Flexible printhead circuit

A flexible circuit for use within a printhead assembly and to connect a printhead body to an external circuit includes a substantially planar portion having one or more layers of conductive material and having a top surface substantially parallel to a top surface of the printhead body. One or more integrated circuits can be mounted onto the planar portion. Multiple leads extend from each integrated circuit, the leads electrically connected to the printhead body. One or more arms are attached to, and substantially perpendicular to, the planar portion, each arm including one or more external connectors configured to connect to the external circuit.

BACKGROUND

The following description relates to a flexible circuit in a printhead assembly.

An ink jet printer typically includes an ink path from an ink supply to an ink nozzle assembly that includes nozzle openings from which ink drops are ejected. Ink drop ejection can be controlled by pressurizing ink in the ink path with an actuator, which may be, for example, a piezoelectric deflector, a thermal bubble jet generator, or an electrostatically deflected element. A typical printhead has a line of nozzle openings with a corresponding array of ink paths and associated actuators, and drop ejection from each nozzle opening can be independently controlled. In a so-called “drop-on-demand” printhead, each actuator is fired to selectively eject a drop at a specific pixel location of an image, as the printhead and a printing media are moved relative to one another. In high performance printheads, the nozzle openings typically have a diameter of 50 microns or less (e.g., 25 microns), are separated at a pitch of 100-300 nozzles per inch and provide drop sizes of approximately 1 to 70 picoliters (pl) or less. Drop ejection frequency is typically 10 kHz or more.

A printhead can include a semiconductor printhead body and a piezoelectric actuator, for example, the printhead described in Hoisington et al., U.S. Pat. No. 5,265,315. The printhead body can be made of silicon, which is etched to define ink chambers. Nozzle openings can be defined by a separate nozzle plate that is attached to the silicon body. The piezoelectric actuator can have a layer of piezoelectric material that changes geometry, or bends, in response to an applied voltage. The bending of the piezoelectric layer pressurizes ink in a pumping chamber located along the ink path.

Printing accuracy can be influenced by a number of factors, including the uniformity in size and velocity of ink drops ejected by the nozzles in the printhead and among the multiple printheads in a printer. The drop size and drop velocity uniformity are in turn influenced by factors, such as the dimensional uniformity of the ink paths, acoustic interference effects, contamination in the ink flow paths, and the uniformity of the pressure pulse generated by the actuators. Contamination or debris in the ink flow can be reduced with the use of one or more filters in the ink flow path.

SUMMARY

A flexible circuit for use in a printhead assembly is described. In general, in one aspect, the invention features a circuit to connect a printhead body to an external circuit. The circuit includes a substantially planar portion, one or more integrated circuits, a plurality of leads and one or more arms. The substantially planar portion includes one or more layers of conductive material and has a top surface substantially parallel to a top surface of the printhead body. The one or more integrated circuits are mounted onto the planar portion. The plurality of leads extends from each integrated circuit and are electrically connected to the printhead body. The one or more arms are attached to, and substantially perpendicular to, the planar portion, each arm including one or more external connectors configured to connect to the external circuit.

Implementations can include one or more of the following features. The circuit can further include a plurality of apertures, each aperture coated with a conductive material and providing an electrical connection to the printhead body. Each of the plurality of leads can extend from an integrated circuit to connect to one of the plurality of apertures.

The planar portion can include at least one layer of copper and at least one layer of polyimide. The planar portion can further include a central portion having of a first layer of polyimide coated on either side with layers of copper, a second layer of polyimide coated on either side with layers of copper, and a layer of adhesive joining the first layer to the second layer, and two distal portions on either side of the central portion, each distal portion having of a layer of polyimide coated with a layer of copper. The two distal portions can be attached to the top surface of the printhead body and the central portion can be raised from the top surface of the printhead body relative to the two distal portions. The leads can include traces of copper affixed to a top surface of the circuit, the top surface formed from polyimide. Each arm can include a distal end that is substantially parallel to the top surface of the planar portion, the distal end including one or more contacts to connect to the external circuit.

The substantially planar portion of the circuit can further include a central portion and two distal portions on either side of the central portion, where the two distal portions are attached to the top surface of the printhead body and the central portion is raised from the top surface of the printhead body relative to the two distal portions. The central portion can include a plurality of layers including at least one conductive layer, and the distal portions can include a plurality of layers, including at least one conductive layer, where the number of layers included in the central portion and the distal portions are not equal.

