Patent Publication Number: US-8118405-B2

Title: Buttable printhead module and pagewide printhead

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to digitally controlled printing systems, and more particularly to making a pagewidth printhead by butting a plurality of printhead modules. 
     BACKGROUND OF THE INVENTION 
     An inkjet printing system typically includes one or more printheads and their corresponding ink supplies. Each printhead includes an ink inlet that is connected to its ink supply and an array of drop ejectors with each ejector including an ink chamber, an ejecting actuator and an orifice through which droplets of ink are ejected. The ejecting actuator may be one of various types, including a heater that vaporizes some of the ink in the chamber in order to propel a droplet out of the orifice, or a piezoelectric device which changes the wall geometry of the chamber in order to generate a pressure wave that ejects a droplet. The droplets are typically directed toward paper or other recording medium in order to produce an image according to image data that is converted into electronic firing pulses for the drop ejectors as relative motion between the print medium and the printhead is established. 
     Motion of the print medium relative to the printhead can consist of keeping the printhead stationary and advancing the print medium past the printhead while the drops are ejected. This architecture is appropriate if the nozzle array on the printhead can address the entire region of interest across the width of the print medium. Such printheads are often referred to as pagewidth printheads. 
     Manufacturing yield of printhead die decreases for larger die sizes, and in many applications it is not economically feasible to fabricate a pagewidth printhead using a single printhead die that spans the width of the print medium, especially when the width of the print medium is larger than four inches. At the same time, the cost of assembly of the plurality of printhead die makes it economically unfeasible to fabricate a pagewidth printhead if the individual printhead die are too small. In order to provide high quality printing, a printhead die suitable for use as a subunit of a pagewidth printhead may have a nozzle density of 1200 nozzles per inch, and have several hundred to more than one thousand drop ejectors on a single die. In order to control the firing of so many drop ejectors on a printhead die, it is preferable to integrate driving transistors and logic circuitry onto the printhead die. 
     As such, there is a need for a buttable printhead module having driving electronics and logic integrated so that a sufficiently large numbers of drop ejectors can be incorporated on a single module, where sufficient room is available at the butting edge so that drop ejectors and associated electronics are not damaged during separation of the module from the wafer. What is also needed is an alignment feature at the butting edge of the module to accomplish alignment of the modules in both directions in the plane of the modules. 
     SUMMARY OF THE INVENTION 
     According to an aspect of the present invention, a modular printhead includes a first printhead and a second printhead. The first printhead module includes a first alignment feature and at least one array of dot forming elements extending in a first direction along a first substrate. A plurality of electrical contacts is operatively associated with the at least one array of dot forming elements. The plurality of electrical contacts extends in a second direction along the first substrate. The second printhead module includes a second alignment feature and at least one array of dot forming elements extending in a first direction along a second substrate. A plurality of electrical contacts is operatively associated with the at least one array of dot forming elements. The plurality of electrical contacts extends in a second direction along the second substrate. The first direction and the second direction of the first printhead module and the second printhead module are positioned at an angle θ relative to each other, in which 0°&lt;θ&lt;90°. The first alignment feature of the first printhead module and the second alignment feature of the second printhead module are contactable with each other. 
     According to another aspect of the present invention, a printhead module includes a substrate and a drop ejector array extending in a first direction along the substrate. A plurality of electrical contacts is operatively associated with the at least one drop ejector array. The plurality of electrical contacts extends in a second direction along the substrate with the first direction and the second direction being positioned at an angle θ relative to each other, in which 0°&lt;θ&lt;90°. 
     According to another aspect of the present invention, a printhead module includes a substrate, a plurality of drop ejector arrays, and electronic circuitry. The substrate includes a butting edge extending in a first direction along the substrate. The plurality of drop ejector arrays extends substantially parallel to the butting edge of the substrate with a first drop ejector array of the plurality of drop ejector arrays being closest to the butting edge of the substrate. A portion of the electronic circuitry is disposed between the first drop ejector array and the butting edge of the substrate. 
