Patent Publication Number: US-6209203-B1

Title: Method for making nozzle array for printhead

Description:
FIELD OF THE INVENTION 
     This invention relates generally to printheads for thermal inkjet print cartridges. More particularly, this invention relates to the manufacture of nozzle plates for printheads. 
     BACKGROUND OF THE INVENTION 
     Thermal inkjet printers utilize print cartridges having printheads for directing ink droplets onto a medium, such as paper, in patterns corresponding to the indicia to be printed on the paper. In general, ink is directed from a reservoir via flow paths to bubble chambers and associated orifices or nozzles for release onto the paper. Heaters are provided adjacent the nozzles for heating ink supplied to the nozzles to vaporize a component in the ink in order to propel droplets of ink through the nozzle holes to provide a dot of ink on the paper. During a printing operation the print head is moved relative to the paper and ink droplets are released in patterns corresponding to the indicia to be printed by electronically controlling the heaters to selectively operate only the heaters corresponding to nozzles through which ink is to be ejected for a given position of the printhead relative to the paper. 
     Printheads typically include a nozzle plate attached, as by adhesive, to a silicon chip containing the heating elements. The flowpaths, bubble chambers and nozzles are typically provided by laser ablating the nozzle plate material to provide such structure. As will be appreciated, the precision and uniformity of such features significantly affect the quality of printing. Thus, for example, if the walls which surround the nozzles and define the bubble chambers do not smoothly interface the silicon chip, leakage can result and adversely affect print quality. Conventional methods for manufacturing nozzle plates often fail to provide the desired precision and uniformity of the flow features thus adversely affecting the yield of usable nozzle plates and/or the performance of the printer. 
     Accordingly it is an object of the present invention to provide an improved method for the manufacture of inkjet printheads. 
     Another object of the present invention is to provide a method of the character described which enables the production of printheads having greater reliability and performance characteristics as compared to printheads provided using conventional techniques. 
     A further object of the present invention is to provide a method for manufacturing a printhead having an improved nozzle and heater array. 
     An additional object of the present invention is to provide a method of the character described which avoids many of the disadvantages of conventional methods. 
     SUMMARY OF THE INVENTION 
     Having regard to the foregoing and other objects, the present invention is directed to a method for making a nozzle plate for an inkjet printer by laser ablating a nozzle plate material. The method includes the steps of a) selecting a plurality of desired nozzle hole locations, b) ablating a first portion of the nozzle plate material in an area of the nozzle plate material adjacent each nozzle hole location to a predetermined depth to provide a plurality of flow paths c) ablating nozzle holes through the full thickness of the nozzle plate material at each desired nozzle hole location, wherein unablated material remains adjacent each nozzle hole to provide an ink chamber, and d) ablating a throat region through a second portion of the nozzle plate material adjacent each nozzle hole so that each ink chamber is in flow communication with at least one flow path outside of the chamber. 
     The method of the invention enables nozzle plates of improved quality and precision as compared to those manufactured using conventional techniques. For example, the method enables the manufacture of nozzle plates having smoother and more uniform surfaces as well as finer flow features. In particular, the invention enables the formation of bubble chamber walls having a thickness of less than about 10 microns and having substantially uniform wall features which provide an improved interface between the nozzle plate and the underlying silicon chip so that problems associated with ink leaking between the upper wall edges of the ink chambers and the silicon chip is substantially avoided. 
