Abstract:
An ink jet head is constructed by a plurality of combined units, wherein each of said units comprises a plurality of abutting portions and at least one recessed portion shaped to engage at least one of the abutting portions formed on another unit, and wherein at least a first of the units includes a first protruded abutting portion and at least a second one of the units includes a second protruded abutting portion, said first and second protruded portions abutting against each other.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an ink jet head and its manufacturing method. 
     2. Description of the Related Art 
     A prior art ink jet head is constructed by a single unit including laminated substrates such as a monocrystalline silicon substrate and a glass substrate (see JP-A-6-218932). This will be explained later in detail. 
     In the above-mentioned prior art ink jet head, however, when the density of nozzles is increased to improve the printing quality while the printing speed is being increased, even if one nozzle is defective in one unit, such a unit has to be scrapped, so that the manufacturing yield of the units is decreased, thus increasing the manufacturing cost of the ink jet head. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide an ink jet head and its manufacturing method capable of decreasing the manufacturing cost. 
     According to the present invention, an ink jet head is constructed by a plurality of combined units. 
     Also, in a method for manufacturing an ink jet head, a plurality of units are formed in a substrate. Then, the units are separated from each other. Finally, one ink jet head is formed by combining at least two of the units. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will be more clearly understood from the description set forth below, as compared with the prior art, with reference to the accompanying drawings, wherein: 
     FIG. 1 is a plan view illustrating a semiconductor wafer where prior art ink jet units are formed; 
     FIG. 2 is a plan view of one of the ink jet units of FIG. 1; 
     FIG. 3 is a cross-sectional view of the periphery of one nozzle of FIG. 2; 
     FIG. 4 is a plan view illustrating a semiconductor wafer where ink jet units according to the present invention are formed; 
     FIG. 5 is a plan view of one of the ink jet units of FIG. 4; 
     FIG. 6 is a partially-enlarged view of the unit of FIG. 5; 
     FIGS. 7A,  7 B,  7 C and  7 D are cross-sectional views taken along the line VII—VII of FIG. 6; 
     FIGS. 8A and 8B are plan views of the semiconductor wafer of FIG. 4 before and after the separation of units, respectively; 
     FIG. 9 is a plan view for explaining the combination of two non-defective units of FIGS. 8A and 8B; and 
     FIG. 10 is a cross-sectional view of the abutting portion of the non-defective units of FIG.  9 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Before the description of the preferred embodiment, a prior art ink jet head will be explained with reference to FIGS. 1,  2  and  3 . 
     A prior art ink jet head is formed by a single unit  101   a  as illustrated in FIG. 1 including laminated substrates such as a monocrystalling silicon substrate and a glass substrate (see JP-A-6-218932). For example, if each unit  101   a  has a size of about 27 mm×27 mm, seven units  101   a  are cut by a dicing blade (not shown) from an about 10-cm diameter monocrystalline silicon wafer  102  as illustrated in FIG.  1 . 
     In FIG. 2, which is a detailed plan view of each of the units  101   a  of FIG. 1, four nozzle columns  11 ,  12 ,  13  and  14  where nozzles  1  are closely arranged in a matrix are provided. In this case, the nozzle columns  11 ,  12 ,  13  and  14  are used for ejecting black ink, yellow ink, cyan ink and magenta ink, respectively. The nozzle columns  11 ,  12 ,  13  and  14  are connected to ink supply holes  21 ,  22 ,  23  and  24 , respectively. 
     As illustrated in FIG. 3, which is a cross-sectional view of the periphery of one nozzle  1  of FIG. 2, one pressure chamber  2  linked to the nozzle  1 , an ink passage  3  and an ink pool (reservoir)  4  are partitioned by a plurality of substrates  31 ,  32  and  33  made of monocrystalline silicon and glass, and a thin vibration plate  5  on which an actuator  6  made of piezoelectric material sandwiched by metal electrodes is formed. Note that the ink pool  4  for each of the nozzle columns  11 ,  12 ,  13  and  14  is comb-shaped as illustrated in FIG.  2 . 
     Also, in FIG. 3, reference D designates an ink droplet. 
     In the ink jet head formed by a single unit  101   a , however, when the density of nozzles is increased to improve the printing quality while the printing speed is being increased, even if one nozzle is clogged or deformed, i.e., defective in one unit  101   a , such a unit has to be scrapped, so that the manufacturing yield of the units  101   a  is decreased, thus increasing the manufacturing cost of the ink jet head. 
