Abstract:
A method for forming a conductor film, which allows the reduction in the thickness of a conductor film formed for an electronic component, and can form, at once, conductor films continuously extending over first and second surfaces of an electronic component which intersect one another. A component body is disposed to be opposed to a discharge nozzle for discharging an coating material which serves as a material for a conductor film, and the coating material charged by applying a voltage between the discharge nozzle and the component body ( 2 ) is discharged from the discharge nozzle. The charged coating material is applied to the component body along lines of electric force.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims benefit of priority to Japanese Patent Application 2013-136046 filed Jun. 28, 2013, and to International Patent Application No. PCT/JP2014/064547 filed May 31, 2014, the entire content of which is incorporated herein by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    This disclosure relates to a method for manufacturing an electronic component, and more particularly, to a method for forming a conductor film on the surface of a component body included in an electronic component. 
       BACKGROUND 
       [0003]    Electronic components generally include component bodies and conductor films formed on the component bodies. The conductor films function as terminal electrodes, function as electrodes for extracting electrical characteristics of the component bodies, or serve as both of the functions. In addition, the component bodies include various shapes, for example, such as a rectangular parallelepiped shape, a disc shape, and a foil shape. In addition, the conductor films formed on the component bodies are often formed to continuously extend over at least two surfaces of the component bodies which intersect one another. 
         [0004]    To explain more specifically,  FIG. 4  illustrates an electronic component  1  including a component body  2  in a rectangular parallelepiped shape. The component main body  2  has two principal surfaces  3  and  4  opposed to each other, two side surfaces  5  and  6  opposed to each other, and two end surfaces  7  and  8  opposed to each other. Two conductor films  9  and  10  are formed on the component body  2 . One conductor film  9  is formed to continuously extend on one end surface  7 , and portions for each of the principal surfaces  3  and  4  and side surfaces  5  and  6  which are adjacent to the end surface. The other conductor film  10  is formed to continuously extend on the other end surface  8 , and portions for each of the principal surfaces  3  and  4  and side surfaces  5  and  6  which are adjacent to the end surface. 
         [0005]      FIG. 5  illustrates an electronic component  11  including a component body  12  in a rectangular parallelepiped shape. The component body  12  has two principal surfaces  13  and  14  opposed to each other, two side surfaces  15  and  16  opposed to each other, and two end surfaces  17  and  18  opposed to each other. Six conductor films  19  to  24  are formed on the component body  12 . Each of the first to third conductor films  19  to  21  is formed to continuously extend on one side surface  15 , and portions for each of the two principal surfaces  13  and  14  which are adjacent to the side surface. Each of the fourth to sixth conductor films  22  to  24  is formed to continuously extend on the other side surface  16 , and portions for each of the two principal surfaces  13  and  14  which are adjacent to the side surface. 
         [0006]      FIG. 6  illustrates a component body  25  in a foil shape, which constitutes a capacitor element in an electrolytic capacitor, for example.  FIG. 6  illustrates an entire electrolytic capacitor as an electronic component including the component body  25 . The component body  25  has two principal surfaces  26  and  27  opposed to each other, and an end surface  28  for connecting between the principal surfaces  26  and  27 . A conductor film  29  is formed to continuously extend on the two principal surfaces  26  and  27  and the end surface  28  adjacent to the principal surfaces. 
         [0007]    The conductor films  9  and  10 , conductor films  19  to  24 , and conductor films  29  mentioned above, when generalized, all have such a form as a conductor film  35  as shown in  FIG. 7 or 8 . The conductor film  35  has to be formed to continuously extend over first, second, and third surfaces  32 ,  33 , and  34  of a component body  31 . 
         [0008]    It is often the case that the conductor film  35  mentioned above is formed in a way that a conductive paste is applied by, for example, a dipping method onto the component body  31 , and baked, as described in, for example, Japanese Patent Application Laid-Open No. 4-263414. In the dipping method, the conductive paste is applied onto the component body  31  in a predetermined region in a way that the component body  31  is dipped toward the conductive paste, and then pulled up from the conductive paste. 
