Abstract:
An inkjet printhead includes a compact substrate having a pair of elongated edge portions for ink channel architecture, a central interior for substrate circuitry, and a pair of truncated end portions for mounting and for electrical interconnects. The ink channel architecture includes a plurality of ink vaporization chambers each having a firing resistor therein, as well as ink feed channels communicating through an ink passage from an underside of the substrate around both edges of the substrate to the vaporization chambers. The central interior portion excludes any ink channel architecture thereby enhancing the structural stability

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part application of U.S. application Ser. No. 08/179,866, filed Jan. 11, 1994 entitled &#34;Ink Delivery System for an Inkjet Printhead,&#34; by Brian J. Keefe, et al., which is a continuation of U.S. application Ser. No. 07/862,068 filed Apr. 2, 1992, and now issued as U.S. Pat. No. 5,278,584. 
     This application also relates to the subject matter disclosed in the following U.S. Patent and co-pending U.S. Applications: 
     U.S. application Ser. No. 07/864,822, filed Apr. 2, 1992, entitled &#34;Improved Inkjet Printhead;&#34; 
     U.S. application Ser. No. 07/864,930, filed Apr. 2, 1992, entitled &#34;Structure and Method for Aligning a Substrate With Respect to Orifices in an Inkjet Printhead;&#34; now issued as U.S. Pat. No. 5,297,331. 
     U.S. application Ser. No. 08/236,915, filed Apr. 29, 1994, entitled &#34;Thermal Inkjet Printer Printhead;&#34; 
     U.S. application Ser. No. 08/235,610, filed Apr. 29, 1994, entitled &#34;Edge Feed Ink Delivery Thermal Inkjet Printhead Structure and Method of Fabrication;&#34; 
     U.S. Pat. No. 4,719,477 to Hess, entitled &#34;Integrated Thermal Ink Jet Printhead and Method of Manufacture;&#34; 
     U.S. Pat. No. 5,122,812 to Hess, et at., entitled &#34;Thermal Inkjet Printhead Having Driver Circuitry Thereon and Method for Making the Same;&#34; 
     U.S. Pat. No. 5,159,353 to Fasen, et al., entitled &#34;Thermal Inkjet Printhead Structure and Method for Making the Same;&#34; 
     U.S. application Ser. No. 08/319,896, filed herewith, entitled &#34;Inkjet Printhead Architecture for High Speed and High Resolution Printing;&#34; 
     U.S. application Ser. No. 08/319,404, filed herewith, entitled &#34;Inkjet Printhead Architecture for High Frequency Operation;&#34; 
     U.S. Application filed herewith, entitled &#34;High Density Nozzle Array for Inkjet Printhead;&#34; 
     U.S. application Ser. No. 08/320,084 filed herewith, entitled &#34;Inkjet Printhead Architecture for High Speed Ink Firing Chamber Refill;&#34; 
     U.S. application Ser. No. 08/319,893, filed herewith, entitled &#34;Barrier Architecture for Inkjet Printhead;&#34; 
     U.S. application Ser. No. 08/319,895 filed herewith, entitled &#34;Compact Inkjet Substrate with a Minimal Number of Circuit Interconnects Located at the End Thereof;&#34; 
     U.S. application Ser. No. 08/648,471, filed herewith, entitled &#34;Self-Cooling Structure for Inkjet Substrate with High Density High Frequency Firing Chambers and Multiple Substrate Circuitry Elements;&#34;and 
     U.S. application Ser. No. 08/319,894, filed herewith, entitled &#34;Stable Substrate Structure for a Wide Swath Nozzle Array in a High Resolution Inkjet Printer.&#34; 
     The above patents and co-pending applications are assigned to the present assignee and are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention generally relates to inkjet and other types of printers and, more particularly, to the printhead portion of an inkjet printer. 
     Inkjet print cartridges operate by causing a small volume of ink to vaporize and be ejected from a firing chamber through one of a plurality of orifices so as to print a dot of ink on a recording medium such as paper. Typically, the orifices are arranged in one or more linear nozzle arrays. The properly sequenced ejection of ink from each orifice causes characters or other images to be printed in a swath across the paper. 
     An inkjet printhead generally includes ink channels to supply ink from an ink reservoir to each vaporization chamber (i.e., firing chamber) proximate to an orifice; a nozzle member in which the orifices are formed; and a silicon substrate containing a series of thin film resistors, one resistor per vaporization chamber. 
