HK1148162A

HK1148162A - Structure of connecting printed wiring boards, method of connecting printed wiring boards, and adhesive having anisotropic conductivity

Info

Publication number: HK1148162A
Application number: HK11100665.1A
Authority: HK
Inventors: Yamamoto Masamichi; Nakatsugi Kyouichirou; Kariya Ayao; Satou Katsuhiro; Okuda Yasuhiro
Original assignee: Sumitomo Electric Industries, Ltd.
Priority date: 2009-03-13
Filing date: 2011-01-24
Publication date: 2011-08-26

Description

Structure and method for connecting printed wiring boards and adhesive having anisotropic conductivity

Technical Field

The present invention relates to a structure for connecting a plurality of printed wiring boards in which electrodes disposed adjacent to each other on two boards are connected to each other by an adhesive having anisotropic conductivity, a method for connecting printed wiring boards, and an adhesive having anisotropic conductivity.

Background

In recent years, in the field of electronic devices, printed wiring boards have been widely used in various applications as electronic devices having features of higher integration, small size, and the like. In this field, a wiring board adherend in which two printed wiring boards are joined together by an adhesive is known. In addition, as a structure for connecting printed wiring boards included in a wiring board adherend, a structure in which two printed wiring boards are connected to each other by an adhesive having anisotropic conductivity (i.e., an adhesive whose conductive ability is anisotropic) is known.

More specifically, as shown in fig. 8, for example, a structure for connecting a plurality of printed wiring boards is known: this structure electrically connects the plurality of first electrodes 112 and 113 disposed adjacent to each other on the first plate 111 and the plurality of second electrodes 122 and 123 disposed adjacent to each other on the second plate 121 by the adhesive 130 containing the conductive particles 131 and having anisotropic conductivity.

In recent years, on the other hand, it is advanced to provide a plurality of electrodes having a fine pitch. Such advancement requires improvement in insulation characteristics between a plurality of electrodes disposed adjacent to each other. As a structure in which the insulating property between the plurality of electrodes is improved, for example, a structure in which a plurality of plates are connected with one protruding insulating member formed between the plurality of electrodes has been disclosed (for example, see patent document 1).

Documents of the prior art

Patent document

Patent document 1: published japanese patent application 2007-250825.

Disclosure of Invention

Although the above description is made, when one protruding insulating member is formed between a plurality of electrodes as described in the above-mentioned patent document 1, there is a problem that: although the insulating property can be improved, it is difficult to form a small protruded insulating member, so that it is not possible to provide a plurality of metal electrodes with a fine pitch by reducing the distance between the plurality of metal electrodes.

In addition, there have been problems in that: when the number of conductive particles included in the adhesive is reduced, although the insulation property between a plurality of electrodes adjacent to each other may be improved, the reliability of the electrical connection between the electrodes facing each other to be connected (for example, the first electrode 112 and the second electrode 122) may be reduced, so that it is difficult to combine the insulation property and the connection reliability.

The present invention has been made in view of the above problems. An object of the present invention is to provide a structure for connecting a plurality of printed wiring boards, which can realize not only provision of a plurality of electrodes with a fine pitch but also combination of insulation property and connection reliability, a method for connecting a plurality of printed wiring boards, and an adhesive having anisotropic conductivity.

The invention provides a structure for connecting a plurality of printed wiring boards. The structure electrically connects a plurality of first electrodes disposed adjacent to each other on a first board and a plurality of second electrodes disposed adjacent to each other on a second board by an adhesive containing conductive particles and having anisotropic conductivity. This structure has the following characteristics:

(a) an adhesive is disposed between a plurality of first electrodes and a plurality of second electrodes facing each other,

(b) heating and pressing the adhesive to form an adhesive layer between the first plate and the second plate, an

(c) In the adhesive layer, cavity portions are formed between the plurality of first electrodes and between the plurality of second electrodes.

According to the above structure, in the adhesive layer formed between the first plate and the second plate, the cavity portions are formed between the plurality of first electrodes and between the plurality of second electrodes. This structure can improve the insulating property between the plurality of first electrodes and between the plurality of second electrodes without providing, for example, a protruding insulating member between the plurality of first electrodes and between the plurality of second electrodes. Accordingly, the plurality of first electrodes and the plurality of second electrodes may be provided to have a fine pitch. Further, since the above-described cavity portion is formed in the adhesive layer, the conductive particles included in the adhesive are liable to be gathered in the region between the plurality of first electrodes provided on the first plate and the plurality of second electrodes provided on the second plate. Accordingly, the reliability of the electrical connection between the plurality of first electrodes and the plurality of second electrodes may be improved. Therefore, the structure can combine the insulation property and the connection reliability.

In the above structure of the present invention, the structure may have the following characteristics. In a cross section obtained by cutting, in a direction perpendicular to the thickness direction, regions between a plurality of first electrodes and a plurality of second electrodes facing each other in the thickness direction of the first plate and the second plate, when a1 denotes a total area of both the adhesive layer and the cavity portion between the plurality of electrodes disposed adjacent to each other in the surface direction perpendicular to the thickness direction, and a2 denotes an area of the cavity portion, a ratio of the area of the cavity portion to the total area, that is, a2/a1, is greater than or equal to 0.3 and less than or equal to 0.9. In the above description, the expression "between a plurality of electrodes disposed adjacent to each other" means not only "between a plurality of first electrodes along the surface direction", but also "between a plurality of second electrodes along the surface direction".

When the above structure is employed, the ratio of the area of the cavity portion in the adhesive layer to the total area of both the adhesive layer and the cavity portion between the plurality of electrodes disposed adjacent to each other in a cross section perpendicular to the thickness direction is 0.3 or more. Therefore, the hollow cavity portion occupies a large proportion of the area between the plurality of electrodes disposed adjacent to each other in the surface direction. Therefore, this structure can reliably improve the insulating property between the plurality of first electrodes and between the plurality of second electrodes. In addition, a ratio of an area of the cavity portion in the adhesive layer to a total area of both the adhesive layer and the cavity portion between the plurality of electrodes disposed adjacent to each other in a cross section perpendicular to the thickness direction is 0.9 or less. Therefore, the adhesive occupies a large proportion of the area among the areas between the plurality of electrodes disposed adjacent to each other in the surface direction. Therefore, the structure can secure the adhesive property between the first plate and the second plate.

