Patent Publication Number: US-2019172775-A1

Title: Flexible substrate and electronic device

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a flexible substrate and an electronic device. 
     Description of the Related Art 
     Some electronic devices include a plurality of electronic components and a flexible substrate for connecting the electronic components, and as a result of such a configuration, electrical communication is possible between the electronic components. The flexible substrate includes a base material made of a flexible resin such as polyimide, for example, and a wiring structure formed by a wiring layer, vias, and the like, and can be formed to have a layered structure in which some layers are stacked (refer to Japanese Patent Laid-Open No. 2007-204696). 
     In many cases, a flexible substrate is bent due to its flexibility when being attached to an electronic device, and after attachment as well, the flexible substrate is fixed in the electronic device in a bent state. It is possible that, in such a process, exfoliation or the like occurs in any of the layers that constitute the flexible substrate. It is also possible that, when the electronic device is used, exfoliation or the like similarly occurs due to thermal expansion of the layers in accordance with the change in temperature. These phenomena may cause degradation in the reliability of the flexible substrate, and in particular, may be a serious problem when the density or the complexity of the wiring structure of the flexible substrate increases in accordance with a substantial increase in the number of terminals of individual electronic components. 
     The present invention aims to improve the reliability of a flexible substrate with a relatively simple configuration. 
     SUMMARY OF THE INVENTION 
     One aspect of the present invention relates to a flexible substrate, and the flexible substrate comprises a first resin layer, a first wiring layer that is arranged on the first resin layer, a second resin layer that is arranged on the first resin layer so as to cover the first wiring layer, and a second wiring layer that is arranged on the second resin layer, wherein the first wiring layer and the second wiring layer are connected to each other with a filled via, and the first wiring layer and the second resin layer are in direct contact with each other. 
     Further features of the present invention will become apparent from the following description of exemplary embodiments (with reference to the attached drawings). 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a cross-sectional view for describing a reference example of the structure and the manufacturing method of a flexible substrate. 
         FIG. 1B  is a cross-sectional view for describing the reference example of the structure and the manufacturing method of a flexible substrate. 
         FIG. 1C  is a cross-sectional view for describing the reference example of the structure and the manufacturing method of a flexible substrate. 
         FIG. 1D  is a cross-sectional view for describing the reference example of the structure and the manufacturing method of a flexible substrate. 
         FIG. 1E  is a cross-sectional view for describing the reference example of the structure and the manufacturing method of a flexible substrate. 
         FIG. 2A  is a cross-sectional view for describing an example of the structure and the manufacturing method of a flexible substrate according to an embodiment. 
         FIG. 2B  is a cross-sectional view for describing the example of the structure and the manufacturing method of the flexible substrate according to the embodiment. 
         FIG. 2C  is a cross-sectional view for describing the example of the structure and the manufacturing method of the flexible substrate according to the embodiment. 
         FIG. 2D  is a cross-sectional view for describing the example of the structure and the manufacturing method of the flexible substrate according to the embodiment. 
         FIG. 3A  is a cross-sectional view for describing various modifications of the structure of the flexible substrate according to the embodiment. 
         FIG. 3B  is a cross-sectional view for describing various modifications of the structure of the flexible substrate according to the embodiment. 
         FIG. 4  is a cross-sectional view for describing an example of the mode of mounting electronic components on the flexible substrate according to the embodiment. 
         FIG. 5A  is a cross-sectional view for describing an example of the structure and the manufacturing method of the flexible substrate according to an embodiment. 
         FIG. 5B  is a cross-sectional view for describing the example of the structure and the manufacturing method of the flexible substrate according to the embodiment. 
         FIG. 5C  is a cross-sectional view for describing the example of the structure and the manufacturing method of the flexible substrate according to the embodiment. 
         FIG. 5D  is a cross-sectional view for describing the example of the structure and the manufacturing method of the flexible substrate according to the embodiment. 
         FIG. 5E  is a cross-sectional view for describing the example of the structure and the manufacturing method of the flexible substrate according to the embodiment. 
