Ink jet printing system

Abstract: An inkjet print cartridge (10) comprises an ink reservoir (12); a substrate (28) with a plurality of ink firing chambers (130) and an ink firing element (70) in each chamber along a top surface thereof a first outer edge (86) along a periphery of substrate; and in close proximity to the ink firing chambers. The ink firing chambers are arranged in first and second arrays and are spaced so as to provide 600 dots per inch printing. An ink channel connects the reservoir with the ink firing chambers and includes a primary channel (52) connected to the reservoir and to a secondary channel. The primary channel allows ink to flow from the ink reservoir, around the first outer edge of the substrate to the secondary channel along the top surface of the substrate. A separate inlet passage (132) defined by a barrier layer (134) for each firing chamber connects the secondary channel with the firing chamber. The separate inlet passage has peninsulas (149) and pinch points (146) formed in the barrier layer to prevent cross-talk and overshoot during high frequency operation. A first circuit (78) on the substrate connects to the firing elements while a second circuit (36) on the cartridge connects to the first circuit means, for transmitting firing signals to the ink firing elements at a frequency greater than 9 kHz.

Description: The present invention generally relates to an inkjet printing system. Thermal inkjet print cartridges operate by rapidly heating a small volume of ink to cause the ink to vaporize and be ejected through one of a plurality of orifices so as to print a dot of ink on a recording medium, such as a sheet of paper. Typically, the orifices are arranged in one or more linear arrays in a nozzle member. The properly sequenced ejection of ink from each orifice causes characters or other images to be printed upon the paper as the printhead is moved relative to the paper. The paper is typically shifted each time the printhead has moved across the paper. The thermal inkjet printer is fast and quiet, as only the ink strikes the paper. These printers produce high quality printing and can be made both compact and affordable. An inkjet printhead generally includes: (1) ink channels to supply ink from an ink reservoir to each vaporization chamber proximate to an orifice; (2) a metal orifice plate or nozzle member in which the orifices are formed in the required pattern; and (3) a silicon substrate containing a series of thin film resistors, one resistor per vaporization chamber. To print a single dot of ink, an electrical current from an external power supply is passed through a selected thin film resistor. The resistor is then heated, in turn superheating a thin layer of the adjacent ink within a vaporization chamber, causing explosive vaporization, and, consequently, causing a droplet of ink to be ejected through an associated orifice onto the paper. In an inkjet printhead, described in US-A-4,683,481, ink is fed from an ink reservoir to the various vaporization chambers through an elongated hole formed in the substrate. The ink then flows to a manifold area, formed in a barrier layer between the substrate and a nozzle member, then into a plurality of ink channels, and finally into the various vaporization chambers. This design may be classified as a "center" feed design, whereby ink is fed to the vaporization chambers from a central location then distributed outward into the vaporization chambers. Some disadvantages of this type of ink feed design are that manufacturing time is required to make the hole in the substrate, and the required substrate area is increased by at least the area of the hole. Also, once the hole is formed, the substrate is relatively fragile, making handling more difficult. Further, the manifold inherently provides some restriction of ink flow to the vaporization chambers such that the energization of heater elements within a vaporization chamber may affect the flow of ink into a nearby vaporization chamber, thus producing crosstalk which affects the amount of ink emitted by an orifice upon energization of a nearby heater element. More importantly, prior printhead design limited the ability of printheads to have the high nozzle densities and the high operating frequencies and firing rates required for increased resolution and throughput. Print resolution depends on the density of ink-ejecting orifices and heating resistors formed on the cartridge printhead substrate. Modern circuit fabrication techniques allow the placement of substantial numbers of resistors on a single printhead substrate. However, the number of resistors applied to the substrate is limited by the conductive components used to electrically connect the cartridge to external driver circuitry in the printer unit. Specifically, an increasingly large number of resistors requires a correspondingly large number of interconnection pads, leads, and the like. This increase in components and interconnects causes greater manufacturing/production costs, and increases the probability that defects will occur during the manufacturing process. In order to solve this problem, thermal inkjet printheads have been developed which incorporate pulse driver circuitry directly on the printhead substrate with the resistors. The incorporation of driver circuitry not he printhead substrate in this manner reduces the number of interconnect components needed to electrically connect the cartridge to the printer unit. This results in an improved degree of production and operating efficiency. This development is described in US-A-4, 719,477 and US-A-5, 122,812. Other prior art inkjet printheads have included drawbacks with regards to the substrate and nozzle member. Alignment of the heating resistors in the substrate with their corresponding orifice in the nozzle member has proved difficult using conventional techniques. In the closest prior art EP-A-0564080, a thermal inkjet print cartridge according to the preamble of claim 1 is disclosed that is comprised of a polymer tape nozzle member including a plurality of nozzles, which is secured over a substrate containing heating elements, the elements and nozzles being conveniently aligned by the use of an automatic inner lead bonder. To produce high-efficiency, integrated printing systems as described above, significant research has been conducted in order to develop improved transistor structures and methods for integrating the same into thermal inkjet printing units. The integration of driver components and printing resistors onto a common substrate results in a need for specialised, multi-layer connective circuitry sot hat the driver transistors can communicate with the resistors and other portions of the printing system. Typically, this connective circuitry involves a plurality of separate conductive layers, each being formed using conventional circuit fabrication techniques. To create the resistors, an electrically conducting layer is positioned on selected portions of the layer of resistive material in order to form covered sections of the resistive materials and uncovered sections thereof. The uncovered sections ultimately function as heating resistors in the printhead. The covered sections are used to form continuous conductive links between the electrical contact regions of the transistors and other components in the printing system. Thus, the layer of resistive material performs dual functions: as heating resistors in the system, and as direct conductive pathways to the drive transistors. This substantially eliminates the need to use multiple layers for carrying out these functions alone. A selected portion of protective material is then applied to the covered and uncovered sections of resistive material. Thereafter, an orifice plate having a plurality of openings through the plate was positioned on the protective material. Beneath the openings, a section of the protective material which was removed forms ink firing cavities or vaporization chambers. Positioned at the bottom surface of each chamber is one of the heater resistors. The electrical activation of each resistor causes the resistor to rapidly heat and vaporize a portion of the ink in the cavity. The rapidly formed (nucleated) ink bubble ejects a droplet of ink from the orifice associated with the activated resistor and ink firing vaporization chamber. To increase resolution and print quality, the printhead nozzles must be placed closer together. This requires that both heater resistors and the associated orifices be placed closer together. To increase printer throughput, the width of the printing swath must be increased by placing more nozzles on the print head. However, adding resistors and nozzles requires adding associated power and control interconnections. These interconnections are conventionally flexible wires or equivalent conductors that electrically connect the transistor drivers on the printhead to printhead interface circuitry in the printer. They may be contained in a ribbon cable that connects on one end to control circuitry within the printer and on the other end to driver circuitry on the printhead. An increased number of heater resistors spaced closer together also creates a greater likelihood of crosstalk and increased difficulty in supplying ink to each vaporization chamber quickly. Interconnections are a major source of cost in printer design, and adding them in increase the number of heater resistors increases the cost and reduces the reliability of the printer. Thus, as the number of drivers on a printhead has increased over the years, there have been attempts to reduce the number of interconnections per driver. A matrix approach offers an improvement over the direct drive approach, yet as previously realized a matrix approach has its drawbacks. The number of interconnections with a simple matrix is still large and still results in an undesirable increase in the number of interconnections. Another concern with inkjet printing is the sufficiency of ink flow to the paper or other print media. Print quality is also a function of ink flow through the printhead. Too