Abstract:
To provide a method of manufacturing a highly reliable circuit device realizing a smaller, thinner and lighter configuration. In the method of manufacturing a circuit device according to the invention, a resin sealed body is separated from a supporting substrate, after the resin sealed body containing a circuit device is formed on a top surface of the supporting substrate. Therefore, manufacture of a circuit device having no substrate becomes possible and it realizes a thinner and lighter circuit device with improved heat dissipation. Moreover, since sealing with a sealing resin can be performed on the supporting substrate, warps, caused by the differences in thermal expansion coefficients between the sealing resin and conductive patterns and between the sealing resin and circuit components, can be prevented. Hence, it becomes possible to prevent flaking of conductive patterns from the substrate and a poor contact between the conductive patterns and a metal thin wire, and consequently to manufacture a highly reliable circuit device.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     Priority is claimed to Japanese Patent Application Number JP2004-222115 filed on Jul. 29, 2004, the disclosure of which is incorporated herein by reference in its entirety.  
         [0002]     1. Technical Field  
         [0003]     The present invention relates to a method of manufacturing a circuit device, more particularly to a method of manufacturing a circuit device whereby a thin-profile circuit device is realized.  
         [0004]     2. Related Art  
         [0005]     As electric appliances have become smaller in size and more sophisticated, miniaturization and density growth for circuit devices used therein has come to be required. With reference to  FIGS. 9A  to  9 C, an example of a method of manufacturing a conventional circuit device will be described. The technology is described for instance in Japanese Patent Application Publication No. 2002-26198.  
         [0006]     First, as shown in  FIG. 9A , a contact hole  103  is formed on a substrate  101  formed of an insulating material such as resin, by use of a laser or the like. Thereafter, plated films  102 A and  102 B are formed on both sides of the substrate  101 , including space inside the contact hole  103 .  
         [0007]     Subsequently, in  FIG. 9B , by etching the plated films  102 A and  102 B, a first conductive pattern  102 A is formed on the top surface of the substrate  101 , and a second conductive pattern  102 B on the back surface.  
         [0008]     As shown in  FIG. 9C , a semiconductor element  104  is mounted on the first conductive pattern  102 A, and the first conductive pattern  102 A and the semiconductor element  104  are connected electrically through a metal thin wire  105 . Subsequently, the semiconductor element  104 , the metal thin wire  105  and the first conductive pattern  102 A are sealed with a sealing resin  107  to be covered therewith. Finally, the second conductive pattern  102 B is coated with a solder resist  109 , and an external electrode  108  is formed at the predetermined location. In this manner, a circuit device  100  is produced.  
         [0009]     In the method of manufacturing the above-mentioned circuit device, however, a glass epoxy substrate has been used as the substrate  101 , for supporting wirings during manufacturing processes. Therefore, it involves problems such as an increase in manufacturing cost, and limitations in producing smaller, thinner and lighter circuit devices due to the thickness of the substrate  101 . Moreover, it has been pointed out that a heat dissipation property diminishes as a result of using the glass epoxy substrate.  
         [0010]     Further, when the sealing resin  107  is being hardened, warps have been caused by the differences in thermal expansion coefficients between the substrate  101  and the sealing resin  107  as well as between the semiconductor element  104  and the sealing resin  107 . This have developed into such a problem that the conductive pattern flakes off from the substrate  101 , or that a poor contact occurs between the first conductive pattern  102 B and the metal thin wire  105 .  
         [0011]     Still further, in the case where the glass epoxy substrate was adopted for the substrate  101 , it has been critical to form the contact hole  103  for electric connection between the two surfaces thereof, thus prolonging the manufacturing process.  
         [0012]     Furthermore, in the case of forming a conductive pattern where a large current flows, the electric capacity thereof has been ensured by increasing the planar dimension of a conductive pattern. Hence, miniaturization of a circuit device has been difficult.  
       SUMMARY OF THE INVENTION  
       [0013]     The present invention is made in consideration of the aforementioned problems. The main object of the present invention is to provide a method of manufacturing a highly reliable circuit device realizing a smaller, thinner and lighter circuit device.  
