JP5798980B2 - Conductive adhesive sheet, method for producing the same, and printed wiring board - Google Patents

Description

  The present invention relates to a conductive pressure-sensitive adhesive sheet, a method for producing the same, and a printed wiring board provided with the conductive pressure-sensitive adhesive sheet.

  Conductive adhesive sheet for shielding printed circuit boards, electromagnetic noise generated from electronic components and external electromagnetic noise, or replacing conductors in printed wiring boards (for example, reference conductors for high-frequency transmission lines) May be attached to printed wiring boards, electronic parts, and the like. Moreover, in order to fix the printed wiring board, electronic component, etc. on which the conductive pressure-sensitive adhesive sheet is adhered to the casing, chassis, etc. of the electronic device, the adhesiveness may be required on both sides of the conductive pressure-sensitive adhesive sheet.

The following are known as conductive adhesive sheets having adhesiveness on both sides.
(1) A conductive pressure-sensitive adhesive sheet containing conductive particles in a sheet made of a pressure-sensitive adhesive (for example, Patent Documents 1 to 3).
However, the conductive adhesive sheet (1) has the following problems.

・ Conductivity between the conductive particles ensures the conductivity in the thickness direction and the surface direction, but the contact between the conductive particles is insufficient or there is contact resistance. Insufficient conductivity.
-In order to ensure sufficient surface conductivity, it is necessary to increase the number of conductive particles. However, when the blending ratio of the conductive particles increases, the ratio of the pressure-sensitive adhesive that serves as a binder for holding the conductive particles decreases, thereby reducing the strength of the conductive pressure-sensitive adhesive sheet, and when peeling from the release film. Torn.
In addition, as conductive particles, expensive particles such as particles of noble metal (silver, etc.) and carbon particles plated with noble metal (gold, etc.) are usually used, so increasing the number of conductive particles increases the production cost. .
-Moreover, when electroconductive particle is increased, an electroconductive adhesive sheet becomes thick. In recent years, electronic devices are required to be reduced in size and thickness, and a thin conductive adhesive sheet is required.
-Since it consists only of an adhesive, an adhesive, and conductive particles, the shape as a sheet cannot be maintained against heat such as soldering, that is, heat resistance is insufficient.

The following are known as conductive adhesive sheets having good surface conductivity.
(2) a resin film having conductive through holes formed in the thickness direction; a metal vapor-deposited film formed on both surfaces of the resin film, and a plating having a thickness of 1.0 μm or more formed on the surface of the vapor-deposited film Conductive adhesive comprising two conductive layers composed of layers; two conductive adhesive layers containing nickel particles produced by a pressure sensitive adhesive and a carbonyl method, formed on the respective surfaces of the two conductive layers Sheet (Patent Document 4).
However, the conductive adhesive sheet (2) has the following problems.

In recent years, electronic devices are required to be smaller and thinner, and a thin conductive adhesive sheet is required. However, since the thickness of the conductive layer is 1.0 μm or more in order to reduce the surface resistance of the conductive layer, the conductive adhesive sheet cannot be made sufficiently thin. Moreover, the flexibility and productivity of the conductive adhesive sheet are not good.
-Nickel particles produced by the carbonyl method have protrusions on the surface. Therefore, the contact area between the conductive layer and the printed circuit board with the ground circuit is small, and the contact resistance is large. When the contact pressure is increased to reduce the contact resistance with the conductive layer and the ground circuit, the nickel particles penetrate the conductive layer and the ground circuit, and the conductivity in the surface direction of the conductive layer and the ground circuit is lowered. Moreover, when the resin film which is a base material is made thin in order to make the conductive adhesive sheet thin, the nickel particles break through the resin film, and the strength of the resin film is lowered.
-Since it is necessary to form a conductive through-hole in a resin film, not only the manufacturing is complicated, but the strength is insufficient due to innumerable holes.
-Since the base material is a thermoplastic resin film, the heat resistance against heat such as soldering is insufficient.

Special table 2009-542860 publication JP-T-2011-504961 JP 2010-168518 A JP 2005-277145 A

  The present invention is a conductive pressure-sensitive adhesive sheet that can be made thinner than conventional conductive pressure-sensitive adhesive sheets, has excellent surface conductivity, is excellent in strength, flexibility and heat resistance, and is inexpensive. Provided is a printed wiring board provided with an adhesive sheet.

  The conductive pressure-sensitive adhesive sheet of the present invention comprises a cured product of a thermosetting resin containing conductive particles, and has a conductive support base having a thickness of 1 to 10 μm having conductivity in the thickness direction, and the conductive support group. A first conductive layer having a thickness of 0.01 μm or more and less than 1 μm having conductivity in the surface direction, formed on one surface of the material, and a surface direction formed on the other surface of the conductive support substrate Including a second conductive layer having a thickness of 0.01 μm or more and less than 1 μm, and conductive particles having a sphericity of 0.8 or more, covering the surface of the first conductive layer. A first conductive pressure-sensitive adhesive layer having a conductive property and a surface of the second conductive layer, including conductive particles having a sphericity of 0.8 or more, and having conductivity in the thickness direction. And 2 conductive adhesive layers.

The conductive particles having a sphericity of 0.8 or more are preferably plated fired carbon particles.
It is preferable that the storage elastic modulus in 120 degreeC of the said electroconductive support base material is 10 < ⁶ > -10 < ⁸ > Pa.
The surface resistance of the first conductive layer and the second conductive layer is preferably 0.5 to 500Ω.
The first conductive layer and the second conductive layer are preferably metal vapor deposition films.
The thickness of the first conductive pressure-sensitive adhesive layer and the second conductive pressure-sensitive adhesive layer is preferably 5 to 15 μm.

