JP2823799B2 - Anisotropic conductive adhesive - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

This invention relates to LCD, EL, LE
D, ECD, two display bodies useful for connection between connection terminals of display bodies such as plasma displays and circuit boards on which the driving parts are mounted, or boards of various electric circuits, etc., are applied to terminal portions of circuit boards. And an anisotropic conductive adhesive for adhering them and electrically connecting the two terminals.

[0002]

2. Description of the Related Art In recent years, various anisotropic conductive adhesives in which conductive particles are uniformly dispersed in an insulating adhesive have been applied in a thin film form between terminals as means for providing electrical conduction between two terminals. Is known. With the widespread use of electronic devices using this anisotropic conductive adhesive, reliability of connection in various environments such as in automobiles and outdoors has been required. Usually, carbon particles, metal particles such as gold, silver, copper, nickel, and aluminum, which are spherical and have a uniform particle size, and plastic balls whose surfaces are plated with metal have been used as the conductive particles. But
Since carbon particles have a high contact resistance and are difficult to maintain a stable connection state, metal particles that provide stable connection with lower resistance and plastic balls whose surfaces are plated with metal are often used.

[0003]

However, when metal particles are used as the conductive particles, the difference in specific gravity from the insulating adhesive is large, so that the conductive particles are uniformly dispersed in the insulating adhesive. However, the conductive particles and the insulating adhesive tend to separate and settle during storage, making it difficult to produce an anisotropic conductive adhesive in which the conductive particles are uniformly dispersed, resulting in poor workability.
Plastic balls with metal plating on the surface do not have this drawback, but the adhesion between the plastic ball surface and the metal plating is weak, and the plastic ball has a large amount of compressive deformation. In some cases, the metal plating was partially peeled off due to cracks, and a leak was easily caused, and stable electrical connection could not be achieved. Plastic balls are also insulative and are easily charged due to their insulating properties.Therefore, conductive particles are likely to form aggregates.Particles after metal plating are also spherical, as well as those that are plated on aggregates. In some cases, nonuniformity or difficulty in dispersing and blending in the insulating adhesive was caused, and a short circuit between adjacent circuits due to agglomerated conductive particles sometimes occurred.

Further, the metal plating usually has a two-layer structure in which a base metal such as Ni is applied to a lower layer and a noble metal such as Au is applied to an upper layer, and the total thickness is often 0.5 μm or less. For example, the base metal of the lower layer is exposed by separation, and even if noble metal plating is performed on the surface, plating corrosion may occur in the lower layer. In addition, since spherical particles come into contact with the connected electrode at only one point, they are not affected by microscopic movement of the insulating adhesive due to changes in temperature, humidity, etc., in the operating environment, or by external forces such as vibration and dropping. On the other hand, the contact points easily come off, and the reliability of electrical conduction is impaired. Therefore, an object of the present invention is to easily remove a contact point even if the conductive particles receive an external force such as microscopic movement, vibration, or drop due to residual stress of the insulating adhesive under various use environments. An object of the present invention is to provide an anisotropic conductive adhesive which keeps no electrical connection, greatly improves the reliability of electrical connection, and has good workability during manufacturing.

[0005]

The inventor of the present invention has found that the reliability of the electrical connection in the anisotropic conductive adhesive depends on the number of contact points of the conductive particles and the cleanliness of the contact points. The higher the cleanliness of a point, the higher its reliability.In addition, if carbon particles are used as the core of the conductive particles, the specific gravity of the conductive particles approaches that of the insulating adhesive, preventing separation during manufacturing. At the same time, the porosity of the carbon particles surface improves the adhesion of metal plating and prevents the plating layer from peeling off during compression, and the conductivity of the carbon particles prevents the conductive particles from being charged due to the conductivity of the carbon particles. The present inventors have found that aggregation can be prevented, and have reached the present invention.
That is, the anisotropic conductive adhesive according to the present invention has (a) 10%
Strength in compression is 10 kgf / mm ² or more, at 80 kgf / mm ² or less, the table
Graphite by attaching tar or pitch to the surface and firing
Carbon particles having a plurality of projections at the core, (ii) the
Base metal plating layer with thickness of 0.05-0.3μm on core surface and thickness
Provided a noble metal plating layer of 50 to 500 Å in sequence, the conductive particles of the overall particle size. 5 to 100 [mu] m, and is characterized in Rukoto such dispersed in (c) an insulating adhesive.

