JP2015127372A - Adhesive sheet, and manufacturing method of adhesive sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an adhesive sheet which can satisfy both improvement in mechanical adhesive strength and improvement in electric conductivity or thermal conductivity in adhesion between a flexible printed wiring board and a metal plate.SOLUTION: An adhesive sheet 1 comprises: a release film 2; and a conductive adhesion layer 3 laminated at least on a partial region of the surface of the release film 2, in which the conductive adhesion layer 3 adheres a printed wiring board and a metal plate which face the layer, and electric conductivity or thermal conductivity is developed at least in a thickness direction between a conductive region of the printed wiring board, where a conductive pattern is exposed on a facing surface, and the metal plate. The conductive adhesion layer 3 has: one or plural types of bumps 5 having electric conductivity or thermal conductivity at least in the thickness direction; and an adhesive layer 6 filled around the one or plural types of bumps 5, and the one or plural types of bumps 5 exist only in an adhesion scheduled region in the conductive region of the printed wiring board.

Description

  The present invention relates to an adhesive sheet and a method for producing the same.

  In recent years, with the demand for higher functionality, smaller size, lighter weight, and the like of electronic devices, thinning of flexible printed wiring boards accommodated in electronic devices has been promoted. In some cases, a reinforcing plate may be partially attached to a surface of the flexible printed wiring board opposite to the component mounting surface to compensate for the strength reduction of the wiring board due to the reduction in thickness.

  As the reinforcing plate, a metal plate such as stainless steel is generally used. Therefore, a flexible printed wiring board has been developed in which the grounding circuit of the printed wiring board is electrically connected to the metal reinforcing board to provide the reinforcing board with a shielding function against electromagnetic noise. As a method of electrically connecting the reinforcing plate and the ground circuit of the printed wiring board, a method of adhering the reinforcing plate to the printed wiring board using an electrically conductive (conductive) adhesive containing conductive particles is proposed. (Japanese Patent Laid-Open No. 2007-189091).

  Moreover, in a flexible printed wiring board on which a large number of elements are mounted, many elements are mounted in a narrow area by increasing the degree of integration by downsizing various electronic devices. In such a flexible printed wiring board, the element itself may be damaged due to a temperature rise due to heat generation of each element. Therefore, a heat sink having fins on the surface opposite to the component mounting surface or the like for the purpose of suppressing the temperature rise. There are cases where a metal plate for heat dissipation is attached.

  As a method of attaching a heat radiating metal plate to a printed wiring board in this way, a method of adhering the heat radiating metal plate to the printed wiring board using a heat conductive adhesive containing heat conductive particles has been proposed (Japanese Patent Application Laid-Open No. 2005-259151). 2008-258254 and JP-A-2008-214524).

  The above-mentioned electrically conductive adhesive and thermally conductive adhesive have a difference in electrical energy or thermal energy between the printed wiring board and the metal plate (reinforcing plate or heat radiating metal plate) adhered to the printed wiring board. It contains particles that conduct these energies so as to be smaller. Moreover, metal particles or ceramics are preferably used as such conductive particles. Therefore, the above-mentioned proposals for the electrically conductive adhesive and the thermally conductive adhesive optimize the particles according to the type of energy to be conducted, and are not different from each other in the technical field.

JP 2007-189091 A JP 2008-258254 A JP 2008-214524 A

  In the above-mentioned conventional electrically conductive adhesive and thermally conductive adhesive, in order to improve the electrical or thermal connectivity between the metal plate and the printed wiring board, the content of particles that conduct electricity or heat is increased. In this case, the mechanical bond strength between the metal plate and the printed wiring board is lowered. On the other hand, in order to improve the mechanical adhesive strength between the metal plate and the printed wiring board, it is necessary to reduce the content of particles that conduct electricity or heat. The electrical conductivity or thermal conductivity between them decreases. That is, when the above-described electrically conductive adhesive or thermally conductive adhesive is used, the mechanical adhesive strength and the electrical energy or thermal energy conductivity are in a trade-off relationship.

  The present invention has been made in view of the above disadvantages, and in bonding between a flexible printed wiring board and a metal plate, it is possible to achieve both improvement in mechanical adhesion strength and improvement in electrical conductivity or thermal conductivity. It aims at providing a sheet | seat and its manufacturing method.

  The invention made in order to solve the above-mentioned problems includes a release film and a conductive adhesive layer laminated on at least a part of the surface of the release film, and the conductive adhesive layer is opposed to the printed wiring. An adhesive sheet that bonds a plate and a metal plate, and develops electrical conductivity or thermal conductivity at least in the thickness direction between the conductive region of the printed wiring board and the conductive region where the conductive pattern is exposed on the opposing surface. The conductive adhesive layer has at least one or more bumps having electrical conductivity or thermal conductivity in the thickness direction, and an adhesive layer filled around the one or more bumps. One or a plurality of bumps are present only in a region to be bonded to the conductive region of the printed wiring board.

  Moreover, another invention made in order to solve the said subject is equipped with the release adhesive film and the conductive adhesive layer laminated | stacked on the at least one part area | region of the surface of this release film, This conductive adhesive layer is Bonding the printed wiring board and the metal plate facing each other, and bonding between the conductive region exposed on the facing surface and the metal plate in the conductive pattern of the printed wiring board to develop electrical conductivity or thermal conductivity at least in the thickness direction A method for producing a sheet, wherein a conductive slurry having electrical conductivity or thermal conductivity is laminated by printing only in a region to be bonded to a conductive region of the printed wiring board on the surface of the release film; and The laminated conductive slurry is cured to form one or a plurality of bumps, and filled with an adhesive to surround the one or the plurality of bumps and the release film. And a step of forming an adhesive layer on a partial region of the surface.

  The adhesive sheet can achieve both improvement in mechanical adhesive strength and improvement in electrical conductivity or thermal conductivity.

