Patent Description:
The Applicant has developed a range of Memjet® inkjet printers as described in, for example, <CIT>, <CIT> and <CIT>. Memjet® printers employ one or more stationary inkjet printheads in combination with a feed mechanism which feeds print media past the printhead in a single pass. Memjet® printers therefore provide much higher printing speeds than conventional scanning inkjet printers.

Currently, multi-color Memjet® printheads for desktop printing are based on a liquid crystal polymer (LCP) manifold described in <CIT>, which delivers four colors of ink through five color channels (CMYKK) of the printhead to a plurality of butted printhead chips. The Memjet® printhead chips are bonded to a surface of the LCP manifold via an apertured die-attach film comprised of a central polymer web sandwiched between opposite adhesive layers. The LCP manifold cooperates with the die-attach film to direct ink from each of five ink channels to respective color planes of each printhead chip via a series of tortuous ink pathways. Redundancy in the black (K) channel is useful for improving print quality and black optical density.

However, at high print speeds, the LCP manifold has some practical limitations. The multiple labyrinthine ink pathways for delivering multiple inks from the LCP manifold to the printhead chips may be responsible for unexpected de-priming when the printhead is running at high speeds. Without a sufficiently large body of ink close to the printhead chips, the chips may become starved of ink under periods of high ink demand and lead to chip de-priming. Secondly, the labyrinthine ink pathways are susceptible to trapping air bubbles; if an air bubble becomes trapped in the system, the printhead chips will become starved of ink and de-prime. It would therefore be desirable to provide a color printhead suitable for high-speed printing, which is tolerant of air bubbles and less susceptible to de-prime events.

Whilst LCP is a satisfactory choice of material for A4 printheads, having a CTE similar to silicon, it typically lacks the required rigidity to manufacture longer printheads (e.g. A3 printheads). It would be desirable to provide a printhead architecture suitable for manufacturing printheads that may be longer than A4-sized.

Printhead electrical connections in pagewide printheads are typically via one or more flex PCBs, which wrap around an exterior sidewall of the printhead. An alternative, more complex approach is to route electrical wiring through layers of a laminated ceramic ink manifold (see, for example, <CIT>). However, flex PCBs are expensive and add significantly to manufacturing costs. Moreover, bending of a flex PCB through a tight angle places strain on the PCB and limits the components that may be incorporated thereon. It would therefore be desirable to provide a robust, inexpensive alternative to conventional electrical wiring arrangements used in pagewide printheads.

For inkjet digital presses, multiple monochrome printheads are typically stacked along a media feed direction, as described in <CIT>. This arrangement enables very high speed printing by making use of multiple ink channels in each printhead to print one color of ink. However, a problem with stacking printheads in this manner is that precise registration of the printheads is required when printheads are replaced by the user. Further, there are high demands on media feed mechanisms, which must maintain alignment of the print media with the printheads through a relatively long print zone. It would therefore be desirable to provide a replaceable printhead suitable for desktop printing, which can print multiple colors at high speeds and does not require registration of multiple printheads in the field.

<CIT> describes a printhead having printhead chips mounted on a polymer substrate having an embedded Invar stiffening layer.

<CIT> describes a printhead having printhead chips mounted on a substrate comprised of laminated LCP layers.

In accordance with the present invention, there is provided an inkjet printhead as defined hereinbelow in the appended claims.

The present invention advantageously enables the construction of relatively long monolithic printheads, which may be longer than A4-sized (e.g. greater than <NUM> in length). For example, the invention according to the second aspect enables the construction of monolithic A3-sized printheads.

As foreshadowed above, LCP is a common choice of material for pagewide printheads due to its moldability, stiffness and relatively low CTE. However, whilst stiffer than other plastics, LCP does not have the requisite rigidity for the construction of long monolithic printhead manifolds. Although metals are an obvious choice of material for constructing rigid printhead manifolds, the thermal expansion properties of metals are not generally considered to be suitable for attachment of printhead chips directly onto the metal due to the mismatch in thermal expansion characteristics between the metal and silicon. One approach to the problem of constructing longer printheads is to thermally isolate each printhead chip on its own respective carrier. However, individual printhead chip carriers are unsuitable for a rows of butting printhead chips and increase a width of the print zone.