In general, in another aspect, the invention features a system to connect a printhead body to an external circuit. The system includes a circuit and an interposer. The circuit is configured to connect to the interposer. The circuit includes a substantially planar portion, one or more integrated circuits, a plurality of leads and one or more arms. The substantially planar portion includes one or more layers of conductive material and has a top surface substantially parallel to a top surface of the printhead body. The one or more integrated circuits are mounted onto the planar portion. The plurality of leads extend from each integrated circuit and are electrically connected to the printhead body. The one or more arms are attached to, and substantially perpendicular to, the planar portion, each arm including one or more external connectors configured to connect to the external circuit.

The interposer includes an upper surface configured to connect to the circuit, a lower surface configured to connect to the printhead body, and a plurality of interposer apertures, each interposer aperture coated with a conductive material and providing an electrical connection to the printhead body. Each of the plurality of interposer apertures is in electrical communication with a corresponding one of the plurality of leads.

Implementations of the invention can include one or more of the following features. The interposer can include a heating element. The circuit can further include a plurality of circuit apertures, each circuit aperture coated with a conductive material and providing an electrical connection to a corresponding interposer aperture. Each of the plurality of leads can extend from an integrated circuit to connect to one of the plurality of circuit apertures, such that each of the plurality of leads is in electrical communication with a corresponding one of the plurality of interposer apertures. The interposer can include one or more recesses formed in the upper surface, the one or more recesses configured to receive the one or more integrated circuits mounted on the planar portion of the circuit. Each of the plurality of leads can extend from an integrated circuit to connect to one of the plurality of interposer apertures, such that each of the plurality of leads is in electrical communication with a corresponding one of the plurality of interposer apertures.

The planar portion of the circuit can include at least one layer of copper and at least one layer of polyimide. Each arm can include a distal end that is substantially parallel to the top surface of the planar portion, the distal end including one or more contacts to connect to the external circuit. The planar portion of the circuit can further include a first layer of polyimide coated on either side with layers of copper, a second layer of polyimide coated on either side with layers of copper, and a layer of adhesive joining the first layer to the second layer.

In general, in another aspect, the invention features a system to connect a printhead body to an external circuit. The system includes a circuit configured to connect to an interposer and an interposer. The circuit includes a substantially planar portion including one or more layers of conductive material and having a top surface substantially parallel to a top surface of the printhead body and one or more integrated circuits mounted onto a bottom surface of the planar portion. The circuit further includes a plurality of leads extending from each integrated circuit, the plurality of leads electrically connected to the printhead body by way of a plurality of interposer apertures. One or more arms are attached to, and substantially perpendicular to, the planar portion, each arm including one or more external connectors configured to connect to the external circuit.

The interposer includes an upper surface configured to connect to the circuit, the upper surface including one or more recesses configured to receive the one or more integrated circuits mounted on the bottom surface of the substantially planar portion of the circuit, and a lower surface configured to connect to the printhead body. A plurality of interposer apertures extend from the upper surface through to the lower surface. Each interposer aperture is coated with a conductive material and configured to provide an electrical connection between the circuit and the printhead body. Each of the plurality of interposer apertures is in electrical communication with a corresponding one of the plurality of leads of the circuit.

In one implementation, the interposer can further include a heating element.

The invention can be implemented to realize one or more of the following advantages. The leads from the integrated circuits mounted on the flexible circuit to the actuators, e.g., piezoelectric actuators, are short, permitting very high speed and dense signal lines near the printhead body. The short leads also have lower resistance and inductance, and can therefore allow higher frequency operation with less waveform distortion in the signals reaching the actuators. Shorter leads also radiate less noise.