little ink on the paper or other media to be printed upon produces faded and hard-to-read printed documents. Ink flow from its storage space to the ink firing chamber has suffered, in previous printhead designs, from an inability to be rapidly supplied to the firing chambers. The manifold from the ink source inherently provides some restriction on ink flow to the firing chambers thereby reducing the speed of printhead operation as well as resulting in crosstalk. The present invention seeks to provide an improved inkjet printing system. According to an aspect of the present invention, there is provided an inkjet printing system as specified in claim 1. It is possible with the preferred embodiments to provide increased printing speed, resolution and quality, increased throughput, reduced number of interconnections, and improved ink flow control for higher frequency firing rates. Prior printhead design limited the ability of printheads to have the high nozzle densities and the high operating frequencies and firing rates required for increased resolution and throughput. Print resolution depends on the density of ink-ejecting orifices and heating resistors formed on the cartridge printhead substrate. To increase resolution and print quality the heater resistors and the associated orifices be placed closer together. An increased number of heater resistors spaced closer together and higher resistor firing frequencies also creates a greater likelihood of crosstalk and increased difficulty in supplying an adequate supply of ink to each vaporization chamber quickly. The edge feed feature, as described in EP-A-0564080 where ink flows around the edges of the substrate and directly into ink channels, has a number of performance advantages over previous printhead designs. The ink is able to flow more rapidly into the vaporisation chambers, since there is less restriction on the ink flow. This more rapid ink flow improves the frequency response of the printhead, allowing higher printing rates. Further, the more rapid ink flow reduces crosstalk between nearby vaporization chambers caused by variations in ink flow as the heater elements in the vaporization chambers are fired. When firing the resistors at high frequencies, i.e., greater than 8 kHz, conventional ink channel barrier designs either do not allow the vaporization chambers to adequately refill or allow extreme blowback or catastrophic overshoot and puddling on the exterior of the nozzle member. An embodiment provides an inkjet print cartridge comprising an ink reservoir; a substrate having a plurality of individual ink firing chambers with an ink firing element in each chamber along a top surface of said substrate and having a first outer edge along a periphery of said substrate; said first outer edge being in close proximity to said ink firing chambers; said ink firing chambers arranged in first chamber array and a second chamber array and said firing chambers spaced so as to provide 600 dots per inch printing; an ink channel connecting said reservoir with said ink firing chambers, said channel including a primary channel connected at a first end with said reservoir and at a second end to a secondary channel; said primary channel allowing ink to flow from said ink reservoir, around said first outer edge of said substrate to said secondary channel along said top surface of said substrate so as to be proximate to said ink firing chambers; a separate inlet passage for each firing chamber connecting said secondary channel with said firing chamber for allowing high frequency refill of the firing chamber; said separate inlet passage for each firing chamber having peninsulas and pinch points formed in said barrier layer to prevent cross-talk and overshoot during high frequency operation; a group of said firing chambers in adjacent relationship forming a primitive in which only one firing chamber in said primitive is activated at a time; first circuit means on said substrate connected to said firing elements; and second circuit means on said cartridge connected to said first circuit means, for transmitting firing signals to said ink firing elements at a frequency greater than 9 kHz. The system can be used with heated and non-heated inkjet printer types. An embodiment of the present invention is described below, by way of example only, with reference to the accompanying drawings, in which: Fig. 1 is a perspective view of an embodiment of inkjet print cartridge. Fig. 2 is a perspective view of the front surface of the Tape Automated Bonding (TAB) printhead assembly (hereinafter "TAB head assembly") removed from the print cartridge of Fig. 1. Fig. 3 is a perspective view of an simplified schematic of the inkjet print cartridge of Fig. 1. for illustrative purposes. Fig. 4 is a perspective view of the front surface of the Tape Automated Bonding (TAB) printhead assembly (hereinafter "TAB head assembly") removed from the print cartridge of Fig. 3. Fig. 5 is a perspective view of the back surface of the TAB head assembly of Fig. 4 with a silicon substrate mounted thereon and the conductive leads attached to the substrate. Fig. 6 is a side elevational view in cross-section taken along line A-A in Fig. 5 illustrating the attachment of conductive leads to electrodes on the silicon substrate. Fig. 7 is a perspective view of the inkjet print cartridge of Fig. 1 with the TAB head assembly removed. Fig. 8 is a perspective view of the headland area of the inkjet print cartridge of Fig. 7. Fig. 9 is a top plan view of the headland area of the inkjet print cartridge of Fig. 7. Fig. 10 is a perspective view of a portion of the inkjet print cartridge of Fig. 3 illustrating the configuration of a seal which is formed between the ink cartridge body and the TAB head assembly. Fig. 11 is a top perspective view of a substrate structure containing heater resistors, ink channels, and vaporization chambers, which is mounted on the back of the TAB head assembly of Fig. 4. Fig. 12 is a top perspective view, partially cut away, of a portion of the TAB head assembly showing the relationship of an orifice with respect to a vaporization chamber, a heater resistor, and an edge of the substrate. Fig. 13 is a schematic cross-sectional view taken along line B-B of Fig. 10 showing the adhesive seal between the TAB head assembly and the print cartridge as well as the ink flow path around the edges of the substrate. Fig. 14 illustrates one process which may be used to form the preferred TAB head assembly. Fig. 15 shows the same substrate structure as that shown in Fig. 11 but having a different barrier layer pattern for improved printing performance. Fig. 16 is a top plan view of a magnified portion of the structure of Fig. 15. Fig. 17 is a top plan view of a magnified portion of an alternative structure to the structure of Fig. 16. Fig. 18 is a top plan view of the structure of Fig. 15 expanded to show four resistors and the associated barrier structure.. Fig. 19 is a perspective view of the back surface of a flexible polymer circuit having ink orifices and cavities formed in it. Fig. 20 is a magnified perspective view, partially cut away, of a portion of the resulting TAB head assembly when the back surface of the flexible circuit in Fig. 19 is properly affixed to the barrier layer of the substrate structure shown in Fig. 15. Fig. 21 is a top plan view of the TAB head assembly portion shown in Fig. 19. Fig. 22 is a view of one arrangement of orifices and the associated heater resistors on a printhead. Fig. 23 is top plan view of one primitive of resistors and the associated ink vaporization chambers, ink channels and barrier architecture. Fig.24 is a table showing an embodiment of spatial location of 300 orifice nozzles. Fig. 25 is a schematic diagram of the heater resistors and the associated address lines, primitive select lines and ground lines which may be employed in the cartridge. Fig. 26 is an enlarged schematic diagram of the heater resistors and the associated address lines, primitive select lines and ground lines of the outlined portion of Fig. 25. Fig. 27 is a schematic diagram of one heater resistor of Figs. 25 and 26 and its associated address line, drive transistor, primitive select line and ground line. Fig. 28 is a table showing an embodiment of primitive select line and address select line for each of the 300 heater orifice/resistors. Fig. 29 is a schematic timing diagram for the setting of the address select and primitive select lines. Fig. 30 is a schematic diagram of the firing sequence for the address select lines when the printer carriage is moving from left to right. Fig. 31 is a diagram showing the layout of the contact pads on the TAB head assembly. Referring to Fig. 1, an inkjet print cartridge (10) incorporating an embodiment of printhead is shown in simplified form for illustrative purposes. The inkjet print cartridge 10 includes an ink reservoir 12 and a printhead 14, where the printhead 14 is formed using Tape Automated Bonding (TAB). The printhead 14 (hereinafter "TAB head assembly 14") includes a nozzle member 16 comprising two parallel columns of offset holes or orifices 17 formed in a flexible polymer flexible circuit 18 by, for example, laser ablation. A back surface of the flexible circuit 18 includes conductive traces 36 formed thereon using a conventional photolithographic etching and/or plating process. These conductive traces 36 are terminated by large contact pads 20 designed to interconnect with a printer. The print cartridge 10 is designed to be installed in a printer so that the contact pads 20, on the front surface of the flexible circuit 18, contact printer electrodes providing externally generated energization signals to the printhead. Windows 22 and 24 extend through the flexible circuit 18 and are used to facilitate bonding of the other ends of the conductive traces 36 to electrodes on a silicon substrate containing heater resistors. The windows 22 and 24 are filled with an encapsulant to protect any underlying portion of the traces and substrate. In the print cartridge 10 of Fig. 1, the flexible circuit 18 is bent over the back edge of