Multilayer board manufacturing method

Abstract

A multilayer board manufacturing technique is provided that enables a multilayer board to be manufactured at low cost. First, a cover sheet (2) is superimposed on a base sheet (1) of the same shape and size. Wiring (11) is provided on one side of the base sheet (1). Holes (21) are opened at positions where electronic components will be attached to the base sheet (1) after the cover sheet (2). The superimposed base sheet (1) and cover sheet (2) are then folded so that the holes (21) are exposed to the outside. The electronic components are inserted into the holes (21) and attached in a state where they are electrically connected to the wiring (11) of the base sheet (1).

Description

[Technical field]

[0001] The present invention relates to a method for manufacturing a multilayer board. [Background technology]

[0002] Many electronic devices contain circuit boards with wiring that make up the circuits, on which various electronic components are attached. Among these boards, there are those called multi-layer boards. A multilayer board is made by stacking multiple boards. Each board has a plate-shaped or sheet-shaped base material, and wiring is provided on at least one surface of the base material. A multilayer board, which has a structure in which multiple boards, each with wiring, are stacked, is of course thicker, but it can contain more circuits and electronic components in the same area than a single-layer board, and can exhibit high integration, so it is widely used.

[0003] Generally, the circuits in each board included in a multi-layer board need to be electrically connected to each other. For this reason, in multilayer boards, holes called through holes are generally drilled through each board included in the stacked multilayer board. In general, a metal layer is provided on the inner periphery of the through hole by plating with a conductive metal, for example, and the wiring in each board is made to be conductive with the metal layer, so that the wiring in each board included in the multilayer board is made to be conductive with each other via the metal layer in the through hole. For example, the wiring provided on both sides of one board is made to be conductive with each other via the metal layer in the through hole. Alternatively, it is possible to connect wiring provided on both sides of a single substrate, or on any surfaces of multiple substrates, with a conductive connecting wire outside the substrate, thereby enabling electrical continuity between wiring located at distant locations, and such technology is also in practical use. Summary of the Invention [Problem to be solved by the invention]

[0004] Although the multilayer board is as described above, there is room for improvement. As mentioned above, conventional multi-layer boards have through holes and connecting lines outside the board. When through holes are present, the manufacturing costs of the multilayer board are increased because it is necessary to carry out a step of drilling holes in the board to form the through holes and a step of forming a metal layer on the inner surface of the through holes. In addition, as described above, since the through holes are electrically connected to the wiring of each board included in the multi-layer board, it is necessary to accurately position the wiring relative to the base material in each board, and to accurately position the multiple boards relative to each other when stacking multiple boards. Of course, the two types of positioning accuracy required for the reasons described above are technically feasible. However, achieving them is time-consuming and likely to cause costs to increase. In addition, the conventional manufacturing process of multilayer boards involves manufacturing multiple boards separately, and then stacking the multiple boards that have been manufactured separately. Alternatively, cover sheets and copper foils are laminated on the top and bottom of a board to form circuits on the top and bottom surfaces of the board, and the number of layers is increased by repeating this procedure. Here, when manufacturing each board, it is common to perform common processes for each board, such as cutting a circuit in the copper foil attached to the base material and plating with gold, and this tends to increase costs due to the repeated execution of common processes for each board. The same is true when cover sheets and copper foils are laminated on the top and bottom of a board. Even when connecting wires are provided outside the board, the process increases the manufacturing cost of the multi-layer board, and the cost of repeating the same process for each board is likely to increase.

[0005] A main object of the present invention is to provide a manufacturing technique for a multilayer board that enables a multilayer board to be manufactured at low cost. [Means for solving the problem]

[0006] The present invention for solving the above-mentioned problems is as follows. The present invention is a method for manufacturing a multilayer board, including a layering step of layering a base sheet, which is a rectangular sheet made of insulating thermoplastic resin and has conductive wiring arranged in an appropriate arrangement on its front surface, and a cover sheet, which is an insulating thermoplastic resin sheet of substantially the same shape and size as the base sheet and has at least one hole formed in a position where an electronic component will later be disposed, on the front surface of the base sheet in a state where the contour of the base sheet matches the contour of the cover sheet; a folding step of folding the layered base sheet and cover sheet so that the hole is exposed to the outside; a fixing step of heating the folded base sheet and cover sheet to melt at least a portion of the cover sheet, and then cooling and hardening the cover sheet, thereby fixing the adjacent base sheets and cover sheets to each other; and an electronic component attachment step of fixing an electronic component inserted in the hole to the base sheet exposed through the hole in a state where the electronic component is electrically connected to the wiring on the front surface of the base sheet exposed through the hole.

[0007] In this method of manufacturing a multilayer board, as described above, the overlapping step, the bending step, the fixing step, and the electronic component mounting step are carried out in that order. In the overlapping step, the cover sheet is overlapped on the front surface of the base sheet. The base sheet is a rectangular sheet made of thermoplastic resin and has insulating properties. Wiring is provided on the front surface of the base sheet. The wiring is not provided on the cover sheet, but only on the base sheet. The wiring is also provided only on one side of the base sheet. The surface of the base sheet on which the wiring is provided is the front surface. The wiring is conductive and is generally made of a conductive metal. There is no limitation on the method of providing the wiring on the base sheet, and the wiring can be provided on the front surface of the base sheet by a known or well-known method. For example, a subtractive method in which copper foil is attached to the entire front surface of the base sheet with an adhesive, and unnecessary parts are removed by chemical etching while leaving the wiring part, and an additive method in which wiring is plated (in most cases, electroless plating and electrolytic plating) on ​​the front surface of the base sheet can be used as a technique for providing wiring on the base sheet. The cover sheet is a rectangular sheet that is virtually the same shape and size as the base sheet. The cover sheet is made of a thermoplastic resin and has insulating properties. At least one hole is provided in the cover sheet. The hole is provided in the cover sheet at a position corresponding to a position where an electronic component will be disposed later on the base sheet. The cover sheet is superimposed on the base sheet so that the contours of the cover sheet and the base sheet match. In the next folding step, the base sheet and the cover sheet in the overlapped state are folded together. The folding is performed at least once, and may be either a mountain fold or a valley fold, or a combination of a mountain fold and a valley fold. After the folding step is performed, the above-mentioned holes provided in the cover sheet are exposed to the outside. By folding together with the cover sheet, at least a part of the base sheet is at least doubly overlapped with the remaining part of the base sheet, although the cover sheet may be inserted between them. As a result, the wiring provided on the front surface of the base sheet is also at least doubly stacked. In the next fixing step, the adjacent base sheet and cover sheet are fixed in a folded state. When such fixing is performed, the folded base sheet and cover sheet are heated to melt at least a part of the cover sheet, and then cooled and hardened, and the melted cover sheet is used like an adhesive to fix the adjacent base sheet and cover sheet. In this application, "cooling" does not require active cooling treatment, and also includes the case where the heated base sheet and cover sheet are left in an atmosphere at a temperature (for example, room temperature) lower than the melting point of the thermoplastic resin constituting the cover sheet. It is acceptable to melt not only the cover sheet but also a part of the base sheet and then cool and harden it. In the fixing step, the adjacent cover sheets of the overlapped base sheet and cover sheet may also be fixed to each other. In any case, by performing the fixing step, the folded base sheet and cover sheet are integrated, and the relative positional relationship between them as a whole is basically fixed. Then, an electronic component mounting step is performed to mount the electronic components on the base sheet. As described above, after the folding step is completed, the holes provided in the cover sheet are exposed to the outside. The holes provided in the cover sheet correspond to the positions where the electronic components are to be mounted. The electronic components are inserted through the holes and fixed to the base sheet seen through the holes in a state where they are electrically connected to the wiring on the front surface of the base sheet seen through the holes. Needless to say, the wiring provided on the base sheet is designed to form an electric circuit in combination with the electronic components when at least one electronic component is mounted on the base sheet. In this manner, a multi-layer board is manufactured. The electronic components used in manufacturing multilayer boards include IC (integrated circuit) chips, BGA (ball grid array), CSP (chip size package), resistors, capacitors, etc., and are no different from the electronic components attached to general boards.