Including an interposer between a flexible circuit and a printhead body can realize one or more of the following advantages. The flexible circuit can be connected to the interposer before attaching the interposer to the printhead body. This allows connections of the flexible circuit, and between the flexible circuit and the interposer, to be tested before the flexible circuit/interposer assembly is attached to the printhead body. If there is a problem with the connections, the flexible circuit can be replaced, without having to replace the printhead body, or without having to remove the flexible circuit from the printhead body which may damage the printhead body. The likelihood of damaging the printhead body during the assembly process is reduced by attaching the flexible circuit to the interposer rather than directly to the printhead body. The surfaces of the interposer and the printhead body that will be in contact with one another can be polished to provide a precise match. This can reduce or eliminate pressure variations along the length of the printhead body that can occur when attaching the circuit directly to the printhead body by soldering. Optionally, the interposer can include a heating element. The flexible circuit can be formed substantially flat, thereby also eliminating the need to shape the circuit, for example, to form bends.

An advantage of an embodiment of the flexible circuit that has the integrated circuits mounted on the same surface as the contact surface with an interposer, is the elimination of apertures to connect the leads to the interposer.

Details of one or more implementations are set forth in the accompanying drawings and the description below. Other features and advantages may be apparent from the description and drawings, and from the claims.

DETAILED DESCRIPTION

Referring toFIG. 1, one embodiment of a flexible circuit100for providing signals for controlling ink drop ejection in a printhead is shown. The flexible circuit100includes external connectors102to connect the flexible circuit100to a second circuit (not illustrated inFIG. 1) for connecting to a source of the signals, such as a processor located within a printer. Integrated circuits, dies or chips104are mounted on the flexible circuit100to receive input signals from the external connectors and to generate output drive signals. The output drive signals are transmitted to a printhead body to selectively eject ink drops from specific nozzles, for example, by selectively firing corresponding actuators in a printhead including a piezoelectric deflector for pressurizing ink in an ink path. The integrated circuits104can be connected to multiple leads on the flexible circuit100. Some of these leads can extend to the external connectors102to carry the input signals. Other leads can extend from the integrated circuits to corresponding conductive apertures formed within the flexible circuit100to carry the output drive signals to a device, e.g., a printhead body, upon which the flexible circuit100is mounted.

Before describing the flexible circuit100in further detail, an example of a printhead assembly in which the flexible circuit100can be used shall be described to provide a context for the description of the flexible circuit100. The printhead assembly described is exemplary and for illustrative purposes only. The flexible circuit100can be adapted to be used within other printhead assemblies not described herein.

Referring toFIGS. 2A and 2B, a printhead body106and a faceplate108are shown. The printhead body106can be, for example, a MEMS silicon die, such as the printhead described in Hoisington, et al., U.S. Pat. No. 5,265,315, or the semiconductor printhead unit described in U.S. Provisional Application Ser. No. 60/510,459, entitled “Print Head with Thin Membrane”, filed Oct. 10, 2003, the disclosures of which are hereby incorporated by reference. The printhead body106can be etched to define ink chambers and an array of ink nozzles to eject ink drops, and can include piezoelectric actuators corresponding to each of the ink nozzles. Each piezoelectric actuator can have a layer of piezoelectric material that changes geometry, or bends, in response to an applied voltage. The bending of the piezoelectric layer pressurizes ink in a chamber located along the ink path. The surface of the printhead body106bearing the ink nozzles is positioned on and affixed to the faceplate108, for example, using an epoxy. However, the faceplate108can include an opening110positioned to expose the ink nozzles.

Referring toFIGS. 3A and 3B, in one embodiment, the flexible circuit100is configured to fit on top of the printhead body106. The flexible circuit100is affixed to the printhead body106, for example, by soldering of electrical connectors.

Referring toFIG. 4A, a printhead housing112can be positioned on the faceplate108, extending around and over the printhead body106and flexible circuit100. The printhead housing112can be affixed to the faceplate108using, for example, an epoxy. Referring toFIG. 4B, in the exemplary printhead shown, the printhead housing112is a molded, plastic housing including a central opening114to receive and house the printhead body106, and including channels116formed in a lower surface117.FIG. 4Cshows a cross-sectional view of the printhead housing112mounted to the printhead body106, taken along line4C-4C ofFIG. 4B. When the lower surface117of the printhead housing112is affixed to the faceplate108, the inner walls119of the channels116contact the top surface107of the printhead body106. The channels116thereby form an ink path directed toward ink nozzles included in the printhead body106. The printhead housing112is described further in U.S. patent application Ser. No. 10/836,456, entitled “Elongated Filter Assembly” of Kevin Von Essen, filed Apr. 30, 2004, the entire contents of which are incorporated herein by reference.FIGS. 4D and 4Eshow the printhead housing112affixed to the face place108, with the flexible circuit100housed within the central opening114.

