JPS6331906B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a conductive connecting member used for connecting circuits. [Prior art] Conventionally, connections have been made in cases where connection terminals are lined up at a fine pitch, such as connection of integrated circuits to wiring boards, connection of display elements to wiring boards, connection of electrical circuits to leads, etc. As a method, methods using soldering or conductive adhesive are widely used. However, in these methods, the connection member must be formed only in the conductive circuit portion, making it difficult to connect fine circuits that are becoming increasingly dense and fine. Recently, connection members for circuit connections have been studied, and have already been published in Japanese Patent Application Laid-Open No. 51-20941 and Japanese Patent Laid-Open No. 55
This method has been proposed in Japanese Patent Application Laid-open No. 104007, Japanese Patent Application Laid-open No. 56-122193, Japanese Patent Application Laid-open No. 21192-1982, etc. The basic idea of all of these is to provide an anisotropically conductive connecting member layer containing a conductive material between opposing circuits, and to provide pressure or heating and pressure means to connect the circuits. At the same time as electrical connection, insulation is provided between adjacent circuits, and opposing circuits are bonded and fixed. However, in such conventional methods, conduction between circuits is mainly achieved through contact between multiple conductive materials, often metal particles, and the reliability of conduction is still lacking. was. As a method for improving the reliability of the conduction, there has been an attempt to fill an adhesive component with heat-melting metal particles and to melt the metal particles by heating during circuit connection. However, this method also has the disadvantage that sufficient connection reliability cannot be obtained because the range of conditions at the time of connection is narrow and strict control of temperature, pressure and time is required. In other words, in order to heat and melt the metal particles during connection, a temperature higher than the melting point of the metal is required, and as the connection temperature becomes higher than the melting point of the metal, the viscosity of the molten metal decreases, making the circuit requiring electrical connection. As a result, sufficient insulation between adjacent circuits could not be obtained, making it impossible to handle fine circuits. Therefore, it was necessary to set the temperature and time conditions with due consideration to the temperature rise curve at the time of connection. An additional drawback is that, for example, if the circuit is ITO
When the circuit and the heat-fusible metal do not have adhesive properties, such as in the case of an indium tin oxide (indium tin oxide) film, the electrical conductivity is poor due to the insulating adhesive present at the interface. The present inventors had previously proposed a conductive adhesive sheet with extremely good transparency for circuit connections, but as a result of intensive study on a method to improve the above-mentioned drawbacks and enable highly reliable connections, the present invention was developed. Achieved invention. [Object of the Invention] It is an object of the present invention to provide a connecting member for connecting microcircuits that has both highly reliable anisotropic conductivity and high adhesive strength through a simple bonding operation. [Disclosure of the Invention] That is, the present invention provides a connecting member comprising an adhesive component and conductive particles, in which substantially the entire surface of a core material comprising thermoplastic particles as conductive particles has a melting point.
The connecting member is characterized by using particles coated with a low melting point metal of 100 to 250°C, and preferably the conductive particles having the coating layer have an average particle size of 1 to 50 μm, and the maximum particle diameter is 1 to 50 μm. The ratio of the minimum diameter to the diameter is 0.5 to 1.0, the connecting member contains 0.1 to 10% by volume, and the thickness of the connecting member is 110% or more of the average particle diameter of the conductive particles, and the total light transmittance is
It is a connecting member with transparency of 40% or more and heat-sensitive adhesive properties. In the connecting member according to the present invention, the low melting point metal coated on the core material is melted by heating or heating and pressure during connection, and is used as a connecting material between the conductive particles or with the conductive circuit part. It is now possible to connect microcircuits with excellent reliability, and when the thermoplastic core material is heated or heated and pressurized, it deforms so as to be pressed along the conductive circuit, and the covered metal deforms accordingly. Since the contact area with the circuit increases, particularly excellent conductivity can be obtained. In addition, since it is sufficient to use a very small amount of metal as the conductive particles, it is possible to reduce the weight of the connecting member and save valuable metal resources. In addition, since adhesives having heat-sensitive pasting properties develop their adhesive properties by heating or heating and pressing during connection, mechanical connection can be made at the same time in the insulated circuit portion. Furthermore, in the connecting member of the present invention, since the core of the conductive particles is thermoplastic, it is mainly softened and deformed between circuits that are short in distance and have good thermal conductivity due to heating or heating and pressurization during connection. Since the particles in the insulating circuit portion do not deform, sufficient insulation from adjacent circuits can be obtained, making it applicable to fine circuits. To explain the structure of the connecting member according to the present invention using drawings, FIG. 1 is a schematic cross-sectional view showing conductive particles used in the present invention, in which the surface of the core material 1 made of thermoplastic particles is a low melting point metal. It shows how it is covered with 2. In this case, it is optimal that the entire surface of the core material 1 is covered with the low melting point metal 2, but there may be some uncoated portions. Examples of the core material 1 used in the present invention include polyethylene, polypropylene, polystyrene,