     According to another aspect of the present invention, a method of forming an individual printhead module including an alignment feature includes providing a wafer including a plurality of printhead modules; forming a first alignment feature on a first printhead module of the plurality of printhead modules and forming a complementary second alignment feature on a second printhead module of the plurality of printhead modules using an etching process; and separating the plurality of printhead modules using a cutting operation. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the detailed description of the preferred embodiments of the invention presented below, reference is made to the accompanying drawings, in which: 
         FIG. 1  is a schematic representation of an inkjet printer system; 
         FIG. 2  is a schematic top view of a modular printhead according to an embodiment of this invention; 
         FIG. 3  is a schematic top view of a single printhead module according to an embodiment of this invention; 
         FIG. 4  is a schematic top view of the example shown in  FIG. 3 , but also showing additional details including ink inlets, electrical contacts and electronic circuitry; 
         FIG. 5  is a schematic top view of an embodiment that is similar to that of  FIG. 4 , but with a different type of ink inlets; 
         FIG. 6  is a schematic top view of a modular printhead having a row of butted printhead modules according to an embodiment of this invention; 
         FIG. 7  is a schematic top view of a single printhead module including two sets of independent arrays according to an embodiment of this invention; 
         FIG. 8  is a schematic top view of a modular printhead having a row of butted printhead modules, each including two sets of independent arrays, according to an embodiment of this invention; 
         FIG. 9  is a schematic top view of a single printhead module including four sets of independent arrays according to an embodiment of this invention; 
         FIG. 10  is a schematic top view of a single printhead module including alignment features according to an embodiment of this invention; and 
         FIG. 11  is a schematic top view of two adjacent printhead modules including complementary alignment features according to an embodiment of this invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present description will be directed in particular to elements forming part of, or cooperating more directly with, apparatus in accordance with the present invention. It is to be understood that elements not specifically shown or described may take various forms well known to those skilled in the art. 
     Referring to  FIG. 1 , a schematic representation of an inkjet printer system  10  suitable for use with the present invention is shown. Printer system  10  is described in U.S. Pat. No. 7,350,902, the disclosure of which is incorporated by reference herein. Inkjet printer system  10  includes an image data source  12 , which provides data signals that are interpreted by a controller  14  as being commands to eject drops. Controller  14  includes an image processing unit  15  for rendering images for printing, and outputs signals to an electrical pulse source  16  of electrical energy pulses that are inputted to an inkjet printhead  100 , which includes at least one inkjet printhead die  110 . 
     In the example shown in  FIG. 1 , there are two nozzle arrays. Nozzles in the first array  121  in the first nozzle array  120  have a larger opening area than nozzles in the second array  131  in the second nozzle array  130 . In this example, each of the two nozzle arrays has two staggered rows of nozzles, each row having a nozzle density of 600 per inch. The effective nozzle density then in each array is 1200 per inch (i.e. d= 1/1200 inch in  FIG. 1 ). If pixels on the recording medium  20  were sequentially numbered along the paper advance direction, the nozzles from one row of an array would print the odd numbered pixels, while the nozzles from the other row of the array would print the even numbered pixels. 
     In fluid communication with each nozzle array is a corresponding ink delivery pathway. Ink delivery pathway  122  is in fluid communication with the first nozzle array  120 , and ink delivery pathway  132  is in fluid communication with the second nozzle array  130 . Portions of fluid delivery pathways  122  and  132  are shown in  FIG. 1  as openings through printhead die substrate  111 . One or more inkjet printhead die  110  are included in inkjet printhead  100 , but for greater clarity only one inkjet printhead die  110  is shown in  FIG. 1 . The printhead die are arranged on a support member as discussed below with reference to  FIG. 2 . In  FIG. 1 , first fluid source  18  supplies ink to first nozzle array  120  via ink delivery pathway  122 , and second fluid source  19  supplies ink to second nozzle array  130  via ink delivery pathway  132 . Although distinct fluid sources  18  and  19  are shown, in some applications it may be beneficial to have a single fluid source supplying ink to nozzle the first nozzle array  120  and the second nozzle array  130  via ink delivery pathways  122  and  132  respectively. Also, in some embodiments, fewer than two or more than two nozzle arrays may be included on printhead die  110 . In some embodiments, all nozzles on inkjet printhead die  110  may be the same size, rather than having multiple sized nozzles on inkjet printhead die  110 . 