[0008] The multilayer board manufactured by the manufacturing method of the multilayer board of the present application described above does not require through holes or connecting wires outside the board because an electric circuit is formed in combination with at least one electronic component that is planned to be attached to the base sheet. Therefore, the process for producing them can be omitted, and the cost of manufacturing the multilayer board can be reduced. Furthermore, in the above-described method for manufacturing a multilayer board, it is possible to obtain multilayer boards of various structures by changing the way in which the superimposed base sheet and cover sheet are folded in the folding step. Furthermore, in the multilayer board manufactured by the above-mentioned manufacturing method for a multilayer board, the front surface of the base sheet is covered with a cover sheet except for the portion where the hole is formed, so that the wiring is protected by the cover sheet and is less likely to break.

[0009] As described above, both the base sheet and the cover sheet used in the present invention are made of a thermoplastic resin. The thermoplastic resin constituting the base sheet and the cover sheet may or may not be the same. The thermoplastic resin constituting the base sheet and the cover sheet can be, for example, liquid crystal polymer (LCP). Other usable materials include polyphenylene sulfide (PPE), polyether ether ketone (PEEK), fluororesin (FR), etc., but other thermoplastic resins can also be used. Liquid crystal polymers are well known as materials having low loss and excellent high frequency characteristics, and are therefore suitable for use as materials for the base sheet and the cover sheet. The thickness of the base sheet and the cover sheet must be thin enough that the folding process can be performed with both sheets stacked on top of each other. On the other hand, the thickness of the cover sheet is preferably greater than the thickness of the wiring formed on the base sheet. As described above, the cover sheet protects the wiring after the fixing process, but if the cover sheet is thinner than the wiring, the wiring may not be protected sufficiently and the wiring may not be covered by the cover sheet and the upper part may be exposed. Even if the wiring can be protected by covering it with the cover sheet, the thickness of the wiring may appear as a convex part on the cover sheet, making it impossible to maintain the flatness of the multilayer board. If this occurs, there is a risk of problems such as poor bonding occurring when mounting electronic components on a surface with poor flatness. The thickness of the cover sheet may be thinner than the thickness of the base sheet. By making the cover sheet thinner than the base sheet, the rigidity during the folding process is reduced and the folding property is improved, and it also leads to reduction in processing costs and material costs.

[0010] As described above, the base sheet used in the present invention is rectangular, and the cover sheet is rectangular with the same shape and size as the base sheet. The base sheet may be square. As described above, the base sheet and the cover sheet are folded by folding them while overlapping each other, but if the base sheet and the cover sheet are square, various folding methods used in origami, a traditional Japanese culture, can be applied, and for example, a multilayer board having a regular shape such as a rectangle or a triangle can be obtained in which the number of sheets, including the base sheet and the cover sheet, present in every part in the thickness direction is the same. For example, the shape of the base sheet and the cover sheet after the electronic component mounting process is completed can be a square or a right-angled isosceles triangle. Such a regular shape is convenient when incorporating a multilayer board into a final product. Two right-angled isosceles triangle multilayer boards can be combined to form a square.

[0011] In the present invention, the folding step can be carried out so that after the electronic component mounting step is completed, all parts of the base sheet and the cover sheet are essentially parallel except for the folded parts. The multilayer board thus manufactured has the base sheet and the cover sheet laminated in parallel except for the folded portions, and has a plate-like shape as a whole. The plate-like multilayer board has the same shape as many conventional multilayer boards or single-layer boards, and is expected to find many applications. On the other hand, it is also possible to make the base sheet and a part of the cover sheet not parallel to the other parts of the base sheet and the cover sheet after the electronic component mounting process is completed. In this case, the multilayer board may have a three-dimensional shape other than a plate shape. Depending on the final product to which the board is to be mounted, a multilayer board having a three-dimensional shape may be convenient. One of the advantages of the method for manufacturing a multilayer board according to the present invention is that multilayer boards of various shapes can be obtained using the same manufacturing method. It is also possible to carry out the folding process so that, after the electronic component mounting process is completed, the number of the base sheets and the cover sheets overlapped in a certain portion other than the folded portion is different from the number of the base sheets and the cover sheets overlapped in other portions. For example, suppose that a plate-shaped multilayer board is manufactured by the manufacturing method of the multilayer board. Then, in a certain area of ​​the completed multilayer board, four base sheets and four cover sheets are stacked, and in another area, eight base sheets and eight cover sheets are stacked. Naturally, the thickness of the other area of ​​the multilayer board is greater than that of the certain area of ​​the multilayer board. It can be said that one of the advantages of the manufacturing method of the multilayer board according to the present invention is that a multilayer board having different thicknesses can be obtained by the same manufacturing method. Since it is possible to manufacture a board having different thicknesses in parts, the thinner board parts use less base material, which has the advantage of contributing to reducing material costs and process costs.