the print cartridge "snout" and extends approximately one half the length of the back wall 25 of the snout. This flap portion of the flexible circuit 18 is needed for the routing of conductive traces 36 which are connected to the substrate electrodes through the far end window 22. The contact pads 20 are located on the flexible circuit 18 which is secured to this wall and the conductive traces 36 are routed over the bend and are connected to the substrate electrodes through the windows 22, 24 in the flexible circuit 18. Fig. 2 shows a front view of the TAB head assembly 14 of Fig. 1 removed from the print cartridge 10 and prior to windows 22 and 24 in the TAB head assembly 14 being filled with an encapsulant. TAB head assembly 14 has affixed to the back of the flexible circuit 18 a silicon substrate 28 (not shown) containing a plurality of individually energizable thin film resistors. Each resistor is located generally behind a single orifice 17 and acts as an ohmic heater when selectively energized by one or more pulses applied sequentially or simultaneously to one or more of the contact pads 20. The orifices 17 and conductive traces 36 may be of any size, number, and pattern, and the various figures are designed to show simply and clearly the features of this embodiment. The relative dimensions of the various features have been greatly adjusted for the sake of clarity. The orifice 17 pattern on the flexible circuit 18 shown in Fig. 2 may be formed by a masking process in combination with a laser or other etching means in a step-and-repeat process, which would be readily understood by one of ordinary skilled in the art after reading this disclosure. Fig. 14, to be described in detail later, provides additional details of this process. Further details regarding TAB head assembly 14 and flexible circuit 18 are provided below. Fig. 3 is a perspective view of a simplified schematic of the inkjet print cartridge of Fig. 1for illustrative purposes. Fig. 4 is a perspective view of the front surface of the Tape Automated Bonding (TAB) printhead assembly (hereinafter "TAB head assembly") removed from the simplified schematic print cartridge of Fig. 3. Fig. 5 shows the back surface of the TAB head assembly 14 of Fig. 4 showing the silicon die or substrate 28 mounted to the back of the flexible circuit 18 and also showing one edge of the barrier layer 30 formed on the substrate 28 containing ink channels and vaporization chambers. Fig. 7 shows greater detail of this barrier layer 30 and will be discussed later. Shown along the edge of the barrier layer 30 are the entrances to the ink channels 32 which receive ink from the ink reservoir 12. The conductive traces 36 formed on the back of the flexible circuit 18 terminate in contact pads 20 ( shown in Fig. 4) on the opposite side of the flexible circuit 18. The windows 22 and 24 allow access to the ends of the conductive traces 36 and the substrate electrodes 40 (shown in Fig. 6) from the other side of the flexible circuit 18 to facilitate bonding. Fig. 6 shows a side view cross-section taken along line A-A in Fig. 5 illustrating the connection of the ends of the conductive traces 36 to the electrodes 40 formed on the substrate 28. As seen in Fig. 6, a portion 42 of the barrier layer 30 is used to insulate the ends of the conductive traces 36 from the substrate 28. Also shown in Fig. 6 is a side view of the flexible circuit 18, the barrier layer 30, the windows 22 and 24, and the entrances of the various ink channels 32. Droplets of ink 46 are shown being ejected from orifice holes associated with each of the ink channels 32. Fig. 7 shows the print cartridge 10 of Fig. 1 with the TAB head assembly 14 removed to reveal the headland pattern 50 used in providing a seal between the TAB head assembly 14 and the printhead body. Fig. 8 shows the headland area in enlarged perspective view. Fig. 9 shows the headland area in an enlarged top plan view. The headland characteristics are exaggerated for clarity. Shown in Figs. 8 and 9 is a central slot 52 in the print cartridge 10 for allowing ink from the ink reservoir 12 to flow to the back surface of the TAB head assembly 14. The headland pattern 50 formed on the print cartridge 10 is configured so that a bead of epoxy adhesive (not shown) dispensed on the inner raised walls 54 and across the wall openings 55 and 56 (so as to circumscribe the substrate when the TAB head assembly 14 is in place) will form an ink seal between the body of the print cartridge 10 and the back of the TAB head assembly 14 when the TAB head assembly 14 is pressed into place against the headland pattern 50. Other adhesives which may be used include hot-melt, silicone, UV curable adhesive, and mixtures thereof. Further, a patterned adhesive film may be positioned on the headland, as opposed to dispensing a bead of adhesive. When the TAB head assembly 14 of Fig. 5 is properly positioned and pressed down on the headland pattern 50 in Fig. 8 after the adhesive (not shown) is dispensed, the two short ends of the substrate 28 will be supported by the surface portions 57 and 58 within the wall openings 55 and 56. Additional details regarding adhesive 90 are shown in Fig. 13. The configuration of the headland pattern 50 is such that, when the substrate 28 is supported by the surface portions 57 and 58, the back surface of the flexible circuit 18 will be slightly above the top of the raised walls 54 and approximately flush with the flat top surface 59 of the print cartridge 10. As the TAB head assembly 14 is pressed down onto the headland 50, the adhesive is squished down. From the top of the inner raised walls 54, the adhesive overspills into the gutter between the inner raised walls 54 and the outer raised wall 60 and overspills somewhat toward the slot 52. From the wall openings 55 and 56, the adhesive squishes inwardly in the direction of slot 52 and squishes outwardly toward the outer raised wall 60, which blocks further outward displacement of the adhesive. The outward displacement of the adhesive not only serves as an ink seal, but encapsulates the conductive traces in the vicinity of the headland 50 from underneath to protect the traces from ink. Fig. 10 shows a portion of the completed print cartridge 10 of Fig. 3 illustrating, by cross-hatching, the location of the underlying adhesive 90 (not shown) which forms the seal between the TAB head assembly 14 and the body of the print cartridge 10. In Fig. 10 the adhesive is located generally between the dashed lines surrounding the array of orifices 17, where the outer dashed line 62 is slightly within the boundaries of the outer raised wall 60 in Fig. 7, and the inner dashed line 64 is slightly within the boundaries of the inner raised walls 54 in Fig. 7. The adhesive is also shown being squished through the wall openings 55 and 56 (Fig. 7) to encapsulate the traces leading to electrodes on the substrate. A cross-section of this seal taken along line B-B in Fig. 10 is also shown in Fig. 13, to be discussed later. This seal formed by the adhesive 90 circumscribing the substrate 28 allows ink to flow from slot 52 and around the sides of the substrate to the vaporization chambers formed in the barrier layer 30, but will prevent ink from seeping out from under the TAB head assembly 14. Thus, this adhesive seal 90 provides a strong mechanical coupling of the TAB head assembly 14 to the print cartridge 10, provides a fluidic seal, and provides trace encapsulation. The adhesive seal is also easier to cure than prior art seals, and it is much easier to detect leaks between the print cartridge body and the printhead, since the sealant line is readily observable. Further details on adhesive seal 90 are shown in Fig. 13. Fig. 11 is a front perspective view of the silicon substrate 28 which is affixed to the back of the flexible circuit 18 in Fig. 5 to form the TAB head assembly 14. Silicon substrate 28 has formed on it, using conventional photolithographic techniques, two rows or colums of thin film resistors 70, shown in Fig. 11 exposed through the vaporization chambers 72 formed in the barrier layer 30. In one embodiment, the substrate 28 is approximately one-half inch long and contains 300 heater resistors 70, thus enabling a resolution of 600 dots per inch. Heater resistors 70 may instead be any other type of ink ejection element, such as a piezoelectric pump-type element or any other conventional element. Thus, element 70 in all the various figures may be considered to be piezoelectric elements in an alternative embodiment without affecting the operation of the printhead. Also formed on the substrate 28 are electrodes 74 for connection to the conductive traces 36 (shown by dashed lines) formed on the back of the flexible circuit 18. A demultiplexer 78, shown by a dashed outline in Fig. 11, is also formed on the substrate 28 for demultiplexing the incoming multiplexed signals applied to the electrodes 74 and distributing the signals to the various thin film resistors 70. The demultiplexer 78 enables the use of much fewer electrodes 74 than thin film resistors 70. Having fewer electrodes allows all connections to the substrate to be made from the short end portions of the substrate, as shown in Fig. 4, so that these connections will not interfere with the ink flow around the long sides of the substrate. The demultiplexer 78 may be any decoder for decoding encoded signals applied to the electrodes 74. The demultiplexer has input leads (not shown for simplicity) connected to the electrodes 74 and has output leads (not shown) connected to the various resistors 70. The demultiplexer 78 circuity is discussed in further detail below. Also formed on the surface of the substrate 28 using conventional photolithographic techniques is the barrier layer 30, which may be a layer of photoresist or some other polymer, in which is formed the vaporization chambers 72 and ink channels 80. A portion 42 of the barrier layer 30 insulates the conductive traces 36 from the underlying substrate 28, as previously discussed with respect to Fig. 4. In order to adhesively affix the top surface of the barrier layer 30 to the