         FIG. 6A  is a cross-sectional view for describing an example of the structure and the manufacturing method of the flexible substrate according to an embodiment. 
         FIG. 6B  is a cross-sectional view for describing the example of the structure and the manufacturing method of the flexible substrate according to the embodiment. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     Hereinafter, suitable embodiments of the present invention will be described with reference to the attached drawings. Note that the drawings are merely schematic diagrams that are described for the purpose of describing structures or configurations, and the sizes of members shown in the drawings may be different from those of actual members. Also, in the drawings, the same members or the same constituent elements are given the same reference numbers, and redundant descriptions will be omitted. 
     Reference Example 
     For the purpose of facilitating understanding of the present invention, first, a reference example of the flexible substrate and the manufacturing method thereof will be described.  FIGS. 1A to 1E  are cross-sectional views that show modes of respective processes in the manufacturing method of the reference example. 
     In the process in  FIG. 1A , a first wiring layer  201  is formed on a first resin layer  101 . The resin layer  101  is a member that serves as a base material or a parent material of the flexible substrate, and polyimide is used as the resin layer  101  in this reference example, but another flexible resin may be used. The wiring layer  201  includes a plurality of wiring patterns (alternatively, expressed as line patterns)  201   a , in a cross-sectional view (when a cross section in a vertical direction is viewed). The plurality of wiring patterns  201   a  can be provided side by side at intervals of about 10 to 100 [μm]. 
     The plurality of wiring patterns  201   a  show a mode in which two or more conductive members are present in a predetermined cross section, and the conductive members need not be electrically isolated. When the plurality of wiring patterns  201   a  are not specifically distinguished, these are collectively referred to as simply a “wiring layer  201 ” in order to simplify the description in this specification. This similarly applies to other later-described wiring layers. 
     Note that, in this specification, the expressions such as upper/lower are used to indicate a relative positional relationship, and here, upper/lower are indicated based on the positional relationship in a vertical direction in the drawings (a direction vertical to the surface direction of the resin layer  101 ). Also, the direction orthogonal to the vertical direction corresponds to a horizontal direction (surface direction). 
     In the process shown in  FIG. 1B , a second resin layer  102  is formed on a structure obtained in the process shown in  FIG. 1A  via an adhesion layer  901 . The resin layer  102  is a member serving as a base material or a parent material of the flexible substrate, similarly to the resin layer  101 , and polyimide is used as the resin layer  102  in this reference example. Note that a known adhesive such as an epoxy-based resin may be used as the adhesion layer  901 . 
     In the process shown in  FIG. 1C , etching is performed from above on the structure obtained in the process shown in  FIG. 1B , and openings OP 1  are formed such that desired portions of the upper surface of the wiring layer  201  are exposed. This process may be performed using a known laser such as a UV laser or a CO2 laser. 
     In the process shown in  FIG. 1D , a second wiring layer  202  including a plurality of wiring patterns  202   a  is formed on the resin layer  102 , and also first vias  301  for connecting the wiring layers  201  and  202  are formed. This process can be realized by performing film forming processing using an electroless plating method or an electroplating method and patterning processing using the photoresist technology. Copper is used in the wiring layer  202  and the vias  301  in this reference example. The structure obtained in this way is a flexible substrate SB 0 . 
     In the example described above, two wiring layers (wiring layers  201  and  202 ) are used, but, as shown in  FIG. 1E , a third wiring layer  203  and second vias  302  and  302 ′ may be further formed, in addition, on a lower side of the flexible substrate SB 0 . This structure is a flexible substrate SB 0 ′. The wiring layer  203  includes a plurality of wiring patterns  203   a , and is formed under the resin layer  101 . The vias  302  and  302 ′ are formed so as to connect the wiring layers  201  and  203 . Copper is used in the wiring layer  203  and the vias  302  and  302 ′, similarly to the wiring layer  202  and vias  301 . 
