JP4794975B2 - Build-up base material for multilayer flexible circuit board and method for producing multilayer flexible circuit board using the base material - Google Patents

Description

  The present invention relates to a structure of a build-up type multilayer flexible circuit board and a manufacturing method thereof, and more particularly to a multilayer flexible circuit board using a build-up base material having conductive protrusions.

  In recent years, miniaturization and high functionality of electronic devices have been promoted more and more, and therefore, there is an increasing demand for higher density of circuit boards. Therefore, the circuit board is made to be a high-density circuit board by changing the circuit board from one side to both sides, or a multilayer flexible circuit board having three or more layers.

  As part of this, a multilayer flexible circuit board that has a flexible cable part that integrates a flexible wiring board and a flexible flat cable that connect a multilayer flexible circuit board and a hard circuit board on which various electronic components are mounted via a connector or the like. However, it is widespread mainly in small electronic devices such as mobile phones.

  The typical structure of a general multilayer flexible circuit board is to use a double-sided or single-sided circuit board as the inner layer, stack the circuit board that is the outer layer on it, integrate it by heating and pressurizing, and then through holes A structure obtained by applying electrical connection between wiring layers by dawning and plating is common.

  However, in the above method, it is necessary to perform a plating process in order to obtain an electrical interlayer connection. The plating process has the disadvantage that the yield of the plating process itself is poor, the process for conducting the interlayer insulating resin layer is complicated, the stable management of the plating process is difficult, and the conductor thickness varies. Have. As a result, the problem of ensuring the flatness of the surface layer and the reliability of the plating treatment with respect to the drilled portion is raised as a problem. The variation in thickness directly affects the circuit formation capability, which is disadvantageous for high-density surface mounting.

  Therefore, in the method shown in Patent Document 1 (refer to claims 1 to 12), conductive protrusions are formed on the copper layer by etching, the conductive protrusions are inserted through the interlayer insulating resin, and sequentially stacked. A method of integration is shown.

  In this method, the electrical interlayer connection between the circuit board serving as the inner layer and the build-up base material having conductive protrusions is obtained by integrating the conductive protrusions and the circuit board serving as the inner layer by heating and pressing. Therefore, plating is not necessary.

  Since plating is not required, the thickness of the metal layer can be obtained stably, the flatness of the multilayer flexible circuit board after lamination can be ensured, and the copper thickness of the surface layer can be stabilized for circuit formation. The advantage is not only that the reliability of the metal part that obtains conduction is ensured, but also that the volume of the metal in the conduction part is relatively large, so that the capacity is electrically large.

  25 to 32 are cross-sectional process diagrams illustrating a method for manufacturing a multilayer flexible circuit board using the conductive protrusions described in Patent Document 1 (see claims 1 to 12) by connection using the conductive protrusions.

  First, as shown in FIG. 25A, a metal substrate 204 having a three-layer structure of a thick copper layer 201 / etching stopper layer 202 made of nickel or the like / a thin copper layer 203 is prepared. Although it is possible to use a metal base material having only a copper layer, it is possible to use a metal base material 204 having an etching stopper layer 202 made of nickel or the like in order to form a conductive protrusion having a stable shape. desirable.

  Next, as shown in FIG. 25 (2), the copper layer 201 and the copper layer 203 of the metal substrate 204 are protected by a photoresist film 205. Next, as shown in FIG. 25 (3), a resist pattern 206 is selectively formed on the copper layer 201 to be a surface on which conductive protrusions to be the opposite surface are formed.

  Subsequently, as shown in FIG. 25 (4), conductive protrusions 207 are formed on the copper layer 203 by a selective etching method. At this time, about 80 to 90% of the total thickness of the copper layer 201 is etched using an etching solution used in a normal copper etching process, for example, an etching solution containing cupric chloride, and then corrosive to nickel. Therefore, an etching solution that selectively etches copper, for example, an alkaline etching solution containing ammonia is used, and the remaining portion of the copper layer 201 is removed by etching to expose the nickel layer 202.

  Thereafter, as shown in FIG. 26 (5), the photoresist 205 and the resist pattern 206 are removed. Next, as shown in FIG. 26 (6), the nickel is exposed to the surface by using an etching solution that has low corrosiveness to copper and selectively etches nickel, for example, an etching solution containing hydrogen peroxide or nitric acid. By removing the layer 202 by etching, the structure shown in FIG. The diameter of the top of the conductive protrusion 207 can be selected from about 100 to 500 μm, and is preferably 200 μm or less.

  Next, as shown in FIG. 26 (7), a B-stage prepreg 209 and a release sheet 210 are attached to the surface on which the conductive protrusions 207 are formed by a press, a laminator, or the like. Instead of the prepreg 209, an insulating resin having adhesiveness such as a polyimide resin having a thermoplastic polyimide resin on both surfaces can be used.

  Subsequently, as shown in FIG. 26 (8), in order to expose the top portions 211 of the conductive protrusions from the release sheet 210, mechanical polishing such as roll polishing or chemical polishing such as CMP is performed. Up to this step, a structure in which the conductive protrusion 207 penetrates the release sheet 210 is obtained. Thereafter, as shown in FIG. 27 (9), the release sheet 210 is removed to obtain a buildup base material 212 in which the conductive protrusions 207 penetrate the prepreg 209.