FIG. 1 is a schematic plan view showing an adhesive sheet according to an embodiment of the present invention. 2 is a schematic cross-sectional view taken along the line XX of the adhesive sheet of FIG. 1 (the cut surface is a surface perpendicular to the conductive adhesive layer). FIG. 3A is a schematic plan view showing an alternative shape of the bump of the adhesive sheet of FIG. 1. 3B is a schematic plan view showing an alternative shape different from that of FIG. 3A of the bumps of the adhesive sheet of FIG. 1. 3C is a schematic plan view showing an alternative shape of the bump of the adhesive sheet of FIG. 1 different from that of FIGS. 3A and 3B. 3D is a schematic plan view showing an alternative shape of the bump of the adhesive sheet of FIG. 1 different from that of FIGS. 3A, 3B, and 3C. 4A is a schematic cross-sectional view (a cut surface is a surface perpendicular to a conductive adhesive layer) showing a manufacturing process of the adhesive sheet of FIG. FIG. 4B is a schematic cross-sectional view (the cut surface is a surface perpendicular to the conductive adhesive layer) showing the next manufacturing step of FIG. 4A. FIG. 5 is a schematic plan view showing an adhesive sheet of an embodiment different from the adhesive sheet of FIG. FIG. 6 is a schematic plan view showing an adhesive sheet of an embodiment different from the adhesive sheets of FIGS. 1 and 5. FIG. 7 is a schematic YY line cross-sectional view of the adhesive sheet of FIG. 6 (the cut surface is a surface perpendicular to the conductive adhesive layer).

[Description of Embodiment of the Present Invention]
The present invention includes a release film and a conductive adhesive layer laminated on at least a part of the surface of the release film, and the conductive adhesive layer bonds an opposing printed wiring board and a metal plate. The conductive sheet of the printed wiring board is an adhesive sheet that exhibits electrical conductivity or thermal conductivity at least in the thickness direction between the conductive region and the metal plate where the conductive pattern is exposed on the opposite surface, and the conductive adhesive layer is One or more bumps having electrical conductivity or thermal conductivity at least in the thickness direction, and an adhesive layer filled around the one or more bumps, the one or more bumps being the print It is an adhesive sheet that exists only in a region to be bonded to the conductive region of the wiring board.

  In this way, the adhesive sheet arranges one or a plurality of bumps that conduct electricity or heat only in the region to be bonded to the conductive region of the printed wiring board in this way, thereby increasing the electrical conductivity or thermal conductivity in the region to be bonded. In addition to improving the adhesive strength of the adhesive layer in a region other than the region to be bonded, a relatively large mechanical bond strength can be obtained. Therefore, it is possible to improve both the mechanical adhesive strength and the electrical conductivity or thermal conductivity.

  In addition, the printed wiring board to which the adhesive sheet is bonded has an insulating layer such as a coverlay laminated in a region other than the conductive region. Therefore, according to the adhesive sheet having bumps other than the region to be bonded to the conductive region, it is necessary to compress the bumps other than the conductive region on the surface of the coverlay or the like to ensure the conductivity of the bumps in the conductive region. On the other hand, since the adhesive sheet of the present invention has no bumps other than the region to be bonded to the conductive region, it is not necessary to compress the bump, and the bump in the region to be bonded to the conductive region can be easily and reliably connected. .

  One bump may be provided for each conductive region. In this way, by configuring one bump to be connected to each conductive region, the adhesive force of the adhesive layer is concentrated on one bump in each conductive region, and a pressure contact force is applied. An electrical or thermal connection by contact can be ensured more reliably.

  The total area ratio of the bumps in the conductive adhesive layer is preferably 0.01% or more and 2% or less. Thus, by setting the total area ratio of the bumps within the above range, good adhesive strength and good electrical conductivity or thermal conductivity can be obtained.

  The conductive pattern exposed in the conductive region is a ground wiring, and the bump may contain electrically conductive particles and a binder thereof. The content of the electrically conductive particles is preferably 40% by volume or more and 70% by volume or less. . Thus, by connecting the metal plate to the ground pattern and grounding, the metal plate can block electromagnetic noise. In addition, when the bump contains the above-described content of the electrically conductive particles and the binder, better electrical conductivity and mechanical strength of the bump can be obtained.

  The bump may contain heat conductive particles and a binder thereof, and the content of the heat conductive particles is preferably 30% by volume or more and 90% by volume or less. As described above, when the bump contains the heat conductive particles and the binder having the above-mentioned contents, better heat conductivity and mechanical strength of the bump can be obtained.

  The central vertical cross-sectional shape of the bump may be trapezoidal. As described above, since the central longitudinal cross-sectional shape of the bump is trapezoidal, the adhesive covers the inclined side of the trapezoid, so that the bump can be prevented from falling off the conductive adhesive layer. Further, when the adhesive sheet is pressure-bonded to the adherend member, the pressure on the side where the bump is small (the top side of the trapezoid) becomes high, so the surface on the side where the bump width is small on the adherend having low adhesion By sticking, the reliability of electric or heat transfer can be improved.

  It is good to have the marking for positioning in the area | region where the conductive adhesive in the said release film is not laminated | stacked. By having the marking in this way, the adhesion planned area can be accurately positioned so as to face the conductive area of the printed wiring board.

  Further, the present invention includes a release film and a conductive adhesive layer laminated on at least a part of the surface of the release film, and the conductive adhesive layer bonds the opposing printed wiring board and metal plate. And a method of manufacturing an adhesive sheet that exhibits electrical conductivity or thermal conductivity in a thickness direction at least between a conductive region exposed on an opposing surface of the conductive pattern of the printed wiring board and a metal plate, the method comprising: And laminating the laminated conductive slurry only in the region of the surface of the release film that is to be bonded to the conductive region of the printed wiring board by printing, and curing the laminated conductive slurry. An adhesive layer is formed around a part of the surface of the release film and around the one or more bumps by forming one or more bumps and filling with the adhesive. It includes processes for the preparation of the adhesive sheet and a step of forming.

  As described above, by laminating conductive slurry having electrical conductivity or thermal conductivity by printing, and curing the laminated conductive slurry to form bumps, and then filling the adhesive, mechanical adhesive strength and electrical conductivity are obtained. An adhesive sheet excellent in conductivity or thermal conductivity can be obtained easily and reliably.