In the above structure of the present invention, the plurality of first electrodes may have a pitch of greater than or equal to 10 μm and less than or equal to 300 μm therebetween, and the plurality of second electrodes may have a pitch of greater than or equal to 10 μm and less than or equal to 300 μm therebetween. In the above description, the length of the space between the plurality of first electrodes is formed by adding the width of one of the plurality of first electrodes to the interval between two adjacent first electrodes. Similarly, the length of the space between the plurality of second electrodes is formed by adding the width of one of the plurality of second electrodes to the interval between two adjacent second electrodes.

When the above structure is employed, the pitch between the plurality of first electrodes and the pitch between the plurality of second electrodes are 300 μm or less. Therefore, a fine pitch can be provided for the plurality of first electrodes and the plurality of second electrodes, so that the plurality of electrodes on the individual printed wiring boards can be provided at high density. Moreover, since the pitch between the plurality of first electrodes and the pitch between the plurality of second electrodes are 10 μm or more, the structure can secure the width of the plurality of electrodes and the interval between the adjacent two electrodes.

In the above structure of the present invention, the adhesive covers not only the plurality of first electrodes and the plurality of second electrodes but also the first plate at a position between the plurality of first electrodes and the second plate at a position between the plurality of second electrodes.

When the above structure is employed, the adhesive covers not only the plurality of first electrodes and the plurality of second electrodes but also the first plate and the second plate at positions between the plurality of first electrodes and between the plurality of second electrodes. Therefore, the structure can sufficiently secure the adhesive property between the first plate and the plurality of first electrodes and the second plate and the plurality of second electrodes.

In the above structure of the present invention, the conductive particles may constitute greater than or equal to 0.0001 vol% and less than or equal to 0.2 vol% with respect to the total volume of the binder.

When the above structure is employed, the conductive particles constitute 0.0001 vol% or more and 0.2 vol% or less of the total volume of the binder. In other words, the concentration of the conductive particles is low. Such a low concentration can improve the insulating property between the plurality of first electrodes and between the plurality of second electrodes.

In the above structure of the present invention, the conductive particles may be metal powder, individual particles in the metal powder have a shape in which a large number of fine metal particles are linked in a linear form or a needle shape, and each conductive particle has an aspect ratio of 5 or more.

When the above structure is adopted, the conductive particles are metal powders, and individual particles in the metal powders have a shape in which a large number of fine metal particles are linked in a linear form or a needle shape. Accordingly, the structure can facilitate electrical connection between the plurality of first electrodes and the plurality of second electrodes while ensuring the insulating property between the plurality of first electrodes and between the plurality of second electrodes. In addition, each of the conductive particles may have an aspect ratio of 5 or more. This feature increases the likelihood of contact between the conductive particles. This case can improve the connection reliability between the plurality of first electrodes and the plurality of second electrodes without increasing the number of conductive particles.

In the above structure of the present invention, the adhesive may have a film shape and the length direction of the long axis of the conductive particle may be oriented in the thickness direction of the adhesive having a film shape.

When the above structure is employed, the adhesive has a film shape. This feature not only facilitates handling of the adhesive, but also improves workability in forming the adhesive layer between the first plate and the second plate by heating and pressing the adhesive. In addition, the length direction of the long axis of the adhesive conductive particle is oriented in the thickness direction of the adhesive having a thin film shape. Therefore, while the insulating property between the plurality of first electrodes and between the plurality of second electrodes is ensured, the structure can also facilitate the electrical connection between the plurality of first electrodes and the plurality of second electrodes.

In the above structure of the present invention, the adhesive may have a thermosetting property and a melt viscosity of 10Pa · s or more and 10000Pa · s or less at 100 ℃.

When the above-described structure is employed, since the adhesive has a melt viscosity of 10000Pa · s or less at 100 ℃, when the adhesive layer is formed by heating and pressing the adhesive, air bubbles tend to grow in the adhesive, so that a large cavity portion is easily formed. In addition, since the adhesive has a melt viscosity of 10Pa · s or more at 100 ℃, when the adhesive layer is formed by heating and pressing the adhesive, gas forming the cavity portion is less likely to escape from the inside of the adhesive. Therefore, when the adhesive between the plurality of first electrodes and the plurality of second electrodes is heated and pressed, the structure can promote the formation of the cavity portion in the adhesive layer.

In the above structure of the present invention, the structure may have the following features:

(a) the adhesive contains an epoxy resin, a phenoxy resin, a curing agent and conductive particles as essential components,

(b) the epoxy resin is a liquid epoxy resin having a viscosity of greater than or equal to 0.1 pas and less than or equal to 150 pas at 25 ℃, and

(c) the liquid epoxy resin constitutes greater than or equal to 30 mass% and less than or equal to 50 mass% with respect to the total amount of the components of the adhesive.

The adhesive having the aforementioned composition becomes a suitable adhesive that can promote the formation of the cavity portion in the adhesive layer. Therefore, the adhesive can provide good insulating properties between the plurality of first electrodes and between the plurality of second electrodes even under a high-temperature and high-humidity environment.

As one aspect of the present invention, a method of connecting a plurality of printed wiring boards is provided. The method electrically connects a plurality of first electrodes disposed adjacent to each other on a first board and a plurality of second electrodes disposed adjacent to each other on a second board by an adhesive containing conductive particles and having anisotropic conductivity. The method has the following characteristics:

(c) Meanwhile, in the adhesive layer, cavity portions are formed between the plurality of first electrodes and between the plurality of second electrodes.

When the above method is employed, in the adhesive layer formed between the first plate and the second plate, the cavity portions are formed between the plurality of first electrodes and between the plurality of second electrodes. This structure can improve the insulating property between the plurality of first electrodes and between the plurality of second electrodes without providing, for example, a protruding insulating member between the plurality of first electrodes and between the plurality of second electrodes. Accordingly, the plurality of first electrodes and the plurality of second electrodes may be provided to have a fine pitch. Further, since the above-described cavity portion is formed in the adhesive layer, the conductive particles included in the adhesive are liable to be gathered in the region between the plurality of first electrodes provided on the first plate and the plurality of second electrodes provided on the second plate. Accordingly, the reliability of the electrical connection between the plurality of first electrodes and the plurality of second electrodes may be improved. Therefore, the structure can combine the insulation property and the connection reliability. In addition, since the cavity portion is formed in the adhesive layer at the same time as the adhesive layer is formed, the method can eliminate the necessity of another step for forming the cavity portion in the adhesive layer.

As another aspect of the present invention, the present invention provides an adhesive that has anisotropic conductivity and is used in a structure in which a plurality of printed wiring boards are connected. The adhesive has a thermosetting property and a melt viscosity at 100 ℃ of 10Pa s or more and 10000Pa s or less, or the adhesive has the following characteristics:

Therefore, the adhesive can be suitably used for forming the cavity portions in the adhesive layer between the plurality of first electrodes and between the plurality of second electrodes while forming the adhesive layer between the first plate and the second plate.