  Next, as shown in FIG. 27 (10), a so-called double-sided copper-clad plate 216 having conductive layers 214 and 215 such as copper layers on both sides of a flexible insulating base material 213 such as polyimide resin is prepared. Next, as shown in FIG. 27 (11), a circuit pattern is formed on the conductive layers 214 and 215 of the double-sided copper-clad plate 216 using an etching method or the like by a normal photofabrication method, and the inner layer circuit 217 is formed. Form.

  Subsequently, as shown in FIG. 27 (12), the cover film 220 is formed by laminating the polyimide resin 218 to the inner layer circuit 217 through the adhesive 219 to obtain an inner layer circuit board.

  Thereafter, as shown in FIG. 28 (13), a so-called single-sided copper-clad plate 224 having a conductive layer 223 such as copper foil on one side of a flexible insulating base material 222 and a desired shape by a mold or the like. An adhesive 225 for bonding to the inner circuit board shown in FIG. 27 (12) is prepared.

  Next, as shown in FIG. 28 (14), a single-sided copper-clad plate 224 and an adhesive 225 are bonded together and punched into a desired shape with a mold or the like to obtain a single-sided copper-clad plate 226 with an adhesive. Next, as shown in FIG. 28 (15), the single-sided copper-clad plate 226 with an adhesive shown in FIG. 28 (14) is laminated on the inner layer circuit board shown in FIG. 28 (13) with an adhesive 222 interposed therebetween.

  Subsequently, as shown in FIG. 29 (16), a conduction hole 227 is formed by an NC drill or the like. At this time, the polyimide resin 218 and the adhesive 219 of the cover film 220 of the inner layer cause thermal sagging during drilling, and the area around the inner layer circuit 217 with through-hole plating deteriorates, so desmear processing is performed. Thereafter, as shown in FIG. 29 (17), the conductive hole 227 is subjected to electroless plating or conductive treatment, and then a through hole 228 is formed by electroplating.

  Next, as shown in FIG. 30 (18), a circuit pattern 229 is formed on the through-hole surface by using an etching method based on a normal photofabrication method to become an inner layer of a build-up type multilayer flexible circuit board. A core substrate 230 is obtained.

  Next, as shown in FIG. 31 (19), the build-up base material 212 obtained in FIG. 15 (9) is prepared, and the surface of the conductive protrusion 207 of the build-up base material 212 is formed on the core substrate 230 as the inner layer. Let them face each other.

  Finally, as shown in FIG. 32 (20), lamination is performed by heating and pressing, and the build-up base material 212 is laminated on the core substrate as the inner layer. Thereafter, surface treatment such as formation of a photo solder resist layer, solder plating, nickel plating, gold plating, or the like is performed on the substrate surface as necessary, and outer shape processing is performed to obtain the multilayer flexible circuit board 231.

  However, as shown in FIG. 26, when an electrical connection between the build-up base material having conductive protrusions and the inner circuit board layer is obtained, the connection between the build-up base material having conductive protrusions and the inner circuit board is provided. For reliability, it is necessary to apply pressure to the conductive protrusions depending on the heating and pressing conditions. The total thickness of the core substrate, the hardness of the interlayer insulating resin used for the core substrate, the presence or absence of conductive protrusions, and the arrangement of the conductive protrusions Depending on the density, the core substrate may be deformed.

  For example, when building up using a build-up base material having conductive protrusions on a multilayer flexible circuit board, if the circuit board as the inner layer is made of a soft constituent material such as a resin film, it has conductive protrusions. After the build-up base material is laminated, distortion to the wiring pattern of the core substrate and generation of cracks become problems.

  Therefore, as a countermeasure to the problem, in the method shown in Patent Document 2 (see claims 1 to 8), at least a part of the bonding surface of the wiring pattern is covered with a reinforcing layer made of a conductive paste for preventing the deformation of the wiring pattern. There has been proposed a method for preventing deformation to a substrate serving as an inner layer when forming and laminating using a build-up base material having conductive protrusions.

  However, when a conductive paste reinforcing layer is formed by coating, there are disadvantages in that the process of forming the conductive paste is increased, the thickness of the conductive paste reinforcing layer is difficult to control, and there is a variation in thickness. Since the conductive paste is formed by coating, there is a drawback that the filling property of the interlayer insulating resin is not uniform at the time of lamination.

Furthermore, when obtaining a connection between the conductive protrusion and the copper layer, the copper-copper bond cannot be obtained by using a conductive paste, and the connection reliability between the conductive protrusion and the copper layer is lower than that of the copper-copper bond. The fault which falls and the fault which a conductor resistance value rises are also mentioned. For this reason, in the solution according to Patent Document 2 (see claims 1 to 8), in addition to being unable to completely solve the conventional problem, a new problem is generated.
JP 2002-141629 A Japanese Patent No. 3334004

  For these reasons, in a multilayer flexible circuit board that uses a build-up base material having conductive protrusions, a manufacturing method that can prevent distortion and cracks in the wiring pattern of the core board is desired.

  In the multilayer flexible circuit board using a build-up base material having conductive protrusions, the present invention achieves both ensuring of conduction reliability due to the conductive protrusions and suppressing distortion and cracking of the core board wiring pattern. It is an object of the present invention to provide a build-up base material for a multilayer flexible circuit board that can be made, and a method for stably and inexpensively manufacturing such a multilayer flexible circuit board.

  In order to achieve the above object, the present invention provides the following inventions.