and acrylonitrile-styrene copolymer,
Particles made from various acrylates such as acrylonitrile-butadiene-styrene copolymer, polycarbonate, and polymethyl methacrylate, synthetic resins such as polyvinyl butyral, polyimide, polyamide, alkylphenol, and polyisobutylene, and various rubbers are used. Moreover, it may be a single substance or a composite of two or more types of these. The shape of the core material 1 is preferably approximately spherical, but the surface may have protrusions or irregularities. In order to be able to set a wide range of conditions during connection work,
It is preferable to use a material that does not exhibit a sharp melting point, ie, is amorphous. 2 is a low melting point metal layer, and a layer having a melting point in the range of 100 to 250°C can be used. If the melting point is lower than 100℃, it is undesirable because the reliability of circuit connection at high temperatures will decrease, and if it is 250℃ or higher, high temperature is required when connecting the circuit, and high temperature will have an adverse effect on the parts installed in the circuit, so it is not preferable. do not have. As these low melting point metal particles, various eutectic alloys, non-eutectic low melting point alloys, or individual metals can be used. For example, Pb88.7%/Sn11.1% (melting point
250℃), and expressed similarly below, Pb82.6/
Cd17.4 (248℃) Pb85/Au (215℃), Tl93.7/
Na6.3 (238℃), Tl92/As8 (220℃), Tl99.4/
Li0.6 (211℃), Tl82.9/Cd17.1 (203℃), Tl97/
Mg3 (203℃), Tl80/Sb20 (195℃), Tl (52.5/
Bi47.5 (188℃), Tl96.5/K3.5 (173℃), Tl73/
Au27 (131℃), Bi97/Na3 (218℃), Bi76.5/
23.5Tl (198℃), Bi60/Cd40 (144℃), Bi57/
Sn43 (139℃), Bi56.5/Pb43.5 (125℃), Sn (232
℃), Sn67.7/Cd32.3 (177℃), Sn56.5/Tl43.5
(170℃), In97.2/Zn2.8 (144℃), In74/Cd26
(123℃), Bi57/Pb11/Sn42 (135℃), Bi56/
Sn40/Zn4 (130℃), Bi53.9/Sn25.9/Cd20.2
(103℃), Sn48/In52 (117℃), In (157℃),
Ag5/Pb15/In80 (149℃), Pb38/Sn62 (183℃),
Pb47/Sn50/S63 (186℃), Pb50/In50 (180℃),
Pb50/Sn50 (183℃) Pb10/Sn90 (183℃),
Au3.5/Pb96.5 (221℃), Pb5/Sn95 (183℃),
Ag10/In90 (204℃) Pb60/Sn40 (183℃),
Examples include Sn95/Sb5 (232℃). Methods for forming the hot melt metal 2 on the surface of the thermoplastic core material 1 include, for example, physicochemical methods such as vapor deposition, sputtering, and plating, and adsorption of hot melt metal powder during synthesis of core material particles. or
Chemical methods such as chemically bonding a core material having a functional group with a heat-fusible metal or adsorption using a surfactant or a setting agent can be employed. Moreover, the thickness of the coating layer can be set arbitrarily. The conductive particles obtained above have an average particle size of 1
~50 μm, the ratio of the minimum particle size to the maximum particle size is
It shall be between 0.5 and 1.0. When the particle size is 1 μm or less, a large amount of conductive particles are required, resulting in a large decrease in adhesive strength, and when the particle size is 50 μm or more, high resolution cannot be obtained because there is a high probability that the particles will exist between adjacent fine circuits. Regarding the shape of the conductive particles, as mentioned above, the ratio of the minimum diameter to the maximum diameter (hereinafter referred to as particle size ratio) is
It should be about 0.5 to 1.0. Outside this range, the balance between conductivity and adhesiveness will be lost. A typical example that satisfies this range is one that is approximately spherical, but is not particularly limited as long as it satisfies the above conditions. Further, the particle surface may have protrusions or irregularities. Further, the particle size is assumed to be the overall average particle size, and it is convenient to measure the particle shape and particle size using, for example, a scanning electron microscope. When the conductive particles are spherical, it is easy to obtain contact between the particles or between the particles and the circuit surface by applying heat and pressure during connection, and it is easy to obtain high conductivity. The conductive particles may exist in a single layer in the thickness direction of the connection member, or may have a structure in which a plurality of conductive particles are arranged or aggregated in the thickness direction. Conductive particles account for 0.1 to 10% by volume in the adhesive
is appropriate. If it is less than 0.1% by volume, satisfactory conductivity cannot be obtained, and if it is more than 10% by volume, the insulation with adjacent circuits decreases and the transparency of the connecting member cannot be obtained. As the adhesive used in the present invention, basically any formulation used in ordinary adhesive sheets exhibiting insulation properties can be used. The formulation used for ordinary adhesive sheets consists of a polymer that imparts cohesive force, and other components such as a tackifier, tackifier, crosslinking agent, anti-aging agent, dispersant, etc., which are used as necessary. These polymer types include ethylene-vinyl acetate copolymer, modified ethylene-vinyl acetate copolymer, polyethylene, ethylene-propylene copolymer, ethylene-acrylic acid copolymer, and ethylene-vinyl acetate copolymer.