         [0014]     According to one aspect of the present invention, a method for manufacturing a circuit device includes the steps of: forming a wiring layer on a supporting substrate, the wiring layer being composed of a first conductive pattern and a second conductive pattern, the second conductive pattern being formed to be thicker than the first conductive pattern; connecting the wiring layer and a circuit component electrically; sealing the top surface of the supporting substrate with a sealing resin in order that the circuit element is coated; and then separating the back surfaces of the wiring layer and the sealing resin from the supporting substrate. In this manner, it is made possible to manufacture a circuit device with no substrate, which enables a circuit device to attain a thinner and lighter configuration, and an improved heat dissipation property, as well as a lower manufacturing cost. In addition, since conductive patterns with different thicknesses can be formed within one circuit device, circuit device can be made smaller by forming each conductive pattern in accordance with a required amount of current.  
         [0015]     Moreover, according to another aspect of the present invention, a method for manufacturing a circuit device includes the steps of: forming a first wiring layer on a surface of a supporting substrate, the first wiring layer having a salient protruding in the thickness-wise direction thereof; depositing a conductive film on the first wiring layer, with an insulation layer interposed therebetween; forming a contact part for providing electrical continuity between the salient and the conductive film; forming a second wiring layer by patterning the conductive film; connecting the second wiring layer and a circuit element electrically; sealing a top surface of the supporting substrate with a sealing resin in order that the circuit element is coated; and separating the back surfaces of the first wiring layer, the insulation film and the sealing resin from the supporting substrate. Therefore, in addition to the effects mentioned above, a circuit device can be made denser by enabling the multi-layered wiring.  
         [0016]     According to a method of manufacturing a circuit device in preferred embodiments of the invention, a circuit device having no substrate can be manufactured. Consequently, it is possible to attain a thinner and lighter circuit device with an improved heat dissipation property.  
         [0017]     Further, according to the method of manufacturing a circuit device in the preferred embodiments of the invention, warps caused by the differences in thermal expansion coefficients between a substrate and a conductive foil, as well as between a sealing resin and a circuit device, can be prevented. Therefore, flaking of a conductive pattern from the substrate, and a poor contact between the conductive pattern and a metal thin wire can be suppressed, and that enables to manufacture a highly reliable circuit device.  
         [0018]     Still further, according to the method of manufacturing a circuit device in the preferred embodiments of the invention, forming of a contact hole which has been necessary in a glass epoxy substrate can be omitted, enabling to dramatically cut down the manufacturing process.  
         [0019]     Moreover, according to the method of manufacturing a circuit device in the preferred embodiment of the invention, conductive patterns can be formed thickly where a large current flows, which enables to form a smaller circuit device.  
         [0020]     Furthermore, according to the method of manufacturing a circuit device in the preferred embodiments of the invention, a through hole can be provided to a insulation layer allowed to be thinly formed with a salient buried therein, whereby it is made possible to easily form a through hole on the insulation layer. Additionally, the through hole can be formed shallowly, thereby facilitating the formation of a plated film into the through hole. Still further, in a case where a plurality of wiring layers are stacked, a contact part which penetrates the insulation layer and provides electrical continuity between wiring layers can be formed. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0021]      FIGS. 1A  to  1 C are sectional views showing a method of manufacturing a circuit device according to a first embodiments of the invention.  
         [0022]      FIGS. 2A  to  2 C are sectional views showing the method of manufacturing a circuit device according to the first embodiment of the invention.  
         [0023]      FIGS. 3A  to  3 C are sectional views showing a method of manufacturing a circuit device according to a second preferred embodiment of the invention.  
         [0024]      FIGS. 4A  to  4 C are sectional views showing the method of manufacturing a circuit device according to the second embodiment of the invention.  
         [0025]      FIGS. 5A  to  5 C are sectional views showing the method of manufacturing a circuit device according to the second embodiment of the invention.  
         [0026]      FIGS. 6A  to  6 C are sectional views showing the method of manufacturing a circuit device according to the second embodiment of the invention.  