         [0009]    When the dipping method is applied as described above, the conductor film  35  formed tends to have, in terms of thickness, bulges in the central parts on each of the first to third surfaces  32  to  34  as shown in  FIG. 7 , due to a surface tension that acts on the conductive paste. Therefore, the proportion of the thickness dimension of the conductor film  35  in an electronic component is increased, thereby interfering with reducing the size of, or lowering the profile of the electronic component. 
         [0010]    On the other hand, lowering the viscosity of the conductive paste is conceivable as a method of further reducing the thickness of the conductor film  35 . However, as the viscosity of the conductive paste is lower, it is more difficult to coat ridge parts  36  of the component body  31  with the conductive paste, and as a result, as shown in  FIG. 8 , the conductor film  35  formed may be cut at the ridge parts  36  of the component body  31 , thereby degrading electrical characteristics of the electronic component. In addition, spreading out of the conductive paste may make the conductor film  35  out of shape, thereby leading to problems in mounting the electronic component or degrading electrical characteristics after the mounting. 
         [0011]    It is to be noted that while the ridge part  36  of intersection between the first and second surfaces  32  with each other and the ridge part  36  of intersection between the second and third surfaces  33  and  34  with each other are illustrated to have acute angles in  FIG. 8 , the edges are actually often subjected to round chamfering. The above-mentioned problem of the conductor film  35  cut on the ridge parts  36  is inevitable, even when the ridge parts  36  are subjected to round chamfering as just described above. 
         [0012]    From the foregoing, in the case of applying a dipping method to form the conductor film  35 , the reduction in the thickness of the conductor film  35  is considered to be limited to approximately 20 μm in thickness. Therefore, it is difficult to further reduce the size of, or lower the profile of the electronic component, and it is also difficult to enhance the performance of the electronic component, for example, in the case of a multilayer ceramic capacitor, to increase the capacitance thereof. 
         [0013]    It is to be noted that the problems mentioned above applies not only to cases of the conductor film  35  formed to continuously extend over the three surfaces  32  to  34  of the component body  31  which intersect one another as shown in  FIGS. 7 and 8 , but also to cases of a conductor film formed to continuously extend over two surfaces which intersect one another. 
       SUMMARY 
     Problem to be Solved by the Disclosure 
       [0014]    Therefore, an object of this disclosure is to provide a method for manufacturing an electronic component, which is able to further reduce the thickness of the conductor film. 
       Means for Solving the Problem 
       [0015]    This disclosure is directed to a method for manufacturing an electronic component including: a component body including at least first and second surfaces intersecting one another; and a conductor film formed on the component body to continuously extend over at least the first surface and second surface, and in order to solve the technical problem mentioned above, the method is characterized by including the steps of: preparing a component body; preparing a fluid coating material containing a conductive material as a material for the conductor film; placing the component body to be opposed to a discharge nozzle for discharging the coating material; and with the coating material charged by applying a voltage between the discharge nozzle and the component body, discharging the coating material from the discharge nozzle and applying the charged coating material to the component body, thereby forming the conductor film containing the conductive material simultaneously to continuously extend over at least the first surface and second surface of the component body. 
         [0016]    In the step of forming the conductor film as mentioned above, the charged coating material flies through the air along lines of electric force. During this flying, the coating material repeats fission due to coulomb repulsive force (Rayleigh fission). The surface area is increased each time the fission is repeated, thus accelerating the evaporation of a liquid component such as a fluxing material or a solvent in the coating material. As a result, the coating material is dried to the extent that the fluidity is almost lost, when the material adheres to the surface of the component body. Therefore, substantially no surface tension acts on the coating material, but the coating material is thus not concentrated on any specific part, and thereby can be applied uniformly to be thin on at least first and second surfaces of the component body. 
         [0017]    The manufacturing method according to this disclosure can be applied to electronic components in various forms. 