  Here, the “metal plate” means a plate-like metal body laminated on the flexible printed wiring board, and is used to reinforce the flexible printed wiring board or to enhance the heat dissipation of the flexible printed wiring board. It is a concept that includes a heat sink. “Bump” refers to a bump or protrusion. The “total area ratio of bumps” refers to the ratio of the sum of the exposed areas of bumps on the surface obtained by cutting the conductive adhesive layer at the approximate center in the thickness direction. The term “trapezoidal shape” means a shape having a base and a top side opposite to the base, the width of which decreases from the base side toward the top side, and includes concepts in which the top side or the side is a curve. is there. The “bump central longitudinal cross-sectional shape” means a cross-sectional shape in a plane that passes through the center of gravity of the bump and is perpendicular to the conductive adhesive layer. The “marking” is used for positioning, and includes the one based on the shape of the release film itself, the one printed on the surface of the release film, the other member, and the like. The “slurry” refers to a material in which a solid content is mixed with a fluid and has a fluidity that can be printed, and includes adhesives, pastes, inks, paints, and the like.

[Details of the embodiment of the present invention]
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[First embodiment]
The adhesive sheet 1 shown in FIGS. 1 and 2 includes a release film 2 and a conductive adhesive layer 3 laminated on a central region on the surface of the release film 2. The adhesive sheet 1 adheres the printed wiring board and the metal plate facing each other by the conductive adhesive layer 3, and at least the thickness between the conductive region and the metal plate where the conductive pattern is exposed on the facing surface of the printed wiring board. It develops electrical conductivity in the direction.

<Release film>
The release film 2 has positioning holes 4 as markings for positioning in both end regions where the conductive adhesive layer 3 is not laminated.

  Examples of the material constituting the release film 2 include polyethylene resin, polypropylene resin, ethylene-vinyl acetate copolymer, ethylene-vinyl alcohol copolymer, polyethylene terephthalate resin, and other synthetic resin films, rubber sheets, paper, cloth, An appropriate film-like body made of a nonwoven fabric, a net, a foam sheet, a metal foil, a laminate of these, or the like can be used. Moreover, in order to improve peelability, it is preferable that the surface of the release film 2 is subjected to release treatment such as silicone treatment, long-chain alkyl treatment, and fluorine treatment as necessary. The peelability of the release film 2 can be controlled by adjusting the type of drug used for the peeling treatment or the coating amount thereof.

<Conductive adhesive layer>
The conductive adhesive layer 3 bonds the flexible printed wiring board and the metal plate facing the front surface side and the back surface side to each other, and between the conductive region and the metal plate where the conductive pattern is exposed on the facing surface of the flexible printed wiring board. It is a layer formed for the purpose of developing electrical conductivity at least in the thickness direction.

  For this purpose, the conductive adhesive layer 3 has a plurality of bumps 5 having electrical conductivity at least in the thickness direction, and an adhesive layer 6 filled around the bumps 5. Thereby, the conductive adhesive layer 3 can conduct electric energy at least in the direction (thickness direction) perpendicular to the surface by the bumps 5 and has adhesiveness by the adhesive layer 6.

〔bump〕
The bump 5 contains electrically conductive particles and a binder thereof. The bumps 5 are arranged in the conductive adhesive layer 3 so as to be present only in the region 7 to be bonded to the conductive region of the flexible printed wiring board shown by the one-dot chain line in FIG.

  The planar view shape of the bump 5 is not particularly limited, and may be a polygonal shape, a cross shape, a star shape or the like in addition to the circular shape. Further, the arrangement pattern of the bumps 5 in plan view can be appropriately designed in accordance with the area, shape, etc. of the adhesion planned region 7, for example, a stripe shape in which a plurality of linear bumps 5 shown in FIG. 3A are juxtaposed. 3B, a grid in which a plurality of linear bumps 5 intersect, a concentric circle made of a plurality of ring-shaped linear bumps 5 shown in FIG. 3C, and a dot-like bump 5 shown in FIG. 3D. However, although not shown, the dotted bumps 5 may be arranged in a staggered manner, or a combination thereof may be used. Each of the above shapes has a region in which the bump 5 is not formed in the adhesion planned region 7 in plan view.

  The total area ratio of the bumps 5 in the conductive adhesive layer 3 is not particularly limited, but the lower limit of the total area ratio of the bumps 5 relative to the area of the conductive adhesive layer 3 is preferably 0.01%. 05% is more preferable. On the other hand, the upper limit of the total area ratio of the bumps 5 with respect to the area of the conductive adhesive layer 3 is preferably 2%, and more preferably 1.5%. When the total area ratio of the bump 5 with respect to the area of the conductive adhesive layer 3 is less than the lower limit, the electrical conductivity of the conductive adhesive layer 3 may be insufficient. When the total area ratio of the bumps 5 with respect to the area of the conductive adhesive layer 3 exceeds the upper limit, the ratio of the adhesive layer 6 is decreased, and the mechanical adhesive strength of the conductive adhesive layer 3 may be reduced. The total area ratio of the bumps 5 with respect to the area of the conductive adhesive layer 3 is the sum of the exposed areas of the bumps 5 on the surface obtained by cutting the conductive adhesive layer 3 at the approximate center in the thickness direction. It is a numerical value divided by the planar view area (including the bump 5).

  Further, the total area ratio of the bumps 5 in the adhesion planned area 7 is not particularly limited, but the lower limit of the total area ratio of the bumps 5 with respect to the area of the adhesion planned area 7 is preferably 0.1%, and preferably 1%. Is more preferable. On the other hand, the upper limit of the total area ratio of the bumps 5 relative to the area of the adhesion planned region 7 is preferably 80%, and more preferably 60%. When the total area ratio of the bumps 5 with respect to the area of the adhesion planned region 7 is less than the above lower limit, the electric conductivity of the conductive adhesive layer 3 may be insufficient. When the total area ratio of the bumps 5 with respect to the area of the adhesion planned region 7 exceeds the upper limit, the ratio of the adhesive layer 6 is decreased, and the mechanical adhesive strength of the conductive adhesive layer 3 may be reduced. The total area ratio of the bumps 5 with respect to the area of the conductive adhesive layer 3 is the sum of the exposed areas of the bumps 5 on the surface obtained by cutting the conductive adhesive layer 3 at the approximate center in the thickness direction. It is a numerical value divided by the planar view area (including the bump 5).

