Patent Publication Number: US-2009229862-A1

Title: Multilayer printed wiring board and method of manufacturing the same

Description:
This Application is a U.S. National Phase Application of PCT International Application PCT/JP2006/322126. 
    
    
     TECHNICAL FIELD 
     The present invention relates to a multilayer printed wiring board used in a portable telephone, a very small portable terminal, and the like, or a multilayer printed wiring board used as an interposer and the like when a semiconductor chip is bare-chip mounted, and a method for manufacturing the same. 
     BACKGROUND ART 
     Conventionally, as this type of multilayer printed wiring board (hereinafter, just referred to as a multilayer board), a multilayer board having an IVH (inner via hole) in an arbitrary position is disclosed in, for example, patent document 1. 
     The market has demanded further thinning of a multilayer board. Hereinafter, a multilayer board using a film as a means for thinning a multilayer board is described. 
       FIG. 11  is a sectional view showing an example of a conventional multilayer printed wiring board, which is an example of a multilayer wiring board in which films are laminated with an adhesive. As shown in  FIG. 11 , on film  10 , a predetermined pattern of wirings  12  is formed. A plurality of films  10  are adhesively bonded together with wirings  12  by using adhesive  14 . Furthermore, by forming IVHs  8  in necessary parts, wirings  12  formed on different layers are coupled to each other. 
     However, in a conventional configuration, since adhesive  14  is used for coupling films  10  to each other, there is a limitation in thinning. 
     For example, in a configuration shown in  FIG. 11 , since films  10  having wiring  12  on one surface thereof are laminated, when a four-layer multilayer board is formed, the thickness for seven layers including three layers of adhesive  14  and four layers of films  10  is needed. Therefore, thinning has been difficult. 
     On the other hand, as an application of the configuration shown in  FIG. 11 , it is thought that two films  10  having wiring  12  on both surfaces thereof are prepared and the two films are attached to each other so as to form a four-layer multilayer board. In this case, films  10  having wiring  12  on both surface thereof are attached to each other with adhesive  14 . However, when they are attached to each other, adhesive  14  is softened and fluidized, so that wirings  12  facing each other may be short-circuited. [Patent document 1] Japanese Patent Unexamined Publication No. 2002-353619 
     SUMMARY OF THE INVENTION 
     A multilayer printed wiring board of the present invention is produced by pressing double-sided printed wiring boards, which uses a resin film having wiring patterns on the front and back surfaces thereof, with a film prepreg sandwiched therebetween and integrating thereof. 
     In such a configuration, a film prepreg obtained by forming a provisionally hardened resin layer on both surfaces of a film is used, instead of a conventional prepreg obtained by impregnating a woven fabric with resin, and the films having a wiring on both surfaces thereof are attached to each other. Therefore, even if they are pressed at high pressure, the film included in the film prepreg can prevent short-circuit of the wiring. Furthermore, the film prepreg is provided with a through hole in advance and the through hole is filled with a conductive paste. Thus, the double-sided printed wiring boards can be adhesively bonded to each other and IVH can be formed simultaneously. 
     Furthermore, a method of manufacturing a multilayer printed wiring board of the present invention includes at least a hole processing step of processing a through hole in an insulating base material; a paste coupling layer formation step of forming a paste coupling layer by filling a through hole with a conductive paste; a double-sided board producing step of producing a double-sided board; a laminating step of laminating the double-sided boards on the front and back surfaces of the paste coupling layer so as to form a laminated body; and hot pressing step of hot pressing the laminate body. 
     With such steps, a multilayer printed wiring board capable of thinning layers can be manufactured. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a sectional view showing a multilayer board in accordance with a first exemplary embodiment. 
         FIG. 2A  is a sectional view to illustrate a method of manufacturing a four-layer printed wiring board in accordance with a second exemplary embodiment. 
         FIG. 2B  is a sectional view to illustrate a method of manufacturing a four-layer printed wiring board in accordance with the second exemplary embodiment. 
         FIG. 2C  is a sectional view to illustrate a method of manufacturing a four-layer printed wiring board in accordance with the second exemplary embodiment. 
         FIG. 3A  is a sectional view to illustrate a method of manufacturing a four-layer printed wiring board in accordance with the second exemplary embodiment. 
         FIG. 3B  is a sectional view to illustrate a method of manufacturing a four-layer printed wiring board in accordance with the second exemplary embodiment. 
         FIG. 3C  is a sectional view to illustrate a method of manufacturing a four-layer printed wiring board in accordance with the second exemplary embodiment. 
         FIG. 4  is a sectional view showing a multilayer printed wiring board in accordance with a third exemplary embodiment. 
         FIG. 5A  is a sectional view to illustrate a method of manufacturing a multilayer printed wiring board in accordance with a fourth exemplary embodiment. 
         FIG. 5B  is a sectional view to illustrate a method of manufacturing a multilayer printed wiring board in accordance with the fourth exemplary embodiment. 
         FIG. 6  is a sectional view showing a multilayer printed wiring board in accordance with a fifth exemplary embodiment. 
         FIG. 7A  is a sectional view to illustrate a method of manufacturing a multilayer printed wiring board in accordance with a sixth exemplary embodiment. 
         FIG. 7B  is a sectional view to illustrate a method of manufacturing a multilayer printed wiring board in accordance with the sixth exemplary embodiment. 
         FIG. 8  is a sectional view showing an example of a method of manufacturing a multilayer printed wiring board having a fine pattern on a surface layer in accordance with a seventh exemplary embodiment. 
         FIG. 9A  is a sectional view showing an example of a method of manufacturing a multilayer printed wiring board having a fine pattern on a surface layer in accordance with the seventh exemplary embodiment. 
         FIG. 9B  is a sectional view showing an example of a method of manufacturing a multilayer printed wiring board having a fine pattern on a surface layer in accordance with the seventh exemplary embodiment. 
         FIG. 10A  is a sectional view to illustrate an example of the method of manufacturing the multilayer printed wiring board having a fine pattern on the surface layer in accordance with the seventh exemplary embodiment. 
         FIG. 10B  is a sectional view to illustrate an example of the method of manufacturing the multilayer printed wiring board having a fine pattern on the surface layer in accordance with the seventh exemplary embodiment. 
         FIG. 11  is a sectional view showing an example of a conventional multilayer printed wiring board. 