     The above-described flexible substrate SB 0 ′ can be realized by forming other openings in the resin layer  101  when the openings OP 1  are formed in the process shown in  FIG. 1C , and forming the wiring layer  203  and the vias  302  and  302 ′ when the wiring layer  202  and the vias  301  are formed in the process shown in  FIG. 1D . Alternatively, the flexible substrate SB 0 ′ can be realized by further performing etching, film forming processing, and patterning processing on the lower side of the flexible substrate SB 0  obtained in the process shown in  FIG. 1D  using procedures similar to the processes shown in  FIGS. 1C and 1D . 
     The via  302  is formed by approximately completely filling the opening provided in the resin layer  101  such that an upper face thereof is flat, and is referred to as a filled via. Also, the via  302 ′ is formed by partially filling the other opening provided in the resin layer  101  such that an upper face thereof has a recessed shape, and is referred to as a conformal via. Any of the vias  302  and  302 ′ may be formed as a member for connecting the wiring layers  201  and  203 . Note that, here, the wiring layer  203  and the via  302  (or  302 ′) are integrally provided, the wiring layer  203  corresponds to a portion that extends in a direction parallel to the direction in which the resin layer  101  extends, and the via  302  (or  302 ′) corresponds to a portion that extends in a direction orthogonal to the direction in which the resin layer  101  extends. 
     The manufacturing method of the above-described reference example can be realized using a known manufacturing technology. Predetermined electronic components are mounted, thereafter, on the flexible substrate SB 0  and/or flexible substrate SB 0 ′ obtained in this way, and the flexible substrate SB 0  and/or flexible substrate SB 0 ′ are/is attached to an electronic device. 
     First Embodiment 
     Hereinafter, a flexible substrate according to a first embodiment and its manufacturing method will be described. The manufacturing method according to the present embodiment can be realized using a known manufacturing technology, similarly to the reference example. In the following, processes and constituents elements that are the same as those in the reference example will not be described, and descriptions thereof are the same as those given in the reference example.  FIGS. 2A to 2D  are cross-sectional views that show modes of respective processes in the manufacturing method according to the present embodiment. 
     After a wiring layer  201  is formed on a resin layer  101  in the process shown in  FIG. 2A  (similarly to  FIG. 1A ), a resin layer  102  is integrally formed on the resin layer  101  so as to cover the wiring layer  201 , in the process shown in  FIG. 2B . In this process, the resin layer  102  is in a B stage (semi-cured state), and can be deformed, and therefore, the resin layer  102  is formed so as to fill portions between adjacent wiring patterns (hereinafter referred to as “adjacent patterns”)  201   a  in the wiring layer  201 , as shown in the diagram. Therefore, the wiring layer  201  is in direct contact with the resin layer  102 . Also, in the present embodiment, the resin layer  102  is directly formed on the resin layer  101  without an adhesion layer  901  being interposed therebetween. The resin layer  102  may be formed using a known thermocompression bonding apparatus. 
     In the process shown in  FIG. 2C , the resin layer  102  in a B stage is cured (so as to be in a C stage) by performing a heat treatment and a drying treatment on the structure obtained in the process shown in  FIG. 2B . Thereafter, etching is performed on this structure from above, and openings OP 1  are formed in the cured resin layer  102  by removing portions of the cured resin layer  102 . The openings OP 1  may be formed using a procedure similar to the process shown in  FIG. 1C . 
     In the process shown in  FIG. 2D , a wiring layer  202  is formed on the resin layer  102 , and also, vias  301  for connecting the wiring layers  201  and  202  are formed. This process can be realized by performing film forming processing using an electroless plating method or an electroplating method and patterning processing using a photoresist technology, similarly to the process shown in  FIG. 1D . The structure obtained in this way is a flexible substrate SB 1 . 
       FIG. 3A  shows a structure in which a wiring layer  203  and vias  302  and  302 ′ are further formed on a lower side of the flexible substrate SB 1 , and this structure is a flexible substrate SB 1 ′. The wiring layer  203  and the vias  302  and  302 ′ can be formed using a procedure similar to the process described with reference  FIG. 1E . 