     According to another aspect of the invention, the invention provides a method for making a nozzle plate for an inkjet printer by laser ablating a nozzle plate material. The method includes the steps of laser ablating the nozzle plate material to provide a first nozzle hole array having a plurality of nozzle holes, each of which is positioned to correspond to a desired print location, with the print location of each of the nozzle holes of the first nozzle array being different from one another; and laser ablating the nozzle plate material to provide a second nozzle hole array having a plurality of nozzle holes, each nozzle hole of the second nozzle hole array being positioned to correspond to a desired print location, with the print location of each of the nozzle holes of the second array corresponding to one of the print locations of the first nozzle hole array such that the first and second nozzle hole arrays each have a nozzle hole corresponding to each desired print location so that at least two nozzle holes are provided for each print location. 
     Preferred nozzle plates manufactured in accordance with the invention provide a redundancy feature in that the resulting printhead includes at least two nozzle holes (and associated heaters) for each print location. During a printing process, the printer controller alternates between the at least two nozzles such that the effect of an improperly operating heater and/or nozzle is significantly reduced. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further advantages of the invention will become apparent by reference to the detailed description of preferred embodiments when considered in conjunction with the following drawings, which are not to scale so as to better show the detail, in which like reference numerals denote like elements throughout the several views, and wherein: 
     FIG. 1 is a perspective view of an inkjet cartridge having a printhead in accordance with a preferred embodiment of the invention. 
     FIG. 2 is an enlarged top plan view of a portion of a printhead for a printer according to the invention. 
     FIG. 3 is a bottom plan view of a printhead for a printer according to the invention. 
     FIG. 4 is an enlarged partial cross-sectional view of a nozzle plate and heater assembly for a printhead according to the invention. 
     FIG. 5 is an enlarged partial bottom plan view of a nozzle plate for a printhead according to the invention. 
     FIG. 5 a  is an enlarged partial top view of a nozzle plate according to the invention. 
     FIG. 5 b  is an enlarged partial top view of another nozzle plate according to the invention. 
     FIG. 6 is an enlarged view of a portion of the nozzle plate of FIG.  5 . 
     FIG. 7 is a top plan view of another nozzle plate in accordance with the invention. 
     FIG. 8 provides schematic diagrams of steps in the manufacture of nozzle plates in accordance with the invention. 
     FIG. 9 is a scanned image of a nozzle plate made in accordance with the method of the invention. 
     FIG. 10 is a scanned image of a nozzle plate having a configuration in accordance with the invention but made using a conventional technique. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the figures, there is depicted in FIG. 1 a print cartridge  10  in accordance with a preferred embodiment of the invention for use with inkjet printers. The cartridge  10  includes a printhead assembly  12  located above an ink reservoir  14  provided by a generally hollow plastic body containing ink or a foam insert saturated with ink. 
     The printhead assembly  12  is preferably located on an upper portion of a nose piece  16  of the body of cartridge  10  for transferring ink from the ink reservoir  14  onto a medium to be printed, such as paper, in patterns representing the desired indicia. As used herein, the term “ink” will be understood to refer generally to inks, dyes and the like commonly used for thermal inkjet printers. 
     With additional reference to FIGS. 2 and 3, the printhead  12  preferably includes a nozzle member  18  attached to a silicon member  20 , with the silicon member in electrical communication with a plurality of electrically conductive traces  22  provided on a back surface  24  of a polymer tape strip  26 . A preferred adhesive attaching the nozzle plate to the substrate is a B-stageable thermal cure resin including, but not limited to phenolic resins, resorcinol resins, urea resins, epoxy resins, ethylene-urea resins, furane resins, polyurethane resins and silicon resins. The thickness of the adhesive layer range from about 1 to about 25 microns. 
