JPS6331905B2 - - 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 JP-A-51-20941 and JP-A-55.
This has been proposed in JP-A-104007, JP-A-56-22193, JP-A-51-21192, 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 connected. However, in such conventional methods, conduction between circuits is mainly obtained 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 during 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. Furthermore, uneven pressure during heating and pressurization causes variations in the thickness of the connecting member of the connecting circuit portion, resulting in a drawback of variations in conductivity. The present inventors previously proposed a conductive adhesive sheet with extremely good transparency for circuit connection;
Furthermore, as a result of intensive studies on a method for improving the above-mentioned drawbacks of the prior art and enabling a highly reliable connection, the present invention was arrived at. [Object of the Invention] An object of the present invention is 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 the conductive particles cover a part or the entire surface of the particle comprising a core material having a melting point of 250°C or higher. 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 ratio of the minimum diameter to the maximum 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% of the average particle diameter of the conductive particles.
This is a connecting member that has transparency with a total light transmittance 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 pressurizing during connection, and acts as a connecting material between the conductive particles or the conductive circuit part. It is possible to connect fine circuits with excellent reliability, and the core material with a melting point of 250℃ or higher acts as a spacer between circuits during connection operations by heating or heating/pressure, giving a uniform thickness to the connection member layer. for,
Provides highly reliable conductivity in the thickness direction and insulation in the planar direction. Furthermore, since adhesives having heat-sensitive pasting properties develop their adhesive properties by heating or heating and pressurizing during connection, mechanical connection between circuits can be obtained at the same time. To explain the structure of the connecting member according to the present invention with reference to the drawings, FIG. It shows that part or the entire surface is covered. As the core material 1, for example, Ni, Fe, Cr, Co, Al, Sb,
There are metal particles such as Mo, Cu, Ag, Pt, Au, Bi, Pb, Pd, and Zn, carbon, etc., and these may be used singly or as alloys, oxides, etc., and also in combinations of one or more of these. It can also be used as The core material 1 may be non-conductive particles such as glass or heat-resistant polymers. The shape of the core material 1 is the first
It is preferable to have a spherical shape as shown in figures a and b, but the surface may have protrusions or irregularities as shown in figures c and d. 2 is a low melting point metal, and a metal having a melting point in the range of 100 to 250°C is applicable. 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 metals, various eutectic alloys, non-eutectic low melting point alloys, or individual metals can be used. For example, Pb88.7%/Sn11.1% (melting point 250
℃), expressed in the same way below, Pb82.6/Cd17.4
(248℃) Pb85/Au15 (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℃), Tl52.5/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
°C), In97.2/Zn2.8 (144 °C), 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/Sb3 (186℃), Pb50/In50 (180℃),
Pb50/Sn50/Sn50 (183℃), Pb10/Sn90 (183
℃), Au3.5/Pb96.5 (221℃), Pb5/Sn95 (183
℃), Ag10/In90 (204℃), Pb60/Sn40 (183℃),
Examples include Sn95/Sb5 (232℃). As a method for configuring the low melting point metal layer 2 on the surface of the core material 1, general methods such as plating method, vapor deposition method, sputtering method, and adsorption method can be applied, and the thickness of the coating layer can be set arbitrarily. It is possible.
At this time, it is also possible to perform surface treatment such as providing a primer layer on the surface of the core material in order to improve adhesion. When the core material 1 is non-conductive, it is preferable to provide the low melting point metal layer over the entire surface. 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 drop in adhesive strength, and when the particle size is 50 μm or less, high resolution cannot be obtained because there is a high probability that the particles will exist between adjacent microcircuits. Regarding the shape, as described above, the ratio of the minimum diameter to the maximum diameter (hereinafter referred to as particle size ratio) is 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. 2 and 3 are schematic cross-sectional views showing the structure of the connecting member according to the present invention, in which conductive particles 4 are present in the adhesive 3. FIG. The conductive particles 4 may exist in a single layer in the thickness direction of the connecting member (FIG. 3), or may have a structure in which a plurality of conductive particles are arranged or aggregated in the thickness direction (FIG. 2). The amount of conductive particles 4 in the adhesive 3 is suitably 0.1 to 10% by volume. 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 will decrease, and the transparency of the connecting member will not 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. Examples of these polymers 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,
Polyvinylbutyral, acrylonitrile-butadiene copolymer, styrene-butadiene block copolymer, styrene-isoprene block copolymer, polybutadiene, ethylene cellulose, polyester, polyamide, polyurethane, natural rubber, silicone rubber, polychloroprene, etc. Synthetic rubbers, polyvinyl ether, etc. are applicable, and may be used alone or in combination of two or more. 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,
Used when it is necessary to increase stability against light, etc., 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 may 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,