Acrylic ester copolymer, ethylene-acrylate copolymer, acrylic ester rubber, polyisobutylene, atactic polypropylene,
Synthetic rubbers such as polyvinyl butyral, acrylonitrile-butadiene copolymer, styrene-butadiene block copolymer, styrene-isoprene block copolymer, polybutadiene, ethylene cellulose, polyester, polyamide, polyurethane, natural rubber, silicone rubber, polychloroprene, etc. etc., polyvinyl ether, etc. can be used alone or in combination of two or more kinds. Tackifiers include dicyclopentadiene resin, rosin, modified rosin, terpene resin, xylene resin, terpene-phenol resin, alkylphenol resin, coumaron-indene resin, etc. These can be used alone or in combination as necessary. Used in combination with the above. Typical tackiness modifiers include various plasticizers such as dioctyl phthalate. The crosslinking agent is used when it is necessary to increase the cohesive force of the polymer, and is a polyfunctional substance that reacts with the functional groups of the polymer, such as polyisocyanates, melamine resins, urea resins, and phenolic resins. Anti-aging agents are activated by polymer binder heat, oxygen,
These are used when it is necessary to increase stability against light, such as stabilizers such as metal soaps, antioxidants such as alkylphenols, and ultraviolet absorbers such as benzophenones and benzotriazoles. These are used alone or in combination of two or more, if necessary. A dispersant may be used to improve the dispersibility of conductive particles. Examples of this include surfactants, which can be used singly or in combination of nonionic, cationic, anionic, and amphoteric surfactants. As a method for manufacturing a connecting member according to the present invention,
An adhesive composition consisting of a polymer and other additives used as necessary is dissolved in a solvent or dispersed in a suspension state in a medium, or heated and melted to a liquid state, and then the conductive particles are processed using a conventional method such as a ball mill. A conductive particle mixed adhesive composition is obtained by mixing according to the method described in the following. When using a solvent, conductive particles with a metal layer formed on the core particles have reduced solubility in solvents, so it is possible to use a solvent, but it is possible to dissolve the adhesive and separate the core particles. It is further preferred to choose a solvent that does not dissolve. As a means for this, for example, it is preferable to form an adhesive into an emulsion and disperse the conductive particles in an aqueous medium. The conductive particle mixed adhesive may be used to form a connecting member layer on one or both circuits to be connected using means such as screen printing or a roll coater, or alternatively, a continuous elongated connecting member may be formed. To obtain this, a connecting member layer may be formed by the above method on a separator made of paper or plastic film, etc., which has been subjected to peeling treatment as necessary, and then rolled up. It is also possible to stack the layers without using a separator. In the above manufacturing method, when a solvent or a dispersion medium is included in the adhesive composition, it is possible to obtain a connecting member in which the conductive particles are more densely arranged in the thickness direction by utilizing the volumetric shrinkage phenomenon in the thickness direction when the solvent dries. This is possible, and in hot-melt coating without a solvent, environmental pollution caused by solvents during production can be prevented. The thickness of the connection member layer is determined relative to the size of the conductive particles and the characteristics of the connection member. That is, in order to sufficiently hold the conductive particles with an adhesive, the adhesive needs to have a minimum particle size of 110% or more of the particle size of the conductive particles. If it is less than 110%, the conductive particles will not be protected by the adhesive, resulting in deterioration in conductivity due to oxidation or corrosion. Further, due to the characteristics of the connecting member, a thickness of 5 to 110 μm is required. If it is less than 5μm, sufficient adhesiveness cannot be obtained, and if it is less than 100μm,
m or more is not practical because a large amount of conductive particles must be mixed in order to obtain sufficient conductivity.