     Drop forming mechanisms are associated with the nozzles. Drop forming mechanisms can be of a variety of types, some of which include a heating element to vaporize a portion of ink and thereby cause ejection of a droplet, or a piezoelectric transducer to constrict the volume of a fluid chamber and thereby cause ejection, or an actuator which is made to move (for example, by heating a bi-layer element) and thereby cause ejection. A drop ejector includes both a drop forming mechanism and a nozzle. Since each drop ejector includes a nozzle, a drop ejector array can also be called a nozzle array. 
     Electrical pulses from electrical pulse source  16  are sent to the various drop ejectors according to the desired deposition pattern. In the example of  FIG. 1 , droplets  181  ejected from the first nozzle array  120  are larger than droplets  182  ejected from the second nozzle array  130 , due to the larger nozzle opening area. Typically other aspects of the drop forming mechanisms associated respectively with nozzle arrays  120  and  130  are also sized differently in order to optimize the drop ejection process for the different sized drops. During operation, droplets of ink are deposited on a recording medium  20 . 
       FIG. 2  shows a schematic top view of a modular printhead  200  according to an embodiment of this invention. Modular printhead  200  includes three printhead modules  210  (similar to inkjet printhead die  110  but not having nozzles in staggered rows) that are bonded to a support member  205 . Each printhead module  205  includes several arrays  211  of drop ejectors  212 , where the arrays  211  extend in a first direction  215  (also called array direction  215 ). Each printhead module  205  has two butting edges  214  that are substantially parallel to first direction  215 , so that the arrays  211  are substantially parallel to the butting edges  214  of the printhead module  205 . In  FIG. 2 , a gap is shown between the butting edges  214  of adjacent printhead modules in order to distinguish the different printhead modules  205 . 
     A portion of a sheet of recording medium  20  is shown near the modular printhead  200 , and a raster line  22  of image data printed by modular printhead  200  is indicated. Array direction  215  is at an angle θ relative to raster line  22 . Toward the right side of  FIG. 2 , raster line  22  has been broken up into three segments  22   a ,  22   b  and  22   c  which are displaced from one another so that they may be more readily distinguished. The pixels in raster line segments  22   a ,  22   b  and  22   c  are printed by arrays  211   a ,  211   b  and  211   c  respectively. Recording medium  20  is moved along media advance direction  208  during printing. The firing of the different drop ejectors  212  within arrays  211  is timed relative to one another so that ink drops land on the horizontal raster line  22 , rather than in the sawtooth arrangement of the arrays  211 . Drop ejectors  212  within an array  211  are arranged such that the projection of the uppermost drop ejector of one array  211  onto raster line  22  is adjacent to the projection of the lowermost drop ejector of the adjacent array  211  onto raster line  22 . In other words, the uppermost drop ejector of one array  211  is “projectionally adjacent” to the lowermost drop ejector of the adjacent array  211 . In this way, the printed dots making up raster line  22  all have the same horizontal spacing. When the adjacent arrays  211  are on different modules  210 , the spacing at the adjacent butting edges  214  needs to be correct so that the projections of the uppermost drop ejector  212  and the lowermost drop ejector onto raster line  22  have the correct horizontal spacing and so that there is not a stitch error seen in the raster line  22 . In, addition, adjacent die modules  210  should not be displaced from one another along direction  208 , or displaced line segments will result at the stitch in the raster line  22 . 
