JP2006120770A - Multi-layer flexible printed wiring board and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a multi-layer flexible printed wiring board ensuring higher connection reliability, just suitable for ultra micro-miniaturization of a wiring layer, and including inter-layer connection excellent for productivity. <P>SOLUTION: The multi-layer flexible printed wiring board comprises a wiring board provided with an insulating layer, wiring layers formed on the front and rear surfaces of the insulating layer, and hole for connecting wiring layers via the insulating layer. This multi-layer flexible printed wiring board is also provided with a resin ball having the diameter smaller than the hole and a metal layer for covering the resin ball and a conductive member inserted, and fixed with pressure in the hole to make conductive the wiring layer. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a flexible printed wiring board (hereinafter referred to as FPC) on which various surface-mount type electronic components are mounted and a manufacturing method thereof, and more particularly to a multilayer FPC having high connection reliability and a manufacturing method thereof.

  In recent years, with the reduction in size and weight of electronic devices and higher functionality, the wiring density of FPCs used also tends to increase further. As a means for increasing the wiring density of the FPC, it is not sufficient that the wiring layer is miniaturized. Therefore, a multilayer FPC in which the wiring density is further increased by stacking the wiring layers through the insulating layers and connecting the wiring layers in a three-dimensional manner by providing an interlayer connection structure in the insulating layers between the wiring layers is attracting attention. ing.

Conventionally, in such a multilayer FPC, a through hole as a through hole is provided in an insulating layer made of polyimide film or the like, a copper plating film is formed on the wall surface of the through hole, and wiring provided on both surfaces of the insulating layer Layers are three-dimensionally connected (see, for example, Patent Document 1). This interlayer connection method is called a plated through hole method and is the most common interlayer connection method. The through-hole method is composed of two major steps: a step of converting the wall surface of an insulating through-hole into a conductor by electroless plating and a step of performing thick copper plating by electrolytic plating. The feature of such a through-hole method is that the thermal expansion coefficient of the copper plating film in the through hole and the insulating layer in which the through hole is formed are substantially the same, so that the copper plating film in the through hole is insulated from the copper plating film. It can be mentioned that there is no peeling of these joint interfaces due to the difference in thermal expansion coefficient from the film, and the connection reliability against heat is excellent.
JP-A-5-175636 (2nd page, FIG. 2) JP-A-7-176847 (5th page, FIG. 2)

  However, when copper thick plating is applied, not only the thickness of the copper plating film in the through hole but also the thickness of the copper foil that is the raw material of the wiring layer is increased. There was a problem that it was difficult to refine the size. In addition, the process is long and the productivity remains a problem.

  Therefore, as a method of interlayer connection that solves these problems, a method has been proposed in which a solder paste is printed in a through hole after the wiring layer is formed and melted and solidified (for example, see Patent Document 2). This interlayer connection method is characterized by high productivity because the interlayer connection can be made by a simple process compared to the plated through hole method described above, and because the interlayer connection is made after the wiring layer is formed, It has no influence on the thickness of the copper foil of the layer, and does not hinder the miniaturization of the wiring layer.

  However, in this interlayer connection method, when the solder is heated after being placed in the through hole, the thermal expansion coefficient of the solder is larger than the thermal expansion coefficient of the insulating layer, so that the solder in the through hole is heated more than the insulating layer. Inflate. For this reason, there is a possibility that the bonding interface between the wiring layer on the surface of the insulating layer and the solder is peeled off due to the difference in the magnitude of the thermal expansion. As described above, the interlayer connection method using solder has a problem that the connection reliability by heat is not sufficient.

As described above, the interlayer connection of the multilayer FPC by the conventional plated through hole method is excellent in connection reliability, but there is a problem in the miniaturization and productivity of the wiring layer, and the interlayer connection method using solder is as follows. Although the wiring layer, which is a problem in the through-hole method, can be miniaturized and productivity can be improved, there is a problem in connection reliability.

  Therefore, in the interlayer connection of the multilayer FPC, there has been a demand for a multilayer FPC and a manufacturing method capable of achieving both high connection reliability and miniaturization of the wiring layer and having high productivity.

  In view of the above problems, an object of the present invention is to provide a multilayer FPC having an interlayer connection between wiring layers that has high connection reliability, is optimal for miniaturization of a wiring layer, and is excellent in productivity, and a manufacturing method thereof. .

  In order to solve the above-mentioned problems, a multilayer FPC according to the present invention includes an insulating layer, a wiring layer formed on the front and back surfaces of the insulating layer, and a hole connecting the wiring layers via the insulating layer. A multilayer flexible printed wiring board having a resin ball having a diameter smaller than the hole diameter of the hole and a metal layer covering the resin ball, and having a conductive member that is press-fitted into the hole and electrically connects the wiring layer Is.

  According to this configuration, since a conductive member having a resin ball and a metal layer covering the resin ball is used as a conductor for interlayer connection, the Young's modulus of the conductive member is optimized with the resin ball. Stress can be relieved, and the conductive member is closely bonded to the wiring layer and the through hole by deforming the metal layer on the surface of the conductive member, so that high connection reliability is obtained. Therefore, according to this configuration, a multilayer FPC having excellent connection reliability can be obtained.

  Further, in order to solve the above problems, a method for manufacturing a multilayer FPC according to the present invention includes a wiring board forming step for forming a wiring board having wiring layers provided on the front and back surfaces of an insulating layer, and a wiring layer for connecting the wiring board. A through-hole forming step of forming a through-hole in the thickness direction of the wiring board; and a resin core metal ball in which a resin ball having an outer diameter smaller than the diameter of the through-hole is covered with a metal layer is press-fitted into the through-hole; And a conduction step of conducting the wiring layers provided on the front and back surfaces of the insulating layer with the resin core metal balls.

  In this manufacturing method, since the resin core metal ball is used as the conductor for interlayer connection, it is possible to reduce the thermal stress by optimizing the Young's modulus of the conductive member with the resin ball, and the metal on the surface of the conductive member. Since the conductive member is tightly bonded to the wiring layer and the through hole by deforming the layer, high connection reliability is obtained. In addition, since the interlayer connection is performed after the wiring layer is formed, there is no influence on the wiring layer in the process, and it is suitable for miniaturization of the wiring layer. Since the interlayer connection is performed by a very simple process, a method for manufacturing a multilayer FPC capable of ensuring high productivity can be obtained.

