JP3150054B2 - Anisotropic conductive film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrical connection between fine circuits, more specifically, a connection between an LCD (hereinafter, referred to as a liquid crystal display) and an FPC (hereinafter, referred to as a flexible circuit board), and a semiconductor IC and an IC mounted. The present invention relates to an anisotropic conductive film that can be used for micro joining of substrates for use.

[0002]

2. Description of the Related Art With the recent miniaturization and thinning of electronic devices, the necessity of connection between minute circuits and connection between minute parts and minute circuits has been dramatically increased. With the development of solder bonding technology, anisotropic conductive adhesives and films have been used as new materials (for example, see JP-A-59-120436 and 60-847).
18, 60-191228, 61-55809, 61-
274394, 61-287974, 62-24414
2, 63-153534, 63-3055591, 64-
47084, 64-81878, JP-A-1-4654
9, 1-251787, each gazette). In particular, it has recently been applied to the connection between an LCD panel that cannot be handled by soldering and a TCP (tape carrier package) equipped with a driver IC, and has become an indispensable connection material for LCDs.

[0003] In this method, an adhesive or a film in which a predetermined amount of conductive particles is dispersed is sandwiched between circuits to be connected, and thermocompression bonding is performed at a predetermined temperature, pressure, and time, thereby electrically connecting the circuits. At the same time as connection is made, insulation between adjacent circuits is ensured. The conductive particles contained in the anisotropic conductive adhesive or the film are usually obtained by applying metal coating to metal particles or a polymer core material.

As shown in FIG. 4, in the case of the metal particles 9, soft particles such as solder particles are often used, and a variation in the space between the opposing circuit terminals 8 is absorbed to increase the contact area between the circuit terminals. This has the advantage that stable conductivity can be obtained. By setting the connection temperature higher than the melting temperature of the metal particles, the connection between the conductive particles and the electrode terminals can be strengthened, and the connection reliability can be further improved. However, since it is difficult to make the particle size of the conductive particles uniform, there is a high possibility that an electrical short circuit will occur between adjacent terminals due to large particles, and there is a limit to the application to the connection of fine circuits. In addition, when metal particles are melted, short-circuiting between terminals occurs, and when subjected to treatments such as high-temperature and high-humidity storage tests and high-temperature storage tests, changes such as oxidation of metal particles occur, resulting in unstable connections. There were problems such as becoming.

In the case of the conductive particles 10 in which a polymer core material is coated with a metal as shown in FIG. 5, the particle size distribution can be extremely sharp depending on the method of producing the polymer core material particles. Even finer circuit connections can be accommodated, and gold coating is often used as the outer layer in many cases, and has the advantage that there is little change such as oxidation of the particle surface due to long-term environmental treatment as described above. Was. However, on the other hand, particles may be agglomerated in the step of applying a metal coating on the surface of the polymer core material, or secondary agglomeration may occur in the step of dispersing the conductive particles in the adhesive. In this case, FIG. As shown, a short circuit occurs between circuit terminals, and the advantage of a sharp particle size distribution cannot be fully exploited, and there has been a problem that application to a fine circuit is limited. As a countermeasure for particle agglomeration, it is considered to provide a disintegration step after metal coating, but it is possible to remove the formed metal coating or add an additive or ultra-fine powder that promotes dispersion when dispersing in the adhesive. Some measures such as sonication have been considered, but none of them has provided a sufficient effect. In order to improve reliability, it is considered to increase the number of conductive particles.However, if the amount of particles is too large, it becomes difficult to maintain electrical insulation between circuits. There was a limit.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in consideration of the above-mentioned drawbacks, and has been made as a result of various studies. An object of the present invention is to provide a highly conductive anisotropic conductive film.

[0007]

That is, the present invention relates to an anisotropic conductive film in which conductive particles are dispersed in an insulating adhesive, wherein the core of the conductive particles is a polymer core material, and An anisotropic conductive film having a nickel film, a gold film on the outer layer of the nickel film, and a phosphorus content in the nickel film of 5 to 20% by weight.

