JPH11209714A - Anisotropically electroconductive adhesive - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an anisotropically electroconductive adhesive that is useful for electric connection of LCD(liquid crystal display) or PDP(plasma display) to a circuit board having its driving circuits on the board. SOLUTION: This anistropically electrodconductive adhesive is characterized by dispersing electroconductive particles 2 that are made of an acrylic resin, each composed of a flexible core 21 and a shell 22 harder than the core 21 and plated with a metal on its surface, in an insulating adhesive composition. In addition, the electroconductive particles have a 10% compression strength of 0.2-5.0 kg/mm<2> and a recovery of 5-90%. Thus, this electroconductive adhesive has a low value of initial connection resistance and retains its performance of excellent reliability for a long period of time.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an LCD (Liquid C
The present invention relates to an anisotropic conductive adhesive used for electrical connection between a crystal display (PDP) or a PDP (Plasma Display) and a circuit board on which the driving circuits are mounted.

[0002]

2. Description of the Related Art Conventionally, anisotropic conductive adhesives have been used for LCDs and P-types.
Display body such as DP and PCB (Printed Circuit Board),
It is used for connection with an FPC (Flexible Printed Circuit) or connection between a PCB and an FPC. The anisotropic conductive adhesive is obtained by dispersing conductive particles in an insulating adhesive.Examples of the conductive particles include furnace black, channel black, carbon particles such as carbon black such as acetylene black, and graphite. Metal particles such as gold, silver, copper, and nickel aluminum, and plastic particles whose surfaces are plated with metal are being studied.

However, among these conductive particles,
Pressure (5 to 100) like metal particles or carbon particles
kgf / cm ^2, usually those that hardly deformed by 20~40kgf / cm ^2), heating during thermocompression bonding can not easily follow the displacement of the physical properties of the insulating adhesive by pressure, various post-connection Under the use environment, the microscopic movement due to the residual stress of the insulating adhesive causes partial conduction failure, high resistance value, etc., which has a serious adverse effect on the long-term reliability of the electrical connection. I have. Therefore, in order to eliminate these adverse effects and the like, the use of conductive particles whose core is made of plastic particles that are more easily deformed than metal particles or carbon particles and whose surface is plated with metal has been studied.

The conductive particles using the plastic particles as nuclei come into surface contact with the adherend in a state of thermocompression bonding, and the larger the contact area, the lower the contact resistance and the more resilient the plastic particles. The higher the contact pressure, the higher the contact pressure with the adherend, so that the contact resistance can be easily kept constant. However, the contact area was contradictory in that the softer the plastic core, the stronger the resilience, and the stronger the resilience. That is, if the contact area is made softer to make it softer, the particles are more likely to undergo plastic deformation, and since they do not have elasticity, the restoration rate becomes lower.On the contrary, if the particles become harder, the restoration rate becomes larger, and the contact pressure increases. There is a problem that the contact area is small and close to a point contact, and in both cases, the long-term reliability of the electrical connection is lacking.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and has been made to solve the problem. In particular, the present invention ensures reliable and highly reliable electrical connection even by a temperature / humidity cycle and thermal shock. It is an object of the present invention to provide an anisotropic conductive adhesive which keeps the property.

[0006]

As a result of various studies on a method for solving the above-mentioned conventional problems, the present inventor has adopted a structure having a core and a shell so that conductive particles have two functions, and has a flexible structure. The core is used to increase the contact area, and the hard shell is used to increase the restoration rate.This has also led to improvements in the reliability of electrical connections in temperature-humidity cycles and thermal shocks. Research on the types and hardness of the components of the material was advanced, and the present invention was completed. In other words, the anisotropic conductive adhesive of the present invention is an insulating adhesive in which conductive particles obtained by plating metal surfaces on acrylic resin particles composed of a core having flexibility and a shell harder than the core are used. Wherein the conductive particles have a 10% compressive strength of 0.2 to 5.0 kg / mm ² and a recovery rate of 5 to 90 kg.
%.

[0007]

Embodiments of the present invention will be described below in detail. As the core of the conductive particles constituting the present invention, the core and the shell are used for the shell so that the adhesion between the core and the shell described below is improved and the core and the shell do not undergo interface separation due to thermal shock or subsequent thermal shock. It is desirable to include a resin component. Therefore, in the present invention, an acrylic resin having excellent heat resistance in both the core and the shell, easy hardness adjustment, and easy suspension polymerization is used. Even if the core and the shell are made of a resin other than the acrylic resin, the desired anisotropic conductive adhesive cannot be obtained.