The first invention is
In a build-up base material for a multilayer flexible circuit board in which a multilayer flexible circuit board is connected between layers by conductive protrusions made of metal , a concave portion is provided on the top of the conductive protrusion.

The second invention is
The contact area between the concave portion formed on the top of the conductive projection and the flexible substrate as the inner layer, and the concave portion formed on the top of the conductive projection by the portion where the conductive projection is erected in the first invention It is characterized by having different depths.

The third invention is
In a method for manufacturing a multilayer flexible circuit board that performs interlayer connection using a build-up base material for a multilayer flexible circuit board having conductive protrusions made of metal,
Prepare a build-up base material for a multilayer flexible circuit board having a recess at the top of the conductive protrusion,
Prepare a core substrate made in a separate process,
Laminating the multilayer flexible circuit board build-up substrate on the core substrate,
It is characterized by that.

  Due to these features, the present invention has the following effects.

  According to the present invention, a core substrate is formed by using a build-up base material in which a recess is formed at the top of a conductive protrusion, and the contact area of the conductive protrusion that secures conduction during build-up and the depth of the recess are processed. The contact between the conductive protrusions and the total pressure applied from the top of the conductive protrusions can be reduced.As a result, not only ensuring stable reliability of the interlayer connection, but also distortion to the wiring pattern of the core substrate, It becomes possible to suppress the occurrence of cracks.

  As a result, according to the present invention, it is possible to provide a method for stably and inexpensively manufacturing a multilayer flexible circuit board using conductive protrusions as build-up base materials, which has been difficult with the conventional manufacturing method.

  Hereinafter, an embodiment of a method according to the present invention will be described with reference to FIGS. 1 to 23, and an embodiment of a build-up substrate according to the present invention will be described with reference to FIG.

Embodiment 1

  1 to 3 are sectional process views showing Embodiment 1 of the present invention.

  First, as shown in FIG. 1 (1), a thick copper layer 1 (for example, 100 μm in thickness) / an etching stopper layer 2 (for example, 2 μm in thickness) made of nickel, etc./a thin copper layer 3 (for example, 18 μm in thickness) A metal substrate 4 having a three-layer structure is prepared. Although it is possible to use a metal substrate having only a copper layer, it is possible to use a metal substrate 4 having an etching stopper layer 2 made of nickel or the like in order to form a conductive protrusion having a stable shape. desirable.

  Next, as shown in FIG. 1 (2), the copper layer 1 and the copper layer 3 of the metal substrate 4 are protected with a photoresist film 5. Subsequently, as shown in FIG. 1 (3), a resist pattern 6 is selectively formed on the copper layer 1 serving as a surface on which conductive protrusions that are opposite to the surface are formed.

  Thereafter, as shown in FIG. 1 (4), conductive protrusions 7 are formed on the copper layer 3 by using a selective etching method. At this time, about 80 to 90% of the total thickness of the copper layer 1 is etched using an etching solution used in a normal copper etching process, for example, an etching solution containing cupric chloride, and then corrosive to nickel. The remaining part of the copper layer 1 is removed by etching to expose the nickel layer 2 by using an etching solution that selectively etches copper, for example, an alkaline etching solution containing ammonia.

  Next, as shown in FIG. 2 (5), the photoresist 5 and the resist pattern 6 are removed. Next, as shown in FIG. 2 (6), the nickel layer exposed to the surface using an etchant that has low corrosiveness to copper and that selectively etches nickel, such as an etchant containing hydrogen peroxide or nitric acid. By removing 2 by etching, the structure shown in FIG. The diameter of the top portion of the conductive protrusion 7 can be selected from about 100 to 500 μm, and is preferably 200 μm or less.

  Subsequently, as shown in FIG. 2 (7), the prepreg 9 and the release sheet 10 in a B stage state are attached to the surface on which the conductive protrusions 7 are formed by a press, a laminator, or the like. Instead of the prepreg 9, an insulating resin having adhesiveness such as a polyimide resin having a thermoplastic polyimide resin on both surfaces can be applied.

  Thereafter, as shown in FIG. 2 (8), in order to expose the top portion 11 of the conductive protrusion from the release sheet 10, mechanical polishing such as roll polishing or chemical polishing such as CMP is performed. Through the steps so far, a structure in which the conductive protrusion 7 penetrates the release sheet 10 is obtained.

  Next, as shown in FIG. 3 (9), with respect to the shape of the conductive protrusion 7, for example, the conductive protrusion 7 (for example, the diameter of the top 150 μm), the shape of the recess provided on the top of the conductive protrusion 7 (for example, Then, the contact area is changed according to the diameter of the top (φ30 μm), and the conductive protrusion 12 is formed in which the shape obtained by changing the processing amount (for example, 50 μm) in the height direction of the conductive protrusion 7 becomes a recess. A means for forming the concave portion of the conductive protrusion 12 is not particularly limited, but the concave portion can be formed simultaneously with the formation of the conductive protrusion 7 by etching. By applying the etching method, it is possible to change the shape at the same time when forming the conductive protrusion 7, which is advantageous in terms of the number of steps and cost.

  In addition, means for irradiating a laser beam to form a recess is applicable, and examples of the laser include a carbon dioxide gas laser and an ultraviolet laser, but the influence of the heat history on the conductive protrusion 12 and the processability of the recess. Therefore, it is desirable to use an ultraviolet laser among lasers. The positional accuracy of the laser processing is high, and it can be processed sufficiently even after the conductive protrusion 12 is formed.