         [0027]      FIGS. 7A  to  7 C are sectional views showing the method of manufacturing a circuit device according to the second embodiment of the invention.  
         [0028]      FIGS. 8A and 8B  are sectional views showing the method of manufacturing a circuit device according to the second embodiment of the invention.  
         [0029]      FIGS. 9A  to  9 C are sectional views showing a conventional method of manufacturing a circuit device. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
     First Embodiment  
       [0030]     With reference to  FIGS. 1A  to  1 C and  FIGS. 2A  to  2 C, a method of manufacturing a circuit device according to a first embodiment of the invention will now be described. First, as shown in  FIG. 1A , a conductive foil  13  is adhered on a supporting substrate  11  by way of an adhesive material  12  interposed therebetween. A material for the conductive foil  13  is selected considering the adhesive, bonding, and plating properties of soldering material. Specific examples of materials adopted for the conductive foil include a Cu-based conductive foil, Al-based conductive foil, and conductive foils composed of alloy such as Fe—Ni. Other materials can be adopted, and particularly, ones which can be etched are suitable. The thickness of the conductive foil  13  is approximately between 10 μm and 300 μm. However, it is also possible to adopt a conductive foil with thickness of 10 μm or less, or at least 300 μm.  
         [0031]     A thermoplastic resin, an UV sheet (of which the adhesive property diminishes by irradiation of ultraviolet ray), or the like is adopted for the adhesive material  12 . The adhesive material  12  may be any material which can be resolved into a flux, can be liquefied by heating, or can decrease its adhesive property by ultraviolet ray irradiation thereon.  
         [0032]     The supporting substrate  11  may be formed of a material such as metal (Cu, Al, etc.) or resin, which has enough strength or thickness for supporting the conductive foil  13  and keeping it leveled and flat. Further, in a case where the UV sheet is adopted for the adhesive material  12 , it is appropriate that a transparent substrate formed of glass, plastic or the like be adopted.  
         [0033]     As shown in  FIG. 1B , patterning of a resist  14  on the top surface of the conductive foil  13  is performed. Then, wet etching is conducted by using the resist  14  as an etching mask, so as to etch on the main surface where the resist  14  is not formed. This etching forms two types of pattern, a salient  18  and a thin conductive foil. After the etching is completed, the resist  14  is removed.  
         [0034]     As shown in  FIG. 1C , conductive patterns  20 A and  20 B are formed by etching the conductive foil  13 . First, patterning of the resist  14  is performed so as to cover the top surface of the region whereon a conductive pattern is to be formed. Here, the patterning of the resist  14  is performed in order that it coats a wider region than that of the salient  18  which is formed relatively thickly. This is done to enable the etching to be required only on the thinner part, and thereby one-time etching can be sufficient for patterning the conductive foil  13 . More specifically, if a displacement of a mask, for example, is taken into consideration, complete separation of the conductive foil  13  can be achieved more credibly when the patterning has been performed in a way that a small portion of extruding edge is formed. Moreover, if the etching is performed in a way that only the thinner part of the conductive foil  13  is separated, the conductive patterns  20 A and  20 B, which have different thicknesses, are formed while reducing the amount of side etching. On the other hand, if the thicker part of the conductive foil  13 , where the salient  18  is formed, is separated by etching, the amount of side etching becomes large. Thus, the widths of the conductive patterns  20 A and  20 B become narrow.  
         [0035]     Therefore, by performing a patterning on conductive patterns with different thicknesses at once on the part of the thinner conductive foil, both thicker and thinner patterns can be formed at once, and for example, respective patterns for power system and small-signal system can be formed in one etching processes.  
         [0036]     Further, compliance with a large current can be achieved not by increasing the planar dimension of a conductive pattern but by increasing the thickness of the conductive pattern, which enables to reduce the size of the planar surface of the circuit device.  
         [0037]     Still further, the heat dissipation property is improved by arranging a circuit element, which generates a large amount of heat, on the thickly formed conductive pattern.  
