Patent Publication Number: US-8523330-B2

Title: Recording apparatus, liquid droplet discharging head, and liquid droplet discharging head circuit board with improved wiring pattern

Description:
TECHNICAL FIELD 
     The present specification describes a recording apparatus, a liquid droplet discharging head, and a liquid droplet discharging head circuit board, and more particularly a recording apparatus, a liquid droplet discharging head, and a liquid droplet discharging head circuit board for discharging a liquid droplet by converting electric power into liquid droplet discharging energy. 
     DISCUSSION OF THE BACKGROUND 
     A recording apparatus, such as a copying machine, a printer, a facsimile machine, or a multifunction printer having copying, printing, scanning, and facsimile functions, forms an image on a recording medium (for example, a sheet) with ink and according to image data. For example, an ink droplet is discharged from a nozzle of a recording head. While the recording head moves in a main scanning direction, the recording head discharges an ink droplet onto a sheet to form an image on the sheet. 
     Generally, the recording head discharges an ink droplet by a bubble jet method, a piezo jet method, or a liquid droplet jet method. In the bubble jet method, a heater heats the ink to generate a bubble. A pressure of the bubble discharges an ink droplet from the recording head. In the piezo jet method, an ink droplet is discharged by an electric and mechanical displacement of a bulk of a piezoelectric element. In the liquid droplet jet method, a micro fluid element and a surface acoustic wave propagate in the ink to cause ejection of an ink droplet. In the bubble jet method, the piezo jet method, and the liquid droplet jet method, electric power of from 0.1 watts to several watts is needed, resulting in migration and a broken wire. 
     To address the above-described problems, the recording head includes a liquid droplet discharging head circuit board in which a protective layer is formed on a wiring pattern.  FIGS. 1 and 2  illustrate a liquid droplet discharging head circuit board  100 R of the recording head.  FIG. 1  is a plane view of the liquid droplet discharging head circuit board  100 R.  FIG. 2  is a sectional view of the liquid droplet discharging head circuit board  100 R taken along line A 1 -A 1  of  FIG. 1 . As illustrated in  FIGS. 1 and 2 , the liquid droplet discharging head circuit board  100 R includes a board  1 R, an oxide film  2 R, an electricity-heat conversion element  3 R, and a wiring pattern  4 R. As illustrated in  FIG. 2 , the liquid droplet discharging head circuit board  100 R further includes a first protective layer  5 R and a second protective layer  6 R. 
     The board  1 R includes silicon. The oxide film  2 R is formed on the board  1 R. The electricity-heat conversion element  3 R includes a heat-generating resistance body film formed at a predetermined position on the oxide film  2 R and having a predetermined size. The electricity-heat conversion element  3 R serves as a discharging energy generating element. The wiring pattern  4 R is formed on the oxide film  2 R and has a predetermined pattern. The wiring pattern  4 R electrically connects the electricity-heat conversion element  3 R to a power source (not shown) to supply power to the electricity-heat conversion element  3 R. The first protective layer  5 R is formed on the electricity-heat conversion element  3 R and the wiring pattern  4 R to cover the electricity-heat conversion element  3 R and the wiring pattern  4 R, and includes an insulating material. The second protective layer  6 R is formed on the first protective layer  5 R and includes an insulating material. The wiring pattern  4 R includes a broad band conductive film having a substantially constant thickness. A width W 1  of the wiring pattern  4 R is not smaller than about 10 μm, for example. 
     The first protective layer  5 R can reduce migration. However, the first protective layer  5 R cannot directly prevent a broken wire of the wiring pattern  4 R. 
     SUMMARY 
     This patent specification describes a novel recording apparatus. One example of a novel recording apparatus includes a liquid droplet discharging head and a tank. The liquid droplet discharging head discharges a liquid droplet. The tank supplies a liquid to the liquid droplet discharging head. The liquid droplet discharging head includes a liquid droplet discharging head circuit board including a board substrate and a writing pattern. The wiring pattern is located on the board substrate to supply power and includes a plurality of divided wiring patterns formed by dividing at least a part of the wiring pattern in a width direction of the wiring pattern. 
     This patent specification further describes a novel liquid droplet discharging head for discharging a liquid droplet. One example of a novel liquid droplet discharging head includes a liquid droplet discharging head circuit board and a liquid droplet outlet. A liquid droplet is discharged through the liquid droplet outlet. The liquid droplet discharging head circuit board includes a board substrate and a wiring pattern. The wiring pattern is located on the board substrate to supply power and includes a plurality of divided wiring patterns formed by dividing at least a part of the wiring pattern in a width direction of the wiring pattern. 