The manufacturing method of the electroconductive adhesive sheet of this invention has the following process (a)-(f), It is characterized by the above-mentioned.
(A) A thermosetting resin composition containing conductive particles is applied to one surface of a release substrate and cured to form a cured product of a thermosetting resin containing conductive particles, in the thickness direction. The process of forming the electroconductive support base material of thickness 1-10 micrometers which has electroconductivity.
(B) A step of forming a first conductive layer having a thickness of 0.01 μm or more and less than 1 μm having conductivity in the surface direction on the surface of the conductive support substrate.
(C) A step of providing a first conductive pressure-sensitive adhesive layer containing conductive particles having a sphericity of 0.8 or more on the surface of the first conductive layer and having conductivity in the thickness direction.
(D) The process of peeling the said peeling base material from the said electroconductive support base material.
(E) A step of forming a second conductive layer having a thickness of 0.01 μm or more and less than 1 μm having conductivity in the surface direction on the surface of the conductive support substrate.
(F) A step of providing a second conductive pressure-sensitive adhesive layer containing conductive particles having a sphericity of 0.8 or more on the surface of the second conductive layer and having conductivity in the thickness direction.

  The printed wiring board of the present invention comprises a printed wiring board main body having a signal circuit and a ground circuit on at least one surface of the substrate, and the conductive adhesive sheet of the present invention. The ground and the first conductive layer or the second conductive layer of the conductive pressure-sensitive adhesive sheet are electrically connected via the first conductive pressure-sensitive adhesive layer or the second conductive pressure-sensitive adhesive layer of the conductive pressure-sensitive adhesive sheet. The first conductive layer or the second conductive layer of the conductive adhesive sheet is disposed in the vicinity of the signal circuit of the printed wiring board body.

The conductive pressure-sensitive adhesive sheet of the present invention can be made thinner than conventional conductive pressure-sensitive adhesive sheets, has excellent surface conductivity, excellent strength, flexibility and heat resistance, and is inexpensive.
According to the method for producing a conductive pressure-sensitive adhesive sheet of the present invention, a conductive pressure-sensitive adhesive sheet that is thinner than conventional conductive pressure-sensitive adhesive sheets, has superior surface conductivity, and is excellent in strength, flexibility, and heat resistance at low cost. And it can be manufactured with good productivity.
The printed wiring board of the present invention has an enhanced ground and improved noise resistance, or has an excellent electromagnetic noise shielding function.

It is sectional drawing which shows an example of the electroconductive adhesive sheet of this invention. It is sectional drawing which shows the manufacturing process of the electroconductive adhesive sheet of this invention. It is sectional drawing which shows an example of the printed wiring board of this invention. It is a graph which shows the measurement result of the storage elastic modulus of a support base material.

In this specification, “sphericity of conductive particles” means that at least 30 conductive particles are randomly selected from an electron microscope image of the conductive particles, and the minimum diameter and the maximum diameter are measured for each conductive particle. Then, the sphericity is obtained from the following formula, and the measured sphericity of at least 30 conductive particles is averaged.
Sphericality = minimum diameter / maximum diameter.
In the present specification, the “average particle diameter of the conductive particles” means that the median value of the minimum diameter and the maximum diameter obtained by the above sphericity is the particle diameter of one particle, and the measured particle diameter of at least 30 particles is Obtained by arithmetic averaging.
In the present specification, “facing” means a state in which at least a part thereof overlaps when viewed from above.

<Conductive adhesive sheet>
FIG. 1 is a cross-sectional view showing an example of the conductive adhesive sheet of the present invention.
The conductive adhesive sheet 10 is formed on the conductive support base 12, the first conductive layer 14 formed on one surface of the conductive support base 12, and the other surface of the conductive support base 12. The second conductive layer 15, the first conductive adhesive layer 16 covering the surface of the first conductive layer 14, the second conductive adhesive layer 18 covering the surface of the second conductive layer 15, and The first release film 20 covering the surface of the first conductive pressure-sensitive adhesive layer 16 and the second release film 22 covering the surface of the second conductive pressure-sensitive adhesive layer 18 are provided.

(Conductive support substrate)
The conductive support substrate 12 is made of a cured product 13 of a thermosetting resin containing the conductive particles 11, has conductivity in the thickness direction, and has little or no conductivity in the surface direction. By making the matrix of the electroconductive support base material 12 into the hardened | cured material 13 of a thermosetting resin, the heat resistance of the electroconductive adhesive sheet 10 becomes favorable.

  Examples of the thermosetting resin include an epoxy resin, a phenol resin, an amino resin, an alkyd resin, a urethane resin, a synthetic rubber, a UV curable acrylate resin, and the like. From the viewpoint of excellent heat resistance, an epoxy resin is preferable.

  Examples of the conductive particles 11 include metal (silver, platinum, gold, copper, nickel, palladium, aluminum, solder, etc.) particles, plated fired carbon particles, and the like. From the viewpoint of conductivity, noble metals (silver, Gold, platinum, etc.) particles, noble metal (gold, silver, etc.) plated non-noble metal (copper, nickel, etc.) particles, noble metals (gold, silver, etc.) fired carbon particles, etc. are preferred. The calcined carbon particles plated with a noble metal (gold, silver, etc.) are preferable because they have high sphericity, and can be stably conducted even at low contact pressure without breaking through a thin conductive layer.