  According to the multilayer FPC according to claim 1 of the present invention, a resin ball is used as the core material of the conductor used for the interlayer connection, the Young's modulus of the conductor can be optimized, and a multilayer FPC having high connection reliability is obtained. There is an effect that it is obtained.

  According to the multilayer FPC according to claim 2 of the present invention, since the metal layer on the surface of the resin core metal ball contains at least one of a soft metal solder alloy, copper, or copper alloy, the resin ball is damaged. Therefore, only the metal layer on the surface of the resin core metal ball can be deformed, and a multi-layer FPC having high connection reliability can be obtained.

According to the multilayer FPC according to claim 3 of the present invention, since the interlayer connection is configured by using the double-sided wiring board which is a very simple process material, the multilayer FPC has a fine wiring layer and high productivity. F
There is an effect that a PC can be obtained.

  According to the multilayer FPC according to claim 4 of the present invention, since the single-sided wiring board having a very fine wiring layer is used as a process material, a multilayer FPC having a further fine wiring layer can be obtained. There is an effect.

  According to the multilayer FPC of the fifth aspect of the present invention, since the conductor is press-fitted and fixed to the blind via hole, there is an effect that a multilayer FPC having high connection reliability can be obtained.

  According to the multilayer FPC described in claim 6 of the present invention, since the multilayer FPC having the high connection reliability of the wiring layer and the fine wiring layer is further laminated, the high connection reliability and the fine wiring layer are provided. There exists an effect that the multilayer FPC which has is obtained.

  According to the method for manufacturing a multilayer FPC according to claim 7 of the present invention, since the interlayer connection is performed by a very simple process of press-fitting into the through hole of the resin core metal ball after the wiring layer is formed, high connection reliability and There is an effect that a multilayer FPC having a fine wiring layer can be realized with high productivity.

  According to the method for manufacturing a multilayer FPC according to claim 8 of the present invention, since a single-sided wiring board having a very fine wiring layer is used as a process material, an effect that a multilayer FPC having a further fine wiring layer can be manufactured. There is.

  According to the method for manufacturing a multilayer FPC according to claim 9 of the present invention, since a blind via hole is used for interlayer connection, there is an effect that a multilayer FPC having higher connection reliability can be manufactured.

  A multilayer FPC according to claim 1 of the present invention has a wiring board comprising an insulating layer, a wiring layer formed on the front and back surfaces of the insulating layer, and a hole connecting the wiring layers via the insulating layer. The multilayer flexible printed wiring board includes a resin ball having a diameter smaller than the hole diameter of the hole and a metal layer that covers the resin ball, and includes a conductive member that is press-fitted into the hole and electrically connects the wiring layer. . With this configuration, a conductive member having a resin ball and a metal layer covering the resin ball is used as a conductor for interlayer connection, so that the Young's modulus of the conductor is optimized with the resin ball, and a thermal expansion difference is achieved. In addition, the thermal stress generated in the step is relaxed, and the interlayer connection is made with a very simple structure in which the metal layer on the surface of the conductive member is deformed.

  The multilayer FPC according to claim 2 of the present invention is the multilayer FPC according to claim 1, wherein the metal layer includes at least one of a solder alloy, copper, and a copper alloy. With this configuration, since the metal layer on the surface of the resin core metal ball includes any one of a soft alloy such as solder alloy, copper, or copper alloy, the metal layer on the surface of the conductive member without damaging the resin ball. Only has the effect that the interlayer connection is made.

  The multilayer FPC according to claim 3 of the present invention is the multilayer FPC according to claim 1, wherein the wiring board is a double-sided wiring board in which the wiring layer is directly formed on the front and back surfaces of the insulating layer. With this configuration, since the double-sided wiring board, which is a very simple process material, is used for the interlayer connection, the multilayer FPC having a fine wiring layer and high productivity is configured with a simple structure. Have.

A multilayer FPC according to a fourth aspect of the present invention is the multilayer FPC according to the first aspect, wherein the wiring board is composed of two single-sided wiring boards in which the wiring layer is provided on one surface of the insulating layer. In this way, they are bonded through an adhesive layer. With this configuration, a multilayer FPC having a finer wiring layer is formed.

  A multilayer FPC according to claim 5 of the present invention is the multilayer FPC according to claim 1, wherein the wiring board includes a first wiring layer formed on one surface of the first insulating layer and a hole. The single-sided wiring board and the second single-sided wiring board in which the second wiring layer is formed on one surface of the second insulating layer are in contact with the first insulating layer and the second wiring layer. And a blind via hole is formed. With this configuration, since the conductor is press-fitted and fixed in the blind via hole, the bonding area between the conductive member and the wiring layer is increased, and the adhesion strength between the two is also increased. Therefore, even when various external stresses are applied, the bonding interface between the wiring layer and the conductive member is not peeled off, and the interlayer connection is made with higher connection reliability.

  A multilayer FPC according to claim 6 of the present invention is the multilayer FPC according to claim 1, wherein a plurality of multilayer flexible printed wiring boards according to claim 1 are laminated. With this configuration, since the multi-layer FPC having the high connection reliability of the wiring layer and the fine wiring layer is further laminated, the number of wiring layers of the multi-layer FPC having the fine wiring layer is increased, and a more multilayer wiring structure is obtained. The multi-layer FPC has an effect of being configured to have high connection reliability and a fine wiring layer.

  According to a seventh aspect of the present invention, there is provided a multilayer FPC manufacturing method comprising: a wiring board forming step for forming a wiring board provided with wiring layers on the front and back surfaces of an insulating layer; and wiring through holes for connecting the wiring layers. A through-hole forming step formed in the thickness direction of the plate, and a resin core metal ball in which a resin ball having an outer diameter smaller than the diameter of the through-hole is covered with the metal layer is press-fitted into the through-hole. And a conduction step of conducting the wiring layer provided on the back surface by the resin core metal ball. According to this method, since the interlayer connection is performed after the wiring layer is formed, the interlayer connection is performed without affecting the wiring layer in the process. In addition, since the interlayer connection is performed by a very simple process of press-fitting deformation using a resin core metal ball, the process is reduced.