[0012] As described above, in the bonding step, the overlapped base sheet and cover sheet are heated. In the bonding step, the overlapped base sheet and cover sheet may be heated while being pressurized. This allows the base sheet and cover sheet, or the cover sheets to be bonded to each other evenly and firmly. The bonding step may be performed by heating (or heating and pressurizing) the entire base sheet and cover sheet after the folding step at once, or by heating (or heating and pressurizing) a part of the base sheet and cover sheet after the folding step and the other part multiple times. When the completed multilayer board has a three-dimensional shape, the bonding step is often performed in the latter manner.

[0013] In the method for manufacturing a multilayer board according to the present invention, a wiring step of providing the wiring on the front surface of the base sheet may be carried out before the laminating step. As already mentioned, there is no particular limitation on the technique that can be used to provide the wiring on the front surface of the base sheet in the wiring step, and any known technique can be used. The width of the wiring may be wider at the portion where the base sheet is folded than the width of both sides in the length direction. In the manufacturing method of the multilayer board of the present application, the wiring is folded together with the base sheet. This may cause some risk of the wiring being broken. If the width of the wiring at the portion where the base sheet is folded is wider than the width of both sides in the length direction, it is useful to prevent the wiring from being broken when folded together with the base sheet. When the wiring step is carried out before the overlapping step, it is also possible to fabricate the wiring so that the width of the wiring at the portion where the base sheet is folded is wider than the width of the portions on both sides in the longitudinal direction. [Brief description of the drawings]

[0014] [Figure 1] FIG. 2 is a diagram showing a base sheet used in one embodiment of the present invention as viewed from the front side. [Diagram 2] FIG. 4 is a diagram showing a base sheet provided with wiring as viewed from the front side. [Diagram 3] An enlarged view of the area around the symbol X in Figure 2. [Figure 4] FIG. 4 is a diagram showing the cover sheet as viewed from the front side. [Diagram 5] FIG. 11 is a diagram showing the base sheet and the cover sheet when the overlapping process is completed in one embodiment, as viewed from the front side. [Figure 6] 4A to 4C are diagrams illustrating how a folding process is performed in one embodiment. [Figure 7] FIG. 2 is a diagram showing a completed multilayer board after an electronic component mounting process is completed in one embodiment. [Figure 8] 10(A) to 10(D) are views showing a method of performing a folding step in Modification 1, and 10(E) is a side view of the base sheet and the cover sheet shown in 10(D). [Figure 9] FIG. 11 is a view of the base sheet and the cover sheet when the overlapping process is completed in the second modified example, as viewed from the front side. [Figure 10] 13A to 13C are diagrams showing a method of performing a folding step in Modification 2. [Figure 11]FIG. 11 is a diagram showing a completed multilayer board after completing an electronic component mounting process in Modification 2. [Figure 12] FIG. 13 is a view of the base sheet and the cover sheet when the overlapping process is completed in Modification Example 3, as viewed from the front side. [Figure 13] 13A to 13C are diagrams showing a method of performing a folding step in Modification 3. [Figure 14] FIG. 13 is a diagram showing a completed multilayer board after completing an electronic component mounting process in Modification 3. [Figure 15] 13 is a view of the base sheet and the cover sheet when the overlapping process is completed in Modification Example 4, as viewed from the front side. [Figure 16] 13A to 13C are diagrams showing a method of performing a bending step in Modification 4. [Figure 17] FIG. 13 is a perspective view showing a completed multilayer board after the electronic component mounting process in Modification 4 is completed. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Hereinafter, an embodiment of the present invention and a modification thereof will be described with reference to the drawings.

[0016] In this embodiment, a method for manufacturing a multi-layer board will be described. The multi-layer board is manufactured by carrying out each step as described below. The multilayer board is manufactured using a base sheet, a cover sheet, and electronic components as materials.

[0017] First, the base sheet will be described. The front surface of the base sheet 1 is shown in Fig. 1. This base sheet 1 has not yet been provided with wiring, which will be described later. The base sheet 1 is rectangular. As will be described later, the base sheet 1 may be square, but in the example shown in FIG. The base sheet 1 is made of a thermoplastic resin and has insulating properties. Examples of the thermoplastic resin constituting the base sheet 1 include liquid crystal polymer (LCP), polyphenylene sulfide (PPE), polyether ether ketone (PEEK), and fluororesin (FR). Although not limited thereto, in this embodiment, liquid crystal polymer (LCP) is selected as the thermoplastic resin constituting the base sheet 1. The thickness of the base sheet 1 can be appropriately selected within a range that allows the base sheet 1 to be folded together with the cover sheet as described below. The thickness can be, for example, 20 μm to 200 μm, preferably 25 μm to 100 μm.

[0018] In this embodiment, wiring 11 is provided on such a base sheet 1 (FIG. 2). Note that the two-dot chain line labeled 12 in FIG. 2 is a folding line indicating the location where the base sheet 1 will be folded later. The wiring 11 is provided only on the front surface of the base sheet 1. The surface of the base sheet 1 on which the wiring 11 is provided is the front surface of the base sheet 1. The wiring 11 is conductive and is generally made of a conductive metal. Although not limited thereto, in this embodiment, the wiring 11 is made of a conductive metal. There is no particular limit to the technology that can be used to provide the wiring 11 on the base sheet 1, and any known or well-known technology can be used. For example, the wiring 11 can be provided on the front surface of the base sheet 1 by a subtractive method in which copper foil is attached to the entire front surface of the base sheet with an adhesive, and unnecessary parts (parts of the copper foil not covered by the mask) are removed by chemical etching while the wiring part is covered with a mask, and the mask is finally removed to leave the copper foil covered by the mask on the front surface of the base sheet 1 as the wiring 11, or by an additive method in which a mask is provided on the front surface of the base sheet 1 so that only the parts corresponding to the wiring 11 are exposed, and then plating (e.g., electroless plating and electrolytic plating) is performed to provide a metal plating layer on the parts where the mask does not exist, and then the mask is removed to obtain the wiring 11 on the base sheet 1. The wiring 11 can be provided on the front surface of the base sheet 1 all at once by performing a process for providing wiring on the base sheet 1, such as a subtractive method or an additive method, but is not limited to this, in this embodiment. 2, the positions enclosed by dashed lines and marked with reference numeral 13 are planned positions where electronic components will be attached later. The size of planned positions Y is not uniform because planned positions 13 are adjusted to the size of the electronic components to be attached there. In addition, the wiring 11 does not necessarily have to be provided on the base sheet 1 shown in FIG. 1. For example, it is naturally possible to adopt a method in which 10×10=100 wirings 11 are provided on a base sheet larger than the base sheet 1 shown in FIG. 1 (for example, a base sheet whose length and width are 10 times that of the base sheet 1 shown in FIG. 1), and then the base sheet 1 is cut into 10 pieces vertically and horizontally, thereby obtaining 100 identical base sheets 1 with wirings 11 shown in FIG. 2 at once. Such a method for producing wirings 11 enables efficient mass production of multilayer boards. Even in this case, the 10×10=100 wirings provided on the large base sheet can be provided collectively by performing a process for providing wiring on the large base sheet once, thereby reducing the cost of manufacturing the base sheet 1.