The present invention enables the structure to provide a plurality of electrodes with a fine pitch and combine the insulation property and the connection reliability.

Drawings

Fig. 1 is a diagram showing an adherend of a plurality of printed wiring boards in one embodiment of the invention, the wiring board adherend being viewed from a direction perpendicular to the surface direction.

Fig. 2 is a sectional view showing a structure of connecting a plurality of printed wiring boards in one embodiment of the present invention, the view showing a sectional view obtained by cutting a wiring board adherend in a direction perpendicular to a surface direction.

Fig. 3 is a vertical sectional view showing one of the conductive particles contained in the adhesive in one embodiment of the present invention.

Fig. 4 is a sectional view showing a structure of linking a plurality of printed wiring boards in one embodiment of the present invention, the view showing a sectional view obtained by cutting a wiring board adherend in a direction perpendicular to the thickness direction.

Fig. 5(a) and 5(b) show cross-sectional views for explaining a method of connecting a plurality of printed wiring boards in one embodiment of the present invention.

Fig. 6 is a graph illustrating a change in melt viscosity of an adhesive in which electrical conductivity is anisotropic in one embodiment of the present invention.

Fig. 7 is a graph showing changes in insulation resistance measured in examples and comparative examples.

Fig. 8 is a sectional view showing a conventional structure of connecting a plurality of printed wiring boards.

Description of the reference symbols

X: a thickness direction; y: a surface orientation; 1: a circuit board adhesive body; 10: a first printed wiring board; 11: a first plate; 12 and 13: a first electrode; 20: a second printed wiring board; 21: a second plate; 22 and 23: a second electrode; 30: a binder; 30 a: an adhesive layer; 31: conductive particles; 32: air bubbles; and 33: a cavity portion.

Detailed Description

Preferred embodiments of the present invention will be described below. Fig. 1 is a diagram showing a configuration of a wiring board adherend having a structure of connecting a plurality of printed wiring boards of the invention. Fig. 2 is a diagram showing a cross-sectional view obtained by cutting the wiring board adherend 1 in a direction perpendicular to the surface direction, the diagram showing an a-a cross-sectional view in fig. 1. Double-headed arrows X and Y in the drawing indicate the thickness direction and the surface direction, respectively. In fig. 1 and 4, a double-headed arrow Y indicating the surface direction shows the direction in which the electrodes extend. In this embodiment, a wiring board adhesive body that connects two flexible wiring boards together is explained as an example.

As shown in fig. 1, a wiring board adherend 1 formed by the present invention is an adherend in which a first printed wiring board 10 as a flexible wiring board and a second printed wiring board 20 as a flexible wiring board are adhered by an adhesive 30 (see fig. 2) having anisotropic conductivity. The plurality of electrodes (shown by dotted lines in fig. 1) included in the individual printed wiring boards 10 and 20 are electrically connected to each other by bonding (connecting) the first printed wiring board 10 and the second printed wiring board 20 with the adhesive 30 having anisotropic conductivity. The structures of the individual printed wiring boards 10 and 20 will be specifically described below.

As shown in fig. 2, a first board 11 and a plurality of first electrodes 12 and 13 arranged on the first board 11 are provided for the first printed wiring board 10. The first electrodes 12 and 13 are arranged adjacent to each other along the surface direction Y (i.e., the direction perpendicular to the thickness direction X). Similarly, a second board 21 and a plurality of second electrodes 22 and 23 arranged on the second board 21 are provided for the second printed wiring board 20. The second electrodes 22 and 23 are arranged adjacent to each other along the surface direction Y.

In a state where the first printed wiring board 10 and the second printed wiring board 20 are connected together, the first electrode 12 and the second electrode 22 face each other in the thickness direction X, and the first electrode 13 and the second electrode 23 face each other in the thickness direction X.

The separate plates 11 and 21 may be formed by using a resin material having good flexibility. In other words, the individual boards 11 and 21 can be formed by using a resin having ordinary adhesiveness (such as polyimide or polyester) for the printed wiring board. In particular, it is desirable that the resin have high heat resistance in addition to flexibility. The foregoing types of resins include polyamide-based resins and polyimide-based resins such as polyimide and polyamide-imide; they may be used appropriately.

The individual electrodes 12, 13, 22, and 23 are metal electrodes formed by using a metal such as copper. The above-mentioned individual electrodes can be formed, for example, by processing a metal foil such as a copper foil by etching using an existing process. In addition, the individual electrodes 12, 13, 22, and 23 may also be formed by a plating process using a semi-additive method.

In this embodiment, the individual electrodes 12, 13, 22 and 23 are formed so that the pitch P1 between the plurality of first electrodes and the pitch P2 between the plurality of second electrodes become, for example, 10 μm or more and 300 μm or less. The length of the pitch P1 between the plurality of first electrodes is formed by adding the width W1 of one of the plurality of first electrodes (i.e., the first electrode 12 or the first electrode 13) to the space S1 between two adjacent first electrodes 12 and 13. Thus. For example, when the width W1 of the individual first electrodes 12 and 13 is 50 μm and the interval S1 between the first electrodes 12 and 13 is 50 μm, the pitch P1 between the first electrodes is 100 μm. Similarly, the length of the pitch P2 between the plurality of second electrodes is formed by adding the width W2 of one of the plurality of second electrodes (i.e., the second electrode 22 or the second electrode 23) to the interval S2 between two adjacent second electrodes 22 and 23. In this embodiment, the width W1 and the width W2 have the same size, and the pitch P1 and the pitch P2 have the same size. Therefore, a pitch P1 between the plurality of first electrodes is equal to a pitch P2 between the plurality of second electrodes.

The adhesive 30 is an adhesive whose electrical conductivity is anisotropic, which contains the conductive particles 31 and has anisotropic electrical conductivity. The adhesive 30 is a thermosetting adhesive containing an epoxy resin, a phenoxy resin as a high molecular weight epoxy resin, a curing agent, and conductive particles 31 as essential components. The adhesive 30 adheres to the first printed wiring board 10 and the second printed wiring board 20. More specifically, the adhesive 30 is adhered not only to the first electrodes 12 and 13 and the second electrodes 22 and 23 but also to the first plate 11 and the second plate 21.

For example, the adhesive 30 is prepared by using an epoxy resin and a phenoxy resin, which are both insulating thermosetting resins, as main components in which conductive particles 31 made of nickel, copper, silver, gold, or the like are dispersed. By using the epoxy resin, the adhesive 30 can improve film formability, heat resistance, and adhesive strength.

