels. With appropriate poling, this wall can be caused to move into or out of the selected ink channel, causing a pressure pulse which ejects an ink droplet through an appropriate channel nozzle. Such a construction is shown, for example, in EP-A-0 364 136.
It is a frequent requirement to provide a high density of such ink channels, with precise registration across a relatively large expanse of printhead, perhaps an entire page width. A construction that is useful to this end is disclosed in WO 98/52763. It involves the use of a flat base plate that supports the piezoelectric material as well as integrated circuits performing the necessary processing and control functions.
Such a construction has several advantages, particularly with regard to manufacture. The base plate acts as a “backbone” for the printhead, supporting the piezoelectric material and integrated circuits during manufacture. This support function is particularly important during the process of butting together multiple sheets of piezoelectric material to form a contiguous, pagewide array of ink channels. The relatively large size of the base plate also simplifies handling.
A problem remains of reliably and efficiently establishing electrical connection between the ink channel electrodes and the corresponding pins of the integrated circuits. If the base plate is of suitable material and suitably finished, conductive tracks can be deposited on it, these tracks connecting in known manner with the IC pins. There remains the difficulty of establishing connections to channel electrodes.
The present invention seeks to provide improved apparatus and methods which address this problem.
Accordingly, the present invention consists in one aspect in a method of manufacturing a component of a droplet deposition apparatus, the component comprising a body of piezoelectric material having a plurality of channels each with a channel surface and a base, the body being attached to a surface of the base which is free of substantial discontinuities; the method comprising the steps of attaching the body to said surface of the base; and depositing a layer of conductive material so as to extend continuously over at least one of said channel surfaces and said surface of the base to provide an electrode on each channel surface and a conductive track on said surface of the base which is integrally connected to the electrode.
The attachment of the body to a surface of the base and subsequent deposition of a continuous layer of conductive material over said at least one channel surface and the base surface results in an effective and reliable electrical connection between channel wall electrodes and substrate conductive tracks. Those tracks can be used to provide connection with one or more integrated circuits carried on the base, either directly or through other tracks and interconnections.
The present invention also consists in a component for a droplet deposition apparatus comprising a body of piezoelectric material formed with a plurality of channels each channel having a channel surface; and a separate base having a base surface free of substantial discontinuities; wherein the body is attached to said base surface and a layer of conductive material extends continuously over said channel surfaces of and said base surface, thereby defining an electrode on each channel surface and a conductive track connected thereto on the base surface.
The invention will now be described by way of example with reference to the accompanying drawings, in which:
FIGS. 6(a) and 6(b) are detail sectional views taken perpendicular and parallel to the channel axis of the device of
It will be helpful to describe first in some detail, examples of the prior art constructions referred to briefly above.
Thus,
The channels are closed by a cover 25 in which are formed nozzles 27 each communicating with respective channels at the mid-points thereof. Droplet ejection from the nozzles takes place in response to the aforementioned pressure pulse, as is well known in the art. Supply of droplet fluid into the channels, indicated by arrows S in
As shown in
Such a construction has several advantages, particularly with regard to manufacture. Firstly, the extended base 86 acts as a “backbone” for the printhead, supporting the piezoelectric sheets 82a, 82b and integrated circuits 84a, 84b during manufacture. This support function is particularly important during the process of butting together multiple sheets 3 to form a single, contiguous, pagewide array of channels, as indicated at 82a and 82b in the perspective view of FIG. 3. One approach to butting is described in WO 91/17051 and consequently not in any further detail here. The size of the extended cover also simplifies handling.
Another advantage arises from the fact that the surface of the base on which the conductive tracks are required to be formed is flat, i.e. it is free of any substantial discontinues. As such, it allows many of the manufacturing steps to be carried out using proven techniques used elsewhere in the electronics industry, e.g. photolithographic patterning for the conductive tracks and “flip chip” for the integrated circuits. Photolithographic patterning in particular is unsuitable where a surface undergoes rapid changes in angle due to problems associated with the spinning method typically used to apply photolithographic films. Flat substrates also have advantages from the point of view of ease of processing, measuring, accuracy and availability.
A prime consideration when choosing the material for the base is, therefore, whether it can easily be manufactured into a form where it has a surface free of substantial discontinuities. A second requirement is for the material to have thermal expansion characteristics to the piezoelectric material used elsewhere in the printhead. A final requirement is that the material be sufficiently robust to withstand the various manufacturing processes. Aluminium nitride, alumina, INVAR or special glass AF45 are all suitable candidate materials.
