JP2018148241A - Junction structure between flexible multilayer substrate and circuit board, manufacturing method of flexible multilayer substrate, and junction method between flexible multilayer substrate and circuit board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a multilayer board capable of easily forming a metal film in a through portion such as a through hole or a cut.SOLUTION: A flexible cable 10 as one example of a multilayer board includes a laminate 16, a through hole 12A, and an interlayer connection conductor 13A. The laminate 16 is formed by laminating an insulating layer 11A and an insulating layer 11B. The through hole 12A has a through hole 17 penetrating the laminate 16 in a lamination direction. In the through hole 12A, a plating film 15 is formed on a sidewall of the through hole 17 so as to interconnect a conductor foil 14A and a conductor foil 14B located on both principal surfaces of the laminate 16. The interlayer connection conductor 13A is formed in the vicinity of the through hole 12A, and penetrates the insulating layer 11A and the insulating layer 11B in the lamination direction. The conductor foil 14A and the conductor foil 14B located on both principal surfaces of the laminate 16 are interconnected via the interlayer connection conductor 13A.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a joint structure between a flexible multilayer board and a circuit board, a method for manufacturing the flexible multilayer board, and a joint method between the flexible multilayer board and the circuit board.

  As a conventional multilayer substrate, for example, there is a build-up substrate described in Patent Document 1. In this build-up substrate, a plating layer is formed to connect the upper copper foil and the lower wiring pattern. This plated layer is manufactured as follows. First, a via hole reaching an inner wiring pattern is formed by irradiating a laser from the copper foil side onto an insulating layer having a copper foil formed on one side. Next, electroless plating is performed on the copper foil and in the via hole, and electrolytic plating is further performed thereon.

Japanese Patent No. 4122159

  In the build-up substrate described in Patent Document 1, it is necessary to perform electroless plating with a slow growth of a plating layer as a pretreatment for performing electrolytic plating. For this reason, it takes time and effort to form a plating layer in the via hole.

  An object of the present invention is to provide a flexible multilayer board-circuit board bonding structure capable of easily forming a metal film in a through portion such as a through hole or a notch, a method for manufacturing the flexible multilayer board, and the An object of the present invention is to provide a method for joining a flexible multilayer board and a circuit board.

  The joint structure of a flexible multilayer board and a circuit board according to the present invention includes a flexible multilayer board and a circuit board, and the flexible multilayer board is formed by laminating a plurality of insulating layers, and penetrates the laminate in the laminating direction. A conductive paste filled with a via hole, and an interlayer connection through part in which a metal film is formed on the side wall of the through part so as to connect the conductive foils located on both main surfaces of the laminate to each other An interlayer connection conductor formed by curing, and the interlayer connection conductor is formed in the vicinity of the interlayer connection penetration so as not to directly contact the interlayer connection penetration, and the interlayer connection A plurality of conductors are formed along the penetrating portion in plan view, and the conductor foils located on both main surfaces of the multilayer body are connected to each other via the interlayer connection conductor, The substrate and the circuit board are joined via the solder is penetrated into the interlayer connection through portion.

  The method for producing a flexible multilayer substrate according to the present invention includes a plurality of interlayer connection conductors by pressing a plurality of insulating bases and curing a conductive paste filled in the holes of the insulating bases during heating and pressing. Forming an interlayer connection through part formed by forming a metal film on a side wall of a through part of the plurality of pressure-bonded insulating bases after the first step, and forming the interlayer connection through part A second step of forming the plurality of interlayer connection conductors so as to be positioned along the interlayer connection through portion without being in direct contact with each other.

  The method for bonding a flexible multilayer substrate and a circuit board according to the present invention includes a plurality of insulating base materials that are pressure-bonded at the time of heating and pressurizing, and a plurality of conductive pastes filled in the holes of the insulating base material are cured. A first step of forming an interlayer connection conductor, and an interlayer connection through portion formed by forming a metal film on a side wall of a through portion of the plurality of pressure-bonded insulating bases after the first step; A second step of forming a flexible multilayer substrate by forming the plurality of interlayer connection conductors so as to be positioned along the interlayer connection through portion without directly contacting the connection through portion, and an electrode of the circuit board The solder and the interlayer connection through part are arranged so that the solder and the interlayer connection through part overlap with each other, and the solder is melted by heating, and the solder is wetted and spread in the interlayer connection through part. And a process.