  The sphericity of the conductive particles 11 is preferably 0.8 or more. The higher the sphericity of the conductive particles 11, the more stable conduction can be obtained even at a low contact pressure without breaking through the thin conductive layer.

  The average particle diameter of the conductive particles 11 is 0.8 to 1.4 times the thickness of the conductive support substrate 12 in terms of electrical connection between the first conductive layer 14 and the second conductive layer 15. Is preferable, 0.9 to 1.2 times is more preferable, and it is more preferable that they are approximately the same.

  The content of the conductive particles 11 is preferably 0.5 to 20% by volume, more preferably 1 to 10% by volume, out of 100% by volume of the conductive support base 12. If content of the electroconductive particle 11 is 0.5 mass% or more, the electroconductivity of thickness direction can fully be ensured. If content of the electroconductive particle 11 is 20 mass% or less, the price of the electroconductive adhesive sheet 10 can be suppressed by suppressing the electroconductivity of a surface direction and the quantity of the electroconductive particle 11 being suppressed.

The storage elastic modulus at 120 ° C. of the conductive support substrate 12 is preferably 10 ⁶ to 10 ⁸ Pa, and more preferably 3 × 10 ⁶ to 8 × 10 ⁷ (Pa). Usually, since a cured product of a thermosetting resin is hard, a film made of this is poor in flexibility, and in particular, when the thickness is reduced, the film is very brittle and does not have enough strength to exist as a self-supporting film. By setting the storage elastic modulus at 120 ° C. of the conductive support base material 12 in the range of 10 ⁶ to 10 ⁸ Pa, the balance between flexibility and strength and heat resistance is improved, and in a high temperature atmosphere to be used. Has sufficient strength.
The storage elastic modulus can be measured as one of the viscoelastic characteristics using a dynamic viscoelasticity measuring device that is calculated from the stress applied to the sample and the detected strain and outputs it as a function of temperature or time.

  The thickness of the conductive support base 12 is 1 to 10 μm, and preferably 1 to 5 μm. When the thickness of the conductive support base 12 is 1 μm or more, the heat resistance is good. If the thickness of the electroconductive support base material 12 is 10 micrometers or less, the electroconductive adhesive sheet 10 can be made thin.

(Conductive layer)
The first conductive layer 14 and the second conductive layer 15 (hereinafter collectively referred to as a conductive layer) are layers made of a conductor (metal). Since the conductive layer is formed so as to extend in the plane direction, it has conductivity in the plane direction and functions as a conductor (such as a reference conductor for a high-frequency transmission line), an electromagnetic wave shield layer, or the like.

  Examples of the conductive layer include metal thin films formed by physical vapor deposition (vacuum vapor deposition, sputtering, ion beam vapor deposition, etc.), CVD, plating, etc., and conductive coating films formed by applying a paint containing conductive particles. From the point of excellent surface conductivity, metal thin film is preferable, and it is possible to reduce the thickness, and even if the thickness is small, it is excellent in surface direction conductivity, and can be easily formed by a dry process. A metal thin film (deposited film) is more preferable.

  Examples of the material for the metal thin film constituting the conductive layer include aluminum, silver, copper, gold, and conductive ceramics. From the viewpoint of electrical conductivity, copper is preferable, and from the viewpoint of chemical stability, conductive ceramics are preferable.

  The thickness of the conductive layer is 0.01 μm or more and less than 1 μm. When the thickness of the conductive layer is 0.01 μm or more, the surface conductivity is further improved. When the thickness of the conductive layer is less than 1 μm, the conductive adhesive sheet 10 can be thinned. In addition, productivity and flexibility are improved.

  When the conductive layer is a reference conductor, the thickness of the reference conductor is more preferably 0.02 to 0.1 μm. If the thickness of the reference conductor is 0.02 μm or more, the ground of the printed wiring board that is electrically connected to the reference conductor via the conductive particles 26 can be further strengthened. When the thickness of the reference conductor is 0.1 μm or less, the conductive adhesive sheet 10 can be further thinned. In addition, productivity and flexibility are further improved.

  When the conductive layer is an electromagnetic wave shielding layer, the thickness of the electromagnetic wave shielding layer is more preferably 0.1 μm or more and less than 1 μm. If the thickness of the electromagnetic wave shielding layer is 0.1 μm or more, the electromagnetic noise shielding effect is further improved. If the thickness of the electromagnetic wave shielding layer is less than 1 μm, the conductive adhesive sheet 10 can be further thinned. In addition, productivity and flexibility are further improved.

  The surface resistance of the conductive layer is 0.5 to 500Ω, preferably 1 to 300Ω. When the surface resistance of the conductive layer is 0.5Ω or more, the conductive layer can be made sufficiently thin. If the surface resistance of the conductive layer is 500Ω or less, it can sufficiently function as a reference conductor.

(Conductive adhesive layer)
The first conductive pressure-sensitive adhesive layer 16 and the second conductive pressure-sensitive adhesive layer 18 (hereinafter collectively referred to as a conductive pressure-sensitive adhesive layer) have conductivity in the thickness direction, and in the surface direction. Is a layer having little or no electrical conductivity and stickiness.
Examples of the conductive pressure-sensitive adhesive layer include a layer including a pressure-sensitive adhesive or adhesive 24 and conductive particles 26 dispersed in the pressure-sensitive adhesive or adhesive 24 as shown in FIG.

