This is the U.S. national phase of International Application No. PCT/GB01/04293 filed Sep. 26, 2001, the entire disclosure of which is incorporated herein by reference.
This invention relates to droplet deposition apparatus, in particular inkjet printheads including methods of manufacturing and components for use in droplet deposition apparatus.
In European Patent Number 0 277 703 and European Patent Number 0 278 590, multi-channel array droplet deposition apparatuses are disclosed, suitable for use as drop-on-demand inkjet printheads. The multi-channel arrays comprise a base sheet of piezoelectric material, poled normal to the sheet, with an array of parallel grooves in the sheet, forming open-topped channels with walls between them, opposite walls of the channels carrying electrodes. Application of electrical pulses to the electrodes on either side of a wall to generate an actuating field normal to the poling direction causes that wall to deflect in the direction of the field, thus changing the pressure in any ink in the adjacent channels.
In European patent Number 0 589 941, a multi-channel array is disclosed in which a closure sheet carries an array of parallel conductive tracks at the same spacing as the channel spacing, the tracks being bonded mechanically and electrically, e.g. by solder, to the electrodes on either side of the channels. Such an arrangement requires a pre-patterning system for the closure sheet which can cope with the three dimensional piezoelectric structure.
The closure sheet must be relatively simple to ensure accurate registration, good track definition and adhesion to the actuator. Ink is supplied from the rear of the channels through a manifold component. More recent ink jet constructions, such as in WO 97/39897 have identified the benefit of supplying ink into the channel through the top cover. The closure sheet, because it bounds the top walls of the channels, is usually of a similar material to the walls. Any large difference in the expansion coefficients of the materials may cause walls to break.
One of the many benefits of the construction in EP 0 589 941 is that the closure sheet, and associated drive circuits can be pre-tested prior to joining to the channelled component. Many of the stages of preparation of a printhead take place after the channels have been formed, and the channelled piezoelectric sheet must be handled with great care to avoid damage.
A further method of constructing a print head is shown in WO 00/29217. A piezoelectric block is mounted onto a planar substrate and channels sawn. The substrate acts both to support and strengthen the piezoelectric in use and during manufacture. Conductive tracks can be formed on the substrate prior to attaching the piezoelectric block. The application recognises the difficulty of attaching active electrodes to the pre-formed tracks and addresses the problem by forming simultaneously with the electrodes on the piezoelectric block, conductive tracks on the substrate. Difficulties sometimes arise in ensuring electrical continuity at the boundary between the piezoelectric block and the substrate.
Laser manufacturing is relatively expensive and better suited to discrete, step-by-step operations rather than to the simultaneous formation of repeating structures. Current markets today demand ever larger printheads with increased numbers of tracks per printhead This demands cost-effective and fast manufacturing steps.
It Is an object of the present invention to address this and other problems.
In one aspect of the present invention there is provided a method of forming a droplet deposition apparatus comprising the steps: forming a substrate having one or more electrically conductive tracks, attaching to said substrate a body of piezoelectric material having a top surface and a bottom surface, said bottom surface overlying said tracks and establishing electrical connection with said tracks for actuation of the piezoelectric material, and forming in said attached piezoelectric material at least one droplet ejection chamber.
Beneficially the substrate having the electrically conductive tracks can also have the drive circuits assembled to it before the piezoelectric material is attached. A protective coating can be deposited over the drive circuit, tracks, substrate and attached piezoelectric material to prevent any debris generated from subsequent processing steps from affecting the finished product
A particularly preferred form of piezoelectric material is a lead zirconate titanate (PZT) and the body may be a single homogenous sheet or formed as a laminate of two thinner sheets. It is desirable that the PZT is poled prior to attaching such that when it is actuated it deforms in shear.
Preferably, electrically conductive points are provided on the bottom surface of the body of piezoelectric material to improve electrical connection thereto. It is preferred if the conductive points extend into the piezoelectric body by forming depressions by sawing or other means.
The electrically conductive points should be electrically isolated from one another by, if need be, removing conductive material that connects them. This can be achieved by any conventional process such as sawing, etching or lift-off.
In a first embodiment, the depressions are filled with a conductive material, preferably a deposited metal. This metal may be used as a solder material to both mechanically and electrically connect the piezoelectric body to the substrate. The ejection chambers, formed by removing material from the top surface of the piezoelectric body, extend into conductive material. An electrode material is applied by electroless plating, vacuum deposition or any other appropriate method to the newly formed chambers such that it contacts the conductive material in the depression. It is preferred that the ejection chambers are formed by sawing.
In a second embodiment, the depressions are coated with a conductive material, but not filled. Ejection chambers formed subsequently open into a respective depression. Electrode material is deposited as above.
In a third embodiment, the depressions are coated with a conductive material and subsequently filled with a non-conductive material. The ejection chambers formed from the top surface extend into the non-conductive material. Beneficially, the conductive material coating the depressions serves as the actuating electrodes. The non-conductive material can usefully act as a passivant to protect the conductive material from chemical attack by ink
In all these embodiments, the ejection chambers can be closed by a separate cover component that can also function as a nozzle plate. The present invention is as equally applicable to roof-shooter arrangements as in WO 00/29217 or end shooter arrangements as in WO 97/39897.