     This patent specification further describes a novel liquid droplet discharging head circuit board. One example of a novel liquid droplet discharging head circuit board includes a board substrate and a wiring pattern. The wiring pattern is located on the board substrate to supply power and includes a plurality of divided wiring patterns formed by dividing at least a part of the wiring pattern in a width direction of the wiring pattern. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete appreciation of the disclosure and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein: 
         FIG. 1  is a plane view of a related art liquid droplet discharging head circuit board; 
         FIG. 2  is a sectional view of the liquid droplet discharging head circuit board shown in  FIG. 1 , taken along line A 1 -A 1  of  FIG. 1 ; 
         FIG. 3  is a schematic view of a recording apparatus according to an exemplary embodiment; 
         FIG. 4  is a perspective view of a printing mechanism of the recording apparatus shown in  FIG. 3 ; 
         FIG. 5  is a perspective view of a liquid cartridge of the printing mechanism shown in  FIG. 4 ; 
         FIG. 6  is a plane view of a liquid droplet discharging head circuit board of the liquid cartridge shown in  FIG. 5 ; 
         FIG. 7  is a sectional view of the liquid droplet discharging head circuit board shown in  FIG. 6 , taken along line B 1 -B 1  of  FIG. 6 ; 
         FIG. 8  is a plane view of a liquid droplet discharging head circuit board of the liquid cartridge shown in  FIG. 5 , according to another exemplary embodiment; 
         FIG. 9  is a sectional view of the liquid droplet discharging head circuit board shown in  FIG. 8 , taken along line B 2 -B 2  of  FIG. 8 ; 
         FIG. 10  is a graph illustrating a relationship between an allowable electric current per unit wiring width and a wiring width of the liquid droplet discharging head circuit board shown in  FIG. 8 ; 
         FIG. 11  is an enlarged view of the liquid droplet discharging head circuit board shown in  FIG. 7 ; 
         FIG. 12  is another enlarged view of the liquid droplet discharging head circuit board shown in  FIG. 7 ; 
         FIG. 13  is a graph illustrating a relationship between a distance between divided wiring patterns and a thickness of a first protective layer between divided wiring patterns of the liquid droplet discharging head circuit board shown in FIG.  12 ; 
         FIG. 14  is a plane view of a liquid droplet discharging head circuit board of the liquid cartridge shown in  FIG. 5 , according to yet another exemplary embodiment; 
         FIG. 15  is a sectional view of the liquid droplet discharging head circuit board shown in  FIG. 14  taken on line B 3 -B 3  of  FIG. 14 ; 
         FIG. 16  is a plane view of an example of the liquid droplet discharging head circuit board shown in  FIG. 14 ; 
         FIG. 17  is a perspective view of a liquid droplet discharging head of the liquid cartridge shown in  FIG. 5 ; and 
         FIG. 18  is a sectional view of the liquid droplet discharging head shown in  FIG. 17 . 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     In describing exemplary embodiments illustrated in the drawings, specific terminology is employed for the sake of clarity. However, the disclosure of this patent specification is not intended to be limited to the specific terminology so selected and it is to be understood that each specific element includes all technical equivalents that operate in a similar manner. 
     Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views, in particular to  FIG. 3 , an image forming apparatus  17  according to an exemplary embodiment is explained. 
       FIG. 3  is a sectional view of the image forming apparatus  17 . As illustrated in  FIG. 3 , the image forming apparatus  17  includes a paper tray  28 , a bypass tray  29 , a feeding roller  31 , a friction pad  32 , a guide  33 , a conveying roller  34 , a roller  35 , a regulating roller  36 , a guide  37 , a printing mechanism  19 , a conveying roller  38 , a spur  39 , an output roller  40 , a spur  41 , guides  42  and  43 , and an output tray  30 . The printing mechanism  19  includes a carriage  18 , a plurality of recording heads  15 , a main guide rod  20 , and a sub guide rod  21 . 
     The image forming apparatus  17 , serving as a recording apparatus, may be a copying machine, a printer, a facsimile machine, and a multifunction printer having copying, printing, scanning, and facsimile functions. In this non-limiting exemplary embodiment, the image forming apparatus  17  functions as a color printer for forming a color image on a recording medium. However, the image forming apparatus  17  may be a monochrome printer for forming a monochrome image on a recording medium and may include a single recording head  15 . 
     The paper tray  28  is disposed in a lower portion of the image forming apparatus  17  and is attachable to and detachable from the front of the image forming apparatus  17 . The paper tray  28  loads a recording medium (for example, sheets P). The bypass tray  29  is opened from and closed to a side of the image forming apparatus  17 . The bypass tray  29  loads a special sheet P (for example, thick paper, a postcard, and an OHP (overhead projector) transparency). The feeding roller  31  and the friction pad  32  feed sheets P one by one from the paper tray  28 . The guide  33  guides the sheet P toward the conveying roller  34 . The conveying roller  34  conveys and reverses the sheet P. The roller  35  pressingly contacts an outer circumferential surface of the conveying roller  34  and feeds the sheet P toward the regulating roller  36 . When a sheet P is placed on the bypass tray  29 , rollers (not shown) disposed between the bypass tray  29  and the roller  35  feed the sheet P from the bypass tray  29  toward the roller  35 . The regulating roller  36  regulates an angle of the sheet P fed by the conveying roller  34  and the roller  35 , and feeds the sheet P toward the printing mechanism  19 . A sub-scanning motor (not shown) rotates the conveying roller  34  via gears. The guide  37  is disposed under the printing mechanism  19 , and guides the sheet P fed by the feeding roller  34  and the regulating roller  36  toward the conveying roller  38  and the spur  39 . The printing mechanism  19  forms an image on the sheet P according to image data. The conveying roller  38  and the spur  39  are disposed downstream from the guide  37 , and feed the sheet P bearing the image toward the output roller  40  and the spur  41 . The guides  42  and  43  form an output path between the guide  37  and the output tray  30 , and guide the sheet P bearing the image from the guide  37  toward the output tray  30 . The output roller  40  and the spur  41  feed the sheet P bearing the image onto the output tray  30 . The output tray  30  receives the sheet P bearing the image. 
     The carriage  18  is movable in a main scanning direction and carries the recording heads  15 . The main guide rod  20  and the sub guide rod  21  are supported by side plates (not shown) and slidably support the carriage  18  in a manner that the carriage  18  is movable in the main scanning direction. The recording heads  15 , serving as liquid droplet discharging heads, discharge liquid droplets (for example, ink droplets) onto a sheet P fed by the conveying roller  34  and the regulating roller  36 . 
     To start printing an image on a sheet P, the carriage  18  moves in the main scanning direction so that the recording heads  15  mounted on the carriage  18  discharge ink droplets according to an image signal. Specifically, the recording heads  15  discharge ink droplets onto a sheet P while the sheet P stops so as to print an image for one line. The sheet P is conveyed for a predetermined length so as to print an image for the next line. When a signal to finish the printing operation or a signal indicating that the tail edge of the sheet P in a sheet conveyance direction reaches a printing area of the printing mechanism  19  is output, the printing operation is finished and the sheet P is output onto the output tray  30 . 