  The method for manufacturing a multilayer FPC according to claim 8 of the present invention is the method for manufacturing a multilayer FPC according to claim 7, wherein the wiring board forming step includes two single-sided wirings in which a wiring layer is provided on one surface of the insulating layer. It includes a single-sided wiring board forming step of forming a board and a bonding step of bonding two single-sided wiring boards through an adhesive layer so that the wiring layer is on the outside. According to this method, since a single-sided wiring board having a very fine wiring layer is used as a process material, a multilayer FPC having a finer wiring layer than the double-sided wiring board can be easily configured.

  In the method for manufacturing a multilayer FPC according to claim 9 of the present invention, the first wiring layer is formed on one surface of the first insulating layer to form the first single-sided wiring board, and the one surface of the second insulating layer is formed. Forming a second wiring layer to form a second single-sided wiring board, and forming a through hole for connecting the first wiring layer and the second wiring layer with the first single-sided wiring board. The first single-sided wiring board and the second single-sided wiring with the through-hole forming step formed in the thickness direction in the wiring board and the first insulating layer and the second wiring layer facing each other through the adhesive layer A bonding step of bonding a plate to form a blind via hole by the through hole and the second wiring layer, and a resin ball having an outer diameter smaller than the opening diameter of the blind via hole is a metal in the blind via hole The resin core metal ball covered with the layer is press-fitted, and the first wiring layer and the second wiring layer And a wiring layer is intended to include, a conducting step of conducting by the resin core metal balls. According to this method, a resin core metal ball is press-fitted into a blind via hole that is non-penetrated and has a wiring layer on the bottom surface, and the surface metal layer is deformed to provide interlayer conduction. Compared with the case of press-fitting, the bonding area between the conductor and the wiring layer is increased, and the adhesion strength between the two is increased.

  Embodiments of the present invention will be described below with reference to the drawings. In addition, in the following drawings, the same code | symbol is attached | subjected to the same member and the overlapping description is abbreviate | omitted. Moreover, the numerical value shown in the following embodiment is an example which can be selected variously, and is not limited to this.

(Embodiment 1)
A multilayer FPC according to an embodiment of the present invention will be described below. First, the multilayer FPC of the present invention will be described with reference to FIG. FIG. 1 is a cross-sectional view of a main part of a multilayer FPC according to Embodiment 1 of the present invention.

  In FIG. 1, reference numeral 100 denotes a multilayer FPC according to the present embodiment in which an upper wiring layer 3 and a lower wiring layer 4 are formed on both surfaces of an insulating layer 2 made of a polyimide film, and a conductor 6 press-fitted into a through hole 5. Thus, an electrical interlayer connection between the wiring upper layer 3 and the wiring lower layer 4 is made. Here, the conductor 6 includes a single resin core metal ball 9 in which a resin ball 7 having a diameter smaller than the hole diameter of the through hole 5 is disposed in the core portion and the surface of the resin ball 7 is covered with the metal layer 8. As will be described later, pressure is applied in the thickness direction of the insulating layer 2 to deform the metal layer 8 on the surface of the resin core metal ball 9 and press-fit into the through hole 5.

  Thus, the conductor 6 that performs interlayer connection of the multilayer FPC 100 has a structure having the resin balls 7 in the core portion. Thereby, the Young's modulus of the conductor 6 can be reduced, and the stress caused by the difference in thermal expansion between the insulating layer 2 and the conductor 6 can be relaxed by the resin balls 7. By using the resin ball 7 which is a sphere, there is an advantage that it is excellent in handling property and manufacturability of the ball member. In addition, the metal layer 8 on the surface of the resin core metal ball 9 is deformed so that the resin core metal ball 9 is in contact with the wiring upper layer 3 and the wiring lower layer 4 and is in close contact with the through hole 5 without any gap. Thus, the resin core metal ball 9 (conductor 6) can be disposed in the through hole 5. As a result, in the multilayer FPC 100, the wiring upper layer 3 and the wiring lower layer 4 are reliably electrically connected, that is, conducted through the resin core metal ball 9 (conductor 6).

  As a result, it is possible to solve the maximum problem in the case of performing interlayer connection using solder. That is, when a conductor composed only of solder is heated, the solder in the through hole expands more than the insulating layer, the bonding interface between the wiring layer and the solder on the surface of the insulating layer peels off, and the connection reliability by heat Can be solved. Therefore, according to the connection structure of the multilayer FPC 100 according to the present embodiment, high connection reliability can be obtained in electrical connection between the wiring upper layer 3 and the wiring lower layer 4.

  Further, by using at least one of soft metals as the metal layer 8 on the surface of the resin core metal ball 9, only the metal layer 8 on the surface of the resin core metal ball 9 can be used without damaging the resin ball 7. It can be deformed, and higher connection reliability can be obtained in the electrical connection between the wiring upper layer 3 and the wiring lower layer 4. Here, in the present invention, the soft metal is a metal that has good conductivity and can be used for wiring among metal having high extensibility that can be plastically deformed. The soft metal is preferably one that can be formed on the surface of the resin core by plating from the viewpoint of manufacturing the resin core metal ball 9, but is not limited to a plating film. Specific examples include solder alloys, copper, copper alloys, nickel, nickel alloys, gold, silver, palladium, and the like. Among these, solder alloys, copper, and copper alloys are preferable. Various solder compositions such as eutectic solder, high-temperature solder, lead-free solder, etc. can be used, and any solder composition may be used according to various conditions.

In addition, the opening shape of the through hole into which the resin core metal ball 9 is press-fitted is not particularly limited, but a circular shape is preferable.

  Next, a manufacturing method of the multilayer FPC 100 according to the present embodiment that realizes high connection reliability in electrical connection between the wiring upper layer 3 and the wiring lower layer 4 by using such a resin core metal ball 9 will be described with reference to FIGS. This will be described in detail with reference to FIG. In the following drawings, the same components as those in FIG. 1 are denoted by the same reference numerals as those in FIG. 1, and detailed description thereof is omitted here.