     
    
    
     REFERENCE MARKS IN THE DRAWINGS 
     
         
           102 ,  102   a ,  102   b ,  102   c  resin film 
           104   a ,  104   b  first wiring 
           106   a ,  106   b ,  106   c ,  106   d  second wiring 
           108  insulating resin 
           110  IVH (inner via hole) 
           112  interlayer coupling part 
           114   a ,  114   b ,  114   c  double-sided board 
           116  paste coupling layer 
           118  retention film 
           120  provisionally hardened resin 
           122  film prepreg 
           124  through hole 
           126  conductive paste 
           128  multilayer board 
           130  interlayer insulating layer 
           132  inner electrode 
           134   a ,  134   b  single-sided board 
           136  blind via 
           138  metal film 
       
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, exemplary embodiments of the present invention are described with reference to drawings. 
     First Exemplary Embodiment 
     Hereinafter, a multilayer board in accordance with a first exemplary embodiment of the present invention is described with reference to drawings. 
       FIG. 1  is a sectional view showing a multilayer board in accordance with the first exemplary embodiment of the present invention. As shown in  FIG. 1 , the multilayer board includes resin films  102   a  and  102   b , first wirings  104   a  and  104   b , second wirings  106   a  and  106   b , insulating resin  108 , IVH  110 , interlayer coupling part  112 , double-sided boards  114   a  and  114   b , paste coupling layer  116 , and retention film  118 . 
     As shown in  FIG. 1 , double-sided board  114   a  includes film  102   a  having first wiring  104   a  on one surface thereof and second wiring  106   a  on the other surface thereof. First wiring  104   a  and second wiring  106   a  are coupled to each other with interlayer coupling part  112 . Similarly, double-sided board  114   b  includes film  102   b  having first wiring  104   b  on one surface thereof and second wiring  106   b  on the other surface thereof. First wiring  104   b  and second wiring  106   b  are coupled to each other with interlayer coupling part  112 . 
     Herein, first wirings  104   a  and  104   b  correspond to wirings exposed on the surface of the printed wiring board of the first exemplary embodiment. On the other hand, second wirings  106   a  and  106   b  are embedded in insulating resin  108  in a state in which they are formed on the surface of double-sided boards  114   a  and  114   b . Since second wirings  106   a  and  106   b  are embedded in insulating resin  108 , the thicknesses of wirings  106   a  and  106   b  are absorbed and do not easily appear as convex and concave portions on the surface of a sample. Furthermore, IVH  110  is an inner via hole (interlayer coupling). Second wiring  106   a  formed on the surface of resin film  102   a  and second wiring  106   b  formed on the surface of resin film  102   b  are electrically coupled by IVH  110 . As shown in  FIG. 1 , IVH  110  penetrates insulating resin  108  and retention film  118 , so that second wiring  106   a  and second wiring  106   b , which face each other, are electrically coupled to each other. Furthermore, paste coupling layer  116  includes insulating resin  108  formed on both surfaces of retention film  118 , and IVH  110  penetrating insulating resin  108  and retention film  118 . 
     With reference to  FIG. 1 , the way of counting the number of wirings or insulating layers is described. When the number is counted from the upper part to the lower part in  FIG. 1 , a first insulating layer (corresponding to a surface layer) that is the first layer counted from the surface layer corresponds to film  102   a ; a second insulating layer that is the second layer counted from the surface layer corresponds to paste coupling layer  116 ; and a third insulating layer that is the third layer counted from the surface layer corresponds to film  102   b , respectively. 
     Similarly, a first wiring (corresponding to a wiring on the surface layer) that is the first layer counted from the surface layer corresponds to first wiring  104   a ; a second wiring that is the second layer counted from the surface layer corresponds to second wiring  106   a ; a third wiring that is the third layer counted from the surface layer corresponds to second wiring  106   b ; and a fourth wiring that is the fourth layer counted from the surface layer corresponds to first wiring  104   b .  FIG. 1  shows a four-layer structure including four layers of electrodes and is symmetrical in the up and down direction. Therefore, there is no difference between counting from the upper part to the lower part and counting from the lower part to the upper part. However, in principle, in the first exemplary embodiment of the present invention, layers and wirings are counted from the upper part to the lower part. 
     Thus, as shown in  FIG. 1 , the second insulating layer formed in the second layer counted from the surface layer is paste coupling layer  116 . An electrical connection penetrating paste coupling layer  116  corresponds to IVH  110 . Second wiring  106   a  that is the second wiring formed in the second layer counted from the surface layer and second wiring  106   b  that is the third wiring formed in the third layer counted from the surface layer are embedded in insulating resin  108 . With insulating resin  108  and retention film  118 , short-circuit does not occur between second wirings  106   a  and  106   b  formed in parts without having IVH  110 . 
     IVH  110  in the first exemplary embodiment is obtained by filling a conductive paste into a through hole formed in insulating resin  108 . With reference to the below-mentioned  FIGS. 2A ,  2 B and  2 C, through hole  124  and conductive paste  126  are described. Furthermore, IVH  110  is formed between double-sided boards  114   a  and  114   b  so as to couple second wirings  106   a  and  106   b . IVH  110  can be formed in arbitrary positions of paste coupling layer  116 . Thus, in the multilayer board in the first exemplary embodiment, the thicknesses of plurality of double-sided boards  114   a  and  114   b  using films  102   a  and  102   b  are absorbed by insulating resin  108  and at the same time, interlayer coupling is carried out by IVH  110 . 
     In the first exemplary embodiment, as members constituting paste coupling layer  116 , a member obtained by forming a predetermined resin on both surfaces of retention film  118  to a predetermined thickness is used. Two double-sided boards  114   a  and  114   b  are attached and integrated to each other by using this member as described with reference to below-mentioned  FIGS. 2A to 3C . Thus, in the first exemplary embodiment, retention film  118  built in insulating resin  108  prevents short-circuit between second wirings  106   a  and  106   b  formed on double-sided boards  114   a  and  114   b . Consequently, the total thickness of the multilayer board itself can be remarkably reduced. Note here that the detail of the resin is described with reference to  FIGS. 2A and 3C . 
     As mentioned above, an electrical connection penetrating the second insulating layer (corresponding to paste coupling layer  116  in  FIG. 1 ) that is formed in the second layer counted from the surface layer is a conductive paste (corresponding to IVH in  110  in  FIG. 1 ). 
     The second wiring that is formed in the second layer counted from the surface layer (in  FIG. 1 , the second wiring corresponds to second wiring  106   a  formed on double-sided board  114   a  when counted from the upper part, and second wiring  106   b  when counted from the lower part) and the third wiring that is formed in the third layer counted from the surface layer are embedded in paste coupling layer  116  and electrically coupled to each other. In  FIG. 1 , when counted from the upper part, the third wiring corresponds to second wiring  106   b  formed on double-sided board  114   b . Similarly, when counted from the lower part, the third wiring corresponds to second wiring  106   a  formed on double-sided board  114   a.    