Referring toFIGS. 5A-C, a heater assembly116including a heater unit118and external circuit120is shown. The external circuit120can connect to a processor located within the printer for controlling ink drop ejection from the ink nozzles. The heater assembly116fits within the central opening114formed in the printhead housing112, and the external connectors102of the flexible circuit100fold over the top of the heater assembly116to contact and provide an electrical connection between the flexible circuit100and the external circuit120, which is described further below.

Referring toFIGS. 6A and 6B, the heater unit118can include two vertical panels122including heating elements124and a horizontal spacer126. The vertical panels122and horizontal spacer126can be formed from a material, such as silicon. The external circuit120includes a connection plate128and a flexible cable130. The connection plate128includes contacts132to electrically connect to the external connectors102of the flexible circuit100. The connection plate128also includes openings134that can provide an electrical connection to heater connectors136extending upwardly from the vertical panels122of the heater unit118. Electrically connecting the heater unit118to the connection plate128, and therefore the flexible cable130, allows the temperature of the heater unit118to be controlled by the processor connected to the external circuit120.

Referring toFIGS. 7A and 7B, a filter assembly138, such as the filter assembly described in U.S. patent application Ser. No. 10/836,456, referred to above, can be positioned on top of the printhead housing. The filter assembly138includes one or more filters through which the ink must pass before entering the printhead housing and then the ink nozzles. A guide140can be included on the filter assembly138to guide the position of the flexible cable130.

Having described one example of a printhead within which an embodiment of the flexible circuit100can be implemented, the flexible circuit100shall now be described in further detail.FIG. 8Ashows an enlarged, partial view of one embodiment of the flexible circuit100mounted on a printhead body106, which is mounted onto a faceplate108. In this embodiment, the flexible circuit100is formed having a “gull-wing” structure. That is, the flexible circuit100includes a substantially planar central portion142that is positioned substantially parallel to the top surface107of the printhead body106. The flexible circuit100further includes distal portions144extending the length of the flexible circuit100and also substantially parallel to the top surface107of the printhead body106. The central portion142and distal portions144are joined by bent portions143that extend at an angle between the central and distal portions142,144.

The central portion142is raised to accommodate the topography of the top surface107of the printhead body106to which the flexible circuit100is mated. In particular, in an embodiment where the printhead body106includes piezoelectric actuators, space is provided between the flexible circuit100and the piezoelectric material on the upper surface of the printhead body106to allow the piezoelectric material room to flex.

Integrated circuits104are affixed to the upper surface of the central portion142of the flexible circuit100. Flexible circuit leads146are shown extending from each integrated circuit104to corresponding apertures148formed in the distal portions144of the flexible circuit100. A flexible circuit lead146is provided for each ink nozzle included in the printhead body106. The flexible circuit lead146transmits a signal from the integrated circuit104to an activator that activates the ink nozzle. For example, in this embodiment, the flexible circuit lead146transmits an electrical signal to activate a piezoelectric actuator to fire an ink nozzle.

On either end of the flexible circuit100an arm150extends upwardly in a direction substantially perpendicular to the surface of the faceplate108upon which the printhead body106is mounted and folds over, such that the distal end of the arm150is substantially parallel to the surface of the faceplate108. External connectors102(shown in phantom) are included on the underside of the distal end of the arm150. As shown previously inFIGS. 5C and 6B, the external connectors102are configured to mate with connectors132on a connection plate128of an external circuit120. In one embodiment, the external connectors102are ball pads that electrically connect to traces on the surface of the connection plate120. In another embodiment, the external connectors are male or female electrical connectors.

FIG. 8Bis a schematic representation of a top view of the flexible circuit100with the integrated circuits104removed and with the arms150spread flat, so as to be in the same plane as the balance of the flexible circuit100. In the regions105where an integrated circuit104would typically be mounted, an array of contacts is shown. In this embodiment, each region105includes a 16×6 array of contacts101. The two outermost rows of contacts on either side of each array are connected to flexible circuit leads146. In one embodiment, the leads can be copper traces with a thin gold plating, to prevent oxidation. Each flexible circuit lead146connects to a corresponding aperture148formed in a distal portion144of the flexible circuit100.

