Abstract:
Size reduction and high integration of each of the laminated substrates are achieved, while forming an excellent wiring which electrically connects the substrates to each other. A conductive ink, i.e., an ink, containing a conductive material is used, and in a state where a voltage is applied between a print head and a substrate unit, an ink droplet of the conductive ink is discharged from the print head, while relatively shifting the substrate unit and the print head substantially parallel to at least the upper surface of the substrate. Thus, a conductive layer which electrically connects electrodes to each other between the substrates is formed.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This is a U.S. national stage application of International Application No. PCT/JP2009/060930, filed on 16 Jun. 2009. Priority under 35 U.S.C. §119(a) and 35 U.S.C. §365(b) is claimed from Japanese Application No. JP2008-170753, filed 30 Jun. 2008, the disclosure of which is also incorporated herein by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates to a wiring forming method. 
       BACKGROUND 
       [0003]    Over recent years, to respond to the needs of the realization of miniaturization and high integration of electronic parts, the development of a method for mounting semiconductor chips three-dimensionally is advancing. As such a method, a method via wire bonding is known in which for example, a plurality of semiconductor chip electrodes laminated are electrically connected together using wires. 
         [0004]    However, in this method, the length limitation of wires themselves limits the shape of semiconductor chips and the position of electrodes. Further, it is necessary to ensure a space mainly in the height direction as an area for wiring. 
         [0005]    Therefore, instead of wire bonding, some methods for forming a conductive layer in a wiring manner have been proposed in which conductive ink droplets are ejected from an ink-jet head between electrodes to connect the electrodes (for example, refer to Patent Documents 1-3). Any of these methods makes it possible to eliminate the above shape limitation using wires. 
       PRIOR ART DOCUMENTS 
     Patent Documents  
       [0006]    Patent Document 1: Examined Japanese Patent Application Publication No. 3918936 
         [0007]    Patent Document 2: Examined Japanese Patent Application Publication No. 4081666 
         [0008]    Patent Document 3: Unexamined Japanese Patent Application Publication No. 2005-302813 
       BRIEF DESCRIPTION OF THE INVENTION 
     Problems to be Solved by the Invention  
       [0009]    However, according to the methods described in above Patent Documents 1 and 2, since an ink-jet head is scanned parallel to the upper sides of semiconductor chips laminated in a staircase pattern, it is difficult to form conductive layers by continuously depositing ink droplets on the surfaces having an steep angle with respect to the ink ejection surface such as the side surfaces of the bump portions of the semiconductor chips. Even via continuous ink droplet deposition, especially when an angular portion is not deposited with an adequate amount of ink droplets, the ink, namely, a conductive layer is broken during drying in some cases. According to the method described in Patent Document 3, a taper-shaped resin portion is provided for the bump portions to eliminate the steep-angle surfaces. However, this method widens the bump portions in the width direction. 
         [0010]    Further, a common on-demand ink-jet head has a short flying distance of ink droplets, which limits the laminating height of semiconductor chips, namely, substrates. 
         [0011]    In view of the above circumstances, the present invention was completed, and the problem thereof is to provide a wiring forming method enabling to realize miniaturization and multi-lamination of substrates with formation of excellent wiring to electrically connect the laminated substrates to one another. 
       Means to Solve the Problems  
       [0012]    To solve the above problem, the invention of item  1  is a wiring forming method in which ink droplets of an ink having chargeability is ejected from an ink-jet system print head and deposited on a plurality of substrates to form wiring to connect a plurality of the substrates, wherein a conductive layer forming step is provided in which using those which are laminated as a plurality of the substrates and also have electrodes on the upper surface or the side surface of each substrate showing an exposed surface, as well as using a conductive ink containing a conductive material as the ink, in the state of applying a voltage between the print head and a plurality of the substrates, while a plurality of the substrates and the print head are relatively shifted approximately parallel to at least the upper surfaces of the substrates, ink droplets of the conductive ink are ejected from the print head to form a conductive layer on the exposed surface to electrically connect the electrodes to one another among the substrates. 
         [0013]    The invention of item  2  is the wiring forming method described in item  1 , wherein the conductive ink has an electrical conductivity of at least 0.1 μS/cm and a specific dielectric constant of at least 10, and an ink droplet of the conductive ink to be ejected has a volume of 0.001 pl-1 pl. 
         [0014]    The invention of item  3  is the wiring forming method described in item  1  or  2 , wherein a voltage applied between the print head and a plurality of the substrates is less than the insulation breakdown voltage of air. 
         [0015]    The invention of item  4  is the wiring forming method described in any of items  1 - 3 , wherein as a plurality of the substrates, substrates laminated so as for the end portions to be arranged in a staircase pattern are used and the maximum diameter on deposition of an ink droplet of the conductive ink to be ejected is at most half of each of the bump portions of the step-like portions. 
         [0016]    The invention of item  5  is the wiring forming method described in any of items  1 - 4 , wherein when a plurality of the substrates and the print head are relatively shifted approximately parallel to the upper surfaces of the substrates, ink droplets of the conductive ink are ejected from the print head at an ejection frequency f 1  satisfying following Expression (1): 
         [0000]        f   1   =V ( L   1   +L   2   −rD )/{ DL   2 (1 −r )} [Hz]  (1)
 
         [0017]    wherein D represents the diameter on deposition of an ink droplet of the conductive ink to be ejected; L 1  represents the total length of the conductive layer formed on each of the side surfaces of a plurality of the substrates; L 2  represents the total length of the conductive layer formed on each of the upper surfaces of a plurality of the substrates; r represents a ratio of the radius direction maximum length of ink droplets to the diameter D in a portion where ink droplets of the conductive ink having been continuously deposited are overlapped; and V represents the relative speed of a plurality of the substrates and the print head. 
         [0018]    The invention of item  6  is the wiring forming method described in item  5 , wherein when the conductive layer is formed on each of the side surfaces of a plurality of the substrates, ink droplets of the conductive ink are ejected at an ejection frequency f 1  satisfying above Expression (1), and when the conductive layer is formed on each of the upper surfaces of a plurality of the substrates, ink droplets of the conductive ink are ejected at an ejection frequency f 2  satisfying following Expression (2): 
         [0000]        f   2   =V ( L   1   +L   2   −rD )/{ D ( L   1   +L   2 )(1− r )} [Hz]  (2)
 