The adhesive 30 may contain an epoxy resin such as a bisphenol a type epoxy resin, a bisphenol F type epoxy resin, a bisphenol S type epoxy resin, a bisphenol AD type epoxy resin, a bisphenol a type-bisphenol F type-copolymer type epoxy resin, a naphthalene type epoxy resin, a phenol type epoxy resin, a biphenyl type epoxy resin, or a dicyclopentadiene type epoxy resin. It is only necessary that the adhesive 30 contain at least one of the above-mentioned epoxy resins.

The molecular weights of the epoxy resin and the phenoxy resin may be appropriately selected in consideration of the properties required for the adhesive 30. For example, when a high molecular weight epoxy resin is used, film formability may be improved, and the melt viscosity of the resin at a connection temperature may be increased, so that a connection operation may be performed without disturbing the later-described orientation of the conductive particles. On the other hand, when a low molecular weight epoxy resin is used, the crosslinking density is increased, so that the heat resistance can be improved. In addition, upon heating, the resin reacts rapidly with the above curing agent, so that the adhesive property can be enhanced. Therefore, it is desirable to use a high molecular weight epoxy resin having a molecular weight of 15000 or more and a low molecular weight epoxy resin having a molecular weight of 2000 or less in combination to achieve a balance of properties. The amount of the high molecular weight epoxy resin and the low molecular weight epoxy resin used can be appropriately selected. The term "molecular weight" is used to indicate the weight average molecular weight according to polystyrene standards obtained from Gel Permeation Chromatography (GPC) dissolved in THF.

The adhesive 30 contains a latent curing agent as a curing agent. The inclusion of a curing agent for promoting curing of the epoxy resin enables high adhesive strength to be achieved. The latent curing agent has excellent storage stability at low temperature so that it does not undergo a curing reaction at room temperature. However, it undergoes a curing reaction rapidly with the aid of heat, light, or the like. Types of such latent curing agents include imidazole-based curing agents; a hydrazide-based curing agent; amine-based curing agents such as boron trifluoride-amine compounds, amino imides, polyamine-based curing agents, tertiary amines, and alkyl urea-based curing agents; a dicyandiamide-based curing agent; an acid anhydride-based curing agent; a phenol-based curing agent; and improved materials for these materials. These materials may be used alone or as a mixture of at least two of these materials.

Among the aforementioned latent curing agents, it is desirable to use an imidazole-based latent curing agent from the viewpoint of excellent storage stability at low temperatures and rapid curing characteristics. As the imidazole-based latent curing agent, a known imidazole-based latent curing agent can be used. More specifically, an adduct compound of an imidazole compound and an epoxy resin may be shown as an example. Types of imidazole compounds include imidazole, 2-methylimidazole, 2-ethylimidazole, 2-propylimidazole, 2-dodecylimidazole, 2-phenylimidazole, 2-phenyl-4-methylimidazole, and 4-methylimidazole.

In particular, it is desirable to cover these latent curing agents with a polymer material such as a polyurethane-based material or a polyester-based material, a metal thin film made of nickel, copper, or the like, or an inorganic substance such as calcium silicide, to form microcapsules, because the microcapsules combine two mutually contradictory characteristics of long-term storability and rapid curing property. Thus, it is particularly desirable to use microcapsule-type imidazolyl latent curing agents.

The adhesive 30, which is an adhesive having anisotropic conductivity, contains dispersed conductive particles 31. The conductive particles 31 are formed of metal powder, individual particles of which have a shape of a large so-called aspect ratio, which is a shape in which a large number of fine metal particles are linked in a linear form or a needle shape. In the above description, the term "fine metal particles" refers to fine spherical metal particles or fine metal particles formed, for example, by electroplating spherical resin particles with a metal. Also, in the above description, the term "aspect ratio" is used to denote a ratio L/R (see fig. 3), where L denotes a major axis length of one of the conductive particles 31 (length of one of the conductive particles 31), and R denotes a minor axis length of the one of the conductive particles 31 (maximum width of a cross section of one of the conductive particles 31). In this embodiment, the conductive particles 31 constitute 0.0001 vol% or more and constitute 0.2 vol% or less of the total volume of the binder 30.

The adhesive 30 is placed between the first plate 11 and the second plate 21 and between the first electrodes 12, 13 and the second electrodes 22, 23. When processed by heating and pressing, the adhesive 30 is first melted and thereafter cured. Through this process, the adhesive 30 forms an adhesive layer 30a between the first printed wiring board 10 and the second printed wiring board 20.

As described above, the structure of the present invention for connecting the printed wiring boards 10 and 20 electrically connects the plurality of first electrodes 12, 13 disposed adjacent to each other on the first board 11 and the plurality of second electrodes 22, 23 disposed adjacent to each other on the second board 21 by the adhesive 30 containing the conductive particles 31 and having anisotropic conductivity.

This embodiment is characterized in that, first, an adhesive 30 is arranged between the first electrodes 12, 13 and the second electrodes 22, 23 facing each other, and thereafter, the adhesive 30 is heated and pressed, thereby forming an adhesive layer 30a between the first plate 11 and the second plate 21, and in the adhesive layer 30a, cavity portions 33 are formed between the plurality of first electrodes 12 and 13 and between the plurality of second electrodes 22 and 23. This structure can improve the insulating property between the plurality of first electrodes 12 and 13 and between the plurality of second electrodes 22 and 23 without providing (in a conventional case, providing) a protruding insulating member (not shown) between the plurality of first electrodes 12 and 13 and between the plurality of second electrodes 22 and 23.

More specifically, bubbles 32 having a cavity portion 33 formed inside are formed in the adhesive layer 30a formed by the adhesive 30 at positions between the plurality of first electrodes 12 and 13, between the plurality of second electrodes 22 and 23, and between the first plate 11 and the second plate 21. The cavity portion 33 is not a space formed by the gas contained in the adhesive 30 before the adhesive 30 is heated and pressed as described above, but a space formed by the gas forcibly pushed into the adhesive 30 when the first printed wiring board 10 and the second printed wiring board 20 are connected to each other by the above-described heating and pressing process. Therefore, the gas in which the bubbles 32 are formed, that is, the gas included in the cavity portion 33, differs depending on the production conditions of the wiring board bonded body 1. The gas included in the cavity portion 33 is composed of, for example, air, nitrogen gas, or inert gas.