The printhead according to the present invention employs a suitable metal alloy (e.g. Invar) shim for adhesive bonding of a plurality of printhead chips to the manifold using, for example, an epoxy adhesive applied as a liquid to one or both bonding surfaces. The shim has minimal expansion at high temperatures and provides a stable structure for mounting a plurality of printhead chips to the manifold. This, in turn, provides greater flexibility in the choice of materials for the manifold. The manifold may be comprised of a material which is the same or different than the shim, and may be selected on the basis of stiffness, cost, manufacturability etc. For example, the manifold may be comprised of a material, such as stainless steel, Invar or a polymer. Typically, the manifold is comprised of a same material as the shim.

As used herein, the term "ink" is taken to mean any printing fluid, which may be printed from an inkjet printhead. The ink may or may not contain a colorant. Accordingly, the term "ink" may include conventional dye-based or pigment-based inks, infrared inks, fixatives (e.g. pre-coats and finishers), 3D printing fluids and the like. Where reference is made to fluids or printing fluids, this is not intended to limit the meaning of "ink" herein.

Referring to <FIG>, there is shown an inkjet printhead <NUM> in the form of a replaceable printhead cartridge for user insertion in a printer (not shown). The printhead <NUM> comprises an elongate molded plastics casing <NUM> having a first casing part 3A and a second casing part 3B positioned at either side of a central locator <NUM>. The central locator <NUM> has an alignment notch <NUM> for positioning the printhead cartridge <NUM> relative to a print module, such as a print module of the type described in <CIT>. The first and second casing parts 3A and 3B are biased towards each other and the central locator <NUM> by means of a spring clip <NUM> engaged between the first and second casing parts (see <FIG>). The two-part casing <NUM> in combination with the spring clip <NUM> enables the casing to expand longitudinally, at least to some extent, to accommodate a degree of longitudinal expansion in a main body <NUM> of the printhead <NUM>. This arrangement minimizes stress or bowing of the main body <NUM> of the printhead <NUM> during use.

Inlet connectors 7A of a multi-channel inlet coupling 8A protrude upwards through openings at one end of the casing <NUM>; and outlet connectors 7B of a multichannel outlet coupling 8B protrude upwards through opening at an opposite end of the casing (only two inlet connectors and two outlet connectors shown in <FIG>). The inlet and outlet connectors 7A and 7B are configured for coupling with complementary fluid couplings (not shown) supplying ink to and from the printhead. The complementary fluid couplings may be, for example, part of an ink delivery module and/or print module of the type described in <CIT>.

The printhead <NUM> receives power and data signals via opposite rows of electrical contacts <NUM>, which extend along respective sidewalls of the printhead. The electrical contacts <NUM> are configured to receive power and data signals from complementary contacts of a printer (not shown) or print module and deliver the power and data to printhead chips <NUM> via a PCB, as will be explained in more detail below.

As shown in <FIG>, the printhead <NUM> comprises a first row <NUM> and a second row <NUM> of printhead chips for printing onto print media (not shown) passing beneath the printhead. Each row of printhead chips is configured for printing two colors of ink, such that the printhead <NUM> is a full color pagewide printhead capable of printing four ink colors (CMYK). The printhead <NUM> is generally symmetrical about a longitudinal plane bisecting the first row <NUM> and the second row <NUM> of printhead chips, notwithstanding the different ink colors in the printhead during use.

In the exploded perspective shown in <FIG>, it can be seen that the main body <NUM> forms a rigid core of the printhead <NUM> for mounting various other components. In particular, the casing <NUM> is snap-fitted to an upper part of the main body <NUM>; the inlet and outlet couplings 8A and 8B (enshrouded by the casing <NUM>) are connected to opposite ends of the main body; a pair of PCBs <NUM> are attached to a lower part of the main body (which are in turn covered by a shield plate <NUM>); and a plurality of leads <NUM> (which define the electrical contacts <NUM>) are mounted to opposite sidewalls of the main body.