  2 to 8 are diagrams for explaining a manufacturing process of the multilayer FPC 100 according to the first embodiment, and FIG. 2 is a schematic diagram of a double-sided copper-clad laminate that is a component of the multilayer FPC according to one embodiment of the present invention. FIG. 3 is a fragmentary sectional view, FIG. 3 is a fragmentary sectional view of a double-sided wiring board in which a wiring layer is formed in one embodiment of the present invention, and FIG. 4 is a double-sided wiring board in which a through hole is formed in one embodiment of the present invention. FIG. 5 is a cross-sectional view of a main part of a double-sided wiring board at the start of press-fitting of a resin core metal ball in one embodiment of the present invention, and FIG. 6 is a resin core metal ball in one embodiment of the present invention. Is a cross-sectional view of the main part of the double-sided wiring board in the middle of press-fitting deformation, FIG. 7 is a cross-sectional view of the main part of the double-sided wiring board at the end of press-fitting deformation of the resin core metal ball in one embodiment of the present invention, and FIG. In principal part sectional drawing of the multilayer FPC after the interlayer connection in one embodiment That. FIG. 9 is a cross-sectional view of the main part of the multilayer FPC after interlayer connection in one embodiment of the present invention.

  In the above figure, the double-sided copper-clad laminate 10 is a double-sided copper-clad laminate in which the copper foil 11 is directly formed on both sides of the insulating layer 2. The double-sided wiring board 12 is a double-sided wiring board in which the double-sided copper-clad laminate 10 is etched to form the wiring upper layer 3 and the wiring lower layer 4. The punching die 13 is used for processing the through hole 5. The pressurizing upper plate 14 and the pressurizing lower plate 15 are used for press-fitting and deforming the resin core metal ball 9.

  Hereinafter, a method for manufacturing the multilayer FPC 100 will be described with reference to the drawings. First, as shown in FIG. 2, a double-sided copper-clad laminate 10 in which copper foils 11 are directly formed on both sides of an insulating layer 2 is prepared. In the present embodiment, a two-layer type double-sided copper clad laminate 10 in which no adhesive layer is interposed between the insulating layer 2 and the copper foil 11 is described as an example. It is not limited to an example, and a double-layered copper clad laminate of a three-layer type in which an adhesive layer is interposed between the insulating layer 2 and the copper foil 11, or a double-sided copper clad laminate having a plurality of layers is used. It is also possible to change as appropriate.

  Next, a mask material is formed on the surface of the copper foil 11 in accordance with the wiring pattern, and an etching process is performed using a copper etching solution such as iron chloride or copper chloride. As shown in FIG. The double-sided wiring board 12 on which the upper layer 3 and the wiring lower layer 4 (hereinafter, the wiring upper layer 3 and the wiring lower layer 4 may be collectively referred to as a wiring layer) is obtained.

  And the punching process is given to the double-sided wiring board 12 in which the wiring layer was formed using the punching metal mold | die 13, and the through-hole 5 is formed as shown in FIG. Further, as shown in FIG. 5, after one resin core metal ball 9 is arranged at the position of the through hole 5, the pressurization upper plate 14 and the pressurization lower plate 15 are used to reach the through hole 5 of the resin core metal ball 9. Press-fit. Thereby, the press-fit deformation of the resin core metal ball 9 is started.

Here, the resin core metal ball 9 has a spherical shape. The spherical shape has the advantage of excellent handling properties and ease of production of the resin core metal ball. Further, the diameter of the resin ball 7 in the core portion of the resin core metal ball 9 is made smaller than the diameter of the through hole 5. Further, as described above, the metal layer 8 on the surface of the resin core metal ball 9 includes at least one kind of soft metal such as solder alloy, copper, or copper alloy. Thereby, only the metal layer 8 on the surface of the resin core metal ball 9 can be deformed without damaging the resin ball 7. The resin core metal ball 9 as a whole has a diameter of the resin core metal ball 9 larger than the diameter of the through hole 5, and the volume of the resin core metal ball 9 is larger than the opening volume of the through hole 5. ing.

  As a method for arranging the resin core metal balls 9, a conventionally known method of mounting solder balls on a semiconductor package called BGA (Ball Grid Array) can be used. Specifically, a suction plate having a suction hole having a diameter smaller than that of the solder ball at a position corresponding to the through hole 5 is prepared and connected to a vacuum pump for adjusting the pressure in the suction hole. Then, using this suction plate, the solder ball is sucked into the suction hole, aligned with the upper portion of the through hole 5, the solder ball is dropped, and the solder ball is placed at the through hole position. It is also possible to use equipment called a ball mounter that performs the above operations. Here, an example of mounting solder balls by vacuum suction has been shown, but other methods such as electrostatic suction may be used.

  Subsequently, as shown in FIG. 6, the resin core metal balls 9 are sequentially press-fitted into the through holes 5 by pressurizing the resin core metal balls 9 with the pressurization upper plate 14 and the pressurization lower plate 15. Here, since the metal layer 8 on the surface of the resin core metal ball 9 includes a soft metal such as a solder alloy, copper, or copper alloy, the metal layer 8 is press-fitted during the press-fitting of the resin core metal ball 9. It will be deformed sequentially. The metal layer 8 is joined to a part of the wiring upper layer 3 and is deformed along the inner wall of the through hole 5, and the inside of the through hole 5 is sequentially filled with the resin core metal balls 9 without a gap. Further, since the resin ball 7 of the core portion of the resin core metal ball 9 having a diameter smaller than that of the through hole 5 is used, the resin ball 7 is not deformed, and the metal layer 8 on the surface of the resin core metal ball 9 is deformed. As a result, the press-fit deformation of the resin core metal ball 9 proceeds. Thereby, the resin core metal ball 9 can be press-fitted into the through hole 5 without damaging the resin ball 7.

  Further, as shown in FIG. 7, the lower metal layer 8 of the resin core metal ball 9, that is, the metal layer 8 of the resin core metal ball 9 on the lower pressure plate 15 side is brought into contact with the lower pressure plate 15 to be deformed. By this, it joins with the wiring lower layer 4, and the press-fit deformation | transformation of the resin core metal ball 9 to the through-hole 5 is completed. Thereby, the interlayer connection between the wiring upper layer 3 and the wiring lower layer 4 is completed. Here, as the resin core metal ball 9, since the volume of the resin core metal ball 9 is larger than the opening volume of the through hole 5, the inside of the through hole 5 is reliably embedded with the resin core metal ball 9, Interlayer connection between the wiring upper layer 3 and the wiring lower layer 4 can be reliably performed. As described above, the multilayer FPC 100 in which the interlayer connection is made as shown in FIG. 8, that is, the wiring upper layer 3 and the wiring lower layer 4 are conducted can be obtained by a very simple process.