  According to the present invention, the metal film can be easily formed in the penetrating portion of the flexible multilayer substrate.

It is an external appearance perspective view which shows the edge part vicinity of the flexible cable which concerns on 1st Embodiment. It is a disassembled perspective view which shows the edge part vicinity of the flexible cable which concerns on 1st Embodiment. It is a disassembled plan view which shows the edge part vicinity of the flexible cable which concerns on 1st Embodiment. It is typical AA sectional view of the flexible cable concerning a 1st embodiment. It is typical sectional drawing which shows the manufacturing method of the flexible cable which concerns on 1st Embodiment. It is typical sectional drawing which shows the manufacturing method of the flexible cable which concerns on 1st Embodiment. It is typical sectional drawing which shows the joining method of the flexible cable and circuit board which concern on 1st Embodiment. It is a typical sectional view of a multilayer substrate concerning a 2nd embodiment. It is typical sectional drawing which shows the manufacturing method of the multilayer substrate which concerns on 2nd Embodiment. It is typical sectional drawing which shows the manufacturing method of the multilayer substrate which concerns on 2nd Embodiment. It is a disassembled plan view which shows the edge part vicinity of the multilayer substrate which concerns on 3rd Embodiment.

<< First Embodiment >>
A flexible cable 10 according to a first embodiment of the present invention will be described. The flexible cable 10 is an example of the multilayer board of the present invention. FIG. 1 is an external perspective view showing the vicinity of the end of the flexible cable 10. FIG. 2 is an exploded perspective view showing the vicinity of the end of the flexible cable 10. FIG. 3 is an exploded plan view showing the vicinity of the end of the flexible cable 10.

  The flexible cable 10 has a rectangular flat plate shape and extends long in the longitudinal direction. The flexible cable 10 includes a laminate 16 formed by laminating an insulating layer 11A and an insulating layer 11B. In the flexible cable 10, the insulating layer 11A is laminated on the upper surface of the insulating layer 11B. An external electrode 21A and an external electrode 21B are formed on the upper surface of the end portion of the flexible cable 10. The flexible cable 10 has a through hole 12A that penetrates the insulating layer 11A, the insulating layer 11B, the external electrode 21A, and the linear conductor 22A in the stacking direction. The insulating layer 11A, the insulating layer 11B, the external electrode 21B, and the linear conductor A through hole 12B penetrating 22B in the stacking direction is formed. The through hole 12A and the through hole 12B are examples of the interlayer connection through portion of the present invention.

  The insulating layer 11A and the insulating layer 11B have a rectangular flat plate shape and extend long in the longitudinal direction. The insulating layer 11A and the insulating layer 11B are made of a thermoplastic resin such as liquid crystal (LCP) or polyimide (PI). The external electrode 21A and the external electrode 21B have a rectangular flat plate shape, and are arranged side by side in the longitudinal direction of the insulating layer 11A so that the long side is along the long side of the insulating layer 11A.

  A linear conductor 22A and a linear conductor 22B are formed on the lower surface of the insulating layer 11B. The linear conductor 22A is formed so as to extend in the longitudinal direction of the insulating layer 11B. The through hole 12A penetrates the end of the linear conductor 22A. The linear conductor 22B is formed to extend parallel to the linear conductor 22A. A part of the linear conductor 22B extends in the lateral direction of the insulating layer 11B at the end of the insulating layer 11B. The through hole 12B penetrates the end of the linear conductor 22B. A linear conductor 22A and a resist (not shown) for protecting the linear conductor 22B are formed on the lower surface of the insulating layer 11B.