     Thus, in the first exemplary embodiment, when a four-layer board (the four-layer herein means that four layers of wirings are provided) is configured by using insulating resin  108 , electrodes facing each other can be prevented from being short-circuited. Therefore, insulating resin  108  can be thinned. As a result, the thickness of the four-layer board can be reduced. 
     Second Exemplary Embodiment 
     Hereinafter, a method of manufacturing a multilayer board in accordance with a second exemplary embodiment of the present invention is described. The second exemplary embodiment shows an example of a method of manufacturing a four-layer board and corresponds to, for example, a method of manufacturing a four-layer board described in the first exemplary embodiment.  FIGS. 2A ,  2 B and  2 C and  FIGS. 3A ,  3 B and  3 C are sectional views to illustrate a method of manufacturing a four-layer printed wiring board in accordance with the second exemplary embodiment. 
     As shown in  FIGS. 2A ,  2 B and  2 C, the four layer printed wiring board in accordance with the second exemplary embodiment includes provisionally hardened resin  120 , film prepreg  122 , through hole  124  and conductive paste  126 . Firstly, as shown in  FIG. 2A , provisionally hardened resin  120  is formed to a predetermined film thickness on both surfaces of retention film  118  so as to prepare film prepreg  122 . Then, as shown in  FIG. 2B , provisionally hardened resin  120  and protective film  118 , which constitute film prepreg  122 , are provided with through holes  124 . Through hole  124  can be formed by using a mold, drill, laser, and the like. Next, as shown in FIG.  2 C, conductive paste  126  is filled into through hole  124 . For example, by using film prepreg  122  and a protective film (not shown) formed thereon as a mask, conductive paste  126  is rubbed by using a squeegee and the like. Alternatively, conductive paste  126  is filled. Thus, conductive paste  126  can be filled into only through hole  124  formed in film prepreg  122  in a self-alignment manner. 
     It is desirable that a protective film (not shown in  FIGS. 2A and 2B ) is attached on the surface of provisionally hardened resin  120  in advance. When the protective film is used, through hole  124  shown in, for example,  FIG. 2B  can be formed easily. Moreover, when this protective film is used as a kind of mask, conductive paste  126  is filled into through hole  124  easily. Then, after conductive paste  126  is filled, the protective film (not shown) is peeled off. Thus, film prepreg  122  is processed in the state shown in  FIG. 2C  (hereinafter, the thus processed prepreg  122  is referred to as  FIG. 2C  product). 
     As retention film  118 , it is desirable to use a heat resistant film such as a polyimide film, a polyamide film, and an aramid film. The use of a highly heat-resistant resin film can improve the heat resistance of the produced multilayer board. Furthermore, it is desirable to select the thickness of retention film  118  of not more than 100 μm, particularly not less than 5 μm and not more than 50 μm, desirably not more than 30 μm, and further not more than 25 μm if possible. By using such a very thin heat resistant film, the total film thickness of the produced multilayer board can be reduced. On both surfaces of retention film  118  including such a heat resistant film, hardened resin is applied to a predetermined thickness by using an applier and provisionally hardened, thereby it can be heated and fully hardened together with double-sided boards as shown in the below mentioned  FIGS. 3B and 3C . Note here that provisional hardening means a slightly hardened state and a state having flexibility. Furthermore, resin in a provisionally hardened state is in a state that is softened when it is re-heated. By adjusting the re-heating state, resin can be fully hardened. 
       FIG. 3A  is a sectional view showing double-sided board  114   a . In  FIG. 3A , double-sided board  114   a  includes first wiring  104   a  formed on one surface of film  102   a  and second wiring  106   a  formed on the other surface. Interlayer coupling part  112  penetrating resin film  102   a  couples between the layer of first wiring  104   a  and the layer of second wiring  106   a.    
     Herein, as a material of resin films  102   a  and  102   b , it is desirable to use heat resistant film such as a polyimide film, a polyamide film and an aramid film similar to retention film  118 . By using such a highly heat-resistant resin film, thermal influence in, for example, soldering can be suppressed. Furthermore, it is desirable to select the thickness of such a heat resistant film of not more than 100 μm, particularly not less than 5 μm and not more than 50 μm, desirably not more than 30 μm, and further not more than 25 μm if possible. In particular, retention film  118  can be about 5 micron because the both surfaces of retention film  118  are coated with provisionally hardened resin  120  and a protective film. By using such a very thin heat resistant film, the total thickness of the obtained multilayer board can be reduced. As double-sided board  114   a , it is possible to select a board material obtained by forming copper foil on both surfaces of a very thin heat resistant film without using an adhesive. For example, it is possible to select the below-mentioned CCL (copper clad laminate). Furthermore, in the case where a very thin heat resistant film is used as retention film  118 , by subjecting the surface thereof to surface modification such as surface roughing treatment and plasma treatment, the adhesiveness with respect to provisionally hardened resin  120  formed thereon can be improved. Similarly, resin films  102   a  and  102   b  can be thinned to, for example, the thickness of 10 microns or 5 microns although they have a copper foil on at least one surface. 
       FIG. 3B  shows a state in which double-sided boards  114   a  and  114   b  are aligned with respect to both surfaces of  FIG. 2C  product. In  FIG. 3B , second wiring  106   a  of double-sided board  114   a  and second wiring  106   b  of double-sided board  114   b  face the side of  FIG. 2C  product. Then, second wirings  106   a  and  106   b  and conductive paste  126  are aligned. In a state in which they are aligned, they are heated and pressed in a vacuum press (vacuum press is not shown). Then, after vacuum pressing is completed, a pressed sample is taken out.  FIG. 3C  is a sectional view showing a sample that has already undergone vacuum pressing. 
     A sample or a predetermined laminated body corresponding to  FIG. 3C  is heated and hardened in a vacuum press at a predetermined temperature profile. Then, provisionally hardened resin  120  is softened and hardened so as to be changed into insulating resin  108 . When provisionally hardened resin  120  is softened, wirings  106   a  and  106   b  formed on double-sided boards  114   a  and  114   b  are embedded in the softened provisionally hardened resin, so that the thickness of the wiring is absorbed. Then, provisionally hardened resin  120  is hardened in a state in which the wiring thickness is absorbed, and turned to be insulating resin  108  so as to strongly fix double-sided boards  114   a  and  114   b . Furthermore, at this time, conductive paste  126  embedded in provisionally hardened resin  120  and retention film  118  is simultaneously hardened and changed into IVH  110 . Thus, four-layer board having IVH  110  is formed. Then, the thickness of second wirings  106   a  and  106   b  or concavity and convexity due to the thickness are reduced or flattened. Furthermore, at the time of vacuum pressing, even if second wirings  106   a  and  106   b  are strongly pressed to each other, a short-circuit between them does not occur because retention film  118  is provided. 