         [0038]     With reference to  FIG. 2A , circuit elements  25 A and  25 B is mounted on conductive patterns  20 , and a resin sealed body  31  sealed by a sealing resin  28  is formed. Here, the first circuit element  25 A is mounted on the first conductive pattern  20 A, and the second circuit component  25 B is mounted on the second conductive pattern  20 B. As shown in  FIG. 2A , the circuit components  25 A and  25 B are electrically connected to the conductive patterns  20  through a metal thin wire  27 . Needless to say, this structure may also be formed facedown.  
         [0039]     In this embodiment, a case is described as the one where there are mounted the first circuit element  25 A in which a relatively small amount of current flows, and the second circuit element  25 B in which a large current flows.  
         [0040]     While adoption of a chip condenser for the first circuit element  25 A is disclosed, other component such as a transistor, an LSI chip, a chip resistor, or solenoid may also be adopted.  
         [0041]     Components for the second circuit element  25 B include power-system transistors which provide a flow of a large current, such as a power MOS, a GTBT (Grounded-Trench-MOS Assisted Bipolar-Mode FET), an IGBT (Insulated Gate Bipolar Transistor), and a thyristor. Moreover, a power-system IC may also be adopted. Since chips used in recent years are small-sized and have sophisticated functions, a massive amount of heat is generated compared to those used in the past. Therefore, it is possible to improve the heat dissipation property of a circuit element which needs to release the heat, if the circuit element is mounted on the second conductive pattern  20 B.  
         [0042]     Moreover, contacts between the circuit elements  25 A and  25 B and the conductive patterns is achieved faceup or facedown, by using a metal thin wire, a soldering material, a conductive paste and the like. Thereafter, the circuit elements  25 A and  25 B are sealed by the sealing resin  28 . Here, the sealing may be conducted with any of transfer-molding, injection-molding, dipping or spreading. Resin materials for sealing may include a thermosetting resin such as an epoxy resin, or a thermoplastic resin such as a polyimide resin.  
         [0043]     Here, the resin sealed body  31  is unified with the supporting substrate  11  having a flat surface, until the sealing resin  28  becomes cured. Thus, its flatness can be maintained.  
         [0044]     With reference to  FIG. 2B , the resin sealed body  31  is separated from the supporting substrate  11 . Here, if the thermoplastic resin is adopted for the adhesive material  12 , separation can be performed by heating and melting the thermoplastic resin. Further, the adhesive material  12  may also be selectively dissolved with such an agent as an organic solvent.  
         [0045]     In the case where the UV sheet is adopted for the adhesive material  12 , separation can be performed by radiating ultraviolet rays. Here, by adopting a material through which ultraviolet rays pass, such as glass, for the supporting substrate  11 , speedy and effective separation can be achieved.  
         [0046]     After the separation from the supporting substrate  11 , a part of the adhesive material  12  may remain on the back surface of the resin sealed body  31 . This trouble is resolved by dissolving and removing the adhesive material, again using such an agent as an organic solvent.  
         [0047]     In  FIG. 2C , the resin sealed body  31  is processed with a back surface treatment, and thereafter is diced and separated into pieces. Thus, a circuit device  10 A is completed. Here, patterning of a solder resist  29  on the back surface of the resin sealed body  31  is performed, and a conductive pattern is exposed, whereat an external electrode  30  formed of a soldering material for example, is formed. However, it is possible to let the conductive pattern  20 , that is exposed from the back surface of the resin sealed body  31 , serve as external electrodes.  
         [0048]     With the structure mentioned above, a thin conductive pattern and a thick conductive pattern are formed, enabling a power-system element and a small-signal system element to be put together into one package. In a case where 6 power components and one controlling IC are packaged into a single package as an inverter module for example, it becomes possible to have a SIP (single in-line package) in one package if: sources and drains of 6 power components may be electrically connected to the thick conductive pattern; and the IC which controls a gate or a power transistor may be connected to the thin conductive pattern.  
       Second Embodiment  
       [0049]     With reference to  FIGS. 3A  to  5 C, a method of manufacturing a circuit device according to a second embodiment of the invention will now be described. The basic process of the method of manufacturing a circuit device in the second embodiment is similar to that of the first embodiment. Therefore, the differences will be mainly described here.  