Referring to <FIG>, the main body <NUM> is itself a two-part machined structure comprising an elongate manifold <NUM> and a complementary cover plate <NUM>. The manifold <NUM> functions as a carrier having a unitary lower surface for mounting both the first and second rows <NUM> and <NUM> of printhead chips. The manifold <NUM> is received between a pair of opposed flanges <NUM>, which extend downwardly from opposite longitudinal sides of the cover plate <NUM>. The flanges <NUM> are configured for snap-locking engagement with complementary snap-locking features <NUM> of the manifold <NUM> to form the assembled main body <NUM>.

The manifold <NUM> and cover plate <NUM> are formed of a metal alloy material having excellent stiffness and a relatively low coefficient of thermal expansion (e.g. Invar). In combination, the manifold <NUM> and cover plate <NUM> provide a stiff, rigid structure at the core of the printhead <NUM> with minimal expansion along its longitudinal axis. As foreshadowed above, the casing <NUM> is configured so as not to constrain any longitudinal expansion of the main body <NUM> and thereby minimizes bowing of the printhead during use. Accordingly, the printhead <NUM> may be provided as an A4-length printhead or an A3-length printhead. It is an advantage of the present invention that a single pagewide printhead may be configured up to A3-length (i.e. up to <NUM>). Hitherto, pagewide printing onto A3-sized media was only possible via multiple printhead modules stitched together in a pagewide array and the printhead <NUM>, therefore, expands the commercial viability for A3-sized, color pagewide printing.

<FIG> shows in detail one of the multi-channel fluid couplings <NUM>, which may be either the inlet coupling 8A or the outlet coupling 8B. However, for the purposes of describing features in connection with <FIG>, the fluid coupling <NUM> shown is assumed to be the inlet coupling 8A.

The fluid coupling <NUM> is designed to transfer four colors of ink through a <NUM>-degree angle for vertical coupling of the printhead <NUM> to, for example, a complementary fluid coupling of a print module, whilst ensuring that four fluid connectors can be geometrically accommodated within the space constraints of the printhead and its surrounds. Furthermore, the fluid coupling <NUM> is designed to equalize any pressure drops through the fluid coupling, such that the four ink colors have the same or similar relative pressures when they enters the manifold <NUM>.

Referring then to <FIG>, the fluid coupling <NUM> comprises four inlet ports 9A-D, which extend vertically upwards from a coupling body <NUM>, and corresponding outlet ports 11A-D extending from the coupling body perpendicular to the inlet ports. The inlet ports 9A-9D are radially arranged about the coupling body <NUM>, such that the two outer inlet ports 9A and 9D are relatively proximal their respective outlet ports 11A and 11D; and the two inner inlet ports 9B and 9C are relatively distal their respective outlet ports. The radial arrangement of the inlet ports 9A-9D enables the inlet ports to be accommodated within the space constraints of a print module (not shown) engaged with the printhead. Furthermore, the inlet ports have coplanar upper surfaces for simultaneous vertical engagement/disengagement during printhead insertion/removal.

Each ink entering the fluid coupling <NUM> has a carefully controlled respective hydrostatic pressure (e.g. by virtue of an upstream pressure regulator) and it is important that the relative hydrostatic pressures of the inks are not changed as the inks flow through the fluid coupling. For example, the four inks may enter the inlets ports 9A-9D with equal hydrostatic pressures and it is desirable that these inks exit the outlet ports 11A-11D into the manifold <NUM> with equal hydrostatic pressures. A degree of pressure drop is, to some extent, inevitable as each ink experiences flow resistance (i.e. viscous drag) through the fluid coupling <NUM>; however, it is important that the pressure drops are equalized for all inks despite the longer fluidic paths for the two inks flowing through the two inner inlet ports 9B and 9C. Accordingly, as shown in <FIG>, a fluid channel 12B connecting the inlet port 9B with the outlet port 11B has a roof 13B sloped upwards from towards the inlet port 9B. A roof 13C of a corresponding fluidic channel connecting the inlet port 9C and the outlet port 11C is, likewise, sloped upwards towards the inlet port 9C. By contrast the fluid channel 12A connecting inlet port 9A with the outlet port 11A does not have a similarly sloped roof, requiring the fluid to turn through a tighter angle without assistance from a more curved fluid path.