     Furthermore, a method of manufacturing a four-layer board in accordance with the second exemplary embodiment is described in detail. Firstly, as retention film  118 , for example, a commercially available polyimide film having a thickness of about 10 micron is selected. On both surfaces of this film, epoxy resin is thinly coated by using a coater (coating device). After the coater is used, the resin is provisionally hardened by using an installed dryer. Then, in order to protect the surface of provisionally hardened resin  120 , a protective film is attached to the surface of provisionally hardened resin  120 . Thus, a sample in a state of  FIG. 2A  is produced. In  FIG. 2A , the protective film on provisionally hardened resin  120  is not shown. 
     Next, as shown in  FIG. 2B , through holes  124  are formed in predetermined positions in a state in which a protective film (not shown in  FIG. 2B ) is formed on a prepreg. Next, on the protective film, a predetermined amount of conductive paste  126  is added and filled into through hole  124  in such a manner as to print conductive paste  126  by using a squeegee (rubber spatula). Thereafter, when a protective film is peeled, as shown in  FIG. 2C , film prepreg  122  is processed. 
     Next, as shown in  FIG. 3A , double-sided board  114   a  is prepared. As double-sided board  114   a , a double-sided copper-clad film is used. Specifically, a film obtained by attaching copper foil on both surfaces of a 10 μm-thick polyimide film without using any adhesives is used. Specifically, it is desirable to use a commercially available CCL. Next, a copper foil part of the double-sided copper-clad film is processed into a predetermined pattern so as to form double-sided board  114   a  shown in  FIG. 3A . It is desirable to select a CCL without using any adhesives. By selecting such a double-sided copper-clad film without using any adhesives, for example, by selecting a film using a thin film method for a base material and the like, it is possible to prevent the occurrence of a problem caused by an adhesive. 
     As shown in  FIG. 3B , on both surfaces of  FIG. 2C  product, double-sided boards  114   a  and  114   b  are aligned by using a predetermined jig (not shown). Thereafter, they are pressed in a vacuum press for a predetermined time at a predetermined temperature, so that they are integrated with each other. At this time, it is desirable that they are heated and pressed if necessary. Furthermore, this pressing condition is made to be a condition in which provisionally hardened resin  120  is softened and then hardened. At the same time, with conductive paste  126 , second wirings  106   a  and  106   b  that are formed at the side of film prepreg  122  of double-sided boards  114   a  and  114   b  are electrically coupled to each other. 
     Thus, a very thin multilayer board as shown in  FIG. 3C  is produced. Herein, the thicknesses of films  102   a  and  102   b , retention film  118  and provisionally hardened resin  120  are reduced to, for example, 40 μm or 20 μm, and furthermore 10 μm. Consequently, a very thin multilayer board having a total thickness of about not more than 100 μm, or not more than 60 μm, furthermore not more than 30 μm can be produced. 
     As mentioned above, it is possible to produce a four-layer printed wiring board including paste coupling layer  116 , in which an electrical connection penetrating a second insulating layer (the second insulating layer corresponds to paste coupling layer  116  in  FIG. 3C ) that is the second layer counted from the surface layer of the four-layer printed wiring board that is conductive paste  126 . A second wiring (corresponding to second wiring  106   a  in  FIG. 3C ) provided in the second layer counted from the surface layer and a third wiring (corresponding to third wiring  106   b  in  FIG. 3C ) provided in the third layer counted from the surface layer are embedded in paste coupling layer  116 . 
     As mentioned above, in the second exemplary embodiment, both “second wiring (corresponding to second wiring  106   a  in  FIG. 3C ) that is a second layer counted from the surface layer” and “third wiring (corresponding to third wiring  106   b  in  FIG. 3C ) that is a third layer counted from the surface layer” can be embedded in paste coupling layer  116 . Therefore, even if the thickness of the board is thinned, the thickness of the wiring can be absorbed. The mounting property of chip components, semiconductor chip, and the like, can be improved so as to be applied for bare chip mounting and furthermore, an interposer for CPU mounting. 
     Furthermore, paste coupling layer  116  includes provisionally hardened resin  120  and conductive paste  126  that is filled into through hole  124  formed in provisionally hardened resin  120 . Consequently, it is possible to freely design positions in which IVH  110  is formed, thus enabling a circuit board to have a small size and high performance. 
     Third Exemplary Embodiment 
     Hereinafter, a multilayer board in accordance with a third exemplary embodiment of the present invention is described with reference to drawings. The third exemplary embodiment is different from the first exemplary embodiment in the number of films to be used for forming the multilayer structure. In the first exemplary embodiment, two films are used; and in the third exemplary embodiment, three films are used. 
       FIG. 4  is a sectional view showing a multilayer printed wiring board in accordance with the third exemplary embodiment. In  FIG. 4 , double-sided boards  114   a ,  114   b , and  114   c  using a film are attached to each other by using two paste coupling layers  116   a  and  116   b . Then, second wiring  106   a  formed on the surface of double-sided board  114   a  and second wiring  106   b  formed on the surface of double-sided board  114   b  are electrically coupled to each other via IVH  110 . Similarly, second wiring  106   d  formed on double-sided board  114   c  and second wiring  106   c  formed on double-sided board  114   b  are electrically coupled to each other via IVH  110 . 
     Thus, three double-sided boards  114   a ,  114   b  and  114   c  are integrated by using paste coupling layers  116   a  and  116   b . Herein, the total number of layers for wiring is six layers, which can be calculated from: two layers of wiring x three sheets. Among the total six layers of wirings, the thickness of four layers of wirings can be absorbed by embedding them in paste coupling layers  116   a  and  116   b . Thus, a multilayer board having reduced thickness and flattened surface can be produced. Herein, in the case shown in  FIG. 4 , the multilayer board is a six-layer board. 
     Paste coupling layers  116   a  and  116   b  include insulating resin  108  and IVH  110 . Herein, IVH  110  is an inner via hole. In the case of this exemplary embodiment, IVHs  110  can be formed in arbitrary portions. As an insulating member constituting paste coupling layer  116 , film prepreg  122  can be used. It is desirable to use hardened conductive paste  126  as a conductive member constituting IVH  110 . Thus, in the multilayer board in accordance with the third exemplary embodiment, by filling the hardened conductive paste into through hole  124  formed in film prepreg  122  and laminating thereof, the multilayer board can be significantly thinned. 