     The nozzle member  18  is preferably provided by a polyimide polymer tape composite material with an adhesive layer on one side thereof, the composite material having a total thickness ranging from about 15 to about 200 microns, with such composite materials being generally referred to as “Coverlay” in the industry. Suitable composite materials include materials available from DuPont Corporation of Wilmington, Del. under the trade name PYRALUX and from Rogers Corporation of Chandler, Ariz. under the trade name R-FLEX. However, it will be understood that the provision of nozzle holes and heaters in accordance with the present invention is applicable to nozzle plates of virtually any material including also, but not limited to, metal and metal coated plastic. 
     Each trace  22  preferably terminates at a contact pad  22   a  and each pad  22   a  extends through to an outer surface  32  of the tape  26  for contacting electrical contacts of the inkjet printer to conduct output signals from the printer to heater elements on silicon member  20 . The traces may be provided on the tape as by plating processes and/or photo lithographic etching. The tape/electrical trace structure is referred to generally in the art as a “TAB” strip, which is an acronym for Tape Automated Bonding. 
     The silicon member  20  is hidden from view in the assembled printhead and is attached to nozzle member  18  in a removed area or cutout portion  28  of the tape  26  such that an outwardly facing surface  30  of the nozzle member is generally flush with and parallel to a front surface  32  of the tape  26  for directing ink onto the medium to be printed via a plurality of nozzle holes  34  in flow communication with the ink reservoir  14 . The nozzle holes  34  are preferably substantially circular, elliptical, square or rectangular in cross section along an axis parallel to a plane defined by the nozzle member  18 . 
     Silicon bonds or wires  35  electrically connect the traces  22  to the silicon member  20  to enable electrical signals to be conducted from the printer to the silicon member for selective activation of the heaters during a printing operation. Thus, the heaters  36  (FIG. 4) are electrically coupled to the conductive traces  22  via the silicon bonds  35  and electrically coupled between the TAB bonds  35  and the contact pads  22   a  for energization thereof in accordance with commands from the printer. In this regard, a demultiplexer  44  (FIG. 3) is preferably provided on the silicon member  20  for demultiplexing incoming electrical signals and distributing them to the heaters  36 . 
     With reference to FIG. 4, the silicon member  20  is preferably a generally rectangular portion of a silicon substrate of the type commonly used in the manufacture of print heads. A plurality of thin film resistors or heaters  36  are provided on the silicon member, with one such heater being located adjacent each one of the nozzle holes  34  for vaporizing ink for ejection through the nozzle holes  34 . In this regard, each heater  36  is preferably located adjacent a bubble chamber  38  associated with each nozzle hole  34  for heating ink conducted into the chamber via a channel  40  from the ink reservoir  14  to vaporize ink in the chamber and eject it out the nozzle hole  34  for condensing into an ink droplet  42  which strikes the medium to be printed at a desired location thereon. 
     The silicon member  20  has a size typically ranging from about 2 to about 3 millimeters wide with a length ranging from about 6 to about 12 millimeters long and from about 0.3 to about 1.2 millimeters in thickness and most preferably from about 0.5 to about 0.8 millimeters thick. The printhead  12  may contain one, two, three or more silicon members  20  and nozzle members  18 , however, for purposes of simplifying the description, the printhead assembly will be described as containing only one silicon member  20  and associated nozzle member  18 . 
     The ink travels generally by gravity and capillary action from the reservoir  14  around the perimeter of the silicon member  20  or through a central via in the silicon member into the channels  40  for passage into the bubble chambers. The relatively small size of the nozzle holes  34  maintains the ink within the chambers  38  until activation of the associated heaters which vaporizes a volatile component in the ink and voids the chamber after which it refills again by capillary action. 
     As will be noted, the lower wall of the bubble chamber  38  and the channel  40  associated with each nozzle hole  34  is provided by the adjacent substantially planar surface  45  of the silicon member. The topographic features of the chambers  38  and the channel  40  are provided by the shape and configuration of a lower surface  46  of the nozzle member  18  which is attached by means of an adhesive layer  47  to the surface  45  of the silicon member  20 . The flow features of the nozzle member  18 , such as the nozzle holes  34 , bubble chambers  38  and channels  40  are preferably formed in the composite material of the nozzle member  18  by laser ablating the material to provide configuration as shown in FIGS. 5 and 6. 