       FIG. 3B  shows a structure in which a third resin layer  103 , a fourth wiring layer  204 , and third vias  303  are further provided on an upper side of the flexible substrate SB 1 ′, and this structure is a flexible substrate SB 1 ″. The resin layer  103 , the wiring layer  204 , and the vias  303  may be formed using procedures similar to the processes shown in  FIGS. 2B to 2D . Copper is used for the wiring layer  204  and vias  303 , similarly to the wiring layer  202  and the vias  301 . 
     As an example, first, a resin layer  103  in a B stage is formed on the upper side of the flexible substrate SB 1  shown in  FIG. 2D  using a procedure similar to the process shown in  FIG. 2B . Then, after the resin layer  103  is cured, the wiring layer  204  and the vias  303  are formed along with forming the wiring layer  203  and the vias  302  by performing etching, film forming processing, and patterning processing using procedures similar to the processes shown in  FIGS. 2C and 2D . 
     Alternatively, as another example, first, the resin layer  103  in a B stage is formed on an upper side of the flexible substrate SB 1 ′ shown in  FIG. 3A  using a procedure similar to the process shown in  FIG. 2B . Then, after the resin layer  103  is cured, the wiring layer  204  and the vias  303  are formed by performing etching, film forming processing, and patterning processing, similarly to the processes shown in  FIGS. 2C to 2D . 
     Note that it is possible to form five or more wiring layers by repeating the processes similar to the processes shown in  FIGS. 2B to 2D . Alternatively, it is possible that the wiring layer  204  and the vias  303  are formed, but the wiring layer  203  and the vias  302  are not formed. 
     Predetermined electronic components are mounted, thereafter, on the flexible substrate SB 1 , SB 1 ′, and/or SB 1 ″ formed as described above, and the flexible substrate SB 1 , SB 1 ′, and/or SB 1 ″ are/is attached to an electronic device. 
       FIG. 4  is a schematic diagram illustrating an example of a mode of mounting an electronic component  11  on the flexible substrate SB 1 ′. Here, a semiconductor apparatus or a semiconductor device in a BGA (Ball Grid Array) package, as the electronic component  11 , is mounted on the flexible substrate SB 1 ′ shown in  FIG. 3A . When the electronic component  11  is mounted, the flexible substrate SB 1 ′ is used in a state in which an upper surface and a lower surface thereof are coated by a solder resist layer  14 . 
     The electronic component  11  includes a plurality of electrodes (solder balls)  111  that are arranged on a lower face of the package body. The mounting of the electronic component  11  on the flexible substrate SB 1 ′ can be realized by electrically connecting the wiring layer  202  with the electrodes  111 . In the present embodiment, a support member  12  is provided on the lower side of the flexible substrate SB 1 ′ via an interposed layer  13  serving as an adhesion layer, for example. With this, the electronic component  11  can be appropriately fixed to the flexible substrate SB 1 ′. When the flexible substrate SB 1 ′ is attached to an electronic device, for example, the portion thereof on which the electronic component  11  is mounted is not bent, and as a result, the electronic component  11  is unlikely to detach from the flexible substrate SB 1 ′. 
     It is preferable that the support member  12  is arranged so as to overlap the electronic component  11  when viewed in an orthogonal projection in a vertical direction or in plan view (when viewed in the vertical direction, which will be hereinafter simply referred to as “orthogonal projection” in the following description). It is further preferable that the support member  12  is arranged such that the outer edges of the support member  12  is outside the corresponding outer edges of the electronic component  11 . A material having higher rigidity than the resin layers  101  and  102  is used as the support member  12 , and a metal material, a resin material, or the like that is relatively difficult to be bent may be used. Note that when the support member  12  itself has an adhesive property or the like, for example, the interposed layer  13  may be omitted. 
     Also, as can be understood from  FIGS. 4 and 3A , in the present embodiment, the vias  301  are formed as filled vias, and the wiring layer  202  is electrically connected to the wiring layer  201  with such vias  301 . Therefore, the electronic component  11  described above can be electrically connected by directly mounting the electronic component  11  on the wiring layer  202  such that the electrodes  111  are on the corresponding vias  301 . The electronic component  11  can be appropriately mounted on the flexible substrate SB 1 ′ with a relatively simple configuration. 