         [0018]    As a first example of the electronic component, there is an electronic component where the component body has a rectangular parallelepiped shape including two principal surfaces opposed to each other, two side surfaces opposed to each other, and two end surfaces opposed to each other, and in the step of forming the conductor film, the conductor film is formed to continuously extend on at least one of the end surfaces, and portions for each of the principal surfaces adjacent to the end surface and portions for each of side surfaces adjacent to the end surface. 
         [0019]    As a second example of the electronic component, there is an electronic component where the component body has a rectangular parallelepiped shape including two principal surfaces opposed to each other, two side surfaces opposed to each other, and two end surfaces opposed to each other, and in the step of forming the conductor film, the conductor film is formed to continuously extend on at least one of the side surfaces, and portions for each of the two principal surfaces adjacent to the side surface. 
         [0020]    As a third example of the electronic component, there is an electronic component where the component body has a foil shape including two principal surfaces opposed to each other and an end surface for connecting between the principal surfaces, and in the step of forming the conductor film, the conductor film is formed to continuously extend on at least one of the principal surfaces and the end surface adjacent to the principal surface. 
         [0021]    In the practice of the manufacturing method according to this disclosure, it is preferable to prepare a mask that covers a region other than a region of the component body on which the conductor film is to be formed, and form the conductor film with the component body covered with the mask. Thus, without being affected by the properties of the coating material, conductor films can be formed with a high degree of pattern accuracy, and contributions can be made to the reduction in size for electronic components. 
       Advantageous Effect of the Disclosure 
       [0022]    According to this disclosure, in the step of forming the conductor film, the coating material flies along lines of electric force as described previously, and the uniform formation of the conductor film on both the first surface and the second surface can be thus achieved simultaneously by applying the coating material from one direction. In addition, the lines of electric force tend to be concentrated on, in particular, ridge parts at intersections between first and second surfaces of the component body, and conductor films can be formed to have appropriate film thicknesses, even including the ridge parts. 
         [0023]    In addition, according to this disclosure, the conductor film including the conductive material can be formed to be as thin as described previously. Therefore, the reduced size or lowered profile of the electronic component can be achieved by the reduced thickness of the conductor film. On the other hand, in the case of maintaining the dimensions of the electronic component, the effective volume which can be occupied by the part other than the conductor film, that is, the effective volume which can be occupied by the component body that fulfills the function can be increased, thereby improving the performance of the electronic component. 
         [0024]    When the electronic component is, for example, a multilayer ceramic capacitor, the volume of a part that produced electrostatic capacitance can be increased, and as a result, higher capacitance can be achieved. In addition, when the electronic component is, for example, a laminate-type aluminum electrolytic capacitor, the surface is composed of anodized aluminum foil, and a capacitor element with the conductor film formed on the surface can be reduced in thickness. Thus, the number of capacitor element laminated can be increased, and thereby the capacitance can be increased. 
         [0025]    In addition, when the conductor film including the conductive material can be formed to be thin as described above, the material used for the formation of the conductor film can be reduced, and the cost of the electronic component as a product can be thus reduced. 
         [0026]    In addition, according to this disclosure, as compared with the formation of conductor films by a dipping method, problems can be avoided such as wetting up and defectively coated ridge parts caused by the properties of the coating material in the dipping method. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0027]      FIG. 1  is a front view schematically illustrating a system for carrying out a step of forming a conductor film in a method for manufacturing an electronic component according to a first embodiment of this disclosure. 
           [0028]      FIG. 2  is a perspective view illustrating an enlarged part around a component body  2  as shown in  FIG. 1 . 
           [0029]      FIG. 3  is a perspective view corresponding to  FIG. 2 , which schematically illustrates a system for carrying out a step of forming a conductor film in a method for manufacturing an electronic component according to a second embodiment of this disclosure. 
           [0030]      FIG. 4  is a perspective view illustrating a first configuration example of a conventional electronic component. 
           [0031]      FIG. 5  is a perspective view illustrating a second configuration example of a conventional electronic component. 
           [0032]      FIG. 6  is a perspective view illustrating a third configuration example of a conventional electronic component. 