back surface of the flexible circuit 18 shown in Fig. 5, a thin adhesive layer 84 (not shown), such as an uncured layer of poly-isoprene photoresist, is applied to the top surface of the barrier layer 30. A separate adhesive layer may not be necessary if the top of the barrier layer 30 can be otherwise made adhesive. The resulting substrate structure is then positioned with respect to the back surface of the flexible circuit 18 so as to align the resistors 70 with the orifices formed in the flexible circuit 18. This alignment step also inherently aligns the electrodes 74 with the ends of the conductive traces 36. The traces 36 are then bonded to the electrodes 74. This alignment and bonding process is described in more detail later with respect to Fig. 14. The aligned and bonded substrate/flexible circuit structure is then heated while applying pressure to cure the adhesive layer 84 and firmly affix the substrate structure to the back surface of the flexible circuit 18. Fig. 12 is an enlarged view of a single vaporization chamber 72, thin film resistor 70, and frustum shaped orifice 17 after the substrate structure of Fig. 11 is secured to the back of the flexible circuit 18 via the thin adhesive layer 84. A side edge of the substrate 28 is shown as edge 86. In operation, ink flows from the ink reservoir 12 around the side edge 86 of the substrate 28, and into the ink channel 80 and associated vaporization chamber 72, as shown by the arrow 88. Upon energization of the thin film resistor 70, a thin layer of the adjacent ink is superheated, causing explosive vaporization and, consequently, causing a droplet of ink to be ejected through the orifice 17. The vaporization chamber 72 is then refilled by capillary action. In a preferred embodiment, the barrier layer 30 is approximately 25 µm (1 mils) thick, the substrate 28 is approximately 500 µm (20 mils) thick, and the flexible circuit 18 is approximately 50 µm (2 mils) thick. Shown in Fig. 13 is a side elevational view cross-section taken along line B-B in Fig. 10 showing a portion of the adhesive seal 90, applied to the inner raised wall 54 and wall openings 55, 56, surrounding the substrate 28 and showing the substrate 28 being adhesively secured to a central portion of the flexible circuit 18 by the thin adhesive layer 84 on the top surface of the barrier layer 30 containing the ink channels and vaporization chambers 92 and 94. A portion of the plastic body of the printhead cartridge 10, including raised walls 54 shown in Figs. 7 and 8, is also shown. Fig. 13 also illustrates how ink 88 from the ink reservoir 12 flows through the central slot 52 formed in the print cartridge 10 and flows around the edges 86 of the substrate 28 through ink channels 80 into the vaporization chambers 92 and 94. Thin film resistors 96 and 98 are shown within the vaporization chambers 92 and 94, respectively. When the resistors 96 and 98 are energized, the ink within the vaporization chambers 92 and 94 is ejected, as illustrated by the emitted drops of ink 101 and 102. The edge feed feature, where ink flows around the edges 86 of the substrate 28 and directly into ink channels 80, has a number of advantages over previous center feed printhead designs which form an elongated central hole or slot running lengthwise in the substrate to allow ink to flow into a central manifold and ultimately to the entrances of ink channels. One advantage is that the substrate or die 28 width can be made narrower, due to the absence of the elongated central hole or slot in the substrate . Not only can the substrate be made narrower, but the length of the edge feed substrate can be shorter, for the same number of nozzles, than the center feed substrate due to the substrate structure now being less prone to cracking or breaking without the central ink feed hole. This shortening of the substrate 28 enables a shorter headland 50 in Fig. 8 and, hence, a shorter print cartridge snout. This is important when the print cartridge 10 is installed in a printer which uses one or more pinch rollers below the snout's transport path across the paper to press the paper against the rotatable platen and which also uses one or more rollers (also called star wheels) above the transport path to maintain the paper contact around the platen. With a shorter print cartridge snout, the star wheels can be located closer to the pinch rollers to ensure better paper/roller contact along the transport path of the print cartridge snout. Additionally, by making the substrate smaller, more substrates can be formed per wafer, thus lowering the material cost per substrate. Other advantages of the edge feed feature are that manufacturing time is saved by not having to etch a slot in the substrate, and the substrate is less prone to breakage during handling. Further, the substrate is able to dissipate more heat, since the ink flowing across the back of the substrate and around the edges of the substrate acts to draw heat away from the back of the substrate. There are also a number of performance advantages to the edge feed design. Be eliminating the manifold as well as the slot in the substrate, the ink is able to flow more rapidly into the vaporization chambers, since there is less restriction on the ink flow. This more rapid ink flow improves the frequency response of the printhead, allowing higher printing rates from a given number of orifices. Further, the more rapid ink flow reduces crosstalk between nearby vaporization chambers caused by variations in ink flow as the heater elements in the vaporization chambers are fired. In another embodiment, the ink reservoir contains two separate ink sources, each containing a different color of ink. In this alternative embodiment, the central slot 52 in Fig. 13 is bisected, as shown by the dashed line 103, so that each side of the central slot 52 communicates with a separate ink source. Therefore, the left linear array of vaporization chambers can be made to eject one color of ink, while the right linear array of vaporization chambers can be made to eject a different color of ink. This concept can even be used to create a four color printhead, where a different ink reservoir feeds ink to ink channels along each of the four sides of the substrate. Thus, instead of the two-edge feed design discussed above, a four-edge design would be used, preferably using a square substrate for symmetry. Fig. 14 illustrates one method for forming the preferred embodiment of the TAB head assembly 14. The starting material is a Kapton or Upilex type polymer tape 104, although the tape 104 can be any suitable polymer film which is acceptable for use in the below-described procedure. Some such films may comprise teflon, polyamide, polymethylmethacrylate, polycarbonate, polyester, polyamide polyethylene-terephthalate or mixtures thereof. The tape 104 is typically provided in long strips on a reel 105. Sprocket holes 106 along the sides of the tape 104 are used to accurately and securely transport the tape 104. Alternately, the sprocket holes 106 may be omitted and the tape may be transported with other types of fixtures. In the preferred embodiment, the tape 104 is already provided with conductive copper traces 36, such as shown in Figs. 2, 4 and 5, formed thereon using conventional metal deposition and photolithographic processes. The particular pattern of conductive traces depends on the manner in which it is desired to distribute electrical signals to the electrodes formed on silicon dies, which are subsequently mounted on the tape 104. In the preferred process, the tape 104 is transported to a laser processing chamber and laser-ablated in a pattern defined by one or more masks 108 using laser radiation 110, such as that generated by an Excimer laser 112 of the F 2 , ArF, KrCl, KrF, or XeCl type. The masked laser radiation is designated by arrows 114. In a preferred embodiment, such masks 108 define all of the ablated features for an extended area of the tape 104, for example encompassing multiple orifices in the case of an orifice pattern mask 108, and multiple vaporization chambers in the case of a vaporization chamber pattern mask 108. Alternatively, patterns such as the orifice pattern, the vaporization chamber pattern, or other patterns may be placed side by side on a common mask substrate which is substantially larger than the laser beam. Then such patterns may be moved sequentially into the beam. The masking material used in such masks will preferably be highly reflecting at the laser wavelength, consisting of, for example, a multilayer dielectric or a metal such as aluminum. The orifice pattern defined by the one or more masks 108 may be that generally shown in Fig. 21. Multiple masks 108 may be used to form a stepped orifice taper as shown in Fig. 12. In one embodiment, a separate mask 108 defines the pattern of windows 22 and 24 shown in Figs. 1 and 2; however, in the preferred embodiment, the windows 22 and 24 are formed using conventional photolithographic methods prior to the tape 104 being subjected to the processes shown in Fig. 14. In an alternative embodiment of a nozzle member, where the nozzle member also includes vaporization chambers, one or more masks 108 would be used to form the orifices and another mask 108 and laser energy level (and/or number of laser shots) would be used to define the vaporization chambers, ink channels, and manifolds which are formed through a portion of the thickness of the tape 104. The laser system for this process generally includes beam delivery optics, alignment optics, a high precision and high speed mask shuttle system, and a processing chamber including a mechanism for handling and positioning the tape 104. In the preferred embodiment, the laser system uses a projection mask configuration wherein a precision lens 115 interposed between the mask 108 and the tape 104 projects the Excimer laser light onto the tape 104 in the image of the pattern defined on the mask 108. The masked laser radiation exiting from lens 115 is represented by arrows 116. Such a projection mask configuration is advantageous for high precision orifice dimensions, because