  In this embodiment, the case where the diameter of the resin core metal ball 9 is larger than the diameter of the through hole 5 is shown. However, the diameter of the resin core metal ball 9 used here is equal to the diameter of the through hole 5. In this case, the wiring layers can be connected by deformation of the upper and lower metal layer portions of the resin core metal ball 9. However, considering the deformation amount margin of the metal layer 8 and the reliability of interlayer connection, it is preferable that the diameter of the resin core metal ball 9 is larger than the diameter of the through hole 5.

  The manufacturing method of the multilayer FPC according to this embodiment as described above has the following characteristics. First, since the resin core metal ball 9 which is a conductor that forms the interlayer connection has the resin ball 7 inside, the difference in the thermal expansion coefficient between the conductor 6 that forms the interlayer connection and the insulating layer 2 is finally reached. The resulting stress can be relieved by the resin balls 7. Thereby, peeling of these joint interfaces due to the difference in thermal expansion coefficient can be prevented, and high connection reliability can be obtained in the electrical connection between the wiring upper layer 3 and the wiring lower layer 4.

Then, since the interlayer connection between the wiring upper layer 3 and the wiring lower layer 4 is performed after the wiring layer is formed, there is no influence on the wiring layer in the process. Therefore, the wiring layer can be miniaturized by reducing the thickness of the copper foil 11, which is suitable for the miniaturization of the wiring layer. Furthermore, since the interlayer connection between the wiring upper layer 3 and the wiring lower layer 4 can be performed by a very simple process of press-fitting deformation of the resin core metal ball 9, the number of processes is smaller than other interlayer connection methods, and productivity and production are reduced. Excellent cost.

  Therefore, according to the manufacturing method of the multilayer FPC according to the present embodiment, the connection reliability between the wiring layers is high, and the multilayer FPC that is optimal for miniaturization of the wiring layer can be manufactured with high productivity.

  In addition, as a formation method of the double-sided wiring board in Embodiment 1, although the copper foil 11 is directly formed on both surfaces of the insulating layer 2, the following methods are also used as a formation method of a double-sided wiring board. Can do. That is, first, the copper foil 11 is directly formed on one side of the insulating layer 2 and further etched to form a wiring layer to form two single-sided wiring boards. Then, the two single-sided wiring boards are bonded together through the adhesive layer with the wiring layer facing outward. By such a method, as shown in FIG. 9, a double-sided wiring board configured by bonding two single-sided wiring boards can be formed. In FIG. 9, 25 is a single-sided wiring board having a wiring upper layer 3 formed on one side of the insulating layer 2, 26 is another single-sided wiring board having a wiring lower layer 4 formed on one side of the insulating layer 2, and 28 is a single-sided wiring board 25. Is a double-sided wiring board formed by adhering the other single-sided wiring board 26 with the adhesive layer 27 with the wiring layer facing outward, and the wiring upper layer 3 and the wiring lower layer 4 are interlayer-connected by the conductor 6. ing. A single-sided wiring board can be made finer than a double-sided wiring board, and this single-sided wiring board is bonded to obtain a double-sided wiring board, so that a double-sided wiring board having a finer wiring layer can be obtained. The miniaturization of the wiring layer of this single-sided wiring board will be described in detail in the second embodiment below.

(Embodiment 2)
In the second embodiment, a method for manufacturing a multilayer FPC according to another embodiment of the present invention, which is excellent in connection reliability between wiring layers and further miniaturization of wiring layers, will be described in detail with reference to FIGS. . FIG. 11 is a cross-sectional view of a principal part of a single-sided copper-clad laminate with an adhesive layer, which is a component of a multilayer FPC in one embodiment of the present invention, and FIG. 12 is an adhesion in which a wiring layer is formed in one embodiment of the present invention. FIG. 13 is a cross-sectional view of a main part of a single-sided wiring board with a layer, FIG. 13 is a cross-sectional view of a main part of a single-sided wiring board with an adhesive layer in which a through hole is formed in one embodiment of the present invention, and FIG. FIG. 2 is a cross-sectional view of a main part at the start of press-fitting of resin core metal balls into a multilayer wiring board in which blind via holes are formed.

  In the above figure, reference numeral 200 denotes a multilayer FPC in which an electrical interlayer connection is made between the wiring upper layer 3 and the wiring lower layer 4 by the conductor 6. Reference numeral 16 denotes a single-sided copper-clad laminate with an adhesive layer in which the copper foil 11 is formed on one side of the insulating layer 2 and the adhesive layer 17 is formed on the other side. Reference numeral 18 denotes a single-sided wiring board with an adhesive layer formed by etching the single-sided copper-clad laminate 16 with an adhesive layer to form an upper wiring layer 3. Reference numeral 20 denotes another single-sided wiring board on which the wiring lower layer 4 laminated with the single-sided wiring board 18 with the adhesive layer is formed. Reference numeral 21 denotes a multilayer wiring board in which a single-sided wiring board 18 with an adhesive layer and another single-sided wiring board 20 are laminated and a blind via hole 19 is formed for interlayer connection. The punching die 13 is used for processing the through hole 5. The pressurizing upper plate 14 and the pressurizing lower plate 15 are used for press-fitting and deforming the resin core metal ball 9.

  In the multilayer FPC 200 according to the present embodiment, as shown in FIG. 10, electrical interlayer connection between the wiring upper layer 3 and the wiring lower layer 4 is made by the conductor 6 press-fitted into the blind via hole 19. . Here, the conductor 6 has a resin core metal ball 9 in which a resin ball 7 having a diameter smaller than the diameter of the blind via hole 19 is disposed in the core portion and the surface of the resin ball 7 is covered with the metal layer 8. As will be described later, the metal layer 8 on the surface of the resin core metal ball 9 is deformed by applying pressure in the thickness direction of the insulating layer 2.

  As described above, the conductor 6 that performs interlayer connection of the multilayer FPC 200 has a structure having the resin ball 7 in the core portion as in the case of the first embodiment. Thereby, the Young's modulus of the conductor 6 can be reduced, and the stress caused by the difference in thermal expansion can be relieved by the resin balls 7. Further, since the metal layer 8 on the surface of the resin core metal ball 9 is deformed, the resin core metal ball 9 is in close contact with the upper wiring layer 3 and the lower wiring layer 4 and in the blind via hole 19 without a gap. In this state, the resin core metal ball 9 (conductor 6) can be disposed in the blind via hole 19. As a result, the wiring upper layer 3 and the wiring lower layer 4 are reliably electrically connected via the resin core metal ball 9 (conductor 6).