The droplet ejection openings 96a, 96b may themselves be formed with a taper, as per the embodiment of
Following the mounting of piezoelectric sheets 82a, 82b and drive chips 84a, 84b onto the substrate 86 and suitable testing as described, for example, in EP-A-0 376 606—a body 80 can be attached. This too has several functions, the most important of which is to define, in cooperation with the base or substrate 86, manifold chambers 90,88 and 92 between and to either side of the two channel rows 82a, 82b respectively. Body 80 is further formed with respective conduits as indicated at 90′, 88′ and 92′ through which ink is supplied from the outside of the printhead to each chamber. It will be evident that this results in a particularly compact construction in which ink can be circulated from common manifold 90, through the channels in each of the bodies (for example to remove trapped dirt or air bubbles) and out through chambers 88 and 92. Body 80 also provides surfaces for attachment of means for locating the completed printhead in a printer and defines further chambers 94a, 94b, sealed from ink-containing chambers 88,90,92 and in which integrated circuits 84a, 84b can be located.
Turning now to an example of the present invention, reference is made to FIG. 5. This is a sectional view similar to that of
As with the previous embodiments, the printhead of
In contrast to the printhead embodiments discussed above, the piezoelectric material for the channel wails is incorporated in a layer 100 made up of two strips 110a, 110b. As in the embodiment of
In accordance with the present invention, a continuous layer of conductive material is then applied over the channel walls and substrate. Not only does this form electrodes 190 for application of electric fields to the piezoelectric walls 13—as illustrated in FIG. 6(a)—and conductive tracks 192 on substrate 86 for supply of voltages to those electrodes as shown in FIG. 6(b)—it also forms an electrical connection between these two elements as shown at 194.
Appropriate electrode materials and deposition methods are well-known in the art. Copper, Nickel and Gold, used alone or in combination and deposited advantageously by electroless processes utilising palladium catalyst will provide the necessary integrity, adhesion to the piezoelectric material, resistance to corrosion and basis for subsequent passivation e.g. using Silicon Nitride as known in the art.
As is generally known, e.g. from the aforementioned EP-A-0 364 136, the electrodes on opposite sides of each actuator wall 13 must be electrically isolated from one another in order that an electric field may be established between them and hence across the piezoelectric material of the actuator wall. This is shown in both the prior art arrangement of FIG. 2 and the embodiment of the present invention shown in FIG. 6(a). The corresponding conductive tracks connecting each electrode with a respective voltage source must be similarly isolated.
In the present invention, such isolation may be achieved at the time of deposition for example by masking those areas—such as the tops of the channel walls—where conductive material is not required. Suitable masking techniques, including patterned screens and photolithographically patterned masking materials are well-known in the art, e.g. from WO 98/17477 and EP-A-0 397 441, and will not be described in any further detail.
Alternatively, isolation may be achieved after deposition by removing conductive material from those areas where it is not required. Localised vaporisation of material by laser beam, as known e.g. from JP-A-09 010 983, has proved most suitable for achieving the high accuracy required, although other conventional removal methods—inter alia sand blasting, etching, electropolishing and wire erosion may also be suitable.
In addition to removing conductive material from the top surface 13′ of each piezoelectric actuator wall 13 so as to separate the electrodes 190′, 190″, on either side of each wall, conductive material must also be removed from the surface of the substrate 86 in such a way as to define respective conductive tracks 192′, 192″ for each electrode 190′ 190″. At the transition between piezoelectric material 100 and substrate 86, the end surface of the piezoelectric material 100 is angled or chamfered as shown at 195. As is known, this has the advantage over a perpendicular cut (of the kind indicated by a dashed line at 197) of allowing the vapourising laser beam—shown figuratively by arrow 196—to impinge on and thereby remove the conductive material without requiring angling of the beam. Preferably, the chamfer 195 is formed by milling after the piezoelectric layer 100 has been attached to the substrate 86 but before the formation of the channel walls which, being typically 300 μm thick and formed of ceramic and glass, are vulnerable to damage. A chamfer angle of 45 degrees has been found to be suitable.
It will also be appreciated that the electrodes and conductive tracks associated with the active portions 140a need to be isolated from those associated with 140b in order that the rows of nozzles might be operated independently. Although this too may be achieved by a laser “cut” along the surface of the substrate 86 extending between the two piezoelectric strips, it is more simply achieved by the use of a physical mask during the electrode deposition process or by the use of electric discharge machining.
Laser machining can also be used in a subsequent step to form the ink ejection holes 96a, 96b in the base of each channel, as is known in the art. Such holes may directly serve as ink ejection nozzles. Alternatively, there may be bonded to the lower surface of the substrate 86 a separate plate (not shown) having nozzles that communicate with the holes 96a, 96b and which are of a higher quality that might otherwise be possible with nozzles formed directly in the ceramic or glass base of the channel. Appropriate techniques are well-known, particularly from WO 93/15911 which discloses a technique for the formation of nozzles in situ, after attachment of the nozzle plate, thereby simplifying registration of each nozzle with its respective channel.
