Patent Publication Number: US-7914123-B2

Title: Inkjet printhead and manufacturing method thereof

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a Continuation of application Ser. No. 10/795,878, filed Mar. 8, 2004, the entirety of which is incorporated by reference herein. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to an inkjet printhead and its manufacturing method, and in particular, the invention relates to an inkjet printhead with high driving force. 
     2. Description of the Related Art 
     In a conventional inkjet printhead  10 , an open-typed ink chamber is provided as shown in  FIG. 1 . Numeral  11  represents a feed channel, numeral  12  represents a heating device, numeral  13  represents an island for filtering the ink, and numeral  14  represents a cross section of an ink slot. The ink flows to the front side of the chip from the rear via the ink slot  14 , and then fills the ink chamber via the feed channel  11 . After a pulse voltage is applied to the heating device  12 , the temperature of the heating device increases to generate bubbles. The ink is then dispensed via a nozzle plate, and re-supplied via the feed channel  11 . 
     During the manufacture of the chip of the conventional inkjet printhead, the ink slot is necessary so that the ink can flow to the feed channel from an ink cartridge. The ink slot is formed by drilling through the chip. During drilling, the chip is continuously etched by fine, hard SiC powder for a long time, making it easily damaged. Also, the reliability of such drilling process is low, reducing the yield of the chip. Additionally, for a color inkjet printer with high resolution, three ink slots are formed on one chip. To reduce the area of the chip, the ink slot is a narrow and long rectangle, thus increasing the difficulty of the formation thereof. 
     Additionally, a nozzle plate is required on the conventional inkjet printhead. During assembly of the nozzle plate and the chip, precise alignment is required, thus increasing the assembly time. Also, assembly takes place individually, thus reducing the efficiency of the manufacture and increasing the cost. 
     Furthermore, since the ink chamber is open, in the conventional inkjet printhead, some liquid may flow back into the feed channel during dispensing. Thus, dispensing force may not be concentrated in the desired direction. 
     Moreover, the height of the ink chamber, the feed channel, and an adhesive layer between the chip and the nozzle plate are defined by organic polymer. Since the organic polymer is easily corroded by the ink, the ink may penetrate between the nozzle plate and the polymer, or between the chip and the polymer, thus reducing adhesive force and generating delamination. 
       FIG. 2  shows a conventional edge-shooting inkjet printhead  20 . Numeral  21  represents a substrate, numeral  22  represents a heating area, numeral  23  represents a channel, numeral  24  represents a hole, numeral  25  represents a cover, and numeral  26  represents an orifice. During the formation of bubbles, driving force is not concentrated in the dispensing direction, reducing efficiency. Additionally, like the conventional inkjet printhead  10 , the hole  24  is required in the cover  25 , and the cover  25  must be precisely aligned with the substrate  21 . 
     In U.S. Pat. No. 6,412,918, a back-shooting inkjet printhead is provided, requiring longer etching time, thus increasing cost and complicating process. 
     SUMMARY OF THE INVENTION 
     In view of this, the invention provides an inkjet printhead and manufacturing method with reduced cost and high driving force with no need for drilling and etching during manufacture. 
     Another purpose of the invention is to provide an inkjet printhead and manufacturing method without organic material, thus avoiding corrosion and allowing use of various ink type. 
     Still another purpose of the invention is to provide an inkjet printhead that can utilize liquid with higher coefficient of viscosity. 
     Accordingly, the invention provides a method for manufacturing an inkjet printhead. The method includes the following steps. A substrate and a porous material are provided. The porous material is a compound fabricated by sintering metallic powders at high temperature and pressure. During fabrication of the porous material, the gap between the metallic powders is smaller if the temperature is higher. That is, the gap between the metallic powders can be adjusted by the temperature. Thus, different kinds of porous material for filtering liquid can be provided. A heating layer and a conductive layer are then formed on the substrate. The conductive layer conducts a current to the heating layer. A heating area is defined by the conductive layer and the heating layer. A chamber for storing liquid is then formed above the heating area. The chamber includes a first side and a second side, with the first side facing the heating area. The second side is connected to the first side. The chamber is formed with an exit, from which liquid is dispensed, at the second side. The porous material is then placed on the chamber, thorough which liquid flows. 