  The plurality of bumps 5 are disposed so as to be surrounded by the adhesive layer 6 in the plan view. In other words, as shown in FIG. 2, the bumps 5 are not present at the periphery of the planned adhesion region 7 so that the adhesive layer 6 is present.

  The bump 5 has a trapezoidal central longitudinal cross section perpendicular to the conductive adhesive layer 3. Specifically, the central vertical cross-sectional shape of the bump 5 has a bottom side that contacts the release film 2 and a top side that appears on the surface of the conductive adhesive layer 3, and has a width from the bottom side toward the top side. Is getting smaller. In other words, the top side is shorter than the bottom side, and the side connecting the top and the bottom is inclined. An adhesive layer 6 is laminated on the inclined side. The bumps 5 may be arranged such that the trapezoidal top side is located on the flexible printed wiring board side, or may be arranged such that the trapezoidal top side is located on the metal plate side. Since the contact area on the top side of the trapezoidal shape of the bump 5 is relatively small with respect to the contact area on the bottom side, the bump 5 is arranged so that the top side is located on the member side where the adhesion pressure is desired to be increased. Thus, the adhesion with this member can be enhanced.

  In the central longitudinal cross-sectional shape, the upper limit of the ratio (w2 / w1) of the average length w2 of the top to the average length w1 of the bottom of the bump 5 is preferably 0.95, and more preferably 0.8. When the ratio of the average length w2 of the top side to the average length w1 of the base exceeds the upper limit, the effect of preventing the bumps 5 from dropping out may not be sufficiently obtained. On the other hand, the lower limit of the ratio (w2 / w1) of the average length w2 of the top to the average length w1 of the bottom of the bump 5 is preferably 0.2, and more preferably 0.4. When the ratio of the average length w2 of the top side to the average length w1 of the bottom side is less than the lower limit, the average length w1 of the bottom side becomes too large, and the filling amount of the adhesive filled around the bump 5 decreases. There is a possibility that the mechanical adhesive strength is lowered, and the average length w2 of the apex side is too small, and the electric conductivity between the adherends is likely to be lowered.

  In the central vertical cross-sectional shape, the average length w1 of the bottom side of the bump 5 can be appropriately designed according to the bonding area of the flexible printed wiring board and the metal plate, and can be set to 50 μm or more and 2000 μm or less, for example. . Similarly, the average length w2 of the top sides of the bumps 5 can be, for example, not less than 10 μm and not more than 1900 μm. Moreover, the average distance (distance between the bottom sides) d between the bumps 5 can be, for example, 50 μm or more and 2000 μm or less. The average length of the bottom and top sides of the bumps 5 means the average value of the base length and the top side length in the central vertical cross-sectional shape in which the bottom length of each bump 5 is minimum, and the average interval between the bumps 5 Means the average value of the minimum distances between adjacent bumps 5.

  As a minimum of average height h of bump 5, 10 micrometers is preferred and 15 micrometers is more preferred. On the other hand, the upper limit of the average height h of the bumps 5 is preferably 50 μm, and more preferably 45 μm. If the average height h of the bumps 5 is less than the lower limit, it may be difficult to form the bumps 5. For example, when a metal plate is bonded to a flexible printed wiring board using the conductive adhesive layer 3, the average height h of the bumps 5 becomes smaller than the thickness of the cover lay laminated on the surface of the conductive pattern, and the conductive pattern is formed. There is a possibility that the pattern and the metal plate cannot be electrically connected. When the average height h of the bump 5 exceeds the above upper limit, the thickness of the conductive adhesive layer 3 may be increased more than necessary.

(Electrically conductive particles)
Examples of the material of the electrically conductive particles contained in the bump 5 include silver, platinum, gold, copper, nickel, palladium, solder and the like. These may be used alone or in combination of two or more. Can do. Among these, silver powder, silver-coated copper powder, solder powder and the like exhibiting excellent electrical conductivity are preferable.

  As a minimum of the content rate of the electroconductive particle in the bump 5, 20 volume% is preferable and 30 volume% is more preferable. On the other hand, the upper limit of the content of conductive particles in the bump 5 is preferably 70% by volume, more preferably 60% by volume. When the content rate of electroconductive particle is less than the said minimum, there exists a possibility that the electrical conductivity between a flexible printed wiring board and a metal plate may become inadequate. When the content of the electrically conductive particles in the bump 5 exceeds the above upper limit, the binder is reduced, so that the formation of the bump 5 may be difficult or the bump 5 may be broken during use to impair the electrical conductivity. .

(binder)
Examples of the binder include an epoxy resin, a phenol resin, a polyester resin, a polyurethane resin, an acrylic resin, a melamine resin, a polyimide resin, a polyamideimide resin, and the like, and one or more of these are used. Can do. Among these, a thermosetting resin that can improve the heat resistance of the bump 5 is preferable, and an epoxy resin is particularly preferable.

  Examples of the epoxy resin used as the binder include bisphenol A type, F type, S type, AD type, copolymerized type of bisphenol A type and bisphenol F type, naphthalene type, novolac type, biphenyl type, dicyclopentadiene type, and the like. And a phenoxy resin which is a polymer epoxy resin.

  The binder can be used by dissolving in a solvent. Examples of the solvent include ester-based, ether-based, ketone-based, ether-ester-based, alcohol-based, hydrocarbon-based, and amine-based organic solvents, and one or more of these are used. be able to. As will be described later, when the bumps 5 are formed by printing a conductive slurry having electrical conductivity, it is preferable to use a high boiling point solvent excellent in printability, specifically, carbitol acetate or butyl carbitol. It is preferable to use acetate or the like.

[Adhesive layer]
The adhesive forming the adhesive layer 6 is not particularly limited as long as it has adhesiveness. For example, epoxy resin, polyimide resin, polyester resin, phenol resin, polyurethane resin, acrylic resin, melamine resin, polyamideimide Resin etc. can be mentioned, a thermosetting resin is preferable from the viewpoint of heat resistance, an epoxy resin or an acrylic resin is particularly preferable from the viewpoint of adhesion to a flexible printed wiring board, and a conductive slurry for forming the bump 5 More preferably, the same kind of adhesive is used.