Conductive particle mixed adhesive is created by dissolving an adhesive composition consisting of a polymer and other additives used as necessary in a solvent or heat-melting it to a liquid state, and then mixing it with conductive particles using a conventional method such as a ball mill. A drug composition is obtained. The conductive particle mixed adhesive may be used to form a connection member layer on one or both of the circuits requiring connection using means such as screen printing or a roll coater, or alternatively, a continuous elongated connection member layer may be formed using the conductive particle mixed adhesive. In order 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 case where the adhesive composition contains a solvent in the above manufacturing method, it is possible to obtain a connecting member in which the conductive particles are more densely arranged in the thickness direction by utilizing the phenomenon of volume reduction in the thickness direction of the connecting member when the solvent dries. Moreover, in hot melt coating without a solvent, it is possible to prevent environmental pollution caused by solvents during manufacturing. The thickness of the connecting member layer is relatively determined in consideration of the particle size of the conductive particles and the characteristics of the connecting 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 100 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 it requires mixing multiple conductive particles 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. As a method for bonding a circuit using the obtained connecting member, for example, a film-like connecting member is temporarily attached to the circuit A, and if there is a separator, the separator is peeled off, or a conductive adhesive composition is applied. After coating and removing the solvent if necessary, circuit B may be attached to the surface using a hot press, a heated roll, or the like. At this time, as shown in FIG. 7, both circuits A5 and B6 are strongly connected due to the softening and flow of the adhesive part, and at the same time, a stable conductive circuit can be formed within the adhesive layer by melting the metal particles 2. . The present invention will be explained in detail below using examples. Examples 1 to 6 and Comparative Examples 1 to 3 (1) Creation of connecting members While stirring Cu spheres with an average particle size of 44 μm as a core material, an alloy consisting of Sn48/In52 (melting point 117°C) was deposited on the surface by vacuum evaporation. Coating treatment was performed. The average thickness of the coating layer was 0.5 μm, and the conductive particles obtained above had an average particle size of 45 μm. The conductive particles were added to an adhesive solution consisting of 100 parts of styrene-butadiene block copolymer (MI2.6), 40 parts of an aromatic tackifier with a softening point of 120°C, and 200 parts of toluene. I changed and blended it. The above formulation was mixed in a ball mill for 48 hours to obtain an adhesive solution containing conductive particles. Apply this solution on the separator (siliconized polyester film) using a bar coater,
The solvent was removed by drying at 100°C for 3 minutes to obtain a film-like connection member. (2) 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 having an adhesive width of 3 mm and a length of 100 mm was placed thereon, and was temporarily attached by heating and pressing at 100° C. for 2 kg/cm ² for 5 seconds to obtain an FPC with a connecting member. Thereafter, the separator was peeled off, another FPC having the same pitch was placed on the separator peeled surface, the FPC circuit was aligned using a microscope, and the circuit was connected by heating and pressing at a pressure of 5 kg/cm ² for 10 seconds. The bonding temperature is as shown in Table 1 and was determined by adjusting the temperature of the hot plate of the press. Since the adhesive sheet in each example was transparent, it was easy to align the circuits with the aid of transmitted light. The properties are shown in Table 1, and all examples showed sufficient connection conduction resistance and insulation with adjacent circuits, and had sufficient adhesive strength. In addition, good characteristics were obtained over 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. The conditions and evaluation results are shown in Table 1. In Comparative Example 1, the thickness of the connecting member is large, resulting in decreased transparency and difficulty in aligning the circuit, and in Comparative Example 2, the large amount of conductive particles added makes it difficult to insulate from adjacent circuits. It was insufficient, and like Comparative Example 1, the transparency decreased. In Comparative Example 3, since the ratio of sheet thickness/particle size was small, the surface of the connecting member was rough and the adhesive strength was reduced. Example 7 Bi57/Sn43 on the surface of a glass sphere with an average particle size of 9 μm
(melting point: 139°C) was plated to a thickness of 1 μm. A thermoplastic polyester resin (glass transition point: 7° C.) as an adhesive was dispersed and mixed in a 30% methyl ketone solution to obtain a film-like connecting member in the same manner as in Examples 1 to 6. The connection between FPCs was evaluated in the same manner as in Examples 1 to 6, and the good characteristics shown in Table 1 were obtained. Example 8 After applying and drying the conductive particle mixed adhesive solution obtained in Example 7 directly onto the circuit of the FPC instead of on the separator to obtain an FPC with a connecting member, other treatments were carried out in the same manner as in Examples 1 to 6. FPC was connected. The results are shown in Table 1, and it was found that it had good properties. Note that in this embodiment, the step of temporarily attaching the connecting member to one circuit is unnecessary, and the step is unnecessary. Comparative Example 4 Same as Example 7 but without core material Bi57/
Single particle of Sn43 (melting point 139℃) (average particle size 11μm)
A connecting member was created using The evaluation results are shown in Table 1. When heated and pressurized at 160°C, which is 21°C higher than the melting point, molten metal flowed between the circuits and was electrically connected to the adjacent circuit, resulting in poor insulation.

【table】

〔Effect of the invention〕

As described in detail above, the connecting member of the present invention uses a heat-fusible metal coated with a core material as conductive particles, so that the conductive particles can be connected to each other or conductive circuits by heating or heating and pressurizing during connection. This allows for highly reliable microcircuit connections due to the fusion connection. Furthermore, since the core material in the conductive particles acts as a spacer between circuits during the connection operation, conductivity in the thickness direction and insulation in the surface direction can be obtained over a wide range of connection conditions. Furthermore, since the connecting member is transparent, it has the advantage that minute alignment of circuits can be easily performed with the aid of transmitted light.

[Brief explanation of the drawing]

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

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 are made of a core material having a melting point of 250°C or higher, and almost the entire surface of the particle has a melting point of 250°C or higher.
A circuit connecting member characterized by being particles coated with a low melting point metal of 100 to 250°C. 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.