Hereinafter, the present invention will be described in detail. FIG.
FIG. 2 is a schematic cross-sectional view of an anisotropic conductive film according to the present invention, FIG. 2 is a cross-sectional view showing a connection state of a circuit using the anisotropic conductive film according to the present invention, and FIG. 3 is a plan view thereof. In the anisotropic conductive film of the present invention, the surface of the polymer nucleus material 2 of FIG. 1 is coated with a nickel film 4 having an optimized phosphorus content, and the nickel film is coated with a gold film 3 on the surface of which the conductive particles 1 are insulated. Dispersed in the adhesive 5. For example, in the case of an LCD application, when the circuit substrate 6 and the glass substrate 7 are connected using an anisotropic conductive film as shown in FIG.
Mechanical contact, and a stable electrical connection between the upper and lower sides can be obtained. By using the anisotropic conductive film of the present invention, the conductive particles between the circuit terminals are uniformly and uniformly dispersed, and the connection between the fine circuit terminals which is difficult to connect due to the short circuit between the terminals in the conventional anisotropic conductive film. Is also possible.

In the present invention, the gold film and the nickel film on the surface of the conductive particles must have a phosphorus content in nickel of 5 to 20% by weight. The thickness of the film is not particularly limited,
If the thickness is too small, the conductivity becomes unstable, and if the thickness is too large, particle deformation becomes difficult or aggregation occurs, so that the thickness of each film is preferably 0.01 to 1 μm. In addition, in the method of forming the coating, the adhesion between the coating and the polymer core material serving as the central core is determined by
It is needless to say that it is better to form the film uniformly in consideration of conductivity and the like, and it is desirable to use electroless plating which has been conventionally used. When conductive particles coated with a phosphorous content of less than 5 % by weight in a nickel film are used to form an anisotropic conductive film, dispersibility of the conductive particles deteriorates and aggregation occurs. Insulation between adjacent terminals may be reduced, resulting in a short circuit, and there is a restriction on fine circuit connection. Conversely, when the content exceeds 20% by weight, the dispersibility is improved, but the conductivity is reduced, and the connection resistance is increased.
There is a problem that long-term connection reliability is reduced.

The polymer core material is not particularly limited in composition and the like. For example, there are polymers such as epoxy resin, urethane resin, melamine resin, phenol resin, acrylic resin, polyester resin, styrene resin and styrene-butadiene copolymer. However, they may be used as a mixture. Regardless of the particles, the optimal particle size, particle size distribution, and blending amount may be selected according to the adherend to be connected. For example, in a connection between an LCD panel and an FPC, which is a main application of the anisotropic conductive film, a preferable particle diameter is 0.5 to 50 μm, and particularly 0.2 to 50 μm.
In the connection of a fine pitch circuit having a pitch of about mm or less, about 2 to 10 μm is desirable. If it is less than 2 μm,
Although it is possible to mix a large number of conductive particles in order to obtain high connection reliability with fine circuit connection, it is extremely difficult with the current technology to uniformly coat the polymer core material without agglomeration In practice, it is difficult to stably connect fine circuits. Conversely, if it exceeds 10 μm, it is possible to apply a uniform metal coating without aggregation, but when connecting a fine circuit, the electrical insulation between the terminals cannot be maintained. It is not possible to mix too much, and there is a limit to improvement in connection reliability. In particular, 0.
In connection of a 1 mm pitch circuit, the average particle size is 2 to 5 μm.
m is desirable. The measurement of the particle diameter of the present invention is based on a Coulter counter, and the cumulative volume distribution obtained is 5%.
The value of 0% was defined as the average particle size. Further, it is preferable that the range of the particle size distribution is sharp. [Average particle diameter− (average particle diameter ×
0.8)] to [average particle diameter + (average particle diameter × 1)]. The compounding amount for the insulating adhesive is 1
-10% by volume is preferred. If the particle size is smaller than this, or if the compounding amount is small, the connection area will be small and the connection reliability will be reduced. Conversely, if the particle size is large or the compounding amount is large, the insulation between adjacent terminals will be poor. And the short circuit may occur.

The adhesive used in the present invention is not particularly limited as long as it has an insulating property, such as thermoplasticity, thermosetting property, and photocuring property. For example, styrene butadiene resin,
Styrene resin, styrene vinyl acetate resin, acrylonitrile butadiene rubber, silicone resin, acrylic resin,
Epoxy resins, urethane resins, phenol resins, amide resins, acrylate resins such as epoxy methacrylate resins, and the like may be used, and they may be used alone or in combination. If necessary, a tackifier, a crosslinking agent, an antioxidant, a coupling agent and the like may be used in combination.