     As mentioned above, it is possible to produce a multilayer board that is a printed wiring board including not less than five layers, in which an electrical connection between second insulating layers (insulating resin  108  in  FIG. 4 ) formed in the second layer counted from at least one of the surface layers is IVH  110  that is a hardened product of conductive paste  126 . This multilayer board has paste coupling layers  116   a  and  116   b  in which the second wiring provided in the second layer from the surface layer and the third wiring provided in the third layer counted from the surface layer are coupled to each other with paste coupling layer  116   a . Similarly, in  FIG. 4 , second wiring  106   c  and second wiring  106   d  are embedded in paste coupling layer  116   b . The second wiring corresponds to second wiring  106   a  formed on double-sided board  114   a  when counted from the upper part in  FIG. 4 . Furthermore, third wiring corresponds to second wiring  106   b  formed on double-sided board  114   b  when counted from the upper part in  FIG. 4 . 
     Herein, “paste coupling layer in which an electrical connection in a second insulating layer that is the second layer counted from the surface layer is a conductive paste” means paste coupling layers  116   a  and  116   b  in  FIG. 4 . Furthermore, the first insulating layer that is the first layer counted from the surface layer corresponds to film  102   a  in  FIG. 4 . The “second wiring provided in the second layer counted from the surface layer” corresponds to second wiring  106   a  in  FIG. 4 . Furthermore, the “third wiring provided in the third layer counted from the surface layer” corresponds to second wiring  106   b  formed on the double-sided board  114   b  and embedded in paste coupling layer  116   b  when the layers are counted from the upper part to the lower part in  FIG. 4  (in the case of wirings, only wirings are counted). 
     Fourth Exemplary Embodiment 
     Hereinafter, a method of manufacturing a multilayer board in a fourth exemplary embodiment of the present invention is described with reference to drawings.  FIGS. 5A and 5B  are sectional views to illustrate a method of manufacturing a multilayer printed wiring board in accordance with the fourth exemplary embodiment. The fourth exemplary embodiment shows an example of a method of manufacturing a multilayer by using a plurality of films, and shows for example, the method of manufacturing a multilayer board in accordance with the third exemplary embodiment. 
     Firstly, as shown in  FIG. 5A , a plurality of film prepregs  122  having through holes filled with conductive pastes  126  are prepared. Similarly, double-sided boards  114   a ,  114   b  and  114   c  using resin films  102   a ,  102   b  and  102   c  are prepared. These are aligned with each other as shown in  FIG. 5A . 
       FIG. 5B  is a sectional view showing a state in which samples in  FIG. 5A  are integrated with each other. Specifically,  FIG. 5B  shows a product obtained by bonding the samples in a state shown in  FIG. 5A  by the use of, for example, a vacuum hot press so as to be hardened and integrated. At this pressing and laminating time, by heating the product at a predetermined temperature profile, provisionally hardened resin  120  is softened and hardened, and then changed into insulating resin  108 . Conductive paste  126  embedded in film prepreg  122  is simultaneously heated and hardened, and then turns into IVH  110 . 
     Furthermore, a method of manufacturing a multilayer board in accordance with the fourth exemplary embodiment is described in detail. Firstly, as provisionally hardened resin  120 , film prepreg  122  obtained by applying epoxy resin on the surface of a polyimide film followed by provisionally hardening thereof is prepared. Then, as shown in  FIG. 2B , through holes  124  are formed in predetermined positions in provisionally hardened resin  120  together with a protective film formed thereon. Next, on the protective film, a predetermined amount of conductive paste  126  is added. Conductive paste  126  is filled into through holes  124  formed in provisionally hardened resin  120  by using a squeegee (rubber spatula). Then, the protective film is peeled. As a result, film prepreg  122  is processed as shown in  FIG. 5A . 
     Next, a double-sided copper-clad film is prepared. Specifically, a film obtained by attaching copper foil on both surfaces of a 10 μm-thick aramid film without using any adhesives is used. As such a film, commercially available CCL can be used. Next, the copper foil part of the double-sided copper-clad film is processed into a predetermined pattern so as to form double-sided boards  114   a ,  114   b  and  114   c  shown in  FIG. 5A . As CCL, it is desirable to select CCL without using an adhesive. Thus, by selecting the double-sided copper-clad film without using an adhesive for bonding of a copper foil, for example, the double-sided copper-clad film by using a thin film method for a base material and the like, problems caused by an adhesive can be prevented. 
     As shown in  FIG. 5A , film prepregs  122  filled with conductive plate  126  and double-sided boards  114   a ,  114   b  and  114   c  are alternately laminated and aligned. Thereafter, they are pressed for a predetermined time and at a predetermined temperature in a vacuum press so as to integrate them. At this time, if necessary, vacuum hot pressing may be employed. Furthermore, this pressing condition is made to be a condition in which provisionally hardened resin  120  is softened and then hardened. Thereby, a plurality of double-sided boards  114   a ,  114   b  and  114   c  can be integrated by using provisionally hardened resin  120   a  in a state in which the plurality of double-sided boards  114   a ,  114   b  and  114   c  are interposed. Furthermore, in the pressing condition, conductive paste  126  electrically couples second wiring  106   a  and second wiring  106   b , which are formed at the side of film prepreg  122  of double-sided boards  114   a ,  114   b  and  114   c.    
     Thus, a very thin multilayer board as shown in  FIG. 5B  can be produced. Herein, when the thicknesses of films  102   a ,  102   b  and  102   c  and provisionally hardened resin  120 , for example, are reduced to, for example, the thickness of 40 μm or 20 μm, and furthermore 10 μm, a very thin multilayer board having a total thickness of about not more than 100 μm, or not more than 60 μm, furthermore not more than 30 μm can be produced. 
     Fifth Exemplary Embodiment 
     Hereinafter, a multilayer board in accordance with a fifth exemplary embodiment of the present invention is described.  FIG. 6  is a sectional view showing a multilayer printed wiring board in accordance with the fifth exemplary embodiment. The fifth exemplary embodiment is different from the third exemplary embodiment in that the central part of the third exemplary embodiment is a two-layer board, but the central part of the fifth exemplary embodiment is a three-layer board. Thus by using the fifth exemplary embodiment, a variety of multilayer boards can be formed by using other than a double-sided board using a film and the like. 