  In etching, the shape of the conductive protrusions 12 may change depending on the density of the conductive protrusions, but in the case of laser processing, stable processing is possible regardless of the density. The step of changing the shape of the conductive protrusion 7 can be selected according to the required shape of the conductive protrusion 12, and is not particularly limited.

  Further, the order of the steps for changing the shape of the conductive protrusion 12 is not particularly limited. For example, when a concave portion is formed in the conductive protrusion 7 using a laser beam, the release sheet 10 is also laminated, and after the prepreg 9 is polished, it is possible to reduce the influence of foreign matter generated by the polishing. . In addition, when priority is given to securing the electric capacity of the conductive portion over miniaturization of the wiring pattern to be formed, the size of the conductive protrusion 7 is increased.

  When the size of the conductive protrusion 7 changes and the hole formed in the concave portion of the conductive protrusion 12 becomes larger (for example, the top diameter φ130 μm), the concave portion of the conductive protrusion 12 combined with not only laser processing but also etching. Can also be processed. Moreover, it is also possible to form the recessed part of the top part of the electroconductive protrusion 12 by machining like a dicing saw.

  By combining such processing means, the concave portion is processed at the top of the conductive protrusion 12. Moreover, the shape of this recessed part is not specifically limited, The shape like the recessed parts 151-154 shown in FIG. 24 can be taken. Furthermore, the depth of the recess and the cross-sectional shape are not particularly limited.

  Next, as shown in FIG. 3 (10), the release sheet 10 is removed to obtain a buildup base material 13 in which the conductive protrusions 12 penetrate the prepreg 9.

Embodiment 2

  4 to 12 are sectional process views showing Embodiment 2 of the present invention.

  First, as shown in FIG. 4A, a thick copper layer 51 (for example, thickness 100 μm) / etching stopper layer 52 (for example, thickness 2 μm) made of nickel, etc./thin copper layer 53 (for example, thickness 18 μm) A metal substrate 54 having a three-layer structure is prepared. Although it is possible to use a metal substrate having only a copper layer, it is possible to use a metal substrate 54 having an etching stopper layer 2 made of nickel or the like in order to form a conductive protrusion having a stable shape. desirable.

  Next, as shown in FIG. 4 (2), the copper layer 51 and the copper layer 53 of the metal base 54 are protected with a photoresist film 55. Next, as shown in FIG. 4 (3), a resist pattern 56 is selectively formed on the copper layer 1 serving as a surface on which conductive protrusions which are opposite to the surface are formed.

  Subsequently, as shown in FIG. 4 (4), conductive protrusions 57 are formed on the copper layer 53 using a selective etching technique. At this time, about 80 to 90% of the total thickness of the copper layer 51 is etched using an etching solution used in a normal copper etching process, for example, an etching solution containing cupric chloride, and then corrosive to nickel. Therefore, an etching solution that selectively etches copper, for example, an alkaline etching solution containing ammonia is used, and the remaining portion of the copper layer 51 is removed by etching to expose the nickel layer 52.

  Thereafter, as shown in FIG. 5 (5), the photoresist 55 and the photoresist 56 are removed. Next, as shown in FIG. 5 (6), the nickel is exposed to the surface using an etchant that has low corrosiveness to copper and that selectively etches nickel, such as an etchant containing hydrogen peroxide or nitric acid. By removing the layer 52 by etching, the structure shown in FIG. The diameter of the top of the conductive protrusion 57 can be selected from about 100 to 500 μm, and is preferably 200 μm or less.

  Next, as shown in FIG. 5 (7), a prepreg 59 and a release sheet 60 in a B-stage state are attached to the surface on which the conductive protrusions 57 are formed using a press, a laminator, or the like. Instead of the prepreg 59, an insulating resin having adhesiveness such as a polyimide resin having a thermoplastic polyimide resin on both surfaces can be applied.

  Subsequently, as shown in FIG. 5 (8), in order to expose the top portion 61 of the conductive protrusion from the release sheet 60, mechanical polishing such as roll polishing or chemical polishing such as CMP is performed. Through the steps so far, a structure in which the conductive protrusion 57 penetrates the release sheet 60 is obtained.

  Thereafter, as shown in FIG. 6 (9), the shape of the conductive protrusion 57, for example, the conductive protrusion 57 (for example, the diameter of the top 150 μm), the shape of the recess of the conductive protrusion 57 (for example, the diameter of the top). The contact area is changed by (φ30 μm), and the conductive protrusions 62 whose recesses are formed by changing the processing amount in the height direction of the conductive protrusions 57 (for example, 50 μm) are formed. The means for forming the concave portion of the conductive protrusion 62 is not particularly limited, but the concave portion can be formed simultaneously with the formation of the conductive protrusion 57 by etching.

  By applying the etching method, it is possible to change the shape in a lump when forming the conductive protrusions 57, which is advantageous in terms of the number of steps and cost. In addition, means for irradiating a laser beam to form a recess is also applicable, and examples of the laser include a carbon dioxide gas laser and an ultraviolet laser, but the influence of the thermal history on the conductive protrusion 62, the processability of the recess. Therefore, it is desirable to use an ultraviolet laser among lasers. The positional accuracy of the laser is high, and it can be sufficiently processed even after the conductive protrusion 62 is formed.