The present invention will now be described, by way of example, with reference to the following drawings in which:
a) to 4(h) depict eight stages in the manufacture of a printhead according to a first embodiment;
a) to 5(e) depict stages in the manufacture of a printhead according to a second embodiment;
a) to 6(e) depict stages in the manufacture of a printhead according to a third embodiment; and
The printhead 110 shown in
Channels 120 sawn into the PZT laminate 112 before it is bonded to the substrate define actuating walls 113. Electrodes 125 deposited in the respective channels lie in electrical contact with the respective tracks 116. In one manufacturing arrangement, solder 124 provided on the tracks is heated to bond with the electrodes.
The construction is completed by a cover 121 which defines an ink manifold 126 and a nozzle plate 120 which carries ink ejection orifices 122.
As described in more detail in the published documents referred to above, the application of a firing waveform through tracks 16 to the electrode 11 in any channel 20, causes chevron-like deformation of both walls 13, through shear mode actuation of the PZT wall material. An acoustic wave travels through ink contained in the channel with a resulting ink droplet being ejected through orifice 22.
A substrate 310 is formed with an array of generally parallel conductive tracks 312 which provide connections to drive and/or control chips 314. In this particular arrangement, the tracks 312 are in places along their length, diverted to avoid ink supply apertures 314 in the substrate. Also carried on the substrate, are pads 316 providing for external connection with print data input devices.
A block of PZT material 318, as will be described in detail below, is mounted on the substrate 310. Ink channels (not shown) are subsequently formed in the PZT material, generally parallel with the underlying tracks. Actuation electrodes in these channels are in electrical connection with the respective tracks. A cover plate 320 serves to close the top of the ink channels with orifices 322 in the cover plate functioning as ink ejection orifices.
a) to 4(g) depict in a series of process steps, a method according to a first embodiment of this invention of forming a print head such as that shown in
A rigid substrate 32 is provided upon which parallel tracks 16 are formed by any conventional method. The tracks connect to a drive circuit (not shown) and can be probed in order to pre-test the connection. The substrate is formed of alumina, a material having a coefficient of thermal expansion comparable to that of PZT.
The PZT block 12 of
The substrate with the tracks and the piezoelectric material are then brought into contact as depicted in
A layer 34 of a lift-off barrier material, such as a wax, is applied to the surface of the sheet 12 opposite to the flat surface 33. The wax material may also cover tracks extending beyond the piezoelectric material and over the drive chips to act as a protective barrier.
As shown in 4(e), the next step is to form channels 11 divided by actuator walls 13 by the known technique of sawing. The channels are formed at the same spacing as the plugs 30, and the channels are cut to such a depth that the surfaces 35 of the plugs remote from the substrate layer 32 are exposed. A layer 34 of lift-off material remains on the top of each wall 13.
f) shows that a continuous layer 20 of metal is applied over the remaining layer 34 of lift-off material and on the sides and bottom of each channel. Any one of the techniques of vapour deposition, electroplating or electroless deposition may for example be used. In this embodiment the method used was electroless deposition. The lift-off material 34 and the metal layer 20 over it are removed e.g. by washing, and, as shown in
h) is a side view before the sawing step. The lift-off coating 34 is shown on the top surface, and beads of wax 38 are also dispensed to protect the ends. The thickness of the plug 30 is shown, and the chevron bond between the oppositely poled parts of the sheet 12 is indicated at 37. The conducting tracks 16 on the substrate sheet 32 extend beyond the edge of the piezoelectric sheet, for connection to electrical chips or other components.
h) also shows a plating mask 36 used when vapour deposition is used to form the electrodes 24,25. The mask prevents the deposition of metal on the part of the track 16 which is not protected by wax 34.
As an alternative, the grooves 31 can be filled with a solder material, surface-skimmed, and placed in electrical connection with the tracks 16 on the substrate 32 which are made of a solder-compatible material using conventional thin film techniques or by using the known zincate process to provide solder-wettable regions.
a) to 5(e) depict a method of manufacture according to a second embodiment. A sheet 12 of piezoelectric material is chevron-poled and a number of shallow parallel grooves 41 are cut in one surface. In this embodiment the grooves are rectangular in cross section.
In
In
Electrical actuating pulses can therefore be applied to the actuating wall 13 via the aluminium strips 46, the aluminium layers 40, and the electrodes 47.
The manufacturing steps according to a third embodiment of the invention are illustrated in
Excess filler is then cleaned from the bottom face of sheet 68 so that the edges of the metal layers 70 on each channel are exposed. A bump 74 of gold is deposited along the exposed edge of metallisation 70 on each channel by a liquid deposition method such as electrolytic plating. In this specification the term “bump” indicates a raised electrically conductive point such as metal area and which is used to form an electrical connection.