     The filled vias  301  and  302  and the conformal via  302 ′ may be selectively provided depending on whether or not the part in which the via is formed is a part of the flexible substrate SB 1 ′ that is to be bent when used. For example, the conformal via  302 ′ may be provided in a part of the flexible substrate SB 1 ′ that is to be bent when used, and the filled vias  301  and  302  may be provided in other parts. From this viewpoint, it can also be said that the electronic component  11  is located/mounted at a position so as to overlap the filled vias  301  and the wiring layer  201  in an orthogonal projection. 
     As described above, according to the present embodiment, the wiring layer  201  and the resin layer  102  are in direct contact with each other, and as a result of the layers being appropriately brought into close contact, the exfoliation thereof (including creases and crinkles) can be prevented/suppressed from occurring. Also, accordingly, the fixing of the resin layer  101  and the resin layer  102  can be appropriately realized. 
     In the present embodiment, the resin layer  102  is in direct contact with an upper face and side faces of each wiring pattern  201   a  in the wiring layer  201  in a cross-sectional view, and with this, they are strongly fixed, and the above-mentioned exfoliation or the like are appropriately prevented. In such a structure, the resin layer  102  has a lower face having an uneven shape. The fixing of the wiring layer  201  and the resin layer  102  can be realized by the resin layer  102  being in direct contact with at least one of the upper face and the side faces (in many cases, the upper face, and a portion/all of the side faces in addition) of each wiring pattern  201   a  of the wiring layer  201 . The larger the contact area, the better. 
     In order to more appropriately prevent the above-mentioned exfoliation, the resin layer  102  may be integrally formed on the resin layer  101  such that portions between the adjacent patterns  201   a  in the wiring layer  201  are filled. Here, if the height of the wiring layer  201  is increased, and the distance between the adjacent patterns  201   a  is reduced, the wiring layer  201  and the resin layer  102  are fixed more strongly. The parameters such as height and distance may be determined based on constituent materials of the flexible substrate SB 1  and the like such as the material of the resin layer  102  (diameters or the like of constituent particles), for example. For example, in the present embodiment, when the height of the wiring layer  201  is denoted as H, and the minimum distance between the adjacent patterns  201   a  is denoted as L, it is preferable that these parameters satisfy H≥5 μm and L≤50 μm. It is further preferable that the height H satisfies H≥7 μm, and more preferably H≥9 μm. Also, it is further preferable that the distance L satisfies L≤40 μm, and more preferably L≤30 μm. 
     In the present embodiment, the wiring layers  201  and  203  are formed to have a height of about 9 μm and the wiring layer  202  is formed to have a height of about 10 μm on the resin layer  101  having a thickness of about 25 μm and the resin layer  102  having a thickness of about 20 μm. The vias  301  and the like are formed to have a diameter of about 30 to 50 μm, and the width of each pattern and the distance between adjacent patterns of the wiring layers  201  to  203  (so-called line and space) are about 25 μm. Note that, at connection portions with the vias  301 , the width of each pattern of the wiring layers  201  to  203  is about 100 μm. 
     Also, in the present embodiment, polyimide is used in the resin layers  101  and  102 , but another resin may be used. Various types of modified resin such as a thermoplastic resin, a thermosetting resin, and an ultraviolet curing resin can be used. Typically, polyimide-based resin (such as polyimide, polyetherimide, and polyamidimide) is preferably used in order to improve elasticity and thermal resistance, but another types of resin such as a polyamide-based resin and a polyester-based resin may be used. Here, the resin layers  101  and  102  may be formed with the same material in order to prevent the aforementioned exfoliation or the like by reducing the difference in the coefficient of thermal expansion therebetween. 