The cavity portion 33 is continuously formed along the direction in which the individual electrodes 12, 13, 22, and 23 extend. In other words, the cavity portion 33 extends along the direction in which the plurality of electrodes extend (the direction is shown by the double-headed arrow Y in fig. 1). In the sectional view obtained by cutting the connecting portion in the direction perpendicular to the thickness direction X, the cavity portion 33 extending in the direction in which the plurality of electrodes extend as described above has an area in a predetermined ratio to the total area between the plurality of electrodes disposed adjacent to each other.

More specifically, in a cross section (see fig. 4) obtained by cutting a region between the first electrodes 12 and 13 and the second electrodes 22 and 23 facing each other in the thickness direction X of the first plate 11 and the second plate 21 (the aforementioned region is a region shown by a double-headed arrow V in fig. 2), when a1 represents the total area of both the adhesive layer 30a (solid-line hatched portion) and the cavity portion 33 present between the plurality of electrodes disposed adjacent to each other in the surface direction, and a2 represents the area of the cavity portion 33, the ratio of the area of the cavity portion 33 to the total area, i.e., a2/a1, is 0.3 or more and 0.9 or less. In the above description, the expression "between a plurality of electrodes disposed adjacent to each other" means not only "between a plurality of first electrodes 12 and 13" but also "between a plurality of second electrodes 22 and 23".

As described above, the total area of the adhesive layer 30a and the cavity portion 33 is the area of the region where the first plate 11 and the second plate 21 are joined together by the adhesive 30; the area is equal to the total area between the plurality of electrodes disposed adjacent to each other in the surface direction perpendicular to the thickness direction X. In a cross section obtained by cutting the region between the first electrodes 12 and 13 and the second electrodes 22 and 23 facing each other in the thickness direction X of the first plate 11 and the second plate 21, the ratio of the area of the adhesive layer 30a between the plurality of electrodes disposed adjacent to each other in the surface direction to the area of the cavity portion 33 is in the range of 7: 3 to 1: 9.

When the plurality of cavity portions 33 exist between the first plate 11 and the second plate 21, between the plurality of first electrodes 12 and 13, and between the plurality of second electrodes 22 and 23, the aforementioned area of the cavity portion 33 in the above cross-sectional view is the total area of the plurality of cavity portions 33.

In this embodiment, the adhesive 30 having a thermosetting property has a melt viscosity of 10Pa · s or more and 10000Pa · s or less at 100 ℃. When such characteristics are given, when the adhesive layer 30a is formed by heating and pressing the adhesive 30, air bubbles 32 tend to grow in the adhesive 30, so that a large cavity portion 33 is easily formed. In addition, the gas forming the cavity portion 33 is less likely to escape from the inside of the adhesive 30. In order to improve the above effect, it is desirable that the adhesive 30 has a melt viscosity of 100Pa · s or more and 10000Pa · s or less at 100 ℃. In order to further improve the above effect, it is desirable that the adhesive 30 has a viscosity of 1000Pa · s or more and 10000Pa · s or less. For example, the melt viscosity of the adhesive 30 may be measured by using a rheometer (not shown), which is a viscosity measuring device capable of measuring the viscosity of a semisolid substance in addition to the viscosity of a liquid.

In this embodiment, in order to obtain an adhesive 30 having a melt viscosity of 10Pa · s or more and 10000Pa · s or less at 100 ℃, the adhesive 30 contains, as an epoxy resin, a liquid epoxy resin having a viscosity of 0.1Pa · s or more and 150Pa · s or less at 25 ℃ and 30 mass% or more and 50 mass% or less of the total amount of components constituting the adhesive. For example, a liquid epoxy resin having a viscosity of 0.1Pa · s or more and 150Pa · s or less at 25 ℃ can be obtained by using a bisphenol a type epoxy resin, a bisphenol F type epoxy resin, a dicyclopentadiene type epoxy resin, or a naphthalene type epoxy resin.

In this embodiment, the adhesive 30 covers not only the plurality of first electrodes 12 and 13 and the plurality of second electrodes 22 and 23 but also the first plate 11 and the second plate 21 at positions between the plurality of first electrodes 12, 13 and the plurality of second electrodes 22, 23. In other words, this embodiment has a structure in which the cavity portion 33 is not formed on the surfaces of the first plate 11, the second plate 21, the plurality of first electrodes 12 and 13, and the plurality of second electrodes 22 and 23.

It is desirable that the aspect ratio of each conductive particle 31 is greater than or equal to 5. The use of the aforementioned metal particles 31 increases the possibility of contact between the conductive particles 31. This facilitates the electrical connection between the first electrode 12 and the second electrode 22 and between the first electrode 13 and the second electrode 23.

The aspect ratio of the conductive particles 31 is directly measured by using a method such as observation under a CCD microscope. When one of the conductive particles 31 has a cross section other than a circle, the maximum width of the cross section is used as the minor axis length to obtain the aspect ratio. Each of the conductive particles 31 does not necessarily have a straight line shape. Even when a part of the conductive particles is slightly bent or branched, they can be used without problems. In this case, the maximum length of the conductive particles 31 is used as the length of the long axis to obtain the aspect ratio.

It is desirable that the adhesive 30 is a film-shaped adhesive 30 in which, at the time of forming the film-shaped adhesive 30, the direction of the long axis length L of the individual conductive particles 31 is oriented in the thickness direction X of the film-shaped adhesive 30 by passing through the film-shaped adhesive 30 by a magnetic field applied in the thickness direction X of the film-shaped adhesive 30. This orientation also facilitates electrical connection between the first electrode 12 and the second electrode 22 and between the first electrode 13 and the second electrode 23.

Next, a method of producing the wiring board adhesive body 1 having a structure of connecting the printed wiring boards 10 and 20 together such as shown in fig. 1, that is, a method of connecting the printed wiring boards 10 and 20 will be explained with reference to fig. 5(a) and 5 (b). Fig. 5(a) and 5(b) are sectional views for explaining the method of connecting a plurality of printed wiring boards 10 and 20 of the present invention.

First, as shown in fig. 5(a), a first plate 11 on which the first electrodes 12 and 13 are disposed and a second plate 21 on which the second electrodes 22 and 23 are disposed are prepared. In addition, the adhesive 30 in which the adhesive layer 30a is formed is prepared.

Next, the adhesive 30 containing the conductive particles 31 is disposed on the first plate 11 having the first electrodes 12 and 13. The adhesive 30 is heated to a predetermined temperature (e.g., 200 c). The adhesive 30 is pressed toward the first plate 11 with a certain pressure (e.g., 4Mpa) under the aforementioned heating condition to temporarily attach it to the first plate 11. The first plate 11 and the second plate 21 are arranged to face each other to align the first electrodes 12 and 13 with the second electrodes 22 and 23. More specifically, not only the first electrode 12 and the second electrode 22 are arranged to face each other in the thickness direction X, but also the first electrode 13 and the second electrode 23 are arranged to face each other in the thickness direction X to place the second plate 21 on the adhesive 30. Thus, the adhesive 30 is positioned between the first plate 11 and the second plate 21. In other words, the adhesive 30 is positioned between the first electrode 12 and the second electrode 22 facing each other and between the first electrode 13 and the second electrode 23 facing each other.