     A schematic top view of a single printhead module  210  is shown magnified in  FIG. 3  in order to clarify the geometry of the arrays  211 . The center to center distance between two corresponding nozzles in adjacent arrays  211  is denoted as D. The center to center distance between two adjacent nozzles in the same array  211  is denoted as d. The number of drop ejectors  212  within a single array  211  is n. The number of arrays  211  on a printhead module  210  is m, so that the total number of drop ejectors  212  within a printhead module is N=m×n. In the example shown in  FIG. 3 , n=15, m=11 and N=165. 
     In order to have the proper horizontal spacing of printhead dots on the raster line  22 , D=nd cos θ. The distance from butting edge  214  to the nearest array  211  is approximately D/2. By appropriately selecting n, d and θ when designing printhead module  210 , a large enough D/2 can be provided so that there is room for electronic circuitry, ink delivery, and alignment features between butting edge  214  and the nearest array  211 . For example, if d=42.3 microns, n=32 and θ=60 degrees, then D=677 microns. The overall length L of the module  210  is L=mD. For a printhead module  210  having 640 drop ejectors  212  in m=20 arrays  211  of n=32 drop ejectors, the length L of the printhead module  210  is 13.54 mm. In this same example, the horizontal spacing of dots on raster line  22  is d cos θ=21.7 microns, i.e. 1200 dots per inch. The height H of the array  211  (a vertical projection of the distance from the uppermost nozzle in the array to the lowermost nozzle) is (n−1) d sin θ=1.14 mm in this example, so the overall height of the printhead module  210  including space for electrical contacts at the non butting edges of the printhead module  210  could be approximately 1.3 mm. 
     The horizontal spacing of dots on raster line  22  can be modified by designing a printhead module having a different angle θ. Because d cos θ decreases as θ approaches 90 degrees, the larger that θ is, the smaller will be the horizontal spacing of dots on raster line  22  (i.e. the higher the printing resolution). For θ=60 degrees, cos θ=0.5. While θ can range between 0 degrees and 90 degrees, most embodiments will have a value of θ that is between 45 degrees and about 85 degrees. 
       FIG. 4  is a schematic top view of the example shown in  FIG. 3 , but also showing additional details including ink inlets  220 , electronic circuitry  230 , and electrical contacts  240 . The ink inlets  220  (shown in the example of  FIG. 4  as staggered segments on both sides of each array  211 ) are of the dual feed type described in more detail in US Patent Application Publication No. US 2008/0180485 A1. Ink can be fed from the back side of printhead module  210  to adjacent groups of drop ejectors by segmented ink inlets  220  consisting of slots  221  that can be made, for example, as described in U.S. patent application Ser. No. 12/241,747, filed Sep. 30, 2008, Lebens et al. Electronic circuitry  230  can include driver transistors to provide electrical pulses from electrical pulse source  16  to fire the drop ejectors  212 , as well as logic electronics to control the driver transistors so that the correct drop ejectors  212  are fired at the proper time, according to image data provided by controller  14  and image processing unit  15 . Leads from the driver transistors are able to access the appropriate drop ejectors  212  from either side of array  211  between slots  221 . Electrical signals are provided to printhead module  210  by a plurality of electrical contacts  240 , which extend along one or both nonbutting edges  209  of printhead module  210  along direction  206 . Electrical contacts  240  are interconnected by wire bonding or tape automated bonding, for example, to a circuit board (not shown in  FIG. 2 ) on support member  205 . Because of the inclusion of the logic and driver circuitry in electronic circuitry  230 , relatively few electrical contacts  240  (on the order of twenty) are required for firing the hundreds of drop ejectors  211 . Note that each array  211  of drop ejectors  212 , including the arrays  211  nearest the butting edges  214 , has associated electronic circuitry  230  located on both sides of the array  211 . As a result, a portion of the electronic circuitry  230  on printhead module  210  is located between a butting edge  214  and the array  211  of drop ejectors  212  that is closest to (and substantially parallel to) that butting edge  214 . 