     Accordingly, and with reference to FIGS. 5-6, the lower surface  46  of the nozzle member  18  is preferably configured to provide a pair of nozzle holes and associated heaters for each print location. The term “print location” will be understood to refer to the location of a nozzle for directing a specific ink bubble or droplet onto the paper to be printed. Conventionally, one nozzle is provided for each print location with sufficient nozzles provided to enable printing of pixel or ink-dot patterns corresponding to virtually any character or image. Thus, failure of a single nozzle can detrimentally affect the printed image. 
     In accordance with the present invention, there is provided a print head having a pair of nozzles at each print location with the heaters  36  for each nozzle being alternatively activated such that the effect of the failure of a single nozzle of the nozzle pair on the quality of the printed image may be reduced. As will be appreciated, this provides a redundancy feature heretofore unavailable which reduces the effect of a failed nozzle or heater. As used herein, the terminology “alternatively activated” refers to the sequencing associated with ejecting ink from the nozzles of a pair by which the nozzles are activated one after the other or one nozzle may be activated two or more times concurrently before the other nozzle is activated. 
     The individual nozzle holes  34  and heaters  36  are independently numbered as shown in drawing FIGS. 5-6, with the nozzles and heaters of each print location bearing the same integer but with the suffix “a” or “b” to represent their plurality. Accordingly, in a preferred embodiment, the nozzle member  18  is formed to provide a nozzle array  51  positioned adjacent side edge  60  of the silicon member  20  and a nozzle array  61  positioned adjacent side edge  70  of the silicon member  20  (FIG.  2 ). 
     Nozzle array  51  includes two rows of nozzles, one row comprising nozzles  52   a ,  54   a ,  56   a ,  58   a , and the other row comprising nozzles  62   a ,  64   a ,  66   a , and  68   a . Nozzle array  61  includes two rows of nozzles, one row comprising nozzles  52   b ,  54   b ,  56   b ,  58   b , and the other row comprising nozzles  62   b ,  64   b ,  66   b , and  68   b . As will be seen, an imaginary line may be drawn to bisect between members of a nozzle pair, e.g., bisecting line M drawn between the center of nozzles  54   a  and  54   b , which nozzles represent the same print location. 
     With reference now to FIG. 6, it will be noted that the nozzles of the array  51  are arranged in two rows, one row having nozzles  54   a ,  56   a  and  58   a , and the other row having nozzles  62   a ,  64   a ,  66   a  and  68   a . Array  61  is similarly configured as to the “b” suffix of the corresponding nozzles in array  51 . As noted previously, the “a” and “b” suffixed nozzles of a common-integered nozzles, e.g., nozzles  52   a  and  52   b , correspond to the same print location and provide a redundancy feature which reduces the effect of the failure of a nozzle or heater at a print location. This is accomplished in a preferred embodiment by alternating between the pair of nozzles (a and b) during a printing sequence. 
     Heater  72   a  is positioned below nozzle  52   a  and heater  72   b  is positioned below nozzle  52   b  as shown in FIG. 5 a . Likewise, heaters  74   a - 74   b ,  76   a - 76   b ,  78   a - 78   b  are positioned below nozzle pairs  54   a - 54   b ,  56   a - 56   b ,  58   a - 58   b , respectively; and heaters  82   a - 82   b ,  84   a - 84   b ,  86   a - 86   b ,  88   a - 88   b  are positioned below nozzle pairs  62   a - 62   b ,  64   a - 64   b ,  66   a - 66   b ,  68   a - 68   b , respectively. As will be appreciated, the printhead preferably includes more than the eight described nozzle/heater pairs and, in a preferred embodiment includes from about 20 to about 20,000 nozzle/heater pairs, preferably from about 200 to about 2,000, with the members of each pair provided in separate arrays. In this regard, it is contemplated that at least two arrays be provided. Further arrays may be included to provide even further redundancy, with each array having a nozzle/heater pair for each print location. 
