Abstract:
A manufacturing method of a mounting part of a semiconductor light emitting element comprising: preparing a semiconductor light emitting element including an electrode which has a surface, and a board which has a surface; forming a plurality of bump material bodies on at least one of the surface of the electrode and the surface of the board by shaping bump material into islands, wherein the bump material is paste in which metal particles are dispersed, a top surface and a bottom surface of the bump material bodies have different areas, and the top surface is practically flat; solidifying the bump material bodies by thermally processing the bump material bodies; and fixing the semiconductor light emitting element and the board through the bumps.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority from Japanese Patent Application No. 2009-045779 filed on Feb. 27, 2009 and Japanese Patent Application No. 2009-263108 filed on Nov. 18, 2009. The latter one claims Japanese domestic priority from the former one. The subject matter of these applications is incorporated herein by reference. 
     TECHNICAL FIELD 
     The present invention relates to an improvement of a bump for fixing a semiconductor light emitting element onto a board. 
     BRIEF DESCRIPTION OF RELATED ART 
     A so called flip-chip type light emitting element is mounted on a board while a surface of the light emitting element, on which a pair of electrode is provided, faces the board. When a flip-chip type light emitting element is mounted on the board, the light emitting element and the board is generally combined by bumps. In this case, the bumps are piled on a surface of a pair of electrodes of the light emitting element. 
     There are three related methods for forming the bumps: electroplate, sputtering, and stud bumps. These methods, however, have disadvantages. In a case of electroplate, the light emitting element may be possibly damaged since electrical current through the element is inevitable. In a case of sputtering, a manufacturing throughput is deteriorated due to slow bump piling speed. In a case of stud bumps, a manufacturing throughput is deteriorated since each bump has to be formed individually. 
     In order to avoid above described disadvantages, a plane like bump  5  is formed by screen printing a paste material  1  on a predetermined region of the electrode surface  2 , a thermal process, and removing a resist  3 . The paste material  1  includes metal particles and is called in this specification as a bump material. 
     References for the related art are JP-A-2007-019144 and JP-A-2008-226864. 
     SUMMARY 
     The inventors of the present invention found the following disadvantage during industrious investigations about the usage of the bump material for fixing a semiconductor light emitting element to a board. 
     The bump material  1  is paste or slurry and, therefore, has fluidity. When the bump material  1  is screen printed on the electrode surface  2 , a center of the bump material  1  recesses as a meniscus of fluidity of the bump material  1  driven by a surface tension ( FIG. 1A ). After the thermal process, the recessed shape of the bump material  1  is kept ( FIG. 1B ). 
     When the semiconductor light emitting element and the board are hot-pressed with the bump  5  therebetween, the press-load is concentrated on a protruded portion of the bump  5  rather than uniformly applied. This non-uniform press-load causes random deformation of the bump  5  and, therefore, an unevenness in bonding between the light emitting element and the board. As a result, there is a possibility that a bonding area is insufficient, a bonding strength is insufficient, and heat dissipation characteristic of the semiconductor light emitting element is deteriorated. 
     Exemplary embodiments of the present invention address above described disadvantages and may address disadvantages not described above. The first aspect of the exemplary embodiments of the present invention is a manufacturing method of a mounting part of a semiconductor light emitting element comprising: preparing a semiconductor light emitting element including an electrode which has a surface, and a board which has a surface; forming a plurality of bump material bodies on at least one of the surface of the electrode and the surface of the board by shaping bump material into islands, wherein the bump material is paste in which metal particles are dispersed, a top surface and a bottom surface of the bump material bodies have different areas, and the top surface is practically flat; solidifying the bump material bodies by thermally processing the bump material bodies; and fixing the semiconductor light emitting element and the board through the bumps. 
     According to the above described first aspect of the exemplary embodiments, since the bump material bodies are islands, each bump has small diameter, the area of the top surface and the area of the bottom surface are different, and the top surface is practically flat, the press-load is concentrated on one of the top surface and the bottom surface having smaller surface area while hot-pressing the semiconductor light emitting element and the board through the bumps. In this case, since the top surface of the bump is practically flat, the press-load is uniformly applied and does not have any negative effects on the deformation of the small area portion of the bump. In this exemplary embodiment, the phrase “practically flat” means that the unevenness of the top surface is smaller at least than the deformation amount of the bump in height by the hot press. 