     For example, if the nozzle  1  has a diameter of about 25 to 40 μm, the average number of defective nozzles  1  is expected to be 4 in one monocrystalline silicon wafer  102 . In this case, four units  101   a  may be defective, so that the manufacturing yield of the units  101   a  in one monocrystalline silicon wafer  102  may be {fraction (3/7)} (=43 percent). 
     An embodiment of the ink jet head according to the present invention is formed by a plurality of units  101   b,  for example, two units  101   b  as illustrated in FIG. 4 including a monocrystalline silicon substrate. For example, if each unit  101   b  has a size of about 27 mm×13 mm, fourteen units  101   b  are cut by a dicing blade from an about 10-cm diameter monocrystalline silicon wafer  102 . 
     In FIG. 5, which is a detailed plan view of each of the units  101   b  of FIG. 4, two nozzle columns  11  and  12  where nozzles  1  are closely arranged in a matrix are provided. In this case, the nozzle columns  11  and  12  are used for ejecting black ink (or cyan ink) and yellow ink (or magenta ink), respectively. The nozzle columns  11  and  12  are connected to ink supply holes  21  and  22 , respectively. 
     As illustrated in FIG. 5, in each of the units  102   b,  a protruded abutting portion  51 , a recessed abutting portion  52 , a protruded abutting portion  53  and a protruded abutting portion  54  are formed. As a result, a relief (recess)  55  is formed between the protruded abutting portions  51  and  53 , and a relief (recess)  56  is formed between the abutting portions  52  and  54 . Note that the protruded abutting portion  51  has the same shape as the recessed abutting portion  52 . 
     In the ink jet head formed by two of the units  101   b,  if the nozzle  9  has a diameter of about 25 to 40 μm, the average number of defective nozzles  1  is also expected to be 4 among one monocrystalline silicon wafer  102 . In this case, four units  101   b  may be defective, so that the manufacturing yield of the units  101   b  among one monocrystalline silicon wafer  102  may be {fraction (3/14)} (=22 percent). Thus, the manufacturing yield can be remarkably increased as compared with the prior art units  101   a.    
     A method for manufacturing an ink jet head according to the present invention is explained next with reference to FIGS. 6,  7 A,  7 B,  7 C,  7 D,  8 A,  8 B,  9  and  10 . Note that FIG. 6 is a partially-enlarged view of the unit  101   b  of FIG. 5, and FIGS. 7A,  7 B,  7 C and  7 D are cross-sectional views taken along the line VII—VII of FIG.  6 . Also, FIGS. 8A and 8B are plan views of the semiconductor wafer of FIG. 4 before and after the separation of units respectively. Further, FIG. 9 is a plan view for explaining the combination of two non-defective units of FIGS. 8A and 8B, and FIG. 10 is a cross-sectional view of the abutting portion of the non-defective units of FIG.  9 . 
     First, referring to FIG. 7A as well as FIG. 6, a photoresist pattern  72  is formed by a photolithography process on a front surface of a monocrystalline silicon substrate  71 . 
     Next, referring to FIG. 7B as well as FIG. 6, the monocrystalline silicon substrate  71  is etched by a reactive ion etching (RIE) dry process using the photoresist pattern  72  as a mask. As a result, a nozzle  1  is perforated in the monocrystalline silicon substrate  71 , and simultaneously, an edge  50  for the abutting portions  51 ,  52 ,  53  and  54  and the reliefs  55  and  56  is perforated. Then, the photoresist pattern layer  72  is removed. 
     Next, referring to FIG. 7C as well as FIG. 6, a photoresist pattern layer (not shown) is formed by a photolithography process on a back surface of the monocrystalline silicon substrate  71 . Then, the monocrystalline silicon substrate  71  is etched by an anisotropic wet etching process using the photoresist pattern layer as a mask. As a result, a pressure chamber  2 , an ink passage  3  and an ink pool (reservoir)  4  are perforated in the monocrystalline silicon substrate  71 , and simultaneously the edge  50  for the abutting portions  51 ,  52 ,  53  and  54  and the reliefs  55  and  56  is completely perforated through the monocrystalline silicon substrate  71 . Then, the photoresist pattern layer is removed. 
     In this state, it is determined whether a clogging state (deformed state) is observed in the nozzle  1 , the pressure chamber  3 , the ink passage  3  and the ink pool (reservoir)  4 . 