     With reference again to FIG. 4, in which it will be understood that nozzle hole  34  is representative of each nozzle of the arrays  51  and  61 , i.e., nozzles  52 - 58  and  62 - 68 , the nozzle hole  34  preferably has a length L of from about 10 to about 100 μm and has tapered walls moving from bubble chamber  38  to the top surface of the nozzle member  18 , the entrance opening n being preferably from about 5 to about 80 μm in width and the exit opening n′ being from about 5 to about 80 μm in width. Each bubble chamber  38  and channel  40 , one each of which feeds a nozzle, is sized to provide a desired amount of ink to each nozzle, which volume is preferably from about 1 pl to about 200 pl. In this regard, each bubble chamber  38  preferably has a volume of from about 1 pl to about 400 pl and each channel  40  preferably has a flow area of from about 20 μm 2  to about 1000 μm 2 . 
     As noted previously, the flow features of the nozzle member  18 , such as the nozzle holes  34 , bubble chambers  38  and channels  40  are preferably formed as by laser ablating a polymeric material to provide configuration as shown in FIGS. 5-6. In this regard, the nozzle member  18  is preferably configured to provide a barrier wall for each nozzle location which is shaped to provide a suitable bubble chamber  38  and channel  40  for flow of ink to the nozzle. For example, nozzle member  18  has formed thereon barrier wall  92   a  for nozzle  52   a  and barrier wall  92   b  for nozzle  52   b . Likewise, barrier walls  94   a - 94   b ,  96   a - 96   b ,  98   a - 98   b  are provided for nozzles  54   a - 54   b ,  56   a - 56   b ,  58   a - 58   b , respectively, and barrier walls  102   a - 102   b ,  104   a - 104   b ,  106   a - 106   b ,  108   a - 108   b  are provided for nozzles  62   a - 62   b ,  64   a - 64   b ,  66   a - 66   b ,  68   a - 68   b . All “a” suffixed barrier walls are preferably substantially identical and all “b” suffixed barrier walls are preferably substantially identical. Accordingly, and for the sake of clarity, only representative ones of the barrier walls will be described, it being understood that the additional barrier walls are of like construction. 
     To facilitate the supplying of ink to the nozzles in a desired manner and to reduce interference from the operation of adjacent nozzles, it is preferred that the nozzles of adjacent rows of an array be spaced apart a distance R corresponding to from about 2 to about 20 heater widths, a “heater width” being from about 10 μm to about 80 μm, such that the nozzles of adjacent rows are spaced apart by a distance of from about 20 μm to about 1000 μm. In addition, for a printer having a resolution of 600 dpi, it is preferred that each nozzle be longitudinally staggered a distance S of from about 40 μm to about 400 μm relative to adjacent nozzles in the same row and latitudinally staggered a distance T of from about 42 μm to about 84 μm relative to adjacent nozzles of the other row. 
     In addition, it is preferred that the channels or flow paths to the bubble chambers of the nozzles closest to the edges  60  and  70  of the silicon member, that is, channels  112   a - 112   b ,  114   a - 114   b ,  116   a - 116   b ,  118   a - 18   b  which supply ink to the bubble chambers of nozzles  52 ( a ),( b )- 58 ( a ), ( b ), respectively, face away from the adjacent edge while channels  122   a - 122   b ,  124   a - 124   b ,  126   a - 126   b ,  128   a - 128   b  which supply ink to the bubble chambers for the nozzles farther from the edges  60  and  70 , that is, nozzles  62 ( a )-( b ),  68 ( a )-( b ), face toward the adjacent edge. For a silicon member having a central ink via  129 , the orientation of the channels for the bubble chambers for each nozzle is reversed as shown in FIG. 5 b.    
     As may be appreciated, the orientation of the channels may be such as to not only provide multiple flow paths to each nozzle, the nozzle orientation also provides flow paths which are of substantially the same length. Thus, for the purpose of an example, it will be noted that flowpaths F 1  and F 2  are available to feed nozzle  58   b  and flowpaths F 1 ′ and F 2 ′ are available to feed nozzle  68   a , and that the length and area of flowpath F 1 , F 1 ′, F 2  and F 2 ′ as measured from the edge  60  of the silicon member are not appreciably different such that the path by which the ink travels to a particular nozzle does not appreciably effect filling of the chamber. In this regard, the flow path to each nozzle is preferably from about 40 μm to about 300 μm and most preferably about 85 μm, with the variance between the flowpaths ranging about ∀20%. 
     Without being bound by theory, and for the purpose of example, it has been observed that the following parameters associated with the positioning and sizing of the barriers and channels may effect the flow of ink to the nozzles: 
     