     To print a single dot of ink in a thermal inkjet printer, 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 U.S. Pat. No. 4,683,481 to Johnson, entitled &#34;Thermal Ink Jet Common-Slotted Ink Feed Printhead,&#34; 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 &#34;center&#34; feed design, with side electrical interconnects to a flex-circuit along the full length of the substrate. Ink is fed to the vaporization chambers from a central location then distributed outward into the vaporization chambers which contain the ruing resistors. 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 and also by extra substrate at both ends of the hole to provide structural integrity. Also, once the hole is formed, the substrate is relatively fragile, making handling more difficult. Such prior printhead design limited the ability of printheads to have compact stable substrates with wide swath high nozzle densities and the lower operating temperatures 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. Modem 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 number and location of the conductive components used to electrically connect the printhead to external driver circuitry in the printer unit. Specifically, an increasingly large number of firing resistors requires a correspondingly large number of interconnection pads, leads, grounds and the like. This increase in components and interconnects and the resulting increase in substrate size causes greater manufacturing/production costs, increases the probability that defects will occur during the manufacturing process, and increases the heat generated during high frequency operation. 
     BRIEF SUMMARY OF THE INVENTION 
     In order to solve the aforementioned problems, thermal inkjet printheads have been developed which efficiently incorporate pulse driver circuitry directly on the printhead substrate with the firing resistors. The incorporation of driver circuitry on the printhead substrate in this manner reduces the number of interconnect components needed to electrically connect the printhead to the printer unit. This results in improved production and operating efficiency. 
     To further produce high-efficiency integrated printing systems, significant research has developed improved transistor structures and unique methods for integrating them into high resolution compact substrates with good structural integrity and improved heat control characteristics. The integration of driver components, address lines, ground lines and firing resistors onto a common substrate is based on specialized, multi-layer connective circuitry so that the driver transistors can communicate with the firing resistors and other portions of the printing system. Typically, this connective circuitry involves a plurality of separate conductive layers. 
     To increase resolution and print quality, the printhead nozzles are placed closer together and are fed through an &#34;edge feed&#34; ink channel architecture. Both firing resistors and the associated orifices are placed closer together along the full length of the outer edges of the substrate, with the related circuitry primarily located in the middle portion of the substrate. To increase printer throughput, the width of the priming swath is increased by placing more nozzles on the print head to create a nozzle array which prints a one-half inch print swath. 
     More specifically, the invention contemplates a compact substrate having a pair of elongated edge portions for ink channel architecture, a central interior for substrate circuitry, and a pair of truncated end portions for mounting and for electrical interconnects. The ink channel architecture includes a plurality of ink vaporization chambers each having a ruing resistor therein, as well as ink feed channels communicating through an ink passage from an underside of the substrate around both edges of the substrate to the vaporization chambers. The central interior portion excludes any ink channel architecture such as a center feed ink slot, thereby enhancing the structural stability of the substrate, and includes various substrate multiplexing circuitry components including primitive select actuation lines, address lines, ground lines, and transistors. The truncated end portions include ESD devices as well as interconnects for bonded connection to printer circuit lines. The cost of the inkjet printhead is significantly reduced due to high efficiency die yields from the silicon wafers, due to the substrate portions that are no longer needed to provide a central ink feed slot, and due to the end substrate portion that were previously required to hold the two halves of the substrate together. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of an inkjet print cartridge according to one embodiment of the present invention. 
     FIG. 2 is a perspective view of the front surface of the Tape Automated Bonding (TAB) printhead assembly (hereinafter &#34;TAB head assembly&#34;) 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 &#34;TAB head assembly&#34;) 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 is a view of one arrangement of orifices and the associated heater resistors on a printhead. 
     FIG. 15 is a schematic diagram of one heater resistor and its associated address line, drive transistor, primitive select line and ground line. 
     FIG. 16 is a schematic diagram of the firing sequence for the address select lines when the printer carriage is moving from left to right. 
     FIG. 17 is a diagram showing the layout of the contact pads on the TAB head assemble. 
     FIG. 18 is a magnified perspective view showing a THA mounted on a print cartridge. 
     FIG. 19 shows one end of a substrate with ruing resistors #1 and #2, with the interconnects identified. 
     FIG. 20 shows the opposite end of the substrate of FIG. 19, with ruing resistors #299 and #300, with the interconnects identified. 
     FIG. 21 shows the substrate schematics and data taken in a direction along the width of the substrate. 
     FIG. 22 shows the substrate schematics and data taken in a direction along the length of the substrate. 