       FIG. 4  is a perspective view of the printing mechanism  19 . As illustrated in  FIG. 4 , the printing mechanism  19  further includes ink cartridges  14 , a sub scanning motor  44 , a main scanning motor  22 , a driving pulley  23 , a timing belt  25 , a driven pulley  24 , and a recovery device  26 . 
     The recording heads  15  discharge ink droplets in yellow, cyan, magenta, and black colors. Each of the recording heads  15  includes a nozzle (not shown) for discharging an ink droplet. The nozzles of the recording heads  15  are arranged in a direction perpendicular to the main scanning direction in a manner that the nozzles discharge ink droplets downward onto a sheet P. The ink cartridges  14 , serving as liquid cartridges, contain yellow, cyan, magenta, and black inks, respectively. The carriage  18  carries the ink cartridges  14 . The ink cartridges  14  can be replaced with new ones when the ink cartridges  14  become empty. 
     The ink cartridge  14  includes a ventilation hole (not shown), an ink supplying hole (not shown), and a porous body (not shown). The ventilation hole is disposed in an upper portion of the ink cartridge  14 . The ink supplying hole is disposed in a lower portion of the ink cartridge  14  and supplies ink to the recording head  15 . The porous body is disposed in the ink cartridge  14  and contains ink. A capillary force of the porous body maintains the ink to be supplied to the recording head  15  to have a slight, negative pressure. According to this non-limiting exemplary embodiment, the printing mechanism  19  includes a plurality of recording heads (i.e., the recording heads  15 ). However, the printing mechanism  19  may include a single recording head. 
     The carriage  18  slidably engages with the main guide rod  20  at a rear portion of the carriage  18  (i.e., at a downstream portion in the sheet conveyance direction). The carriage  18  slidably engages with the sub guide rod  21  at a front portion of the carriage  18  (i.e., at an upstream portion in the sheet conveyance direction). The sub scanning motor  44  moves the carriage  18  in a sub scanning direction. 
     The main scanning motor  22  moves the carriage  18  in the main scanning direction. Specifically, the main scanning motor  22  drives the driving pulley  23 . The timing belt  25  is looped over the driving pulley  23  and the driven pulley  24 . The rotating driving pulley  23  rotates the driven pulley  24  via the timing belt  25 . The timing belt  25  is fixed to the carriage  18 . Thus, when the main scanning motor  22  rotates back and forth, the carriage  18  moves back and forth in the main scanning direction. 
     The recovery device  26  is disposed in one of non-printing areas in the main scanning direction, where the recording heads  15  do not discharge ink droplets onto a sheet P. The recovery device  26  recovers the recording heads  15 . The recovery device  26  includes caps (not shown), sucking members (not shown), cleaners (not shown), and a waste ink container (not shown). 
     While the recording heads  15  are in a standby mode and do not discharge ink droplets, the carriage  18  stops above the recovery device  26 . The caps of the recovery device  26  cap the nozzles of the recording heads  15  to cause the nozzles to retain moisture. Thus, ink droplets on the nozzles are not dried and thereby faulty discharging can be prevented. Further, the recording heads  15  discharge ink droplets not used for printing an image on a sheet P. Thus, viscosities of ink droplets on the nozzles are maintained at a predetermined level and thereby a steady discharging performance level may be maintained. 
     In the recovery device  26 , when faulty discharging occurs, the caps cap the nozzles. The sucking members are connected to the caps, and suck ink droplets and air bubbles from the nozzles of the recording heads  15  via tubes (not shown). The cleaners remove ink droplets and dust adhered to the nozzles. Thus, faulty discharging is dissolved. The sucked ink droplets are delivered to the waste ink container disposed in a lower portion of the image forming apparatus  17  (depicted in  FIG. 3 ). The waste ink container contains an ink absorber for absorbing and holding the ink droplets. 
       FIG. 5  is a perspective view of the ink cartridge  14 . As illustrated in  FIG. 5 , the ink cartridge  14  includes the recording head  15  and an ink tank  16 . The recording head  15  includes a liquid droplet discharging head circuit board  100  and an ink outlet  11   a . The ink tank  16  for holding a supply of ink, serving as a tank for holding a supply of ink, supplies ink to the recording head  15 . In the ink cartridge  14 , the ink tank  16  is integrated with the recording head  15  including the liquid droplet discharging head circuit board  100 . The liquid droplet discharging head circuit board  100  converts electric power into ink droplet discharging energy to discharge an ink droplet. The ink droplet is discharged through the ink outlet  11   a  (i.e., a liquid droplet outlet) onto a sheet P. 
     When the ink tank is integrated with the recording head in conventional ink cartridges, a decreased yield of the recording head causes a failure of the ink cartridge. On the other hand, when the recording head  15  is configured as described above to reduce ink droplet discharging errors of the recording head  15  caused by heat, the number of defective ink cartridges  14  produced in manufacturing processes can be reduced, resulting in an increased yield and reduced manufacturing costs of the ink cartridge  14 . 
       FIGS. 6 and 7  illustrate the liquid droplet discharging head circuit board  100  according to an exemplary embodiment.  FIG. 6  is a plane view of the liquid droplet discharging head circuit board  100 .  FIG. 7  is a sectional view of the liquid droplet discharging head circuit board  100  taken along line B 1 -B 1  of  FIG. 6 . As illustrated in  FIGS. 6 and 7 , the liquid droplet discharging head circuit board  100  includes a board substrate  1  (depicted in  FIGS. 6 and 7 ), an oxide film  2  (depicted in  FIGS. 6 and 7 ), an electricity-heat conversion element  3  (depicted in  FIGS. 6 and 7 ), a wiring pattern  4  (depicted in  FIG. 6 ), a first protective layer  5  (depicted in  FIG. 7 ), and a second protective layer  6  (depicted in  FIG. 7 ). The wiring pattern  4  includes a plurality of divided wiring patterns  4   a  (depicted in  FIGS. 6 and 7 ) and a plurality of slits S 1  (depicted in  FIG. 6 ). 