       FIG. 5  is a schematic top view of an embodiment that is similar to that of  FIG. 4 , but with a different type of ink inlets  220 , such that the ink flows continuously beneath the corresponding array  211 , from one end of the array to another end. In  FIG. 5 , the ink inlets  220  have a first end  222  from which the ink flows (beneath the array  211 ) toward a second end  223 . Ink can exit at the backside of printhead module  211  from second end  223  and be recirculated to enter at the backside near first end  222 . As described in US Patent Application Publication No. US 2007/0291082 A1, a second flow path (not shown in  FIG. 5 , but optionally below the first flow path) can be provided opposite the first flow path in order to provide stagnation points adjacent each nozzle opening. 
       FIG. 6  is a schematic top view of a modular printhead  200  having a row  213  of three butted printhead modules  210 , according to an embodiment of this invention, but with more details provided for the printhead modules  210  than are provided in  FIG. 2 . In particular, ink inlets  220  of the type shown in  FIG. 5 , as well as electronic circuitry  230 , and electrical contacts  240  are shown. In particular, portions of electronic circuitry  230  located between a butting edge  214  and an adjacent array  211  are shown for two adjacent printhead modules  210 . For all three printhead modules  210  in row  213 , arrays  211  of drop ejectors  212  extend along a first direction (array direction  215 ), and a plurality of electrical contacts  240  extend along a second direction (direction of plurality of electrical contacts  206 ), where the angle θ between the first direction  215  and the second direction  206  is greater than 0 degrees and less than 90 degrees. Butting edges  214  are substantially parallel to first direction  215  and nonbutting edges  209  are substantially parallel to second direction  206 . Alignment features (described below with reference to at least  FIGS. 10 and 11 ) are contactable between adjacent printhead modules  210 . 
     In the embodiments described above, there is only one drop ejector  212  on a printhead module  210  that can line up with a given pixel site on raster line  22 . In such embodiments, in order to print different colored inks, for example, a second row of printhead modules  210  can be provided on the support member  205 , where the second row of printhead modules  210  is parallel to row  213 . The second row of printhead modules  210  can be used to print a different color ink, or different sized dots of the same color ink, or redundant dots of the same color ink in different embodiments. 
       FIG. 7  shows an embodiment of the present invention in which, rather than a second row of printhead modules  210 , two sets of independent arrays  211   a  and  211   b  are provided on a single printhead module  210 , such that a first array  216  of the arrays  21  la has a second corresponding array  217  of the arrays  211   b , where drop ejectors  212  in first array  216  line up (or offset at desired distance, e.g., ½ pixel) with drop ejectors  212  in corresponding second array  217 . Excellent alignment of drop ejectors  212  in first array  216  and drop ejectors  212  in corresponding second array  217  is provided because first array  216  and corresponding second array  217  are fabricated together on the same printhead module  210 . Thus excellent registration of dots printed by drop ejectors in first array  216  and corresponding second array  217  is readily achieved. In some embodiments of this type, different colored ink will be supplied at ink inlets  220   a  for arrays  211   a  than the ink supplied at ink inlets  220   b  for arrays  220   b , so that the printhead module  210  of  FIG. 7  can be a two-color printhead module. Four color printing (cyan, magenta, yellow and black) can be achieved by having two rows of two-color modules  210  on a support member  205 , for example. In other embodiments, the same color ink is supplied at ink inlets  220   a  and  220   b , and redundant drop ejectors  212  are thus provided in order to disguise print defects (as is well known in the art). Alternatively, if the drop ejectors  212  in arrays  211   a  provide different sized ink drops than the drop ejectors  212  in arrays  211   b , smoother gradations in image tone can be provided. 
       FIG. 8  shows a row  213  of two butted printhead modules  210   a  and  210   b  of the type shown in  FIG. 7  (two butted 2-color printhead modules, for example). Note that at the butting edges  214 , first array  216   a  on printhead module  210   a  has corresponding second array  217   b  that is located on printhead module  210   b . Also note that first array  216   b  on printhead module  210   b  has no corresponding second array, and second array  217   a  on printhead module  210   a  has no corresponding first array. Thus, the very end arrays in a row  213  of printhead modules are not capable of full color printing, but that is typically small wastage. 