[0019] The wiring 11 may or may not be designed to have the same width at all portions. As will be described later, it is also possible to provide an appropriate width to each of the linear wirings 11 connecting the electronic components attached to the base sheet 1. For example, the width of at least one of the linear wirings 11 may be different from the width of the other linear wirings 11. In addition, the width of one linear wiring 11 does not need to be constant over the entire length. As can be seen from FIG. 2, the linear wiring 11 may cross the folding line 12. In such a case, the width of the wiring 11 at the position where it crosses the folding line 12 may be wider than the width on both sides in the length direction of the wiring 11. An example of this case is shown in FIG. 3. FIG. 3 is an enlarged view of the part of the broken line X in FIG. 2. In this way, the wiring 11 is wider at the part where it crosses the folding line 12 than both sides or front and rear in the length direction. Although not limited to this, all wirings 11 that cross the folding line 12 in this embodiment have a width wider at the part where it crosses the folding line 12 than both sides or front and rear in the length direction. In this embodiment, when the wiring 11 is provided on the base sheet 1, the width of the wiring 11 at the part where it crosses the folding line 12 is wider than both sides or front and rear in the length direction. Of course, FIG. 3 is an example. In FIG. 3, the width of wiring 11 at the portion spanning bend line 12 is linearly wider than both sides or the front and back in the longitudinal direction; however, for example, the width of wiring 11 at the portion spanning bend line 12 may be curvedly wider than both sides or the front and back, or may be crank-shaped wider from a certain position.

[0020] Next, the cover sheet will be described. 4 shows the cover sheet 2 as viewed from the front side. The front side of the cover sheet 2 is the side that does not face the base sheet 1 when the cover sheet 2 is later laminated on the base sheet 1. The cover sheet 2 is a rectangular sheet having substantially the same shape and size as the base sheet 1. The cover sheet 2 has no wiring provided thereon. The cover sheet 2 is made of a thermoplastic resin and has insulating properties. Examples of the thermoplastic resin that constitutes the cover sheet 2 include liquid crystal polymer (LCP), polyphenylene sulfide (PPE), polyether ether ketone (PEEK), and fluororesin (FR). It is possible. Although not limited thereto, in this embodiment, liquid crystal polymer (LCP) is selected as the thermoplastic resin constituting the cover sheet 2. The thermoplastic resin constituting the cover sheet 2 and the thermoplastic resin constituting the base sheet 1 may or may not be the same. Whether the base sheet 1 and the cover sheet 2 are made of the same material or different materials, the base sheet 1 and the cover sheet 2 can be subjected to necessary processing by adjusting the processing conditions such as the heating temperature and heating time in the fixing step described later, and the pressure applied as necessary. The thickness of the cover sheet 2 can be appropriately selected within a range that allows the cover sheet 2 to be folded together with the base sheet 1 as described below. The thickness can be, for example, 20 μm to 200 μm, and preferably 25 μm to 100 μm. The thickness of the base sheet 1 and the cover sheet 2 may or may not be the same. As already mentioned, the thickness of the base sheet 1 and the cover sheet 2 must be thin enough that the folding process can be carried out with both sheets stacked together. On the other hand, it is preferable that the thickness of the cover sheet 2 is greater than the thickness of the wiring 11 formed on the base sheet 1. If the thickness of the cover sheet 2 is thinner than the thickness of the wiring 11, the cover sheet 2 may not cover the wiring 11 well after the fixing step described later is performed. Also, if the cover sheet 2 is thinner than the thickness of the wiring 11, even if the cover sheet 2 covers the wiring 11 after the fixing step, the thickness of the wiring 11 may appear as a convex portion on the surface of the cover sheet 2 covering the wiring 11 (the surface on the side not in contact with the base sheet 1). If the thickness of the wiring 11 appears as a convex portion on the surface of the cover sheet 2, there is a risk of problems such as poor bonding occurring when mounting electronic components on a surface with poor flatness, but such problems are unlikely to occur if the thickness of the cover sheet 2 is made thicker than the thickness of the wiring 11. The thickness of the cover sheet 2 may be thinner than that of the base sheet 1. By making the cover sheet 2 thinner than the base sheet 1, the rigidity during the folding process described below is reduced, improving foldability, and also reducing processing and material costs. At least one hole 21 is provided in the cover sheet 2. The hole 21 is provided at a position where an electronic component will be disposed later on the base sheet 1, that is, at a position corresponding to the planned position 13. The holes 21 are not of uniform size because they are adjusted to the size of the electronic component to be attached thereto. Although not limited to this, seven holes 21 are provided in the cover sheet 2 in this embodiment. 4 is a fold line indicating the location where the cover sheet 2 will be folded together with the base sheet 1. The fold line 12 of the base sheet 1 and the fold line 22 of the cover sheet 2 are located at corresponding positions because the superimposed base sheet 1 and cover sheet 2 are folded together.

[0021] After the above-described base sheet 1 and cover sheet 2 are prepared, a laminating step is first carried out. In the overlapping process, the cover sheet 2 is overlapped on the front surface of the base sheet 1 so that the contours of the two match (Fig. 5). As a result, the holes 21 in the cover sheet 2 each match with the intended positions 13 in the base sheet 1. The wiring 11 is exposed near the periphery of each hole 21.