     The board substrate  1  includes silicon. The oxide film  2  is formed on the board substrate  1 . The electricity-heat conversion element  3 , serving as a discharging energy generating element, includes a heat-generating resistance body film formed at a predetermined position on the oxide film  2  and having a predetermined size. The electricity-heat conversion element  3  bridges both end portions of the wiring pattern  4  formed on the oxide film  2 . The wiring pattern  4  is formed on the oxide film  2  and has a predetermined pattern. The wiring pattern  4  includes a conductive material and electrically connects the electricity-heat conversion element  3  to a power source (not shown) to supply power to the electricity-heat conversion element  3 . The first protective layer  5  is formed on the electricity-heat conversion element  3  and the wiring pattern  4  and includes an insulating material. The second protective layer  6  is formed on the first protective layer  5  and includes an insulating material. 
     A width W 1  (depicted in  FIG. 6 ) of the wiring pattern  4  is not smaller than about 10 μm for example. At least a part of the wiring pattern  4  is divided in a width direction of the wiring pattern  4  into the plurality of divided wiring patterns  4   a . According to this non-limiting exemplary embodiment, the wiring pattern  4  is divided into four divided wiring patterns  4   a , for example. The divided wiring pattern  4   a  has a narrow width (i.e., a width W 2  depicted in  FIGS. 6 and 7 ). Namely, the wiring pattern  4  does not include a conductive film having the width W 1  like the wiring pattern  4 R having the width W 1  illustrated in  FIG. 1 , but includes the plurality of divided wiring patterns  4   a  arranged in parallel to each other. The slit S 1 , at which the oxide film  2  is exposed, is formed between the adjacent divided wiring patterns  4   a . Thus, the plurality of slits S 1  extend in a longitudinal direction of the divided wiring patterns  4   a.    
     The width W 2  corresponds to a width of an area in which an allowable electric current per unit wiring width increases. 
     As described above, according to this non-limiting exemplary embodiment, the liquid droplet discharging head circuit board  100  includes the electricity-heat conversion element  3  and the wiring pattern  4 . The electricity-heat conversion element  3  bubbles the ink so that the nozzle of the recording head  15  discharges an ink droplet. The wiring pattern  4  connects the electricity-heat conversion element  3  to the power source to supply power to the electricity-heat conversion element  3 . At least a part of the wiring pattern  4  is divided into the plurality of divided wiring patterns  4   a  having a narrow width in the width direction of the wiring pattern  4 . The divided wiring patterns  4   a  are spaced from each other with the slit S 1  in between. According to this non-limiting exemplary embodiment, the wiring pattern  4  is divided into the four divided wiring patterns  4   a . However, the wiring pattern  4  may be divided into an arbitrary number of the divided wiring patterns  4   a.    
       FIGS. 8 and 9  illustrate a liquid droplet discharging head circuit board  100   b  according to another exemplary embodiment.  FIG. 8  is a plane view of the liquid droplet discharging head circuit board  100   b .  FIG. 9  is a sectional view of the liquid droplet discharging head circuit board  100   b  taken along line B 2 -B 2  of  FIG. 8 . As illustrated in  FIGS. 8 and 9 , the liquid droplet discharging head circuit board  100   b  includes the board substrate  1  (depicted in  FIG. 9 ), the oxide film  2  (depicted in  FIG. 9 ), an electricity-heat conversion element  3   b  (depicted in  FIG. 8 ), a wiring pattern  4   b  (depicted in  FIG. 8 ), the first protective layer  5 , and the second protective layer  6  (depicted in  FIG. 9 ). The electricity-heat conversion element  3   b  includes a plurality of divided heat-generating resistance body films  3   ba  (depicted in  FIGS. 8 and 9 ). The wiring pattern  4   b  includes a plurality of divided wiring patterns  4   ba  (depicted in  FIGS. 8 and 9 ) and slits S 2  (depicted in  FIG. 8 ). 
     The board substrate  1  includes silicon. The oxide film  2  is formed on the board substrate  1 . The electricity-heat conversion element  3   b , serving as a discharging energy generating element, includes a heat-generating resistance body film formed at a predetermined position on the oxide film  2  and having a predetermined size. The electricity-heat conversion element  3   b  bridges both end portions of the wiring pattern  4   b  formed on the oxide film  2 . The wiring pattern  4   b  is formed on the oxide film  2  and has a predetermined pattern. The wiring pattern  4   b  electrically connects the electricity-heat conversion element  3   b  to a power source (not shown) to supply power to the electricity-heat conversion element  3   b . The first protective layer  5  is formed on the electricity-heat conversion element  3   b  and the wiring pattern  4   b . The second protective layer  6  is formed on the first protective layer  5 . 
     The heat-generating resistance body film of the electricity-heat conversion element  3   b  is divided in a width direction of the electricity-heat conversion element  3   b  into the plurality of divided heat-generating resistance body films  3   ba  serving as divided discharging energy generating elements. The slit S 2  is formed between the adjacent divided heat-generating resistance body films  3   ba . Corresponding to the divided heat-generating resistance body films  3   ba , the wiring pattern  4   b  is also divided into the plurality of divided wiring patterns  4   ba . Each of the divided heat-generating resistance body films  3   ba  bridges both end portions of the at least one divided wiring pattern  4   ba.    
     The divided wiring pattern  4   ba  may have a band shape like the divided wiring pattern  4   a  illustrated in  FIG. 6 . According to this non-limiting exemplary embodiment, the divided wiring pattern  4   ba  has a line shape and has a width W 3  (depicted in  FIGS. 8 and 9 ) smaller than the width W 2  of the divided wiring pattern  4   a  illustrated in  FIG. 6 . The width W 3  corresponds to a width of an area in which an allowable electric current per unit wiring width increases. 