  The above-mentioned solvent, curing agent, auxiliary agent and the like can be appropriately added to the adhesive layer 6. Moreover, in order to improve the electrical conductivity of the conductive adhesive layer 3, electrically conductive particles can be added to the adhesive layer 6.

  The upper limit of the amount of electrically conductive particles added to the adhesive layer 6 is preferably 20% by volume, more preferably 10% by volume, and even more preferably 5% by volume. When the addition amount of the conductive particles in the adhesive layer 6 exceeds the above upper limit, the adhesiveness of the adhesive layer 6 may be lowered due to an increase in impurities in the adhesive layer 6.

  The lower limit of the average thickness of the adhesive layer 6 is preferably 10 μm, and more preferably 15 μm. On the other hand, the upper limit of the average thickness of the adhesive layer 6 is preferably 40 μm, more preferably 35 μm, and even more preferably 30 μm. When the average thickness of the adhesive layer 6 is less than the lower limit, the conductive adhesive layer 3 may not exhibit sufficient mechanical adhesive strength and electrical connectivity. When the average thickness of the adhesive layer 6 exceeds the above upper limit, the thickness of the electronic component formed by bonding the flexible printed wiring board and the metal plate using the conductive adhesive layer 3 may be increased more than necessary. There is. The average thickness of the adhesive layer 6 means the average thickness of the adhesive layer 6 in a region where the bumps 5 do not exist in the thickness direction. Further, the average height h of the bumps 5 may be larger than the average thickness of the adhesive layer 6. By making the average height h of the bump 5 larger than the average thickness of the conductive adhesive layer 3 and causing the bump 5 to protrude from the surface of the adhesive layer 6, the electrical conductivity of the conductive adhesive layer 3 can be improved. However, if the protruding length of the bump 5 is too large, the bonding area between the adhesive layer 6 and the flexible printed wiring board and the metal plate may be decreased, and the mechanical adhesive strength may be decreased. The upper limit of the thickness (the average height h of the bump 5 minus the average thickness of the adhesive layer 6) is preferably 20 μm, and more preferably 10 μm.

<How to use the adhesive sheet>
The adhesive sheet 1 can be used in the following procedure. First, the surface (surface opposite to the release film 2) is attached to a flexible printed wiring board having a conductive region where the conductive pattern is exposed. At this time, for example, a positioning hole having the same shape is formed in advance in the position corresponding to the positioning hole 4 of the adhesive sheet 1 in the flexible printed wiring board, and the positioning hole of the flexible printed wiring board and the corresponding positioning of the adhesive sheet 1 are performed. By detecting the state in which the holes 4 are arranged in the thickness direction of the adhesive sheet 1 by optical means such as laser light, the conductive area of the flexible printed wiring board and the adhesion expected area of the adhesive sheet 1 are accurately overlapped. be able to. Further, by inserting a pin into the positioning hole of the printed wiring board and the corresponding positioning hole 4 of the adhesive sheet 1, the bonding expected area of the adhesive sheet 1 is aligned with the conductive area of the flexible printed wiring board. Also good. Next, the release film 2 is peeled off, and the back surface of the conductive adhesive layer 3 (the surface on which the release film 2 is laminated) is attached to a metal plate. The conductive adhesive layer 3 and the metal plate are aligned by, for example, forming a positioning hole in the metal plate or its jig that can be positioned using optical means such as laser light or mechanical means such as a pin. be able to. Moreover, you may align by visual observation by making the conductive contact bonding layer 3 and a metal plate into the same shape.

  Moreover, it is preferable that the conductive pattern corresponding to the adhesion plan area 7 of the adhesive sheet 1 and exposed in the conductive area of the flexible printed wiring board is a ground wiring. With this configuration, when the conductive adhesive layer 3 exhibits electrical conductivity, the metal plate is connected to the ground wiring and grounded, so that a shielding effect is obtained.

  As described above, when the surface of the adhesive sheet 1 is affixed to a flexible printed wiring board and the trapezoidal top of the central longitudinal section of the bump 5 is brought into contact with the conductive pattern exposed in the conductive region, the bump The contact area with the conductive pattern 5 can be made relatively smaller than the contact area with the metal plate, and the adhesion pressure of the bump 5 to the conductive pattern can be increased. As a result, the adhesion of the adhesive sheet 1 to the conductive pattern can be improved. Further, since the contact area of the bump 5 with the metal plate is increased, the energy transmission area between the conductive adhesive layer 3 and the metal plate is increased, and the electrical conductivity can be further improved.

  In addition, the surface of the said adhesive sheet 1 may be affixed on a metal plate, and the trapezoidal top side in the center longitudinal cross-sectional shape of the bump 5 may contact | abut to a metal plate. If the adhesive sheet 1 is adhered in such a direction, the contact area of the bump 5 with the metal plate is made relatively smaller than the contact area with the conductive pattern of the flexible printed wiring board, and conductive bonding is performed. The adhesion pressure of the layer 3 to the metal plate can be further increased.

<Method for producing adhesive sheet>
Next, a method for producing the adhesive sheet 1 will be described with reference to FIG. The manufacturing method of the said adhesive sheet has the following processes.
(1) A step of laminating a conductive slurry having electrical conductivity only in the region 7 to be bonded to the conductive region of the printed wiring board on the surface of the release film 2 by printing. (2) The laminated conductive slurry. (3) The process which forms the adhesive bond layer 6 in the one part area | region of the periphery of the several bump 5 and the release film 2 by filling with an adhesive agent

<(1) Conductive slurry lamination process>
In the conductive slurry laminating step, as shown in FIG. 4A, a conductive slurry containing electrically conductive particles and a binder thereof is laminated on the surface of the release film 2 so as to have a desired three-dimensional shape by printing. The method for printing the conductive slurry is not particularly limited, and for example, screen printing, gravure printing, offset printing, flexographic printing, inkjet printing, dispenser printing, and the like can be used.