     The bump is deformed from the small area portion in all-round directions when the press-load concentrates on the small area portion. As a result, a sufficient bonding area between the semiconductor light emitting element and the board is obtained. The deformed bumps are sometimes combined each other. This fusion of the bumps improves the thermal conductivity. 
     The bump may have a shape that gradually reduces or increases its width along its height (a direction from the bottom surface to the top surface). Also, the bump may have a shape that includes a portion where gradually reduces its width along its height and a portion where gradually increase its width along its height. The bump shape preferably has a trapezoidal vertical cross section, such as conical trapezoid and a stripe with trapezoidal cross section. 
     According to another aspect of the exemplary embodiments of the present invention according to the first aspect, the plurality of the bump material bodies are formed with a mask covering at least one of the surface of the electrode and the surface of the board, the mask includes a plurality of openings which are tapered in a thickness direction of the mask, and the bump material is filled into the openings. 
     Since the bump material bodies are shaped with the mask, the shape of each bump material body is securely stable. Also a process forming the bump material bodies are fast-acting and performed at a low cost. 
     According to another aspect of the exemplary embodiments of the present invention according to the first aspect, the mask is a resist. Since the mask is made from a resist, it is easy to remove the mask and the process forming the bump material bodies are fast-acting. 
     According to another aspect of the exemplary embodiment of the present invention according to the first aspect, the bump material is filled into the openings from an upper surface of the mask by screen printing. Since the bump material is filled into the openings by screen printing, the process forming the bump material bodies are fast-acting, and the through put of the process fixing the semiconductor light emitting element to the board is improved. 
     According to another aspect of the exemplary embodiment of the present invention according to the first aspect, the bump material includes a thermoplastic sealant, and a manufacturing method of a mounting part of a semiconductor light emitting element comprising: sealing the semiconductor light emitting element by hot pressing the semiconductor light emitting element and the board. According to this method, the bonding between the semiconductor light emitting element and the board and the sealing by the thermoplastic sealant are performed simultaneously, by arranging the semiconductor light emitting element on the board and hot pressing. Therefore the through put of the process is improved. Especially, as the thermoplastic sealant, low melting point glass is preferable. 
     The second aspect of the exemplary embodiments of the present invention is a manufacturing method of a mounting part of a semiconductor light emitting element comprising: preparing a semiconductor light emitting element including an electrode, and a board including a surface; forming a plurality of bump material bodies on at lease one of a surface of the electrode and the surface of the board by shaping bump material into islands, wherein the bump material is paste in which metal particles are dispersed, and a width of the bump material bodies changes along a height direction thereof; solidifying the bump material bodies by thermally processing the bump material bodies; fixing the semiconductor light emitting element and the board through the bumps. 
     According to the second aspect of the exemplary embodiments, since the bump material bodies are formed so that the width of the bump material bodies change its width along its height direction, the press-load concentrates on the portion with a small width and thus formed bump material bodies are deformed in all-round direction from the small width portion. As a result, the sufficient bonding area between the semiconductor light emitting element and the board is obtained. The deformed bumps are sometimes combined each other. This fusion of the bumps improves the thermal conductivity. 
     According to another aspect of the second aspect of the exemplary embodiments, the width of the bump material bodies gradually reduces along the height direction while departing from at least one of the surface of the semiconductor light emitting element and the surface of the board where the bump material bodies are formed. Since such a shape of the bump materials is easy to shape (or mold), the through put of the process is improved. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a cross sectional view showing a characteristic of the related bump material. 
         FIG. 2  is a plan view showing bumps formed in a dot array manner on an electrode surface of the semiconductor light emitting element. 
         FIG. 3  is a plan view showing bumps formed in a stripe shape on an electrode surface of the semiconductor light emitting element. 
         FIGS. 4A to 4D  show a manufacturing process for the bumps according to the first exemplary embodiment. 
         FIGS. 5A and 5D  show a bonding process between the semiconductor light emitting element and the board with the bump according to the first exemplary embodiment. 
         FIG. 6A  is a plan view showing bumps formed on the electrode surface of the semiconductor light emitting element according to the second exemplary embodiment. 
         FIG. 6B  is an expanded perspective view of the bump of  FIG. 6A . 
         FIG. 6C  is a side view of the bump in  FIG. 6A . 