     In a preferred embodiment, the method further includes the following steps. A conductive layout is formed on the conductive layer to conduct a pulse voltage signal to the heating area. Before the conductive layer is formed on the heating layer, a thermally-resistant layer is formed on the substrate. The thermally-resistant layer is formed between the substrate and the heating layer. After the conductive layer is formed on the heating layer, an isolation layer is formed on the conductive layer. The isolation layer is formed between the conductive layer and the chamber. After the isolation layer is formed on the conductive layer, a protective layer is formed on the isolation layer. The protective layer and the heating area overlap in a plumb direction. After the isolation layer is formed on the conductive layer, a notch is formed on the isolation layer. A connector is formed in the notch, connecting to the conductive layout. 
     And then the chamber is formed by light-sensitive polymer via exposure and developing. The light-sensitive polymer is a dry film or a liquid photoresist. The porous material is adhered to the light-sensitive polymer by hot press, and the light-sensitive polymer is used as an adhesive layer for the porous material. 
     In another preferred embodiment, the chamber is formed by electroplating metal. The metal may be Ni. After the chamber is formed, an adhesive layer is formed on the chamber. The adhesive layer comprise metal with a low melting point, such as PbSn (melting point 183° C.). The adhesive layer may be formed on the chamber by electroplating or screen printing. The adhesive layer is then covered by the porous material via hot press so that the porous material adheres to the adhesive layer. 
     It is understood that the porous material may be formed by sintering metallic powders or ceramic material, or may be polymer. 
     In another preferred embodiment, the method further includes the following step. A nozzle plate is provided, adhered to the second side of the chamber. 
     In the invention, an inkjet printhead is provided. The inkjet printhead comprises a substrate, a heating layer, a conductive layer, a chamber, and porous material. The heating layer is disposed on the substrate to dispense liquid. The conductive layer is disposed on the substrate to conduct a current to the heating layer. A heating area is defined by the conductive layer and the heating layer. The chamber is disposed on the heating area, and has a first side and a second side. The first side faces the heating area, and the second side is connected to the first side. The chamber is formed with an exit, from which the liquid is dispensed, on the second side. The porous material is disposed on the substrate, through which liquid flows. 
     In a preferred embodiment, the conductive layer is formed with a conductive layout to conduct a pulse voltage to the heating area. 
     In another preferred embodiment, the inkjet printhead further includes an isolation layer, a protective layer, a connector, and a thermally-resistant layer. The isolation layer is disposed between the conductive layer and the chamber. The protective layer is disposed between the isolation layer and the chamber. The connector is disposed on the isolation layer. The thermally-resistant layer is disposed between the substrate and the heating layer. 
     It is understood that the chamber may be formed by light-sensitive polymer or metal. 
     In another preferred embodiment, the inkjet printhead further includes an adhesive layer and a nozzle plate. The adhesive layer is disposed between the chamber and the porous material. The nozzle plate is disposed on the second side of the chamber. 
     In the invention, another method for manufacturing an inkjet printhead is provided. The method includes the following steps. A substrate, a porous material, and a nozzle plate are provided. A heating layer and a conductive layer are then formed on the substrate. The conductive layer conducts a current to the heating layer. A heating area is defined by the conductive layer and the heating layer. An adhesive layer is then formed on the conductive layer. The porous material is then placed on the chamber to form a chamber for storing liquid, through which liquid flows. The chamber includes a first side and a second side. The first side faces the heating area so that the liquid in the chamber is located above the heating area. The second side is connected to the first side. The nozzle plate is then adhered to the second side of the chamber, and comprises at least one orifice. 
     In a preferred embodiment, the adhesive layer comprises light-sensitive polymer, and includes a groove by cutting to form the chamber before placing on the adhesive layer. 
     In the invention, another inkjet printhead is provided, and comprises a substrate, a heating layer, a conductive layer, an adhesive layer, a porous material, and a nozzle plate. The heating layer is disposed on the substrate to dispense liquid. The conductive layer is disposed on the substrate to conduct a current to the heating layer. A heating area is defined by the conductive layer and the heating layer. The adhesive layer is disposed on the conductive layer. The porous material is disposed on the substrate, and includes a chamber. The liquid flows to the chamber through the porous material. The chamber has a first side and a second side. The first side faces the heating area such that the liquid in the chamber is located above the heating area. The second side is connected to the first side. The nozzle plate is disposed on the second side of the chamber, and includes at least one orifice. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein: 
         FIG. 1  is a schematic view of a conventional inkjet printhead; 
         FIG. 2  is a schematic view of a conventional edge-shooting inkjet printhead; 
         FIGS. 3A-5  are schematic views showing a method for manufacturing an inkjet printhead as disclosed in a first embodiment of the invention, wherein  FIG. 4B  is a right side view of  FIG. 4A , and  FIG. 4C  is a top view of  FIG. 4A ; 