Thus, the roof configuration of the two inner fluid channels 12B and 12C has the effect of negating any additional flow resistance that might be caused by their relatively longer fluidic paths compared to the two outer fluid channels 12A and 12D. Thus, a pressure drop through the fluid coupling <NUM> is the same or similar for all four fluid channels 12A-12D and each of the four outlet ports 11A-11D will have equal hydrostatic pressures when inks entering the four inlet ports 9A-D have equal hydrostatic pressures. By contrast, fluid connectors for printheads known in the art, such as the fluid connector described in <CIT>, have appreciable differences in flow resistances (and pressure drops) for various fluid channels with different lengths.

<FIG> is a magnified view of an outlet end of the manifold <NUM> and cover plate <NUM> together with the outlet coupling 8B. It will be seen that the cover plate <NUM> has a plurality of vent holes <NUM> spaced apart along its length, which are open to atmosphere so as to allow free flexing of a flexible film <NUM> attached to an upper part of the manifold <NUM>. The function of the flexible film <NUM> will be described in further detail below.

Still referring to <FIG>, the multi-channel outlet coupling 8B receives ink from manifold ports <NUM> at one end of the manifold <NUM>. Likewise, the multi-channel inlet coupling 8A delivers ink to manifolds ports <NUM> at an opposite end of the manifold <NUM>. Of course, alternative coupling arrangements are within the ambit of the present invention.

Referring now to <FIG> and <FIG>, the ink manifold <NUM> comprises four ink supply channels <NUM> extending longitudinally and parallel with manifold sidewalls <NUM>. Each ink supply channel <NUM> is supplied with ink from a manifold port <NUM> at one end of the manifold <NUM> and ink exits the ink supply channel via a manifold outlet <NUM> at an opposite end of the manifold. The ink supply channels <NUM> are capped by the flexible film <NUM>, covering an upper part of the manifold <NUM>, with the flexible film <NUM> including a plurality of discrete corrugated sections or bellows <NUM>.

Typically, printing systems are developed with several subsystems having differing fluidic response frequencies and the bellows <NUM> are designed to respond rapidly to hydrostatic pressure changes in the printhead <NUM>. In order to maintain optimum ejection performance, internal pressures within the printhead <NUM> should optimally be maintained within a relatively narrow pressure window so as to allow nozzle refill consistency. Since ink delivery systems, which supply ink to the printhead <NUM>, typically have a relatively slow response to dynamic pressure changes, rapid refill of inkjet nozzles in the printhead is controlled locally by the bellows <NUM> taking up an ejected volume of ink until the ink delivery system can respond. Similarly, the bellows <NUM> also perform a dampening function and can "absorb" pressure spikes when printing at full ink flow stops suddenly.

It will be appreciated that the number and configuration of bellows <NUM> may be modified to optimize the performance of the printhead <NUM>. In particular, the number and configuration of bellows <NUM> may be optimized to minimize undesirable resonance effects along the length of the ink supply channel <NUM>. In this way, high ink demand in one portion of the ink supply channel <NUM> can be met by a number of bellows <NUM>, without inducing a standing wave across an entire length of the flexible film <NUM>. The bellows <NUM> may be separated into discretely operating units either by being spaced apart along the length of the film (e.g. with intervening planar sections of the film), or, as shown in <FIG>, by dividing the flexible film <NUM> into longitudinal sections using transverse baffles <NUM>. The baffles <NUM> minimize generation of standing waves along a whole length of the film <NUM>, whilst enabling the film to be molded from a single piece covering all four ink supply channels, thereby facilitating fabrication of the printhead <NUM>.

It will be further appreciated that the bellows <NUM> can respond to pressure fluctuations without requiring air boxes, such as those described in <CIT>. Therefore, the printhead <NUM> is suitable for use with degassed inks.