For the connection member layer, a conductive or non-conductive core material made of, for example, non-woven fabric may be used as required. The obtained connection member surface may be covered with a separator to prevent dust from adhering to it, if necessary.
Alternatively, continuous winding is also possible by using double-sided separators. The connecting member thus obtained has considerable transparency. When the connecting member is transparent, quality control during manufacturing is easy to perform and the appearance is good.
Furthermore, when adhering display elements, etc., it becomes possible to adopt a configuration in which the adherend can be seen through. A method of bonding a circuit using the obtained connecting member is, for example, by temporarily pasting a film-like connecting member on the circuit A and peeling off the separator if there is a separator, or applying a conductive adhesive composition. If necessary, the circuit B may be attached to the surface after the solvent has been removed using a hot press or a heated roll. FIGS. 2 and 3 schematically show a state in which circuits are connected by this method. As the adhesive 3 softens and flows due to heat and pressure, the conductive particles 7 also soften and deform, and come into contact with each other. So both circuits 4,
It becomes possible to conductively bond between the two. If one or both of the circuits 4 and 5 do not have adhesive properties, for example
Even in the case of transparent conductive glass made of ITO, since the core material has thermoplasticity, stable high conductivity can be obtained because the circuit and the low melting point metal layer on the surface of the core material are in surface contact. The present invention will be explained in more detail below using examples. Examples 1 to 6 (1) Preparation of conductive particles Polystyrene particles having an average particle diameter of 35 μm and a molecular weight of 5000 were obtained as a core material by an emulsion polymerization method. on the other hand
Low melting point metal particles made of Sn48/In52 with a particle diameter of 5 μm (melting point 117° C.) were dispersed in a 2% aqueous solution of a titanium coupling agent, and the core material was added while stirring, and stirring was continued for one more time. After washing the dispersion obtained above with water on a wire mesh with an opening of 30μ,
Conductive particles were obtained by drying the water and removing unadsorbed excess metal. These conductive particles are substantially spherical particles in which metal particles with a particle size of 5 μm are adsorbed and densely packed in a single layer on the polystyrene surface with a particle size of 35 μm using a coupling agent. (2) Preparation of conductive particle mixed dispersion and connection member After mixing the conductive particles in an acrylic acid ester emulsion (glass transition point -30°C) with varying amounts, conductive particles are created by performing ultrasonic dispersion. A mixed dispersion of particles was obtained. This dispersion was applied onto a separator (siliconized polyester film) using a bar coater.
C. for 10 minutes to remove water as a dispersion medium to obtain a connecting member. (3) Evaluation Flexible circuit board (FPC) with a total circuit width of 100 mm and a circuit with a line width of 0.1 mm and a pitch of 0.2 mm.
The above-mentioned connecting member cut into a piece with an adhesive width of 3 mm and a length of 100 mm was placed thereon, and the connecting member was connected to the FPC by being lightly crimped by hand. Since the connecting member had adhesive properties even at room temperature, the above-mentioned temporary connection could be easily performed. After that, the separator is peeled off, another FPC with the same pitch is placed on the separator peeled surface, the FPC circuit is aligned under a microscope, and the circuit is connected by heating and pressing at a pressure of 5 kg/cm ² for 10 seconds. did. The connection temperature is as shown in Table 1, and was determined by adjusting the hot plate temperature of the press. At this time, since the adhesive sheet was transparent, it was extremely easy to align the circuits with the aid of transmitted light. The properties of this product are shown in Table 1, and in all Examples, it had sufficient connection resistance and insulation between adjacent circuits, and also exhibited sufficient adhesive strength. Further, as seen in Examples 3 to 5, the above characteristics were obtained under a wide range of connection conditions. Comparative Examples 1 to 3 Same as Examples 1 to 6, but the amount of conductive particles added and the thickness were changed. Table 1 shows the conditions and their evaluation results. In Comparative Examples 1 and 2, alignment of the circuits was difficult due to insufficient transparency of the connecting member, and in Comparative Example 2, insulation with adjacent circuits was insufficient due to the large amount of conductive particles added. In Comparative Example 3, the adhesive strength decreased because the ratio of sheet thickness to conductive particle diameter was small. Example 7 While stirring polyvinyl butyral particles
Pb38/Sn62 (melting point 183°C) solder was vacuum deposited. The conductive particles obtained above have a core particle size of approximately 10μ.