  In etching, the shape of the conductive protrusions 62 may change depending on the density of the conductive protrusions. However, when a laser is used, stable processing is possible regardless of the density. The step of changing the shape of the conductive protrusion 57 can be selected according to the shape of the conductive protrusion 62 required, and is not particularly limited. Further, the order of the steps for changing the shape of the conductive protrusion 62 is not particularly limited.

  For example, when forming a recess in the conductive protrusion 57 using a laser, it is possible to reduce the influence of foreign matter generated by polishing if the release sheet 60 is also laminated and the prepreg 59 is polished. In addition, when priority is given to securing the electric capacity of the conductive portion over miniaturization of the wiring pattern to be formed, the size of the conductive protrusion 7 is increased. When the size of the conductive protrusion 7 changes and the hole formed in the concave portion of the conductive protrusion 62 becomes larger (for example, the top diameter φ130 μm), the concave portion of the conductive protrusion 62 combined with etching as well as laser processing Can also be processed.

  It is also possible to form a concave portion at the top of the conductive protrusion 62 by machining such as a dicing saw. By combining such processing means, the shape of the concave portion at the top of the conductive protrusion 62 is processed. Moreover, the shape of this recessed part is not specifically limited, The shape like the recessed parts 151-154 shown in FIG. 24 can be taken. Furthermore, the depth of the recess and the cross-sectional shape are not particularly limited. Next, as shown in FIG. 6 (10), the release sheet 60 is removed to obtain a buildup substrate 63 in which the conductive protrusions 62 penetrate the prepreg 59.

  Next, as shown in FIG. 7 (11), a so-called double-sided copper-clad plate 67 having conductive layers 65 and 66 such as copper foil on both sides of a flexible insulating base material 64 such as polyimide resin is prepared. Subsequently, as shown in FIG. 7 (12), a circuit pattern is formed on the conductive layer 65 of the double-sided copper-clad plate 67 using an etching method or the like by a normal photofabrication method to form an inner layer circuit 68. .

  Thereafter, as shown in FIG. 7 (13), a cover film 71 is formed by laminating a polyimide resin 69 to the inner layer circuit 68 via an adhesive 70, thereby forming a double-sided copper clad plate 72 with a cover film.

  Next, as shown in FIG. 8 (14), a so-called single-sided copper-clad plate 75 having a conductive layer 74 such as a copper foil on one side of a flexible insulating base material 73 and a desired shape using a mold or the like. An adhesive 76 for bonding to the double-sided copper-clad plate 72 with a cover film shown in FIG. The thickness of the copper foil layer 74 at this time is 50 μm or less, and particularly preferably 35 μm or less.

  Next, as shown in FIG. 8 (15), the single-sided copper-clad plate 75 and the adhesive 76 are bonded together, and this is punched into a desired shape with a mold or the like to obtain a single-sided copper-clad plate 77 with an adhesive. Subsequently, as shown in FIG. 8 (16), the single-sided copper-clad plate 77 with adhesive shown in FIG. 8 (15) is laminated on the double-sided copper-clad plate 72 with cover film shown in FIG. To do.

  Thereafter, as shown in FIG. 9 (17), a conduction hole 78 is formed by an NC drill or the like. At this time, the polyimide resin 69 and the adhesive 70 of the inner layer cover film 71 cause heat sagging during drilling, and the surroundings with the through-hole plating on the conductive layers 65 and 66 of the inner layer circuit 68 are deteriorated. .

  Next, as shown in FIG. 9 (18), the electroconductive plating 78 is subjected to electroless plating or conductive treatment, and then a through hole 79 is formed by electroplating. The plating thickness of the through hole 79 at this time is preferably about 30 to 50 μm in order to ensure reliability.

  Next, as shown in FIG. 10 (19), a circuit pattern 80 is formed on the through-hole surface by using an etching method based on a normal photofabrication method to obtain a core substrate 81 of a multilayer flexible circuit board.

  Subsequently, as shown in FIG. 11 (20), the build-up base 63 obtained in FIG. 6 (10) is prepared, and the surface of the conductive protrusion 62 of the build-up base 63 faces the core substrate 81. Let me face you.

  Finally, as shown in FIG. 12 (21), lamination is performed by heating and pressing, and the build-up base 63 is laminated on the core substrate 82 as the inner layer. Thereafter, surface treatment such as formation of a photo solder resist layer, solder plating, nickel plating, and gold plating is performed on the substrate surface as necessary, and outer shape processing is performed to obtain the multilayer flexible circuit board 82.

Embodiment 3

  13 to 23 are sectional process views showing Embodiment 3 of the present invention.

  First, as shown in FIG. 13 (1), a thick copper layer 101 (for example, 100 μm in thickness) / etching stopper layer 102 (for example, 2 μm in thickness) made of nickel, etc./a thin copper layer 103 (for example, 18 μm in thickness) A metal substrate 104 having a three-layer structure is prepared. Although it is possible to use a metal substrate having only a copper layer, it is possible to use a metal substrate 104 having an etching stopper layer 102 made of nickel or the like in order to form a conductive protrusion having a stable shape. desirable.

  Next, as shown in FIG. 13 (2), the copper layer 101 and the copper layer 103 of the metal substrate 104 are protected by a photoresist film 105. Next, as shown in FIG. 13 (3), a resist pattern 106 is selectively formed on the copper layer 101 which is a surface on which conductive protrusions which are opposite to the surface are formed.