[0022] Next, the folding process is carried out. In the folding process, the base sheet 1 and the cover sheet 2, which are superimposed, are folded together. The folding is performed along the folding lines 12 of the base sheet 1 and 22 of the cover sheet 2, which overlap each other. The folding is performed at least once. The folding may be either a mountain fold or a valley fold, or a combination of mountain folds and valley folds. However, after the folding process is performed, the above-mentioned hole 21 provided in the cover sheet 2 is exposed to the outside. By the hole 21 being exposed to the outside, it is meant that the hole 21 is not covered by the base sheet 1 or the cover sheet 2. In addition, after the overlapping step, a temporary fixing step may be performed to temporarily fix the base sheet 1 and the cover sheet 2 in order to prevent the contours of the overlapped base sheet 1 and the cover sheet 2 from shifting when the folding step is performed. Although this is not necessarily the case, this is the case in this embodiment. The temporary fixing can be performed by bonding a part (for example, the four corners) of the abutting part of the base sheet 1 and the cover sheet 2 with an adhesive. However, there is no limitation on the method of temporary fixing. A pin lamination method used in a general multilayer board manufacturing method may be used, in which boards with holes are stacked and pins are inserted into the holes provided in each board to position each board, or a temporary fixing tool (such as a clip) that clamps the base sheet 1 and the cover sheet 2 together may be used to temporarily fix them.

[0023] Although not limited to this, in the folding step in this embodiment, first, the portions of the base sheet 1 and the cover sheet 2 (FIGS. 5 and 6(A)) overlapped as a result of the overlapping step, above the fold lines 12 and 22 running horizontally, are folded back toward the back side of FIG. 6 at the fold lines 12 and 22 running horizontally. This results in the base sheet 1 and the cover sheet 2 being in the state shown in FIG. 6(B). Next, the portions of the base sheet 1 and cover sheet 2 in the state shown in Fig. 6(B) to the right of the fold lines 12, 22 running vertically in Fig. 6(B) are folded back toward the back side of Fig. 6 at the fold lines 12, 22 running vertically. In this way, the base sheet 1 and cover sheet 2 folded by folding are in the state shown in Fig. 6(C). When the folded base sheet 1 and cover sheet 2 are viewed from the back of Fig. 6(C), they are in the state shown in Fig. 6(D). The folding process in this embodiment is now complete. After the folding process is complete, four holes 21 are exposed on the surface shown in Fig. 6(C) and three holes 21 are exposed on the surface shown in Fig. 6(D). In other words, all of the seven holes 21 in the cover sheet 2 that were originally present are exposed to the outside after the folding process is complete. In the example described with reference to Fig. 6, all parts of the base sheet 1 and the cover sheet 2 are virtually all parallel except for the folded parts. In other words, the folded base sheet 1 and cover sheet 2 are in a state in which the base sheet 1 and the cover sheet 2 are layered in the following order from the surface shown in Fig. 6(C) to the surface shown in Fig. 6(D): cover sheet 2, base sheet 1, base sheet 1, cover sheet 2, cover sheet 2, base sheet 1, base sheet 1, cover sheet 2. All of the wiring 11 that crosses the folding lines 12 has a width wider at the portion crossing the folding lines 12 than on either side or in the front and rear in the longitudinal direction, so that even if the wiring 11 is folded together with the base sheet 1, there is little risk of the wiring 11 being damaged, such as being broken.

[0024] The fixing step is then carried out. In the fixing step, the base sheet 1 and the cover sheet 2 are fixed together after the folding step. The bonding step is performed by heating the folded base sheet 1 and cover sheet 2. When performing the bonding step, it is preferable to not only heat the base sheet 1 and cover sheet 2, but also to pressurize the folded base sheet 1 and cover sheet 2 so as to sandwich them from both the surface shown in Fig. 6(C) and the surface shown in Fig. 6(D). This is done in this embodiment. The conditions for heating and pressing the base sheet 1 and the cover sheet 2 can be adjusted depending on the thickness and melting point of the material. The heating and pressing conditions described below are an example in which both the thermoplastic resins constituting the base sheet 1 and the cover sheet 2 are liquid crystal polymers, more precisely, the base sheet 1 is a liquid crystal polymer with a melting point of 335°C, and the cover sheet 2 is a liquid crystal polymer with a melting point of 280°C. The reason why the thermoplastic resin constituting the cover sheet 2 is selected to have a melting point lower than that of the liquid crystal polymer as the thermoplastic resin constituting the base sheet 1 is that the liquid crystal polymer constituting the cover sheet 2 that has been softened and fluidized by the cover sheet 2 can fill the gap between the adjacent base sheet 1 and the cover sheet 2 (where unevenness due to the wiring 11 may exist) or the gap between the adjacent cover sheets 2. In this way, in the present application, the thermoplastic resins constituting the base sheet 1 and the cover sheet 2 can be selected so that the melting point of the thermoplastic resin constituting the cover sheet 2 is lower than the melting point of the thermoplastic resin constituting the base sheet 1. For example, the base sheet 1 and the cover sheet 2 can be heated using a general pressing device. (1) First, the temperatures of the base sheet 1 and the cover sheet 2 are raised from room temperature to a temperature at which the thermoplastic resins constituting them (particularly the thermoplastic resin constituting the cover sheet) soften slightly, for example 150°C, and this temperature is maintained for several minutes. This process is carried out for the purpose of softening at least the cover sheet 2 out of the base sheet 1 and the cover sheet 2, thereby filling to some extent the gaps between adjacent base sheets 1 and cover sheets 2 or between adjacent cover sheets 2 with the thermoplastic resin that has softened and become fluid. (2) Next, the temperatures of the base sheet 1 and the cover sheet 2 are raised to a temperature close to the melting point of the thermoplastic resin that constitutes them (particularly the thermoplastic resin that constitutes the cover sheet), for example 290°C, and this temperature is maintained for about 30 minutes. This step is carried out for the purpose of further softening at least the cover sheet 2 out of the base sheet 1 and the cover sheet 2, so that the gap between adjacent base sheets 1 and cover sheets 2 or the gap between adjacent cover sheets 2 is virtually completely filled with the softened and fluidized thermoplastic resin. (3) Finally, the temperatures of the base sheet 1 and the cover sheet 2 are cooled, for example, to room temperature. Through this process, the thermoplastic resin that has virtually completely filled the gap between the adjacent base sheet 1 and cover sheet 2, or the gap between the adjacent cover sheets 2, hardens. As a result, the gap between the adjacent base sheet 1 and cover sheet 2, or the gap between the adjacent cover sheets 2, becomes virtually filled with the thermoplastic resin, and the adjacent base sheet 1 and cover sheet 2, or the adjacent cover sheets 2, become fixed to each other. In carrying out the above-mentioned steps (1) to (3), the base sheet 1 and the cover sheet 2 are pressed in a press device. In this embodiment, for example, no pressure is applied for a while after the start of the above-mentioned step (1), and from the middle to the end of the period during which the temperature of the base sheet 1 and the cover sheet 2 are maintained at 150° C. in the same step, the base sheet 1 and the cover sheet 2 are pressed while maintaining a constant pressure, for example, at 3 MPa. This is to allow the fluidized thermoplastic resin to better fill gaps between adjacent base sheets 1 and cover sheets 2, or gaps between adjacent cover sheets 2. Then, from the start of the above-mentioned step (2) to the end of the step (3), the base sheet 1 and the cover sheet 2 are pressed at a constant pressure of 1 MPa. The reason why the pressure applied at this time is smaller than the pressure applied during the time period in which the temperatures of the base sheet 1 and the cover sheet 2 in the step (1) are kept at 150° C. (as described above, in this example, this pressure is 3 MPa) is that, although it is necessary to apply a constant pressure in order to better fill the gaps between adjacent base sheets 1 and cover sheets 2 or the gaps between adjacent cover sheets 2 with the fluidized thermoplastic resin, applying too strong a pressure may cause the fluidized thermoplastic resin to leak out from the gaps between adjacent base sheets 1 and cover sheets 2 or the gaps between adjacent cover sheets 2.