At this stage in the manufacturing process it is possible to make temporary electrical connections between a pair of bumps 74 on each channel, and test equipment (not shown). The integrity of the metallisation on the channel walls and base can be tested channel-by-channel. Capacitance measurements can useful provide useful test data on the poled PZT. This is important in allowing faulty metallised PZT sheets to be rejected at a relatively early stage in the manufacturing process.
b) illustrates a substrate layer 80 carrying an array of parallel conducting tracks 82 at the same spacing as the channels 66 in the first array, each track 82 being wider than each channel 66 so as to span the gold bumps 74 at the edges of the metal layers 70 on opposite walls of the channels 66 The tracks 82 may be solder tracks.
The substrate layer 80 also carries drive chips and control chips (not shown), or single chips providing both functions. These chips may be connected in a wide variety of ways, for example by the technique known as “flip chip”. Any other necessary processing, which may involve high temperatures which would be detrimental to poled PZT, maybe applied. The substrate layer and the electrical components which it carries can then be tested electrically, before connection to the PZT material.
Electrical connections between each conducting track and the gold bumps 74 are made by techniques such as direct pressure using a glue, or by soldering.
In
The top surface of the piezoelectric material may be lapped to such a depth that conductive material exposed to the ejection channel is removed as shown in
It will be apparent that during the majority of steps of the manufacturing process, the channels 66 in the PZT sheets 62, 64 are filled by the filler, so the component is more robust and handling is easier than In comparison with prior art manufacturing processes.
As shown in
It is apparent from the transverse section provided in this figure, that the circular saw used to form the channels 66 can conveniently leave an arcuate run-off region 98. This region then provides an ink conduit between the supply manifold 92 and the active region of the respective channels.
There is also shown in
In the above described embodiments, the PZT material is positioned over an array of parallel tracks, with channels being subsequently formed in the PZT to provide ejection chambers which overlie the respective tracks. It should be understood that the track need not in all embodiments extend the full length of an ejection chamber, Also, arrangements can be contemplated in which the tracks are not parallel with the ejection chambers.
Thus, as shown diagrammatically in
The connecting plugs or contact layers which in previous embodiments have been described as extending the length of the respective channels are replaced in this arrangement by point-like connecting plugs 712. These plugs are formed by drilling into the bottom surface of the PZT material and depositing conductive material. The plugs 712 are positioned, as shown in
The present invention has been explained with reference to the accompanying figures but is not of course restricted to such embodiments. Features described in a particular combination in the various embodiments may also be combined usefully in different combinations. This disclosure should be regarded as extending to all such combinations. A wide variety of further modifications are possible without departing from the scope of claim. Thus, whilst chevron-like deflection of both chamber walls has been described as a technique for ink droplet ejection, alternative techniques disclosed for example in the quoted references, may readily be employed. In so-called “roof-shooter” constructions, a cover plate provided on the top surface of the piezoelectric material provides ink jet nozzles, either directly or via a separate nozzle plate. Appropriate ink supply manifolds are then provided at or near one or both ends of the chambers. In an “end shooter” arrangement, the cover plate may be plain or may contain an ink supply manifold. This may supply ink from a common source to all chambers or may provide for the supply of—for example—different colour inks to respective sets of ink chambers. A nozzle plate would typically be attached at one end of the chambers, with the other end of the chambers being closed or communication with an ink manifold.
Whilst the use of an alumina substrate has the advantage of thermal characteristics matching PZT, other substrate materials may be employed. In certain applications, a flexible substrate can offer important advantages.
The example of an ink jet printhead has been used to explain this invention. It will be understood that the same or similar techniques can be employed with other forms of droplet deposition apparatus.
All documents, particularly patent applications, referred to are incorporated in the present application by reference.
Number | Date | Country | Kind |
---|---|---|---|
0023544.0 | Sep 2000 | GB | national |
0117295.6 | Jul 2001 | GB | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
---|---|---|---|---|
PCT/GB01/04293 | 9/26/2001 | WO | 00 | 10/14/2003 |
Publishing Document | Publishing Date | Country | Kind |
---|---|---|---|
WO02/26501 | 4/4/2002 | WO | A |
Number | Name | Date | Kind |
---|---|---|---|
5463414 | Temple et al. | Oct 1995 | A |
5598196 | Braun | Jan 1997 | A |
5818483 | Mizutani | Oct 1998 | A |
6095641 | Kishi | Aug 2000 | A |
Number | Date | Country |
---|---|---|
277 703 | Aug 1988 | EP |
278 590 | Aug 1988 | EP |
589 941 | Apr 1994 | EP |
734 865 | Oct 1996 | EP |
1 029 678 | Aug 2000 | EP |
09-207331 | Aug 1997 | JP |
11-115195 | Apr 1999 | JP |
11151814 | Jun 1999 | JP |
WO 9739897 | Oct 1997 | WO |
WO 0029217 | May 2000 | WO |
Number | Date | Country | |
---|---|---|---|
20040113992 A1 | Jun 2004 | US |