  Subsequently, as shown in FIG. 13 (4), conductive protrusions 107 are formed on the copper layer 103 by using a selective etching method. At this time, about 80 to 90% of the total thickness of the copper layer 101 is etched using an etching solution used in a normal copper etching process, for example, an etching solution containing cupric chloride, and then corrosive to nickel. Therefore, an etching solution that selectively etches copper, for example, an alkaline etching solution containing ammonia is used, and the remaining portion of the copper layer 101 is removed by etching to expose the nickel layer 102.

  Thereafter, as shown in FIG. 14 (5), the photoresist 105 and the resist pattern 106 are removed. Next, as shown in FIG. 14 (6), nickel is exposed to the surface by using an etchant that has low corrosiveness to copper and selectively etches nickel, for example, an etchant containing hydrogen peroxide or nitric acid. By removing the layer 102 by etching, the structure shown in FIG. The diameter of the top of the conductive protrusion 107 can be selected from about 100 to 500 μm, and is preferably 200 μm or less.

  Next, as shown in FIG. 14 (7), a B-stage prepreg 109 and a release sheet 110 are attached to the surface on which the conductive protrusions 107 are formed using a press, a laminator, or the like. Instead of the prepreg 109, an insulating resin having adhesive properties such as a polyimide resin having a thermoplastic polyimide resin on both sides can be used.

  Subsequently, as shown in FIG. 14 (8), in order to expose the top 111 of the conductive protrusion from the release sheet 110, mechanical polishing such as roll polishing or chemical polishing such as CMP is performed. Through the steps so far, a structure in which the conductive protrusion 107 penetrates the release sheet 110 is obtained.

  Thereafter, as shown in FIG. 15 (9), the shape of the conductive protrusion 107, for example, the shape of the recess of the conductive protrusion 107 (for example, the diameter of the top) with respect to the conductive protrusion 107 (for example, the diameter of the top 150 μm). The contact area is changed by φ30 μm), and the shape of the conductive protrusion 107 whose height is changed (for example, 50 μm) is a recess, and the shape of the recess of the conductive protrusion 107 (for example, the top) The contact area is changed depending on the diameter (φ50 μm), and the conductive protrusion 113 is formed in which the shape obtained by changing the processing amount (for example, 50 μm) in the height direction of the conductive protrusion 107 becomes a recess.

  The shape of the recesses of the obtained conductive protrusions 112 and 113 can be different depending on the layer structure and material of the inner layer of the circuit board that is laminated and becomes the inner layer. The means for forming the recesses of the conductive protrusions 112 and 113 is not particularly limited, but the recesses can be formed simultaneously with the formation of the conductive protrusions 107 by etching. By applying the etching method, it is possible to change the shape in a lump when forming the conductive protrusions 107, which is advantageous in terms of the number of steps and cost.

  In addition, a means for forming a recess by irradiating a laser beam can be applied. Examples of the laser include a carbon dioxide laser, an ultraviolet laser and the like. Considering processability, it is desirable to use an ultraviolet laser among lasers. The positional accuracy of the laser is high, and it can be sufficiently processed even after the conductive protrusions 112 and 113 are formed. In the etching, the shape of the conductive protrusions 113 and 114 may change depending on the density of the conductive protrusions. However, when a laser is used, stable processing is possible regardless of the density. The step of changing the shape of the conductive protrusions 112 and 113 can be selected according to the required shape of the conductive protrusions 112 and 113, and is not particularly limited.

  Further, the order of steps for changing the shapes of the conductive protrusions 112 and 113 is not particularly limited. For example, when forming recesses in the conductive protrusions 112 and 113 using a laser, it is possible to reduce the influence of foreign matter generated by polishing if the release sheet 110 is also laminated and the prepreg 109 is polished. Become.

  In addition, when priority is given to securing the electric capacity of the conductive portion over miniaturization of the wiring pattern to be formed, the size of the conductive protrusion 107 is increased. When the size of the conductive protrusion 107 changes and the hole formed in the concave portion of the conductive protrusions 112 and 113 becomes larger (for example, the diameter of the top portion is 130 μm), the conductive protrusion 112 combined with etching as well as laser processing. , 113 can be processed.

  It is also possible to form a concave portion at the top of the conductive protrusion 107 by machining such as a dicing saw. By combining such processing means, the shape of the concave portion at the top of the conductive protrusion 107 is processed. Moreover, the shape of this recessed part is not specifically limited, The shape like the recessed parts 151-154 shown in FIG. 24 can be taken. Furthermore, the depth of the recess and the cross-sectional shape are not particularly limited.

  Next, as shown in FIG. 15 (10), the release sheet 110 is removed to obtain a buildup substrate 114 in which the conductive protrusions 112 and 113 penetrate the prepreg 109.

  Next, as shown in FIG. 16 (11), a so-called double-sided copper-clad plate 118 having conductive layers 116 and 117 such as copper foil on both surfaces of a flexible insulating base material 115 such as polyimide resin is prepared. Subsequently, as shown in FIG. 16 (12), a circuit pattern is formed on the conductive layers 116 and 117 of the double-sided copper-clad plate 118 using an etching method or the like by a normal photofabrication method, and the inner layer circuit 119 is formed. And

  Thereafter, as shown in FIG. 16 (13), a cover film 122 is formed by laminating a polyimide resin 120 to the inner layer circuit 119 via an adhesive 121, thereby forming a double-sided copper-clad plate 123 with a cover film.