[0025] As described above, in the folded base sheet 1 and cover sheet 2 after the folding process, the base sheet 1 and cover sheet 2 are laminated in the order of cover sheet 2, base sheet 1, base sheet 1, cover sheet 2, cover sheet 2, base sheet 1, base sheet 1, cover sheet 2, in the order of cover sheet 2, base sheet 1, cover sheet 2 ... As a result, when the fixing step is completed, the folded base sheet 1 and cover sheet 2 are fixed in a plate-like shape.

[0026] After the fixing step is completed, the electronic component mounting step is carried out. The electronic components include IC chips, BGAs, CSPs, resistors, capacitors, etc., and are appropriately selected according to the performance required of the multilayer board. The electronic component 3 is electrically connected to the base sheet 1, which has become plate-like after the fixing process is completed, and to wiring 11 provided on the front surface of the base sheet 1 included in the cover sheet 2 (Figures 7(A) and (B)), thereby being fixed to the base sheet 1. The electronic component 3 is inserted into a hole 21 drilled in the cover sheet 2, and a terminal protruding from the electronic component 3 is connected to the wiring 11 in a conductive state by, for example, soldering the terminal to the wiring 11. Since it is necessary to insert the electronic component 3 into the hole 21 in order to fix the electronic component 3 to the wiring 11, the hole 21 needs to be one size larger than the electronic component 3. Otherwise, when the electronic component 3 is inserted into the hole 21 when the electronic component 3 is attached to the base sheet 1 through the hole 21, pressure may be applied to the electronic component 3 when the electronic component 3 is inserted into the hole 21, and the electronic component 3 may be damaged, or it may be difficult to move the electronic component 3 horizontally relative to the front surface of the base sheet 1. In addition, in order to enable the electronic component 3 to be connected to the wiring 11 in a conductive state, the hole 21 needs to have a size and shape such that the end of the wiring 11 can be seen from its periphery. The hole 21 in this embodiment is of such a size. It is also possible to combine adjacent holes 21 into one hole 21. For example, two holes 21 that are smaller than the other holes 21 located side by side on the upper left of Fig. 7(A) can be combined into one. In such a case, two electronic components 3 are attached in one hole 21. All of the intended electronic components 3 are fixed to the base sheet 1, and an electric circuit is formed by the wiring 11 and the electronic components 3, thereby completing the multilayer board. In the multilayer board manufactured in this embodiment, the base sheet 1 and the cover sheet 2 are substantially parallel except for the folded portion, and the number of overlapping base sheets 1 and cover sheets 2 (the sum of these) is the same in all parts of the multilayer board (8 in this embodiment). A multilayer board having such a structure is plate-shaped. In a multilayer board manufactured by this manufacturing method for a multilayer board, the front surface of the base sheet 1 is covered with the cover sheet 2 except for the portion where the hole 21 is formed. As a result, the wiring 11 is protected by the cover sheet 2, making the wiring 11 less likely to break.

[0027] <Variation 1> The method for manufacturing the multilayer board of the first modification is almost the same as the method for manufacturing the multilayer board described in the embodiment. The multilayer board is manufactured using a base sheet 1, a cover sheet 2, and an electronic component 3 as materials. The configurations of the base sheet 1 and the cover sheet 2 are basically the same between the first modification and the above-mentioned embodiment. However, the hole 21 at the bottom right of the cover sheet 2 shown in FIG. 4 is slightly smaller in the first modification, and the position of the hole 21 is slightly shifted toward the bottom left corner of the cover sheet 2. In addition, in the first modification, the configuration of the wiring 11 provided on the front surface of the base sheet 1 is appropriately modified in accordance with the change in the position and size of the hole 21.

[0028] In the first modification, the same overlapping step as in the above embodiment is carried out. In addition, in the first modification, the same folding process as in the above embodiment is performed. In the above embodiment, the superimposed base sheet 1 and cover sheet 2 are folded twice, but in the first modification, the base sheet 1 and cover sheet 2 are folded twice in the same manner. As a result, the base sheet 1 and cover sheet 2 are in the state shown in Figures 8(A) and (B). Figures 8(A) and (B) are views based on Figures 6(C) and (D). In the folding process of the first modified example, the overlapped base sheet 1 and cover sheet 2 are folded once more from this state. This third folding is performed along the folding lines 12 and 22 shown in Figures 8(A) and (B). The third fold is performed by folding back the portions of the base sheet 1 and cover sheet 2 below the horizontal fold lines 12 and 22, which are overlapped in Fig. 8(A), toward the back side of Fig. 8(A) at the horizontal fold lines 12 and 22. This results in the base sheet 1 and cover sheet 2 being in the state shown in Fig. 8(C) and (D). Fig. 8(C) and (D) are views of the base sheet 1 and cover sheet 2, respectively, from the same direction as Fig. 8(A) and (B). This completes the bending process of the first modification. Even in this case, after the folding process is completed, all of the seven holes 21 in the cover sheet 2 are exposed to the outside. Also in this case, after the folding process is completed, all parts of the base sheet 1 and the cover sheet 2 are substantially parallel to each other except for the folded parts. Moreover, the upper parts of the folded base sheet 1 and cover sheet 2 are in a state where 8 sheets are stacked together, including the base sheet 1 and the cover sheet 2, and the lower parts are in a state where 16 sheets are stacked together, including the base sheet 1 and the cover sheet 2. As a result, in the first modification, the base sheet 1 and the cover sheet 2 after the folding process have a step as shown in Fig. 8(E), in other words, they have a stepped cross section.