the mask is physically remote from the nozzle member. Soot is naturally formed and ejected in the ablation process, traveling distances of about one centimeter from the nozzle member being ablated. If the mask were in contact with the nozzle member, or in proximity to it, soot buildup on the mask would tend to distort ablated features and reduce their dimensional accuracy. In the preferred embodiment, the projection lens is more than two centimeters from the nozzle member being ablated, thereby avoiding the buildup of any soot on it or on the mask. Ablation is well known to produce features with tapered walls, tapered so that the diameter of an orifice is larger at the surface onto which the laser is incident, and smaller at the exit surface. The taper angle varies significantly with variations in the optical energy density incident on the nozzle member for energy densities less than about two joules per square centimeter. If the energy density were uncontrolled, the orifices produced would vary significantly in taper angle, resulting in substantial variations in exit orifice diameter. Such variations would produce deleterious variations in ejected ink drop volume and velocity, reducing print quality. In the preferred embodiment, the optical energy of the ablating laser beam is precisely monitored and controlled to achieve a consistent taper angle, and thereby a reproducible exit diameter. In addition to the print quality benefits resulting from the constant orifice exit diameter, a taper is beneficial to the operation of the orifices, since the taper acts to increase the discharge speed and provide a more focused ejection of ink, as well as provide other advantages. The taper may be in the range of 5 to 15 degrees relative to the axis of the orifice. The preferred embodiment process described herein allows rapid and precise fabrication without a need to rock the laser beam relative to the nozzle member. It produces accurate exit diameters even though the laser beam is incident on the entrance surface rather than the exit surface of the nozzle member. After the step of laser-ablation, the polymer tape 104 is stepped, and the process is repeated. This is referred to as a step-and-repeat process. The total processing time required for forming a single pattern on the tape 104 may be on the order of a few seconds. As mentioned above, a single mask pattern may encompass an extended group of ablated features to reduce the processing time per nozzle member. Laser ablation processes have distinct advantages over other forms of laser drilling for the formation of precision orifices, vaporization chambers, and ink channels. In laser ablation, short pulses of intense ultraviolet light are absorbed in a thin surface layer of material within about 1 micrometer or less of the surface. Preferred pulse energies are greater than about 100 millijoules per square centimeter and pulse durations are shorter than about 1 microsecond. Under these conditions, the intense ultraviolet light photodissociates the chemical bonds in the material. Furthermore, the absorbed ultraviolet energy is concentrated in such a small volume of material that it rapidly heats the dissociated fragments and ejects them away from the surface of the material. Because these processes occur so quickly, there is no time for heat to propagate to the surrounding material. As a result, the surrounding region is not melted or otherwise damaged, and the perimeter of ablated features can replicate the shape of the incident optical beam with precision on the scale of about one micrometer. In addition, laser ablation can also form chambers with substantially flat bottom surfaces which form a plane recessed into the layer, provided the optical energy density is constant across the region being ablated. The depth of such chambers is determined by the number of laser shots, and the power density of each. Laser-ablation processes also have numerous advantages as compared to conventional lithographic electroforming processes for forming nozzle members for inkjet printheads. For example, laser-ablation processes generally are less expensive and simpler than conventional lithographic electroforming processes. In addition, by using laser-ablations processes, polymer nozzle members can be fabricated in substantially larger sizes (i.e., having greater surface areas) and with nozzle geometries that are not practical with conventional electroforming processes. In particular, unique nozzle shapes can be produced by controlling exposure intensity or making multiple exposures with a laser beam being reoriented between each exposure. Precise nozzle geometries can be formed without process controls as strict as those required for electroforming processes. Another advantage of forming nozzle members by laser-ablating a polymer material is that the orifices or nozzles can be easily fabricated with various ratios of nozzle length (L) to nozzle diameter (D). In the preferred embodiment, the L/D ratio exceeds unity. One advantage of extending a nozzle's length relative to its diameter is that orifice-resistor positioning in a vaporization chamber becomes less critical. In use, laser-ablated polymer nozzle members for inkjet printers have characteristics that are superior to conventional electroformed orifice plates. For example, laser-ablated polymer nozzle members are highly resistant to corrosion by water-based printing inks and are generally hydrophobic. Further, laser-ablated polymer nozzle members have a relatively low elastic modulus, so built-in stress between the nozzle member and an underlying substrate or barrier layer has less of a tendency to cause nozzle member-to-barrier layer delamination. Still further, laser-ablated polymer nozzle members can be readily fixed to, or formed with, a polymer substrate. Although an Excimer laser is used in the preferred embodiments, other ultraviolet light sources with substantially the same optical wavelength and energy density may be used to accomplish the ablation process. Preferably, the wavelength of such an ultraviolet light source will lie in the 150 nm to 400 nm range to allow high absorption in the tape to be ablated. Furthermore, the energy density should be greater than about 100 millijoules per square centimeter with a pulse length shorter than about 1 microsecond to achieve rapid ejection of ablated material with essentially no heating of the surrounding remaining material. As will be understood by those of ordinary skill in the art, numerous other processes for forming a pattern on the tape 104 may also be used. Other such processes include chemical etching, stamping, reactive ion etching, ion beam milling, and molding or casting on a photodefined pattern. A next step in the process is a cleaning step wherein the laser ablated portion of the tape 104 is positioned under a cleaning station 117. At the cleaning station 117, debris from the laser ablation is removed according to standard industry practice. The tape 104 is then stepped to the next station, which is an optical alignment station 118 incorporated in a conventional automatic TAB bonder, such as an inner lead bonder commercially available from Shinkawa Corporation, model number IL-20. The bonder is preprogrammed with an alignment (target) pattern on the nozzle member, created in the same manner and/or step as used to created the orifices, and a target pattern on the substrate, created in the same manner and/or step used to create the resistors. In the preferred embodiment, the nozzle member material is semi-transparent so that the target pattern on the substrate may be viewed through the nozzle member. The bonder then automatically positions the silicon dies 120 with respect to the nozzle members so as to align the two target patterns. Such an alignment feature exists in the Shinkawa TAB bonder. This automatic alignment of the nozzle member target pattern with the substrate target pattern not only precisely aligns the orifices with the resistors but also inherently aligns the electrodes on the dies 120 with the ends of the conductive traces formed in the tape 104, since the traces and the orifices are aligned in the tape 104, and the substrate electrodes and the heating resistors are aligned on the substrate. Therefore, all patterns on the tape 104 and on the silicon dies 120 will be aligned with respect to one another once the two target patterns are aligned. Thus, the alignment of the silicon dies 120 with respect to the tape 104 is performed automatically using only commercially available equipment. By integrating the conductive traces with the nozzle member, such an alignment feature is possible. Such integration not only reduces the assembly cost of the printhead but reduces the printhead material cost as well. The automatic TAB bonder then uses a gang bonding method to press the ends of the conductive traces down onto the associated substrate electrodes through the windows formed in the tape 104. The bonder then applies heat, such as by using thermocompression bonding, to weld the ends of the traces to the associated electrodes. A schematic side view of one embodiment of the resulting structure is shown in Fig. 6. Other types of bonding can also be used, such as ultrasonic bonding, conductive epoxy, solder paste, or other well-known means. The tape 104 is then stepped to a heat and pressure station 122. As previously discussed with respect to Figs. 9 and 10, an adhesive layer 84 exists on the top surface of the barrier layer 30 formed on the silicon substrate. After the above-described bonding step, the silicon dies 120 are then pressed down against the tape 104, and heat is applied to cure the adhesive layer 84 and physically bond the dies 120 to the tape 104. Thereafter the tape 104 steps and is optionally taken up on the take-up reel 124. The tape 104 may then later be cut to separate the individual TAB head assemblies from one another. The resulting TAB head assembly is then positioned on the print cartridge 10, and the previously described adhesive seal 90 is formed to firmly secure the nozzle member to the print cartridge, provide