         [0019]    The invention of item  7  is the wiring forming method described in any of items  1 - 6 , wherein prior to the conductive layer forming step, an insulating layer forming step is provided in which using an insulating ink containing an insulating material as the ink, in the state of applying a voltage between the print head and a plurality of the substrates, while a plurality of the substrates and the print head are relatively shifted approximately parallel to at least the upper surfaces of the substrates, ink droplets of the insulating ink are ejected from the print head to form an insulating layer on the exposed surface to insulate the substrates and the conductive layer. 
         [0020]    The invention of item  8  is the wiring forming method described in item  7 , wherein the insulating ink has an electrical conductivity of at least 0.1 μS/cm and a specific dielectric constant of at least 10, and an ink droplet of the insulating ink to be ejected has a volume of 0.001 pl-1 pl. 
         [0021]    The invention of item  9  is the wiring forming method described in item  7  or  8 , wherein the insulating layer is formed only in a portion where the conductive layer is formed. 
         [0022]    The invention of item  10  is the wiring forming method described in any of items  7 - 9 , wherein the insulating layer is formed with a single insulating material. 
         [0023]    The invention of item  11  is the wiring forming method described in any of items  7 - 10 , wherein after the insulating layer forming step, a surface treatment step is provided prior to the conductive layer forming step. 
         [0024]    The invention of item  12  is the wiring forming method described in any of items  1 - 11 , wherein the substrates are semiconductor chips. 
       Effects of the Invention  
       [0025]    According to the invention described in item  1 , using a conductive ink containing a conductive material as an ink, in the state of applying a voltage between a print head and a plurality of substrates, ink droplets are ejected, whereby a conductive layer is formed on an exposed surface to electrically connect electrodes to one another among the substrates. Thereby, by applying an electrostatic attractive force, moving toward the substrates, to ink droplets having been ejected from the print head, ink droplets can continuously be deposited even on the surfaces having a steep angle with respect to the ink ejection surface of the print head without providing a taper member to reduce the angle. Especially, an adequate amount of ink droplets can be deposited on the angular portions where electrical force lines are concentrated. Therefore, miniaturization of the laminated substrates can be realized with formation of excellent wiring to electrically connect each laminated substrate. 
         [0026]    Further, since ink droplets are ejected in the state of applying a voltage between a print head and a plurality of substrates, compared to the conventional on-demand ink-jet head with no applied electrostatic attractive force, the flying distance of ink droplets can be extended. Therefore, high loading of substrates can be realized. 
         [0027]    According to the invention described in item  2 , a conductive has an electrical conductivity of at least 0.1 μS/cm and a specific dielectric constant of at least 10 and an ink droplet of the conductive ink to be ejected has a volume of 0.001 pl-1 pl, whereby an attractive force adequate for deposition on substrates along electrical force lines can be allowed to act on ink droplets with inhibited air resistance and inertia force acting on the ink droplets. Therefore, more excellent wiring can be formed to electrically connect each laminated substrate. 
         [0028]    According to the invention described in item  3 , a voltage applied between a print head and a plurality of substrates is less than the insulation breakdown voltage of air, which causes no electrical short circuit. Therefore, wiring can stably be formed. 
         [0029]    According to the invention described in item  4 , the maximum diameter on deposition of an ink droplet to be ejected is at most half of each of the bump portions of the step-like portions, whereby at least 2 ink droplets are deposited on each bump portion, and thereby differently from the case of depositing one ink droplet, the ink is prevented from becoming wet and spreading in the bump portion to a large extent. Therefore, high precision wiring can be formed to electrically connect each laminated substrate. 
         [0030]    According to the invention described in item  5 , when a plurality of substrates and a print head are relatively shifted approximately parallel to the upper surfaces of the substrates, ink droplets of a conductive ink are ejected from the print head at an ejection frequency f 1 =V(L 1 +L 2 −rD)/{DL 2 (1−r)} [Hz], whereby ink droplets are ejected only at an ejection frequency in which the ejection frequency V(L 1 +L 2 −rD)/{DL 2 (1−r)} [Hz] of ink droplets having been continuously deposited so as to be overlapped on the surface parallel to the ink ejection surface at a length rD is multiplied by (L 1 +L 2 )/L 2 . In such a manner, ink droplets are ejected at an adequate amount for deposition on the side surfaces of substrates where ink droplets are hard to deposit. Therefore, under simple print head drive conditions, excellent wiring can certainly be formed to electrically connect each laminated substrate. Incidentally, in actual wiring formation, the electrode position is previously aligned and then the first shot of ink droplets is allowed to be deposited on the electrode. Thereafter, the ejection frequency f 1  is memorized in the control member of the print head and then ink droplets are ejected at the ejection frequency f 1 . 
         [0031]    According to the invention described in item  6 , when a conductive layer is formed on each of the side surfaces of a plurality of substrates, ink droplets of a conductive ink are ejected at the ejection frequency f 1 , and when a conductive layer is formed on each of the upper surfaces of a plurality of substrates, ink droplets of a conductive ink are ejected at an ejection frequency f 2 =V(L 1 +L 2 −rD)/{D(L 1 +L 2 )(1−r)} [Hz], whereby as ink droplets are ejected at an adequate amount for deposition on each of the side surfaces of the substrates when ink droplets are hard to deposit, an appropriate amount of ink droplets can be ejected on each of the upper surfaces where ink droplets are easy to deposit. Therefore, excellent wiring can certainly and efficiently be formed to electrically connect each laminated substrate. Incidentally, in actual wiring formation, the electrode position is previously aligned and then the first shot of ink droplets is allowed to be deposited on the electrode. Thereafter, the ejection frequencies f 1  and f 2  are memorized in the control member of the print head and then ink droplets are ejected as the ejection frequencies f 1  and f 2  are switched. 
         [0032]    According to the invention described in item  7 , prior to a conductive layer forming step, using an insulating ink containing an insulating material as an ink, ink droplets are ejected in the state of applying a voltage between a print head and a plurality of substrates to form an insulating layer on the exposed surface to insulate the substrates and a conductive layer. Thereby, by applying an electrostatic attractive force, moving toward the substrates, to ink droplets having been ejected from the print head, ink droplets can continuously be deposited even on the surfaces having a steep angle with respect to the ink ejection surface of the print head without providing a taper member to reduce the angle. Especially, an adequate amount of ink droplets can be deposited on the angular portions where electrical force lines are concentrated. Therefore, miniaturization of the laminated substrates can be realized with formation of an excellent insulating layer to insulate the substrates and a conductive layer. 
         [0033]    Further, since ink droplets are ejected in the state of applying a voltage between a print head and a plurality of substrates, compared to the conventional on-demand ink-jet head with no applied electrostatic attractive force, the flying distance of ink droplets can be extended. Therefore, high loading of substrates can be realized. 
         [0034]    According to the invention described in item  8 , an insulating ink has an electrical conductivity of at least 0.1 μS/cm and a specific dielectric constant of at least 10, and an ink droplet of the insulating ink to be ejected has a volume of 0.001 pl-1 pl. Thereby, an attractive force adequate for deposition on substrates along electrical force lines can be applied to ink droplets with inhibited air resistance and inertia force acting on the ink droplets. Therefore, an excellent insulating layer to insulate the substrates and a conductive layer can certainly is formed on each laminated substrate. 
         [0035]    According to the invention described in item  9 , an insulating layer is formed only in a portion where a conductive layer is formed, whereby the insulating layer is formed only in a portion which needs to be insulated. Therefore, an insulating layer is efficiently formed. 
         [0036]    According to the invention described in item  10 , an insulating layer is formed with a single insulating material, whereby the wetting and charged state of conductive ink droplets forming a conducting layer on the insulating layer becomes uniform. Therefore, excellent wiring to electrically connect each laminated substrate can stably be formed. 
         [0037]    According to the invention described in item  11 , after an insulating layer forming step, surface treatment, to enhance adhesion properties of a conductive ink, is carried out for the surface of an insulating layer prior to a conductive layer forming step, whereby adhesion properties of ink droplets of this conductive ink is enhanced and also the wetting and charged state of the ink droplets become uniform. Therefore, excellent wiring to electrically connect each laminated substrate can stably be formed. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0038]      FIG. 1  is a schematic view showing the entire constitution of an ink-jet apparatus in an embodiment; 