Next, by using a pressure connecting member (not shown), the adhesive 30 is pressed toward the first printed wiring board 10 by the second printed wiring board 20 at a certain pressure. In this case, the adhesive 30 is heated and melted. The heating temperature is further increased to cure the adhesive 30. Thus, the adhesive layer 30a is formed. In other words, as described above, since the adhesive 30 contains the thermosetting resin as a main component, when the adhesive 30 is heated, the melt viscosity is first reduced as shown in fig. 6. However, when the temperature is further increased, the adhesive 30 is cured. During the above process, when the adhesive 30 is melted, the gas existing between the first plate 11 and the second plate 21 enters inside the melted adhesive 30. Thereafter, a cavity portion 33 is formed in the adhesive layer 30a formed of the adhesive 30. Finally, when the predetermined curing time of the adhesive 30 has elapsed, the heating condition given by the pressure-attaching member is terminated. Thus, the production wiring board adhesive body 1 as shown in fig. 5(b) is completed.

This embodiment can achieve the following effects:

(1) by heating and pressing the adhesive 30 disposed between the first electrodes 12 and 13 and the second electrodes 22 and 23 facing each other, an adhesive layer 30a is formed between the first plate 11 and the second plate 21, and in the adhesive layer 30a, cavity portions 33 are formed between the plurality of first electrodes 12 and 13 and between the plurality of second electrodes 22 and 23. This structure can improve the insulating property between the plurality of first electrodes 12 and 13 and between the plurality of second electrodes 22 and 23 without providing, for example, between the plurality of first electrodes 12 and 13 and between the plurality of second electrodes 22 and 23, a protruding insulating member (not shown) which is conventionally provided. Accordingly, a fine pitch may be provided for the plurality of first electrodes 12 and 13 and the plurality of second electrodes 22 and 23. Moreover, since the above-described cavity portion 33 is formed in the adhesive layer 30a, the conductive particles 31 included in the adhesive 30 are easily gathered in the region between the plurality of first electrodes 12, 13 provided on the first plate 11 and the plurality of second electrodes 22, 23 provided on the second plate 21. Therefore, the reliability of the electrical connection between the first electrode 12 and the second electrode 22 and between the first electrode 13 and the second electrode 23 can be improved. Therefore, the structure can combine the insulation property and the connection reliability.

(2) The ratio of the area of the cavity portion 33 in the adhesive layer 30a to the total area of both the adhesive layer 30a and the cavity portion 33 between the plurality of electrodes disposed adjacent to each other in a cross section perpendicular to the thickness direction X is 0.3 or more. Therefore, as shown in fig. 2, a large proportion of the area is occupied by the cavity portion 33 in the area between the plurality of electrodes disposed adjacent to each other in the surface direction Y (i.e., the area between the first electrodes 12 and 13 and the area between the second electrodes 22 and 23). Therefore, this structure can reliably improve the insulating property between the plurality of first electrodes 12 and 13 and between the plurality of second electrodes 22 and 23. In addition, the ratio of the area of the cavity portion 33 in the adhesive layer 30a to the total area of the cavity portions 33 in the adhesive layer 30a present between the plurality of electrodes disposed adjacent to each other in a cross section perpendicular to the thickness direction is 0.9 or less. Therefore, a large proportion of the area is occupied by the adhesive 30 in the area between the plurality of electrodes disposed adjacent to each other along the surface direction Y shown in fig. 2. Therefore, this structure can secure the adhesive property between the first plate 11 and the second plate 12.

(3) A pitch P1 between the plurality of first electrodes and a pitch P2 between the plurality of second electrodes are 300 μm or less. Accordingly, a fine pitch can be provided for the plurality of first electrodes 12, 13 and the plurality of second electrodes 22, 23, so that the plurality of electrodes on the individual printed wiring boards 10 and 20 can be provided at high density. Moreover, since the pitch P1 between the plurality of first electrodes and the pitch P2 between the plurality of second electrodes are 10 μm or more, this structure can secure the width W1 and the width W2 of the plurality of electrodes and the interval S1 and the interval S2 between the adjacent two electrodes.

(4) The adhesive 30 covers not only the plurality of first electrodes 12 and 13 and the plurality of second electrodes 22 and 23 but also the first plate 11 and the second plate 21 at positions between the plurality of first electrodes 12 and 13 and the plurality of second electrodes 22 and 23. Therefore, this structure can sufficiently secure the adhesive property between the first plate 11 and the plurality of first electrodes 12, 13 and the second plate 21 and the plurality of second electrodes 22, 23.

(5) The conductive particles 31 constitute 0.0001 vol% or more and 0.2 vol% or less with respect to the total volume of the binder 30. In other words, the concentration of the conductive particles 31 is low. Such a low concentration can improve the insulating property between the plurality of first electrodes 12 and 13 and between the plurality of second electrodes 22 and 23.

(6) The conductive particles 31 are metal powders in which individual particles have a shape in which a large number of fine metal particles are linked in a linear form or a needle shape. Therefore, the structure can facilitate the electrical connection between the plurality of first electrodes 12, 13 and the plurality of second electrodes 22, 23 while ensuring the insulating property between the plurality of first electrodes 12 and 13 and between the plurality of second electrodes 22 and 23.

(7) Each of the conductive particles 31 may have an aspect ratio of 5 or more. This feature increases the possibility of contact between the conductive particles 31. This case can improve the connection reliability between the plurality of first electrodes 12 and 13 and the single second electrodes 22 and 23 without increasing the number of the conductive particles 31.

(8) The adhesive 30 has a film shape. This feature not only facilitates the handling of the adhesive 30, but also improves workability in forming the adhesive layer 30a between the first plate 11 and the second plate 21 by heating and pressing the adhesive 30.

(9) The long axis of the conductive particles 31 is oriented in the thickness direction X of the adhesive 30 having a thin film shape. Therefore, while the insulating property between the plurality of first electrodes 12 and 13 and between the plurality of second electrodes 22 and 23 is ensured, the structure can also facilitate the electrical connection between the plurality of first electrodes 12 and 13 and the plurality of second electrodes 22 and 23.