     The wiring pattern  4   b  has a width not smaller than about 10 μm, for example. At least a part of the wiring pattern  4   b  is divided in a width direction of the wiring pattern  4   b  into the plurality of divided wiring patterns  4   ba . The divided wiring pattern  4   ba  has a narrow width (i.e., the width W 3 ). Namely, the wiring pattern  4 R illustrated in  FIG. 1  formed of a single conductive film can be divided into the plurality of divided wiring patterns  4   ba . Corresponding to the divided wiring patterns  4   ba , the electricity-heat conversion element  3   b  is also divided into the plurality of divided heat-generating resistance body films  3   ba  having a narrow width. Thus, in a photolithographic process, that is, one of manufacturing processes determining the acceptable quality level of shape and dimensions of the liquid droplet discharging head circuit board  100   b , a heat-shrunk registration film may not partially narrow the electricity-heat conversion element  3   b  or the wiring pattern  4   b , resulting in an improved dimension control. 
     The wiring pattern  4  (depicted in  FIG. 6 ) including the plurality of divided wiring patterns  4   a , each of which has the width W 2  narrower than the width W 1 , and the wiring pattern  4   b  (depicted in  FIG. 8 ) including the plurality of divided wiring patterns  4   ba , each of which has the width W 3  narrower than the width W 1  (depicted in  FIG. 1 ), can reduce product failures caused by a broken wire and can increase yields compared to the single, broad wiring pattern  4 R (depicted in  FIG. 1 ). 
     When the width W 2  of the divided wiring pattern  4   a  and the width W 3  of the divided wiring pattern  4   ba  are regulated to have a predetermined width or greater, an allowable electric current per unit wiring width can be increased even when the divided wiring patterns  4   a  and  4   ba  occupy an area common to the divided wiring pattern  4 R. Thus, when the liquid droplet discharging head circuit board  100  (depicted in  FIG. 6 ) or  100   b  (depicted in  FIG. 8 ) is installed in the image forming apparatus  17  (depicted in  FIG. 3 ), the image forming apparatus  17  can provide an increased reliability. 
     As illustrated in  FIGS. 6 and 8 , when the slits S 1  and S 2  are regulated to have a predetermined width or greater and the first protective layer  5  and the second protective layer  6  (depicted in  FIGS. 7 and 9 ) provide a proper coverage, the liquid droplet discharging head circuit boards  100  and  100   b  can provide an improved ink-proof level, resulting in an increased reliability of the image forming apparatus  17 . Modifying only the wiring patterns  4  and  4   b  or the electricity-heat conversion elements  3  and  3   b  can provide the above-described effects. 
     As described above, when the electricity-heat conversion element  3 R or the wiring pattern  4 R (depicted in  FIG. 1 ) formed of a conductive film being consecutive in the width direction of the electricity-heat conversion element  3 R or the wiring pattern  4 R is divided in the width direction into the plurality of narrow divided heat-generating resistance body films  3   ba  (depicted in  FIG. 8 ) or the narrow divided wiring patterns  4   a  (depicted in  FIG. 6 ) or  4   ba  (depicted in  FIG. 8 ), respectively, the liquid droplet discharging head circuit board  100  (depicted in  FIG. 6 ) or  100   b  (depicted in  FIG. 8 ) can provide increased manufacturing yields, an increased allowable electric current per unit wiring width, and an maintained or improved ink-proof level without increasing the number of manufacturing processes. 
       FIG. 10  is a graph illustrating a relationship between an allowable electric current per unit wiring width and a width of a wiring pattern (i.e., a wiring width). The allowable electric current per unit wiring width corresponds to a maximum current satisfying a predetermined wiring life. 
     As illustrated in  FIG. 10 , when the wiring width is greater than about 5 μm the allowable electric current per unit wiring width does not vary. However, when the wiring width of the wiring pattern (i.e., the divided wiring pattern) is not greater than about 4 μm, especially about 2 μm, the allowable electric current per unit wiring width increases. For example, the allowable electric current of a broad wiring width of about 9 μm (for example, the width W 1  of the wiring pattern  4 R depicted in  FIG. 1 ) is about 1 A. The allowable electric current of a narrow wiring width of about 1 μm is about 13 A. Therefore, when five divided wiring patterns, each of which has the width of about 1 μm, are arranged with a space of about 1 μm (for example, the width of the slit S 1  depicted in  FIG. 6 ) provided between two adjacent divided wiring patterns, the five divided wiring patterns provide the allowable electric current of about 65 A. Namely, both one broad wiring pattern having the width of about 9 μm and five divided wiring patterns each having the width of about 1 μm occupy the width of about 9 μm and thereby occupy a common area. However, the five divided wiring patterns provide a greater allowable electric current than the one broad wiring pattern. Thus, when the wiring width is not greater than about 4 μm and a space of at least about 1 μm is provided between two adjacent divided wiring patterns, each of the divided wiring patterns provides an increased allowable electric current per unit wiring width. 
     As illustrated in  FIGS. 6 and 8 , according to this non-limiting exemplary embodiment, the wiring patterns  4  and  4   b  include the narrow divided wiring patterns  4   a  and  4   ba , respectively. Thus, each of the wiring patterns  4  and  4   b  can provide an increased allowable electric current per unit wiring width. Namely, when a single, broad wiring pattern (for example, the wiring pattern  4 R depicted in  FIG. 1 ) is divided to include a plurality of narrow, divided wiring patterns (for example, the divided wiring patterns  4   a  or  4   ba ), a user or a service engineer of the image forming apparatus  17  (depicted in  FIG. 3 ) can easily cope with wear of the wiring patterns and a partially broken wire. 
     When the image forming apparatus  17  includes a thermal type recording head, a protective layer may be formed on a surface of the electricity-heat conversion element  3  or  3   b . The protective layer can prevent erosion by ink, sticking of an ink component, and cavitation (i.e., an impact caused by a shrunk bubble) from directly affecting and damaging the electricity-heat conversion element  3  or  3   b , resulting in a longer life of the electricity-heat conversion element  3  or  3   b.    