Examples of the pressure-sensitive adhesive or adhesive 24 include epoxy resin, polyester, polyimide, polyamideimide, polyamide, phenol resin, polyurethane, acrylic resin, melamine resin, polystyrene, and polyolefin. The epoxy resin may contain a rubber component (carboxyl-modified nitrile rubber or the like) for imparting flexibility and a tackifier.
Furthermore, in order to increase the strength of the pressure-sensitive adhesive or adhesive 24 and improve the punching characteristics, a cellulose resin can be added, or microfibrils such as glass fibers can be added to such an extent that adhesion and conduction are not hindered.

  Examples of the conductive particles 26 include metal (silver, platinum, gold, copper, nickel, palladium, aluminum, solder, etc.) particles, plated fired carbon particles, and the like. From the viewpoint of conductivity, noble metals (silver, Gold, platinum, etc.) particles, noble metal (gold, silver, etc.) plated non-noble metal (copper, nickel, etc.) particles, noble metals (gold, silver, etc.) fired carbon particles, etc. are preferred. The calcined carbon particles plated with a noble metal (gold, silver, etc.) are preferable because they have high sphericity, and can be stably conducted even at low contact pressure without breaking through a thin conductive layer.

  The sphericity of the conductive particles 26 is 0.8 or more, preferably 0.9 or more, and more preferably 0.95 or more. The higher the sphericity of the conductive particles 26, the more stable conduction can be obtained even at a low contact pressure without breaking through the thin conductive layer.

  The average particle diameter of the conductive particles 26 is the thickness of the conductive pressure-sensitive adhesive layer after the conductive pressure-sensitive adhesive sheet 10 is attached to the printed wiring board from the viewpoint of electrical connection between the conductive layer and the ground of the printed wiring board. It is preferably 0.8 to 1.4 times, more preferably 0.9 to 1.2 times, and even more preferably about the same.

  The content of the conductive particles 26 is preferably 0.5 to 20% by volume, more preferably 1 to 10% by volume, out of 100% by volume of the conductive pressure-sensitive adhesive layer. If content of the electroconductive particle 26 is 0.5 mass% or more, the electroconductivity of thickness direction can fully be ensured. If content of the electroconductive particle 26 is 20 mass% or less, the price of the electroconductive adhesive sheet 10 can be suppressed by suppressing the electroconductivity of a surface direction and the quantity of the electroconductive particle 26 being suppressed.

  5-15 micrometers is preferable and, as for the thickness of a conductive adhesive layer, 2-10 micrometers is more preferable. When the thickness of the conductive pressure-sensitive adhesive layer is 5 μm or more, sufficient adhesion strength can be obtained for the adherend. If the thickness of the conductive pressure-sensitive adhesive layer 16 is 15 μm or less, the conductive pressure-sensitive adhesive sheet 10 can be made thin, and the amount of the conductive particles 26 can be suppressed.

(Peeling film)
The first release film 20 and the second release film 22 (hereinafter collectively referred to as a release film) protect the conductive pressure-sensitive adhesive layer, and the conductive pressure-sensitive adhesive sheet 10 can be used as a printed wiring board or the like. When sticking to, it is removed from the conductive adhesive layer.

  As the release film, a known release film such as a separator whose one surface is subjected to a release treatment may be used.

(Thickness of conductive adhesive sheet)
10-45 micrometers is preferable and, as for the thickness (except a peeling film) of the electroconductive adhesive sheet 10, 15-30 micrometers is more preferable.

(Function and effect)
In the conductive adhesive sheet 10 described above, the conductive layer having conductivity in the surface direction formed on both surfaces of the conductive support base 12 has excellent conductivity in the surface direction. Therefore, it is not necessary to give the conductive pressure-sensitive adhesive layer surface conductivity, and the conductive pressure-sensitive adhesive layer can be made thinner than a conventional conductive pressure-sensitive adhesive sheet. In addition, the conductive support base 12 itself is sufficiently thin and has high strength. Therefore, the conductive adhesive sheet 10 can be thinned.

Moreover, in the conductive adhesive sheet 10 described above, since the conductivity in the thickness direction of the conductive support base 12 is ensured by the conductive particles 11, the conductive support base 12 has a conductive penetration. There is no need to form holes. Therefore, even if the conductive support base 12 is thin, the strength is high.
Moreover, in the conductive adhesive sheet 10 described above, since the sphericity of the conductive particles 26 of the conductive adhesive layer is 0.8 or more, the conductive particles 26 are unlikely to break through the conductive layer. The conductivity in the direction is difficult to decrease. In addition, the conductive particles 26 are unlikely to break through the conductive support substrate 12, and even if the conductive support substrate 12 is thin, the strength is unlikely to decrease.

Moreover, in the conductive adhesive sheet 10 demonstrated above, since a conductive layer is thin, the flexibility of the conductive adhesive sheet 10 is good, and the conductive adhesive sheet 10 can be made thin enough.
Moreover, in the electroconductive adhesive sheet 10 demonstrated above, since the electroconductive support base material 12 consists of hardened | cured material of a thermosetting resin, it is excellent in heat resistance. In addition, although the electroconductive support base material 12 is a thin film which consists of hardened | cured material of a thermosetting resin, by making the storage elastic modulus in 120 degreeC of the electroconductive support base material 12 into the range of 10 < ⁶ > -10 < ⁸ > Pa. The balance between flexibility and strength and heat resistance is improved.

  Moreover, in the conductive adhesive sheet 10 demonstrated above, it is not necessary to make a conductive adhesive layer thin compared with the conventional conductive adhesive sheet, and to have electroconductivity of a surface direction. Therefore, the amount of expensive conductive particles 26 included in the conductive adhesive layer can be reduced. Therefore, it is cheaper than the conventional conductive adhesive sheet. Moreover, since the quantity of the electroconductive particle 26 can be reduced, the intensity | strength of electroconductive adhesive layer itself is high.