         FIGS. 7  A to  7 E show a manufacturing process for the bump material body  390 . 
         FIG. 8  shows a modification of the second exemplary embodiment.  FIG. 8  is a plan view showing bumps formed in a dot shape and in a stripe shape on the electrode surface of the semiconductor light emitting element. 
         FIGS. 9A to 9D  show a process forming a bump material body  500  in the third embodiment of the present invention. 
     
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     In an exemplary embodiment of the present invention, a flip-chip type group III nitride semiconductor light emitting element is adopted as a semiconductor light emitting element. The flip-chip type light emitting element is provided with a P-layer and a N-layer formed on an insulator substrate and a P-electrode and a N-electrode on one surface thereof. Also, a group III nitride semiconductor light emitting element, which is provided with a P-electrode on one surface thereof and a N-electrode on the other surface thereof, may be adopted. The group III nitride semiconductor light emitting element has an active layer made from group III nitride composite semiconductors. The group III nitride composite semiconductors are described by a general formula of quartenary composite Al x Ga y In 1-x-y N (0≦x≦1, 0≦y≦1, 0≦x+y≦1). The general formula includes binary composites AlN, GaN, and InN, and ternary composites Al x Ga 1-x N, Al x In 1-x N, and Ga x In 1-x N. At least a part of group III element may be substituted by boron (B), thallium (Tl), or the like. Also, at least a part of nitrogen (N) may be substituted by phosphorus (P), arsenic (As), antimony (Sb), bismuth (Bi), or the like. Also, the group III nitride composite semiconductors may contain any kind of impurities. Examples of P-type impurity are Si, Ge, Se, Te, C, or the like. Examples of N-type impurity are Mg, Zn, Be, Ca, Sr, Ba, or the like. A sapphire substrate (Al 2 O 3 ), a gallium nitride substrate (GaN), a silicon carbide substrate (SiC), and a silicon substrate (Si) may be used as a crystal growth substrate for the group III nitride composite semiconductors. 
     The group III nitride composite semiconductor layer is formed by metal organic chemical vapor deposition (MOCVD), molecular beam epitaxy (MBE), halide vapor phase epitaxy (HVPE), sputtering, ion plating, electron shower, or the like. 
     An electron beam radiation, plasma radiation, or annealing in a furnace for group III nitride composite semiconductors after doping P type impurity is possible, but is not mandatory. 
     An light emitting element is formed by stacking the group DI nitride composite semiconductor layers. Examples of the layered structure for light emission are a quantum well structure (multi-quantum well structure or single quantum well structure), a single hetero-junction, a double hetero-junction, or a homo-junction. 
     Since the flip-chip type light emitting element emits light from the substrate side thereof and the wirings on the board and the upper surface of the light emitting element, on which the P-electrode and the N-electrode are provided, are fixed by the bumps. The bumps are required conductivity, thermal conductivity, and mechanical strength. Especially, mechanical strength is necessary to strongly bond the light emitting element and the board. 
     The bumps are formed on the surface of the electrodes of the semiconductor light emitting element and/or on the surface of the electrodes of the board. More specifically, the bumps are formed on the P-electrode and N-electrode of the semiconductor light emitting element and/or on the wiring pads of the board. 
     The bumps are formed as islands each of which has a space between adjacent other bumps. The island shape of the bumps may be a dot (bump  11 ,  FIG. 2 ), a stripe (bump  13 ,  FIG. 3 ), or the like. It is preferable to uniformly arrange the bumps on the electrodes of the semiconductor light emitting element (P-electrode  15 , N-electrode  17 ) and/or the wiring pads of the board. Also, it is possible to arrange the bumps non-uniformly and make the bumps in shape defined by a free curve. 
     In the exemplary embodiments of the present invention, an area of the top surface of the bump and an area of the bottom surface of the bump are different. As a result of this are difference, a stress concentrates on the small area portion of the bump and a deformation starts therefrom during the hot press. The stress concentration onto contact portions, where the semiconductor light emitting element and the bumps or the board and the bumps contact each other, makes the bonding easy. If all bumps have a same shape, each bump deforms in a same manner from the small area portion thereof and the bump is uniformly filled in a space between the semiconductor light emitting element and the board. In other words, a bump density in the bonding plane of the semiconductor light emitting element and the board is uniform. The shape of the bumps and the arrangement of the bumps may be modified depending on the bump shape, and the shapes and the deformations of the semiconductor light emitting element and the board. 