The integrated circuit104has integrated circuit (IC) leads formed on the surface that will contact the flexible circuit100. The IC leads can be, for example, a 16×6 ball grid array has is configured to correspond to the 16×6 contact array formed on the flexible circuit100. When the integrated circuit104is positioned on the flexible circuit100, the ball grid array aligns with the contact array on the flexible circuit100. The IC leads can be soldered to the contacts101in the contact array, thereby connecting the integrated circuit104to the flexible circuit100, and forming an electrical connection between the IC leads and the contacts101.

The flexible circuit leads146are connected to the contacts101, which contacts101are connected to the IC leads. The flexible circuit leads146are also connected to the printhead body106by the conductive apertures148. The top surface107of the printhead body106includes ground contacts positioned along the edges of the printhead body106and drive contacts positioned laterally inward of their associated ground contacts. The ground contacts of the printhead body106are connected (and thereby grounded) to a common ground103that is formed along the length of the distal portions of the flexible circuit100. Each drive contact of the printhead body106is connected to a conductive aperture148of the flexible circuit100. As such, output drive signals generated by the integrated circuits104are transmitted from the integrated circuits104to the drive contacts of the piezoelectric actuators in the printhead body106to apply a voltage to the actuators and thereby selectively drive the corresponding ink nozzles.

The contacts101in the two inner rows can be used to connect the integrated circuit100to connective layers within the flexible circuit100. For example, an aperture can be formed in the flexible circuit100that extends to a connective layer, e.g., a copper layer, and the aperture filled or coated with a conductive material. An IC lead on the integrated circuit100touches the contact to form an electrical connection to the connective layer. The connective layer extends the length of the flexible circuit100, including the arms150, and is electrically connected to at least one of the electrical connectors102formed on the distal ends of the arms150. As such, input signals from the external circuit120are transmitted from the external circuit120to the integrated circuits1.04. Referring again toFIG. 8B, the arms150are extended flat, exposing the underside of each distal end. The external connectors102on the underside of each distal end of an arm are shown.

Referring toFIG. 8C, an enlarged view of one region105of the flexible circuit100is shown. In this embodiment, there are at least 64 flexible circuit leads146connected to each integrated circuit104, which integrated circuit104drives64ink nozzles included in the printhead body106.

FIG. 9shows a cross-sectional view of the flexible circuit100taken along line9-9shown inFIG. 8A. The integrated circuit104is mounted on top of the central portion142of the flexible circuit100. A flexible circuit lead146is shown extending from beneath the integrated circuit104toward a distal portion144of the flexible circuit100. The flexible circuit lead146extends to a corresponding aperture148formed in the flexible circuit100. The aperture148extends through the thickness of the circuit and is aligned to a drive contact152on the printhead body106. For example, the drive contact152can be a trace on the top surface107of the printhead body106. The flexible circuit lead146extends through the aperture148. For example, the aperture148can be coated in a conductive material, such as gold or copper. An electrical signal passing from the integrated circuit104through the flexible circuit lead146travels through the conductive material to the drive contact152, thereby establishing a connection between the integrated circuit104and the printhead body106, for example, to apply a voltage to a piezoelectric actuator.

FIG. 10Ashows an enlarged cross-section view of a portion of the flexible circuit100. In the embodiment shown, the central portion142of the flexible circuit100is formed from a different number of layers as compared to the distal portions144. The distal portions144are formed from layers160and161, where layer160can be a conductive layer such as a copper layer, and layer161can be an insulator layer such as a polyimide layer, e.g., Kapton® available from DuPont High Performance Materials of Ohio. The central portion142includes additional layers162-166of copper; adhesive; copper; Kapton; and copper, respectively. That is, the central portion142includes four layers of copper, where each copper layer is separated by a layer of Kapton or adhesive. The central portion142can be formed as two Kapton layers161,165coated on either side with copper and then joined by an adhesive163. In the central portion142where the integrated circuits104are attached to the flexible circuit100, the additional layers provide interconnects (the copper layers), e.g., to connect the integrated circuits104to the external connectors102, and support rigidity.