As best seen in <FIG>, the bellows <NUM> 'hang' from an upper surface of the manifold <NUM> into each of the ink supply channels <NUM>. The bellows <NUM> hang down to a level corresponding to a level of the manifold ports <NUM>, such that any air bubbles cannot become trapped in a headspace of the ink supply channels <NUM> below the bellows. Thus, if undesired air bubbles enter the ink supply channels <NUM>, then these can be flushed out of the manifold <NUM> with a flow of ink through the manifold ports <NUM>, rather than becoming trapped in a headspace above the ink flow.

Still referring to <FIG>, the four ink supply channels <NUM> are arranged in pairs, with each pair being separated by a longitudinal dividing wall <NUM>. A relatively thicker longitudinal central wall <NUM> separates the two pairs of ink channels <NUM>. At a base <NUM> of each ink supply channel <NUM> and at opposite sides of the dividing wall <NUM> are defined a plurality of through-holes <NUM>. The through-holes <NUM> supply ink to two parallel rows of printhead chips <NUM>, as will now be described with reference to <FIG>.

The through-holes <NUM> corresponding to one pair of ink supply channels <NUM> extend downwardly from the bases <NUM> of the ink supply channels towards a lower surface <NUM> of the manifold <NUM>. Each through-hole <NUM> has a first portion <NUM> which meets with a cavity roof <NUM> of a longitudinal ink cavity <NUM> defined in the lower surface <NUM> of the manifold <NUM>. A longitudinal rib <NUM> extends downwardly from the cavity roof <NUM> and divides the longitudinal ink cavity <NUM> into a pair of longitudinal ink feed channels <NUM> positioned at opposite sides of the rib. The longitudinal rib <NUM> has an end surface <NUM> coplanar with the lower surface <NUM> of the manifold.

The longitudinal ink cavity <NUM> has cavity sidewalls <NUM>, which extend downwardly from the cavity roof <NUM> to meet with the lower surface <NUM> of the manifold <NUM>. A second portion <NUM> of each through-hole <NUM> extends beyond the cavity roof <NUM> to meet with the lower surface <NUM>. In this way, the second portions <NUM> of the through-holes <NUM> form notches in the cavity sidewalls <NUM>. Similarly, and as best shown in <FIG>, at least part of the first portions <NUM> of the through-holes <NUM> form notches in opposite sides of the dividing wall <NUM>.

The notches defined by the second portions <NUM> of the through-holes <NUM> provide a space for air bubbles to expand and rise away from the printhead chips <NUM> during use. In the embodiment shown, the through-holes <NUM> are circular in cross-section with the first portion <NUM> and second portion <NUM> being generally semi-circular. However, it will be appreciated that the through-holes <NUM> may be of any suitable cross-sectional shape for optimizing ink flow and bubble management.

As best shown in <FIG> and <FIG>, an Invar shim <NUM> is adhesively bonded to the lower surface <NUM> of the manifold <NUM> and the coplanar end surfaces <NUM> of the longitudinal ribs <NUM> so as to bridge across each of the longitudinal ink feed channels <NUM>. Thus, the shim <NUM> seals across the second portions <NUM> of the through-holes <NUM>, which meet with the lower surface <NUM> of the manifold <NUM>.

In the embodiment shown, the shim <NUM> is a single-part shim bonded to the lower surface <NUM> of the manifold <NUM> so as to bridge across all four longitudinal ink feed channels <NUM> corresponding to the four colors of ink. Rows of butting printhead chips <NUM> are adhesively bonded to the shim <NUM> over a respective pair of ink feed channels <NUM> to form the first row <NUM> and the second row <NUM> of printhead chips.

The Invar shim <NUM>, shown in isolation in <FIG>, provides a stable platform for each row of printhead chips <NUM> with negligible thermal expansion during use. The shim <NUM> has a comparable thickness to the printhead chips <NUM> (e.g. about <NUM> to <NUM> microns in thickness). Effectively, the Invar shim <NUM> enables construction of long printheads based on a monolithic manifold to which a plurality of printhead chips can be mounted.