     Although a size and a pitch (a size of the space between the adjacent bumps) of the bumps may be arbitrarily determined, such a size and a pitch are preferable that a volume of the bump deformed during the hot press is substantially equal to a volume of the space between the bumps. Accordingly, the bumps spread over the whole surface of the semiconductor light emitting element and the board, and a strong bonding between the semiconductor light emitting element and the board is obtained. 
     The bump is obtained by thermal processing a bump material body. Since the bump material has fluidity, a meniscus is caused when the surface of the bump material is large (as shown in  FIG. 1A ). Therefore, in this exemplary embodiment, the bump had an area of the top surface so as not to cause the meniscus. Therefore, it is preferable to make the bump so that the area of the top surface of the bump is small and the area of the bottom surface of the bump is large. In a case where the top surface of the bump is circle (dot shaped bump), the diameter of the bump is 3˜7 μm in order to prevent the meniscus. Also, in a case where the top surface of the bump is a rectangular (stripe shape bump), the width of the short direction of the bump is 3˜7 μm in order to prevent the meniscus. 
     It is preferable to use a mask in order to shape the bump material body with fluidity into a conical shape, for example. The mask has an opening and a peripheral wall of the opening defines the peripheral surface of the bump material body. By using the mask, it is possible to arbitrarily design the shape and arrangement density of the bump material bodies. Materials for the mask may be arbitrarily adopted. It is preferable to adopt a resist because a tapered mask is easily formed by the resist. For example, a metal film, a resist, or the like may be adopted. 
     As the bump material, slurry including metal particles dispersed in organic solvent may be adopted. An elemental substance of gold, silver, platinum, palladium, or the like and mixtures of more than two of them are used as the metal particles. Alcohol may be used as the organic solvent. Examples of the alcohol are ester, terpineol, pine oil, butyl carbitol acetate, butyl carbitol, carbitol, and the like. As a preferable organic solvent of ester series is 2,2,4,-trimethyl-3-hydroxypentaisobutyrate (C 12 H 24 O 3 ). 
     For the purpose of dispersion of the metal particles, polymer may be added to the organic solvent. Examples of the polymer are acrylic resin such as methyl methacrylate polymer, cellulosic resin such as ethyl cellulose, alkyd resin such as phthalic anhydride resin. 
     Also the metal particles may be dispersed in a thermoplastic resin. Examples of the thermoplastic resin are olefin resin, vinyl resin including halogen (such as polyvinyl chloride, fluoride resin), acrylic resin, styrene resin, polycarbonate resin, polyester resin (such as polyethylene telephthalate, polybuthylene telephthalate), polyacetal resin, polyamide resin, polyphenylene sulfide resin, polyimide resin, polyether ketone resin, thermoplastic elastomer, or the like. Such thermoplastic resins are used in elemental substance or mixtures of more than two of them. 
     The thermal process of the bump material body removes the organic solvent from the bump material body and drives the fusion of the metal particles. The condition of the thermal process is suitably adjusted depending on what the bump material is and depending on the size of the bump material body. 
     In the exemplary embodiment, the group III nitride semiconductor light emitting element may have a P-electrode on one surface of the conductive substrate and has a N-electrode on the other surface of the conductive substrate. When such a semiconductor light emitting element is used, the bumps are formed one of the surface of the P-electrode and the N-electrode. Then the surface on which the bumps are formed faces the wiring board and the semiconductor light emitting element is hot pressed. Also, the semiconductor light emitting element is hot pressed after forming the bumps on the wiring board. 
     In the exemplary embodiments of the present invention, the bumps are formed so as to change the width along its height direction. Examples of method to form the bump material body in this manner are dot printing, transfer printing by a dispenser, needle application, anastatic printing, gravure printing, offset printing, inkjet printing, nano-inprint, or the like. The thermal treatment process (provisional calcination) for the bump material and the bump material body are performed by the above described methods. Also, the provisional calcinations may be omitted depending on the semiconductor element condition on which the bumps are formed. 
     First Exemplary Embodiment 
     The first exemplary embodiment of the present invention is explained below with reference to the drawings. 