(Conductive slurry)
The conductive slurry for forming the bump 5 is a composition having electrical conductivity by including the conductive particles constituting the bump 5 and a binder, the binder is not cured, and the pattern is formed by a printing technique. What is necessary is just to have the moderate fluidity | liquidity which can be formed and to be hardened in the hardening process mentioned later. Therefore, as the conductive slurry having electrical conductivity, for example, those commercially available under the names of conductive paste, conductive ink, conductive paint, conductive adhesive and the like may be used.

  A curing agent can be added to the conductive slurry. Examples of the curing agent include amine curing agents, polyaminoamide curing agents, acid and acid anhydride curing agents, basic active hydrogen compounds, tertiary aminos, and imidazoles.

  Furthermore, in addition to the components described above, auxiliary agents such as thickeners and leveling agents can be added to the conductive slurry. Moreover, a conductive slurry can be obtained by mixing each said component, for example with a three roll, a rotary stirring deaerator, etc.

<(2) Bump formation process>
In the bump forming step, the conductive slurry is cured by heating by an appropriate method according to the type of binder of the conductive slurry laminated on the surface of the release film 2, for example, when the binder is a thermosetting resin. The bump 5 is formed. When the conductive slurry contains a solvent, the solvent is evaporated in this bump forming step.

<(3) Adhesive filling process>
In the adhesive filling step, as shown in FIG. 4B, the adhesive film 6 is formed by filling the surface of the release film 2 on which the plurality of bumps 5 are formed (around the bumps 5) with the adhesive. As a method for filling the adhesive, a printing method or a coating method can be used. The printing method is not particularly limited, and for example, screen printing, gravure printing, offset printing, flexographic printing, inkjet printing, dispenser printing, and the like can be used. Moreover, it does not specifically limit as said coating method, For example, knife coating, die coating, roll coating, etc. can be used.

<Advantages>
The adhesive sheet 1 includes a plurality of bumps 5 having a conductive adhesive layer 3 formed in an adhesion planned region 7 to a conductive region where a conductive pattern of a flexible printed wiring board is exposed, and the bumps 5. When the flexible printed wiring board and the metal plate are bonded by the conductive adhesive layer 3, the conductive adhesive layer 3 becomes a conductive region of the flexible printed wiring board. Electrical conductivity is developed in the thickness direction between the conductive pattern exposed on the opposing surface and the metal plate. Further, the adhesive layer 6 is not required to have electrical conductivity, and the bumps 5 are not present in areas other than the adhesion planned region 7, so that a relatively large adhesive force is expressed. That is, the adhesive sheet 1 can achieve both improvement in mechanical adhesion strength between the flexible printed wiring board and the metal plate and improvement in electrical conductivity.

  In addition, the adhesive sheet 1 ensures electrical continuity by contact of a plurality of conductive particles because the bumps 5 are in contact with the conductive pattern of the flexible printed wiring board and the metal plate at the same time, thereby securely connecting them. As compared with the conventional electrically conductive adhesive, variation in resistance value can be suppressed.

  In addition, in the conventional adhesive in which particles having electric conductivity are dispersed, a plurality of electric conduction paths that do not contribute to electric conduction (do not electrically connect the conductive pattern and the metal plate) are constituted by electric conductive particles. In the adhesive sheet 1, this is prevented, and the reliability of electrical connection can be improved.

  In addition, since the adhesive sheet 1 has no bumps 5 in regions other than the planned adhesion region 7, the conductive adhesive layer 3 can exhibit a relatively large adhesive force in regions other than the planned adhesion region 7. Thereby, the adhesive strength of a flexible printed wiring board and a metal plate can be improved more.

  Moreover, since the bump 5 has a trapezoidal central longitudinal section, the adhesive sheet 1 can cover the inclined side of the trapezoid with the adhesive layer 6 and prevent the bump 5 from falling off. .

  Furthermore, since the adhesive sheet 1 has a plurality of bumps 5 in the planned bonding region 7, even if one bump 5 is separated from the conductive pattern or metal plate of the printed wiring board, the printed wiring is formed by other bumps 5. The electrical conductivity between the conductive pattern of the plate and the metal plate can be maintained.

[Second Embodiment]
The adhesive sheet 11 in FIG. 5 includes a release film 12 and a plurality of conductive adhesive layers 13 formed on the release film 12 in a predetermined pattern. The adhesive sheet 11 has a back surface of the conductive adhesive layer 13 in which two conductive adhesive layers 13 are laminated on a plurality of flexible printed wiring boards having a shape P indicated by a two-dot chain line, and the release film 12 is peeled off. In addition, it is used for laminating metal plates each having a planar shape substantially equal to each conductive adhesive layer 13.

<Release film>
The release film 12 has two positioning holes 14 for each region corresponding to each flexible printed wiring board in order to perform positioning with each flexible printed wiring board on which the two conductive adhesive layers 13 are laminated. As the material of the release film 12, the same material as the release film 2 in the adhesive sheet 1 of FIG. 1 can be used.

<Conductive adhesive layer>
Each conductive adhesive layer 13 includes one bump 15 and an adhesive layer 16 filled around the bump 15. Each of the conductive adhesive layers 13 has one planned adhesion region 17, and each of the planned adhesion regions 17 has the bump 15. The individual bumps 15 are the same as the bumps 5 in the adhesive sheet 1 of FIG. Moreover, since the adhesive layer 16 is the same as the adhesive layer 6 in the adhesive sheet 1 of FIG. 1 except for the planar shape corresponding to the arrangement of the bumps 15, description thereof is omitted.

<Advantages>
The adhesive sheet 11 has one bump 15 in each adhesion planned area 17, and pressure due to the adhesive force of the adhesive layer 16 is concentrated on the bump 15, so that the conductive pattern of the bump 15 and the flexible printed wiring board An electrical connection that allows electrical conduction between them is ensured. Further, the bump 15 determines the distance between the flexible printed wiring board and the metal plate at the contact position. However, since there is only one bump 15 in each bonding scheduled area 17, the flexible printed wiring board is surrounded around the bump 15. Flexibility reduces the distance between the flexible printed wiring board and the metal plate. As a result, the adhesive layer 16 is more reliably brought into contact with the flexible printed wiring board and the metal plate, so that a larger adhesive force can be obtained.