  The external electrode 21A and the linear conductor 22A are connected by eight interlayer connection conductors 13A. The interlayer connection conductor 13A passes through the insulating layer 11A and the insulating layer 11B in the stacking direction. A plurality of interlayer connection conductors 13A are formed so as to surround the through hole 12A in plan view, and overlap the external electrode 21A and the linear conductor 22A. That is, the interlayer connection conductor 13A is formed in the vicinity of the through hole 12A and penetrates the insulating layer 11A and the insulating layer 11B in the stacking direction. A plurality of interlayer connection conductors 13A are formed along the penetrating portion in plan view.

  The external electrode 21B and the linear conductor 22B are connected by eight interlayer connection conductors 13B. The interlayer connection conductor 13B penetrates the insulating layer 11A and the insulating layer 11B in the stacking direction. The interlayer connection conductor 13B is formed so as to surround the through hole 12B in plan view, and overlaps the external electrode 21B and the linear conductor 22B. The interlayer connection conductor 13A and the interlayer connection conductor 13B are formed by curing the conductive paste filled in the via holes.

  FIG. 4 is a schematic AA cross-sectional view of the flexible cable 10. The external electrode 21A and the linear conductor 22A are connected by the inner wall portion of the through hole 12A. The external electrode 21A is made of a conductor foil 14A covered with a plating film 15. The linear conductor 22A is made of a conductor foil 14B covered with a plating film 15. The linear conductor 22B is made of a conductor foil 14C covered with a plating film 15.

  The through hole 12 </ b> A has a plating film 15 formed on the inner wall of the through hole 17. The plating film 15 connects the conductor foil 14A and the conductor foil 14B. That is, the through hole 12A has a through hole 17 that penetrates the stacked body 16 in the stacking direction. In the through hole 12A, a plating film 15 is formed on the side wall of the through hole 17 so as to connect the conductor foil 14A and the conductor foil 14B located on both main surfaces of the laminate 16 to each other. The through hole 17 is an example of the through portion of the present invention. Conductor foil 14A, conductor foil 14B, and conductor foil 14C are made of copper foil or the like. The plated film 15 is made of an electroplated (electrodeposited) metal film or the like.

  The conductor foil 14A is formed on the upper surface of the insulating layer 11A. The conductor foil 14B is formed on the lower surface of the insulating layer 11B so as to overlap the conductor foil 14A in plan view. The conductor foil 14 </ b> A and the conductor foil 14 </ b> B are penetrated by the through hole 17. The conductor foil 14A and the conductor foil 14B are joined to the interlayer connection conductor 13A. The conductor foil 14A and the conductor foil 14B located on both main surfaces of the multilayer body 16 are connected to each other via the interlayer connection conductor 13A. The interlayer connection conductor 13A tapers from the lower surface of the insulating layer 11A toward the upper surface, and tapers from the upper surface of the insulating layer 11B toward the lower surface. The plating film 15 continuously covers the inner walls of the conductor foil 14 </ b> A, the conductor foil 14 </ b> B, and the through hole 17. That is, the plating film 15 is formed so as to cover the conductor foil 14 </ b> A and the conductor foil 14 </ b> B located on the side wall of the through hole 17 and both main surfaces of the multilayer body 16. The structure near the through hole 12B is formed in the same manner as the structure near the through hole 12A.

  5 and 6 are schematic cross-sectional views illustrating a method for manufacturing the flexible cable 10. First, as shown in FIG. 5A, a base material 25A in which a conductor foil 14A and a conductor foil for the external electrode 21B (see FIG. 1) are formed on one side is prepared. The base material 25A is made of a thermoplastic resin such as liquid crystal (LCP) or polyimide (PI). Below, the main surface in which conductor foil was formed among the main surfaces of a base material is called a 1st main surface, and the main surface in which conductor foil is not formed is called a 2nd main surface.