     As shown in  FIG. 6 , a multilayer board in accordance with the fifth exemplary embodiment includes multilayer board  128 , interlayer insulating layer  130  and inner electrode  132 . Herein, multilayer board  128  includes a plurality of inner electrodes  132  that are interlayer-insulated by interlayer insulating layers  130 , interlayer coupling part  112 , and the like. On the surface thereof, second wirings  106   b  and  106   c  are exposed. As shown in  FIG. 6 , second wirings  106   b  and  106   c  that are wirings formed on the surface of multilayer board  128  are both embedded in paste coupling layers  116   a  and  116   b . Similarly, on the surfaces of films  102   a  and  102   b , first wirings  104   a ,  104   b , second wirings  106   a , and  106   d  are formed and both are electrically coupled to each other by interlayer coupling part  112 . Thus, double-sided boards  114   a  and  114   b  are formed. 
     As shown in  FIG. 6 , second wiring  106   a  formed at the side of paste coupling layer  116   a  of double-sided board  114   a  and second wiring  106   b  formed at the side of paste coupling layer  116   a  of multilayer board  130  are both embedded in paste coupling layer  116   a  so as to be electrically coupled to each other with IVH  110 . Similarly, second wiring  106   d  on double-sided board  114   b  and second wiring  106   c  on multilayer board  128  are coupled to each other with IVH  110  penetrating paste coupling layer  116   b.    
     Thus, multilayer board  128  is disposed at the center and double-sided boards  114   a  and  114   b  are formed on both side or both surfaces of multilayer board  128 . The wiring thicknesses can be absorbed by paste coupling layer  116 , and they are integrated to each other. Thus, interlayer coupling can also be carried out. Furthermore, in the fifth exemplary embodiment, since paste coupling layers  116   a  and  116   b  including a hardened product of film prepreg  122  are used, even if a paste coupling layer is thinned, short-circuit between second wirings  106   a  and  106   b , or between second wirings  106   c  and  106   d  can be prevented. 
     Sixth Exemplary Embodiment 
     A method of manufacturing a multilayer board in a sixth exemplary embodiment is described in more detail with reference to  FIGS. 7A and 7B .  FIGS. 7A and 7B  are sectional views to illustrate a method of manufacturing a multilayer printed wiring board in accordance with the sixth exemplary embodiment, for example, a method of manufacturing the multilayer board of the fifth exemplary embodiment. 
     Firstly, as shown in  FIG. 7A , multilayer board  128  is prepared. In multilayer board  128 , inner electrodes  132  are sandwiched by interlayer insulating layers  130  and coupled to each other via interlayer coupling part  112 . Furthermore, on the surface of multilayer board  128 , second wirings  106   b  and  106   c  are exposed. As such multilayer board  128 , a commercially available glass epoxy multilayer board can be used. 
       FIG. 7B  is a sectional view showing a state in which double-sided board is set in the center and films are disposed at the both sides thereof. In  FIG. 7B , film prepregs  122  filled with conductive paste  126  are set at both sides of multilayer board  128  so that conductive paste  126  is disposed in a predetermined position. Then, at the outside of film prepreg  122 , double-sided boards  114   a  and  114   b  are set in a state in which they are aligned with each other. In this state, when they are heated and pressed by using, for example, a vacuum press, these members are integrated. Then, as shown in  FIG. 6 , a multilayer board is produced. 
     In particular, in the case of a multilayer board, the surface layer is often required to have a fine pattern. In such a case, a conventional multilayer board, for example, multilayer board  128  shown in  FIG. 7A  cannot sometimes meet the requirement. Then, as shown in  FIG. 7B , by attaching double-sided boards  114   a  and  114   b  corresponding to a fine pattern on the necessary surface, a fine pattern can be realized. When lamination and integration of double-sided boards  114   a  and  114   b  by using film prepreg  122  are not necessarily on both surfaces. They may be carried out on only a necessary surface, for example, on only a single surface. 
     It is desirable that the hardening temperature of film prepreg  122  is in the range from 85° C. to 220° C. The temperature of not less than 230° C. may cause variation in hardening of resin and affect the dimension property. On the other hand, the temperature of lower than 85° C. may increase the time for hardening the resin and affect the hardening state. Furthermore, in particular, when the thickness of the film constituting retention film  118  is thin, for example, not more than 50 μm, it is desirable that film prepreg  122  is hardened in the range from not less than 180° C. and not more than 220° C. Thus, among the wirings formed on the surfaces of double-sided board  114   a  and  114   b , second wirings  106   a  and  106   d  formed at the side of provisionally hardened resin  120  can be embedded in provisionally hardened resin  120  or in the thickness of provisionally hardened resin  120 . 
     Furthermore, it is desirable that the range of pressure at the time of laminating film prepreg  122  is not less than 2 MPa (MPa stands for megapascal, that is, a unit for pressure) and not more than 6 MPa. The pressure of less than 2 MPa may cause variation of adhesiveness of the multilayer board shown in  FIG. 7B . Furthermore, it is desirable that the time of applying pressure is not less than one minute and less than three hours. The time of applying pressure of less than one minute may cause variation in the pressure. Furthermore, the time of applying pressure of more than three hours may affect the productivity. Therefore, it is desirable that the pressure is 2 MPa or more and 6 MPa or less, and in particular 4 MPa or more and 6 MPa or less. In the case of general multilayer boards, lamination is carried out at the pressure in the range from 2 MPa to 3 MPa or less. However, in the method of manufacturing the multilayer printed wiring board in the sixth exemplary embodiment, since film  102  is thin and conductive paste  126  that is susceptible to the effect of the variation in thickness is used, it is desirable that the laminating pressure is about 5 MPa, for example, not less than 4 MPa and not more than 6 MPa, which is rather higher pressure. 
     The following is a further specific description. Firstly, as film prepreg  122 , a long-length heat resistant resin film in which thermosetting resin is applied to a predetermined thickness on both surfaces thereof is produced. The thickness of application is not less than 5 microns and not more than 100 microns, desirably not less than 10 microns and not more than 50 microns, further preferably not less than 15 microns and not more than 30 microns. In the case where the resin thickness is less than 2 microns, only a thin electrode having a thickness of about 2 microns can be embedded in the resin. Therefore, it is desirable that the thickness of provisionally hardened resin  120  constituting film prepreg  122  is, for example, the same level or larger than the thickness of embedded wirings corresponding to second wirings  106   a ,  106   b ,  106   c  and  106   d . Thus, second wirings  106   a  and  106   b , and the like, can be embedded, and at the same time, the thickness can be absorbed. 