Use of a singular shim <NUM> having a pair of longitudinal shim sections 66A and 66B minimizes relative skew of the first row <NUM> and second row <NUM> of printhead chips <NUM> by ensuring parallelism between the two shim sections 66A and 66B. Alignment of the shim <NUM> relative to the manifold <NUM> is facilitated using mechanical alignment tabs <NUM> on the shim, which engage with alignment features <NUM> in the form of recesses defined in the lower surface (see <FIG>). It will be appreciated that the shim <NUM> has a number of alignment tabs <NUM> positioned for engagement with a corresponding plurality of alignment features <NUM> in the manifold <NUM>. A plurality of alignment tabs <NUM> ensures alignment in both x- and y-axes.

A central longitudinal portion of the shim <NUM> defines voids <NUM> between a series of shim trusses <NUM> connecting the two main longitudinal sections 66A and 66B. Accordingly, a region between the first row <NUM> and second row <NUM> of printhead chips <NUM> is relatively thermally isolated from the lower surface <NUM> of the manifold <NUM>, which acts a heat sink cooled by ink circulating through the manifold. Thermal isolation of this central region of the printhead <NUM> assists in minimizing cool spots between the first row <NUM> and second row <NUM> and advantageously minimizes condensation of ink onto the underside of the printhead during printing.

In use, each row of printhead chips <NUM> receives two inks from a respective pair of ink supply channels <NUM>. Ink is supplied into the pair of longitudinal ink feed channels <NUM> via the through-holes <NUM>, and thence into the backsides the printhead chips <NUM> via a pair of longitudinal shim slots <NUM> defined in each longitudinal shim section 66A and 66B. The longitudinal shim slots <NUM> extend along opposite sides of a longitudinal shim rib <NUM>, which is itself aligned with the longitudinal rib <NUM> of the manifold <NUM>.

The longitudinal ink feed channels <NUM> provide an open ink channel architecture, whereby a relatively large body of ink is in close proximity to the backsides of the printhead chips <NUM>. This arrangement is suitable for printing at high print frequencies, whilst ensuring that inkjet nozzles in the printhead chips do not become starved of ink. Furthermore, the enlarged through-holes <NUM>, each having a second portion <NUM> meeting with the shim <NUM> and offset from the printhead chips <NUM>, provide a bubble-tolerant architecture whereby the risk of trapped air bubbles blocking a flow of ink into the printhead chips is minimized. Moreover, the first portions <NUM> and second portions <NUM> of the through-holes <NUM> facilitate venting of trapped air bubbles into the ink supply channels from where any air bubbles may be readily flushed from the printhead <NUM>.

Ink is supplied from the shim slots <NUM> to corresponding ink delivery slots defined in the backside of each printhead chip <NUM>. A typical Memjet® printhead chip <NUM>, shown in <FIG>, comprises five color channels for potentially printing five inks. Five color channels in a single printhead chip provides flexibility for various different printing configurations and, hitherto, Memjet® printhead chips <NUM> have been plumbed for printing CMYK(IR), as described in <CIT>; CMYKK as described in <CIT>, CCMMY as described in <CIT>, or monochrome (e.g. KKKKK) as described in <CIT>. In the printhead <NUM>, the first row <NUM> contains Memjet® printhead chips <NUM>, which are typically plumbed for printing two colors of ink and the second row <NUM> contains Memjet® printhead chips, which are typically plumbed for printing two different colors of ink for full-color (CMYK) printing. Thus, the printhead <NUM> only makes use of four of the five available color channels in the Memjet® printhead chip. As shown in <FIG>, two outer color channels 71A are used to print one color of ink fed from a respective ink feed channel <NUM>; two opposite outer color channels 71B are used to print another color of ink fed from another respective ink feed channel; and the central color channel 71C contains a dummy row of non-ejecting nozzles, which do not receive any ink from the manifold <NUM>. As best shown in <FIG>, a central portion of the printhead chip <NUM> corresponding to the dummy color channel 71C is aligned with the longitudinal rib <NUM> of the manifold <NUM> to provide additional mechanical support for mounting the printhead chip. A backside ink delivery slot corresponding to the dummy channel 71C in the printhead chip <NUM> may be non-etched or only partially etched to provide additional mechanical support. In some embodiments, partial etching of backside channels may be useful for accommodating adhesive squeeze-out during mounting of the printhead chips <NUM>.