As the acrylic resin used as the core, an alkyl ester having an alkyl group having a large molecular weight of 4 to 18 carbon atoms (alkyl group) or an alkyl ester having 4 to 18 carbon atoms (alkyl group) for imparting flexibility. One or more of the methacrylate esters of No. 18 are appropriately selected, and as the polyfunctional group monomer for crosslinking this, ethylene glycol dimethacrylate, 1,3 butylene glycol dimethacrylate, neopentyl glycol dimethacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, Methylolpropane trimethacrylate, allyl glycidyl ether,
Monomers such as N-methylol methacrylamide and diallyl phthalate are used. Further, in order to adjust flexibility, vinyl chloride, vinyl acetate, butadiene rubber, acrylonitrile and the like may be copolymerized. The suspension polymerization can be performed by a conventionally known method.

The shell constituting the present invention is an acrylic acid ester having 1 to 7 carbon atoms (alkyl group) having a small molecular weight of an alkyl group so as to be hard, on the surface of a nucleus obtained by suspension polymerization. (Alkyl group) The methacrylic acid ester of 1 to 7 or the like may be used, and the above-mentioned copolymer may be appropriately mixed, and it is obtained by performing a polymerization reaction and forming a shell on the core surface. The weight ratio between the core and the shell is determined by the compressive strength,
Although this greatly affects the restitution rate, it is adjusted in consideration of these factors, and the shell / core is set to a weight ratio of 1/20 to 2/1. If the shell / nucleus is out of the range of the above-mentioned weight ratio, it will be difficult to adjust the compressive strength and the recovery rate described later by selecting the above-mentioned materials. That is, the weight ratio of shell / core is 1 /
When it is smaller than 20, it becomes difficult to have a restoration rate as the performance of the shell, and when it is larger than 2/1, it becomes difficult to express the compressive strength as the performance of the core. The nucleus material obtained by the above-mentioned nucleus material or polymerization reaction usually has a compressive strength of more than 0 to 3 kg / mm ² alone, and has a recovery rate of more than 0 to 40%. By forming a shell harder than the nucleus by the above-mentioned shell material or polymerization reaction on the nucleus, it is possible to obtain acrylic resin particles having almost the same compressive strength and recovery rate as the target conductive particles. In other words, the acrylic resin particles are subjected to metal plating on the surface as described below, but the metal plating does not significantly change the compressive strength and the recovery ratio, and even if they do, the compressive strength is ± 0.3 kg / mm. ^{About 2} 、 Restoration rate ± 3%
The nucleus may be formed in consideration of this.

[0010] The surface of the acrylic resin particles thus produced is subjected to metal plating in order to give conductivity. In order to obtain a good connection, the outermost surface is preferably made of noble metal plating, for example, Ni / Au, Ni / P
d, noble metal plating of a two-layer structure such as Ag / Au.
This plating method can also be formed by using a conventionally known electroless plating method or the like. The plating thickness is usually 0.05 to 0.5 μm for the first layer of Ni, Ag, or the like.
The thickness of the layer, such as Au and Pd, may be 0.005 to 0.05 μm.

The average particle size of the obtained conductive particles varies depending on the terminal pitch of the substrate to be connected, but is usually in the range of 1 to 50 μm. As the terminal pitch of the substrate becomes smaller, the connection reliability and line-to-line insulation resistance cannot be compatible unless conductive particles having a small average particle size are used.
Further, the particle diameter is desirably as uniform as possible, and more preferably 40% or less as the CV value. The “average particle size” defined in the present invention indicates an average particle size in a weight distribution measured by a commercially available Coulter counter (particle size distribution measuring device), and the CV value is (standard deviation / average particle size). ) × 100.