     A resist  33  is applied on the surface of the electrode  31  of the semiconductor light emitting element. Then, a plurality of dot holes (circular holes)  34  are uniformly formed on the resist  33 . As shown in  FIG. 4A , the cross section of each dot hole is preferably a trapezoidal shape. (the inner surface of the resist  33  is reversely tapered in the thickness direction of the resist  33 ). In this exemplary embodiment, the resist  33  is a negative-resist. 
     Next, by applying paste of the bump material  35  over the resist  33 , the dot holes  34  are filled by the paste and surplus paste is removed by a squeegee  37  ( FIG. 4B ). As the bump material, slurry including metal particles are used. 
     Next, the bump material  35  is culcinated for 30 minutes under 230 degrees Celsius ( FIG. 4C ). By this process, the metal particles in the bump material  35  are combined each other and the bumps are solidified while there are many spaces between the bumps. 
     Next, the resist  33  is removed and the dot bumps  39  are formed on the surface of the electrode  31 . Each of the dot bumps has a conical trapezoide shape. 
     In the first exemplary embodiment, the bumps have a height of 2 μm, a bottom diameter of 3 μm, an upper diameter of 1 μm, and the pitch (distance between the axes of the conical shape adjacent bumps) of 5 μm. 
     As shown in  FIGS. 5A and 5B , the electrode  31  of the semiconductor light emitting element is abutted to the wiring board  40  while the bumps  39  are formed on the electrode  31 . The wiring board  40  is mounted on a base  41 . After that, the semiconductor light emitting element and the wiring board  40  are hot pressed under 230 degrees Celsius and the bumps  39  deform. At this time, since the bumps  39  has a conical trapezoid shape, stress is concentrated on the top surface (the small area portion) and deforms therefrom. Since the shape of the bumps  39  is uniform, the deformation of the bumps  39  is also uniform. Therefore, it is possible to fill the bumps  39  between the electrode  31  and the wiring board  40  without spaces ( FIGS. 5C and 5D ). 
     Accordingly, the bonding between the electrode  31  of the semiconductor light emitting element and the wiring board  40  is imparted stable and sufficient strength, and the heat dissipation characteristics of the semiconductor light emitting element is sufficient. 
     Second Exemplary Embodiment 
     The second exemplary embodiment of the present invention is explained below with reference to the drawings. In the second exemplary embodiment, the bump material bodies  390  are formed on the surface of the electrode  31  of the semiconductor light emitting element by needle application.  FIG. 6A  shows the surface of the electrodes (P-electrode  15  and N-electrode  17 ) under the bump formation.  FIG. 6B  is an expanded perspective view of the bump material body  390  and  FIG. 6C  is a side view of the bump material body  390 . As shown in  FIG. 6A , the bump material bodies  390  are formed on the surface of the electrodes  15  and  17  in a dot array manner. For example, the needle type dispenser  100  (Applied Micro Systems Inc.) may be used for forming the bump material bodies  390 .  FIGS. 7A to 7E  show a manufacturing process for the bump material bodies  390  by the dispenser device  100 . As shown in  FIG. 7A , the dispenser device  100  is provided with a glass tube  101  having an opening at a tip thereof, and a tungsten needle  102 . The bump material  391  is held at the opening by the surface tension of the bump material  391 . 
     The bump material bodies  390  are formed as explained below. Firstly, the glass tube  101  is set at a predetermined position over the electrode  15 , and the tungsten needle  102  descends so as to pass the bump material  391  held at the tip of the glass tube  101  ( FIG. 7B ). In this way, the bump material  391  adheres at the tip of the needle  102 . Then, the needle  102  descends further so as to contact the bump material  391  to the surface of the electrode  15  ( FIG. 7C ). After that, the needle  102  ascends ( FIG. 7D ). Accordingly, the bump material body  390  is formed by transfer printing the bump material  391  on the surface of the electrode  15  ( FIG. 7E ). Thus formed bump material bodies  390  have a shape which gradually reduces its width along its height as being distant from the surface of the electrode  15 . Therefore, the side surface of the bump material bodies  391  inclines. Each of the bump material bodies  390  has the height of 50 μm, the bottom diameter of 50 μm. The bump material bodies  390  have same shape and are arranged on the surface of the electrodes  15  and  17  with pitch of 5 μm (pitch is distance between the center line of adjacent bump material bodies). 