Hereinafter, the present invention will be described with reference to embodiments. Example 1 25 parts by weight of an epoxy resin (Epicoat 828, manufactured by Yuka Shell Epoxy Co., Ltd.), 25 parts by weight of a polyvinyl butyral resin (Eslec BM-S, manufactured by Sekisui Chemical Co., Ltd.), an imidazole-based latent curing agent (Novacure HX-3
721, manufactured by Asahi Kasei Corporation) is prepared. In this adhesive, polystyrene resin is used as a core material, nickel is adjusted to have a phosphorus content of 5% by weight, and electroless plating is performed with nickel having a thickness of 0.1 μm. 2 μ% of conductive particles having an average particle size of 5 μm and a particle size distribution of 3 to 8 μm formed in 0.1 μm are dispersed in the above-mentioned adhesive, coated and dried on a polyester carrier film, and slit into 2 mm width to be anisotropically. A conductive film was produced.

The anisotropic conductive film is provided with a circuit width of 0.05
mm, circuit pitch 0.1 mm, FP with 160 terminals
Place on the connection terminal of C, 80 ° C, 8kg / cm ² , 2s
Temporary pressure bonding was performed by heating and pressing under the conditions of ec. Thereafter, the carrier film on the surface is peeled off, placed on a glass substrate (ITO glass) with a transparent conductive film, and placed at 175 ° C., 30 kg
Pressure bonding was performed by applying heat and pressure under the conditions of / cm ² and 20 sec. The FPC used here was made of a 75 μm polyimide substrate and a 25 μm copper foil, and had a surface plated with tin after circuit processing. In order to evaluate the electrical insulation between adjacent terminals, an FPC was also connected to a normal glass substrate having no transparent conductive film under the same conditions as described above. The connection resistance value between the adjacent terminals of the FPC of this connection body was measured (measurement current: 1 μA). The insulation resistance between adjacent terminals was as good as 10 ¹⁰ Ω or more (50 v, 20 sec) between all terminals. Also, this sample was subjected to a high-temperature and high-humidity treatment test device (8
5 ° C., 85% RH), and observed changes in connection resistance and insulation resistance between adjacent terminals. As a result, the increase in connection resistance from the initial stage after treatment for 1000 hours was 3Ω or less at all terminals, and the insulation resistance was low. In this case, good connectivity of 10 ¹⁰ Ω or more was obtained.

Example 2 The same adhesive as in Example 1 was prepared, and a polystyrene resin was used as a core material, and nickel having a thickness of 0.1 μm, which was adjusted to have a phosphorus content of 10% by weight, was electrolessly electrolessly prepared. Plating was performed, and electroless plating was applied on the surface to form a gold coating of 0.1 μm. 1.5% by volume of conductive particles having an average particle size of 3 μm and a particle size distribution of 2 to 5 μm were dispersed in the adhesive of Example 1, and the polyester was dispersed. 2m applied and dried on a carrier film
An anisotropic conductive film was prepared by slitting to an m width. A sample of this anisotropic conductive film was prepared and evaluated in the same manner as in Example 1. The connection resistance value between adjacent terminals was good with little variation of 1Ω or less between all terminals, and the insulation resistance value was good at 10 ¹⁰ Ω or more between all terminals. or,
1000 hours after high temperature and high humidity treatment (85 ° C, 85% RH)
Also, the connection resistance increases 3Ω at all terminals below, good connectivity and insulation resistance value 10 ¹⁰ Omega above were obtained. Example 3 The same adhesive as in Example 1 was prepared, and a melamine resin was used as a core material, and nickel having a thickness of 0.2 μm adjusted to have a phosphorus content of 15% by weight was electrolessly plated. Further, a gold coating of 0.1 μm was formed on the surface by electroless plating.
2% by volume of conductive particles having an average particle size of 4.5 μm and a particle size distribution of 3 to 10 μm are dispersed in the adhesive of Example 1,
An anisotropic conductive film was prepared by slitting the coated and dried polyester carrier film to a width of 2 mm. A sample of this anisotropic conductive film was prepared and evaluated in the same manner as in Example 1. The connection resistance value between adjacent terminals was good with little variation of 1Ω or less between all terminals, and the insulation resistance value was good at 10 ¹⁰ Ω or more between all terminals. After 1000 hours of high temperature and high humidity treatment (85 ° C, 85%
RH), the connection resistance increased at all terminals of 3Ω or less and the insulation resistance was 10 ¹⁰ Ω or more.