       FIGS. 11 and 12  illustrate an enlarged view of the liquid droplet discharging head circuit board  100  shown in  FIG. 7 . The liquid droplet discharging head circuit board  100   b  (depicted in  FIG. 9 ) may have a structure common to the liquid droplet discharging head circuit board  100  shown in  FIGS. 11 and 12 . 
     As illustrated in  FIG. 11 , when the adjacent divided wiring patterns  4   a  are spaced with a substantial distance provided between the divided wiring patterns  4   a , the first protective layer  5  is formed between the divided wiring patterns  4   a  and has a substantial thickness. However, when the distance between the adjacent divided wiring patterns  4   a  is small as illustrated in  FIG. 12 , the first protective layer  5  formed between the divided wiring patterns  4   a  has a small thickness. In  FIG. 12 , an upper thickness St represents a thickness of the first protective layer  5  provided between the adjacent divided wiring patterns  4   a  at a level higher than the top surface of the divided wiring pattern  4   a . A lower thickness Sb represents a thickness of the first protective layer  5  provided between the adjacent divided wiring patterns  4   a  at a level lower than the top surface of the divided wiring pattern  4   a . A position Cv represents a position at which the slit S 1  (depicted in  FIG. 6 ) is formed. 
       FIG. 13  is a graph illustrating a relationship between a coverage and the distance between the adjacent divided wiring patterns  4   a . The coverage corresponds to a ratio of the distance between the adjacent divided wiring patterns  4   a  to the thickness of the first protective layer  5  between the adjacent divided wiring patterns  4   a . When the distance between the adjacent divided wiring patterns  4   a  is not smaller than about 1 μm, the coverage is nearly 100 percent and the liquid droplet discharging head circuit board  100  has the shape in cross section as illustrated in  FIG. 11 . 
     When the distance between the adjacent divided wiring patterns  4   a  is smaller than about 1 μm, the liquid droplet discharging head circuit board  100  has the shape in cross section as illustrated in  FIG. 12 . When the distance between the adjacent divided wiring patterns  4   a  is smaller than about 0.7 μm, the slit S 1  (depicted in  FIG. 6 ) is formed at the position Cv illustrated in  FIG. 12 . When an ink erosion occurs, ink erodes the position Cv when the distance between the adjacent divided wiring patterns  4   a  is smaller than about 0.8 μm. To maintain a proper ink-proof level, the distance between the adjacent divided wiring patterns  4   a  is preferably set to be not smaller than about 1 μm. 
     As described above, when the distance between the adjacent divided wiring patterns  4   a  is not smaller than about 1 μm, the first protective layer  5  having a uniform thickness can be formed in the whole liquid droplet discharging head circuit board  100 , including the space provided between the adjacent divided wiring patterns  4   a . As a result, the liquid droplet discharging head circuit board  100  can provide an improved ink-proof level. 
     When the image forming apparatus  17  includes a thermal type recording head, a protective layer may be formed on a surface of the electricity-heat conversion element  3  (depicted in  FIG. 6 ) or  3   b  (depicted in  FIG. 8 ). The protective layer can prevent erosion by ink, sticking of an ink component, and cavitation (i.e., an impact caused by a shrunk bubble) from directly affecting and damaging the electricity-heat conversion element  3  or  3   b , resulting in a longer life of the electricity-heat conversion element  3  or  3   b.    
     As described above, the liquid droplet discharging head circuit board  100  (depicted in  FIG. 6 ) or  100   b  (depicted in  FIG. 8 ) can be any type of circuit board used for a liquid droplet discharging head, as long as the circuit board includes a plurality of electricity-heat conversion elements including a heat-generating resistance body. However, the liquid droplet discharging head circuit board  100  or  100   b  is preferably used as a circuit board for a liquid droplet discharging head of an inkjet recording apparatus. 
       FIGS. 14 and 15  illustrate a liquid droplet discharging head circuit board  100   c  according to yet another exemplary embodiment.  FIG. 14  is a plane view of the liquid droplet discharging head circuit board  100   c .  FIG. 15  is a sectional view of the liquid droplet discharging head circuit board  100   c  taken along line B 3 -B 3  of  FIG. 14 . As illustrated in  FIGS. 14 and 15 , the liquid droplet discharging head circuit board  100   c  includes the board substrate  1  (depicted in  FIGS. 14 and 15 ), the oxide film  2  (depicted in  FIGS. 14 and 15 ), the electricity-heat conversion element  3  (depicted in  FIG. 14 ), a wiring pattern  4   c  (depicted in  FIG. 14 ), the first protective layer  5 , and the second protective layer  6  (depicted in  FIG. 15 ). The wiring pattern  4   c  includes a plurality of narrow wiring patterns  4   cb  (depicted in  FIGS. 14 and 15 ) and  4   cc  (depicted in  FIG. 14 ) and slits S 3  (depicted in  FIG. 14 ). 
     The oxide film  2  is formed on the board substrate  1 . The electricity-heat conversion element  3  is formed on the oxide film  2  and generates heat to discharge an ink droplet. The wiring pattern  4   c  electrically connects the electricity-heat conversion element  3  to a power source (not shown) to supply power to the electricity-heat conversion element  3 . At least a part of the wiring pattern  4   c  connected to one electricity-heat conversion element  3  or at least one divided heat-generating resistance body film  3   ba  (depicted in  FIG. 8 ) includes a mesh wiring pattern formed by the narrow wiring patterns  4   cb  and  4   cc  crossed each other. Specifically, the narrow wiring patterns  4   cb  have a narrow width and extend in a longitudinal direction of the wiring pattern  4   c . The narrow wiring patterns  4   cc  have a narrow width and extend in a width direction of the wiring pattern  4   c . The plurality of narrow wiring patterns  4   cb  and  4   cc  are crossed each other to form the slits S 3  through which the oxide film  2  is exposed. The slit S 3  is formed near an intersection point of the narrow wiring patterns  4   bc  and  4   cc  and has a narrow, rectangular shape. The width of each of the narrow wiring patterns  4   cb  and  4   cc  is set in a range in which an allowable electric current per unit wiring width increases (for example, about 4 μm or smaller), as described above in the description for  FIG. 10 . 