Referring toFIG. 10B, in one embodiment the layers forming the flexible circuit100, such as the flexible circuit100shown inFIG. 10A, can have the thicknesses as shown. The two layer distal portion can have a thickness of 42 microns and the 7 layer central portion can have a thickness of 143 microns. A solder mask can be applied on top of the copper layer162and to the copper layer166(e.g., to connect to the printhead body106), which can add an additional 25 microns per solder mask. The thickness can therefore be as much as 193 microns.

Including only two layers in the distal portions144of the flexible circuit100provides flexibility in the gull-wing region (i.e., the bent portion143) to bend the flexible circuit100into a desired shape. Because there are less layers in the sides100, which includes the apertures148, alignment of the layers within the apertures148is facilitated.

For example, in one embodiment, the conductive material (e.g., copper) forming the leads146and any other electrical connections can be formed as follows. A negative of an artwork for the electrical circuit, including the leads146, is formed on a film, for example, by a laser photo plotting technique (the “artwork negative film”). A photo-defineable film is layered over top of a sheet of copper, which is bonded to a Kapton® layer. The artwork negative film is placed over top of the copper, which is then exposed to light. A solution is then applied to the photodefinable coated copper, and the solution etches away the copper that was not exposed to the light. The photodefinable film can then be removed, and the remaining copper (i.e., copper not removed by etching) reflects the desired circuit. A second sheet of copper can be bonded to the opposite side of the Kapton, and the same process followed to form the leads146on the opposite side. If more than one layer of Kapton are being used, the process is repeated for each Kapton layer, which copper/Kapton layers must then be bonded together while maintaining alignment of the circuits formed in copper thereon. Precise alignment can be required to achieve connections between the layers. As such, the fewer layers to align (or no alignment at all), facilitates the fabrication.

Other materials can be used can be used to form the flexible circuit100. For example, the metal layer can be gold and the Kapton layer can be Liquid Crystal Polymer (LCP). Additional layers can be included in either the distal portions144or central portion142.

Referring toFIG. 11A, in another embodiment, an interposer170can be positioned between the printhead body106and the flexible circuit100. The interposer170is attached to the upper surface of the printhead body106. The interposer170can be formed, for example, from silicon. In the embodiment shown, the interposer170includes an optional integrated heating element172. The heating element172can be formed by etching a trough into the silicon interposer170and filling the trough with a conductive material, such as nickel chromium. Alternatively, the heating element172can be formed on the opposite surface of the interposer170.

Referring toFIG. 11B, an enlarged view of a portion of the interposer170mounted on the printhead body106is shown. The interposer170includes apertures174along both sides of the interposer170. For illustrative purposes, only a few of the apertures174are depicted on each side, however, similar apertures174are positioned along substantially the entire length of the interposer170. The apertures174are coated with a conductive material, such as gold. One aperture174corresponds to each ink nozzle included in the ink nozzle assembly of the printhead body106. Each metalized conductive aperture174provides an electrical connection to the drive contact for the corresponding actuator for the ink nozzle, such as a piezoelectric actuator configured to fire the ink nozzle. The interposer170can be attached to the printhead body106using a thin epoxy, such that when pressure and heat is applied, the gold connects through the epoxy to connectors on the printhead body106. The epoxy can be unfilled or filled, such as a conductive particle filled epoxy. The epoxy can be a spray-on epoxy.

If the interposer170includes a heating element172, as shown, then a thermistor176can be included on the interposer170to control the temperature of the heating elements, and leads178can provide a connection from the interposer170to the flexible circuit100to receive signals controlling the thermistor176.

Referring toFIG. 1C, an enlarged view of a portion of the flexible circuit100mounted on the interposer170, which is mounted on the printhead body106affixed to the faceplate108, is shown. Each aperture148formed in the flexible circuit100is aligned with a corresponding aperture174formed in the interposer170. A signal can thereby travel from an integrated circuit104, through a flexible circuit lead146to a conductive aperture148in the flexible circuit100, to a conductive aperture174in the interposer170, and finally to an ink nozzle activator in the printhead body106.