           [0039]      FIGS. 2   a  through  2   c  are perspective views of a substrate unit in the embodiment; 
           [0040]      FIG. 3  is an exploded perspective view of a print head; 
           [0041]      FIG. 4  is a side sectional view of the print head; 
           [0042]      FIG. 5  is a view illustrating how ink droplets are deposited on the side surfaces of substrates; 
           [0043]      FIG. 6  includes a view showing (a) the moment when a plurality of ink droplets have been deposited on the bump portion of a substrate unit and a view showing (b) the moment when one ink droplet has been deposited thereon; 
           [0044]      FIG. 7  includes (a) a schematic view showing one example of and (b) a schematic view showing another example of the entire constitution of an ink-jet apparatus in a modified example of the embodiment; and 
           [0045]      FIG. 8  is a perspective view of a substrate unit in the modified example of the embodiment. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0046]    With reference to the drawings, the embodiment of the present invention will now be described. 
         [0047]    Initially, the entire constitution of an ink-jet apparatus  1  according to the present embodiment will now be described with reference to  FIGS. 1 and 2 . 
         [0048]      FIG. 1  is a schematic view showing the entire constitution of the ink-jet apparatus  1  and  FIG. 2  is a perspective view of a substrate unit  10  to be described later. 
         [0049]    As shown in  FIG. 1 , the ink-jet apparatus  1  is provided with a print head  2  in which a nozzle  211  is formed to eject ink droplets R of an ink I having chargeability and an opposite surface opposed to the nozzle  211  of the print head  2 , as well as an opposite electrode  3  supporting a substrate unit  10  in which ink droplets R are deposited on the opposite surface and a control member  4  to drive the print head  2  to eject ink droplets R from the nozzle  211 . This ink-jet apparatus  1  allows ink droplets R having conductivity to be deposited on a substrate unit  10  for wiring formation of the substrate unit  10 . 
         [0050]    The opposite electrode  3  is flat plate-shaped supporting a substrate unit  10  and arranged parallel to the ink ejecting surface  211   c  of the print head  2  with a predetermined clearance distance. The clearance distance between the opposite electrode  3  and the print head  2  is appropriately set in the range of about 0.1-5.0 mm. Further, the opposite electrode  3  is grounded and always maintained at the ground potential. Thereby, as described later, when charged ink droplets R are deposited on a substrate unit  10 , the opposite electrode  3  allows the charge to escape via grounding. Herein, the opposite electrode  3  is equipped with an unshown positioning member to position the substrate unit  10 . Further, the opposite electrode  3  can be shifted parallel to the plane when the substrate unit  10  is placed. 
         [0051]    The control member  4  is a computer containing an unshown CPU, ROM, and RAM, and is connected to an electrostatic voltage power source  41  to apply an electrostatic voltage to the print head  2  and a piezoelectric element  23 , to be described later, of the print head  2 . This control member  4  applies an electrostatic voltage to the print head  2  by controlling the electrostatic voltage power source  41  to generate an electrostatic field between the nozzle plate  21  and the opposite electrode  3  and also to eject ink droplets R from the nozzle  211  by controlling the deformation of the piezoelectric element  23 . Further, the control member  4  can control the scanning of the print head  2 . Herein, a voltage applied by the electrostatic voltage power source  41  may be direct or alternating current. Further, it is possible that the electrostatic voltage power source  41  is connected to the opposite electrode  3  to apply a voltage to the opposite electrode  3  and the print head  2  is grounded. Still further, in the state when the print head  2  is fixed, the control member  4  may carry out scan-controlling of the stage (the placement plane of a substrate unit  10 ) of the opposite electrode  3 . 
         [0052]    The ink I is an ink exhibiting conductivity and chargeability by containing a metal nanoparticle. As this metal nanoparticle, listed are, for example, silver, gold, cupper, palladium, platinum, nickel, rhodium, tin, and indium, or alloys thereof. 
         [0053]    The production method of such a metal nanoparticle is roughly divided into 2 types. One is a physical method and the other is a chemical method. The physical method is a method to produce nanoparticles by commonly pulverizing bulk metal. The chemical method is a method to produce nanoparticles in which metal atoms are generated and their aggregation is controlled. 
         [0054]    The chemical method is roughly categorized into a wet method carried out in liquid and a dry method carried out in air or under reduced pressure ambience. A chemical reduction method known as a wet method is a method to produce nanoparticles in which a reducing agent is added to a metal ion solution or a metal salt solution containing a reducing agent is heated to reduce metal ions. As an ink containing such nanoparticles, an ink as disclosed in Examined Japanese Patent Application Publication No. 3933138 is usable. As the dry method, an in-gas evaporation method is known. The in-gas evaporation method is a method to produce nanoparticles in which a metal is evaporated in an inert gas and then cooled and aggregated via collision with the gas. It is known that the dry method can allow particle diameter to be smaller than the wet method. The dry method can allow the particle diameter to become even several nm. 
         [0055]    The particle diameter of a metal nanoparticle in an ink I used for the present embodiment is 1-100 nm, preferably 1-50 nm. A metal nanoparticle of a particle diameter of less than 1 nm can be used. However, such a particle is extremely difficult to produce, being therefore unpractical. Further, when a metal nanoparticle having a particle diameter of more than 100 nm is used, the nozzle  211  may be clogged. 
         [0056]    The concentration of a metal nanoparticle contained in the ink I is preferably high so that the resistance value of a conductive layer  12 , to be described later, formed by drying the ink I becomes a value close to the resistance value of an electrode  112 . Specifically, the value is preferably at least 10% by weight, more preferably 20% by weight. Herein, the concentration of this metal nanoparticle can be allowed to be up to about 80% by weight. 
         [0057]    In the ink I, as a solvent allowed to contain a metal nanoparticle, water or a water-soluble organic solvent is used. Such a so-called aqueous ink exhibits excellent electrical conductivity compared to an oil-based ink employing a nonpolar solvent. Further, this solvent preferably exhibits lower vapor pressure and higher boiling point so that the viscosity of the ink I does not easily increase and drying does not easily occur. The boiling point of the solvent is preferably at least 150° C., more preferably at least 200° C. The water content is preferably at most 40% by weight from the viewpoint of drying performance. 
         [0058]    The viscosity of the ink I is, at the ejection temperature, preferably 2 mPa·s-10 mPa·s, more preferably 3 mPa·s-6.5 mPa·s from the viewpoint of ejection stability. The ejection temperature is preferably 20-60° C., more preferably 25-50° C. In the case of less than 25° C., cooling is required in some cases. In the case of more than 50° C., the print head  2  and the flow path member of the ink I may be burdened. 
         [0059]    The surface tension of the ink I is preferably 20 mN/m-50 mN/m, being, however, more preferably 25 mN/m-45 mN/m from the viewpoint of ejection stability. 
         [0060]    The electrical conductivity of the ink I is, to allow electrostatic attraction force to act, preferably 0.1 μS/cm-2000 μS/cm, being, however, more preferably 1 μS/cm-1000 μS/cm from the viewpoint of high precision drawing. 
         [0061]    The specific dielectric constant of the ink I is preferably at least 10. 
         [0062]    As shown in  FIG. 2A , a substrate unit  10  is produced by laminating a plurality of substrates  11  so as for the side portions to be formed in a staircase pattern. In the present embodiment, 3-step lamination is carried out. The substrates  11  are not specifically limited, which are semiconductor chips and may be semiconductor wafers. On the substrates  11 , a plurality of integrated circuits (for example, circuits having a transistor and memory)  111  and a plurality of electrodes (for example, pads)  112  are mounted. 
         [0063]    Further, in the substrates  11 , at least one insulating film (not shown) is formed. This insulating film is referred to as a passivation film, which is formed, for example, using SiO 2 , Si 3 N 4 , or a polyimide resin. Herein, the insulating film allows at least part of an electrode  112  to be exposed. 
         [0064]    The electrode  112  is provided on the upper surface of each substrate  11  exposed in the step-like portion. In the present embodiment, the same number of the electrodes is arranged in each substrate  11 . Each electrode  112  is electrically connected with an integrated circuit  111 . Further, the electrode  112  is formed of an aluminum-based or cupper-based metal and with no limitation, the surface shape is rectangular. 
         [0065]    This electrode  112  is electrically mutually connected to another electrode  112  corresponding thereto among substrates  11  via a conductive layer  12 . The conductive layer  12  is formed, by a method to be described later, via drying of ink droplets R of an ink I having been ejected from the print head  2 . In the present embodiment, this conductive layer  12  is formed at least on the upper surface and the side surface of each substrate  11  in the step-like portion. 
         [0066]    Herein, as shown in  FIG. 2B , the substrate unit  10  may be provided with taper-shaped insulating members  13  in the step-like bump portions, or lamination may be carried out by matching the outer circumference of each substrate  11  as shown in  FIG. 2C . However, in the latter case, each electrode  112  of the substrates  11  except the top one is provided on the exposed side surfaces of the substrates  11 . 