(10) The adhesive 30 has a melt viscosity of 10 pas or more and 10000 pas or less at 100 ℃. Since the adhesive 30 has a melt viscosity of 10000Pa · s or less at 100 ℃, when the adhesive layer 30a is formed by heating and pressing the adhesive 30, air bubbles 32 tend to grow in the adhesive 30, so that a large cavity portion 33 is easily formed. In addition, since the adhesive 30 has a melt viscosity of 10Pa · s or more at 100 ℃, when the adhesive layer 30a is formed by heating and pressing the adhesive 30, the gas forming the cavity portion 33 is less likely to escape from the inside of the adhesive 30. Therefore, this structure can facilitate the formation of the cavity portion 33 in the adhesive layer 30a when the adhesive 30 between the plurality of first electrodes 12 and 13 and the plurality of second electrodes 22 and 23 is heated and pressed.

(11) The adhesive 30 contains, as an epoxy resin, a liquid epoxy resin having a viscosity of 0.1Pa · s or more and 150Pa · s or less at 25 ℃, and the liquid epoxy resin constitutes 30 mass% or more and 50 mass% or less of the total amount of components of the adhesive 30. The adhesive 30 having the aforementioned composition is suitable for achieving the effects described in (10) above. In other words, the adhesive 30 having the aforementioned composition becomes a suitable adhesive 30 that can facilitate the formation of the cavity portions 33 in the adhesive layer 30 a. Therefore, the adhesive 30 can provide good insulating properties between the plurality of first electrodes 12 and 13 and between the plurality of second electrodes 22 and 23 even under a high-temperature and high-humidity environment.

(12) In the method of connecting a plurality of printed wiring boards 10 and 20 of the present invention, when the adhesive layer 30a is formed between the first board 11 and the second board 21, the cavity portion 33 is simultaneously formed in the adhesive layer 30 a. In other words, in the adhesive layer 30a formed between the first plate 11 and the second plate 21, the cavity portions 33 are formed between the plurality of first electrodes 12 and 13 and between the plurality of second electrodes 22 and 23. This structure can improve the insulating property between the plurality of first electrodes 12 and 13 and between the plurality of second electrodes 22 and 23 without providing a protruding insulating member between the plurality of first electrodes 12 and 13 and between the plurality of second electrodes 22 and 23. Accordingly, the plurality of first electrodes 12 and 13 and the plurality of second electrodes 22 and 23 may be provided to have a fine pitch. Moreover, since the above-described cavity portion 33 is formed in the adhesive layer 30a, the conductive particles 31 included in the adhesive 30 are liable to gather in the region between the plurality of first electrodes 12 and 13 provided on the first plate 11 and the plurality of second electrodes 22 and 23 provided on the second plate 21. Accordingly, the reliability of the electrical connection between the plurality of first electrodes 12 and 13 and the plurality of second electrodes 22 and 23 may be improved. Therefore, the structure can combine the insulation property and the connection reliability. In addition, since the cavity portion 33 is formed in the adhesive layer 30a at the same time as the adhesive layer 30a is formed, the method can eliminate the necessity of another step for forming the cavity portion 33 in the adhesive layer 30 a.

(13) The adhesive 30 of the present invention having anisotropic conductivity has the physical properties in the above (10) or the components in the above (11). Therefore, the adhesive 30 can be suitably used for forming the cavity portions 33 in the adhesive layer 30a between the plurality of first electrodes 12 and 13 and between the plurality of second electrodes 22 and 23 while forming the adhesive layer 30a between the first plate 11 and the second plate 21.

The present invention is not limited to the above-described embodiments. Various design modifications may be made based on the spirit of the present invention. Such design modifications should not be excluded from the scope of the present invention. For example, the above-described embodiment may be modified in the following manner.

Although the first printed wiring board 10 is a flexible wiring board in the above-described embodiment, it may be a rigid wiring board. Similarly, the second printed wiring board 20 may also be a rigid wiring board. When a rigid wiring board is used as the printed wiring board, the board can be formed by using a glass epoxy resin board or a glass board on which wiring is formed.

Examples of the invention

The present invention is explained based on examples and comparative examples. The present invention is not limited to the following examples. Examples may be modified or changed based on the spirit of the present invention. Such modifications or variations are not to be excluded from the scope of the present invention.

Examples of the invention

Preparation of the adhesive

Ni powder may be used as the conductive particles. More specifically, the conductive particles are formed of straight-chain fine nickel particles having a major axis length L distributed in the range of 3 to 20 μm and a minor axis length R distributed in the range of 0.1 to 0.3 μm. The following epoxy resins, phenoxy resins, and curing agents were used:

epoxy resin in liquid state at 25 ℃:

(1) bisphenol A type Epoxy resin (manufactured by Epoxy Resins Co., Japan, trade name jER828EL, viscosity at 25 ℃ C.: 14 Pa. s),

(2) bisphenol F type Epoxy resin (manufactured by Epoxy Resins Co., Japan, trade name: jER807, viscosity at 25 ℃ C.: 4Pa · s), and

(3) naphthalene type epoxy resin (manufactured by DIC Co., trade name EPICLONHP4032, viscosity at 25 ℃ C: 100 pas),

(4) a phenoxy resin (manufactured by InChem Co., under the trade name PKHH), and

curing agent:

(5) an imidazole-based curing agent (manufactured by ADEKA Co., Ltd.; trade name ADEKAHARDENER EH-4346S).

According to the following proportion: (1) these components (1) to (5) were used in a ratio of 5: 25: 5: 50: 15 to (2) to (3) to (4) to (5). Thus, in the example, the epoxy resin constitutes 35 mass% of the total amount of the components. The epoxy resin, phenoxy resin and curing agent are dissolved in 2-ethoxyethyl acetate. After they were dispersed, they were stirred using three rollers to form a solution with a solids fraction of 50% by weight. The aforementioned Ni powder was added to the solution so that the metal content became 0.2 vol%, which is expressed by the proportion in the total amount of the solid portion (Ni powder and resin). The solution was stirred by using a centrifugal stirring mixer to uniformly disperse the Ni powder. Thus, a constituent material of the adhesive is produced. The composition material was coated on the PET film treated with the releasing agent using a doctor blade. Thereafter, the constituent material was dried at 60 ℃ for 50 minutes in a magnetic field having a magnetic flux density of 100mT to solidify it. This operation causes the linear particles in the film to be oriented in the direction of the magnetic field. Thus, an adhesive having a thin film shape with a thickness of 35 μm and having anisotropic conductivity was produced.