     Seventh Exemplary Embodiment 
     A seventh exemplary embodiment is described with reference to  FIGS. 8 ,  9 A,  9 B,  10 A, and  10 B.  FIGS. 8 ,  9 A,  9 B,  10 A, and  10 B are sectional views showing an example of a method of manufacturing a multilayer printed wiring board having a fine pattern on the surface layer thereof. In the seventh exemplary embodiment, the case in which a multilayer board having a surface layer made of a film is used and interlayer coupling and wirings of the surface layer are made to be finer by using a plating technique is described. 
       FIG. 8  is a sectional view to illustrate a method of manufacturing a multilayer board in accordance with the seventh exemplary embodiment. The seventh exemplary embodiment shows an example of the method of manufacturing a multilayer board described in the sixth exemplary embodiment and the method can be also applied to the first exemplary embodiment and the third exemplary embodiment. In particular, in the seventh exemplary embodiment, an electrode on the surface layer of the multilayer board, that is, an insulating material forming a first insulating layer that is the first layer counted from the surface layer is a resin film, the first wiring counted from the surface layer and an interlayer coupling part coupled to the wiring are integrated by using a plating technique. Thus, a high performance and fine a pattern can be achieved. 
     As shown in  FIG. 8 , single-sided board  134   a  includes resin film  102   a  and second wiring  106   a  formed on one surface of single-sided board  134   a . Similarly, single-sided board  134   b  includes resin film  102   b  and second wiring  106   d  formed on one surface of single-sided board  134   b . Furthermore, multilayer board  128  includes inner electrode  132 , interlayer insulating layer  130  and interlayer coupling part  112 . On the surface of multilayer board  128 , second wirings  106   b  and  106   c  are formed. 
     Furthermore, a hole penetrating film prepreg  122  is filled with conductive paste  126 . Then, these members are aligned as shown in  FIG. 8 . Thereafter, by using a vacuum press and the like, as shown in  FIG. 9A , heating and integration is carried out so as to form a multilayer board.  FIG. 9A  is a sectional view showing a state of the multilayer board after being integrated. 
       FIG. 9B  is a sectional view showing a state in which the surface is provided with a blind via. As shown in  FIG. 9B , blind via  136  is provided by forming a hole in resin films  102   a  and  102   b  that are the first layers counted from the surface layer by using, for example, a laser. Herein, by adjusting the laser power, its wavelength, pulse, and the like, as shown in  FIG. 9B , second wirings  106   a  and  106   d  embedded in insulating resin  108  are exposed on the bottom of blind via  136 . 
     Next, with reference to  FIGS. 10A and 10B , a method of manufacturing a multilayer board in accordance with the seventh exemplary embodiment is described in detail.  FIG. 10A  is a sectional view showing a state in which the blind via is embedded in a metal film.  FIG. 10A  shows that blind via  136  and resin films  102   a  and  102   b  are covered with metal film  138 . Next, as shown in  FIG. 10B , metal film  138  is patterned in a predetermined shape. As shown in  FIG. 10B , first wirings  104   a  and  104   b  that are the first wiring counted from the surface layer are formed by patterning metal film  138 . 
     In order to form metal film  138 , a plating method or a thin film method can be used. Furthermore, metal film  138  may be formed on both surfaces of the board as shown in  FIG. 10A , or may be formed on only one surface if necessary. Furthermore, from  FIG. 10A , metal film  138  formed so as to cover blind via  136  is electrically coupled to second wirings  106   a  and  106   d  formed at the side of insulating resin  108  of films  102   a  and  102   b.    
     As shown in  FIG. 10B , when metal film  138  is patterned into a predetermined shape, a part of metal film  138  covering blind via  136  is also remained as a via fill or via embedding material, so that first wirings  104   a  and  104   b  are formed. Then, first wirings  104   a  and  104   b  are electrically coupled to second wirings  106   a  and  106   d  via blind via  136 . 
     Thus, as shown in  FIGS. 10A and 10B , by forming metal film  138  in blind via  136 , first wiring  104  and second wiring  106  can be electrically coupled to each other via an electrical connection in the first insulating layer of the first layer counted from the surface layer, that is, blind via  136  formed in film  102 . Therefore, interlayer coupling having a high reliability and low wiring resistance can be achieved. 
     Eighth Exemplary Embodiment 
     In an eighth exemplary embodiment, a case in which the thin film method or the combination of the thin film method and the plating method is employed instead of the plating method is described. The eighth exemplary embodiment is different from the seventh exemplary embodiment in that the eighth exemplary embodiment uses the thin film method and the seventh exemplary embodiment uses the plating method. Since they are different from each other only in this point and they have many common points, this exemplary embodiment is described with reference to  FIG. 9  used in the seventh exemplary embodiment. 
     Firstly, in order to form blind via  136  shown in  FIG. 9B , a laser device of YAG and CO 2 , and the like, can be used. Furthermore, in order to form metal film  138  on the surface of blind via  136 , and the like, firstly, a base material layer (which is also referred to as “seed layer”) is formed to the thickness of about 10 Å to about 50 Å by NiCr etc, and then copper may be electroplated thereon. Alternatively, copper may be electroless-plated on film  102  without using a seed layer. Alternatively, copper may be directly deposited on film  102  by using the thin film method using an electron beam, sputtering, and the like. In these cases, if a thickness is not less than 10 Å and desirably, a thickness sufficient to obtain conductivity capable of being used for electroplating, the conductivity is used so as to form copper to the thickness necessary for wiring by electroplating. It is desirable that the thickness necessary for wiring is, for example, 5 μm to 30 μm, and 3 μm to 15 μm if thinning is required. In this way, by using a seed layer (or a metal base material) or by devising a method of forming a metal film, adhesive strength with respect to films  102   a  and  102   b  can be enhanced. 
     Thus, by fixing at least one of the first wiring formed in the first layer counted from the surface layer and the second wiring formed in the second layer counted from the surface layer to the first insulating layer that is the first layer counted from the surface layer via a sputtered film, the adhesiveness of metal film  138 , first wiring  104  and second wiring  106 , and the like, with respect to the surface of film  102  can be enhanced. 
     As mentioned above, a multilayer printed wiring board has three insulating layers. The second insulating layer (corresponding to paste coupling layer  116  in  FIG. 1 ) that is the second layer counted from the surface layer is paste coupling layer  116  in which an electrical connection penetrating the second insulating layer is conductive paste  126  (or IVH  110  that is a hardened product thereof), and includes at least a second wiring (corresponding to second wiring  106   a  in  FIG. 1 ) formed in the second layer counted from the surface layer and embedded in the paste coupling layer and a third wiring (corresponding to third wiring  106   b  in  FIG. 1 ) formed in the third layer counted from the surface layer and embedded in the paste coupling layer. Thus, the multilayer printed wiring board can be thinned. 