  Moreover, the said adhesive sheet 11 can laminate | stack two conductive adhesive layers 13 simultaneously with respect to a some flexible printed wiring board, respectively. For this reason, the electronic component comprised by adhere | attaching a flexible printed wiring board and a metal plate by the conductive contact bonding layer 13 can be manufactured efficiently.

[Third embodiment]
The adhesive sheet 21 in FIGS. 6 and 7 includes a release film 2 and a conductive adhesive layer 23 that is laminated in a central region on the surface of the release film 2. The adhesive sheet 1 adheres the printed wiring board and the metal plate facing each other by the conductive adhesive layer 3, and at least the thickness between the conductive region and the metal plate where the conductive pattern is exposed on the facing surface of the printed wiring board. It develops thermal conductivity in the direction. In the adhesive sheet 21 of FIGS. 6 and 7, the release film 2 is the same as the release film 2 of the adhesive sheet 1 of FIGS.

<Conductive adhesive layer>
The conductive adhesive layer 23 adheres the flexible printed wiring board and the metal plate facing the front side and the back side to each other, and at least the thickness between the conductive region and the metal plate of the flexible printed wiring board where the conductive pattern is exposed. It is a layer formed for the purpose of developing thermal conductivity in the direction.

  For this purpose, the conductive adhesive layer 23 has a plurality of bumps 25 having thermal conductivity at least in the thickness direction, and an adhesive layer 6 filled around the bumps 25. Thereby, the conductive adhesive layer 23 can conduct heat energy at least in the direction (thickness direction) perpendicular to the surface by the bumps 25 and has adhesiveness by the adhesive layer 6. In this conductive adhesive layer 23, the adhesive layer 6 is the same as the adhesive layer 6 in the conductive adhesive layer 23 of the adhesive sheet 1 of FIGS.

〔bump〕
The bump 25 contains thermally conductive particles and a binder thereof. The bumps 25 are the same except for the bumps 5 and the thermally conductive particles in the conductive adhesive layer 23 of the adhesive sheet 1 shown in FIGS. 1 and 2, so that the shape and arrangement, the material of the binder, etc. overlap. Description is omitted.

(Thermal conductive particles)
Examples of the material of the thermally conductive particles contained in the bump 25 include aluminum nitride (AlN), silicon nitride (Si ₃ N ₄ ), alumina (Al ₂ O ₃ ), boron nitride (BN), and beryllium oxide (BeO). ) And the like. Among these, aluminum nitride and boron nitride are preferable from the viewpoint of thermal conductivity. In addition, you may use the said heat conductive particle individually or in combination of 2 or more types.

  The lower limit of the average particle diameter of the heat conductive particles is preferably 2 μm, more preferably 3 μm, and even more preferably 5 μm, although it depends on the thickness of the adhesive sheet 21. On the other hand, the upper limit of the average particle size of the heat conductive particles is preferably 30 μm, more preferably 20 μm, and even more preferably 15 μm. When the average particle diameter of the heat conductive particles is less than the above lower limit, it may be difficult to mold the heat conductive particles. When the average particle diameter of the heat conductive particles exceeds the above upper limit, the surface of the bump 25 may become rough and the adhesiveness with the member to be bonded may be impaired. The “average particle size” means a particle size value at which the integrated amount is 50% by mass based on the integrated distribution obtained from the total particle mass under the sieve of each particle size obtained by the sieving method for the particle group. To do.

  As a minimum of the content rate of the heat conductive particle of bump 25, 30 volume% is preferred and 50 volume% is more preferred. On the other hand, as an upper limit of the content rate of the heat conductive particle of the bump 25, 90 volume% is preferable and 70 volume% is more preferable. When the content rate of a heat conductive particle is less than the said minimum, there exists a possibility that the heat conductivity between to-be-adhered members may fall. When the content of the heat conductive particles in the bump 25 exceeds the above upper limit, the binder is decreased, so that the formation of the bump 25 may be difficult, or the bump 25 may be broken during use to impair the heat conductivity. .

<How to use the adhesive sheet>
The adhesive sheet 21 can be used in the following procedure. First, the surface (surface opposite to the release film 2) is attached to a flexible printed wiring board having a conductive region where the conductive pattern is exposed. Next, the release film 2 is peeled off, and the back surface of the conductive adhesive layer 23 (the surface on which the release film 2 is laminated) is attached to a metal plate. The metal plate that is bonded to the flexible printed wiring board by the adhesive sheet 21 is preferably a heat sink having fins that protrude perpendicularly to the flexible printed wiring board.

<Method for producing adhesive sheet>
The manufacturing method of the said adhesive sheet 21 of FIG.6 and FIG.7 has the following processes.
(1) The process of laminating the conductive slurry having thermal conductivity only in the area 7 to be bonded to the conductive area of the printed wiring board on the surface of the release film 2 by printing. (2) The laminated conductive slurry. (3) The process which forms the adhesive bond layer 6 in the one part area | region of the surroundings of the several bump 25 and the release film 2 by filling with an adhesive agent

  Since the manufacturing method of the said adhesive sheet 21 is the same except the adhesive sheet 1 of the above-mentioned FIG.1 and FIG.2 differing in conductive slurry, the overlapping description is abbreviate | omitted.

(Conductive slurry)
The conductive slurry for forming the bump 25 is a composition having thermal conductivity by including the thermally conductive particles constituting the bump 25 and a binder, and the binder is not cured, and the pattern is formed by a printing technique. What is necessary is just to have the moderate fluidity | liquidity which can be formed and to be hardened in a hardening process.

<Advantages>
The adhesive sheet 21 includes a plurality of bumps 25 having a thermal conductivity, in which a conductive adhesive layer 23 is formed in a region 7 to be bonded to a conductive region where a conductive pattern of a flexible printed wiring board is exposed, When the flexible printed wiring board and the metal plate are bonded by the conductive adhesive layer 23, the conductive adhesive layer 23 is formed in the conductive region of the flexible printed wiring board. Thermal conductivity is developed in the thickness direction between the exposed conductive pattern and the metal plate. Further, the adhesive layer 6 is not required to have thermal conductivity, and the bumps 25 are not present in areas other than the adhesion planned region 7, so that a relatively large adhesive force is expressed. That is, the adhesive sheet 21 can achieve both improvement in mechanical adhesion strength and improvement in thermal conductivity between the flexible printed wiring board and the metal plate.