  As a result, even in the multilayer FPC 200 according to the second embodiment, it is possible to solve the greatest problem in the case of performing interlayer connection using solder. That is, when a conductor composed only of solder is heated, the solder in the through hole expands more than the insulating layer, and the bonding interface between the wiring layer and the solder on the surface of the insulating layer is peeled off, thereby connecting by heat. The problem that reliability cannot be ensured can be solved. Therefore, also in the connection structure of the multilayer FPC 200 according to the second embodiment, high connection reliability can be obtained in electrical connection between the wiring upper layer 3 and the wiring lower layer 4.

  In the present embodiment, the interlayer connection conductor 6 is press-fitted into a blind via hole 19 having a wiring lower layer 4 on the bottom surface. For this reason, compared with the case where the conductor 6 for interlayer connection is press-fitted into the through hole, the bonding area between the conductor 6 and the wiring layer is increased, and the adhesion strength between the two is also increased. Therefore, in this multilayer FPC 200, even when various external stresses are applied, the bonding interface between the wiring layer and the conductor 6 does not peel off, and this quality multilayer FPC 200 having higher connection reliability is realized. Has been.

  Further, as the metal layer 8 on the surface of the resin core metal ball 9, as in the case of the first embodiment, a soft metal, particularly at least one of a solder alloy, copper, or a copper alloy is used for the resin ball 7. Only the metal layer 8 on the surface of the resin core metal ball 9 can be deformed without causing damage, and higher connection reliability can be obtained in electrical connection between the wiring upper layer 3 and the wiring lower layer 4.

  Next, a manufacturing method of the multilayer FPC 200 according to the second embodiment that realizes such high connection reliability will be described in detail with reference to the drawings.

  First, as shown in FIG. 11, a single-sided copper-clad laminate 16 with an adhesive layer in which the copper foil 11 is directly formed on one surface of the insulating layer 2 and the adhesive layer 17 is formed on the other surface is prepared. In the present embodiment, a single-sided copper-clad laminate 16 with an adhesive layer in which no adhesive layer is interposed between the insulating layer 2 and the copper foil 11 is described as an example. It is not limited to this example, It is also possible to use a single-sided copper-clad laminate having an adhesive layer between the insulating layer 2 and the copper foil 11, or a single-sided copper-clad laminate having a plurality of layers. It can be changed as appropriate.

  Next, a mask material is formed on the surface of the copper foil 11 in accordance with the wiring pattern, and an etching process is performed using a copper etching solution such as iron chloride or copper chloride to form the wiring upper layer 3 as shown in FIG. A single-sided wiring board 18 with an adhesive layer is obtained. Here, in the present embodiment, unlike the case where the wiring layer of the double-sided wiring board is formed, single-sided etching suitable for miniaturization is possible, and further miniaturization of the wiring upper layer 3 is possible. Therefore, the wiring upper layer 3 of the single-sided wiring board 18 with the adhesive layer obtained in the present embodiment can be further miniaturized as compared with the wiring layer of the double-sided wiring board.

The reason is described below. Normally, in forming a wiring layer of a double-sided wiring board, the copper foil on both sides of the double-sided copper-clad laminate is simultaneously etched, so it is necessary to apply the etching solution uniformly from the top and bottom of the double-sided copper-clad laminate. . However, when the etching solution is sprayed from above and below the double-sided copper-clad laminate, the etching solution after spraying on the upper surface forms a puddle on the upper surface, and etching uniformity cannot be maintained. is there. Therefore, in the double-sided wiring board, the etching conditions are uneven and unstable, and it is difficult to form a very fine wiring layer.

  On the other hand, in the formation of the wiring layer of the single-sided wiring board, only the etching liquid spray from the lower side of the single-sided copper-clad laminate (the copper foil forming side is the lower surface) is required. Therefore, the optimum range of etching conditions can be widened. Therefore, this wiring layer forming method for a single-sided wiring board is suitable for miniaturization of the wiring layer.

  Next, the single-sided wiring board 18 with the adhesive layer on which the wiring upper layer 3 is formed is punched using a punching die 13 to form the through holes 5 as shown in FIG. Then, as shown in FIG. 14, the single-sided wiring board 18 with the adhesive layer in which the through-hole 5 is formed and the other single-sided wiring board 20 in which the wiring lower layer 4 is formed are opposed to the lower wiring layer 4 and the adhesive layer 17. In this state, the multilayer wiring board 21 in which the blind via hole 19 for interlayer connection is formed is obtained by pasting together through the adhesive layer 17.

  In addition, in the other single-sided wiring board 20 in which the wiring lower layer 4 is formed, similarly to the single-sided wiring board 18 with the adhesive layer in which the wiring upper layer 3 is formed, the lower side of the single-sided copper-clad laminate (the copper foil forming side is the lower side) The wiring lower layer 4 can be formed by spraying the etching solution from the above. That is, the wiring lower layer 4 is also miniaturized similarly to the wiring upper layer 3. Therefore, since the multilayer wiring board 21 obtained here is a laminate of single-sided wiring boards whose wiring layers are miniaturized, the wiring layers are further finer than the wiring layers of the double-sided wiring boards.

  Next, as shown in FIG. 10, after placing one resin core metal ball 9 at the opening position of the blind via hole 19, the resin core metal ball 9 is formed using the pressure upper plate 14 and the pressure lower plate 15. Press-fit into the blind via hole 19. Thereby, the press-fit deformation of the resin core metal ball 9 is started. Then, the entire resin core metal ball 9 is press-fitted into the blind via hole 19, so that the resin core metal ball 9 is formed as a conductor 6 press-fitted into the blind via hole 19 as shown in FIG. 3 and the wiring lower layer 4 are formed, and a multilayer FPC 200 excellent in miniaturization of the wiring layer is obtained.

  Here, in the resin core metal ball 9 press-fitted into the blind via hole 19, the diameter of the resin ball 7 in the core portion of the resin core metal ball 9 is set smaller than the opening diameter of the blind via hole 19. Further, the metal layer 8 on the surface of the resin core metal ball 9 is made of a soft metal such as a solder alloy, copper, or copper alloy as in the case of the first embodiment. As the entire resin core metal ball 9, the diameter of the resin core metal ball 9 is larger than the opening diameter of the blind via hole 19, and the volume of the resin core metal ball 9 is larger than the opening volume of the blind via hole 19. Is also considered large. The effect by these is the same as that of the first embodiment described above.