       
         
           
               
               
               
             
               
                   
                   
               
               
                   
                    parameter 
                 description 
               
               
                   
                   
               
             
            
               
                   
                 a 
                 bubble chamber width 
               
               
                   
                 b 
                 bubble chamber length 
               
               
                   
                 c 
                 width of the smallest repeating element 
               
               
                   
                 d1 
                 length of the bubble chamber entry region 
               
               
                   
                 d2 
                 length of the bubble chamber entry region 
               
               
                   
                 e 
                 wall thickness 
               
               
                   
                 w1 
                 width of the bubble chamber entry region 
               
               
                   
                 w2 
                 width of the bubble chamber entry region 
               
               
                   
                   
               
            
           
         
       
     
     Preferred ranges for these parameters are as follows for a printer resolution of 600 dpi and a silicon member having a length of about 14.5 mm, a width of about 0.4 mm and having 2 arrays spaced apart about 804 μm, with 304 nozzles per array. 
     
       
         
           
               
               
               
             
               
                   
                   
               
               
                   
                      Parameter 
                 dimension (μ m) 
               
               
                   
                   
               
             
            
               
                   
                 a 
                      42 ± 10 
               
               
                   
                 b 
                 42 ± 10 
               
               
                   
                 c 
                 42⅓  
               
               
                   
                 d1 
                 20 ± 10 
               
               
                   
                 d2 
                 20 ± 10 
               
               
                   
                 e 
                 10 ± 5  
               
               
                   
                 w1 
                 20 ± 10 
               
               
                   
                 w2 
                 20 ± 10 
               
               
                   
                   
               
            
           
         
       