       FIG. 9  shows a printhead module  210  capable of four color printing (cyan, magenta, yellow and black), according to an embodiment of the present invention. A first array  216  and its corresponding second array  217 , corresponding third array  218  and corresponding fourth array  219  are indicated. Electrical contacts  240  disposed along both nonbutting edges  209  of the printhead module  210  provide signals for the electronic circuitry  230  corresponding to the arrays closest to the nonbutting edges of the printhead module  210 , as well as for the electronic circuitry corresponding to arrays within the interior of the printhead module  210 . In the discussion above regarding a single-color printhead module  210  having m=20 arrays  211 , each array having 32 drop ejectors  212  with a d=42.3 microns and θ=60 degrees, the length of the printhead module  210  (the distance between butting edges  214 ) was calculated to be 13.54 mm, and the distance between nonbutting edges  209  was estimated to be around 1.3 mm. For a four-color printhead module  210  having similar array geometries, the distance between butting edges  214  would still be 13.54 mm, but the distance between nonbutting edges  209  would be about 5 mm. 
     In some embodiments relative alignment of the printhead modules  210  can be accomplished in various ways, for example, visually aligning the printhead modules. In other embodiments, however, alignment features can be provided such that when alignment features of adjacent printhead modules  210  contact each other, the printhead modules  210  are aligned with respect to each other.  FIG. 10  schematically shows a printhead module  210  having such alignment features according to an embodiment of this invention. In the example of  FIG. 10 , the alignment features include two projections  252  on the butting edge  214  on the left side of the printhead module  210 , and two corresponding indentations  254  on the butting edge  214  on the right side of printhead module  210 . The projections  252  are sized to fit into the indentations  254  of an adjacent printhead module  210  (see  FIG. 11 ), such that when the projections  252  contact the indentations  254  of the adjacent printhead module  210 , the two printhead modules  210  are aligned relative to one another in two dimensions. Optionally, the dimensions of the projections  252  and the corresponding indentations  254  can be designed such that when projections  252  of one printhead module  210  contact the indentations  254  of an adjacent printhead module  210 , a gap  256  is provided at butting edge  214 , except at the contact points of the projections  252  and indentations  254 . Such a gap  256  can be advantageous, in that there is less susceptibility to misalignment due to contamination or other unintended material being present at the butting edge  214 . A convenient place to locate the projections  252  and indentations  254 , as shown in  FIG. 10 , is at the butting edge  214 , but near the nonbutting edge  209 , because there are typically no critical features such as electronic circuitry  230  adjacent the butting edge  215  near the nonbutting edge  209 . 
     The configuration of projections  252  and indentations  254  shown in  FIG. 10  is just one example of alignment features that can be used in different embodiments of the invention. Rather than having two projections  252  on one butting edge  214  and two indentations  254  on the other butting edge  214 , there can be a projection  252  near the top of one butting edge  214  and an indentation  254  near the bottom of that butting edge  214 . The other butting edge  214  would have an indentation  254  near the top and a projection  252  near the bottom. In other words, a first alignment feature on a first printhead module can include two projections  252 , and a second alignment feature on a second printhead module can include two indentations  254  that are complementary to the two projections  252  of the first alignment feature, as in  FIGS. 10 and 11 . Alternatively, the first alignment feature on the first printhead module can include a projection  252  and an indentation  254 , and the second alignment feature on the second printhead module can include an indentation  254  and a projection  252  that are complementary to the projection  252  and indentation  254  of the first alignment feature. 
     Projections  252  and indentations  254  can have a variety of shapes, including triangular, trapezoidal, rounded, etc., as long as the indentations  254  of one printhead module  210  have the proper shape and dimensions to contact the projections  252  of the adjacent printhead module  210  and provide relative alignment of the two printhead modules  210 . Projections  252  and indentations  254  can have complementary shapes relative to one another. 