           [0033]      FIG. 7  is a cross-sectional view illustrating a conductor film  35  on a component body  31  for explaining a first problem of the conductor film  35  formed by applying a dipping method. 
           [0034]      FIG. 8  is a cross-sectional view illustrating the conductor film  35  on the component body  31  for explaining a second problem of the conductor film  35  formed by applying the dipping method. 
       
    
    
     DETAILED DESCRIPTION 
       [0035]    A method for manufacturing an electronic component  1  including a component body  2  in a rectangular parallelepiped shape as shown in  FIG. 4  will be described as a first embodiment of this disclosure. For manufacturing this electronic component  1 , the component main body  2  is prepared first. 
         [0036]    On the other hand, a fluid coating material containing a conductive material is prepared which serves as conductor films and  10 . For example, besides metal powders such as silver, silver-palladium alloys, and coppers, conductive materials such as carbon, conductive ceramics, and conductive polymers can be used as the conductive material. 
         [0037]    A conductor film formation system  41  shown in  FIG. 1  is used in order to form conductors  9  and  10 . 
         [0038]    Referring to  FIG. 1 , the conductor film formation system  41  includes a storage tank  43  that contains the coating material  42  described above. The storage tank  43  is connected to discharge nozzle  45  through a supply pipe  44 . 
         [0039]    On the other hand, a stage  47  is provided to be opposed to the discharge nozzle  45 , and the component body  2  as an object on which the conductor films  9  and  10  to be formed is placed on the stage  47 . The stage  47  is preferably composed of a conductive material. 
         [0040]    A pulse voltage, a direct-current voltage, or an alternating-current voltage from a power supply  48  is applied to the coating material  42  passing through the discharge nozzle  45 . 
         [0041]    As described above, steps of forming the conductor films  9  and  10  are carried out while the voltage is applied. It is to be noted that the step of forming the conductor film  9  and the step of forming the conductor film  10  are individually carried out in sequence. First, the step of forming the conductor film  9  will be described. In this embodiment, a region of the component body  2 , except a region on which the conductor film  9  is to be formed, is covered with a mask  51  as shown in  FIG. 2 . In addition, an end surface  7  on which the conductor film  9  is to be formed is oriented to the discharge nozzle  45  as shown in  FIG. 1 . 
         [0042]    In this condition, the internal pressure of the storage tank  43  is increased as indicated by arrows  52 . 
         [0043]    Thus, the coating material  42  in the storage tank  43  is supplied through the supply pipe  44  to the discharge nozzle  45  with the voltage applied thereto, thereby charging the coating material  42 . 
         [0044]    Lines of electric force  53  are generated from the charged coating material  42 . The coating material  42  is discharged from the discharge nozzle  45  toward the component body  2 . 
         [0045]    The coating material  42  repeats (while flying through the air along the lines of electric force  53 ) fission due to coulomb repulsive force (Rayleigh fission), thereby turning into a spray. Accordingly, the coating material  42  further increases its surface area each time the fission is repeated, and thus, the coating material  42  is progressively dried to accelerate the evaporation of a liquid component such as a fluxing material or a solvent included in the coating material  42 . 
         [0046]    As a result, the coating material  42  is dried to the extent that the fluidity is almost lost, when the material adheres to the surface of the component body  2 . Therefore, substantially no surface tension acts on the coating material  42 , but the coating material  42  is thus not concentrated on any specific part of the component body  2 , and thereby can be provided uniformly to be thin on the component body  2 .  FIG. 2  schematically illustrates the lines of electric force  53 , which are generated by the charged coating material  42 . The charged coating material  42  adheres to the component body  2  along the lines of electric force  53 . In this regard, the lines of electric force  53  tend to be concentrated on, in particular, ridge parts of the component body  2 , and the coating material  42  can be thus allowed to adhere uniformly, even including the ridge parts. 
         [0047]    On the other hand, as shown in  FIG. 2 , the predetermined part of the component body  2  is covered with the mask  51 , and thus, the coating material  42  will not reach the part of the component body  2 , which is covered with the mask  51 . 