The conductive tracks 192′, 192″ defined by laser may extend all the way from the transition area 195 to the integrated circuits 84 located at either side of the substrate. Alternatively, the laser track definition process may be restricted to an area directly adjacent the piezoelectric material and a different—e.g. photolithographic—process used to define further conductive tracks that connect the laser-defined tracks with the integrated circuits 84.
Having established tile electrical connections, it remains only to adhesively bond (e.g. using an offset method) a cover member 130 to the surface of substrate 86. This cover fulfils several functions: firstly, it closes each channel along those portions 140a, 140b where the walls incorporate piezoelectric material in order that actuation of the material and the resulting deflection of the walls might generate a pressure pulse in the channel portions and cause ejection of a droplet through a respective opening. Secondly, the cover and substrate define between them ducts 150a, 150b and 150c which extend along either side of each row of active channel portions 140a, 140b and through which ink is supplied. The cover is also formed with ports 88, 90, 92 which connect ducts 150a, 150b and 150c with respective parts of an ink system. In addition to replenishing the ink that has been ejected, such a system may also circulate ink through the channels (as indicated by arrows 112) for heat, dirt and bubble removing purposes as is known in the art. A final function of the cover is to seal the ink-containing part of the printhead from the outside world and particularly the electronics 84. This has been found to be satisfactorily achieved by the adhesive bond between the substrate 86 and cover rib 132, although additional measures such as glue fillets could be employed. Alternatively, cover rib may be replaced by an appropriately shaped gasket member.
Broadly expressed, the printhead of
It will be appreciated that restricting the use of piezoelectric material to those “active” portions of the channel where it is required to displace the channel walls is an efficient way, of utilising what is a relatively expensive material. The capacitance associated with the piezoelectric material is also minimised, reducing the load on—and thus the cost of—the driving circuitry.
Whereas the printhead of
Various methods of manufacturing such “chevron” actuator walls are known in the art, e.g. from EP-A-0 277 703, EP-A-0 326 973 and WO 92/09436. For the printhead of
One consequence of the entire actuator wall height being defined by piezoelectric material is that there is no need to saw wall-defining grooves into the inactive substrate 86. There remains, of course, the need for the length of the nozzles 96a, 96b to be kept to a minimum so as to minimise losses that would otherwise reduce the droplet ejection velocity. To this end, the substrate can be reduced in thickness either locally by means of a trench 300 as shown in FIG. 9 and formed advantageously by sawing, grinding or moulding—or overall per FIG. 10. Both arrangements need to provide free passage for a disc cutter (shown diagrammatically in dashed lines at 320) used to form the channels in the piezoelectric strips.
Following channel formation and in accordance with the present invention, conductive material is then deposited and electrodes/conductive tracks defined. In the examples shown, piezoelectric strips 110a and 110b are chamfered to facilitate laser patterning, as described above. Nozzle holes 96a, 96b are also formed at two points along each channel.
Finally a cover member 130 is bonded to the tops of the channel walls so as to create the closed, “active” channel lengths necessary for droplet ejection. In the printhead of
In the embodiment of
Turning to the embodiment of
However, elsewhere on the substrate—as indicated at 510—more conventional techniques, for example photolithographic, can be used to define not only tracks 192 leading from the channel electrodes to the integrated circuits 84 but also further tracks 520 for conveying power, data and other signals to the integrated circuits. Such techniques may be more cost effective, particularly where the conductive tracks are diverted around ink supply ports 92 and which would otherwise require complex positional control of a laser. They are preferably formed on the alumina substrate in advance of the ink supply ports 88, 90, 92 being drilled (e.g. by laser) and of the piezoelectric strips 110a, 110b being attached, chamfered and sawn. Following deposition of conductive material in the immediate area of the strips, a laser can then be used to ensure that each track is connected only with its respective channel electrode and no other.
Thereafter, both electrodes and tracks will require passivation, e.g. using Silicon Nitride deposited in accordance with WO 95/07820. Not only does this provide protection against corrosion due to the combined effects of electric fields and the ink (it will be appreciated that all conductive material contained within the area 420 defined by the inner profile 430 of spacer member 410 will be exposed to ink), it also prevents the electrodes on the opposite sides of each wall being short circuited by the planar cover member 430. Both cover and spacer are advantageously made of molybdenum which, in addition to having similar thermal expansion characteristics to the alumina used elsewhere in the printhead, can be easily machined, e.g. by etching, laser cutting or punching, to high accuracy. This is particularly important for the holes for droplet ejection 96 and, to a lesser extent, for the wavy, bubble-trap-avoiding, inner profile 430 of the spacer member 410. Bubble traps are further avoided by positioning the trough 440 of the wavy profile such that it aligns with or even overlies the edge of the respective ink port 92. Crest 450 of the wavy profile is similarly dimensioned (to lie a distance—typically 3 mm, approximately 1.5 times the width of each strip 110a, 110b—from the edge of the adjacent strip 110a, 110b to ensure avoidance of bubble traps without affecting the ink flow into the channels.