         [0067]    Subsequently, the constitution of a print head  2  will now be described with reference to  FIGS. 3 and 4 . 
         [0068]      FIG. 3  is an exploded perspective view of the print head  2 , and  FIG. 4  is a side sectional view of the print head  2 . 
         [0069]    As shown in  FIG. 3 , the print head  2  has a nozzle plate  21 , a body plate  22 , and piezoelectric elements  23 . The nozzle plate  21  is a silicon substrate or a silicon oxide substrate having a thickness of about 150-300 μm. A plurality of nozzles  211  are formed in the nozzle plate  21  and a plurality of these nozzles  211  are arranged in a line. 
         [0070]    The body plate  22  is a silicon substrate having a thickness of about 200-500 μm. In the body plate  22 , an ink supply orifice  221 , an ink reservoir  222 , a plurality of ink supply paths  223 , and a plurality of pressure chambers  224  are formed. The ink supply orifice  221  is a circular penetrated hole of a diameter of about 400-1500 μm The ink reservoir  222  is a groove having a width of about 400-1000 μm and a depth of about 50-200 μm. The ink supply path 223 is a groove having a width of about 50-150 μm and a depth of about 30-150 μm. The pressure chamber  224  is a groove having a width of about 150-350 μm and a depth of about 50-200 μm. 
         [0071]    The nozzle plate  21  and the body plate  22  are formed so as to be bonded together. In the bonded state, the nozzles  211  of the nozzle plate  21  and the pressure chambers  224  of the body plate  22  are formed so as to correspond one-on-one. 
         [0072]    In the state where the nozzle plate  21  and the body plate  22  are bonded together, an ink is supplied to the ink supply orifice  221  and then the ink is temporally reserved in the ink reservoir  222 . Thereafter, the ink is supplied to each pressure chamber  224  through each ink supply path  223  from the ink reservoir  222 . 
         [0073]    The piezoelectric element  23  is formed so as to be allowed to adhere to the position corresponding to each pressure chamber  223  of the body plate  22 . The piezoelectric element  23  is an actuator formed of PZT (lead zirconium titanate) and is deformed via voltage application to eject an ink within the pressure chamber  224  from the nozzle  211 . 
         [0074]    Herein, although not shown in  FIG. 3 , a borosilicate glass plate  24  (refer to  FIG. 4 ) is present between the nozzle plate  21  and the body plate  22 . 
         [0075]    As shown in  FIG. 4 , one nozzle  211  and one pressure chamber  224  each are constituted corresponding to one piezoelectric element  23 . 
         [0076]    In the nozzle plate  21 , steps are formed in the nozzle  211  and the nozzle  211  is constituted of a lower step portion  211   a  and an upper step portion  211   b . The lower step portion  211   a  and the upper step portion  211   b  each are circularly shaped. The diameter S 1  (the distance in the horizontal direction in  FIG. 4 ) of the lower step portion  211   a  is smaller than the diameter S 2  (the distance in the horizontal direction in  FIG. 4 ) of the upper step portion  211   b.    
         [0077]    The lower step portion  211   a  of the nozzle  211  is a section to directly eject an ink having flowed from the upper step portion  211   b . The diameter S 1  of the lower step portion  211   a  is 1-10 μm and the length H (the distance in the vertical direction in  FIG. 4 ) thereof is 1.0-5.0 μm. The reason why the height H of the lower step portion  211   a  is limited in the range of 1.0-5.0 μm is that ink deposition accuracy can be enhanced dramatically. 
         [0078]    On the other hand, the upper step portion  211   b  of the nozzle  211  is a section to allow an ink having flowed from the pressure chamber  224  to flow to the lower step portion  211   a , and the diameter S 2  thereof is 10-60 μm. The reason why the lower limit of the diameter S 2  of the upper step portion  211   b  is limited to be at least 10 μm is that in the case of less than 10 μm, with respect to the flow channel resistance of the entire nozzle  211  (the lower step portion  211   a  and the upper step portion  211   b ), the flow channel resistance of the upper step portion  211   b  becomes a value which is not negligible, whereby the ejection efficiency of the ink is decreased. 
         [0079]    In contrast, the reason why the upper limit of the diameter S 2  of the upper step portion  211   b  is limited to be at most 60 μm is that as the diameter S 2  of the upper step portion  211   b  is increased, the lower step portion  211   a , serving as the ink ejection section, becomes thinner and weaker (due to the area increase of the lower step portion  211   a , mechanical strength is decreased), whereby the deformation thereof easily occurs during ink ejection, resulting in a decrease in ink deposition accuracy. Namely, when the upper limit of the diameter S 2  of the upper step portion  211   b  exceeds 60 μm, with ink ejection, the deformation of the lower step portion  211   a  occurs to a very large extent, whereby it may be impossible to allow the deposition accuracy to fall within a specified value (±0.5° with respect to a desired ejection direction). 
         [0080]    A borosilicate glass plate  24  of a thickness of several hundred μm is provided between the nozzle plate  21  and the body plate  22 . An opening portion  24   a  to communicatively connect the nozzle  211  and the pressure chamber  224  is formed in the borosilicate glass plate  24 . The opening portion  24   a  is a penetrated hole leading from the pressure chamber  224  to the upper step portion  211   b  of the nozzle  211 , being a section functioning as a flow channel to pass an ink from the pressure chamber  224  toward the nozzle  211 . The pressure chamber  224  is a section to apply pressure to the ink within the pressure chamber  224  via the deformation of the piezoelectric element  23 . 
         [0081]    In the print head  2  having the above constitution, when the piezoelectric element  23  is deformed, a pressure is applied to an ink within the pressure chamber  224 , and then the ink is passed from the pressure chamber  224  to the opening portion  24   a  of the borosilicate glass plate  24  to reach the nozzle  211 , whereby finally, the ink is ejected from the lower step portion  211   a  of the nozzle  211 . 
         [0082]    Incidentally, the print head  2  is provided for the apparatus main body so as to be scanned in the direction parallel to the ink ejection surface  211   c  (in the X direction of  FIG. 1 ). 
         [0083]    Next, a wiring forming method to form a conductive layer  12  on a substrate unit  10  will now be described with reference to  FIGS. 5 and 6 . 
         [0084]      FIG. 5  is a view illustrating how ink droplets R are deposited on the side surfaces of substrates  11 .  FIG. 6  is a view illustrating how ink droplets R are deposited on the bump portion of a substrate unit  10 . 
         [0085]    Initially, the following conductive layer forming step is performed to deposit ink droplets R, becoming a conductive layer  12 , on a substrate unit  10  from the ink-jet apparatus  1 . 
         [0086]    First, a substrate unit  10  is positioned and fixed to the opposite electrode  3 . Then, an electrostatic voltage is applied to the print head  2  by controlling the electrostatic power source  41  using the control member  4  to generate an electrostatic field between the nozzle plate  21  and the opposite electrode  3 . In this case, attention should be made so that the potential difference produced between the print head  2  and the substrate  11  is less than the insulation breakdown voltage of air (about 3 kV/mm). 
         [0087]    In this state, as sown in  FIG. 5 , as the print head  2  is scanned, above the step-like portions of the substrate unit  10 , parallel to the upper surfaces of the substrates  11  in the direction of increasing the gap with respect to the substrates  11 , ink droplets R are ejected from the nozzle  211 . Then, by an electrostatic field between the nozzle plate  21  and the opposite electrode  3 , electrical force lines as shown by dashed lines of the drawing are formed between the print head  2  and the substrate unit  10 , whereby ink droplets R having been applied with an electrostatic force fly in the direction along these electric force lines to deposit on the substrates  11 . Herein, the scanning initiation position of the print head  2  is set so that the first shot of ink droplets R is deposited on electrodes  112  of the top substrate  11  (refer to  FIGS. 2 and 8 ). Further, the diameter on deposition of ink droplet R depends on physical properties of an ink I and the surface energy or surface state of a substrate  11  where deposition is made. When deposition is made on a substrate  11  not absorbing an ink I, the above diameter is about 1.5-4.0 times of the diameter during flying. 
         [0088]    In this manner, an electrostatic attractive force, moving toward the substrates  11 , is applied to ink droplets R having been ejected, whereby the ink droplets R can continuously be deposited even on the side surfaces of the substrates  11  having a steep angle with respect to the ink ejection surface  211   c  of the print head  2  without providing a taper member to reduce the angle. Especially, an adequate amount of ink droplets R can be deposited on the angular portions where electrical force lines are concentrated. 
         [0089]    In this case, the ejection frequency of the print head  2  to eject ink droplets R is determined, based on the shape of the step-like portion, as follows: 
         [0090]    The case of forming a conductive layer  12  from point A to point B shown in  FIG. 5  is taken into account. In this case, when a conductive layer  12  is formed on the side surfaces of substrates  11 , ink droplets R are ejected at a frequency f 1  satisfying following Expression (1). When a conductive layer  12  is formed on each of the upper surfaces of the substrates  11 , ink droplets R are ejected at a frequency f 2  satisfying following Expression (2). 
         [0000]        f   1   =V ( L   1   +L   2   −rD )/{ DL   2 (1− r )} [Hz]  (1)
 