         [0048]    In this way, the thin conductor film  9  with a uniform thickness is formed with a high degree of pattern accuracy to continuously extend on one end surface  7  of the component body  2 , and portions for each of the principal surfaces  3  and  4  and side surfaces  5  and  6  which are adjacent to the end surface. 
         [0049]    Then, a step of applying heat treatment to the conductor film  9  is carried out. 
         [0050]    Then, in order to form the other conductor film  10 , the same step as the above-mentioned step of forming the conductor film  9  is repeated after reversing the orientation of the component body  2  on the stage  47 , and attaching the mask  51  so as to cover a region except a region on which the conductor film  10  is to be formed. 
         [0051]    Next, a step of applying heat treatment to the conductor film  10  is carried out as in the case of the conductor film  9 . 
         [0052]    It is to be noted that the heat treatment step mentioned above may be applied at once to both the conductor films  9  and  10  after the formation of the conductor films  9  and  10 . 
         [0053]    Based on the first embodiment described above, an experiment was carried out for forming the conductor films  9  and  10  on the component body  2 . 
         [0054]    As the coating material  42 , a paste-like material of an Ag powder dispersed in an epoxy resin was used which was further provided with fluidity by the use of dipropylene methyl ether acetate so that the viscosity was 500 mPa·s at 1 rpm on an E-type viscometer. 
         [0055]    The conductor films  9  and  10  were formed on the component body  2  with the use of the conductor film formation system  41  described with reference to  FIGS. 1 and 2 , and then subjected to heat treatment for 1 hour at a temperature of  150 ° C. in a circulating hot air oven. 
         [0056]    In this way, when the conductor films  9  and  10  were formed for each thickness of 4 μm, 8 μm, 10 μm, 14 μm, 28 μm, 40 μm, and 100 μm, the conductor films  9  and  10  were able to be formed for each thickness, but the conductor films  9  and  10  were not found to be cut at ridge parts. 
         [0057]    Next, a second embodiment of this disclosure will be described with reference to  FIG. 3 . In this embodiment, a conductor film  29  is formed a component body  25  in a foil shape as shown in  FIG. 6 . 
         [0058]    The conductor film formation system  41  shown in  FIG. 1  is used also in the second embodiment. In the second embodiment, as shown in  FIG. 3 , the component body  25  with a mask  55  attached thereto is placed on the stage  47  shown in  FIG. 1 . 
         [0059]    Referring to  FIG. 3 , a charged coating material  42  adheres to the component body  25  along lines of electric force  53 . In this regard, the lines of electric force  53  tend to be concentrated on, in particular, ridge parts of the component body  25 , and the coating material  42  can be thus allowed to adhere uniformly, even including the ridge parts. On the other hand, the predetermined part of the component body  25  is covered with the mask  55 , and thus, the coating material  42  will not reach the part of the component body  25 , which is covered with the mask  55 . 
         [0060]    In this way, a part of the thin conductor film  29  with a uniform thickness is formed with a high degree of pattern accuracy to continuously extend on one end surface  26  of the component body  25 , and the end surface  28  which is adjacent to the end surface. 
         [0061]    Next, in order to form the rest of the conductor film  29 , the same step as the step described above is repeated after reversing the orientation of the component body  25  on the stage  47 . 
         [0062]    While this disclosure has been described above in connection with the first and second embodiments illustrated, the conductor film formation system  41  shown in  FIG. 1  can be also applied in a step of forming the conductor films  19  to  24  on the component body  12 , for example, in manufacturing the electronic component  11  shown in  FIG. 5 . Furthermore, for the electronic components including component bodies that have configurations other than the component bodies  2 ,  12 , and  25  shown in  FIGS. 4 through 6 , or for electronic components including conductor films other than the conductor films  9  and  10 , the conductor films  19  to  24 , and the conductor film  29 , the conductor film formation system  41  shown in  FIG. 1  can be used in steps of forming the conductor films on the component bodies.