     Furthermore, a multilayer printed wiring board has not less than four insulating layers. The second insulating layer (corresponding to paste coupling layer  116  in  FIG. 1 ) that is the second layer counted from at least one of the surface layers is paste coupling layer  116  in which an electrical connection penetrating the second insulating layer is conductive paste  126  or IVH  110  that is a hardened product thereof. The second insulating layer includes paste coupling layer  116  in which an electrical connection penetrating paste coupling layer  116  is a conductive paste or IVH  110  that is a hardened product thereof is provided. The second wiring layer formed in the second layer (corresponding to second wiring  106   a  in  FIG. 1 ) counted from at least one of the surface layers and the third wiring layer formed in the third layer (corresponding to second wiring  106   a  in  FIG. 1 ) counted from at least one of the surface layers are embedded in the conductive paste coupling layer. Thus, the multilayer printed wiring board can be further thinned. 
     Furthermore, paste coupling layer  116  includes film prepreg  122  made of retention film  118  and provisionally hardened resin  120  that is a provisionally hardened thermosetting resin formed on both surfaces of retention film  118 , and conductive paste  126  filled in through hole  124  formed in film prepreg  122 . Thus, a multilayer board can be further thinned. 
     Furthermore, the surface layer includes a resin film. A first insulating layer that is the first layer counted from the surface layer including a resin film, for example, resin films  102   a  and  102   b  in  FIG. 1 , and a wiring formed on the surface of the first insulating layer without using an adhesive and, for example, by using the thin film method for a base material, for example, first wirings  104   a  and  104   b  or second wirings  106   a  and  106   b  in  FIG. 1 , and the like, are provided. Thereby, adhesive strength between the resin film and the wirings can be enhanced. At the same time, since an adhesive is not used for bonding, thinning can be achieved. 
     Furthermore, a first wiring formed in the first layer counted from the surface layer, for example, first wiring  104   a  in  FIG. 1 , and a second wiring formed in the second layer counted from the surface layer, for example, second wiring  106   a  in  FIG. 1 , are fixed to the first insulating layer that is the first layer counted from the surface layer, for example, resin film  102   a  in  FIG. 1 , via a sputtered film. Thus, coupling strength can be enhanced. It is possible to provide a multilayer printed wiring board that can be further thinned. 
     Furthermore, at least one of the first wiring formed in the first layer counted from the surface layer, for example, first wiring  104   a  in  FIG. 1  and the second wiring formed in the second layer counted from the surface layer, for example, second wiring  106   a  in  FIG. 1  is fixed to the first insulating layer that is the first layer counted from the surface layer, for example, resin film  102   a  in  FIG. 1  via a plating film. Thus, coupling strength can be enhanced. It is possible to provide a multilayer printed wiring board that can be further thinned. 
     Furthermore, when interlayer coupling part  112  that is an electrical connection penetrating the first insulating layer formed in the first layer counted from the surface layer, for example, resin film  102   a  in  FIG. 1  is made by plating, a multilayer board whose surface layer is made to have fine pattern can be thinned as shown in  FIGS. 8 ,  9 A,  9 B,  10 A and  10 B. 
     Furthermore, it is possible to thin a multilayer printed wiring board by carrying out a hole processing step of processing through hole  124  in film prepreg  122  that is an insulating base material; a paste coupling layer formation step of filling conductive paste  126  into through hole  122  so as to form paste coupling layer  116 ; a double-sided board formation step of forming double-sided board  114   a  shown in  FIG. 3A ; a laminating step of laminating double-sided boards  114   a  and  114   b  on the front and back surfaces of film prepreg  122  so as to form a laminated body by using film prepreg  122  as paste coupling layer  116 ; and a hot pressing step of hot pressing the laminated body in a vacuum press, and the like, and integrating the hot-pressed laminated body. 
     It is possible to produce a multilayer printed wiring board that can be thinned by carrying out at least a hole processing step of processing through hole  124  in an insulating base material including film prepreg  122 ; a paste coupling layer formation step of filling conductive paste  126  into through hole  124  so as to form paste coupling layer  116 ; multilayer printed wiring board formation step of forming multilayer printed wiring board  128  having not less than two layers as shown in  FIG. 8 ; laminating step of laminating double-sided boards  114   a  and the like described in, for example,  FIG. 3A  on the front and back surfaces of the paste coupling layer obtained by adding conductive paste  126  to film prepreg  122  so as to form a laminated body; and further hot pressing step of hot pressing the laminated body by using a vacuum press, and the like, and integrating the hot-pressed laminated body. 
     Furthermore, wirings formed on the front and back surfaces of double-sided board  114   a , and the like, are electrically coupled to each other by the method described in  FIGS. 9A ,  9 B to  FIGS. 10A and 10B . Thus, it is possible to thin a multilayer printed wiring board capable of realizing semiconductor bare chip mounting, and the like, and in which wirings formed on the outermost layer are made to have a fine pattern. 
     Furthermore, an electrical connection of wirings formed on the front and back surfaces of the double-sided board are formed by plating as described in  FIGS. 9A ,  9 B to  FIGS. 10A and 10B . Thus, it is possible to thin a multilayer printed wiring board capable of realizing semiconductor bare chip mounting, and the like, and having a fine pattern of the wiring formed on the outermost layer. 
     If necessary, an electrical connection on the front and back surfaces of double-sided board  114   a  and the like can be made by using conductive paste  126  other than plating. In this case, needless to say, the process can be used in  FIGS. 2A ,  2 B,  2 C and the like. 
     Furthermore, as shown in  FIG. 10B , an interlayer coupling formation step of forming interlayer coupling for electrically coupling between the wirings on the front and back surfaces of double-sided board  114   a , that is, between first wiring  104   a  and second wiring  106   b  is made after being pressed and integrated following the hot pressing step and in a state in which the dimension is stable as described with respect to  FIGS. 9A and 9B  to  FIGS. 10A and 10B . Thus, dimension precision, handling, and the like, can be further improved. 
     Furthermore, as shown in  FIG. 10B , since interlayer coupling formation step of double-sided board  114   a  includes at least a via processing step of forming blind via  136 , it can be employed for, for example, semiconductor bare chip mounting and a multilayer printed wiring board having a fine patterned wiring on the outer surface layer can be thinned. 
     INDUSTRIAL APPLICABILITY 
     As mentioned above, a multilayer board and method of manufacturing the same in the present invention can produce a very thin multilayer board that has not been achieved conventionally by combining a film and a multilayer board, and therefore, can be used for reducing the size and thickness of various electronic equipment and portable equipment.