     Next, referring to FIG. 7D as well as FIG. 6, a wafer-type thin vibration plate  5 , which is perforated in advance to be adapted to the edge  50 , is adhered by a contact bonding process to the back surface of the monocrystalline silicon substrate  71 . Then, one actuator  6  made of piezoelectric material sandwiched by metal electrodes is adhered by a contact bonding process to the thin vibration plate  5  in correspondence with each nozzle  1 . 
     In FIG. 7D, note that it is possible to adhere actuators  6  to a wafer-type thin vibration plate  5  before the wafer-type thin vibration plate  5  is adhered to the back surface of the monocrystalline silicon substrate  71 . 
     Next, the separation of the units  101   b  is explained with reference to FIGS. 8A and 8B. 
     After the process as illustrated in FIG. 7D, the monocrystalline silicon substrate  71  is divided by the edge  50  along the Y-direction into columns of the units  101   b,  as illustrated in FIG.  8 A. 
     Next, as illustrated in FIG. 8B, the monocrystalline silicon substrate  71  is cut by a dicing blade (not shown) along the X-direction. As a result, each of the units  101   b  is completely separated from each other. 
     In this state, it is again determined whether a clogging state (deformed state) is observed in each of the units  101   b.  Then, defective units  101   b  having a clogging state (deformed state) are scrapped. 
     Next, referring to FIG. 9, an ink jet head is constructed by combining two non-defective units  101   b - 1  and  101   b - 2 . That is, the recessed abutting portion  52  of the non-defective unit  101   b - 1  abuts against the protruded abutting portion  51  of the non-defective unit  101   b - 2 , while the protruded abutting portion  54  of the non-defective unit  101   b - 1  abuts against the protruded abutting portion  53  of the non-defective unit  101   b - 2 . In this case, the contact characteristics between the non-defective units  101   b - 1  and  101   b - 2  can be improved due to the presence of the reliefs  55  and  56  thereof. Then, the abutting portions of the nondefective units  101   b - 1  and  101   b - 2  indicated by arrows X in FIG. 9 are filled with adhesives  73 , as illustrated in FIG.  10 . 
     Finally, electrical connections are formed on the back surface of the combined units  101   b - 1  and  101   b - 2 , and the ink supply holes  21  and  22  thereof are coupled to individual ink tanks for black ink, yellow ink, cyan ink and magenta ink, respectively. 
     The combination of the units  101   b - 1  and  101   b - 2  can be carried out without an expensive alignment apparatus, which would decrease the manufacturing cost. 
     Also, since the abutting portions  51 ,  52 ,  53  and  54  are formed by a photolithography and etching process, not a dicing blade, the accuracy of the distance between the edge  50  of the abutting portions  51 ,  52 ,  53  and  54  and the nozzles  1  of each of the combined units  101   b - 1  and  101   b - 2  can be high, i.e., about ±1 μm. As a result, the accuracy of the alignment of the nozzles  1  between the combined units  101   b - 1  and  101   b - 2  can be high, i.e., about ±5 μm. Note that, if the abutting portions  51 ,  52 ,  53  and  54  are formed by a dicing blade, the above-mentioned distance accuracy may be ±10 μm, and the above-mentioned alignment accuracy may be ±10 μm. 
     Thus, the deviation of droplets among black ink, yellow ink, cyan ink and magenta ink can be decreased, which could not degrade the printing quality. 
     In the above-described embodiment, one ink jet head is constructed by two combined units  101   b - 1  and  101   b - 2 ; however, one ink jet head can be constructed by three or more combined units. For example, if one unit is formed for one nozzle column, one ink jet head can be constructed by four combined units. 
     Also, in the above-described embodiment, the substrate  71  is made of monocrystalline silicon; however, the substrate  71  can be made of other crystal or metal. If the substrate  71  is made of metal, a mechanical pressing process or an electroforming process can be performed thereon, so that the nozzles  1  and the like can be formed. 
     Further, in the above-described embodiment, the nozzles  1  are arranged in a matrix in each of the nozzle columns  11  and  12 ; however, the arrangement of the nozzles  1  can be staggered in each of the nozzle columns  11  and  12 . 
     As explained hereinabove, according to the present invention, since one ink jet head is constructed by a plurality of combined units, the manufacturing yield of each unit is increased, so that the manufacturing yield of the ink jet head can be increased, which would decrease the manufacturing cost.