         [0000]        f   2   =V ( L   1   +L   2   −rD )/{ D ( L   1   +L   2 )(1 −r )} [Hz]  (2)
 
         [0091]    wherein D represents the diameter on deposition of an ink droplet R to be ejected; L 1  represents the total length of a conductive layer  12  formed on the side surfaces of the substrates  11 ; L 2  represents the total length of a conductive layer  12  formed on the upper surfaces of the substrates  11 ; r represents a ratio of the radius direction maximum length of ink droplets R to the diameter D in a portion where ink droplets R having been continuously deposited are overlapped (refer to  FIG. 6A  and herein, this drawing shows the state of immediately prior to deposition of ink droplet R); and V represents the scanning speed of the print head. 
         [0092]    These ejection frequencies f 1  and f 2  are memorized in the control member  4  and appropriately switched via control of the piezoelectric elements  23  by the control member  4 . 
         [0093]    For example, in the case where D=0.01 mm, L 1 =1 11 +1 12 =0.5 mm, L 2 =1 21 +1 22 +1 23 =1 mm, V=33.3 mm/sec, r=0.5, 1 11 =0.3 mm, 1 12 =0.2 mm, 1 21 =0.4 mm, 1 22 =0.2 mm, and 1 23 =0.4 mm, initially, as the print head  2  is shifted from the state of being located above point A at a scanning rate V, ink droplets R are ejected on the upper surface of the top substrate  11  at an ejection frequency f 2 =33.3(0.5+1−0.5×0.01)/{0.01×(0.5+1)×(1−0.5)}≈6700 Hz=6.7 kHz. When a necessary number of shots, namely, (1 21 −rD)/{D(1−r)}=(0.4−0.005)/(0.01×0.5)=79 shots of ink droplets R are ejected, switching is made to an ejection frequency f 1 =33.3(0.5+1−0.5×0.01)/{0.01×1×(1−0.5)}≈10000 Hz=10 kHz, whereby ink droplets R are ejected on the side surface of the top substrate  11 . Also, in this case, when the ejection of a necessary number of shots, namely, (1 11 −rD)/{D(1−r)}=(0.3−0.005)/(0.01×0.5)=59 shots of ink droplets R is terminated, switching is again made to a ejection frequency f 2 =6.7 kHz. In this manner, with respect to the upper surface and the side surface of the middle surface  11  and the upper surface of the bottom substrate  11 , as the ejection frequencies f 1  and f 2  are appropriately switched for each, ink droplets R are continuously ejected and deposited until reaching point B. 
         [0094]    In this manner, as the ejection frequencies f 1  and f 2  are appropriately switched, ink droplets R are ejected, whereby as ink droplets R are ejected at an adequate amount to be deposited on the side surfaces of substrates  11  where ink droplets R are hard to deposit, an appropriate amount of ink droplets R can be ejected on the upper surfaces of the substrates  11  where ink droplets R are easy to deposit. 
         [0095]    Incidentally, ink droplets R may be ejected at a constant ejection frequency f 1 . Even under this single print head  2  drive condition, ink droplets R can be ejected at an adequate amount to be deposited on the side surfaces of substrates  11  where ink droplets R are hard to deposit. 
         [0096]    Further, with regard to ink droplets R to be ejected on the step-like portions, as shown in  FIG. 6A , the maximum diameter on deposition is preferably at most half of each bump portion of the step-like portions. As shown in  FIG. 6B , if only one ink droplet R is deposited on the step-like portion, this ink droplet R becomes wet and spreads on the step-like portion to a large extent. Therefore, an ink droplet R is ejected so that the maximum diameter thereof is at most half of each bump portion of the step-like portion, whereby at least 2 ink droplets R are deposited on the each bump portion. Thereby, the ink can be prevented from being wet and spreading on the bump portion. 
         [0097]    Further, an ink droplet R to be ejected preferably has a volume of 0.001 pl-1 pl. Thereby, air resistance and inertia force acting on the ink droplet can be inhibited. 
         [0098]    After the conductive layer forming step has been terminated by depositing ink droplets R on the substrate unit  10 , the ink droplets R are fired. The firing method includes firing using a dryer or a hot plate. In the present embodiment, to control the wettability of an ink I to enhance deposit performance, a subbing agent (a silane coupling agent or titanium coupling agent) is coated on substrates  11 . Therefore, firing is preferably carried out under conditions to ensure the heat resistance of various types of coupling agents. 
         [0099]    In such firing, it is preferable to carry out predrying at 100-150° C. for 10-30 minutes and then main drying at 150-200° C. for 60-180 minutes. When no predrying is carried out, a solvent remains in a fused metal, whereby the resistance value may be increased. When the temperature of predrying is less than 100° C., almost no solvent is evaporated, whereby no effect may be produced. At a temperature of more than 150° C., fusion of metal nanoparticles may be initiated. When the temperature of main drying is less than 150° C., no fusion of the metal nanoparticles occurs, whereby the resistance value may be increased. At a temperature of more than 200° C., a subbing agent is degraded and thereby mixing with a fused metal occurs, resulting in the possibility of an increase in the resistance value. For main drying, a hot plate is preferably used. The reason is that use of a hot plate makes it possible that heat is directly transferred to an ink I, resulting in acceleration of fusion of metal nanoparticles. 
         [0100]    Via the above firing, the solvent of ink droplets R is evaporated, whereby a conductive layer  12  is fixed to the substrate unit  10 . 
         [0101]    As describe above, according to the firing forming method of the present embodiment, ink droplets R can continuously be deposited even on the side surfaces of substrates  11  having a steep angle with respect to the ink ejection surface  211   c  of the print head  2  without providing a taper member to reduce the angle. Especially, an adequate amount of ink droplets R can be deposited on the angular portions where electrical force lines are concentrated. Therefore, miniaturization of a substrate unit  10  can be realized with formation of excellent wiring to electrically connect each laminated substrate  11 . 
         [0102]    Further, ink droplets R are ejected in the state of applying a voltage between the print head  2  and the substrates  11 , whereby compared to the conventional on-demand ink-jet head with no applied electrostatic attractive force, the flying distance of ink droplets R can be extended. Therefore, high loading of substrates  11  can be realized. 
         [0103]    Further, the ink I has an electrical conductivity of at least 0.1 μS/cm and a specific dielectric constant of at least 10, and an ink droplet to be ejected has a volume of 0.001 pl-1 pl. Thereby, an attractive force adequate for deposition on the substrates  11  along electrical force lines can be applied to ink droplets R with inhibited air resistance and inertia force acting on the ink droplets R. Therefore, more excellent wiring can be formed to electrically connect each laminated substrate  11 . 
         [0104]    Further, the potential difference produced between the print head  2  and the substrates  11  is less than the insulation breakdown voltage of air, resulting in no electrical short circuit. Therefore, wiring formation can stably be carried out. 
         [0105]    Further, at least 2 ink droplets R are deposited on each bump portion of the step-like portions of a substrate unit  10 , and thereby differently from the case of depositing one ink droplet R, the ink I is prevented from becoming wet and spreading in the bump portion to a large extent. Therefore, high precision wiring can be formed to electrically connect each laminated substrate  11 . 
         [0106]    Further, if ink droplets R are ejected at a constant ejection frequency f 1 , under a single print head  2  drive condition, ink droplets R can be ejected at an adequate amount to be deposited on the side surfaces of the substrates  11  where ink droplets R are hard to deposit. Therefore, under simple print head  2  drive conditions, excellent wiring can certainly be formed to electrically connect each laminated substrate  11 . 
         [0107]    Further, when ink droplets R are ejected as the ejection frequencies f 1  and f 2  are appropriately switched, an appropriate amount of ink droplets R can be ejected on the upper surfaces of the substrates  11  where ink droplets R are easy to deposit as ink droplets R are ejected at an adequate amount to be deposited on the side surfaces of the substrates  11  where ink droplets R are hard to deposit. Thereby, excellent wiring can certainly and efficiently be formed to electrically connect each laminated substrate  11 . 
       MODIFIED EXAMPLE 
       [0108]    Subsequently, an ink-jet apparatus  1 A as a modified example of the ink-jet apparatus  1  according to the above-described embodiment will now be described with reference to  FIGS. 7 and 8 . 