Notwithstanding the mechanical advantages of the central dummy color channel 71C in the printhead chip <NUM>, additional advantages may be achieved in terms of temperature regulation. Although the row(s) of nozzles corresponding to the dummy color channel 71C do not receive any ink, they may still be electrically connected to a printer controller in order to heat the printhead chip, as required. Temperature regulation across all color channels in a printhead chip is important for achieving consistent print quality and a central dummy row of non-ejecting nozzles, each having an active heater element, may be used achieve improved temperature regulation across the printhead chip.

Turning to <FIG>, the electrical wiring arrangements for the printhead <NUM> will now be described in more detail. A pair of longitudinal PCBs <NUM> flank the first row <NUM> and second row <NUM> of printhead chips <NUM> at opposite sides thereof, each PCB being bonded to the lower surface <NUM> of the manifold <NUM>. Each PCB <NUM> comprises a rigid substrate (e.g. FR-<NUM> substrate) for mounting of various electronics components and has one edge butting against a step <NUM> defined in the lower surface <NUM> of the manifold <NUM>. Each PCB <NUM> extends laterally outwards beyond the sidewalls <NUM> of the manifold <NUM>. The shield plate <NUM> is bonded to a lower surface of each PCB <NUM> and surrounds the first and second rows <NUM> and <NUM> of printhead chips <NUM> as well as a central longitudinal region between the first and second rows. The protruding portions of each PCB <NUM> and the shield plate <NUM> define opposite wings <NUM> of the printhead <NUM>, while a uniformly planar lower surface of the shield plate <NUM> is configured for engagement with a perimeter capper (not shown) surrounding both rows of printhead chips.

An edge of each PCB <NUM> proximal a respective row of printhead chips <NUM> has a respective row of pinouts <NUM>, each pinout being connected to a respective bond pad <NUM> on one of the printhead chips via a wirebond connection (not shown). An encapsulant <NUM> protects the wirebonds and extends between the proximal edge of each PCB <NUM> and an opposed edge of the printhead chips <NUM> containing the bond pads <NUM>. The PCBs <NUM> generate heat and warm the shield plate <NUM> exposed to ink aerosol during printing. As foreshadowed above, a central portion of the shield plate <NUM> is relatively thermally isolated from the manifold <NUM> by virtue of the voids <NUM> defined in the shim <NUM>. Accordingly, condensation of ink onto a central longitudinal region of the shield plate <NUM>, between the first row <NUM> and second row <NUM> of printhead chips <NUM>, is minimized.

As best seen in <FIG>, a row of contact pads <NUM> extends longitudinally along a distal edge portion of an upper surface of each PCB <NUM>. Each lead <NUM> has one end connected to a contact pad <NUM> and extends upwardly towards a respective sidewall of the main body <NUM>. The leads <NUM> have an upper portion mounted to a respective flange <NUM> of the cover plate <NUM> via a lead retainer <NUM> affixed thereto, and a lower portion which flares laterally outwards towards the contact pads <NUM>. Each lead <NUM> also has a portion defining the electrical contact <NUM> for connection to external power and data connectors of a printer. In this way, each row of printhead chips <NUM> receives power and data from the electricals contacts <NUM> via respective leads <NUM> and a respective PCB <NUM> adjacent the row of printhead chips.

The printhead <NUM> described hereinabove therefore has a number of features for addressing the challenges of pagewide printing, especially full-color pagewide printing using relatively long printheads.

Claim 1:
An inkjet printhead (<NUM>) comprising:
a rigid elongate manifold (<NUM>) having one or more ink supply channels (<NUM>) extending along its length and a plurality of ink outlets (<NUM>) defined therein;
a shim (<NUM>) attached to the manifold, the shim having a plurality of shim apertures (<NUM>) for receiving ink from the ink outlets; and
a plurality of printhead chips (<NUM>) adhesively bonded directly to the shim, each printhead chip receiving ink from one or more of the ink outlets;
characterized in that:
the shim consists of a metal alloy having a CTE of <NUM> ppm/°C or less; and
the manifold is comprised of a same material as the shim.