  In this embodiment, the conductor 6 (resin core metal ball 9) for interlayer connection is press-fitted into the blind via hole 19 having the wiring lower layer 4 on the bottom surface. For this reason, compared with the case where the conductor 6 (resin core metal ball 9) for interlayer connection is press-fitted into the through hole, the bonding area between the conductor 6 and the wiring layer is increased, and the adhesion strength between them is also increased. . Therefore, even when various external stresses are applied, the bonding interface between the wiring layer and the conductor 6 is not peeled off, and it is possible to obtain higher connection reliability.

  In the manufacturing method of the multilayer FPC according to the second embodiment as described above, the single-sided wiring board is laminated, so that the wiring layer becomes finer than when the double-sided wiring board is used. Furthermore, since the resin core metal ball 9 is press-fitted and deformed to press-fit the conductor 6 into the blind via hole 19, it is compared with the case where the resin core metal ball 9 is press-fitted and deformed into the through hole 5 to press-fit the conductor 6. Thus, higher connection reliability between the wiring layers can be obtained. Therefore, also in this embodiment, the connection reliability between the wiring layers is high, and a multilayer FPC optimal for miniaturization of the wiring layers can be obtained with high productivity.

(Embodiment 3)
In the third embodiment, a multilayer FPC according to an embodiment of the present invention in which the multilayer FPC described above is further laminated will be described. 15 is a cross-sectional view of the main part of the multilayer FPC after lamination in one embodiment of the present invention, and FIG. 16 is a cross-sectional view of the main part of another multilayer FPC after lamination in one embodiment of the present invention.

  First, in FIG. 15, reference numeral 300 denotes the two multilayer FPCs 100 a and 100 b manufactured in the first embodiment described above and the multilayer FPC 200 a manufactured in the second embodiment described above via the adhesive layer 23 and the adhesive layer 24. It is a multilayer FPC that is laminated. Here, in the multilayer FPC 300, the multilayer FPCs 100a and 100b and the multilayer FPC 200a, which are constituent materials, have high connection reliability between wiring layers and a fine wiring layer. Therefore, also in the multilayer FPC 300 in which the multilayer wiring is formed more than in the case of the first and second embodiments, the multilayer FPC having high connection reliability between the wiring layers and excellent in miniaturization of the wiring layer is realized. .

  In order to manufacture such a multilayer FPC 300, the two multilayer FPCs 100a and 100b manufactured in the above-described first embodiment are stacked via the adhesive layer 23 and bonded together. Further, the multilayer FPC in which the two multilayer FPCs 100a and 100b are stacked and the multilayer FPC 200a manufactured in the second embodiment described above are further stacked via the adhesive layer 24 and bonded together. Thereby, the multilayer FPC 300 having an increased number of wiring layers can be obtained. In addition, since the manufacturing method of multilayer FPC100a, 100b and multilayer FPC200a is the same as the above, detailed description is abbreviate | omitted here. Alternatively, the multilayer FPC 100a may be bonded after the multilayer FPC 100b and the multilayer FPC 200a are bonded.

  In FIG. 16, reference numeral 400 denotes the two multilayer FPCs 100 c and 100 d manufactured in the first embodiment described above and the multilayer FPC 200 b manufactured in the second embodiment described above via the adhesive layer 23 and the adhesive layer 24. It is a multilayer FPC laminated so that each conductor 6 contacts. Here, in the multilayer FPC 400, the multilayer FPCs 100c and 100d, which are constituent materials, and the multilayer FPC 200b have high connection reliability between wiring layers and a fine wiring layer. Therefore, also in the multilayer FPC 400 in which the multilayer wiring is made even more than in the case of the first and second embodiments, a multilayer FPC having high connection reliability between the wiring layers and excellent in miniaturization of the wiring layer is realized. . Since the surface of the conductor 6 is a metal layer, adjacent wiring layers can be connected in the multilayer FPCs 100c and 100d and the multilayer FPC 200b.

  In order to manufacture such a multilayer FPC 400, the conductors 6 (100c) and 6 (100d) are brought into contact with the two multilayer FPCs 100c and 100d manufactured in the first embodiment through the adhesive layer 23. Laminate and paste together. Further, the multilayer FPC obtained by laminating the two multilayer FPCs 100c and 100d and the multilayer FPC 200b manufactured in the second embodiment described above are electrically connected to the conductor 6 (100d) of the multilayer FPC 100d and the multilayer FPC 200b via the adhesive layer 24. It laminates | stacks further so that the body 6 (200b) may contact, and it bonds together. Thereby, the multilayer FPC 400 with an increased number of wiring layers can be obtained. Here, since the surface of the conductor 6 is a metal layer, adjacent wiring layers can be easily connected in the multilayer FPCs 100c and 100d and the multilayer FPC 200b.

  In addition, since the manufacturing method of multilayer FPC100c, 100d and multilayer FPC200b is the same as the above, detailed description is abbreviate | omitted here. Alternatively, the multilayer FPC 100c may be bonded after the multilayer FPC 100d and the multilayer FPC 200b are bonded. Furthermore, in this manufacturing method, when a resin core metal ball in which solder or solder alloy is arranged on the surface of the conductor 6 (100c), 6 (100d), 6 (200b) is used, the conductor 6 (100c) , 6 (100d) and 6 (200b) are heated and cooled while being brought into contact with each other, so that the solder or solder alloy on the surfaces of the conductors 6 (100c), 6 (100d) and 6 (200b) is melted and solidified. Thus, the conductors 6 (100c), 6 (100d), and 6 (200b) can be easily joined to each other, and the connection reliability can be improved.

  The multilayer FPCs 300 and 400 according to the present embodiment obtained as described above are formed by further laminating multilayer FPCs having high connection reliability and fine wiring layers. High and excellent in miniaturization of the wiring layer. Furthermore, since the conductor is also used for the interlayer connection of the multilayer FPC, a new productivity is obtained without newly using an interlayer connection material. Therefore, also according to the present embodiment, it is possible to obtain a multi-layer FPC that has high connection reliability between wiring layers, is optimal for miniaturization of wiring layers, and is excellent in productivity.