The 10% compressive strength of the conductive particles is 0.1%.
^{2 to} 5.0 kg / mm ² , preferably 0.5 to 3.5 kg / mm
It is desirable to set it to ² . 10% compressive strength is 0.2kg / mm
^If it is less than ^2, it is easily deformed too much and cannot penetrate the insulating adhesive film covering the periphery of the conductive particles, and the connection becomes unstable or the conductive particles are short-circuited due to short circuit. Problems such as the inability to maintain the resistance occur, which is not preferable.
On the other hand, if the 10% compressive strength exceeds 5 kg / mm ² , it becomes difficult to make surface contact with the adherend as described above, and it is close to point contact, which undesirably lacks long-term connection reliability. The “10% compressive strength” specified in the present invention is a commonly used micro compression tester (Shimadzu Corporation: MCTM-
500) is 10%.
It shows the strength when displaced.

Further, the restoration rate of the conductive particles is 5 to 90.
%, Preferably 10 to 60%.
If the restoration rate is less than 5%, the deformation is close to plastic deformation, and the contact pressure required for connection cannot be kept high. If the restoration rate exceeds 90%, it becomes difficult to manufacture due to the relationship with the compressive strength, Not preferred. The “restoration rate” defined in the present invention
Is measured by the above-mentioned micro compression tester, and the load is removed from the point where a load of 1 g is applied, and the degree to which the displacement returns is indicated by "%". More specifically, when a load is applied to the conductive particles with a micro compression tester, the load-compression displacement relationship increases as the relationship increases, as shown in FIG. When the load is removed with, the displacement returns. The restoration amount b with respect to the compression amount a at this time
%, That is, (b / a) × 100 is the restoration rate (%).

The insulating adhesive constituting the anisotropic conductive adhesive of the present invention may be a commonly used insulating adhesive, and may be either thermoplastic or thermosetting as long as it exhibits adhesiveness when heated. . Specifically, ethylene-vinyl acetate copolymer, carboxyl-modified ethylene-vinyl acetate copolymer, ethylene-isobutyl acrylate copolymer, polyamide, polyester, polymethyl methacrylate,
Polyvinyl ether, polyvinyl butyral, polyurethane, styrene-butylene-styrene (SBS) copolymer, carboxyl-modified SBS copolymer, styrene-isoprene-styrene (SIS) copolymer, styrene-ethylene-butylene-styrene (SEBS) copolymer Polymer, maleic acid-modified SBES copolymer, polybutadiene rubber, chloroprene rubber (CR), carboxyl-modified CR, styrene-butadiene rubber, isobutylene-isoprene copolymer, acrylonitrile-butadiene rubber (NBR),
Examples include those prepared by using one or a combination of two or more selected from carboxyl-modified NBR, amine-modified NBR, epoxy resin, phenol resin, silicone rubber, and acrylic rubber as a main component.

[0015] The insulating adhesive includes the above-described main component,
One or two of rosin as a tackifier, rosin derivative, terpene resin, terpene phenol resin, petroleum resin, cumarone-indene resin, styrene resin, isoprene resin, alkylphenol resin, xylene resin, etc.
At least one kind; a reactive auxiliary; a polyol as a crosslinking agent, an isocyanate, a melamine resin, a urea resin, an utropine, an amine, an acid anhydride, a peroxide, a metal oxide, and a chromium trifluoroacetate salt. Salts, alkoxides such as titanium, zirconia and aluminum, organometallic compounds such as dibutyltin dioxide; photoinitiators such as 2,2-diethoxyacetophenone and benzyl; sensitizers such as amines, phosphorus compounds and chlorine compounds Is optional, and may also include a curing agent, a vulcanizing agent, a deterioration inhibitor, a heat-resistant additive, a heat conduction improver, a softener, a coloring agent, various coupling agents, a metal deactivator, and the like. May be appropriately added.

The anisotropic conductive adhesive of the present invention can be obtained by dispersing and mixing the above-mentioned conductive particles in the above-mentioned insulating adhesive according to a conventional method. The compounding amount of the conductive particles is
0.01 to 1 with respect to 100 parts by volume of the insulating adhesive
It is in the range of 00 parts by volume, preferably 1 to 10 parts by volume. When the amount of the conductive particles is less than 0.01 parts by volume,
Continuity failure is likely to occur, and conversely, if it exceeds 100 parts by volume, insulation failure tends to occur, which is not preferable. In addition, when the adhesive and the adhesive component are solid at room temperature or a high-viscosity liquid, this insulating adhesive is used as an ester, ketone, ether ester, ether, alcohol,
Hydrocarbon solvents, for example, ethyl acetate, methyl ethyl ketone, butyl cellosolve acetate, ethyl carbitol, diisoamyl ether, cyclohexanol, petroleum spirit, dissolved in a solvent such as toluene, to form a solution,
This may be applied to a desired position on the electrode to be connected by an appropriate printing method, a coating method, and after being formed on the separator, cut to a desired size, and transferred to the connection electrode. When used, or when the adhesive or adhesive component is in a liquid state, it can be used by applying it to the connection electrode during the connection operation.