         [0050]     First, with reference to  FIG. 3A , a salient  18  is formed on a first conductive film  33  adhered on a supporting substrate  11  through an adhesive material  12 . As a result of half-etching the first conductive film  33  by using a resist  14  as a mask, the salient  18  which is a thicker part, as well as the rest thinner part, are formed. After the salient  18  is formed, the resist  14  is removed.  
         [0051]     With reference to  FIG. 3B , in a manner similar to the previous embodiment, the thinner part is etched so as to form a thick conductive pattern and a thin conductive pattern. Here, patterning of the resist  14  is performed in order that it covers a wider region than that of the salient  18 . Subsequently, wet etching is conducted using the resist  14  as a mask to form a first wiring layer  40  composed of: a first conductive pattern  40 A; and a second conductive pattern  40 B which is formed to be thicker than the first conductive pattern  40 A.  
         [0052]     With reference to  FIG. 3C , a second conductive film  34  is deposited on the top surface of the first wiring layer  40 , with an insulation layer  41  interposed therebetween. This is achieved by closely adhering the second conductive film  34  where the insulation layer  41  formed of an adhesion layer or the like is provided on the surface, to the first wiring layer  40 . It is also possible to deposit the second conductive film  34 , after spreading the insulation layer  41  on the first wiring layer.  
         [0053]     Here, the salient  18  is closely adhered by the insulation layer  41 , in order that it is buried therein. By conducting this adhering process with a vacuum press, it becomes possible to prevent a void from being generated by the air between the first wiring layer  40  and the insulation layer  41 . Moreover, the side surface of the salient  18  formed by isotropic etching is a smooth curved surface. Hence, upon burying the first wiring layer  40  into the insulation layer  41 , resin infiltrates along the curve and thereby eliminates an unfilled part. Consequently, occurrence of a void can be suppressed also by the shape of the side surface of the salient  18 . Further, the adhesion strength between the first wiring layer  40  and the insulation layer  41  can be improved by burying the salient  18  into the insulation layer  41 .  
         [0054]     In the embodiment, in order to improve the heat dissipation property, a dielectric resininto which filler is mixed, such as epoxy resin or the like, is adopted as the material for the insulation layer  41 . Here, the material for the filler for mixing-in may be SiO2, Al2O3, SiC, AlN or the like. Needless to say, resin without filler mixed therein can also be adopted for the insulation layer  41 .  
         [0055]     With reference to  FIGS. 4A  to  4 C, a process of forming a contact part, which provides electrical continuity between the first wiring layer  40  and the second conductive film  34 , is described. First, by using the resist  14  as a mask, etching of the region whereon a contact part  43  is to be formed is performed, and a through hole  42  is formed in order that the surface of the insulation film  41  is exposed. Subsequently, by irradiating a laser beam while using the second conductive film  34  as a mask, the salient  18  is exposed from the lowest part of the through hole  42 . Thereafter, by forming a plated layer in the through hole  42 , the contact part  43  is formed. The first wiring layer  40  and the second conductive film  34  can be provided with electrical continuity therebetween by forming the contact part  43 .  
         [0056]     The details of the forming process of the contact part  43  will be described later with reference to  FIGS. 6A  to  8 B.  
         [0057]     As shown in  FIG. 5A , a second wiring layer  45  is formed by patterning the second conductive film  34 . Subsequently, after electrically connecting circuit elements  25 A and  25 B on the second wiring layer  45 , the package is sealed with the sealing resin  28 .  
         [0058]     Here, the first wiring layer  40  and the second conductive film  45  can be formed to intersect if seen in a plan view. Furthermore, the first wiring layer  40  and the second wiring layer  45  are interconnected at a predetermined location through the contact part  43 . Consequently, in the case where the circuit elements  25 A and  25 B have a multiple number of electrodes, a multi-layered wiring structure enables crossover, thereby allowing the wiring to be flexibly routed. Needless to say, it is also possible to increase the number of stacked layers to three, four, five and more, depending on the number of electrodes in the circuit element, the package density, and the like.  