an ink-proof seal around the substrate between the nozzle member and the ink reservoir, and encapsulate the traces in the vicinity of the headland so as to isolate the traces from the ink. Peripheral points on the flexible TAB head assembly are then secured to the plastic print cartridge 10 by a conventional melt-through type bonding process to cause the polymer flexible circuit 18 to remain relatively flush with the surface of the print cartridge 10, as shown in Fig. 1. To increase resolution and print quality, the printhead nozzles must be placed closer together. This requires that both heater resistors and the associated orifices be placed closer together. To increase printer throughput, the firing frequency of the resistors must be increased. When firing the resistors at high frequencies, i.e., greater than 8 kHz, conventional ink channel barrier designs either do not allow the vaporization chambers to adequately refill or allow extreme blowback or catastrophic overshoot and puddling on the exterior of the nozzle member. Also, the closer spacing of the resistors created space problems and restricted possible barrier solutions due to manufacturing concerns. The TAB head assembly architecture shown schematically in Fig. 15 is advantageous when a very high density of dots is required to be printed (e.g., 600 dpi). However, at such high dot densities and at high firing rates (e.g., 12 kHz) cross-talk between neighboring vaporization chambers becomes a serious problem. During the firing of a single nozzle, bubble growth initiated by a resistor displaces ink outward in the form of a drop. At the same time, ink is also displaced back into the ink channel. The quantity of ink so displaced is often described as "blowback volume." The ratio of ejected volume to blowback volume is an indication of ejection efficiency, which may be on the order of about 1:1 for the TAB head assembly 14 of Fig. 11. In addition to representing an inertial impediment to refill, blowback volume causes displacements in the menisci of neighboring nozzles. When these neighboring nozzles are fired, such displacements of their menisci cause deviations in drop volume from the nominally equilibrated situation resulting in nonuniform dots being printed. A second embodiment of the present invention shown in the TAB head assembly architecture of Fig. 15 is designed to minimize such cross-talk effects. Elements in Figs. 9 and 13 which are labelled with the same numbers are similar in structure and operation. The significant differences between the structures of Figs. 9 and 13 include the barrier layer pattern and the increased density of the vaporization chambers. In Fig. 15, vaporization chambers 130 and ink channels 132 are shown formed in barrier layer 134. Ink channels 132 provide an ink path between the source of ink and the vaporization chambers 130. The flow of ink into the ink channels 132 and into the vaporization chambers 130 is generally similar to that described with respect to Figs. 10 and 11, whereby ink flows around the long side edges 86 of the substrate 28 and into the ink channels 132. The vaporization chambers 130 and ink channels 132 may be formed in the barrier layer 134 using conventional photolithographic techniques. The barrier layer 134 may be similar to the barrier layer 30 in Figs. 5 and 10 and may comprise any high quality photoresist, such as Vacrel or Parad. Thin film resistors 70 in Fig. 15 are similar to those described with respect to Fig. 11 and are formed on the surface of the silicon substrate 28. As previously mentioned with respect to Fig. 11, resistors 70 may instead be well known piezoelectric pump-type ink ejection elements or any other conventional ink ejection elements where vaporization of ink is not necessarily occurring in chambers 130. If a piezoelectric ink ejection element is used, such chambers 130 may be broadly referred to as ink ejection chambers. To form a completed TAB head assembly, the substrate structure of Fig. 15 is affixed to the nozzle member 136 of Fig. 17 in the manner shown in Fig. 19 which is described in greater detail later. The resulting TAB head assembly is very similar to the TAB head assembly 14 in Figs. 2, 4, 5, and 6. Generally, the particular architecture of the ink channels 132 in Fig. 15 provides advantages over the architecture shown in Fig. 11. Further details and other advantages of the TAB head assembly architecture will be described with respect to Fig. 16, which is a magnified top plan view of the portion of Fig. 15 shown within dashed outline 150. The architecture of the ink channels 132 in Fig. 16 has the following differences from the architecture shown in Fig. 11. The relatively narrow constriction points or pinch point gaps 145 created by the pinch points 146 in the ink channels 132 provide viscous damping during refill of the vaporization chambers 130 after firing. This viscous damping helps minimize cross-talk between neighboring vaporization chambers 130. The pinch points 146 also help control ink blow-back and bubble collapse after firing to improve the uniformity of ink drop ejection. The addition of "peninsulas" 149 extending from the barrier body out to the edge of the substrate provided fluidic isolation of the vaporization chambers 130 from each other to prevent cross-talk and allowed support of the nozzle member 136 at the edge of the substrate. The enlarged areas or reefs 148 formed on the ends of the peninsulas 149 near the entrance to each ink channel 132 increase the nozzle member 136 support area at the edges of the barrier layer 134 so that the nozzle member 136 lies relatively flat on barrier layer 134 when affixed to barrier layer 134. Adjacent reefs 148 also act to constrict the entrance of the ink channels 132 so as to help filter large foreign particles. The pitch D of the vaporization chambers 130 shown in Fig. 16 provides for 600 dots per inch (dpi) printing using two rows of vaporization chambers 130 as shown in Fig. 22 and to be described below. Within a single row or column of vaporization chambers 130, a small offset E (shown in Fig. 21) is provided between vaporization chambers 130. This small offset E allows adjacent resistors 70 to be fired at slightly different times when the TAB head assembly is scanning across the recording medium to further minimize cross-talk effects between adjacent vaporization chambers 130. There are twenty two different offset locations, one for each address line. Further details are provided below with respect to Figs. 22-24. The definition of the dimensions of the various elements shown in Figs. 16, 17, 20 and 21 are provided in Table I. DEFINITION OF INK CHAMBER DEFINITIONS Dimension Definition A Substrate Thickness B Barrier Thickness C Nozzle Member Thickness D Orifice/Resistor Pitch E Resistor/Orifice Offset F Resistor Length G Resistor Width H Nozzle Entrance Diameter I Nozzle Exit Diameter J Chamber Length K Chamber Width L Chamber Gap M Channel Length N Channel Width O Barrier Width P Reef Diameter Q Cavity Length R Cavity Width S Cavity Depth T Cavity Location U Shelf Length The dimensions of the various elements formed in the barrier layer 134 shown in Fig. 16 are given in Table II below. Also shown in Table II is the orifice diameter I shown in Fig. 21. INK CHAMBER DIMENSIONS IN MICRONS Dimension Minimum Nominal Maximum E 1 1.73 2 F 30 35 40 G 30 35 40 I 23 26 34 J 45 50 55 K 45 50 55 L 0 8 10 M 20 35 50 N 15 30 55 O 10 25 40 P 30 40 50 U 75 155-190 270 An alternative embodiment of the TAB head assembly architecture will be described with respect to Fig. 17, which is a modified top plan view of the portion of the ink channels 132 shown in Fig. 16. The architecture of the ink channels 132 in Fig. 17 has the following differences from the architecture shown in Fig. 16. As the shelf length U decreases in length, the nozzle frequency increases. In the embodiment shown in FIG. 17 the shelf length is reduced. As a consequence, the fluid impedance is reduced, resulting in a more uniform frequency response for all nozzles. Edge feed permits use of a second saw cut partially through the wafer to allowing a shorter shelf length, U, to be formed. Alternatively, precise etching may be used. This shelf length is shorter than that of other commercially available printer cartridges and permits firing at much higher frequencies. The frequency limit of a thermal inkjet pen is limited by resistance in the flow of ink to the nozzle. However, some resistance in ink flow is necessary to damp meniscus oscillation, but too much resistance limits the upper frequency at which a print cartridge can operate. Ink flow resistance (impedance) is intentionally controlled by the pinch point gap 145 gap adjacent the resistor with a well-defined length and width. The distance of the resistor 70 from the substrate edge varies with the firing patterns of the TAB head assembly. An additional component to the fluid impedance is the entrance to the firing chamber. The entrance comprises a thin region between the nozzle member 16 and the substrate 28 and its height is essentially a function of the thickness of the barrier layer 134. This region has high fluid impedance, since its height is small. The refill ink channel was reduced to a minimum shelf length, to allow the fastest possible refill, and "pinched" to the minimum width, to create the best damping. The short shelf length reduced the mass of the moving ink during ink chamber refill, thus reducing the sensitivity to damping features. This allowed wider processing tolerances while at the same time maintaining controlled damping. The principal difference is that the peninsulas 149 have been shortened and the reefs 148 have been removed. In addition, every other peninsula 149 has been shortened further to the pinch points 146. Also as shown in Fig. 17 the shape of the pinch points 146 have been modified. The pinch points 146 can be on one or both sides of the ink channel 130 with various tip configurations. This architecture allows greater than 8 kHz ink refill speed while providing sufficient overshoot damping. The shorter ink channel allows barrier