         FIGS. 6A-6F  are schematic views showing a method for manufacturing an inkjet printhead as disclosed in a second embodiment of the invention; 
         FIG. 7  is a schematic view showing a variant embodiment of an inkjet printhead in  FIG. 6F ; and 
         FIGS. 8A-8E  are schematic views showing a method for manufacturing an inkjet printhead as disclosed in a third embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     First Embodiment 
       FIGS. 3A-5  are schematic views showing a method for manufacturing an inkjet printhead  30  as disclosed in a first embodiment of the invention. In this embodiment, the inkjet printhead  30  is an edge-shooting type, provided with a porous material to generate high driving force. The manufacturing method thereof is described in the following. 
     A chip  31  and a porous material  39 , as shown in  FIG. 5 , are provided. The chip  31  is used as a substrate, and is formed with a thermally-resistant layer (thermal isolation layer)  32  as shown in  FIG. 3A  to prevent heat from dissipating toward the chip  31 . A heating layer  33  is then formed on the thermally-resistant layer  32  as shown in  FIG. 3B . A conductive layer  34  is then formed on the heating layer  33  as shown in  FIG. 3C . A notch  341  and a conductive layout  342  (shown in  FIG. 4C ) are formed on the conductive layer  34  by photolithography and etching. Referring to  FIG. 5 , the notch  341  is used as a heating area  331 ; that is, the heating area  331  is defined by the conductive layer  34  and the heating layer  33 . The conductive layer  342  conducts a pulse voltage signal to the heating area  331 . An isolation layer  35  is then formed on the conductive layer  34 , and shaped as shown in  FIG. 3D  to provide isolation. It is noted that a notch  351  is formed in the isolation layer  35 . A protective layer  36  is then formed above the heating area  331 , and shaped as shown in  FIG. 3E  to prevent reaction force generated by breakage of bubbles from damaging the heating area  331 . A conductive connector  37  is formed in the notch  351  as shown in  FIG. 3F , and shaped by photolithography and etching to electrically connect to the exterior. The basic structure of the inkjet printhead  30  is thus completed. 
     Referring to  FIG. 4A , a chamber (ink chamber)  38  is formed on the chip  31 , as shown in  FIG. 3F , with layout thereon by light-sensitive polymer  381 . The polymer  381  is formed with a plurality of nozzles (exits)  382  and a plurality of diverging sections  383  as shown in  FIG. 4C . The polymer  381  is disposed on the chip  31  by hot press (dry film) or rotating coating (liquid photoresist). The thickness of the polymer  381  is about 20 μm, and the pattern thereof is defined by photolithography as shown in  FIGS. 4A-4C , illustrating the exit  382 . The porous material  39  is then adhered to the polymer  381  by hot press as shown in  FIG. 5 . 
     Specifically, the inkjet printhead  30  manufactured by the method disclosed in this embodiment is shown in  FIG. 5 , and comprises the substrate  31 , the thermally-resistant layer  32 , the heating layer  33 , the conductive layer  34 , the isolation layer  35 , the protective layer  36 , the connector  37 , the chamber  38 , and the porous material  39 . The heating layer  33  comprises the heating area  331  to heat the liquid. The conductive layer  34  is formed with the notch  341  to expose the heating area  331 . The chamber  38  has a first side  38   a  and a second side  38   b , with the first side  38   a  facing the heating area  331 . The second side  38   b  is connected to the first side  38   a . The chamber  38  is formed with the exit  382 , from which the liquid is dispensed, on the second side  38   b . The porous material  39  is disposed on the chamber  38 , through which liquid flows. It is noted that although the porous material  39  is disposed on the chamber  38  in the embodiment, the invention is not limited thereto. For example, the porous material can be disposed on the other position of the substrate as long as the liquid can flow to the chamber thereby. 
     It is understood that the inkjet printhead may further comprise a nozzle plate (not shown) and piezo-electric film (not shown). The nozzle plate can be disposed on the second side  38   b  of the chamber  38 . The heating area can be replaced by the piezo-electric film. 
     In this embodiment, the inkjet printhead is provided with a closed-type ink chamber. As shown in  FIG. 5 , numeral B 1  represents a generated bubble, and numeral B 2  represents a dispensed droplet. The closed-type ink chamber is sealed by organic polymer, and formed with a single exit in a dispensing direction. When the bubble is generated, driving force is entirely applied in the dispensing direction, enhancing the driving force. A comparison between the driving force in this embodiment and that in the conventional inkjet printhead is described in the following. 
     In the chip of the conventional inkjet printhead, an initial velocity V 1  of the liquid droplet from a chamber provided by the generation of the bubble can be defined by a channel formula, as shown in  FIG. 1 . The pressure differential between the exterior and interior of the chamber is proportional to the velocity of the fluid. The formula is: 
               -       ∂   P       ∂   X         ∝   V         
wherein P is pressure, X is a direction of the channel, and V is velocity.
 