     When the narrow wiring patterns  4   cb  and  4   cc  are crossed each other to form a mesh, the wiring pattern  4   c  partially has a narrow width. Thus, the wiring pattern  4   c  can provide effects similar to the effects provided by the wiring patterns  4  (depicted in  FIG. 6) and 4   b  (depicted in  FIG. 8 ). The widths of the wiring patterns  4  and  4   b  are formed by the plurality of divided wiring patterns  4   a  (depicted in  FIG. 6) and 4   ba  (depicted in  FIG. 8 ), respectively. The width of each of the divided wiring patterns  4   a  and  4   ba  is set to a width (for example, about 4 μm or smaller) in which an allowable electric current per unit wiring width increases. Namely, the electric current per unit wiring width flown in a conductive film forming the wiring pattern  4   c  can be increased so that a user or a service engineer of the image forming apparatus  17  (depicted in  FIG. 3 ) can easily cope with wear of the wiring pattern  4   c  and a partially broken wire. 
     When the distance between the narrow wiring patterns  4   cb  or  4   cc  (i.e., the width of the slit S 3 ) is not smaller than about 1 μm, the first protective layer  5  having a uniform thickness can be formed in the whole liquid droplet discharging head circuit board  100   c , including the space provided between the narrow wiring patterns  4   cb  or  4   cc . As a result, the liquid droplet discharging head circuit board  100   c  can provide an improved ink-proof level. 
       FIG. 16  illustrates another example of the slit S 3 . The slit S 3  illustrated in  FIG. 16  has an oval or ellipse shape. However, the slit S 3  may have other shapes. In  FIG. 16 , the slits S 3  are aligned in a longitudinal direction of the wiring pattern  4   c . However, the slits S 3  may be provided in a zigzag condition. 
       FIGS. 17 and 18  illustrate the recording head  15  including the liquid droplet discharging head circuit board  100 .  FIG. 17  is a perspective view of the recording head  15 .  FIG. 18  is a sectional view of the recording head  15 . The following describes a circuit board installed in the recording head  15  as an example of the liquid droplet discharging head circuit board  100 . The following description is also applicable to the liquid droplet discharging head circuit boards  100   b  and  100   c . As illustrated in  FIGS. 17 and 18 , the recording head  15  includes the liquid droplet discharging head circuit board  100 , a wall  11 , an ink room  12 , and an ink inlet  13 . As illustrated in  FIG. 18 , the liquid droplet discharging head circuit board  100  includes the board substrate  1 , the oxide film  2 , and a heat generator  10 . The heat generator  10  includes the electricity-heat conversion element  3 , the divided wiring pattern  4   a , the first protective layer  5 , and the second protective layer  6 . As illustrated in  FIGS. 17 and 18 , the wall  11  includes the ink outlet  11   a.    
     The board substrate  1  includes silicon. The oxide film  2  is formed on the board substrate  1 . The electricity-heat conversion element  3  and the divided wiring pattern  4   a  are provided on the oxide film  2 . The first protective layer  5  is formed on the electricity-heat conversion element  3  and the divided wiring pattern  4   a . The second protective layer  6  is formed on the first protective layer  5 . 
     The heat generators  10  are disposed with a predetermined pitch provided between the adjacent heat generators  10 . The electricity-heat conversion element  3  includes a heat-generating resistance body film bridging both end portions of the divided wiring pattern  4   a.    
     The wall  11  is disposed above the heat generator  10  and includes a photosensitive resin. The ink outlet  11   a , through which an ink droplet is discharged, is formed in the wall  11 . The ink room  12 , from which an ink droplet is supplied to the ink outlet  11   a , is formed between the wall  11  and the liquid droplet discharging head circuit board  100 . The ink inlet  13 , through which an ink droplet is supplied to the ink room  12 , is formed on the liquid droplet discharging head circuit board  100 . 
     The following describes how to manufacture the recording head  15 . A heat-generating resistance body film forming the electricity-heat conversion element  3  and a conductive film forming the wiring pattern  4  or the divided wiring pattern  4   a  are patterned on a large silicone wafer by using a photolithographic technology. The wall  11  is formed in an area corresponding to the board substrate  1  to form the ink room  12 . The ink outlet  11   a  is formed in the wall  11 . The ink outlet  13  is formed on the liquid droplet discharging head circuit board  100  by anisotropic etching, for example. Then, the silicone wafer is cut into a predetermined size. 
     The following describes how to manufacture the liquid droplet discharging head circuit board  100 . The following description is also applicable to the liquid droplet discharging head circuit boards  100   b  (depicted in  FIG. 9) and 100   c  (depicted in  FIG. 14 ). A silicone board is prepared as the board substrate  1 . The silicone board is thermally oxidized to form an oxide silicone film having a thickness of about several micrometers as the oxide film  2 . 
     A heat-generating resistance body film having a thickness of about 50 nm as the electricity-heat conversion element  3  is formed on a predetermined position on the oxide film  2  by spattering. According to this non-limiting exemplary embodiment, the heat-generating resistance body film forming the electricity-heat conversion element  3  includes tantalum nitride (TaN). However, the heat-generating resistance body film may include hafnium diboride (HfB 2 ) and/or tantalum silicon nitride (TaSiN). Etching is performed on the heat-generating resistance body film to form the electricity-heat conversion element  3  having a predetermined pattern by the photolithographic technology, for example. 
     A conductive film including aluminum and having a thickness of about 200 nm as the wiring pattern  4  or the divided wiring pattern  4   a  is formed by spattering. According to this non-limiting exemplary embodiment, the wiring pattern  4  or the divided wiring pattern  4   a  includes aluminum. However, the wiring pattern  4  or the divided wiring pattern  4   a  may include an alloy, for example, aluminum-silicone (Al—Si), aluminum-cupper (Al—Cu), and/or aluminum-silicone-copper (Al—Si—Cu). 