[0015]

[0016] Prepare the same adhesive as in Comparative Example 1 Example 1, a melamine resin as a core material in this, electroless thickness 0.2μm of nickel was adjusted to phosphorus content of 25 wt% Plating, and a gold coating was formed on the surface by electroless plating to a thickness of 0.1 μm.
Anisotropic conductive film is prepared by dispersing 2% by volume of conductive particles having an average particle size of 5.5 μm and a particle size distribution of 3 to 10 μm in the above adhesive, coating and drying a polyester carrier film to a width of 2 mm. did. Using this, a connection sample of the same FPC and glass as in Example 1 was prepared,
An evaluation was performed. The appearance of the film was uniform in the dispersion of the conductive particles as in the case of the example. Using this film, the same connection sample of FPC and glass as in Example 1 was prepared and evaluated. As a result, the insulation resistance between adjacent terminals after bonding was 10% for all terminals both in the initial stage and after the high temperature and high humidity treatment. ^{Although the} resistance was as good as ¹⁰ Ω, the connection resistance value was 3 Ω or more at all terminals in the initial stage, and there was a large variation. After 1000 hours of high temperature and high humidity treatment, the connection resistance value was 10 Ω or more at all terminals.

Comparative Example 2 An anisotropic conductive film was similarly prepared by dispersing 2% by volume in the same adhesive as in Example 1 using solder particles of tin / lead = 63/37 (average particle size: 10 μm) as the conductive particles. did. Using this, the same connection sample of FPC and glass as in Example 1 was prepared and evaluated. As a result, the initial connection resistance after crimping was as good as 1Ω or less for all terminals, but the high-temperature and high-humidity treatment was 1000.
After a lapse of time, the connection resistance value was 5Ω or more at all terminals. In addition, there are several terminals with an insulation resistance value of 10 ⁸ Ω or less at the initial stage.
After the high-temperature and high-humidity treatment, the number of portions of 10 ⁸ Ω or less increased. When the external appearance in the vicinity was observed with a microscope, large conductive particles were observed between the terminals.

[0018]

According to the anisotropic conductive film of the present invention, conductive particles are uniformly and uniformly dispersed in the film, and it can be applied to fine circuit connection which was difficult with the conventional anisotropic conductive film. Become. Conventionally, a large amount of conductive particles were blended in order to obtain high connection reliability.However, in order to obtain the same conductivity, the amount of conductive particles can be reduced because the dispersion is good, so that not only can the cost be reduced, Application to a finer circuit becomes possible.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view illustrating an anisotropic conductive film according to the present invention.

FIG. 2 is a sectional view showing a connection state of a circuit when an anisotropic conductive film according to the present invention is used.

FIG. 3 is a plan view showing a connection state of a circuit when an anisotropic conductive film according to the present invention is used.

FIG. 4 is a plan view showing a connection state of a circuit when an anisotropic conductive film to which conventional metal particles are applied is used.

FIG. 5 is a plan view showing a connection state of a circuit when using an anisotropic conductive film in which particles obtained by applying a metal coating to a conventional polymer nucleus material are used.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Conductive particle 2 Polymer core material 3 Gold film 4 Nickel film 5 Insulating adhesive 6 Circuit board 7 Glass substrate 8 Circuit terminal 9 Metal particle 10 Conductive particle (conventional product)

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01B 1/00-1/22 H01B 5/00-5/16 H01B 13/00

Claims (5)

(57) [Claims] 1. An anisotropic conductive film in which conductive particles are dispersed in an insulating adhesive, wherein the core of the conductive particles is a polymer material and has a nickel film on the surface thereof. An anisotropic conductive film further comprising a gold film in an outer layer, wherein the nickel film has a phosphorus content of 5 to 20% by weight. 2. The conductive particles have a particle size of 0.5 to 50 μm.
The anisotropic conductive film according to claim 1, wherein the average particle diameter is 2 to 10 m. 3. The anisotropic conductive film according to claim 1, wherein the gold and nickel films of the conductive particles each have a thickness of 0.01 to 1 μm. 4. The range of the particle size distribution of the conductive particles is from [average particle diameter− (average particle diameter × 0.8)] to [average particle diameter +
(Average particle diameter × 1)] μm.
Or the anisotropic conductive film according to claim 3. 5. The method according to claim 5, wherein the conductive particles are contained in the insulating adhesive in an amount of 1 to 10%.
Claim 1, Claim 2, Claim 3, which is dispersed by volume%.
Or the anisotropic conductive film according to claim 4.