  Next, as shown in FIG. 5 (B), the punch 29 is pushed out from the first main surface side of the base material 25A toward the second main surface side, thereby penetrating through the conductor foil 14A and the base material 25A. 26A is formed. Next, as shown in FIGS. 5C and 5D, the base material 25A is turned upside down, and the laser is irradiated from the second main surface side of the base material 25A toward the first main surface side. Thus, the via hole 27 is formed so as to surround the through hole 26A in plan view. At this time, the laser output is adjusted so that the laser penetrates the base material 25A but does not penetrate the conductor foil 14A. As a result, a via hole 27 is formed which penetrates the base material 25A from the second main surface side toward the first main surface side and whose bottom surface is made of the conductor foil 14A. In order to form the via hole 27, an etching technique or the like may be used instead of laser processing. Next, as shown in FIG. 5E, the via hole 27 is filled with a conductive paste 28A. The conductive paste 28A is made of, for example, a conductive material whose main component is tin or copper.

  Next, as shown in FIG. 6 (A), the conductive foil 14B and the conductive foil 14C are formed on one side by the same process as the process shown in FIGS. 5 (A) to 5 (E). A through hole 26B and a via hole are formed, and the via hole is filled with a conductive paste 28B. Then, the second main surfaces of the base material 25A and the base material 25B face each other, and the base material 25A and the base material 25B are laminated. At this time, the through hole 26A formed in the base material 25A and the through hole 26B formed in the base material 25B overlap each other in plan view.

  Next, as shown in FIG. 6B, the laminated base material 25A and the base material 25B are simultaneously heated while being heated at a temperature at which the thermoplastic resin constituting the base material 25A and the base material 25B is sufficiently softened. Press (heat pressure bonding). Thereby, base material 25A and base material 25B are integrated, and insulating layer 11A and insulating layer 11B are formed. In addition, the conductive paste 28A and the conductive paste 28B are cured and integrated, whereby the conductive foil 14A and the interlayer connection conductor 13A joined to the conductive foil 14B are formed. Further, a through hole 17 penetrating the insulating layer 11A and the insulating layer 11B is formed.

  Next, as shown in FIG. 6C, a plating film 15 is formed on the surfaces of the conductor foil 14A, the conductor foil 14B, and the conductor foil 14C by electrolytic plating. At this time, the conductor foil 14A and the conductor foil 14B are connected by the interlayer connection conductor 13A, and the conductor foil 14A and the conductor foil 14B can be almost at the same potential, so that the plating film 15 is also formed on the inner wall of the through hole 17. Is done. Thereby, the through hole 12A is formed. The through hole 12B (see FIG. 2) is formed by the same process as the above process in parallel with the above process. The flexible cable 10 is completed through the above steps.

  FIG. 7 is a schematic cross-sectional view showing a method for joining the flexible cable 10 and the circuit board 31. First, as shown in FIG. 7A, the solder 32 is printed on the electrode formed on the upper surface of the circuit board 31. And the flexible cable 10 is arrange | positioned on the upper surface of the circuit board 31 so that the through-hole 12A and the solder 32 of the flexible cable 10 may overlap with planar view. Next, as shown in FIG. 7B, the solder 32 is melted by reflow heating. Since the inner wall surface of the through hole 12A is formed of the plated film 15, the solder 32 spreads in the through hole 12A with good wettability. The solder 32 fills the through hole 12 </ b> A and reaches the upper surface of the flexible cable 10. Thus, the flexible cable 10 and the circuit board 31 are joined.

  In the first embodiment, as described in conjunction with FIG. 4, the conductor foil 14A and the conductor foil 14B are connected by the interlayer connection conductor 13A. For this reason, the conductor foil 14A and the conductor foil 14B can be set to substantially the same potential in the vicinity of the through hole 12A. Thereby, when forming the plating film 15 on the side wall of the through-hole 17, it becomes easy to form the plating film 15 on the side wall of the through-hole 17 by electroplating without performing electroless plating. Note that the conductor foil 14A and the conductor foil 14B are somewhat pushed into the through hole 17 by the above-described extrusion process, so the distance between the conductor foil 14A and the conductor foil 14B in the through hole 17 is shortened. For this reason, the plating film 15 is easily formed on the inner wall of the through hole 17.