     The aluminum film is processed into the wiring pattern  4  or the divided wiring pattern  4   a  having a predetermined pattern by using the photolithographic technology. Specifically, etching (for example, dry etching) is performed on a conductive film. Thus, a portion not eroded by etching forms the wiring pattern  4  or the divided wiring pattern  4   a.    
     The first protective layer  5  including plasma nitride silicon (P—SiN) is formed by a CVD (chemical vapor deposition) method to have a thickness of about 300 nm. The first protective layer  5  may include oxide silicone. The second protective layer  6  including tantalum (Ta) is formed by spattering to have a thickness of about 230 nm. The second protective layer  6  may include tantalum nitride (TaN) and/or tantalum silicon nitride (TaSiN) instead of tantalum (Ta). The second protective layer  6  is patterned again by a photolithographic method, and is etched by dry etching to remove an unnecessary tantalum portion. 
     Electric wiring used for sending and receiving an electric signal to drive the electricity-heat conversion element  3  is connected to the liquid droplet discharging head circuit board  100  by a mounting technology. Namely, a power transistor and a CMOS (complementary metal oxide semiconductor) logic circuit are formed on the liquid droplet discharging head circuit board  100  by using a semiconductor technology. The power transistor switches an electric current flow to the electricity-heat conversion element  3 . The CMOS logic circuit controls the power transistor. The power transistor and the CMOS logic circuit are connected to the electricity-heat conversion element  3  via the wiring pattern  4  or the divided wiring pattern  4   a.    
     According to this non-limiting exemplary embodiment, the ink outlets  11   a  disposed in parallel to each other and opposing each other via the ink inlet  13  are shifted or staggered each other by a half pitch. The ink room  12  corresponding to the ink outlet  11   a  is spaced from the adjacent ink room  12  by a pitch of about 600 dpi in each row of the ink outlets  11   a . The heat generator  10  is spaced from the adjacent heat generator  10  by a predetermined pitch on an inner bottom of the ink room  12 . Thus, the ink outlet  11   a  discharges an ink droplet in a predetermined amount. 
     As illustrated in  FIG. 4 , the printing mechanism  19  includes the recording head  15 . The recording head  15  can reduce ink droplet discharging errors caused by heat, resulting in a stable ink droplet discharging operation and an increased quality of an image formed with ink droplets discharged by the recording head  15 . The recording head  15  can discharge a pigment, a dye, or a mixture of the pigment and the dye as a colorant. 
     As illustrated in  FIG. 3 , the image forming apparatus  17  including the recording head  15  can reduce variations in ink droplet discharging property, providing an improved reliability. Therefore, the recoding head  15  can also be used as a line type recording head which does not move in the main scanning direction to discharge an ink droplet and can provide an improved reliability. 
     The liquid droplet discharging head circuit boards  100  (depicted in  FIG. 6 ),  100   b  (depicted in  FIG. 8 ), and  100   c  (depicted in  FIGS. 14 and 16 ) are applicable to any circuit board used for discharging an ink droplet, as long as the circuit board includes a plurality of heat-generating resistance bodies. The recording head  15  (depicted in  FIG. 5 ) including the liquid droplet discharging head circuit board  100 ,  100   b , or  100   c  is applicable to the image forming apparatus  17  (depicted in  FIG. 3 ), for example, a copying machine, a printer, a facsimile machine, and a multifunction printer having copying, printing, scanning, and facsimile functions. 
     The liquid droplet discharging head circuit boards  100 ,  100   b , and  100   c  are also applicable to a liquid droplet discharging head and a liquid droplet discharging device for discharging a liquid droplet other than ink, for example, a DNA (deoxyribonucleic acid) sample and a material for registration and patterning. 
     According to the above-described non-limiting exemplary embodiments, at least a part of a broad wiring pattern (i.e., the wiring pattern  4  depicted in  FIG. 6 , the wiring pattern  4   b  depicted in  FIG. 8 , or the wiring pattern  4   c  depicted in  FIG. 14  or  16 ) includes a plurality of narrow, divided wiring patterns (i.e., the divided wiring patterns  4   a  depicted in  FIG. 6 , the divided wiring patterns  4   ba  depicted in  FIG. 8 , or the narrow wiring patterns  4   cb  and  4   cc  depicted in  FIG. 14  or  16 ). The widths of the divided wiring patterns are in a predetermined range, resulting in an increased migration resistance, reduced variations in finished dimension, and an increased allowable electric current per unit wiring width. The distance between the divided wiring patterns is regulated, resulting in formation of an insulating film with an increased coverage, an increased ink resistance, and an increased reliability. 
     When the broad wiring pattern is divided into the plurality of divided wiring patterns having a narrow width, an allowable electric current per unit wiring width increases substantially, preventing the wiring pattern from being damaged or partially broken. 
     According to the above-described non-limiting exemplary embodiments, the wiring pattern includes a conductive film connected to a discharging energy generating element (i.e., the electricity-heat conversion element  3  depicted in  FIG. 6  or the electricity-heat conversion element  3   b  depicted in  FIG. 8 ) as one example. However, the structure of the wiring pattern can be applied to general wiring patterns formed on a board (i.e., the board substrate  1  depicted in  FIGS. 7 ,  9 , and  15 ). 
     Numerous additional modifications and variations are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the disclosure of this patent specification may be practiced otherwise than as specifically described herein. For example, elements and/or features of different illustrative embodiments may be combined with each other and/or substituted for each other within the scope of this disclosure and appended claims. 
     This patent specification is based on Japanese patent application No. 2006-026413 and Japanese application No. 2006-280752 filed on Feb. 2, 2006 and Oct. 13, 2006, respectively, in the Japan Patent Office, the entire contents of which are hereby incorporated herein by reference.