Measurement of melt viscosity

The melt viscosity of the produced adhesive at 100 ℃ was measured using a rheometer (visco analyst var100 manufactured by reorganics Instruments AB). More specifically, the adhesive produced was sandwiched between two parallel disks having a diameter of 15 mm. The sample was heated from 20 ℃ to 250 ℃ at a temperature ramp rate of 10 ℃/min while vibrating at 1 Hz. As a result of measurement of the melt viscosity, the adhesive in this example had a melt viscosity of 7000Pa · s at 100 ℃.

Measurement of insulation resistance

The following circuit boards were prepared: a flexible wiring board as a printed wiring board in which 100 gold-plated copper electrodes having a width of 100 μm, a length of 3mm and a height of 18 μm are arranged at intervals of 100 μm; and a rigid wiring board as a printed wiring board in which 100 gold-plated copper electrodes having a width of 100 μm, a length of 3mm and a height of 18 μm are arranged at intervals of 100 μm. In other words, two printed wiring boards having an electrode pitch of 200 μm were prepared. The adhesive produced is sandwiched between a flexible wiring board and a rigid wiring board. A punch heated to an appropriate temperature (240 c) in order to heat the adhesive to a specific temperature (200 c) is placed on the flexible wiring board. The punch is moved toward the rigid wiring board to heat the adhesive to a specific temperature (200 ℃), so that a cavity portion can be formed in the adhesive layer formed by the adhesive. At the same time, the punch applies a pressure of 4MPa to the assembly for 10 seconds to perform bonding, thereby completing the mounting operation. The foregoing operation produces an adhered body of the flexible wiring board and the rigid wiring board in which the electrodes are connected to each other by the adhesive. The cavity portion in the adhesive layer had an area ratio of 0.4. Subsequently, the obtained adherend was placed in an environment having a temperature of 85 ℃ and a humidity of 85% RH. Under this condition, a direct current voltage of 15V was continuously applied between electrodes adjacent to each other in the surface direction to measure the resistance defined as the insulation resistance. The result is shown by the solid line in fig. 7. The measurement of the insulation resistance continues until the insulation resistance drops and has to be stabilized.

Comparative example

The adhesive was produced by the same method as used in the above example except that the naphthalene type epoxy resin was not used, in the following proportions: (1) these components were used in a weight ratio of (2): (4): (5): 6: 17: 67: 10, and the epoxy resin constituted 23 mass% of the total amount of the components. The melt viscosity was measured under the same conditions as those used in the above examples. The result is shown that the adhesive in the comparative example has a melt viscosity of 15000Pa · s at 100 ℃. The same method as that used in the above example was used to obtain an adherend. No cavity portion was found in the adhesive layer. Subsequently, the insulation resistance was measured under the same conditions as those used in the above-described examples. The result is shown by the chain double-dashed line in fig. 7.

Fig. 7 shows that, in the example, even when a direct-current voltage of 15V was continuously applied for 500 hours, the insulation resistance was not significantly reduced. This result proves that the insulating property between the electrodes disposed adjacent to each other is good even under a high-temperature and high-humidity environment. On the other hand, in the comparative example, fig. 7 shows that after a direct-current voltage of 15 was continuously applied for 300 hours, the insulation resistance significantly decreased and became unstable.

INDUSTRIAL APPLICABILITY

Examples of applications of the present invention include a wiring board adhesive body having a structure in which a printed wiring board in which a plurality of electrodes provided adjacent to each other on each of two boards are electrically connected to each other by an adhesive having anisotropic conductivity is connected.

Claims

1. A structure for connecting a plurality of printed wiring boards, which electrically connects a plurality of first electrodes disposed adjacent to each other on a first board and a plurality of second electrodes disposed adjacent to each other on a second board by an adhesive containing conductive particles and having anisotropic conductivity;

wherein:

2. The structure for connecting a plurality of printed wiring boards according to claim 1, wherein in a cross section obtained by cutting along a direction perpendicular to a thickness direction a region between a plurality of first electrodes and a plurality of second electrodes facing each other in a thickness direction of the first plate and the second plate, when a1 denotes a total area of both the cavity portion and the adhesive layer between the plurality of electrodes disposed adjacent to each other in a surface direction perpendicular to the thickness direction, and a2 denotes an area of the cavity portion, a ratio of the area of the cavity portion to the total area, that is, a2/a1, is 0.3 or more and 0.9 or less.

3. The structure for connecting a plurality of printed wiring boards according to claim 1, wherein the plurality of first electrodes have a pitch of 10 μm or more and 300 μm or less therebetween, and the plurality of second electrodes have a pitch of 10 μm or more and 300 μm or less therebetween.

4. The structure for connecting a plurality of printed wiring boards according to claim 1, wherein the adhesive covers not only the plurality of first electrodes and the plurality of second electrodes but also the first plate at a position between the plurality of first electrodes and the second plate at a position between the plurality of second electrodes.

5. The structure for connecting a plurality of printed wiring boards according to claim 1, wherein the conductive particles constitute greater than or equal to 0.0001 vol% and less than or equal to 0.2 vol% with respect to the total volume of the adhesive.

6. The structure for connecting a plurality of printed wiring boards according to claim 1, wherein:

(a) the conductive particles are metal powders in which individual particles have a shape of a needle or a needle in which a large number of fine metal particles are linked in a linear form, and

(b) each conductive particle has an aspect ratio greater than or equal to 5.

7. The structure for connecting a plurality of printed wiring boards according to claim 1, wherein:

(a) the adhesive has a film shape; and is

(b) The length direction of the long axis of the conductive particles is oriented in the thickness direction of the adhesive having a film shape.

8. The structure for connecting a plurality of printed wiring boards according to claim 1, wherein the adhesive has a thermosetting property and a melt viscosity of 10Pa · s or more and 10000Pa · s or less at 100 ℃.

9. The structure for connecting a plurality of printed wiring boards according to any one of claims 1 to 8, wherein:

(a) the adhesive contains an epoxy resin, a phenoxy resin, a curing agent, and conductive particles as essential components;

(b) the epoxy resin is a liquid epoxy resin having a viscosity of greater than or equal to 0.1 pas and less than or equal to 150 pas at 25 ℃; and

10. A method of connecting a plurality of printed wiring boards, which electrically connects a plurality of first electrodes disposed adjacent to each other on a first board and a plurality of second electrodes disposed adjacent to each other on a second board by an adhesive containing conductive particles and having anisotropic conductivity;

wherein:

(a) disposing an adhesive between a plurality of first electrodes and a plurality of second electrodes facing each other;

(b) heating and pressing the adhesive to form an adhesive layer between the first plate and the second plate; and

11. An adhesive having anisotropic conductivity and used in the structure for connecting a plurality of printed wiring boards as defined by claim 8 or 9.