     In the present embodiment, the resin layer  101  and the resin layer  102  are in direct contact with each other, and with this, the resin layers  101  and  102  are appropriately in close contact with each other without the adhesion layer  901  being interposed therebetween. As described with reference to  FIG. 2B  and the like, the resin layer  102  is formed by curing a resin material in a B stage, that is, formed by curing a resin material that has been applied in a semi-cured state. Therefore, the resin layer  101  and the resin layer  102  are strongly fixed to each other. In this case, an epoxy-based resin, a urethane-based resin, a silicone-based resin, or the like may be used as the resin layer  102 . Also, as a result of the resin layer  101  and the resin layer  102  being in direct contact with each other, and the adhesion layer  901  being not used, the thickness of the flexible substrate SB 1  or the like can be reduced, and the flexible substrate SB 1  or the like can have appropriate flexibility. 
     Here, a description has been given focusing on the fixing between the wiring layer  201  and the resin layer  102 . In the case of the flexible substrate SB 1 ″ shown in  FIG. 3B , the same idea can be applied to the fixing between the wiring layer  204  and the resin layer  103 . This can similarly be applied to a case where the number of wiring layers is five or more. 
     Furthermore, with regard to the manufacturing method, in the process shown in  FIG. 2B , when the resin layer  102  in a B stage is bonded to the resin layer  101  through thermocompression bonding, a pressing surface of a thermocompression bonding apparatus that performs the thermocompression bonding may have an uneven shape. With this, the resin layer  102  can be formed such that the upper surface thereof has an uneven shape, and therefore, the exfoliation of the wiring layer  202  that is formed in a later process from the resin layer  102  can be appropriately suppressed. Also, as a result of providing projections on a pressing surface of a thermocompression bonding apparatus, openings for vias  301  that are formed in a later process can be formed in the resin layer  102  along with performing the thermocompression bonding. That is, the process shown in  FIG. 2C  can be omitted. 
     The resin layer  101  prepared for use in the process shown in  FIG. 2A  may be a resin layer on which a metal film such as a copper film has been formed, in advance, via a predetermined adhesion layer. However, this adhesion layer is used when the metal film and the resin layer  101  are adhered to each other, and in many cases, this adhesion layer has been already modified and lost its adhesive force at some point in time during the process shown in  FIG. 2B . According to the present embodiment, even in a case where such a resin layer  101  is used, the wiring layer  201  and the resin layer  102  can be fixed to each other, and accordingly, fixing between the resin layer  101  and the resin layer  102  can be appropriately realized. 
     The flexible substrate SB 1  or the like according to the present embodiment is used as a connection portion in which an electronic component  11  can be mounted, or as a connection portion for connecting two or more electronic components  11 , and can be preferably applied to various electronic devices such as a printer and a scanner. A BGA package is shown in  FIG. 4  as an example of the electronic component  11 , but the electronic component  11  is not limited to this example. For example, another semiconductor package such as QFP (Quad Flat Package) may be mounted on the flexible substrate SB 1  or the like, or may be connected to the flexible substrate SB 1  or the like or a rigid substrate. The electronic component  11  is, through the electrodes  111 , directly mounted on the wiring layer  202  that is connected to the wiring layer  201  by the filled vias  301 , and is electrically connected to the wiring layer  202 . Accordingly, the electronic component  11  can be appropriately mounted with a relatively simple configuration. 
     Second Embodiment 
     The second embodiment differs from the first embodiment in that a wiring layer  202  is embedded in a resin layer  102 . The same effects as those of the first embodiment can also be achieved in the present embodiment.  FIGS. 5A to 5E  show modes of respective processes in the manufacturing method according to the present embodiment. 
     First, in the process shown in  FIG. 5A , a resin layer  102  in a B stage is formed on a resin layer  101  so as to cover the wiring layer  201  with procedures similar to those shown in  FIGS. 2A and 2B . Thereafter, in the process shown in  FIG. 5B , a resin layer  103  in which a wiring layer  202  is arranged on a lower face thereof is bonded to this structure from above. In this process, since the resin layer  102  is in a B stage (deformable), the resin layers  102  and  103  are brought into close contact with each other such that portions between adjacent patterns  202   a  of the wiring layer  202  on the lower face of the resin layer  103  are filled by the resin layer  102 . Accordingly, the resin layer  102  is in direct contact with side faces of the wiring patterns  202   a  of the wiring layer  202 , and the resin layer  102  has an upper surface having an uneven shape. To put it differently from a viewpoint of the wiring layer  202 , the wiring layer  202  is located on the resin layer  102  such that the wiring layer  202  is embedded in the resin layer  102 . This process may be performed using a known application apparatus. 