     In contrast, with porous material covering the ink chamber in this embodiment, fluid in the chamber can only flow out in two directions, the dispensing direction and toward the porous material. Since resistance of the porous material exceeds the channel condition, the driving force by the bubble is largely applied in the dispensing direction. Specifically, initial velocity V 2  of the fluid toward the porous material due to the bubble can be defined by Darcy&#39;s law. The pressure differential between the exterior and interior of the chamber is proportional to the sum of first power and third power of the velocity of the fluid. The formula is: 
               -       ∂   P       ∂   X         =         μ   K     ⁢   V     +         γρ   2     μ     ⁢     V   3               
wherein P is pressure, X is a direction of the channel, V is velocity, μ is the coefficient of viscosity, and ρ is density of fluid.
 
     Thus, the pressure differential in the porous material exceeds that in the channel condition; that is, P 1  exceeds P 2 . As a result, pressure by the bubble in this embodiment exceeds that in  FIG. 1 . Most pressure remains in the chamber to propel the droplet toward the exit  382 . That is, flow of the liquid is limited toward the porous material  39 , thus enhancing driving force. 
     Furthermore, the supply of ink via the porous material is described in the following. 
     According to the test data of the porous material, the flow rate of deionized water through the inslot of the chip from the porous material is tested under various positive pressures as follows. The porous material is combined with the chip that is sandblasted and provided with defined dry film. The porous material is then assembled with a liquid reservoir (cartridge) by adhesive. The liquid reservoir is then connected with a steel bottle under adjustable pressure. By means of a computer, the steel bottle provides regulated pressure to the cartridge. Test results are shown in the following table. 
     
       
         
           
               
               
               
             
               
                   
                   
               
               
                   
                 Pressure 0.5 kg/cm 2   
                 Pressure 0.2 kg/cm 2   
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                 Radius 10 μm 
                 Flow rate 24.66 cc/min 
                 Flow rate 8.36 cc/min 
               
               
                 Radius 5 μm 
                 Flow rate 11.06 cc/min 
               
               
                 Radius 2 μm 
                 Flow rate 6.38 cc/min 
                 Flow rate 1.38 cc/min 
               
               
                 Radius 0.5 μm 
                 Flow rate 2.25 cc/min 
               
               
                   
               
            
           
         
       
     