m, and the thickness of the solder layer was approximately 0.5 μm. Next, the content of the conductive particles was varied in an adhesive solution consisting of 100 parts of styrene-butadiene block copolymer (MI2.6), 50 parts of an aromatic tackifier with a softening point of 120°C, and 200 parts of toluene. After mixing for 48 hours, an adhesive solution containing conductive particles was obtained. Since polyvinyl butyral is insoluble in toluene, the conductive particles were not dissolved and existed stably even though there was a part of the layer not covered with solder. Using the above solution, a film-like connection member was created in the same manner as in Examples 1 to 6, and the film was placed on the FPC at 120°C.
After making a temporary connection by heating and pressurizing under the conditions of -5Kg/cm-5 seconds, a 1mm-thick ITO-based transparent conductive glass (surface resistance 200Ω/
□) was aligned and connected. The results are shown in Table 1, and it was found that it had good anisotropic conductivity. When the cross section of the connection was observed using an electron microscope, it was found that the transparent conductive glass surface and the hot melt metal were in surface contact as if pressed together by a core material. Examples 8-9 The adhesive solution containing the conductive particles obtained in Example 7 was
After screen printing on the FPC substrate, it was dried at 90°C for 10 minutes to obtain an FPC with connecting members. The connection of the transparent conductive glass used in Example 7 to this connection member surface was evaluated. The properties are shown in Table 1, and it showed good anisotropic conductivity. Furthermore, in this embodiment, the step of temporarily connecting the connecting member to one circuit can be omitted. Although the conduction resistance values of Examples 7 to 9 are slightly high values due to the influence of the transparent conductive glass, they are sufficiently practical. Comparative Example 4 An adhesive solution containing conductive particles was obtained by using solder particles of Pb38/Sn62 (melting point 183° C.) with an average particle size of 11 μm without using a thermoplastic core material as the conductive particles. FPC with connection members in the same manner as Examples 8 and 9
After obtaining, it was connected to transparent conductive glass in the same manner as in Example 7. At this time, it is 32℃ higher than the melting temperature of the solder.
When connections were made at a high temperature of 215°C, the solder flowed out of the conductive circuit and was electrically connected to the adjacent circuit, resulting in poor insulation.

〔Effect of the invention〕

As described in detail above, according to the connecting member of the present invention, particles in which the surface of the core material made of thermoplastic particles is coated with a low melting point metal are used as the conductive particles, so that the conductive particles can be connected to each other or connected to a conductive circuit. Since the thermoplastic core material is easily deformed along the circuit under pressure, the circuit and conductive particles are arranged in surface contact, making it possible to connect fine circuits with excellent reliability. Become. Furthermore, since the combination of low melting point metal and thermoplastic core material can be specified, highly reliable connections can be made over a wide range of connection conditions. In addition, since the connection is made with adhesive in the insulating part, a flexible connection is possible, and since the connection member is transparent, it is possible to easily align fine circuits with the help of transmitted light. has advantages.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of conductive particles, and FIGS. 2 and 3 are schematic cross-sectional views showing a state in which a circuit is connected using a connecting member according to the present invention. Explanation of symbols, 1...Nuclear material, 2...Low melting point metal,
3... Adhesive, 4, 5... Circuit, 6... Insulating substrate, 7... Conductive particles.

Claims (1)

[Claims] 1. In a circuit connecting member in which conductive particles are dispersed in an insulating adhesive component to such an extent that a conductive path is formed only in the thickness direction when the volume is reduced in the thickness direction. , the conductive particles cover almost the entire surface of the core material made of thermoplastic resin particles with a melting point of 100 to 250°C.
A circuit connecting member characterized by being particles coated with a low melting point metal. 2 The conductive particles have an average particle diameter of 1 to 50 μm, a ratio of the minimum diameter to the maximum diameter of the particles of 0.5 to 1.0, are contained in the connection member at 0.1 to 10% by volume, and the thickness of the connection member is the same as that of the conductive particles. 110% or more of the average particle diameter of
The circuit connection member according to claim 1, which is the above. 3. The circuit connecting member according to claim 1 or 2, wherein the adhesive component is mainly composed of a thermoplastic polymer and has heat-sensitive adhesion properties.