[0029] Thereafter, in the first modified example, a fixing step and an electronic component mounting step are carried out in the same manner as in the above-described embodiment, thereby completing the multilayer board. The completed multilayer board will be as shown in Figures 8(C), (D), and (E) except for the attachment of electronic components 3. As a result, the multilayer board manufactured by the manufacturing method of Modification 1 will have a step as shown in Figure 8(E), in other words, a stepped cross section.

[0030] <Variation 2> The method for manufacturing the multilayer board of the second modification is almost the same as the method for manufacturing the multilayer board described in the embodiment. The multilayer board is manufactured using a base sheet 1, a cover sheet 2, and an electronic component 3 as materials. The configurations of the base sheet 1 and the cover sheet 2 are basically the same between the modified example 2 and the above-described embodiment. However, in the modified example 2, both the base sheet 1 and the cover sheet 2 are square. Although not shown in its entirety again, wiring 11 similar to that in the above-described embodiment is provided on the front surface of the base sheet 1 of the second modified example.

[0031] In the second modification, the overlapping step is performed in the same manner as in the above-described embodiment (FIG. 9). The cover sheet 2 has holes 21 formed therein in the same manner as in the above-described embodiment. The number of holes 21 in the second modification is eight, although this is not limited thereto. In the second modified example, the folding step is performed after the overlapping step, as in the above-described embodiment. The dashed line 22A shown in Fig. 9 is a mountain fold line along which the base sheet 1 and the cover sheet 2 are mountain-folded, and the two-dot chain line 22B is a valley fold line along which the base sheet 1 and the cover sheet 2 are valley-folded. In this embodiment, the base sheet 1 and the cover sheet 2 are folded from the state shown in FIG. 10(A) through the state shown in FIG. 10(B) to the plate-like state shown in FIG. 10(C) by simultaneously performing mountain folding along the mountain fold line 22A and valley folding along the valley fold line 22B. This type of folding method is common in origami. In FIG. 10(B), the centers of the base sheet 1 and the cover sheet 2 are located on the front side of the paper, and the edges of the base sheet 1 and the cover sheet 2 are located on the back side of the paper. This completes the folding process of the second modification. Even in this case, all of the eight holes 21 in the cover sheet 2 are exposed to the outside after the folding process is completed (FIG. 11). Note that FIG. 11(A) is a diagram of one side of the base sheet 1 and cover sheet 2 of Modification Example 2 that have been made into a plate shape after the folding process is completed, and FIG. 11(B) is a diagram of the other side. Also in this case, after the folding process is completed, all parts of the base sheet 1 and the cover sheet 2 are substantially parallel to each other except for the folded parts.

[0032] Thereafter, in the second modification, a fixing step and an electronic component mounting step are carried out in the same manner as in the above embodiment, thereby completing the multilayer board. The completed multilayer board will be as shown in Figures 10(C) and 11, except for the presence of electronic components 3. As a result, the multilayer board manufactured by the manufacturing method of Modification 2 has the shape of an isosceles right triangle with electronic components 3 attached to both the front and back sides.

[0033] <Variation 3> The method for manufacturing a multilayer board according to the third modification is different from that according to the second modification in the way in which the base sheet 1 and the cover sheet 2 are folded in the folding process, but is otherwise the same as the second modification. The multilayer board is manufactured using a base sheet 1, a cover sheet 2, and an electronic component 3 as materials. The configurations of the base sheet 1 and the cover sheet 2 are basically the same in Modification 3 and Modification 2. In Modification 3, both the base sheet 1 and the cover sheet 2 are square. Although not shown in its entirety again, wiring 11 similar to that in the above-described embodiment is provided on the front surface of the base sheet 1 of the third modified example.

[0034] In the third modification, the overlapping step is performed in the same manner as in the second modification (FIG. 12). The cover sheet 2 has holes 21 formed therein in the same manner as in the above-described embodiment. The number of holes 21 in the third modification is eight, although this is not limited thereto. In the third modification, the folding step is performed after the overlapping step, as in the above embodiment. The dashed line 22A shown in Fig. 12 is a mountain fold line along which the base sheet 1 and the cover sheet 2 are mountain-folded, and the two-dot chain line 22B is a valley fold line along which the base sheet 1 and the cover sheet 2 are valley-folded. In this embodiment, the base sheet 1 and the cover sheet 2 are folded from the state shown in FIG. 13(A) through the state shown in FIG. 13(B) to the plate-like state shown in FIG. 13(C) by simultaneously performing mountain folding along the mountain fold line 22A and valley folding along the valley fold line 22B. This type of folding method is common in origami. In FIG. 13(B), the centers of the base sheet 1 and the cover sheet 2 are located on the front side of the paper, and the edges of the base sheet 1 and the cover sheet 2 are located on the back side of the paper. This completes the bending process of the third modification. Even in this case, all of the eight holes 21 in the cover sheet 2 are exposed to the outside after the folding process is completed (FIG. 14). Note that FIG. 14(A) is a diagram of one side of the base sheet 1 and cover sheet 2 of Modification Example 3 that have been made into a plate shape after the folding process is completed, and FIG. 14(B) is a diagram of the other side. Also in this case, after the folding process is completed, all parts of the base sheet 1 and the cover sheet 2 are substantially parallel to each other except for the folded parts.

[0035] Thereafter, in the third modification, a fixing step and an electronic component mounting step are carried out in the same manner as in the above-described embodiment, thereby completing the multilayer board. The completed multilayer board will be as shown in Figures 13(C) and 14, except for the attachment of electronic components 3. As a result, the multilayer board manufactured by the manufacturing method of modified example 3 will be a square plate-like board with electronic components 3 attached to both the front and back sides.

[0036] <Modification 4> The manufacturing method of the multilayer board of variant 4 differs from variant 2 in that the way in which the base sheet 1 and the cover sheet 2 are folded in the folding process is different, and in that the method of carrying out the fixing process is different, but in other respects it is the same as variant 2. The multilayer board is manufactured using a base sheet 1, a cover sheet 2, and an electronic component 3 as materials. The configurations of the base sheet 1 and the cover sheet 2 are basically the same in Modification 4 and Modification 2. In Modification 4, both the base sheet 1 and the cover sheet 2 are square. Although not shown in its entirety again, wiring 11 similar to that in the above-described embodiment is provided on the front surface of the base sheet 1 of the fourth modified example.