     Thus, flow rate increases with pressure. Under the same pressure, flow rate increases with the radius. Accordingly, ink can be effectively supplied to the chamber via the porous material. 
     As stated above, the inkjet printhead of the embodiment is provided with a closed-type chamber, and dispensed by edge-shooting. Also, the liquid can enter into the chamber via the porous material due to pressure from the ink reservoir. After the bubble is generated in the chamber, the liquid can be dispensed in a direction perpendicular to the direction in which the bubble is generated. Thus, there is no requirement for sand-blasting, the alignment of the nozzle plate, or etching of the chip during manufacture. Thus, costs are reduced. 
     Furthermore, in the embodiment, since the porous material and the chip are assembled wafer to wafer, the manufacturing method is simpler and more efficient. Before cutting the combination of chip and porous material, the rear of the chip can be marked for mass-production. However, the sequence of the assembly and the cutting is not limited thereto. For example, the porous material and the chip can be cut prior to assembly. 
     Additionally, in this embodiment, the closed-type chamber is formed by the porous material and light-sensitive polymer, the height thereof defined by the light-sensitive material. Since the exits are only formed in the dispensing direction of the light-sensitive polymer, the driving force of the bubble is entirely applied in the dispensing direction. 
     Second Embodiment 
       FIGS. 6A-6F  are schematic views showing a method for manufacturing an inkjet printhead  40  as disclosed in a second embodiment of the invention. This embodiment differs from the first embodiment in that an ink chamber  38 ′, provided with divergent sections and shown in  FIG. 6F , is defined by metal. The metal is then combined with the porous material  39 , thus forming a no organic structure. Since the metal avoids corrosion from the ink, the lifetime of the chip is increased. Specifically, in conventional inkjet printhead, the height of the chamber is defined by organic polymer. The organic polymer is easily corroded by the ink, which may penetrate between the nozzle plate and the polymer, or between the chip and the polymer, causing the delamination of the polymer. By contrast, in this embodiment, since the chamber is formed by metal, it better resists corrosion. As a result, the structure of this embodiment can utilize various kinds of ink or organic chemical, and can be applied in various areas, such as printers, bio-chips, medicine transport, color filtering, fuel nozzle, or other industry types. 
     The method includes the following steps. Photoresist  41  is uniformly coated on the chip  31 , shown in  FIG. 3F  and provided with layout, by rotation. After development, the thickness of the photoresist  41  is about 40 μm as shown in  FIG. 6A , and is used as a sacrifice layer during electroplating. As shown in  FIG. 6B , a Ni-layer  42  is formed on an area without photoresist  41  covering, with thickness of about 10 μm. Another metallic layer  43 , such as Au, is then formed on the chip  31  by evaporation, with thickness of about 1000 Å as shown in  FIG. 6C . The metallic layer  43  acts as an adhesion layer between the Ni-layer  42  and a metallic layer  44  with low melting point. The metallic layer  44  is then formed thereon by electroplating as shown in  FIG. 6D , with thickness of about 10 μm. The metallic layer  44  may be PbSn, with melting point of 183° C. The chip  31  is then placed in a solution removing the photoresist  41  but not damage the metallic layers or thin film on the chip, as shown in  FIG. 6E . The porous material  39  is then disposed on the chip after electroplating. By heating and pressurizing the porous material  39 , the surface, contacting the porous material  39 , of the metallic layer  44  is melted due to its low melting point. After cooling, the porous material  39  is combined to form a no organic structure as shown in  FIG. 6F . 
     Additionally, the entire chamber may be defined by metal with low melting point. For example, in an inkjet printhead of  FIG. 7 , numeral  381 ′ represents the metallic layer with low melting point. The metallic layer  381 ′ may be formed by electroplating or screen printing. 
     As stated, an inkjet printhead requiring no organic elements is provided in this embodiment. The porous material is combined with the chip via the metallic layer with low melting point, and the printhead can utilize various ink types. 
     Third Embodiment 
       FIGS. 8A-8E  are schematic views showing a method for manufacturing an inkjet printhead  50  as disclosed in a third embodiment of the invention. This embodiment differs from the first embodiment in that the porous material is additionally processed before combining with the chip. Specifically, the porous material is cut to define the chamber, and then combined with the chip. A nozzle plate is disposed on one side of the porous material to complete the inkjet printhead of this embodiment. 
     The method includes the following steps. A metallic layer  51  with low melting point is formed on the chip  31  with layout, at thickness of about 10 μm as shown in  FIG. 8A . Additionally, a porous material  52  is processed as shown in  FIG. 8B . Specifically, the porous material  52  is cut by a series of cutters at 30 μm thickness to define the size of the chamber; with section a 60 μm, section b 60 μm, section c 80 μm, and section d 70 μm. The porous material  52  is then combined with the chip by hot press as shown in  FIG. 8C . A nozzle plate  53  is then adhered to the side of the chip as shown in  FIGS. 8D-8E . The nozzle plate  53  is metallic plate with adhesive thereon, and is processed by laser to form orifices  531 . 
     As stated above, the inkjet printhead provides higher driving force to dispense liquid with high coefficient of viscosity. Additionally, no organic structures in the inkjet printhead allow use of various ink types. 
     While the invention has been described by way of example and in terms of the preferred embodiment, it is to be understood that the invention is not limited to the disclosed embodiment. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.