         [0109]      FIG. 7  is a schematic view showing the entire constitution of the ink-jet apparatus  1 A, and  FIG. 8  is a perspective view of a substrate unit  10 A to be described later. 
         [0110]    As shown in  FIG. 7A , in addition to the constitution of the in-jet apparatus  1  in the above embodiment, the ink-jet apparatus  1 A is provided with a print head  2 A for insulating layer formation, an electrostatic voltage power source  41 A to apply an electrostatic voltage to the print head  2 A, a dryer  51  to dry an insulating layer  14  to be described later, and a dryer  52  to dry a conductive layer  12 , the ink-jet apparatus  1 A carrying out wiring formation with respect to the substrate unit  10 A instead of the substrate unit  10  in the above embodiment. 
         [0111]    The print head  2 A is constituted in the same manner as the print head  2  in the above embodiment. Herein, the print head  2 A ejects an ink L containing an insulating material as ink droplets R n  from its nozzle  211 , instead of an ink I n  containing a conductive material. This print head  2 A forms an insulating layer  14  on the step-like portions of the substrate unit  10 A to insulate the substrates  11  and a conductive layer  12  (refer to  FIG. 8 ). 
         [0112]    The Ink I n  contains a resin composition as an insulating material. As such a resin composition, any resin compositions may be used as long as they contain a material exhibiting electrical insulating properties. For example, included are compositions containing a monomer, an oligomer, a polymer, and the like, which composes resins such as epoxy resin, phenol resin, polyimide resin, polyamide resin, polyamide-imide resin, silicone modified polyamide-imide resin, polyester resin, cyanate ester resin, BT resin, acrylic resin, methacrylic resin, melamine resin, urethane resin, and alkyd resin. These compositions may be used alone or in combination of at least two kinds thereof. The above resin composition is preferably contains a heat curable resin. The insulation layer  14  composed of cured products of the ink I n  containing the heat curable resin is superior in heat-resisting property, insulation reliability, and connection reliability. 
         [0113]    In a modified example of the present embodiment, among the above-described resins, the above resin composition particularly preferably contains the epoxy resin. Using the epoxy resin can improve adhesion properties to the conductive layer  12 . 
         [0114]    The epoxy resin includes, for example, bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol S type epoxy resin, bisphenol type epoxy resin, cycloaliphatic epoxy resin, aliphatic chain epoxy resin, glycidyl ester type epoxy resin, and glycidyl ether compounds prepared by a condensation reaction between a phenol compound and an aldehyde compound. These epoxy resins may be contained in combination of at least two kinds thereof. Further, in a modified example of the present embodiment, the above resin composition preferably contains the above epoxy resin and a hardener which hardens the epoxy resin. 
         [0115]    The hardener includes, for example, amines such as diethylenetriamine, triethylenetetramine, methaxylenediamine, diaminodiphenylmethane, diaminodiphenylsulfone, m-phenylenediamine, dicyandiamide; acid anhydrides such as phthalic anhydride, tetrahydro phthalic anhydride, hexahydro phthalic anhydride, methyltetrahydro phthalic anhydride, methylhexahydro phthalic anhydride, methyl nadic anhydride, pyromellitic anhydride, trimellitic anhydride; imidazoles such as imidazole, 2-ethylimidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole, 2-undecylimidazole, 1-benzyl-2-methylimidazole, 2-heptadecylimidazole, 4,5-diphenylimidazole, 2-methylimidazoline, 2-phenyl imidazoline, 2-undecylimidazoline, 2-heptadecylimidazoline, 2-isopropylimidazole, 2,4-dimethylimidazole, 2-phenyl-4-methylimidazole, 2-ethylimidazoline, 2-isopropylimidazoline, 2,4-dimethylimidazoline, and 2-phenyl-4-methylimidazoline; imidazoles in which an imino group is masked by acrylonitrile, phenylene diisocyanate, toluidine isocyanate, naphthalene diisocyanate, methylene bisphenyl isocyanate, melamine acrylate, and the like; phenol compounds such as bisphenol F, bisphenol A, and bisphenol S; and condensation products of phenol compounds and aldehyde compounds. These hardeners may be incorporated alone or in combination of at least two kinds thereof. Further, in the resin composition, there may be contained various additives such as a hardening accelerator, a coupling agent, an antioxidant, and a filler, in accordance with desired properties and condition, in addition to the above-described constituents. 
         [0116]    As the solvent of the ink I n , any solvents may be used as long as they disperse or dissolve the constituents of the above resin composition, and examples thereof include γ-butyrolactone, and cyclohexanone. 
         [0117]    The viscosity of the ink I n  is preferably at most 20 mPa·s at the ejection temperature, more preferably 2-8 mPa·s. When the viscosity is lower than 2 mPa·s, the concentration of the ink I n  becomes smaller, whereby it may take longer to carry out curing. Further, when the viscosity is higher than 8 mPa·s, ejection failure may occur. Similarly to the ink I, the ejection temperature is preferably 20-60° C., more preferably 25-50° C. 
         [0118]    The surface tension of the ink I n  is preferably at least 20 mN/m, more preferably 25-45 mN/m. In the case of less than 25 mN/m, wetting/spreading occurs on ejection, whereby ejection may be hard to carry out. In contrast, in the case of more than 45 mN/m, the ink I n  tends not to be filled. 
         [0119]    The electrical conductivity of the ink I n  is preferably at least 0.1 μS/cm at 25° C. to allow electrostatic attraction force to act, being, however, more preferably at least 1 μS/cm from the viewpoint of high precision drawing. 
         [0120]    The specific dielectric constant of the ink I n  is preferably at least 10. 
         [0121]    The electrostatic voltage power source  41 A is constituted in the same manner as the electrostatic voltage power source  41  in the above embodiment. However, instead of the print head  2 , the print head  2 A is applied with an electrostatic voltage. 
         [0122]    Both the dryer  51  and the dryer  52  are provided above the opposite electrode  3  and connected to the control member  4 . These dryers  51  and  52  can blow hot air downward via control of the control member  4 , and then this hot air dries an insulating layer  14  and a conductive layer  12  each. 
         [0123]    As shown in  FIG. 8 , in addition to the constitution of the substrate unit  10  of the above embodiment, a substrate unit  10 A is formed with an insulating layer  14  to insulate substrates  11  and a conductive layer  12  by a method to be described later. 
         [0124]    Subsequently, a wiring forming method to form a conductive layer  12  and an insulating layer  14  on a substrate unit  11  will now be described. 
         [0125]    Initially, the following insulating layer forming step is performed to deposit ink droplets R n , becoming an insulating layer  14 , on a substrate unit  10 A from the print head  12 A of the ink-jet apparatus  1 A. 
         [0126]    This insulating layer forming step is performed in the same manner as the above-described conductive layer forming step. Namely, in the state when an electrostatic field is generated between the nozzle plate  21  of the print head  2 A and the opposite electrode  3 , ink droplets R n  are ejected. Therefore, by applying an electrostatic attractive force, moving toward the substrates  11 , to ink droplets R n  having been ejected from the print head  2 A, ink droplets R n  can continuously be deposited even on the side surfaces of the substrates  11  having a steep angle with respect to the ink ejection surface  211   c  of the print head  2 A without providing a taper member to reduce the angle. Especially, an adequate amount of ink droplets R n  can be deposited on the angular portions where electrical force lines are concentrated. 
         [0127]    In this case, an insulating layer  14  is preferably formed only in a portion when a conductive layer  12  is formed. Thereby, an insulating layer  14  is formed only in a portion required to be insulated and the insulating layer  14  can efficiently be formed. 
         [0128]    Next, the insulating layer  14  is fired. The opposite electrode  3  is shifted, whereby the substrate unit  10  is positioned below the dryer  51 . Then, the dryer  51  blows hot air downward via control of the control member  4  to dry and then fire the insulating layer  14  of the substrate unit  10 . 
         [0129]    Then, a surface treatment step is performed. In this step, the surface of the insulating layer  14  is surface-treated to enhance contact properties of ink droplets R n . 