The thus obtained anisotropic conductive adhesive of the present invention comprises, for example, as shown in FIG. 2, a flexible core 21, a harder shell 22, and a metal plating on the surface. This is used by providing an anisotropic conductive adhesive 1 obtained by dispersing conductive particles 2 composed of an insulating material 23 in an insulating adhesive 3 between an LCD substrate 4 and a flexible printed substrate 5. Reference numeral 6 denotes a conductor (circuit). This anisotropic conductive adhesive is generally interposed between two opposing electrons and an electrode group on an electric circuit board, and is pressed from above one of the electrons and the electric circuit board, and simultaneously heated or irradiated with light or an electron beam. To activate the adhesive, fix the two circuit boards with an anisotropic conductive adhesive, and electrically connect opposing electrode groups via conductive particles. As this circuit board, for example,
Glass such as a display panel, a metal such as an LSI chip, a metal oxide, a flexible printed circuit based on a polyimide resin, a polyester resin, or the like is used.

[0018]

EXAMPLES The present invention will be described below in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples. In addition, 10% compressive strength in Examples and Comparative Examples,
The restoration rate was measured using a micro compression tester (manufactured by Shimadzu Corporation, MC
Test mode 1
(Compression test), test load 50.00 gf, displacement full scale 50 μm, indenter plane 50 μm φ, load speed 1.97
The measurement was performed under the conditions of 5 gf / sec, and the restoration rate was determined in test mode 2 (load and unloading tests), and the reverse load value was 1.00 g.
f, load speed 0.455 gf / sec, displacement full scale 50 μm, indenter plane 50 μmφ, load value for origin 0.1
It was measured under the condition of 0 gf.

Example 1 (1) Preparation of Insulating Adhesive Solution NBR 100 parts by weight, epoxy equivalent 1000-1200
150 parts by weight of bisphenol type epoxy resin, 20 parts by weight of 2-methylimidazole, titanium oxide (TiO ₂ )
To 50 parts by weight, 300 parts by weight of cyclohexanone was added and dissolved to prepare an insulating adhesive solution.

(2) Preparation of conductive particles Stearyl acrylate 100 parts by weight, ethylene glycol dimethacrylate 4 parts by weight, butadiene rubber 3
0 parts by weight and 0.5 parts by weight of benzoyl peroxide in water 20
Suspension polymerization was carried out in 0 parts by weight at 100 ° C. under a rotation of 1000 rpm for 2 hours to obtain a suspension containing a core having an average particle diameter of 7 μm and a CV value of 28%. A small amount of this nucleus was taken and the compressive strength and the recovery rate were measured. The compressive strength was 0.8 kg / mm ² and the recovery rate was 3
%Met. Further, 50 parts by weight of ethyl methacrylate and 2 parts by weight of ethylene glycol dimethacrylate were added to the suspension while stirring, and polymerized at 90 ° C. for 2 hours under a rotation of 1000 rpm to form a shell on the surface, followed by cooling, washing with water, After drying, acrylic resin particles having an average particle size of 10 μm and a CV value of 35% were obtained. When a small amount of the acrylic resin particles were taken and the compressive strength and the recovery rate were measured, the compressive strength was 2.1 kg / mm ² ,
The restoration rate was 50%. Next, electroless plating was performed on the surface of the particles in the order of nickel plating 0.3 μm and gold plating 0.02 μm to obtain conductive particles (average particle diameter 10 μm, CV value 35%). The 10% compressive strength of the conductive particles is
2.2 kg / mm ² and the restoration rate were 50.1%.

(3) Preparation of Anisotropic Conductive Adhesive 10 parts by volume of the conductive particles prepared in (2) above were added to 100 parts by volume of solid content of the insulating adhesive solution prepared in (1) above. A conductive adhesive was produced.