     In the process shown in  FIG. 5C , the resin layer  102  in a B stage is cured (so as to be in a C stage) by performing a heat treatment and a drying treatment on a structure obtained in the process shown in  FIG. 5B . 
     In the process shown in  FIG. 5D , a wiring layer  203  and vias  302  and  302 ′ are formed on a lower side of the structure obtained in the process shown in  FIG. 5C . This wiring layer  203  and these vias  302  and  302 ′ can be formed using procedures similar to those used in the above-described first embodiment or the reference example. The structure obtained in this way is a flexible substrate SB 2 . 
     Also, as shown in  FIG. 5E , a wiring layer  204  and vias  303  and  303 ′ may be formed, in addition, on an upper side of the flexible substrate SB 2 . This structure is a flexible substrate SB 2 ′. Also, five or more wiring layers may be provided using similar procedures. 
     The wiring layer  204  and the via  303 , of the wiring layer  204  and the vias  303  and  303 ′, are the same as those in the first embodiment, and therefore, the description thereof will be omitted (refer to  FIG. 3B ). On the other hand, the via  303 ′ is provided so as to connect the wiring layers  201  and  204 . In the present embodiment, since the resin layer  102  is in a B stage in the process shown in FIG.  5 B, a connection portion (or any member for connecting the wiring layers  201  and  202 ) corresponding to the via  301  is not formed in this resin layer  102 , and the via  303 ′ is formed in the process shown in  FIG. 5E . With this, electrical connection similar to the first embodiment can be realized. 
     Note that, in the present embodiment, an opening is provided in the wiring layer  202  through which the via  303 ′ will pass by performing etching using a laser in the process shown in  FIG. 5E , and thereafter, the via  303 ′ is formed so as to pass through the opening. In another embodiment, this wiring layer  202  may be provided in a state in which an opening has been formed in advance (at some point in time during the process shown in  FIG. 5B ). For example, a resin layer  103 , in which a wiring layer  202 ′ having an opening OP 2  is arranged on a lower face thereof, is bonded to a structure obtained by the process shown in  FIG. 5A  from above, as shown in  FIG. 6A . As a result of thereafter forming the wiring layers  203  and  204  and the vias  302 ,  303 , and  303 ′ using procedures similar to those shown in  FIGS. 5C to 5E , a wiring structure similar to the flexible substrate SB 2 ′ can be relatively easily formed, as shown in  FIG. 6B . 
     According to the present embodiment, similarly to the fixing between the wiring layer  201  and the resin layer  102 , the wiring layer  202  and the resin layer  102  can be strongly fixed to each other. Therefore, according to the present embodiment, the reliability of the flexible substrate SB 2  or the like can be improved. 
     Others 
     Some preferable embodiments have been illustrated above, but the present invention is not limited to these examples, portions thereof may be modified without departing from the spirit of the invention. Also, the individual terms recited herein are merely used for the purpose of describing the present invention, and the invention is not intended to be limited to a strict interpretation of the meaning of those terms, and can also include equivalents thereof. For example, in this specification, the wiring layers  201  and the like refer to layers in which wiring patterns are formed and that are arranged above/below the resin layers  101  and the like or therebetween, but may be expressed as conductive layers, metal layers, or the like. Similarly, the vias  301  and the like refer to portions for connecting two wiring layers that overlap in the vertical direction, but may be expressed as plugs or the like. 
     While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions. 
     This application claims the benefit of Japanese Patent Applications No. 2017-232719, filed Dec. 4, 2017, and No. 2018-223936, filed Nov. 29, 2018, which are hereby incorporated by reference herein in their entirety.