     Since the width of the bump material bodies shorten along the height direction, stress concentrates on the portion with the small width and deformation starts therefrom as same as the first exemplary embodiment. Since the shape of the bump material bodies  390  is uniform, the deformation of the bump material bodies  390  is also uniform. Therefore, it is possible to fill the bump material bodies  390  between the electrodes  15 ,  17  and the wiring board  40  without spaces. Also, since the tiny drop application device  100  is used, workability is improved as compared to the case where the resist is used. 
     In the above described second exemplary embodiment, the bump material bodies  390  are arranged on the surface of the N-electrode  15  and P-electrode  17  of the semiconductor light emitting element in a dot array manner. Instead, as shown in  FIG. 8 , it is possible to form the bump material bodies  390  on the P-electrode  17  in a stripe shape. The stripe shape bump material bodies  390  may be formed by reducing the pitch of transfer printing of the bump material by the tiny drop application device  100  along the longitudinal direction of the stripe shape so that the dot bump material bodies  390  is combined along the longitudinal direction. 
     Third Exemplary Embodiment 
     The third exemplary embodiment of the present invention is explained below with reference to the drawings.  FIGS. 9A to 9D  show a surface of the electrode (P-electrode  15  or N-electrode  17 ) while the bump material body  500  is formed. The bump material body  500  is formed on the surface of the electrodes of the semiconductor light emitting element by, for example, an air-pulse dispenser (Musashi Engineering Inc.).  FIGS. 9A to 9D  also show the process to form the bump material body  500  by the dispenser  510 . As shown in  FIG. 9A , the dispenser  510  includes a syringe provided with a nozzle  511  at the tip thereof. The nozzle  511  has a circular opening at the tip thereof and the inner diameter of the opening is about 50 μm and the outer diameter of the opening is about 80 μm. The inside of the nozzle is filled by the bump material  391  and the bump material  391  is discharged from the opening. 
     The bump material body  500  is formed by the manner explained below. At first, the nozzle  511  is set at a predetermined position above the electrode  15  ( FIG. 9A ) and the bump material  391  is discharged from the opening of the nozzle  511  ( FIG. 9B ) so as to contact the bump material  391  onto the surface of the electrode  15  ( FIG. 9C ). After that, the nozzle  511  ascends ( FIG. 9D ) and the bump material  391  is transfer printed onto the surface of the electrode  15 . In this exemplary embodiment, the bump material  391  is discharged under the condition that the discharging pressure of 200 KPa and the discharging time 0.03 seconds. Such discharge condition can be determined depending on the viscosity of the bump material  391  or the like. 
     After forming the bump material body  500 , a provisional calcination is performed under the condition that the temperature of 200 degrees Celsius and the calcination time is 10 minutes. By this provisional calcination, the solvent in the bump material body  500  evaporates and the metal particles in the bump material body  500  are combined with each other in the presence of a lot of spaces therebetween (provisional fusion) and are provisionally combined with the electrode  15 . Accordingly, the bump material body  500  is fixed to the electrode  15  and becomes easily deformable. 
     The shape of the bump material body  500  has a width gradually reducing along the height direction thereof while distant from the surface of the electrode  15  (tapered shape). Therefore, the side surface of the bump material body  500  inclines. In this exemplary embodiment, the height of the bump material body  500  is 50 μm and the diameter of the bottom surface of the bump material body  500  is 50 μm. The bump material body  500  is arranged on the surface of the electrodes  15  and  17  in about 5 μm pitch (distance between the central axes of adjacent bump material bodies) as same as the bump material body  390  of the second exemplary embodiment. 
     In the third exemplary embodiment, the dispenser  510  provided with the nozzle  511  which has a circular opening at the tip thereof, is described as an example. Instead, for example, a dispenser provided with a nozzle which has a rectangular opening. By using such a dispenser with rectangular opening, bump material bodies which have a rectangular bottom surface can be formed and it is possible to arrange the bump material bodies more densely as compared to the bump material bodies with circular bottom surface. 
     In the third exemplary embodiment, the nozzle having the opening whose inner diameter is 50 μm is used. Instead, for example, a nozzle having an opening whose inner diameter is 20 μm. Accordingly, bump material bodies whose bottom surface is 20 μm diameter circle can be formed and it is possible to arrange the bump material bodies more densely. 
     While the present invention has been shown and described with reference to certain exemplary embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.