<Method for producing conductive adhesive sheet>
The manufacturing method of the electroconductive adhesive sheet of this invention is a method which has the following process (a)-(f).
(A) A thermosetting resin composition containing conductive particles is applied to one surface of a release substrate and cured to form a cured product of a thermosetting resin containing conductive particles, in the thickness direction. The process of forming the electroconductive support base material of thickness 1-10 micrometers which has electroconductivity.
(B) A step of forming a first conductive layer having a thickness of 0.01 μm or more and less than 1 μm having conductivity in the surface direction on the surface of the conductive support substrate.
(C) A step of providing a first conductive pressure-sensitive adhesive layer containing conductive particles having a sphericity of 0.8 or more on the surface of the first conductive layer and having conductivity in the thickness direction.
(D) The process of peeling a peeling base material from an electroconductive support base material.
(E) A step of forming a second conductive layer having a thickness of 0.01 μm or more and less than 1 μm having conductivity in the surface direction on the surface of the conductive support substrate.
(F) A step of providing a second conductive pressure-sensitive adhesive layer containing conductive particles having a sphericity of 0.8 or more on the surface of the second conductive layer and having conductivity in the thickness direction.

(Process (a))
As shown in FIG. 2, a thermosetting resin composition containing conductive particles is applied to one surface of a third release film 28 (peeling substrate), cured, and thermoset containing conductive particles. The conductive support substrate 12 made of a cured product of the conductive resin is formed.
A thermosetting resin composition contains the thermosetting resin mentioned above, electroconductive particle, a solvent as needed, and another component.

Since the electroconductive support base material 12 is formed by application | coating of a thermosetting resin composition, the electroconductive support base material 12 can be made thin. In addition, since the hardened | cured material of a thermosetting resin is hard, when the electroconductive support base material 12 is made thin, intensity | strength becomes inadequate, but as mentioned above, the storage elasticity in 120 degreeC of the electroconductive support base material 12 is sufficient. By setting the rate within the range of 10 ⁶ to 10 ⁸ Pa, the balance between flexibility and strength and heat resistance is improved.

Control of the storage elastic modulus of the conductive support substrate 12 is performed by the reactive monomers, oligomers, curing agents, etc. from the viewpoint of equivalents (crosslink density) of the reactive monomers, oligomers, curing agents and the toughness resulting from the structure. This is done by selecting the type and composition of the resin and adjusting the storage elastic modulus of the cured product of the thermosetting resin.
In addition, the storage elastic modulus adjusts the curing conditions such as temperature and time when curing the thermosetting resin, or selects a thermoplastic resin such as a thermoplastic elastomer as a component that does not have thermosetting properties, It can be adjusted by adding.

(Process (b))
As shown in FIG. 2, the 1st conductive layer 14 which has electroconductivity in a surface direction is formed in the surface of the electroconductive support base material 12. As shown in FIG.

  Examples of the method for forming the first conductive layer 14 include a method of forming a metal thin film by physical vapor deposition, CVD, plating, and the like, a method of applying a paint containing conductive particles, and the like. From the point that one conductive layer 14 can be formed, a method of forming a metal thin film by physical vapor deposition, CVD, plating, or the like is preferable, and the thickness of the first conductive layer 14 can be reduced and the surface direction can be reduced. The method by physical vapor deposition is more preferable because the first conductive layer 14 having excellent conductivity can be formed and the first conductive layer 14 can be easily formed by a dry process.

(Process (c))
As shown in FIG. 2, a first conductive pressure-sensitive adhesive layer 16 having conductivity in the thickness direction is formed on the surface of the first conductive layer 14. Further, the surface of the first conductive pressure-sensitive adhesive layer 16 is covered with the first release film 20.

  As a method of forming the first conductive pressure-sensitive adhesive layer 16, a method of applying a conductive pressure-sensitive adhesive composition or a conductive adhesive composition to the surface of the first conductive layer 14, and a conductive pressure-sensitive adhesive sheet are pasted. The method of wearing, etc. are mentioned. From the viewpoint that the first conductive pressure-sensitive adhesive layer 16 can be formed thin, a method of applying a conductive pressure-sensitive adhesive composition or a conductive adhesive composition is preferable.

(Process (d))
As shown in FIG. 2, the third release film 28 is peeled from the conductive support base 12.

(Process (e))
As shown in FIG. 2, the 2nd conductive layer 15 which has electroconductivity in a surface direction is formed in the surface of the electroconductive support base material 12. As shown in FIG.

  Examples of the method for forming the second conductive layer 15 include the same method as the method for forming the first conductive layer 14, and the preferred method is also the same.

(Process (f))
As shown in FIG. 2, a second conductive pressure-sensitive adhesive layer 18 having conductivity in the thickness direction is provided on the surface of the second conductive layer 15. Further, the surface of the second conductive pressure-sensitive adhesive layer 18 is covered with the second release film 22.

  As a formation method of the 2nd conductive adhesive layer 18, the method similar to the formation method of the 1st conductive adhesive layer 16 is mentioned, A preferable method is also the same.

(Function and effect)
In the manufacturing method of the electroconductive adhesive sheet of this invention demonstrated above, since it has process (a)-(f) mentioned above, the electroconductive adhesive sheet of this invention can be manufactured at low cost and with high productivity.