     FIG. 23 shows a silicon wafer prior to the individual dies being cut and separated from the wafer. 
     FIG. 24 shows the schematic and data for curing a silicon wafer into individual dies. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Generally speaking the invention provides an improved ink delivery system between an ink reservoir and ink ejection chambers in an inkjet printhead operating at high firing frequencies. In a preferred embodiment, a barrier layer containing ink channels and vaporization chambers is located between a rectangular substrate and a nozzle member containing an array of orifices. The substrate contains two linear arrays of heater elements, and each orifice in the nozzle member is associated with a vaporization chamber and heater element. The ink channels in the barrier layer have ink entrances generally running along two opposite edges of the substrate so that ink flowing around the edges of the substrate gain access to the ink channels and to the vaporization chambers. Piezoelectric elements can be used instead of heater elements. 
     More particularly, the features of the invention include an ink delivery system for an array of nozzle orifices in a print cartridge comprising an ink reservoir; a substrate having a plurality of individual ink firing chambers with an ink firing element in each chamber; 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; 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; 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. Referring to FIG. 1, reference numeral 10 generally indicates an inkjet print cartridge incorporating a printhead according to one embodiment of the present invention simplified 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 &#34;TAB head assembly 14&#34;) 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 &#34;snout&#34; 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 simply and clearly show the features of the invention. 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. 1 for illustrative purposes. FIG. 4 is a perspective view of the front surface of the Tape Automated Bonding (TAB) printhead assembly (hereinafter &#34;TAB head assembly&#34;) 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 army 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 columns 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 ct,amber 72 is then refilled by capillary action. 
     In a preferred embodiment, the barrier layer 30 is approximately 1 mils thick, the substrate 28 is approximately 20 mils thick, and the flexible circuit 18 is approximately 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 are 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&#39;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. 
     In order to make a finished printhead, the TAB head assembly is 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. Referring to FIG. 14, 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. 14. For clarity of understanding, the orifices 17 are conventionally assigned a number as shown, starting at the top right 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 ruing 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 of the present invention 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 FIG. 14. Within a single row or column of resistors, a small offset E 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 twenty 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. 14) 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. 
     As described, the firing heater resistors 70 of the preferred embodiment are organized as fourteen primitive groups of twenty or twenty-two resistors. It can be seen that each resistor (numbered 1 through 300 and corresponding to the orifices 17 of FIG. 14) 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 &#34;Address Select&#34; terminal and an electrical power source at its &#34;Primitive Select&#34; 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. 15 is a schematic diagram of an individual heater resistor and its FET drive transistor. As shown in FIG. 15, 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 I shows the correlation between the firing resistor/orifice and the Address Select and Primitive Select Lines. 
     
                                           TABLE I__________________________________________________________________________Nozzle Number by Address Select and Primitive Select LinesP1    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                                     262A2  7  4 51 48  95              92                139                   136                      183                         180                            227                               224                                  271                                     268A3 13 10 57 54 101              98                145                   142                      189                         186                            233                               230                                  277                                     274A4 19 16 63 60 107             104                151                   148                      195                         192                            239                               236                                  283                                     280A5 25 22 69 66 113             110                157                   154                      201                         198                            245                               242                                  289                                     286A6 31 28 75 72 119             116                163                   160                      207                         204                            251                               248                                  295                                     292A7 37 34 81 78 125             122                169                   166                      213                         210                            257                               254   298A8    40 43 84  87             128                131                   172                      175                         216                            219                               260                                  263A9  5  2 49 46  93              90                137                   134                      181                         178                            225                               222                                  269                                     266A10   11  8 55 52  99              96                143                   140                      187                         184                            231                               228                                  275                                     272A11   17 14 61 68 105             102                149                   146                      193                         190                            237                               234                                  281                                     278A12   23 20 67 64 111             108                155                   152                      199                         196                            243                               240                                  287                                     284A13   29 26 73 70 117             114                161                   158                      205                         202                            249                               246                                  293                                     290A14   35 32 79 76 123             120                167                   164                      211                         208                            255                               252                                  299                                     296A15   38 41 82  86             126                129                   170                      173                         214                            217                               258                                  261A16    3    47 44  91              88                135                   132                      179                         176                            223                               220                                  267                                     264A17    9  6 53 50  97              94                141                   138                      185                         182                            229                               226                                  273                                     270A18   15 12 59 56 103             100                147                   144                      191                         188                            235                               232                                  279                                     276A19   21 18 65 62 109             106                153                   150                      197                         194                            241                               238                                  285                                     282A20   27 24 71 68 115             112                159                   156                      203                         200                            247                               244                                  291                                     288A21   33 30 77 74 121             118                165                   162                      209                         206                            253                               250                                  297                                     294A22   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 from left to right and from A22 to A1 when printing from right to left. The print data retrieved from the printer memory turns an 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 &#34;set&#34; before power is applied to the Primitive Select lines, and conversely, power is turned off before the Address Select lines are changed. 