         [0059]     While the second wiring layer  45  is formed with patterns with the same thickness in this embodiment, it can also be configured to have patterns with different thicknesses as described in  FIGS. 1A  to  1 C. Hence, by forming thickly formed conductive patterns, the electric capacity can be ensured, and a heat sink function is provided thereto. Additionally, the contact part  43  can be allowed to serve as a thermal via.  
         [0060]     As shown in  FIG. 5B , a resin sealed body  31  is separated from the supporting substrate  11 . The method of the separation can be performed in the method mentioned previously. The resin sealed body  31  is then processed with a back surface treatment, and thereafter is diced and separated into pieces. Thus, a circuit device  10 B as shown in  FIG. 5C  is completed.  
         [0061]     The method of forming the contact part  43  is described with reference to  FIGS. 6A  to  8 B.  
         [0062]     Referring to  FIG. 6A , the second conductive film  34  is deposited on the top surface of the first wiring layer  40 , with the insulation layer  41  interposed therebetween. Here, in the second conductive film  34 , the region where the contact part  43  is to be formed is removed. In addition, a surface of the insulation layer  41  is exposed at the lowest part of the through hole  42 . Moreover, filler is mixed into the insulation layer  41 , in consideration of the improvement in heat dissipation property. First, magnified views of the contact part forming region  44  are shown in  FIGS. 6B and 6C , and hereafter, the method of forming the through hole  42  will be described in detail.  
         [0063]     In the embodiment, as shown in  FIG. 6B , the film thickness of the insulation layer  41  under the through hole  42  becomes thinner, since the salient  18  is buried therein. Subsequently, by removing the insulation film in the thinner region with the laser beam  39 , the top surface of the salient  18  is exposed at the lowest part of the through hole  42 . The thickness T 2  for the major part of the insulation layer  41  is, for example, approximately 50 μm. On the other hand, the thickness T 1  of the insulation layer  41  which corresponds to the lower part of the through hole  42  is thinner, which is, for example, approximately between 10 μm and 25 μm.  
         [0064]     When the contact part  43  is formed by plating in the later process, the through hole  42  needs to be formed in a low aspect ratio. This is because if the aspect ratio is high, the mobility of plating liquid inside the through hole  42  worsens and the supply of the plating liquid becomes insufficient, thereby making the forming of the contact part  43  difficult.  
         [0065]     Here, since the aspect ratio of the through hole  42  enabling the reliable contact part  43  to be formed by plating is confirmed to be 1 or less, the through hole  42  in the embodiment is formed with the aspect ratio of 1 or less. The aspect ratio mentioned here is a value indicated by L/D, where L is a depth of the through hole  42  and D is a diameter of the through hole  42 .  
         [0066]     Moreover, if filler for ensuring the heat dissipation property is mixed into the insulation layer  41 , the forming of the through hole  42  with the laser beam becomes slightly difficult. In this case, it is beneficial to form the insulation layer  41  in which the through hole  42  is formed thin.  
         [0067]     In  FIG. 6C , a sectional view, after the through hole  42  is formed by the above-mentioned method, is shown. The top surface of the salient  18  is exposed from the bottom of the through hole  42 . In addition, on the sidewall of the through hole  42  formed by a laser processing, the filler mixed into the insulation layer  41  is exposed. Particles of the filler mixed into the insulation layer  41  have a wide variety of diameters, so as to improve the heat dissipation property. Therefore, the sidewall of the through hole  42  has an irregular surface. In the case where there is a residue remaining in the bottom of the through hole  42  after the above-mentioned laser processing, a cleaning is conducted so as to remove the residue.  
         [0068]     The planar size of the salient  18  is formed to be larger than that of the through hole  42  which is to be formed thereabove. In other words, the shapes of the through hole  42  and the salient  18  from a top view are both round, for example, and the diameter of the salient  18  is formed to be larger than that of the through hole  42 . In a concrete example, if a diameter W 1  of the through hole  42  is approximately 100 μm, then a diameter W 2  of the salient  18  is formed to be approximately between 150 μm and 200 μm. Alternatively, if the diameter W 1  of the through hole  42  is approximately from 30 μm to 50 μm, then the diameter W 2  of the salient  18  is adjusted to be approximately from 50 μm to 70 μm. As described, by setting the planar size of the salient  18  larger than that of the through hole  42 , the through hole  42  can be placed on the salient  18 , even if the through hole  42  is formed in a slightly deviated position. Consequently, the connection reliability decline caused by the position deviation can be prevented. The shape of salient  18  from the top view can be other than a round shape.  