<Printed wiring board>
FIG. 3 is a cross-sectional view showing an example of the printed wiring board of the present invention.
The printed wiring board 1 has a printed wiring board main body 30 having a signal circuit 34 and a ground circuit 36 on one side of a substrate 32; an adhesive layer 44 on one side of a base film 42, and a signal circuit of the printed wiring board main body 30. A coverlay film 40 which is attached to the printed wiring board main body 30 with an adhesive layer 44 so as to cover the surface on the side having the 34 and the ground circuit 36 and has an opening 46 immediately above the ground circuit 36; The coverlay film 40 and the ground in the opening 46 so as to cover the surface of the base film 42 on the side of the substrate 40 and so that the first conductive adhesive layer 16 is in contact with the ground circuit 36 in the opening 46. The circuit includes the conductive adhesive sheet 10 attached to the circuit 36 with the first conductive adhesive layer 16.

  The second conductive pressure-sensitive adhesive layer 18 of the conductive pressure-sensitive adhesive sheet 10 is attached to another member 50 such as a housing or a chassis of an electronic device, for example.

  In the vicinity of the signal circuit 34 and the ground circuit 36, the first conductive layer 14 of the conductive adhesive sheet 10 is disposed through the cover lay film 40 and the first conductive adhesive layer 16 except for the opening 46. It is spaced and opposed.

  The distance between the signal circuit 34 and the first conductive layer 14 is the thickness of the base film 42 of the coverlay film 40, the thickness of the adhesive layer 44, and the first conductive adhesive layer 16 of the conductive adhesive sheet 10. Is the sum of the thicknesses. The separation distance is preferably 30 to 200 μm. If the separation distance is smaller than 30 μm, the impedance of the signal circuit 34 becomes low. Therefore, in order to have a characteristic impedance of 100Ω or the like, the line width of the signal circuit 34 must be reduced, and the variation in the line width is characteristic impedance. There is a disadvantage that reflection resonance noise due to impedance mismatching easily rides on an electric signal. When the separation distance is larger than 200 μm, there is a problem that the printed wiring board 1 becomes thick and the flexibility is insufficient. The separation distance is more preferably 60 to 200 μm.

(Printed wiring board body)
The printed wiring board body 30 is obtained by processing a copper foil of a copper-clad laminate into a desired pattern by a known etching method to form a wiring circuit such as a signal circuit 34, a ground circuit 36, and a ground layer.
As a copper clad laminated board, what laminated | stacked copper foil on the one or both surfaces of the board | substrate 32 via the adhesive bond layer (not shown); what cast the resin solution etc. which form the board | substrate 32 on the surface of copper foil, etc. Is mentioned.

substrate:
Examples of the material of the substrate 32 include glass fiber reinforced epoxy resin, epoxy resin, polyester (polyethylene terephthalate, polyethylene naphthalate, polycarbonate, etc.), polyvinylidene, polyimide, polyamideimide, polyamide, polyphenylene sulfide, liquid crystal polymer, polystyrene, and the like. .
When the printed wiring board 1 is a flexible printed wiring board, the substrate 32 is preferably a polymer film.

The surface resistance of the polymer film is preferably 1 × 10 ⁶ Ω or more.
As a polymer film, the film which has heat resistance is preferable, and a polyimide film, a liquid crystal polymer film, etc. are more preferable.
The thickness of the polymer film is preferably 5 to 200 μm, more preferably 6 to 25 μm, and particularly preferably 10 to 25 μm from the viewpoint of flexibility.

Wiring circuit:
Examples of the copper foil constituting the wiring circuit (signal circuit 34, ground circuit 36, ground layer, etc.) include rolled copper foil, electrolytic copper foil, and the like, and rolled copper foil is preferred from the viewpoint of flexibility.
1-50 micrometers is preferable and, as for the thickness of copper foil, 18-35 micrometers is more preferable.
The end (terminal) in the length direction of the wiring circuit is not covered with the cover lay film 40 or the conductive adhesive sheet 10 for solder connection, connector connection, component mounting, or the like.

Adhesive layer:
Examples of the material for the adhesive layer that bonds the copper foil (wiring circuit) to the substrate 32 include epoxy resin, polyester, polyimide, polyamideimide, polyamide, phenol resin, polyurethane, acrylic resin, and melamine resin.
As for the thickness of an adhesive bond layer, 0.5-30 micrometers is preferable.

(Coverlay film)
The coverlay film 40 is obtained by forming an adhesive layer 44 on one surface of a base film 42 by applying an adhesive, sticking an adhesive sheet, or the like.

Base film:
The surface resistance of the base film 42 is preferably 1 × 10 ⁶ Ω or more.
Examples of the material of the base film 42 include polyimide, liquid crystal polymer, fluororesin, polyamide, polyphenylene sulfide, polyamide imide, polyether imide, polyethylene naphthalate, polyethylene terephthalate, alicyclic polyolefin, polyphenylene ether, and the like. Since the dielectric constant is low and the dielectric loss is low, the signal circuit is not deteriorated, and it is advantageous for adjusting the impedance of the signal circuit 34. Are preferred, and liquid crystal polymers, fluororesins or alicyclic polyolefins are particularly preferred.
1-100 micrometers is preferable and, as for the thickness of the base film 32, 3-25 micrometers is more preferable from a flexible point.