  An interlayer connection conductor 13A is formed around the through hole 12A. The interlayer connection conductor 13A is harder than the insulating layers 11A and 11B. For this reason, the deformation of the through hole 12A can be suppressed, and consequently, the disconnection of the plating film 15 formed on the inner wall of the through hole 17 can be made difficult to occur. A reinforcing material may be further disposed in the vicinity of the through hole 12A. The reinforcing material may be made of a resin material as long as it is harder than the insulating layers 11A and 11B.

  The conductor foil 14A and the conductor foil 14B are joined to the interlayer connection conductor 13A. For this reason, it is possible to prevent the conductor foil 14A and the conductor foil 14B from being separated from the insulating layer 11A and the insulating layer 11B in the vicinity of the through hole 12A.

  In addition, as described with FIG. 6, since the plating film 15 is formed on the inner wall surface of the through hole 12A, the solder 32 is likely to spread in the through hole 12A. For this reason, since the inner wall of the through hole 12A covered with the plating film 15 and the solder 32 are reliably bonded, it is possible to perform strong bonding through the through hole 12A. Further, it can be confirmed from above whether the solder 32 is wet in the through hole 12A.

<< Second Embodiment >>
A multilayer substrate 40 according to a second embodiment of the present invention will be described. FIG. 8 is a schematic cross-sectional view of the multilayer substrate 40. The multilayer substrate 40 includes a laminated body 46 formed by laminating insulating layers 41A to 41C in order from the top. A conductive foil 44A is formed on the upper surface of the insulating layer 41A. A conductor foil 44B is formed between the insulating layer 41A and the insulating layer 41B. A conductive foil 44C is formed on the lower surface of the insulating layer 41C.

  The multilayer substrate 40 includes a through hole 42 in which a plating film 45 is formed on the inner wall of the through hole 47. The through-hole 47 penetrates the insulating layers 41A to 41C and the conductor foils 44A to 44C in the stacking direction. The plating film 45 continuously covers the inner walls of the conductor foil 44 </ b> A, the conductor foil 44 </ b> C, and the through hole 47. That is, the through hole 42 has a through hole 47 that penetrates the stacked body 46 in the stacking direction. In the through hole 42, a plating film 45 is formed on the side wall of the through hole 47 so as to connect the conductor foil 44 </ b> A and the conductor foil 44 </ b> C located on both main surfaces of the multilayer body 46.

  A plurality of interlayer connection conductors 43A and interlayer connection conductors 43B are formed so as to surround the through hole 42 in plan view. The interlayer connection conductor 43A penetrates the insulating layer 41A in the stacking direction and is joined to the conductor foil 44A and the conductor foil 44B. The conductor foil 44A and the conductor foil 44B are connected by an interlayer connection conductor 43A. The interlayer connection conductor 43B penetrates the insulating layer 41B and the insulating layer 41C in the stacking direction, and is joined to the conductor foil 44B and the conductor foil 44C. The conductor foil 44B and the conductor foil 44C are connected by an interlayer connection conductor 43B. The interlayer connection conductor 43A and the interlayer connection conductor 43B overlap in plan view.

  That is, the interlayer connection conductor 43A and the interlayer connection conductor 43B are formed in the vicinity of the through hole 42 and penetrate the insulating layers 41A to 41C in the stacking direction. The conductor foil 44A and the conductor foil 44C located on both main surfaces of the multilayer body 46 are connected to each other via the interlayer connection conductor 43A and the interlayer connection conductor 43B.

  9 and 10 are schematic cross-sectional views showing a method for manufacturing the multilayer substrate 40. First, as shown in FIG. 9A, a base material 46A having a conductor foil 44A formed on one side is prepared. Next, as shown in FIG. 9B, a via hole 49 is formed at a predetermined position by irradiating a laser from the second main surface side of the base material 46A toward the first main surface side. Next, as shown in FIG. 9C, the via hole 49 is filled with a conductive paste 48A.