         [0069]     Moreover, by forming the insulation film  41  with a first and a second resin films (not shown), it is possible to form the through hole  42  easily. Specifically, the lower part of the layer of the insulation layer  41  is formed with the first resin film. Here, the top surface of the first resin layer is set to be located at the same height as that of the salient  18 . Thereafter, the second resin film is formed on the top surface of the first resin film. In the above, the first resin film is filled in with the filler in a high filling ratio so as to preserve the heat dissipation property, while the second resin film is filled in with the filler in a low filling ratio in order that the through hole  42  can be formed easily by the laser. Consequently, the above method serves to prevent jamming of the through hole  42  from occurring due to the residue of the filler inside the through hole or due to the filler flaking from the side surface of the through hole  42 . Therefore, the forming of a highly reliable contact part becomes possible. Further, the diameters of filler particles mixed into the second resin film may be made small. Still further, the filler may not need to be mixed into the second resin film.  
         [0070]     Moreover, another method can be applied for forming the through hole  42 , although in the above-mentioned description, the through hole  42  is formed after covering the insulation layer  41  with the second conductive film  34 . More specifically, the through hole  42  is formed by removing the insulation layer  41  before covering the second conductive film  34 , and thus the top surface of the salient  18  can be exposed at the lowest part of the through hole  42 . Here, a YAG (yttrium-aluminum-garnet) laser or wet etching can be adopted as a method for removing resin. Thereafter, the contact part  43  and the second conductive layer  34  can be formed with electroless plating. Moreover, by performing electroplating where the second conductive film  34  formed with electroless plating is used as a cathode, it is possible to form a conductive film with a certain degree of thickness.  
         [0071]     Next, with reference to  FIGS. 7A  to  8 B, processes of forming plated films on the through hole  42 , forming the contact part  43 , and providing electronic continuity between the first wiring layer  40  and the second conductive film  34 , will be described. There are two possible methods for forming plated films. The first method is to perform film deposition of a plated film with electroless plating, and to subsequently perform film deposition of another plated film with electroplating again. The second method is to perform film deposition of plated films only with the electroplating processing.  
         [0072]     The first method of forming the plated film is described with reference to  FIGS. 7A  to  7 C. First, as shown in  FIG. 7A , a first plated film  46  is formed with electroless plating processing on the surface of the second conductive film  34 , including the sidewall of the through hole  42 . The thickness of the first plated film  46  can be set to approximately between 3 μm and 5 μm.  
         [0073]     Subsequently, as shown in  FIG. 7B , another film, i.e. a second plated film  47 , is formed with an electroplating method on the surface of the first plated film  46 , including the sidewall of the through hole  46 . More specifically, by using the second conductive film  34  on which the first plated film  46  is formed as a cathode electrode, the second plated film  47  is additionally formed by way of an electroplating method. In the inner wall of the through hole  42 , the first plated film  46  is formed with the electroless plating mentioned above. Therefore, the second plated film  47  formed in this process has an even thickness, including the inner wall of the through hole  42 . As described, the contact part  43  is formed of the plated film. The specific example for the thickness of the second plated film  47  is approximately 20 μm. Materials for the first plated film  46  and the second plated film  47  mentioned above, may include copper, which is the same material as that of the second conductive film  34 . Metals other than copper may also be adopted as a material for the first plated film  46  and the second plated film  47 .  
         [0074]     Referring to  FIG. 7C , in this case, the through hole  42  is buried with the second plated film  47  with filling plating. Filling plating here enables to improve the mechanical strength of the contact part  43 .  
         [0075]     Hereafter, with reference to  FIGS. 8A and 8B , methods of forming the contact part  43  with electroplating will be described.  