processing of narrow ink channel widths that could not previously be accomplished. The dimensions of the various elements formed in the barrier layer 134 shown in Fig. 16 are identified in Table III below. Fig. 18 shows the effect of the offset from resistor to resistor on the shape long and shortened peninsulas due to the pinch points 146. INK CHAMBER DIMENSIONS IN MICRONS Dimension Minimum Nominal Maximum E 1 1.73 2 F 30 35 40 G 30 35 40 I 20 28 40 J 45 51 75 K 45 51 55 L 0 8 10 M 20 25 50 N 15 30 55 O 10 25 40 R B 5 15 25 R P 5 12.5 20 R T 0 5 20 U 0 90-130 270 Fig. 19 is a preferred nozzle member 136 in the form of a flexible polymer tape 140, which, when affixed to the substrate structure shown in Fig. 15, forms a TAB head assembly similar to that shown in Figs. 4 and 5. Elements in Figs. 5 and 15 which are labelled with the same numbers are similar in structure and operation. The flexible polymer nozzle member 136 in Fig. 19 primarily differs from the flexible circuit 18 in Fig. 5 by the increased density of laser-ablated nozzles 17 in the nozzle member 136 (to produce a higher printing resolution) and by the inclusion of cavities 142 which are laser-ablated through a partial thickness of the nozzle member 136. A separate mask 108 in the process shown in Fig. 14 may be used to define the pattern of cavities 142 in the nozzle member 136. A second laser source may be used to output the proper energy and pulse length to laser ablate cavities 142 through only a partial thickness of the nozzle member 136. Conductors 36 on flexible circuit 140 provide an electrical path between the contact pads 20 (Fig. 4) and the electrodes 74 on the substrate 28 (Fig. 15). Conductors 36 are formed directly on flexible circuit 140 as previously described with respect to Fig. 5. Fig. 20 is a magnified, partially cut away view in perspective of the portion of the nozzle member 136 shown in the dashed outline 154 of Fig. 19 after the nozzle member 136 has been properly positioned over the substrate structure of Fig. 20 to form a TAB head assembly 158 similar to the TAB head assembly 14 in Fig. 5. As shown in Fig. 20, the nozzles 17 are aligned over the vaporization chambers 130, and the cavities 142 are aligned over the ink channels 132. Fig. 20 also illustrates the ink flow 160 from an ink reservoir generally situated behind the substrate 28 as the ink flows over an edge 86 of the substrate 28 and enters cavities 142 and ink channels 132. Preferred dimensions A, B, and C in Fig. 20 are provided in Table IV below, where dimension C is the thickness of the nozzle member 136, dimension B is the thickness of the barrier layer 134, and dimension A is the thickness of the substrate 28. Fig. 21 is a top plan view of the portion of the TAB head assembly 158 shown in Fig. 20, where the vaporization chambers 130 and ink channels 132 can be seen through the nozzle member 136. The various dimensions of the cavities 142, the nozzles 17, and the separations between the various elements are identified in Table IV below. In Fig. 21, dimension H is the entrance diameter of the nozzles 17, while dimension I is the exit diameter of the nozzles 17. The other dimensions are self-explanatory. The cavities 142 minimize the viscous damping of ink during refill as the ink flows into the ink channels 132. This helps compensate for the increased viscous damping provided by the pinch points 146, reefs 148, and increased length of the ink channels 132 along the substrate shelf. Minimizing viscous damping helps increase the maximum firing rate of the resistors 70, since ink can enter into the ink channels 132 more quickly after firing. Thus, the damping function is provided primarily by the pinch points rather than the viscous damping which is different individual vaporization chambers due to the different shelf lengths for individual vaporization chambers caused by the offsets, E, between the vaporization chambers. SUBSTRATE, INK CHANNEL AND NOZZLE MEMBER DIMENSIONS IN MICRONS Dimension Minimum Nominal Maximum A 600 625 650 B 19 25 32 C 25 50 75 D 84.7 H 40 55 70 Q 80 120 200 R 20 35 50 S 0 25 50 T 50 100 150 Tables I, II and III above lists the nominal values of the various dimensions A-U of the TAB head assembly structure of Figs. 13-18 as well as their preferred ranges. It should be understood that the preferred ranges and nominal values of an actual embodiment will depend upon the intended operating environment of the TAB head assembly, including the type of ink used, the operating temperature, the printing speed, and the dot density. Referring to Fig. 22, as discussed above, the orifices 17 in the nozzle member 16 of the TAB head assembly are generally arranged in two major columns of orifices 17 as shown in Fig. 22. For clarity of understanding, the orifices 17 are conventionally assigned a number as shown, starting at the top rght as the TAB head assembly as viewed from the external surface of the nozzle member 16 and ending in the lower left, thereby resulting in the odd numbers being arranged in one column and even numbers being arranged in the second column. Of course, other numbering conventions may be followed, but the description of the firing order of the orifices 17 associated with this numbering system has advantages. The orifices/resistors in each column are spaced 1/300 of an inch apart in the long direction of the nozzle member. The orifices and resistors in one column are offset from the orifice/resistors in the other column in the long direction of the nozzle member by 1/600 of an inch, thus, providing 600 dots per inch (dpi) printing. In one embodiment the orifices 17, while aligned in two major columns as described, are further arranged in an offset pattern within each column to match the offset heater resistors 70 disposed in the substrate 28 as illustrated in Figs. 22 and 23. Within a single row or column of resistors, a small offset E (shown in Fig. 21) is provided between resistors. This small offset E allows adjacent resistors 70 to be fired at slightly different times when the TAB head assembly is scanning across the recording medium to further minimize cross-talk effects between adjacent vaporization chambers 130. Thus, although the resistors are fired at twent two different times, the offset allows the ejected ink drops from different nozzles to be placed in the same horizontal position on the print media. The resistors 70 are coupled to electrical drive circuitry (not shown in Fig. 22) and are organized in groups of fourteen primitives which consist of four primitives of twenty resistors (P1, P2, P13 and P14) and ten primitives of twenty two resistors for a total of 300 resistors. The fourteen resistor primitives (and associated orifices) are shown in Fig. 22. Fig. 23 shows the offset of the resistors and the ink channels 132, peninsulas 149, pinch point gaps 145 and pinch points 146 of primitive P5. The spatial location of the 300 resistor/orifices with respect to the centroid of the substrate is provided in Fig. 24. The TAB head assembly orifices 17 are positioned directly over the heater resistors 70 and are positioned relative to its most adjacent neighbor in accordance with Fig. 16. This placement and firing sequence provides a more uniform frequency response for all resistors 70 and reduces the crosstalk between adjacent vaporization chambers. As described, the firing heater resistors 70 of the preferred embodiment are organized as fourteen primitive groups of twenty or twenty-two resistors. Referring now to the electrical schematic of Fig. 25 and the enlargement of a portion of Fig. 25 shown in Fig. 26, it can be seen that each resistor (numbered 1 through 300 and corresponding to the orifices 17 of Fig. 22) is controlled by its own FET drive transistor, which shares its control input Address Select (A1-A22) with thirteen other resistors. Each resistor is tied to nineteen or twenty-one other resistors by a common node Primitive Select (PS1-PS14). Consequently, firing a particular resistor requires applying a control voltage at its "Address Select" terminal and an electrical power source at its "Primitive Select" terminal. Only one Address Select line is enabled at one time. This ensures that the Primitive Select and Group Return lines supply current to at most one resistor at a time. Otherwise, the energy delivered to a heater resistor would be a function of the number of resistors 70 being fired at the same time. Fig. 27 is a schematic diagram of an individual heater resistor and its FET drive transistor. As shown in Fig. 27, Address Select and Primitive Select lines also contain transistors for draining unwanted electrostatic discharge and pull down resistors to place all unselected addresses in an off state. Table V and Fig. 28 show the correlation between the firing resistor/orifice and the Address Select and Primitive Select Lines. Nozzle Number by Address Select and Primitive Select Lines P1 P2 P3 P4 P5 P6 P7 P8 P9 P10 P11 P12 P13 P14 A1 1 45 42 89 86 133 130 177 174 221 218 265 262 A2 7 4 51 48 95 92 139 136 183 180 227 224 271 268 A3 13 10 57 54 101 98 145 142 189 186 233 230 277 274 A4 19 16 63 60 107 104 151 148 195 192 239 236 283 280 A5 25 22 69 66 113 110 157 154 201 198 245 242 289 286 A6 31 28 75 72 119 116 163 160 207 204 251 248 295 292 A7 37 34 81 78 125 122 169 166 213 210 257 254 298 A8 40 43 84 87 128 131 172 175 216 219 260 263 A9 5 2 49 46 93 90 137 134 181 178 225 222 269 266 A10 11 8 55 52 99 96 143 140 187 184 231 228 275 272 A11 17 14 61 58 105 102 149 146 193 190 237 234 281 278 A12 23 20 67 64 111 108 155 152 199 196 243 240 287 284 A13 29 26 73 70 117 114 161 158 205 202 249 246 293 290 A14 35 32 79 76 123 120 167 164 211 208 255 252 299 296 A15 38 41 82 85 126 129 170 173 214 217 258 261 A16 3 47 44 91 88 135 132 179 176 223 220 267 264 A17 9 6 53 50 97 94 141 138 185 182 229 226 273 270 A18 15 12 59 56 103 100 147 144 191 188 235 232 279 276 A19 21 18 65 62 109 106 153 150 197 194 241 238 285 282 A20 27 24 71 68 115 112 159 156 203 200 247 244 291 288 A21 33 30 77 74 121 118 165 162 209 206 253 250 297 294 A22 39 36 83 80 127 124 171 168 215 212 259 256 300 The Address