Some of the carbon particles as the core of the conductive particles have a plurality of protrusions in order to increase the number of contact points.
Using et al is. If the projections are too small or too small,
Since contact at multiple points becomes impossible after plating of the surface, the conductive particles protrude 0.5 μm or more, particularly 2 μm or more from the virtual maximum inscribed sphere diameter, and preferably have 4 or more particles per particle. Carbon particles may include the high strength for load to the protrusion during crimp connection to the terminal to focus, specifically, in the strength at 10% compression 10 kgf / mm ² or more, particularly 15kgf
/ mm ² or more and usually 80 kgf / mm ² or less, and the compressive breaking strength of the particles is preferably 30 kgf / mm ² or more, particularly preferably 50 kgf / mm ² or more and usually 100 kgf / mm ² or less. As such carbon particles, tar or pitch, which can be easily graphitized, is attached to the surface of the raw spherical carbon particles, and then about 8%.
It is preferable to graphitize by baking at 00 to 3,000 ° C., which results in high-strength particles having a more uniform particle size.

Since the surface of the carbon particles has high contact resistance and the contact points are easily contaminated, it is necessary to apply a noble metal plating of gold, silver, platinum, palladium or the like to the carbon particles to have a clean surface. Make it easy to apply precious metal plating,
In order to obtain a low resistance, plating of a base metal such as nickel and then noble metal plating is generally performed. At this time, the thickness of the base metal plating layer , such as nickel, is too thin to facilitate the precious metal plating as described above, and the effect of making the resistance low is reduced. Therefore, the thickness of the noble metal plating layer should be as small as possible from the viewpoint of cost, and should be 50 to 500 mm, especially 100 to 300 mm so as to cover the surface surely.
And it is sufficient. The outer diameter of the conductive particles including the protrusions thus formed is preferably as uniform as possible. If the diameter is too large, a short circuit is likely to occur between adjacent electrodes.
Those within the range of m are preferred.

The obtained conductive particles are then dispersed in an insulating adhesive to form the anisotropic conductive adhesive of the present invention. Thermoplastic, thermosetting may be any.The thermoplastic is bonded at a relatively low temperature and heating for a short time, the pot life is long, and the thermosetting one has high adhesive strength and excellent heat resistance, These may be appropriately selected according to the purpose of use. Specific examples of the insulating adhesive include ethylene / vinyl acetate copolymer, carboxyl-modified ethylene / vinyl acetate copolymer, ethylene / isobutyl acrylate copolymer, polyamide, polyester, polymethyl methacrylate, polyvinyl ether, and polyvinyl butyral. , Polyurethane, styrene-butylene-styrene (SBS) copolymer, carboxyl-modified SBS copolymer, styrene-isoprene-styrene (SIS) copolymer, styrene-ethylene-butylene-styrene (SEB)
S) Copolymer, maleic acid-modified SEBS copolymer, polybutadiene rubber, chloroprene rubber (CR), carboxyl-modified CR, styrene-butadiene rubber, isobutylene-isoprene copolymer, acrylonitrile-butadiene rubber (NBR), carboxyl-modified NBR , Epoxy resin, silicone rubber (SR) and the like, and these are used alone or in combination of two or more. The amount of the conductive particles dispersed in the insulating adhesive is too large, so that the conductive particles are stochastically connected in a planar direction so as not to impair the anisotropic conductivity. The particles on the electrode to be connected are reduced, resulting in poor connection, disconnection,
0.1 to 30 parts by volume, especially 1 to 100 parts by volume of insulating adhesive
15 parts by volume are preferred.