     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 &#34;Address Select&#34; terminal and an electrical power source at its &#34;Primitive Select&#34; 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. 16 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. The resistor firing frequency is shown as F in FIG. 16. A brief rest period of approximately ten percent of the period, 1/F is allowed between cycles. This rest period prevents Address Select cycles from overlapping due to printer carriage 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 11. FIG. 17 shows the location of the interface pads 20 on the TAB head assembly of FIG. 2. 
     
                       TABLE II______________________________________Odd Side of Head  Even Side of HeadPad #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 411   G3     Common 3      12   PS4  Primitive Select 413   PS3    Primitive Select 3                     14   A15  Address Select 1515   A7     Address Select 7                     16   A17  Address Select 1717   A5     Address Select 5                     18   G2   Common 219   G1     Common 1      20   PS2  Primitive Select 221   PS1    Primitive Select 1                     22   A19  Address Select 1923   A3     Address Select 3                     24   A21  Address Select 2125   A1     Address Select 1                     26   A22  Address Select 2227   TSR    Thermal Sense 28   R10×                               10× Resistor29   A2     Address Select 2                     30   A20  Address Select 2031   A4     Address Select 4                     32   PS14 Primitive Select 1433   PS13   Primitive Select 13                     34   G14  Common 1435   G13    Common 13     36   A18  Address Select 1837   A6     Address Select 6                     38   A 16 Address Select 1639   A8     Address Select 8                     40   PS12 Primitive Select 1241   PS11   Primitive Select 11                     42   G12  Common 1243   G11    Common 11     44   G10  Common 1045   A10    Address Select 10                     46   PS10 Primitive Select 1047   A12    Address Select 12                     48   G8   Commons 849   PS9    Primitive Select 9                     50   PS8  Primitive Select 851   G9     Common 9      52   A14  Address Select 14______________________________________ 
    
     FIG. 18 shows the relative positions of the even # nozzles 2 through 300 and the odd # nozzles 1 through 299 when the THA is mounted on a print cartridge. 
     FIGS. 19-20 are an enlarged illustration of both truncated end portions 202, 204 of the substrate showing the ESD devices 206 and the interconnect junctions 208. 
     FIGS. 21-22 includes schematic drawings as well as related data tables showing the dimensions, electrical resistance and identification of the various circuitry portions of the substrate. It will be appreciated by those skilled in the art that substantial heat is generated by all of the circuitry on the substrate. More particularly, each firing resistor requires 300 milliamps whenever it is selected for firing. For a 12 KHertz firing frequency of F, and in reference to the firing diagram of FIG. 16, when all of the twenty-two address lines are activated in a duty cycle with each pulse width being 2.3 microseconds, then 2.3×22 equals a result divided by 83 microseconds to create a 61% duty cycle. Therefore it is possible when all primitives are firing at the same time to pass a current of approximately 25 amps through the substrate (300 milliamps×14×0.61). The cooling characteristices of the edge feed design are therefore very helpful in avoiding the overheating of the substrate during normal operation. 
     Also, in the present design it was the required width of the interconnects which determined the maximum width of the substrate, thereby making the multiplexing on the substrate very important in order to provide only 52 interconnects to selectively actuate 300 firing resistors in the vaporization compartments. 
     FIGS. 23-24 show the dimensions for cutting a silicon wafer in order to obtain a high yield for the substrate dies of the present invention. Although some of the dies such as 210 which extend into the 5 mm wide exclusion zone 212 are not usable if critical components of the multilayer substrate lie inside such exclusion zone, nevertheless the invention still provides significantly better yield than for an estimated yield for a center feed ink channel design having the same 300 nozzle 600 dpi specifications as the presently preferred embodiment of the present invention. 
     While specific illustrated embodiments have been shwon and described, it will be appreciated by those skilled in the art that various modifications, changes and additions can be made to the methods, structurs and apparauts of the invention without departing from the spirit and scope of the invention as set forth in the following claims.