Spacer member 410 is subsequently secured to the upper surface of substrate 86 by a layer of adhesive. In addition to its primary, securing function, this layer also provides back-up electrical isolation between the conductive tracks on the substrate. Registration features such as notch 440 are used to ensure correct alignment.
The last two members to be adhesively attached—either separately or following assembly to one another—are the planar cover member 420 and nozzle plate 430. Optical means may be employed to ensure correct registration between the nozzles formed in the nozzle plate and the channels themselves. Alternatively, the nozzles can be formed once the nozzle plate is in situ as known, for example, from WO 93/15911.
A further feature is illustrated in
A further modification is explained with reference to FIG. 15. As already explained above, the piezoelectric material for the channel walls is incorporated in a layer 100 made up of two strips 110a, 110b each butted with other strips in the direction W necessary for a wide array of channels. Depending on whether the actuator is of the “cantilever” or “chevron” type, the piezoelectric layer will be polarised in one or two (opposed) directions and, in the latter case, may be formed from two oppositely-polarised sheets laminated together as shown at 600 and 610 in FIG. 15. To facilitate relative positioning, strips 110a, 110b are connected together by a bridge piece 620 that is removed in the chamfering step that takes place once strip 100 and substrate 86 have been bonded together using adhesive.
A still further modification is illustrated in FIG. 16. Here, the integrated circuit 84 is not mounted on the substrate 86 but on an auxiliary substrate 700, which may be single or multi-layer. The substrate 86 is appropriately bonded to the auxiliary substrate 700 and wire bonds 702 connect the conductive tracks on the substrate 86 with the pins of the integrated circuit. Further wire bonds 704 then interconnect the integrated circuit with pads 708 on the auxiliary substrate 700.
The present invention has been explained with regard to the figures contained herein but is in no way restricted to such embodiments. In particular, the present techniques are applicable to printheads of varying width and resolution, pagewide double-row being merely one of many suitable configurations. Printheads having more than two rows, for example, are easily realised using tracks used in multiple layers as well-known elsewhere in the electronics industry.
All documents, particularly patent applications, referred to are incorporated in the present application by reference.
| Number | Date | Country | Kind |
|---|---|---|---|
| 9824998 | Nov 1998 | GB | national |
| 9919201 | Aug 1999 | GB | national |
This is a continuation of International Application No. PCT/GB99/03799 filed Nov. 15, 1999, the entire disclosure of which is incorporated herein by reference.
| Number | Name | Date | Kind |
|---|---|---|---|
| 5193256 | Ochiai et al. | Mar 1993 | A |
| 5248998 | Ochiai et al. | Sep 1993 | A |
| 5347712 | Yasuda et al. | Sep 1994 | A |
| 5767878 | Murphy | Jun 1998 | A |
| 5787558 | Murphy | Aug 1998 | A |
| 5889539 | Kamoi et al. | Mar 1999 | A |
| Number | Date | Country |
|---|---|---|
| 0 277 703 | Aug 1988 | EP |
| 0 326 973 | Aug 1989 | EP |
| 0 364 136 | Apr 1990 | EP |
| 0 376 606 | Jul 1990 | EP |
| 0 397 441 | Nov 1990 | EP |
| 0 505 065 | Sep 1992 | EP |
| 0 522 814 | Jan 1993 | EP |
| 0 704 305 | Apr 1996 | EP |
| 0 755 792 | Jan 1997 | EP |
| 0 839 656 | May 1998 | EP |
| 5-64893 | Mar 1993 | JP |
| 5-147215 | Jun 1993 | JP |
| 9-10983 | Jan 1997 | JP |
| 3292 146 | Mar 2002 | JP |
| WO 9117051 | Nov 1991 | WO |
| WO 9209436 | Jun 1992 | WO |
| WO 9222429 | Dec 1992 | WO |
| WO 9315911 | Aug 1993 | WO |
| WO 9504658 | Feb 1995 | WO |
| WO 9817477 | Apr 1998 | WO |
| WO 9852763 | Nov 1998 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 20020008741 A1 | Jan 2002 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/GB99/03799 | Nov 1999 | US |
| Child | 09853520 | US |