As described above, the anisotropic conductive adhesive of the present invention is applied to two terminals to be connected to bond the display body and / or the substrate and to electrically connect both terminals. However, examples of the display include a flexible printed circuit board based on glass such as a display panel, metal such as an LSI chip, metal oxide, polyimide, polyester resin, or the like. These surfaces have -OH, -COOH, -C = O, -COO
Since the insulating adhesive has a polar group such as CH _3, it is preferable that the insulating adhesive has a functional group corresponding to the polar group, and the solubility parameter is preferably 8.5 or more, particularly preferably 9.0 or more. In adjusting these solubility parameters, the above-mentioned acrylic resin, nitrile rubber, chloroprene rubber, an adhesive mainly composed of vinyl acetate resin, etc.,
Since the base polymer itself has a high solubility parameter, this may be used as is, but when a resin having a low solubility parameter such as polyisobutylene, polybutadiene, or polystyrene is used as a base material, rosin, rosin derivative, terpene resin, terpene / phenol copolymer Coalescing,
Petroleum resin, coumarone-indene resin, styrene resin,
The polarity can be adjusted by adding a tackifier such as an isoprene-based resin, an alkylphenol resin, or a phenol resin.

The anisotropic conductive adhesive of the present invention may further comprise, if necessary, a reactive auxiliary agent, a phenol resin as a crosslinking agent, a polyol, an isocyanate, a melamine resin,
Urea resins, urotropin resins, amines, acid anhydrides, peroxides, metal oxides, organic metal salts such as chromium trifluoroacetate, alkoxides such as titanium, zirconia and aluminum, and organic metal compounds such as dibutyltin dioxide , Photoinitiators such as 2,2-diethoxyacetophenone and benzyl, sensitizers such as amines, phosphorus compounds and chlorine compounds, as well as curing agents, vulcanizing agents, control agents, deterioration inhibitors, heat-resistant additives, Heat conduction improvers, softeners, coloring agents, various coupling agents, metal deactivators, and the like can be appropriately added.

In the anisotropic conductive adhesive of the present invention, when the adhesive component is in a solid state or a high-viscosity liquid at room temperature and without a solvent, this is dissolved in an appropriate solvent, and the solution is prepared by a known method such as printing, coating and spraying. It can be used by directly applying it to the display unit to be connected or the terminal part of the electronic / electric circuit board, but after forming it on the separator film or sheet, it is cut to the desired size and this is connected to the connection terminal part. Alternatively, when the adhesive component is in a liquid state, it can be used by applying it to a connection terminal portion during connection work. After application, one display unit to be connected, pressurized from above the electronic / electric circuit board, and simultaneously activate the adhesive by heating or irradiation of light or electron beam to bond the two display units and / or the circuit board. In addition to bonding and fixing with an agent, both opposing terminal portions are electrically connected via conductive particles.

[0012]

The anisotropic conductive adhesive of the present invention has a structure in which conductive particles have a plurality of projections and the surface is covered with a clean noble metal, and thus has low contact resistance at many points with electrodes to be connected. Withstands shocks such as vibration and dropping, improves the reliability of the connection in a long-term use environment, and has good adhesion between the carbon particle surface and the metal plating. Thus, stable electrical connection is achieved without any problem, and since the specific gravity is close to that of the insulating adhesive, there is no separation, and there is no aggregation of particles.