[0037] In the fourth modification, the overlapping step is performed in the same manner as in the second modification (FIG. 15). The cover sheet 2 has holes 21 formed therein in the same manner as in the above-described embodiment. The number of holes 21 in the fourth modification is ten, although this is not limited thereto. In the fourth modification, the folding step is performed after the overlapping step, as in the above embodiment. The dashed line 22A shown in Fig. 12 is a mountain fold line along which the base sheet 1 and the cover sheet 2 are mountain-folded, and the two-dot chain line 22B is a valley fold line along which the base sheet 1 and the cover sheet 2 are valley-folded. In this embodiment, the base sheet 1 and the cover sheet 2 are folded from the state shown in FIG. 16(A) through the state shown in FIG. 16(B) to the plate-like state shown in FIG. 16(C) by simultaneously performing mountain folding along the mountain fold line 22A and valley folding along the valley fold line 22B. This type of folding is common in origami. In FIG. 16(B), the centers of the base sheet 1 and the cover sheet 2 are located on the front side of the paper, and the edges of the base sheet 1 and the cover sheet 2 are located on the back side of the paper. In FIG. 16(B), the holes 21 in the cover sheet 2 and the wiring 11 in the base sheet 1 peeking through the holes 21 are omitted. This completes the bending process of the fourth modification. In the case of variant example 4, after the folding process is completed, the base sheet 1 and the cover sheet 2 have the shape of isosceles right-angled triangular plates of the same size extending in four symmetrical directions when viewed in a plane, connected so that the non-hypotenuse sides of the isosceles right-angled triangles overlap (see Figures 16(C) and 17). Even in this case, all ten holes 21 in the cover sheet 2 are exposed to the outside after the folding process is completed. This is because all ten holes 21 are located on either side of the four plate-like portions of the right-angled isosceles triangle described above after the folding process is completed. Note that Fig. 17 is a perspective view of the base sheet 1 and cover sheet 2 of the fourth modified example after the folding process is completed. In the fourth modification, after the folding process is completed, a portion of the base sheet 1 and the cover sheet 2 are not parallel to other portions of the base sheet 1 and the cover sheet 2. As a result, in the fourth modification, after the folding process is completed, the base sheet 1 and the cover sheet 2 have a three-dimensional shape.

[0038] Thereafter, in the fourth modification, a fixing step and an electronic component mounting step are carried out in the same manner as in the above-described embodiment, thereby completing the multilayer board. However, in this embodiment, the fixing process is carried out four times for each of the plate-shaped portions of the right-angled isosceles triangle. Each plate-shaped portion of the right-angled isosceles triangle is heated while being pressurized. By doing so, the base sheet 1 and the cover sheet 2 that are in contact with each other, and the base sheet 1 and the base sheet 1 that are in contact with each other are fixed in each of the four plate-shaped portions. The completed multilayer board will be as shown in Figures 16(C) and 17, except for the attachment of electronic components 3. As a result, the multilayer board manufactured by the manufacturing method of Modification 4 has a three-dimensional structure as described above. In addition, the angle between adjacent plate-like portions of each isosceles right triangle when viewed in a plane (θ in Figure 17) is basically 90 degrees, but this angle is variable because the plate-like portions of the isosceles right triangle can rotate around an axis that is not the hypotenuse side that overlaps among the four plate-like portions. [Explanation of symbols]

[0039] 1 Base sheet 2 Cover Sheet 3. Electronic Components 11 Wiring 12 Bend lines 21 holes 22 Bend Line

Claims

1. A superimposing step involves superimposing a cover sheet, which is an insulating sheet made of thermoplastic resin and substantially the same shape and size as the base sheet, onto the base sheet, which is an insulating rectangular sheet made of thermoplastic resin and has conductive wiring arranged in an appropriate manner on its front surface, on the front surface of the base sheet, with at least one hole provided at the position where electronic components will be placed later, such that the contours of the base sheet and the cover sheet coincide. A folding step in which the superimposed base sheet and cover sheet are folded and folded so that the holes are exposed to the outside, A fixing step in which the folded base sheet and the cover sheet are heated to melt at least a portion of the cover sheet, and then cooled and hardened to fix adjacent base sheets and cover sheets together. An electronic component mounting step, in which the electronic component inserted into the hole is fixed to the base sheet visible through the hole, such that the electronic component is electrically connected to the wiring on the front surface of the base sheet visible through the hole, including, A method for manufacturing multilayer substrates.

2. The aforementioned base sheet is square. A method for manufacturing a multilayer substrate according to claim 1.

3. The shape of the base sheet and the cover sheet after the electronic component mounting process is completed is a square or a right-angled isosceles triangle. A method for manufacturing a multilayer substrate according to claim 2.

4. The bending process is performed such that, after the electronic component mounting process is completed, all parts of the base sheet and the cover sheet are parallel except for the folded parts. A method for manufacturing a multilayer substrate according to claim 1.

5. The folding process is performed such that, after the electronic component mounting process is completed, the number of base sheet sheets and cover sheets overlapping in a certain portion other than the folded portion is different from the number of base sheet sheets and cover sheets overlapping in other portions. A method for manufacturing a multilayer substrate according to claim 4.

6. In the aforementioned fixing process, among the overlapping base sheet and cover sheet, adjacent cover sheets are also fixed together. A method for manufacturing a multilayer substrate according to claim 1.

7. In the aforementioned fixing step, the superimposed base sheet and the cover sheet are heated while under pressure. A method for manufacturing a multilayer substrate according to claim 1 or 5.

8. Prior to the overlapping step, a wiring step is performed in which the wiring is provided on the front surface of the base sheet. A method for manufacturing a multilayer substrate according to claim 1.

9. The wiring is configured such that the width of the portion where the base sheet is bent is wider than the width of the portions on both sides in the longitudinal direction. A method for manufacturing a multilayer substrate according to claim 1 or 8.

10. The thickness of the cover sheet is thinner than the thickness of the base sheet. A method for manufacturing a multilayer substrate according to claim 1.

11. The thickness of the cover sheet is thinner than the thickness of the base sheet. A method for manufacturing a multilayer substrate according to claim 9.

Images