     
     Accordingly, a significant advantage of the invention relates to the provision of at least two nozzle/heater pairs for each print location. This enables a heretofore unavailable redundancy feature which reduces the detrimental effect of an impaired or failed heater/nozzle. For example, during operation of the printhead, a signal may be received to activate the heater for a desired print location. In the event this heater has failed or its associated nozzle is clogged or otherwise malfunctioning, there will be a lack of ink on the paper to be printed due to the problem with the heater/nozzle. However, due to the redundancy of the printhead of the invention, this lack of ink will only occur during every other print cycle for the desired location, since the corresponding heater/nozzle pair will be activated during the next activation of the instant print location. For example, nozzle/heater  52   a / 72   a  and nozzle/heater  52   b / 72   b  each correspond to the same print location, but are operated alternatively when the print location is activated such that the effect of failure of one of the pair is reduced. 
     Another significant advantage of the invention is that multiple flow paths to a given nozzle/heater may be provided. In this regard, it is noted that nozzle disfunction may result from clogging of the flow path rather than from a problem specific to the heater or nozzle. Thus, provision of more than one flow path, such as the described flow paths F 1  and F 1 ′, reduces the likelihood of nozzle misfunction due to clogging of flowpaths. 
     With reference now to FIG. 7, there is shown another embodiment of a nozzle array in accordance with the invention. Reference numerals corresponding to the embodiment described in connection with FIGS. 5-5 b  are used to indicate the nozzles and related structure, but with a prime (′) suffix. In this embodiment, a single flowpath is provided to flow ink to each nozzle pair of the arrays. For example, a single flowpath feeds nozzles  52   a ′ and  62   a′.    
     Turning now to FIG. 8, there is shown a preferred method for making nozzle plates and arrays in accordance with the invention. In this regard, it is initially noted that prior methods of making nozzle arrays by laser ablation are generally ill-suited for the manufacture of nozzle arrays having a structure in accordance with the invention. 
     For example, flow features provided in accordance with the invention include flow paths and ink chamber arrays that are much more closely spaced relative to one another than conventional ink chamber and nozzle arrays which provide only one nozzle hole for each print location. In addition, the ink chambers according to the invention have finer features, such as a substantially decreased wall thickness, as compared to conventional structures having walls of from about 10 to about 30 microns thick, generally about 10 microns thick. In contrast, ink chambers provided in accordance with the invention preferably have wall thicknesses ranging from about 2 to about 30 microns thick, generally about 4 microns thick. Conventional techniques cannot effectively provide nozzle plates having such features, as explained below in connection with FIGS. 9 and 10, which show, respectively, nozzle structures provided by the method of the invention and provided by a conventional manufacture method. The images of FIGS. 9 and 10 were digitally scanned from images of nozzle plates obtained by use of a scanning electron microscope (SEM) and show about 1% of the total nozzle plate at a magnification of about 500×. 
     As will be noted, the nozzle plate of FIG. 9, which was made in accordance with the method of the invention, is more uniform in construction than the nozzle plate of FIG. 10, which includes a nozzle array structure in accordance with the invention but which was manufactured using a conventional laser ablation method. 
     In this regard, it is initially noted that, conventionally, laser ablation of nozzle plates is accomplished by first ablating the flow channel, ink chamber and via region, after which the nozzle openings, typically circular in shape, are ablated into the centers of the chambers. It has been experienced that this process typically results in damaged or irregular contoured chamber walls which may fail during bonding of the nozzle plate to the chip and/or otherwise fail to provide a suitable ink-tight interface at the chip/plate juncture. As will be appreciated, this results in a lower yield of usable nozzle plates, leakage of ink between the upper edges of the ink chamber walls and the chip, and otherwise unsatisfactory printer performances. 
     It has been further experienced that such shortcomings of conventional processes are manifested to an even greater degree when used to provide structures having finer detail, such as the nozzle plate structures of the invention. For example, with reference to FIG. 10, it will be noticed that the upper edges of the walls are of irregular shape and somewhat ragged. As will be appreciated, these surfaces are difficult to bond to the chip in a manner which provides a substantially ink-tight bond. A result of this is leakage of ink between the upper edges of the chamber walls and the chip. 
     In contrast, FIG. 9 shows a nozzle array of the invention provided in accordance with the preferred method of the invention. As will be noticed, the walls do not include the irregularities of the walls of the array of FIG.  10  and the upper wall edges all lie substantial in the same plane, hence a bond between the chip and the upper wall edges which is significantly more resistant to ink leakage. It will further be noticed that the walls are significantly thinner than those of the array of FIG.  10  and that the other topographical features are significantly finer in detail and more precise than features formed in a nozzle plate member by a conventional technique. 
     Returning now to FIG. 8, a nozzle array structure is provided in accordance with the invention by first selecting the desired locations for the nozzle holes and ablating the area  132  of the nozzle plate material or substrate  130  surrounding the future location of the holes to a predetermined depth, preferably from about 10 to about 40 microns. Next, as indicated by reference numeral  134 , the nozzle holes  136  are ablated in the material, with the unremoved material surrounding each nozzle hole  136  providing sidewalls  138 ,  140  and  142  of a bubble or ink chamber  144 . Each nozzle hole  136  preferably has a square configuration and extends the full thickness of the substrate  130 . The throat regions  146  are then ablated, connecting the bubble chamber  144  with the flow path outside of the chamber  144  to provide the completed structure  148 . 
     While specific embodiments of the invention have been described with particularity above, it will be appreciated that the invention is equally applicable to different adaptations well known in those skilled in the art.