     Many printhead modules  210  are fabricated together on a single wafer. For example, a printhead module  210  that is a thermal inkjet printhead die is typically fabricated on a silicon wafer that is around six inches or eight inches in diameter. After wafer processing is completed, it is necessary to separate the individual printhead modules  210  from the wafer. For printhead modules  210  having straight edges, the printhead modules  210  can be separated from the wafer by dicing, even if the printhead module  210  is parallelogram-shaped. However, if edges of the printhead module  210  have projections  252  extending outward, such projections  252  would be cut off during dicing. One way to precisely form the projections  252  and the corresponding indentations  254  is to use an etching process, such as deep reactive ion etching (commonly known in the art as DRIE). DRIE can provide butting alignment features with accuracy on the order of 1 micron. 
       FIG. 11  was described above in relation to butting two adjacent printhead modules  210  together to assemble a modular printhead. However,  FIG. 11  can also be used to describe the separation of two adjacent printhead modules  210  on a printhead wafer. As described above, the separation of adjacent printhead modules  210  at the projections  252  and corresponding indentations  254  on the adjacent module can be performed by DRIE. One method of achieving separation along the rest of the butting edge without cutting through projections  252  is to use a cutting operation such as water jet or laser microjet, where nonstraight cuts are possible. In water jet a high pressure, high velocity stream of water cuts by erosion. In laser microjet a pulsed laser beam is guided by a low pressure water jet, so that the water removes debris and cools the material. The width of the cut (or kerf) provided by water jet or laser microjet is typically wider than would be provided by DRIE at the projections  252  and indentations  254 , so that a gap  256  is provided between adjacent printhead modules  210  when they are subsequently butted with the corresponding projections  252  and indentations  254  in contact with one another. The precision and straightness of the portions of butting edge  214  that are cut by water jet or laser microjet does not need to be as good as that provided by DRIE to make the projections  252  and indentations  254 , because the gap  256  prevents those portions of the butting edge from coming into contact. Cutting of the nonbutting edges  209  can be done with water jet or laser microjet. Alternatively, after separation along the butting edges  214  of all of the printhead modules  210  on the wafer has been completed, the adjacent nonbutting edges  209  can be cut by dicing. 
     The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the scope of the invention. In particular, although the embodiments described above were done so with reference to inkjet drop ejectors, more generally the invention can be used for dot forming elements (other than drop ejectors) on printhead modules other than inkjet printhead modules. 
     PARTS LIST 
     
         
           10  Inkjet printer system 
           12  Image data source 
           14  Controller 
           15  Image processing unit 
           16  Electrical pulse source 
           18  First fluid source 
           19  Second fluid source 
           20  Recording medium 
           22  Raster line 
           100  Inkjet printhead 
           110  Inkjet printhead die 
           111  Printhead die substrate 
           120  First nozzle array 
           121  Nozzle(s) in first nozzle array 
           122  Ink delivery pathway (for first nozzle array) 
           130  Second nozzle array 
           131  Nozzle(s) in second nozzle array 
           132  Ink delivery pathway (for second nozzle array) 
           181  Droplet(s) (ejected from first nozzle array) 
           182  Droplet(s) (ejected from second nozzle array) 
           200  Modular printhead 
           205  Support member 
           206  Direction of plurality of electrical contacts 
           208  Media advance direction 
           209  Nonbutting edge 
           210  Printhead module 
           211  Array(s) (of drop ejectors) 
           212  Drop ejector(s) 
           213  Row 
           214  Butting edge(s) 
           215  Array direction 
           216  First array 
           217  Corresponding second array 
           218  Corresponding third array 
           219  Corresponding fourth array 
           220  Ink inlet(s) 
           221  Slots 
           230  Electronic circuitry 
           240  Electrical contacts 
           252  Alignment feature (projection) 
           254  Alignment feature (indentation) 
           256  Gap