[0013]

EXAMPLES Specific embodiments of the present invention will be described below with reference to examples and comparative examples. EXAMPLE Spherical phenol resin particles having an average particle size of 20 μm were fired to produce carbon particles having an average particle size of 14 μm.
15 parts by weight of tar was added to 100 parts by weight, and calcined at 3,000 ° C. with stirring in an inert gas atmosphere to obtain carbon particles 2 having a large number of projections and an average particle diameter of 20 μm as shown in FIG. Nickel plating (base metal plating) on its surface
3 was subjected to 0.1 μm, and further gold plating (noble metal plating) 4 was applied to this surface at 200 ° to obtain conductive particles 1. On the other hand, 100 parts by weight of chloroprene rubber (CR), 10 parts by weight of a saturated polyester resin, 45 parts by weight of an alkylphenol-based tackifier, 15 parts by weight of a terpene phenol-based tackifier, 5 parts by weight of magnesium oxide, and 4 parts by weight of zinc oxide were dissolved in toluene. To prepare a 40% by weight insulating adhesive solution. The conductive particles 1 were added to 100 parts by volume of the insulating adhesive 5.
10 parts by volume were added and mixed with an agitator for 1 hour to obtain an anisotropic conductive adhesive 7 shown in FIG. The above anisotropic conductive adhesive is applied on a flexible printed circuit board (FPC, connected substrate) 6 having a circuit of 0.3 mm pitch formed of silver paste on a 25 μm PET film so that the film thickness after drying is 14 μm. 7 was applied to obtain an FPC with an anisotropic conductive adhesive layer.

Comparative Example Nickel plating was applied on the surface of spherical phenol resin particles having an average particle diameter of 20 μm to 0.1 μm, and gold plating was further applied to the surface.
Conducted conductive particles were obtained at 200Å. The conductive particles 10 were added to 100 parts by volume of the insulating adhesive solution prepared in Example 1 above.
The volume was added and mixed for 1 hour with a stirrer, but about 5 to 30 aggregates were present. Hereinafter, an FPC with an anisotropic conductive adhesive layer was obtained in the same manner as in Example 1.

As shown in FIG. 2, the FPCs of the embodiment and the comparative example were heat-sealed with an ITO thin film (substrate 6 to be connected) having a sheet resistance of 30Ω at 140 ° C. for 30 kg for 12 seconds.
℃, 30 minutes ~ 85 ℃, thermal shock test with one cycle of 30 minutes
The measurement was performed for 1,000 hours, and the resistance value between the adjacent electrodes of the FPC was measured. Table 1 shows the obtained results. In the table, * indicates the value at the short-circuited point, and ** indicates that cracks were present on the gold-plated surface of the conductive particles.

[Table 1]

[0016]

According to the anisotropic conductive adhesive of the present invention, a short circuit due to agglomeration of conductive particles is prevented, contact resistance is not destabilized due to peeling of noble metal plating, and insulating adhesive due to environmental changes. High electrical connection reliability by withstanding external forces such as small movements of the agent, vibration, and dropping, mitigating detachment of contact points due to various dynamic stresses in the operating environment, and maintaining low contact resistance Electrical and electronic parts having good workability.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of conductive particles used in an anisotropic conductive adhesive of the present invention.

FIG. 2 is a longitudinal sectional view showing one usage example of the anisotropic conductive adhesive of the present invention.

[Explanation of symbols]

1) conductive particles 2) carbon particles,
3 ‥ base metal plating layer , 4 ‥ precious metal plating layer , 5 ‥ insulating adhesive,
6 ‥ Connected substrate, 7 ‥ Anisotropic conductive adhesive.

Claims (1)

(57) [Claims] 1. A (i) 10% strength in compression 10 kgf / mm ² or more, at 80 kgf / mm ² or less, with the tar or pitch to the surface
Carbon particles having a plurality of protrusions graphitized by deposition and firing are used as nuclei, and (b) the surface of the nuclei has a thickness of 0.05 to 0.3 μm.
m base metal plated layer and the thickness of 50 to 500 Å and a noble metal plating layer <br/> sequential provided in the conductive particles of the total particle diameter. 5 to 100 [mu] m, dispersed in (c) an insulating adhesive anisotropic conductive adhesive agent characterized Rukoto such Te.