(4) Preparation of Flexible Printed Circuit Board (FPC) with Anisotropic Conductive Adhesive A commercially available silver paste (DW-250H-5, Toyobo Co., Ltd.) was placed on a flexible substrate made of a PET film having a thickness of 25 μm. Was printed by screen printing to form conductive lines having a pitch of 0.2 mm, and then dried and cured in an oven at 130 ° C. for 5 hours. Next, the anisotropic conductive adhesive prepared above is removed from the solvent by removing the solvent to form a thickness of 9 μm on the connection terminal portion by screen printing to form an anisotropic conductive adhesive layer. A commercially available insulating resist (JEH-112, manufactured by Acheson Japan) was provided and cut into desired dimensions to obtain an FPC with an anisotropic conductive adhesive. Next, the FPC with the anisotropic conductive adhesive thus obtained was placed between a connection terminal of a transparent conductive oxide film substrate (ITO) having a sheet resistivity of 50Ω / □ and the FPC at 160 ° C., 30 kgf / cm ² for 12 seconds. Thermocompression bonding under high temperature conditions, 110 ° C under high temperature, 30 minutes to low temperature
Perform an environmental test for 20 cycles at 20 ° C for 30 minutes.
When the resistance between the two connection terminals was measured, the results shown in Table 1 below were obtained.

Comparative Example 1 As conductive particles, conductive particles obtained by plating a single component styrene resin particles with Ni and Au (10% compressive strength 12 kg / mm ² , recovery rate 49%, average particle diameter 10 μm, CV Except for using a value of 35%), an FPC with an anisotropic conductive adhesive was obtained in the same manner as in Example 1. When the resistance value between the two connection terminals was measured in the same manner as in Example 1, the results shown in Table 1 below were obtained.

Comparative Example 2 Conductive particles obtained by plating Ni and Au on single-component acrylic resin particles as the conductive particles (10% compressive strength 1 kg / mm ² , restoration rate 3%, average particle size 10%)
FPC with an anisotropic conductive adhesive was obtained in the same manner as in Example 1 except that μm and a CV value of 45% were used. When the resistance value between the two connection terminals was measured in the same manner as in Example 1, the results shown in Table 1 below were obtained.

Comparative Example 3 Acrylic resin particles having 10% compressive strength of 0.8 kg / mm ² , a restoration rate of 3%, and an average particle diameter of 7 μm were used as conductive particles as a core, and suspension polymerization was performed using styrene resin as a shell. Resin particles having an average particle size of 10 μm (10% compression strength 2.8 kg / mm ² , restoration rate 53%) were subjected to Ni and Au plating on conductive particles (10% compression strength 2.8 kg / mm ² , restoration rate 5).
An FPC with an anisotropic conductive adhesive was obtained in the same manner as in Example 1 except that 3% and an average particle size of 10 μm were used. When thermocompression bonding was performed in the same manner as in Example 1 and the resistance value between both terminals was measured, destruction of particles was observed during thermocompression bonding, and the results shown in Table 1 below were obtained.

[0026]

[Table 1]

(Consideration of Table 1) As is apparent from the results of Table 1, the initial connection resistance of the first embodiment, which falls within the scope of the present invention, is lower than that of Comparative Examples 1 to 3, which fall outside the scope of the invention. Low,
And 110 ° C. for 30 minutes at high temperature to −20 ° C. for 30 minutes at low temperature
The resistance test between the connection terminals did not change even when the environmental test was performed for 1000 cycles for a minute, and it was found that the adhesive was an anisotropic conductive adhesive having excellent performance for long-term connection reliability.

[0028]

According to the present invention, since the conductive particles have flexibility and a high restoring force, the conductive particles have a low initial connection resistance and an excellent long-term connection reliability. One sided conductive adhesive can be provided.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram for explaining a restoration rate.

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

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 anisotropic conductive adhesive 2 conductive particles 3 insulating adhesive 4 LCD substrate 5 FPC 21 nucleus 22 shell 23 metal plating

Claims (2)

[Claims] An acrylic resin particle comprising a core having flexibility and a shell harder than the core is formed by dispersing conductive particles obtained by plating metal on the surface of the resin particle in an insulating adhesive. An anisotropic conductive adhesive. 2. The conductive particles have a 10% compressive strength of 0.2 to 0.2%.
^{2. The} anisotropic conductive adhesive according to claim 1, wherein the adhesive is 5.0 kg / mm < ² > and the recovery rate is 5 to 90%.