[Other Embodiments]
The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is not limited to the configuration of the embodiment described above, but is defined by the scope of the claims, and is intended to include all modifications within the meaning and scope equivalent to the scope of the claims. The

  By way of example, an adhesive sheet comprising thermally conductive bumps and other features similar to the adhesive sheet 11 of FIG. 5 is also contemplated by the present invention.

  Furthermore, the planar shape of the adhesive sheet and the conductive adhesive layer is not limited to that of the above-described embodiment, and can be any shape depending on the shape of the printed wiring board and metal plate to be bonded.

  Moreover, the said adhesive sheet contains what adhere | attaches a metal plate with respect to an inflexible printed wiring board.

  In the adhesive sheet, the bump may have both electrical conductivity and thermal conductivity. That is, the conductive slurry that forms the bumps can include electrically conductive particles and thermally conductive particles. In this case, the lower limit and the upper limit of the content ratio of the electrically conductive particles and the thermally conductive particles of the bumps are determined according to the volume ratio of the electrically conductive particles and the thermally conductive particles. What is necessary is just to set it as the value which proportionally distributed the minimum and upper limit of the above-mentioned heat conductive particle.

  In the adhesive sheet, bumps having electrical conductivity by containing electrically conductive particles and bumps having thermal conductivity by containing thermally conductive particles may be separately formed. In this case, depending on the design of the printed wiring board, the bumps having electrical conductivity and the bumps having thermal conductivity may be disposed in the same adhesion planned region, and the bumps having electrical conductivity and the thermal conductivity are disposed. Bumps having s may be disposed in separate bonding scheduled areas.

  In each said embodiment, although the said adhesive sheet was equipped with the release film only in the one surface (back surface) side of the conductive adhesive layer, the release film was provided in the other surface (front surface) side of the conductive adhesive layer. You may prepare.

  The adhesive sheet may be laminated on the metal plate first, and then the flexible printed wiring board may be adhered to the back surface of the conductive adhesive layer from which the release film has been peeled off.

  The bump may have a shape in which the width on the back side on which the release sheet is laminated is small and the width on the front side is large. Furthermore, the bump may be a laminate of a plurality of bumps in the thickness direction of the adhesive sheet.

  Further, the shape of the cross section perpendicular to the conductive adhesive layer of the bump of the present invention is not limited to a strict trapezoid as in the above embodiment, for example, a trapezoid in which the top of the trapezoid is an arc, or the base and the top May be a trapezoidal shape that is non-parallel. It is also possible to adopt semicircular shapes other than trapezoids, triangles, rectangles, constricted shapes whose width decreases toward the central portion in the height direction, barrel shapes whose width increases toward the central portion in the height direction, etc. It is.

  Further, in the conductive adhesive layer of the adhesive sheet, bumps may be formed so as not to be exposed on one or both of the front surface side and the back surface side. In this way, even if there is an adhesive layer on the front or back surface of the bump, the adhesive on the front or back surface of the bump is exposed to the outside due to the pressing force when the conductive adhesive layer is bonded to the flexible printed wiring board or metal plate. Extruded and the bump can be brought into contact with the conductive pattern of the flexible printed wiring board or the metal plate.

  In the adhesive sheet, the marking for positioning may be a notch or protrusion, a mark printed on a release film, or the like in addition to the through hole as in the above embodiment.

  The adhesive sheet of this invention can be used suitably for adhesion | attachment with a flexible printed wiring board and a metal plate, for example.

1, 11, 21 Adhesive sheet 2, 12 Release film 3, 13, 23 Conductive adhesive layer 4, 14 Positioning hole 5, 15, 25 Bump 6, 16 Adhesive layer 7, 17 Planned adhesion region

Claims (8)

A release adhesive film and a conductive adhesive layer laminated on at least a part of the surface of the release film are provided. The conductive adhesive layer adheres an opposing printed wiring board and metal plate, and the printed wiring board. An adhesive sheet that develops electrical conductivity or thermal conductivity at least in the thickness direction between the conductive region of the plate where the conductive pattern is exposed on the opposite surface and the metal plate,
The conductive adhesive layer has at least one or more bumps having electrical conductivity or thermal conductivity in the thickness direction, and an adhesive layer filled around the one or more bumps,
The adhesive sheet in which the one or more bumps are present only in a region to be bonded to the conductive region of the printed wiring board.   The adhesive sheet according to claim 1, wherein one bump is disposed for each conductive region.   The adhesive sheet according to claim 1 or 2, wherein a total area ratio of the bumps in the conductive adhesive layer is 0.01% or more and 2% or less.   The conductive pattern exposed in the conductive region is a ground wiring, and the bump contains electrically conductive particles and a binder thereof, and the content of the electrically conductive particles is 40% by volume or more and 70% by volume or less. 3. The adhesive sheet according to 3.   The adhesive sheet according to claim 3, wherein the bump contains thermally conductive particles and a binder thereof, and the content of the thermally conductive particles is 30% by volume or more and 90% by volume or less.   The adhesive sheet according to any one of claims 1 to 5, wherein a central longitudinal cross-sectional shape of the bump is a trapezoidal shape.   The adhesive sheet according to any one of claims 1 to 6, further comprising a marking for positioning in a region where the conductive adhesive in the release film is not laminated. A release adhesive film and a conductive adhesive layer laminated on at least a part of the surface of the release film are provided. The conductive adhesive layer adheres an opposing printed wiring board and metal plate, and the printed wiring board. A method for producing an adhesive sheet that exhibits electrical conductivity or thermal conductivity in a thickness direction at least between a conductive region exposed on an opposing surface of a conductive pattern of a plate and a metal plate,
Laminating the conductive slurry having electrical conductivity or thermal conductivity only in the planned adhesion region with the conductive region of the printed wiring board among the surfaces of the release film by printing,
Curing the laminated conductive slurry and forming one or more bumps;
And a step of forming an adhesive layer in a part of the surface of the release film around the one or the plurality of bumps by filling with an adhesive.

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