  Next, as shown in FIG. 9 (D), via holes are formed in the base material 46B having the conductor foil 44B formed on one side by the same processes as those shown in FIGS. 9 (A) to 9 (C). The via hole is filled with a conductive paste 48B. Also, a via hole is formed in the base material 46C having the conductor foil 44C formed on one side, and the via hole is filled with a conductive paste 48C. Then, the base materials 46A to 46C are laminated so that the second main surface of the base material 46A and the first main surface of the base material 46B face each other, and the second main surfaces of the base material 46B and the base material 46C face each other. To do.

  Next, as shown in FIG. 9E, the laminated base materials 46A to 46C are simultaneously heated while being heated at a temperature at which the thermoplastic resins constituting the base materials 46A to 46C are sufficiently softened. Press. Thereby, base material 46A-base material 46C are integrated, and insulating layer 41A-insulating layer 41C are formed. Also, the conductive paste 48A to conductive paste 48C are cured, whereby the interlayer connection conductor 43A and the interlayer connection conductor 43B are formed.

  Next, as shown in FIG. 10 (A) and FIG. 10 (B), the punch 29 is pushed through the insulating layer 41A to the insulating layer 41C and the conductor foil 44A to the conductor foil 44C in the laminating direction. A hole 47 is formed. Next, as shown in FIG. 10C, a plating film 45 is formed on the inner walls of the conductor foil 44A, the conductor foil 44C, and the through hole 47 by electrolytic plating. Through the above steps, the multilayer substrate 40 in which the through holes 42 are formed is completed.

  When a through hole is formed in a multilayer substrate by forming each through hole in each base material and then thermocompression bonding the base material, the through hole may be blocked during the thermocompression bonding. In the second embodiment, the through-hole 47 is formed after the base material 46A to the base material 46C are thermocompression bonded. For this reason, the through hole 42 can be reliably formed.

  Further, after forming the interlayer connection conductor 43A and the interlayer connection conductor 43B, the through hole 47 is formed by extrusion. For this reason, since the periphery of the part to be extruded is reinforced by the interlayer connection conductor 43A and the interlayer connection conductor 43B, the through hole 47 can be easily formed.

  The conductor foils 44A to 44C are connected by the interlayer connection conductor 43A and the interlayer connection conductor 43B. Since the conductive foil 44B is exposed on the inner wall of the through hole 47 at the start of electrolytic plating, the interval between the conductive foil 44A to the conductive foil 44C is narrowed in the inner wall portion of the through hole 47. For this reason, it becomes easy to form the plating film 45 on the inner wall of the through hole 47.

<< Third Embodiment >>
A multilayer substrate 50 according to a third embodiment of the present invention will be described. FIG. 11 is an exploded plan view showing the vicinity of the end of the multilayer substrate 50. The multilayer substrate 50 includes a laminate formed by laminating an insulating layer 51A on the upper surface of the insulating layer 51B. A cutout 52 is formed at the edge of the laminate. A conductor foil 54A is formed on the edge of the upper surface of the insulating layer 51A. On the lower surface of the insulating layer 51B, a conductor foil 54B extending from the edge along the longitudinal direction of the insulating layer 51B is formed. The notch 52 passes through the insulating layer 51A, the insulating layer 51B, the conductor foil 54A, and the conductor foil 54B in the stacking direction.

  Three interlayer connection conductors 53 are formed so as to surround the notch 52 in plan view. The interlayer connection conductor 53 penetrates the insulating layer 51A and the insulating layer 51B in the stacking direction, and is joined to the conductor foil 54A and the conductor foil 54B. The conductor foil 54A and the conductor foil 54B are connected by an interlayer connection conductor 53. The side walls of the conductor foil 54A, the conductor foil 54B, and the notch 52 are continuously covered with a plating film (not shown).