         [0130]    The surface treatment method includes a chemical method and a physical method as described in, for example, sections 2 and 3 of chapter 2 of “Hyomen Shori Gijutu Handbook (Surface Treatment Technology Handbook)” (published by NTS Inc., Jan. 7, 2000). Further, the treatment can also be carried out by combination of both methods. A chemical method is employed in the modified example of the present embodiment. 
         [0131]    Of the chemical methods, treatment using a coupling agent is preferable since during electronic device production, contact problems exist and then small film thickness is preferable. As this coupling agent, for example, silane-based, titanate-based, aluminum-based, and zirconium-based coupling agents are listed. The concentration of such a coupling agent is preferably 0.005-30% by weight, more preferably 0.01-5% by weight to realize formation of a film exhibiting excellent wettability and uniformity. As the coating method, any appropriate existing method such as an ink-jet, dipping, spray coating, or spin coating method is usable. Herein, the physical method includes plasma treatment, corona treatment, and UV treatment. Any of these can be applied at the extent that a preexistent insulating layer on the substrates  11  is not destroyed. 
         [0132]    In this manner, the insulating layer  14  is surface-treated, whereby contact properties of ink droplets R n  are enhanced and also the wetting and charged state of the ink droplets R n  can be uniformed, 
         [0133]    Next, a conductive layer forming step is performed. This step is carried out in the entirely same manner as in the above embodiment. 
         [0134]    Then, a conductive layer  12  is fired. The opposite electrode  3  is shifted, whereby the substrate unit  10  is positioned below the dryer  52 . Then, the dryer  52  blows hot air downward via control of the control member  4  to dry and then fire the conductive layer  11  of the substrate unit  10 . Temperature conditions during firing are the same as in the above embodiment. 
         [0135]    Incidentally, as shown in  FIG. 7B , the ink-jet apparatus  1 A may be constituted without the dryer  51 . In this case, firing of the insulating layer  14  is omitted. 
         [0136]    As described above, according to the wiring forming method in the modified example of the present embodiment, it goes without saying that the same effects as in the above embodiment can be produced, and also ink droplets R n  can continuously be deposited even on the side surfaces of the substrates  11  having a steep angle with respect to the ink ejection surface  211   c  of the print head  2 A without providing a taper member to reduce the angle. Especially, an adequate amount of ink droplets R n  can be deposited on the angular portions where electrical force lines are concentrated. Therefore, miniaturization of the substrate unit  10 A can be realized with formation of an excellent insulating layer  14  on each laminated substrate  11  to insulate the substrates  11  and a conductive layer  12 . 
         [0137]    Further, since ink droplets R n  are ejected in the state of applying a voltage between the print head  2 A and substrates  11 , compared to the conventional on-demand ink-jet head with no applied electrostatic attractive force, the flying distance of ink droplets R n  can be extended. Therefore, high loading of substrates  11  can be realized. 
         [0138]    Further, the ink I n  has an electrical conductivity of at least 0.1 μS/cm and a specific dielectric constant of at least 10, and an ink droplet R n  to be ejected has a volume of 0.001 pl-1 pl. Thereby, an attractive force adequate for deposition on the substrates  11  along electrical force lines can be applied to ink droplets R n  with inhibited air resistance and inertia force acting on the ink droplets Rn. Therefore, an excellent insulating layer can be formed on each laminated substrate  11  to insulate the substrates  11  and a conductive layer. 
         [0139]    Further, an insulating layer  14  is formed only in a portion required to be insulated, whereby the insulating layer can efficiently be formed. 
         [0140]    Further, an insulating layer  14  is formed using a single resin composition, that is, an insulating material, whereby the wetting and charged state of ink droplets R to form a conductive layer  12  on the insulating layer  14  becomes uniform. Therefore, excellent wiring can stably be formed to electrically connect each laminated substrate  11 . 
         [0141]    Further, the surface of the insulating layer  14  is surface-treated to enhance contact properties of ink droplets R, whereby contact properties of the ink droplets R are enhanced and also the wetting and charged state of the ink droplets R becomes uniform. Therefore, excellent wiring can stably be formed to electrically connect each laminated substrate  11 . 
       EXAMPLES 
     Example 1  
       [0142]    The present invention will now specifically be described with reference to examples. 
         [0143]    &lt;Substrate Unit&gt; 
         [0144]    A conductive layer  12  and an insulating layer  14  were formed on the following substrate unit  10 A under varied forming conditions for wiring state evaluation. 
         [0145]    An electrode  112  is made of aluminum of □60 μm, and  10  thereof are placed for each substrate  11 . The total drawing length between the electrodes  112  of each substrate  11  is 1.5 mm. The substrates  11  are covered with an insulating layer expect the side surfaces thereof. The thicknesses of the substrates  11  were 100 μm, 150 μm, and 50 μm in the order from the top. Namely, in above Expressions (1) and (2), L 1 =250 μm and L 2 =1.25 mm. 
         [0146]    &lt;Print Head&gt; 
         [0147]    Five types of Si heads having nozzles  211  of different orifice diameters S 1  were used. Two types of inks were used which were an ink I n  for insulating layer formation on the substrate side surfaces and an Ag ink I for wiring among the electrodes  112 . Further, the gap in the vertical direction between the upper surface of the top substrate  11  and the ink ejection surface  211   c  of the print heads  2  and  2 A was set to be 1 mm-4 mm. Still further, the print heads  2  and  2 A were grounded and a direct voltage was applied to the opposite electrode  3 , and thereby the voltage between the upper surface of the top substrate  11  and the print heads  2  and  2 A was allowed to vary to eject ink droplets R and R n . 
         [0148]    Further, as a comparative experiment, in the state of applying no voltage to the opposite electrode, ink droplets R and R n  were ejected. 
         [0149]    &lt;Insulating Layer Formation and Firing&gt; 
         [0150]    As the ink I n  for insulating layer formation, an ink produced by Hitachi Chemical Co., Ltd. was used. Physical properties of this ink I n  are as follows: concentration: 9% by weight, viscosity: 3 mPa·s (25° C.), surface tension: 25 mN/m, electrical conductivity: 5 μS/cm, and specific dielectric constant: 31. 
         [0151]    The print head  2 A was scanned parallel to the side surfaces of the substrates  11  at a constant rate of 30 mm/s. In this case, under ejection conditions in which the volume of a ink droplet R n  was 0.5 pl and the ejection frequency was 6 kHz, overlapping drawing was carried out 5 times. Thereafter, the ink droplets R n  were thermally cured at 180° C. for 60 minutes. Herein, the slope of the insulating layer after curing was approximately 70° from the upper surfaces of the substrates  11 . 
         [0152]    &lt;Conductive Layer Formation and Firing&gt; 
         [0153]    As the Ag ink I, an ink produced by Sumitomo Electric Industries, Ltd. was used. Physical properties of this Ag ink I are as follows: concentration: 15%, viscosity: 13 mPa·s (25° C.), surface tension: 30 mN/m, electrical conductivity: 27 μS/cm, and specific dielectric constant: 25. Herein, this viscosity became at most 10 mPa·s during ejection of ink droplets R by heating the head. 
         [0154]    The print head  2  was scanned at a constant rate of 30 mm/s. In this case, the diameter D on deposition of an ink droplet R was designated as the deposition diameter shown in Table 1 and r=0.5. Then, the ejection frequencies f 1  and f 2  calculated by above Expressions (1) and (2) were switched to carry out drawing. Thereafter, firing was carried out at 180° C. for 100 minutes. 
         [0155]    &lt;Evaluation&gt; 
         [0156]    In Table 1, shown are 12 patterns of forming conditions of the conductive layer  12  and the insulating layer  14 , as well as the evaluation results of the wiring state of the conductive layer  12  in which 10 thereof were formed for each pattern. Herein, the wiring state of the conductive layers  12  was evaluated based on the following criteria: A: all the conductive layers  12  are conductive, and also wiring formation on the side surfaces is smooth and no loss influence is produced at high frequency; B: part of the conductive layers  12  are disconnected, and also wiring formation is wavy and a loss influence may be produced at high frequency; and C: all the conductive layers  12  are disconnected. 
         [0000]    
       