  Next, as shown in FIG. 17 (14), a so-called single-sided copper-clad plate 126 having a conductive layer 125 such as copper foil on one side of a flexible insulating base material 124 and a desired shape by a mold or the like. An adhesive 127 for bonding to the double-sided copper-clad plate 123 with a cover film of FIG. The thickness of the copper foil layer 125 at this time is 50 μm or less, and particularly preferably 35 μm or less.

  Next, as shown in FIG. 17 (15), the single-sided copper-clad plate 126 and the adhesive 127 are bonded together and punched into a desired shape using a mold or the like to obtain a single-sided copper-clad plate 128 with an adhesive. Next, as shown in FIG. 17 (16), the single-sided copper-clad plate 128 with adhesive of FIG. 17 (15) is laminated on the double-sided copper-clad plate with cover film 123 of FIG. 16 (13) through the adhesive 127. To do.

  Thereafter, as shown in FIG. 18 (17), a conduction hole 129 is formed by an NC drill or the like. At this time, the polyimide resin 120 of the inner layer cover film 122 and the adhesive 126 cause heat sagging during drilling, and the surroundings with the through-hole plating on the conductive layers 116 and 117 of the double-sided copper clad plate 123 with the cover film deteriorate. Therefore, desmear processing is performed.

  Next, as shown in FIG. 18 (18), the electroconductive plating 129 is subjected to electroless plating or conductive treatment, and then the through hole 130 is formed by electroplating. In this case, the plating thickness of the through hole 130 is preferably about 30 to 50 μm in order to ensure reliability.

  Next, as shown in FIG. 19 (19), a circuit pattern 131 is formed on the through-hole surface by using an etching method based on a normal photofabrication method, and the core that becomes the inner layer of the build-up type multilayer flexible circuit board A substrate 132 is obtained.

  Subsequently, as shown in FIG. 20 (20), a copper foil is provided on one side of a low-flow type prepreg (see Japanese Patent Laid-Open No. 2004-247761, claim 1) or an adhesive insulating resin 133 with a low flow-out such as a bonding sheet. A copper foil 135 with a prepreg having a conductive layer 134 such as is prepared. Thereafter, as shown in FIG. 20 (21), the copper foil 135 with prepreg is laminated on the core substrate 132 obtained in FIG. 19 (19).

  Next, as shown in FIG. 21 (22), a conduction hole 136 is formed by a laser or the like. Next, as shown in FIG. 21 (23), the conductive hole 136 is subjected to electroless plating or conductive treatment, and then a via hole 137 is formed by electroplating. A core substrate 138 with a build-up base material is obtained by applying a surface treatment such as formation of a solder resist layer, solder plating, nickel plating, gold plating and the like, and performing external processing.

  Subsequently, as shown in FIG. 22 (24), the buildup base material 115 obtained in FIG. 15 (10) is prepared, and the conductive protrusion 112 of the buildup base material 114 is formed on the core substrate 138 with the buildup base material. , 113 face to face each other.

  Finally, as shown in FIG. 23 (25), lamination is performed by heating and pressing, and the buildup base material 114 is laminated on the core substrate 138 with the buildup base material. Thereafter, a surface treatment such as formation of a photo solder resist layer, solder plating, nickel plating, gold plating, or the like is performed on the surface of the substrate as necessary, and outer shape processing is performed to obtain a multilayer flexible circuit board 139.