  According to the present invention, it is possible to provide a multi-layer FPC having a high connection reliability, optimal for miniaturization of a wiring layer, and having an interlayer connection between wiring layers excellent in productivity, and a manufacturing method thereof.

Sectional drawing of the principal part of the multilayer FPC in one embodiment of this invention Sectional drawing of the principal part of the double-sided copper clad laminated board which is a component of the multilayer FPC in one embodiment of this invention Sectional drawing of the principal part of the double-sided wiring board in which the wiring layer in one embodiment of this invention was formed Sectional drawing of the principal part of the double-sided wiring board in which the through-hole in one embodiment of this invention was formed Sectional drawing of the principal part of the double-sided wiring board at the time of the press injection start of the resin core metal ball in one embodiment of the present invention Sectional drawing of the principal part of the double-sided wiring board in the middle of press-fitting deformation of the resin core metal ball in one embodiment of the present invention Sectional drawing of the principal part of the double-sided wiring board at the time of completion | finish of press injection deformation of the resin core metal ball in one embodiment of this invention Sectional drawing of the principal part of multilayer FPC after the interlayer connection in one embodiment of this invention Sectional drawing of the principal part of multilayer FPC after the interlayer connection in one embodiment of this invention Sectional drawing of the principal part of multilayer FPC after the interlayer connection in one embodiment of this invention Sectional drawing of the principal part of the single-sided copper clad laminated board with the adhesive layer which is a component of the multilayer FPC in one embodiment of this invention Sectional drawing of the principal part of the single-sided wiring board with the adhesive layer in which the wiring layer in one embodiment of this invention was formed Sectional drawing of the principal part of the single-sided wiring board with an adhesive layer in which the through-hole in one embodiment of this invention was formed Sectional drawing of the principal part at the time of the press injection of the resin core metal ball into the multilayer wiring board in which the blind via hole is formed in one embodiment of the present invention Sectional drawing of the principal part of multilayer FPC after lamination in one embodiment of the present invention Sectional drawing of the principal part of the other multilayer FPC after lamination in one embodiment of the present invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 2 Insulating layer 3 Wiring upper layer 4 Wiring lower layer 5 Through-hole 6 Conductor 7 Resin ball 8 Metal layer 9 Resin core metal ball 10 Double-sided copper clad laminated board 11 Copper foil 12 Double-sided wiring board 13 Punching die 14 Pressure upper plate 15 Addition Reduction plate 16 Single-sided copper-clad laminate with adhesive layer 17 Adhesive layer 18 Single-sided wiring board with adhesive layer 19 Blind via hole 20 Single-sided wiring board 21 Multilayer wiring board 23 Adhesive layer 24 Adhesive layer 25 Single-sided wiring board 26 Single-sided wiring board 27 Adhesive layer 28 Double-sided wiring board 100 Multi-layer FPC
100a multilayer FPC
100b Multi-layer FPC
100c multilayer FPC
100d multilayer FPC
200 Multi-layer FPC
200a Multi-layer FPC
200b Multi-layer FPC
300 Multi-layer FPC
400 multilayer FPC

Claims (9)

In a multilayer flexible printed wiring board having a wiring board comprising an insulating layer, a wiring layer formed on the front and back surfaces of the insulating layer, and a hole connecting the wiring layers through the insulating layer,
A multi-layer flexible, comprising: a resin ball having a diameter smaller than the hole diameter of the hole; and a metal layer covering the resin ball, and a conductive member that is press-fitted into the hole and electrically connects the wiring layer. Printed wiring board. The multilayer flexible printed wiring board according to claim 1, wherein the metal layer includes at least one of a solder alloy, copper, and a copper alloy. 2. The multilayer flexible printed wiring board according to claim 1, wherein the wiring board is a double-sided wiring board in which the wiring layer is directly formed on the front and back surfaces of the insulating layer. 2. The wiring board according to claim 1, wherein two single-sided wiring boards each having a wiring layer provided on one surface of an insulating layer are bonded together with an adhesive layer so that the wiring layer is on the outside. The multilayer flexible printed wiring board described. In the wiring board, a first wiring layer is formed on one surface of a first insulating layer, and a first single-sided wiring board having the holes and a second wiring layer are formed on one surface of a second insulating layer. The second single-sided wiring board formed is bonded to the first insulating layer and the second wiring layer through an adhesive layer so as to face each other to form a blind via hole. The multilayer flexible printed wiring board according to claim 1. A multilayer flexible printed wiring board comprising a plurality of the multilayer flexible printed wiring boards according to claim 1 laminated. A wiring board forming step of forming a wiring board provided with a wiring layer on the front and back surfaces of the insulating layer;
A through hole forming step of forming a through hole for connecting the wiring layer in the thickness direction of the wiring board;
A resin core metal ball in which a resin ball having an outer diameter smaller than the hole diameter of the through hole is covered with a metal layer is press-fitted into the through hole, and a wiring layer provided on the front and back surfaces of the insulating layer is formed into the resin core. A conduction step of conducting with a metal ball;
A method for producing a multilayer flexible printed wiring board, comprising: The wiring board forming step
A single-sided wiring board forming step of forming two single-sided wiring boards provided with a wiring layer on one surface of the insulating layer;
A bonding step of bonding the two single-sided wiring boards through an adhesive layer so that the wiring layer is on the outside;
The manufacturing method of the multilayer flexible printed wiring board of Claim 7 characterized by the above-mentioned. A first wiring layer is formed on one surface of the first insulating layer to form a first single-sided wiring board, and a second wiring layer is formed on one surface of the second insulating layer to form a second single-sided wiring board A single-sided wiring board forming step to form
A through hole forming step of forming a through hole for connecting the first wiring layer and the second wiring layer in the thickness direction of the first single-sided wiring board;
With the first insulating layer and the second wiring layer facing each other, the first single-sided wiring board and the second single-sided wiring board are bonded together via an adhesive layer, and the through hole and the first wiring layer are bonded together. A bonding step of forming a blind via hole with two wiring layers;
A resin core metal ball in which a resin ball having an outer diameter smaller than the opening diameter of the blind via hole is pressed into the blind via hole is press-fitted, and the first wiring layer and the second wiring layer are pressed. And a conduction step for conducting the resin core metal balls,
A method for producing a multilayer flexible printed wiring board, comprising:

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