         
               
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                   
                 Ink Droplet 
                 Gap between 
                   
                   
               
               
                   
                 Voltage between 
                 Amount 
                 Head and 
                 Wiring State 
               
               
                   
                 Head and Substrate 
                 [pl]/Deposition 
                 Substrate Top 
                 of Conductive 
               
               
                   
                 Top Surface [kV] 
                 Diameter [μm] 
                 Surface [mm] 
                 Layer 
                 Remarks 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 1 
                 2.9 
                    1/24 
                 1 
                 A 
                 Inventive 
               
               
                 2 
                 2.9 
                    1/24 
                 4 
                 A 
               
               
                 3 
                 2.9 
                  0.5/20 
                 1 
                 A 
               
               
                 4 
                 2.0 
                  0.5/20 
                 1 
                 A 
               
               
                 5 
                 1.5 
                  0.5/20 
                 1 
                 A-B 
               
               
                 6 
                 2.9 
                 0.007/10 
                 1 
                 A 
               
               
                 7 
                 2.9 
                 0.001/2  
                 1 
                 A 
               
               
                 8 
                 2.0 
                 0.007/10 
                 1 
                 A 
               
               
                 9 
                 1.5 
                 0.007/10 
                 1 
                 A 
               
               
                 10 
                 1.0 
                 0.007/10 
                 1 
                 A-B 
               
               
                 11 
                 0 
                    1/24 
                 1 
                 C 
                 Comparative 
               
               
                 12 
                 0 
                  0.5/20 
                 1 
                 C 
               
               
                   
               
             
          
         
       
     
       Example 2 
       [0157]    In Example 1, insulating layer formation and firing were changed as described below. Then, of 12 patterns in Table 1, with respect to 11 patterns, conductive layers  12  were formed for wiring state evaluation. 
         [0158]    &lt;Insulating Layer Formation and Firing&gt; 
         [0159]    Using a dispenser, drawing was carried out with an ink I n  at a width of about 150 μm on the substrates  11  and also the bump portions were filled with the ink I n . Then, the ink I n  was thermally cured at 180° C. for 60 minutes. 
         [0160]    &lt;Evaluation&gt; 
         [0161]    In Table 2, shown are 11 patterns of forming conditions of the conductive layer  12 , as well as the evaluation results of the wiring state of the formed conductive layer  12 . Herein, the wiring state evaluation of the conductive layer  12  is the same as in Example 1. 
         [0000]    
       
         
               
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                   
                 Ink Droplet 
                 Gap between 
                   
                   
               
               
                   
                 Voltage between 
                 Amount 
                 Head and 
                 Wiring State 
               
               
                   
                 Head and Substrate 
                 [pl]/Deposition 
                 Substrate Top 
                 of Conductive 
               
               
                   
                 Top Surface [kV] 
                 Diameter [μm] 
                 Surface [mm] 
                 Layer 
                 Remarks 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 1 
                 2.9 
                   2/32 
                 1 
                 B-A 
                 Inventive 
               
               
                 2 
                 2.9 
                   1/24 
                 1 
                 A 
               
               
                 3 
                 2.9 
                   1/24 
                 5 
                 A 
               
               
                 4 
                 2.9 
                 0.5/20 
                 1 
                 A 
               
               
                 5 
                 2.0 
                 0.5/20 
                 1 
                 A 
               
               
                 6 
                 1.5 
                 0.5/20 
                 1 
                 A 
               
               
                 7 
                 1.0 
                 0.5/20 
                 1 
                 B 
               
               
                 8 
                 2.9 
                 0.007/10  
                 1 
                 A 
               
               
                 9 
                 2.9 
                 0.001/2   
                 1 
                 A 
               
               
                 10 
                 0 
                   1/24 
                 1 
                 C 
                 Comparative 
               
               
                 11 
                 0 
                 0.5/20 
                 1 
                 C 
               
               
                   
               
             
          
         
       
     
       Example 3  
       [0162]    Under the same forming conditions of a conductive layer  12  and a insulating layer  14  as in Example 1, a conductive layer  12  was formed on a substrate unit  10  in which substrates  11  were laminated by matching the outer circumferences thereof as shown in  FIG. 2C  for wiring state evaluation. 
         [0163]    &lt;Evaluation&gt; 
         [0164]    In Table 3, shown are forming conditions of the conductive layer  12  and the insulating layer  14 , as well as the evaluation results of the wiring state of the formed conductive layer  12 . Herein, the wiring state evaluation of the conductive layer  12  is the same as in Example 1. 
         [0000]    
       
         
               
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                   
                 TABLE 3 
               
               
                   
                   
               
               
                   
                   
                 Ink Droplet 
                 Gap between 
                   
                   
               
               
                   
                 Voltage between 
                 Amount 
                 Head and 
                 Wiring State 
               
               
                   
                 Head and Substrate 
                 [pl]/Deposition 
                 Substrate Top 
                 of Conductive 
               
               
                   
                 Top Surface [kV] 
                 Diameter [μm] 
                 Surface [mm] 
                 Layer 
                 Remarks 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 1 
                 2.9 
                   1/24 
                 1 
                 A 
                 Inventive 
               
               
                 2 
                 2.9 
                   1/24 
                 4 
                 A 
               
               
                 3 
                 2.9 
                 0.5/20 
                 1 
                 A 
               
               
                 4 
                 2.0 
                 0.5/20 
                 1 
                 A 
               
               
                 5 
                 1.5 
                 0.5/20 
                 1 
                 A-B 
               
               
                 6 
                 2.9 
                 0.007/10  
                 1 
                 A 
               
               
                 7 
                 2.9 
                 0.001/2   
                 1 
                 A 
               
               
                 8 
                 2.0 
                 0.007/10  
                 1 
                 A 
               
               
                 9 
                 1.5 
                 0.007/10  
                 1 
                 A 
               
               
                 10 
                 1.0 
                 0.007/10  
                 1 
                 A-B 
               
               
                 11 
                 0 
                   1/24 
                 1 
                 C 
                 Comparative 
               
               
                 12 
                 0 
                 0.5/20 
                 1 
                 C 
               
               
                   
               
             
          
         
       
     
         [0165]    As shown in Examples 1-3 described above, the present invention makes it possible to form a conductive layer  12  exhibiting an excellent wiring state under a wide range of forming conditions. 
         [0166]    Incidentally, in the present embodiment and its modified example, the print heads  2  and  2 A and substrate units  10  and  10 A need only to be relatively shifted in the X direction. For example, employable is a constitution in which substrate units  10  and  10 A are scanned with respect to non-scanned line-type print heads  2  and  2 A. 
         [0167]    Further, the print heads  2  and  2 A need only to be relatively shifted approximately parallel to at least the upper surfaces of substrates  11 . For example, it is possible that the print heads  2  and  2 A are shifted approximately parallel to the upper surfaces of the substrates  11  and thereafter shifted approximately parallel to the side surfaces of the substrates  11  via rotation of the ink ejection surface  211   c.    
         [0168]    Still further, also with regard to respects other than the above ones, it goes without saying that the present invention is not limited only to the above-described embodiment and its modified example and can appropriately be converted. 
       DESCRIPTION OF THE SYMBOLS 
       [0169]      2  and  2 A: print heads 
         [0170]      10  and  10 A: substrate units 
         [0171]      11 : substrate 
         [0172]      12 : conductive layer 
         [0173]      14 : insulating layer 
         [0174]      112 : electrode 
         [0175]      211   c : ink ejection surface 
         [0176]    D: ink droplet diameter 
         [0177]    f 1 : ejection frequency 
         [0178]    f 2 : ejection frequency 
         [0179]    I and I n : inks 
         [0180]    L 1 : the total length of a conductive layer formed on the side surfaces of substrates 
         [0181]    L 2 : the total length of a conductive layer formed on the upper surfaces of substrates 
         [0182]    r: a ratio of the radius direction maximum length to the diameter in a portion where ink droplets are overlapped 
         [0183]    R and R n : ink droplets 
         [0184]    V: print head scanning speed