Adhesive layer:
Examples of the material of the adhesive layer 44 include epoxy resin, polyester, polyimide, polyamideimide, polyamide, phenol resin, polyurethane, acrylic resin, melamine resin, polystyrene, and polyolefin. The epoxy resin may contain a rubber component (carboxyl-modified nitrile rubber or the like) for imparting flexibility.
1-100 micrometers is preferable and, as for the thickness of the adhesive bond layer 44, 1.5-60 micrometers is more preferable.

(Printed wiring board manufacturing method)
The printed wiring board 1 is manufactured as follows, for example.
First, the printed wiring board body 30 having the signal circuit 34 and the ground circuit 36 on one side of the substrate 32, the adhesive layer 44 on one side of the base film 42, and the opening 46 at a position corresponding to the ground circuit 36. The cover lay film 40 having the printed circuit board body 30 is overlapped so that the surface of the printed wiring board main body 30 having the signal circuit 34 and the ground circuit 36 is in contact with the adhesive layer 44 of the cover lay film 40, and a press machine (not shown). The cover lay film 40 is adhered to the surface of the printed wiring board main body 30 by the adhesive layer 44 by hot pressing using the adhesive layer 44.

  Next, the printed wiring board body 30 with the coverlay film 40, the conductive adhesive sheet 10, the base film 42 of the coverlay film 40, and the first conductive adhesive layer 16 of the conductive adhesive sheet 10 are provided. They are stacked so as to come into contact with each other, cold-pressed by a press (not shown) or the like (heated if necessary), and the ground circuit 36 is formed by the conductive particles in the first conductive adhesive layer 16 at the opening 46. The first conductive adhesive layer 16 is attached to the surface of the cover lay film 40 so that the first conductive layer 14 is connected to the first conductive layer 14.

  If necessary, the second conductive pressure-sensitive adhesive layer 18 of the conductive pressure-sensitive adhesive sheet 10 is attached to another member 50 such as a housing or chassis of the electronic device, and the printed wiring board 1 is fixed.

(Function and effect)
The printed wiring board 1 described above includes the printed wiring board main body 30 having the signal circuit 34 and the ground circuit 36, and the conductive adhesive sheet 10, and the ground circuit 36 and the first conductive layer 14 include: The first conductive layer 14 is disposed in the vicinity of the signal circuit 34 because the first conductive layer 14 is disposed in the vicinity of the signal circuit 34 and is electrically connected through the first conductive adhesive layer 16. The layer 14 becomes a reference conductor for the signal circuit 34, the ground is strengthened, and noise resistance is improved. Or if the 1st conductive layer 14 has sufficient thickness, it is excellent also in the shielding function of electromagnetic wave noise.

(Other forms)
The printed wiring board of the present invention comprises a printed wiring board main body having a signal circuit and a ground circuit on at least one surface of the substrate and the conductive adhesive sheet of the present invention, and the ground circuit of the printed wiring board main body or the outside The conductive layer of the conductive adhesive sheet and the conductive layer of the conductive adhesive sheet are electrically connected via the conductive adhesive layer of the conductive adhesive sheet, and the conductive layer may be disposed in the vicinity of the signal circuit. The printed wiring board 1 is not limited.
For example, the printed wiring board body may have a ground layer on the back side. The printed wiring board main body may have a signal circuit and a ground circuit on the back side, and a cover lay film and the conductive adhesive sheet of the present invention may be attached to the back side.

  Examples are shown below. The present invention is not limited to these examples.

[Example 1]
(Manufacture of conductive adhesive sheet)
Step (a):
On the surface of the release-treated side of a 37 μm thick polyester film (third release film 28) having a release treatment on one side, epoxy resin and gold-plated fired carbon particles having an average particle size of 5 μm An epoxy resin containing fired carbon particles plated with gold, plated with a thermosetting resin composition containing 5% by volume of (conductive particles 11), allowed to stand at 140 ° C. for 0.5 hour, cured epoxy resin A conductive support substrate 12 having a thickness of 5 μm and a storage elastic modulus at 120 ° C. of 4 × 10 ⁶ Pa was formed. The storage elastic modulus was measured using a dynamic viscoelasticity measuring apparatus (Rheometric Scientific, Inc., RSAII). The measurement results are shown in FIG.

Step (b):
Copper was physically vapor-deposited on the surface of the conductive support substrate 12 by EB vapor deposition to form a vapor-deposited film (first conductive layer 14) having a thickness of 0.04 μm and a surface resistance of 100Ω.

Step (c):
A conductive pressure-sensitive adhesive composition was prepared by dispersing 5% by volume of gold-plated fired carbon particles (conductive particles 26) having an average particle diameter of 10 μm in an insulating pressure-sensitive adhesive composition made of a modified acrylic resin.
The conductive adhesive composition was applied to the surface of the first conductive layer 14 so that the dry film thickness was 10 μm, and the first conductive adhesive layer 16 was formed.
Furthermore, a 50 μm-thick polyester film (first release film 20) having a release treatment on one side is formed on the surface of the first conductive pressure-sensitive adhesive layer 16, and the surface on the release-treated side is the first. It covered so that the conductive adhesive layer 16 might be touched.

Step (d):
The third release film 28 was peeled from the conductive support base 12.

Step (e):
Copper was physically vapor-deposited on the surface of the conductive support substrate 12 by EB vapor deposition to form a vapor-deposited film (second conductive layer 15) having a thickness of 0.04 μm and a surface resistance of 100Ω.

Step (f):
The same conductive adhesive composition as in step (c) was applied to the surface of the first conductive layer 14 so that the dry film thickness was 10 μm, and the second conductive adhesive layer 18 was formed.
Further, a 37 μm-thick polyester film (second release film 22) having a release treatment on one side is formed on the surface of the second conductive pressure-sensitive adhesive layer 18, and the release-treated surface is a second surface. The conductive adhesive sheet 10 having a thickness of 25 μm (excluding the release film) was obtained so as to be in contact with the conductive adhesive layer 18.