         [0076]     Referring to  FIG. 8A , first, a liquid solution which includes metal ions is allowed to touch the through hole  42 . Here, materials adoptable for a plated film  48  may include copper, gold, silver or palladium. Subsequently, an electric current is applied by using the second conductive film  34  as a cathode electrode, and metal is precipitated on the second conductive film  34  which serves as a cathode. Consequently, the plated film is formed. The way in which the plated film grows is represented by a  48 A and a  48 B in  FIGS. 8A and 8B . In the electroplating method, a plated film is formed preferentially at the locations where the electric field is stronger. In the embodiment, the electric field becomes stronger at the part in the second conductive film  34  where it faces the perimeter part of the through hole  42 . Hence, as shown in this drawing, the plated film grows preferentially from the part in the second conductive film  34  where it faces the perimeter part of the through hole  42 . The first wiring layer  40  and the second conductive film  34  becomes electrically continuous at the time when the formed plated film touches the salient  18 . Thereafter, the plated film is formed in a uniform manner inside the through hole  42 . Consequently, the contact part  43  unified with the second conductive film  34  is formed inside the through hole  42 .  
         [0077]     Hereafter, another method of forming the contact part  43  will be described with reference to  FIG. 8B . In this case, an overhang  50  is provided in a perimeter part of the through hole  42 , thus enabling an easy formation of the contact part  43  with the electroplating method. The “overhang” mentioned here indicates a portion composed of the second conductive film  34  that overhangs in a way that it covers the perimeter part of the through hole  42 . The specific method of manufacturing the overhang  50  is possible by increasing the laser&#39;s power output when the through hole  42  is formed with a laser beam. By increasing the laser&#39;s power output, the removal of the insulation layer  41  by the laser beam proceeds to a horizontal direction, and thus the resin in the lower region under the overhang  50  is removed. Subject to the above-mentioned condition, by conducting the electroplating processing where the second conductive film  34  is used as the cathode electrode, the plated film grows preferentially from the overhang  50 . Since the plated film grows from the overhang  50 , a plated film can be grown preferentially downward, compared to the case in  FIG. 8A . Therefore, it becomes possible to ensure that the through hole  42  with the plated film.  
         [0078]     As mentioned above, the sidewall of the through hole  42  in the embodiment has an irregular surface. In addition, at the sidewall of the through hole  42 , the filler mixed into the insulation layer  41  is exposed. Hence, it is difficult to form the plated film on the sidewall of the through hole  42 . In general, a plated film is hard to adhere onto a surface of filler that is composed of an inorganic substance. Specifically, if AlN is exposed on the sidewall of the through hole  42 , the plated film is difficult to form. Therefore, in this embodiment, the contact part  43  is formed with the above-mentioned electroplating method.  
         [0079]     Furthermore, for the case where the through hole  42  is buried by performing the filling plating, the filling plating can also be easily conducted since the through hole  42  is formed shallow, as described above.  
         [0080]     In the embodiment, the location where the above-mentioned the salient  18  contacts the contact part  43  is positioned in a middle portion in the thickness-wise direction of the insulation film  41 . Here, the “middle portion” means that it is above the top surface of the first wiring layer  40  and below the bottom surface of the second wiring layer  45 . Hence, in the drawing, the location where the salient  18  contacts the contact part  43  is approximately at the central part of the insulation film in the direction of the thickness. The location can be changed within the range of the middle portion mentioned above. Considering that the contact part  43  is formed by the plating processing, it is desirable that the part where the salient  18  contacts the contact part  43  be arranged between the top surface of the first wiring layer  40  and the bottom surface of the second wiring layer  45  and above the mid point thereof. Consequently, there is an advantage, that the formation of the contact part  43  formed of plated film becomes easy. That is to say, when the through hole  42  is formed in order to form the contact part  43 , the depth of the through hole  42  can be set shallow. Further, since the depth of the through hole  42  is shallow, the diameter thereof can also be set small. Still further, since the diameter of the through hole  42  is small, the space between the each through hole  42  can be narrowed. Therefore, a microscopic pattern can be realized as a whole, enabling miniaturization of a circuit device.