Select lines are sequentially turned on via TAB head assembly interface circuitry according to a firing order counter located in the printer and sequenced (independently of the data directing which resistor is to be energized) from A1 to A22 when printing form left to right and from A22 to A1 when printing from right to left. The print data retrieved from the printer memory turns on any combination of the Primitive Select lines. Primitive Select lines (instead of Address Select lines) are used in the preferred embodiment to control the pulse width. Disabling Address Select lines while the drive transistors are conducting high current can cause avalanche breakdown and consequent physical damage to MOS transistors. Accordingly, the Address Select lines are "set" before power is applied to the Primitive Select lines, and conversely, power is turned off before the Address Select lines are changed as shown in Fig. 29. In response to print commands from the printer, each primitive is selectively fired by powering the associated primitive select interconnection. To provide uniform energy per heater resistor only one resistor is energized at a time per primitive. However, any number of the primitive selects may be enabled concurrently. Each enabled primitive select thus delivers both power and one of the enable signals to the driver transistor. The other enable signal is an address signal provided by each address select line only one of which is active at a time. Each address select line is tied to all of the switching transistors so that all such switching devices are conductive when the interconnection is enabled. Where a primitive select interconnection and an address select line for a heater resistor are both active simultaneously, that particular heater resistor is energized. Thus, firing a particular resistor requires applying a control voltage at its "Address Select" terminal and an electrical power source at its "Primitive Select" terminal. Only one Address Select line is enabled at one time. This ensures that the Primitive Select and Group Return lines supply current to at most one resistor at a time. Otherwise, the energy delivered to a heater resistor would be a function of the number of resistors 70 being fired at the same time. Fig. 30 shows the firing sequence when the print carriage is scanning from left to right. The firing sequence is reversed when scanning from right to left. A brief rest period of approximately ten percent of the period is allowed between cycles. This rest period prevents Address Select cycles from overlapping due to printer cordage velocity variations. The interconnections for controlling the TAB head assembly driver circuitry include separate primitive select and primitive common interconnections. The driver circuity of the preferred embodiment comprises an array of fourteen primitives, fourteen primitive commons, and twenty-two address select lines, thus requiring 50 interconnections to control 300 firing resistors. The integration of both heater resistors and FET driver transistors onto a common substrate creates the need for additional layers of conductive circuitry on the substrate so that the transistors could be electrically connected to the resistors and other components of the system. This creates a concentration of heat generation within the substrate. Referring to Figs. 1 and 2, the print cartridge 10 is designed to be installed in a printer so that the contact pads 20, on the front surface of the flexible circuit 18, contact printer electrodes which couple externally generated energization signals to the TAB head assembly. To access the traces 36 on the back surface of the flexible circuit 18 from the front surface of the flexible circuit, holes (vias) are formed through the front surface of the flexible circuit to expose the ends of the traces. The exposed ends of the traces are then plated with, for example, gold to form the contact pads 20 shown on the front surface of the flexible circuit in Fig. 2. In the preferred embodiment, the contact or interface pads 20 are assigned the functions listed in Table VI. Fig. 31 shows the location of the interface pads 20 on the TAB head assembly of Fig. 2. ELECTRICAL PAD DEFINITION Odd Side of Head Even Side of Head Pad# Name Function Pad# Name Function 1 A9 Address Select 9 2 G6 Common 6 3 PS7 Primitive Select 7 4 PS6 Primitive Select 6 5 G7 Common 7 6 A11 Address Select 11 7 PS5 Primitive Select 5 8 A13 Address Select 13 9 G5 Common 5 10 G4 Common 4 11 G3 Common 3 12 PS4 Primitive Select 4 13 PS3 Primitive Select 3 14 A15 Address Select 15 15 A7 Address Select 7 16 A17 Address Select 17 17 A5 Address Select 5 18 G2 Common 2 19 G1 Common 1 20 PS2 Primitive Select 2 21 PS1 Primitive Select 1 22 A19 Address Select 19 23 A3 Address Select 3 24 A21 Address Select 21 25 A1 Address Select 1 26 A22 Address Select 22 27 TSR Thermal Sense 28 R10X 10X Resistor 29 A2 Address Select 2 30 A20 Address Select 20 31 A4 Address Select 4 32 PS14 Primitive Select 14 33 PS13 Primitive Select 13 34 G14 Common 14 35 G13 Common 13 36 A18 Address Select 18 37 A6 Address Select 6 38 A 16 Address Select 16 39 A8 Address Select 8 40 PS12 Primitive Select 12 41 PS11 Primitive Select 11 42 G12 Common 12 43 G11 Common 11 44 G10 Common 10 45 A10 Address Select 10 46 PS10 Primitive Select 10 47 A12 Address Select 12 48 G8 Common 8 49 PS9 Primitive Select 9 50 PS8 Primitive Select 8 51 G9 Common 9 52 A14 Address Select 14 The subject matter disclosed herein can be used with the subject matters disclosed in US-A-4, 926,197; US-A-4, 719, 477; US-A-5, 122,812; US-A-5, 159,353; and our co-pending European patent application nos. EP-A2-0 705 694; EP-A2-0 705 693; EP-A2-0 707 967; EP-A2-0 705 696; EP-A2-0 705 705; all filed the same day as this application.

Claims: An inkjet printing system comprising an ink reservoir (12); a substrate (28) including a plurality of individual ink firing chambers (130) with an ink firing element (70) in each chamber disposed along a top surface of said substrate and comprising a first outer edge (86) disposed along a periphery of said substrate and in close proximity to said ink firing chambers; an ink channel connecting said reservoir with said ink firing chambers and including a primary channel (52) connected at a first end to said reservoir and at a second end to a secondary channel; said primary channel being operative to allow ink (88) to flow from said ink reservoir, around said first outer edge of said substrate to said secondary channel along said top surface of said substrate; a separate inlet passage (132) connecting said secondary channel with each firing chamber; said inlet passage defined by side walls of a barrier layer (134); the inkjet printing system being characterized by: said side walls leading to each ink firing chamber (130) having a pinch point (146) extending to the inlet passage to form a restricted portion (145) for viscous damping of ink after energising an ink firing element (70) associated with said inlet passage, at least one of said walls for each fluid channel also forming an elongated peninsula (149) between said restricted portion (145) and said first outer edge (86) of said substrate, the peninsulas (149) and restricted portion (145) acting to reduce cross-talk between fluid channels when energising said ink ejection elements. An inkjet printing system according to claim 1, wherein said substrate (28) includes a second outer edge; said primary channel (52) being operative to allow ink (88) to flow from said ink reservoir (12), around said second outer edge of said substrate to a secondary channel along said top surface of said substrate. An inkjet printing system according to claim 1 or 2, wherein said barrier layer (134) forms a plurality of peninsulas including: a first peninsula (149) terminating in close proximity to said outer edge (86) of said substrate (28) at a termination point located a first displacement distance from said outer edge; and at least one second truncated peninsula terminating in proximity to said outer edge of said substrate at another termination point located a second displacement distance from said outer edge, said second displacement distance being greater than said first displacement distance. An inkjet printing system according to claim 3, wherein said first peninsula (149) is immediately adjacent the or one of the second truncated peninsulas. An inkjet printing system according to claim 3, wherein said first peninsula (149) is immediately adjacent and between two second truncated peninsulas. An inkjet printing system according to any preceding claim, wherein said barrier layer (134) forms a separation wall between adjacent firing chambers (130) and having a width greater than said peninsula or peninsulas (149). An inkjet printing system according to any preceding claim, wherein said barrier layer (134) forms a separation wall between adjacent firing chambers (130) and is integral with said pinch point (146). An inkjet printing system according to any preceding claim, wherein said pinch point (146) forms a constricted portion (145) to said inlet passage (132) proximate an entrance of said ink firing chambers (130). An inkjet printing system according to claim 8, wherein said constricted portion (145) has a width between substantially 15 and 55 micrometres. An inkjet printing system according to any preceding claim, wherein the or each peninsula (149) provides an increased support (148) in proximity of said outer edge (86) of said substrate (28) for a nozzle member (16) when said nozzle member is positioned on the top surface of said substrate.

Inventors: CHAPMAN TERRI I, CHILDERS WINTHROP D, COURIAN KENNETH J, HO MAY FONG, KEEFE BRIAN J, KNIGHT WILLIAM R, MORITZ JULES G, STEINFIELD STEVEN W, TAPPON ELLEN R, TRUEBA KENNETH E, CHAPMAN, TERRI I., CHILDERS, WINTHROP D., COURIAN, KENNETH J., HO, MAY FONG, KEEFE, BRIAN J., KNIGHT, WILLIAM R., MORITZ, JULES G., STEINFIELD, STEVEN W., TAPPON, ELLEN R., TRUEBA, KENNETH E.
Applicants: HEWLETT PACKARD CO, HEWLETT-PACKARD COMPANY
Application year: 1995
Main classification: B41J2
IPC codes: B41J2, G01D15