1 is a conceptual cross-sectional configuration diagram illustrating Embodiment 1 of the present invention. 1 is a conceptual cross-sectional configuration diagram illustrating Embodiment 1 of the present invention. 1 is a conceptual cross-sectional configuration diagram illustrating Embodiment 1 of the present invention. The conceptual cross-sectional block diagram which shows Embodiment 2 of this invention. The conceptual cross-sectional block diagram which shows Embodiment 2 of this invention. The conceptual cross-sectional block diagram which shows Embodiment 2 of this invention. The conceptual cross-sectional block diagram which shows Embodiment 2 of this invention. The conceptual cross-sectional block diagram which shows Embodiment 2 of this invention. The conceptual cross-sectional block diagram which shows Embodiment 2 of this invention. The conceptual cross-sectional block diagram which shows Embodiment 2 of this invention. The conceptual cross-sectional block diagram which shows Embodiment 2 of this invention. The conceptual cross-sectional block diagram which shows Embodiment 2 of this invention. The conceptual cross-sectional block diagram which shows Embodiment 3 of this invention. The conceptual cross-sectional block diagram which shows Embodiment 3 of this invention. The conceptual cross-sectional block diagram which shows Embodiment 3 of this invention. The conceptual cross-sectional block diagram which shows Embodiment 3 of this invention. The conceptual cross-sectional block diagram which shows Embodiment 3 of this invention. The conceptual cross-sectional block diagram which shows Embodiment 3 of this invention. The conceptual cross-sectional block diagram which shows Embodiment 3 of this invention. The conceptual cross-sectional block diagram which shows Embodiment 3 of this invention. The conceptual cross-sectional block diagram which shows Embodiment 3 of this invention. The conceptual cross-sectional block diagram which shows Embodiment 3 of this invention. The conceptual cross-sectional block diagram which shows Embodiment 3 of this invention. The conceptual cross-section block diagram which shows the planar shape of the electroconductive protrusion by Embodiment 1 thru | or 3 of this invention. The conceptual cross-sectional block diagram of the manufacturing method of the multilayer flexible circuit board which has the electroconductive protrusion by a conventional construction method. The conceptual cross-sectional block diagram of the manufacturing method by a conventional construction method similarly. The conceptual cross-sectional block diagram of the manufacturing method by a conventional construction method similarly. The conceptual cross-sectional block diagram of the manufacturing method by a conventional construction method similarly. The conceptual cross-sectional block diagram of the manufacturing method by a conventional construction method similarly. The conceptual cross-sectional block diagram of the manufacturing method by a conventional construction method similarly. The conceptual cross-sectional block diagram of the manufacturing method by a conventional construction method similarly. The conceptual cross-sectional block diagram of the manufacturing method by a conventional construction method similarly.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Thick copper layer 2 Stopper layer 3 made of nickel, etc. Thin copper layer 4 Metal substrate 5 Photoresist film 6 Resist pattern 7 Conductive protrusion 8 Circuit substrate 9 Prepreg 10 Release sheet 11 Top portion 12 of conductive protrusion is processed Conductive protrusion 13 that has become a recess Build-up base 51 Thick copper layer 52 Stopper layer 53 made of nickel, etc. Thin copper layer 54 Metal base 55 Photoresist film 56 Resist pattern 57 Conductive protrusion 58 Circuit base 59 Prepreg 60 Peeling Sheet 61 Top part 62 of conductive protrusions Conductive protrusion 63 whose top part is processed into a concave part Build-up base 64 Flexible insulating base material 65 Copper foil 66 Copper foil 67 Double-sided copper-clad board 68 Inner layer circuit 69 Polyimide resin 70 Adhesion Agent 71 Cover film 72 Inner layer circuit board 73 Flexible insulating base material 74 Copper foil 75 Single-sided copper Plate 76 Adhesive 77 Single-sided copper-clad plate with adhesive 78 Conductive hole 79 Through hole 80 Circuit pattern 81 Core substrate 82 Multilayer flexible circuit substrate 101 Thick copper layer 102 Stopper layer 103 made of nickel, etc. Thin copper layer 104 Metal base material 105 Photoresist film 106 Resist pattern 107 Conductive protrusion 108 Circuit base material 109 Prepreg
110 Peeling sheet 111 Top part 112 of conductive protrusions Conductive protrusion 113 processed into a concave part by processing the top part Conductive protrusion 114 processed into a concave part from the top part 114 Build-up base material 115 Flexible insulating base material 116 Copper foil 117 Copper Foil 118 Double-sided copper-clad plate 119 Inner layer circuit 120 Polyimide resin 121 Adhesive 122 Cover film 123 Inner-layer circuit board 124 Flexible insulating base material 125 Copper foil 126 Single-sided copper-clad plate 127 Adhesive 128 Single-sided copper-clad plate 129 with adhesive Through-hole 130 Through-hole 131 Circuit pattern 132 Core substrate 133 Prepreg 134 Copper foil 135 Copper foil with prepreg 136 Conductive hole 137 Via hole 138 Core substrate with build-up base 139 Multilayer flexible circuit board 151 Shape of recess at top of conductive protrusion 152 Concave on top of conductive protrusion Shape 153 Shape of recess at the top of the conductive protrusion 154 Shape of recess at the top of the conductive protrusion 201 Thick copper layer 202 Stopper layer 203 made of nickel, etc. Thin copper layer 204 Metal substrate 205 Photoresist film 206 Resist pattern 207 Conductivity Protrusion 208 Circuit Base 209 Prepreg
210 Release sheet 211 Top portion 212 of conductive protrusion 212 Build-up base material 213 Flexible insulating base material 214 Copper foil 215 Copper foil 216 Double-sided copper-clad plate 217 Inner layer circuit 218 Polyimide resin 219 Adhesive 220 Cover film 221 Inner layer circuit board 222 Possible Flexible insulating base material 223 Copper foil 224 Single-sided copper-clad plate 225 Adhesive 226 Single-sided copper-clad plate with adhesive 227 Conductive hole 228 Through hole 229 Circuit pattern 230 Core substrate 231 Multilayer flexible circuit substrate

Claims (3)

In the build-up base material for a multilayer flexible circuit board that performs interlayer connection of the multilayer flexible circuit board by conductive protrusions made of metal ,
A build-up base material for a multilayer flexible circuit board, wherein a concave portion is provided on a top portion of the conductive protrusion. In the build-up base material for multilayer flexible circuit boards according to claim 1,
The sites are erected in the conductive protrusion, and wherein the depth of the recess formed in the top of the contact area, and the conductive protrusions of the flexible substrate as a top and an inner layer of the conductive protrusions are different Build-up base material for multilayer flexible circuit boards. In a method for manufacturing a multilayer flexible circuit board that performs interlayer connection using a build-up base material for a multilayer flexible circuit board having conductive protrusions made of metal,
Prepare a build-up base material for a multilayer flexible circuit board having a recess at the top of the conductive protrusion,
Prepare a core substrate made in a separate process,
Laminating the multilayer flexible circuit board build-up substrate on the core substrate,
A method for manufacturing a multilayer flexible circuit board.

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