(Manufacture of printed wiring boards)
First, an insulating adhesive composition made of a nitrile rubber-modified epoxy resin is applied to the surface of a 10 μm-thick polyimide film (base film 42) so that the dry film thickness is 20 μm. The cover lay film 40 was obtained. An opening 46 is formed in the coverlay film 40 at a position corresponding to the ground circuit 36.

Next, a printed wiring board body 30 having a signal circuit 34 and a ground circuit 36 formed on one side of a polyimide film (substrate 32) having a thickness of 12 μm was prepared.
The coverlay film 40 was stuck to the printed wiring board main body 30 by hot pressing.

  Next, after peeling the first release film 20 from the conductive pressure-sensitive adhesive sheet 10, the first conductive pressure-sensitive adhesive sheet 10 was stuck to the surface of the cover lay film 40 by a cold press to obtain the printed wiring board 1. . At this time, the first conductive layer 14 was grounded to the ground circuit 36 by conductive particles in the opening 46.

  The conductive adhesive sheet of the present invention is an electromagnetic shielding member, a reference conductor member, etc. in a flexible printed wiring board for an electronic device such as a smartphone, a mobile phone, an optical module, a digital camera, a game machine, a notebook computer, or a medical device. Useful as.

DESCRIPTION OF SYMBOLS 1 Printed wiring board 10 Conductive adhesive sheet 11 Conductive particle 12 Support base material 13 Hardened | cured material of a thermosetting resin 14 1st conductive layer 16 1st conductive adhesive layer 15 2nd conductive layer 18 2nd Conductive pressure-sensitive adhesive layer 20 First release film 22 Second release film 24 Adhesive or adhesive 26 Conductive particles 28 Third release film (release substrate)
30 Printed Wiring Board Body 32 Substrate 34 Signal Circuit 36 Ground Circuit 40 Coverlay Film 42 Base Film 44 Adhesive Layer 46 Opening 50 Other Member

Claims (8)

A conductive support substrate having a thickness of 1 to 10 μm, which is made of a cured product of a thermosetting resin containing conductive particles, and has conductivity in the thickness direction;
A first conductive layer formed on one surface of the conductive support substrate and having a thickness of 0.01 μm or more and less than 1 μm having conductivity in the plane direction;
A second conductive layer having a thickness of 0.01 μm or more and less than 1 μm having conductivity in the surface direction, formed on the other surface of the conductive support substrate;
A first conductive pressure-sensitive adhesive layer that covers the surface of the first conductive layer, includes conductive particles having a sphericity of 0.8 or more, and has conductivity in the thickness direction;
A second conductive adhesive layer that covers the surface of the second conductive layer, includes conductive particles having a sphericity of 0.8 or more, and has conductivity in the thickness direction. Sheet.   The conductive adhesive sheet according to claim 1, wherein the conductive particles having a sphericity of 0.8 or more are plated fired carbon particles. The conductive adhesive sheet of Claim 1 or 2 whose storage elastic modulus in 120 degreeC of the said electroconductive support base material is 10 < ⁶ > -10 < ⁸ > Pa.   The conductive adhesive sheet according to any one of claims 1 to 3, wherein a surface resistance of the first conductive layer and the second conductive layer is 0.5 to 500Ω.   The conductive adhesive sheet according to any one of claims 1 to 4, wherein the first conductive layer and the second conductive layer are metal deposition films.   The electroconductive adhesive sheet as described in any one of Claims 1-5 whose thickness of a said 1st electroconductive adhesive layer and a said 2nd electroconductive adhesive layer is 5-15 micrometers, respectively. The manufacturing method of an electroconductive adhesive sheet which has the following process (a)-(f).
(A) A thermosetting resin composition containing conductive particles is applied to one surface of a release substrate and cured to form a cured product of a thermosetting resin containing conductive particles, in the thickness direction. The process of forming the electroconductive support base material of thickness 1-10 micrometers which has electroconductivity.
(B) A step of forming a first conductive layer having a thickness of 0.01 μm or more and less than 1 μm having conductivity in the surface direction on the surface of the conductive support substrate.
(C) A step of providing a first conductive pressure-sensitive adhesive layer containing conductive particles having a sphericity of 0.8 or more on the surface of the first conductive layer and having conductivity in the thickness direction.
(D) The process of peeling the said peeling base material from the said electroconductive support base material.
(E) A step of forming a second conductive layer having a thickness of 0.01 μm or more and less than 1 μm having conductivity in the surface direction on the surface of the conductive support substrate.
(F) A step of providing a second conductive pressure-sensitive adhesive layer containing conductive particles having a sphericity of 0.8 or more on the surface of the second conductive layer and having conductivity in the thickness direction. A printed wiring board body having a signal circuit and a ground circuit on at least one surface of the substrate;
A conductive pressure-sensitive adhesive sheet according to any one of claims 1 to 6,
The ground circuit of the printed wiring board main body or the external ground and the first conductive layer or the second conductive layer of the conductive adhesive sheet are the first conductive adhesive layer or the second conductive layer of the conductive adhesive sheet. Electrically connected through the conductive adhesive layer of
A printed wiring board in which the first conductive layer or the second conductive layer of the conductive adhesive sheet is disposed in the vicinity of a signal circuit of the printed wiring board body.

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