  That is, the multilayer substrate 50 includes a stacked body formed by stacking the insulating layers 51A and 51B. The laminate has a cutout portion 52 that penetrates the laminate in the stacking direction, and a plating film is formed on the side wall of the cutout portion 52 so as to connect the conductor foil 54A and the conductor foil 54B located on both main surfaces of the laminate. An interlayer connection through portion in which is formed is formed. The interlayer connection conductor 53 is formed in the vicinity of the interlayer connection through portion, and penetrates the insulating layer 51A and the insulating layer 51B in the stacking direction. The conductor foil 54 </ b> A and the conductor foil 54 </ b> B located on both main surfaces of the multilayer body are connected to each other via the interlayer connection conductor 53.

10 ... Flexible cables 11A, 11B, 41A to 41C, 51A, 51B ... Insulating layers 12A, 12B, 42 ... Through-hole (interlayer connection penetration)
13A, 13B, 43A, 43B, 53 ... Interlayer connection conductors 14A-14C, 44A-44C, 54A, 54B ... Conductive foils 15, 45 ... Plating film (metal film)
16, 46 ... Laminated body 17, 47 ... Through-hole (penetration part)
21A, 21B ... external electrodes 22A, 22B ... linear conductors 25A, 25B, 46A-46C ... base materials 26A, 26B ... through holes 27, 49 ... via holes 28A, 28B, 48A-48C ... conductive paste 29 ... punch 31 ... circuit Substrate 32 ... solder 40, 50 ... multilayer substrate 52 ... notch

Claims (6)

With a flexible multilayer board and circuit board,
The flexible multilayer substrate is
A laminate formed by laminating a plurality of insulating layers;
An interlayer connection through part having a through part penetrating the laminated body in the laminating direction and having a metal film formed on a side wall of the through part so as to connect conductor foils located on both principal surfaces of the laminated body; ,
An interlayer connection conductor formed by curing the conductive paste filled in the via hole,
The interlayer connection conductor is formed in the vicinity of the interlayer connection through portion so as not to directly contact the interlayer connection through portion,
A plurality of the interlayer connection conductors are formed along the penetrating portion in plan view,
The conductor foils located on both main surfaces of the laminate are connected to each other via the interlayer connection conductor,
The flexible multilayer substrate and the circuit board are bonded to each other through a solder penetrating into the interlayer connection through portion.   The junction structure of a flexible multilayer substrate and a circuit board according to claim 1, wherein the interlayer connection conductor penetrates the insulating layer in which the penetrating portion is formed in a laminating direction.   The joint structure of a flexible multilayer substrate and a circuit board according to claim 2, wherein the solder is continuously present up to a main surface opposite to a surface facing the circuit board of the flexible multilayer substrate. A first step of forming a plurality of interlayer connection conductors by press-bonding a plurality of insulating base materials at the time of heating and pressurizing, and curing a conductive paste filled in the holes of the insulating base materials;
After the first step, an interlayer connection through portion in which a metal film is formed on a side wall of the through portion of the plurality of pressure-bonded insulating bases is not directly in contact with the interlayer connection through portion. And a second step of forming the plurality of interlayer connection conductors so as to be positioned along the interlayer connection through portion. A first step of forming a plurality of interlayer connection conductors by press-bonding a plurality of insulating base materials at the time of heating and pressurizing, and curing a conductive paste filled in the holes of the insulating base materials;
After the first step, an interlayer connection through portion in which a metal film is formed on a side wall of the through portion of the plurality of pressure-bonded insulating bases is not directly in contact with the interlayer connection through portion. A second step of forming the plurality of interlayer connection conductors along the interlayer connection through portion to form a flexible multilayer substrate;
The solder and the interlayer connection through part are arranged so that the solder and the interlayer connection through part overlap the upper surface of the electrode of the circuit board, the solder is melted by heating, and the solder is wetted and spread in the interlayer connection through part. And a third step of bonding the flexible multilayer substrate and the circuit board.   6. The method of joining a flexible multilayer substrate and a circuit board according to claim 5, wherein, in the third step, the solder is spread to the main surface opposite to the surface of the flexible multilayer substrate opposite to the circuit board.

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