Referring toFIG. 11D, a cross-sectional view of the assembly ofFIG. 11Cis shown along line11D-11D. The flexible circuit100is mounted onto the interposer170, for example, using an epoxy connection, solder connection or ACF (anisotropic conductive film). A flexible circuit lead146on the surface of the flexible circuit100connects to a conductive aperture148formed in a distal portion144of the flexible circuit100. The aperture148is aligned with a conductive aperture174in the interposer170. The aperture174in the interposer is aligned with an activator in the printhead body106for activating an ink nozzle. In the embodiment shown, the activator is a piezoelectric actuator including a piezoelectric material that bends in response to a voltage applied, thereby pressurizing ink in a corresponding ink chamber and causing the ejection of an ink drop from an ink nozzle. The underside of the interposer170, i.e., the surface that connects to the printhead body106, includes a recess173to provide clearance for the piezoelectric material included on the top surface of the printhead body106.

In another embodiment, the flexible circuit100can be substantially flat, that is the central portion142and distal portions144can all be flush with the top surface of the interposer170. This can be an advantage, since it can eliminate the fabrication step of forming bends in the flexible circuit100.

There are a number of advantages to including an interposer170between the flexible circuit100and the printhead body106. The flexible circuit100can be connected to the interposer170before attaching the interposer170to the printhead body106. This allows connections of the flexible circuit100and between the flexible circuit100and the interposer170to be tested before the flexible circuit100/interposer170assembly is attached to the printhead body106. If there is a problem with the connections, the flexible circuit100can be replaced, without having to replace the printhead body106or attempt to remove the flexible circuit100from the printhead body106without damaging the printhead body106. The likelihood of damaging the printhead body106during the assembly process is reduced by attaching the flexible circuit100to the interposer170rather than directly to the printhead body106. The surfaces of the interposer170and the printhead body106that will be in contact with one another can be polished to provide a precise match. This can reduce or eliminate pressure variations along the length of the printhead body106that can occur when attaching the circuit directly to the printhead body106by soldering. Optionally, as described above, the interposer170can include a heating element172.

Referring toFIG. 12, a cross-sectional perspective view of another embodiment of a flexible circuit180is shown. In this embodiment, the integrated circuits184are mounted onto the same surface of the flexible circuit180that is attached to an interposer190. The interposer190includes a recess192that is configured to accommodate the integrated circuit184suspended from the flexible circuit180. The interposer190can include one recess192that extends the length of the interposer190, or multiple recesses192positioned to correspond to the positions of the multiple integrated circuits184mounted on the circuit. On the opposite side, the interposer190includes a recess193to provide clearance for the piezoelectric material included in the printhead body106. In this embodiment, the leads182from the integrated circuits184are on the same surface that is attached to the interposer190, and accordingly apertures, such as the apertures148in the flexible circuit100described above, are not required. Rather, the leads182can extend to contact directly the corresponding conductive apertures194formed in the interposer190, similar to the conductive apertures174described above in reference to the interposer170shown inFIGS. 11A-D. The conductive apertures194are in contact with the drive contacts196for the actuators for corresponding ink nozzles located in the printhead body106, such as piezoelectric actuators.

An advantage of the embodiment of the flexible circuit180shown inFIG. 12is the elimination of apertures to connect the leads182to the interposer190. The flexible circuit180can be formed substantially flat, as shown, thereby also eliminating the need to shape the flexible circuit180, for example, to form bends as in the embodiment shown inFIG. 1. The flexible circuit180can be formed from layers of polyimide coated with copper, as described above in reference toFIG. 10. However, because the flexible circuit180is substantially flat and does not require apertures, in one embodiment, the flexible circuit180can include two layers of polyimide and four layers of copper throughout, rather than having thinner sides as in the embodiment depicted inFIG. 10. Other materials and numbers of layers can be used, as described above in reference to the flexible circuit100.

The use of terminology such as “upper” and “lower” and “top” and “bottom” throughout the specification and claims is for illustrative purposes only, to distinguish between various components of the flexible printhead circuit and other elements described herein. The use of “upper” and “lower” and “top” and “bottom” does not imply a particular orientation of the flexible printhead circuit. For example, the upper surface of the interposer described herein can be orientated above, below or beside a lower surface, and visa versa, depending on whether the interposer is positioned horizontally face-up, horizontally face-down or vertically.

Although only a few embodiments have been described in detail above, other modifications are possible. Other embodiments may be within the scope of the following claims.