JP3516379B2 - 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 electrical connection between minute circuits, and more particularly to LCD (liquid crystal display).
And an anisotropic conductive film that can be used for connecting a flexible circuit board and micro-joining of a semiconductor IC and an IC mounting board.

[0002]

2. Description of the Related Art With the recent miniaturization and thinning of electronic equipment, the need for connecting minute circuits to each other, connecting minute parts to minute circuits, etc. has been dramatically increasing. With the progress of soldering technology, anisotropic conductive adhesives and films are used as new materials (for example, JP-A-59-120436, 60-84718, 60-19122).
8, 61-55809, 61-274394, 61-287974, 62-244142,
63-153534, 63-305591, 64-47084, 64-81878, JP-A-1-46549, 1-251787, etc.). In particular, recently, it has been applied to connection between an LCD (liquid crystal display) panel that cannot be soldered and a TCP (tape carrier package) equipped with a driver IC, and has become an indispensable connection material for an LCD.

In this method, an adhesive or film containing a predetermined amount of conductive particles is sandwiched between circuit boards (for example, TCP (4) and LCD glass (5)) to be connected as shown in FIG. By thermocompression bonding according to the temperature, pressure, and time, electrical connection between the circuit boards is made, and at the same time, insulation is secured between the adjacent circuit terminals (6).

As the conductive particles contained in the anisotropic conductive adhesive or the film, metal particles or polymer core material coated with a metal are generally used. In the case of metal particles, soft particles such as solder particles are often used, and the contact area between circuit terminals can be increased by absorbing the variation in the spacing between opposing circuit terminals, and stable conductivity can be obtained. There was an advantage called. Also, by making the connection temperature higher than the melting temperature of the metal particles, it becomes possible to strengthen the connection between the conductive particles and the circuit terminals,
The connection reliability can be further improved. However, on the other hand, it is difficult to make the particle diameters of the conductive particles uniform. For example, solder particles having an average particle diameter of about 10 μm may be used for connecting circuits having a pitch of about 200 μm, but the particle diameter distribution is wide. Since large particles of 30 μm or more are mixed therein, there is a high possibility that an electrical short circuit will occur between adjacent circuit terminals due to this, and there is a limit to application to the connection of fine circuits.

In addition, when the metal particles are melted, a short circuit between terminals occurs, and when a treatment such as a high temperature and high humidity storage test or a high temperature storage test is performed, a change such as oxidation of the metal particles occurs, resulting in a connection. There was a problem such as instability. On the other hand, in the case of particles obtained by coating the polymer core material with a metal, the particle size distribution of the polymer core material can be made extremely sharp depending on the production method. Generally, an average particle size of about 5 to 10 μm and a particle size distribution of about ± 3 μm or less can be easily obtained. For this reason, it is possible to correspond to even finer circuit connections than metal particles, and in particular, there are many cases where a gold coating is used for the outermost layer, and changes such as oxidation of the particle surface due to long-term environmental treatment as described above. It had the advantage of being few.

However, on the other hand, particles may aggregate in the step of coating the surface of the polymer core material with metal, or secondary aggregation may occur in the step of dispersing the conductive particles in the adhesive resin. In this case, a short circuit occurs between circuit terminals, and the advantage that the particle size distribution is sharp cannot be fully utilized, and there is a problem that application to a fine circuit is limited. As a measure for agglomeration of particles, it is also considered to provide a crushing process after metal coating, but the formed metal coating may be peeled off, or an additive that promotes dispersion when dispersed in resin or Some ideas such as ultrasonic treatment have been considered, but none of them were able to obtain sufficient effects. In addition, it is considered to increase the number of conductive particles in order to improve the connection reliability, but it is difficult to maintain electrical insulation between circuits if the amount of particles is too large. There was also a limit.

On the other hand, the actual use of the anisotropic conductive film requires optical characteristics. For example, in order to electrically connect the circuit terminal provided on the LCD glass substrate and the circuit terminal of the TCP on which the driving semiconductor chip is mounted, the target circuits must be accurately connected. 50 μm pitch or 25 μm for high density circuits
There are some examples of connecting circuit comrades. A specific connection procedure will be described below. First, a complex oxide of indium oxide / tin oxide (hereinafter abbreviated as ITO) is formed on a glass substrate and etched into a desired pattern to produce a transparent circuit terminal portion. On this, an anisotropic conductive film is heat-pressed and stuck (temporary pressure bonding). Further, generally, the circuit terminals of the TCP, which is a copper circuit board formed on a polyimide on which a semiconductor chip is mounted, are accurately aligned, and then heated and pressed (main pressure bonding) to form a glass substrate. Electrically connect TCP. At this time, it becomes necessary to recognize the transparent electrode terminals on the glass substrate with the anisotropic conductive film attached.

To recognize the transparent electrode on the glass substrate, the light transmitted through the glass substrate is reflected by the interface between the glass and the insulating adhesive resin (7) as shown in FIG. The contrast due to the light amount difference between the electrode (10) and the reflected light (8) at the insulating adhesive resin interface enables recognition. Here, since the technology related to glass and transparent electrodes has already been established and is stable, the intrinsic refractive index of the insulating adhesive resin and this constituent material becomes very important. However, although the progress of the optical system for position recognition is recognized, it is further desired to improve the recognizability by making the transparent electrode finer and thinning it by decreasing the specific resistance of the transparent electrode itself. It is the actual situation. Further, in the case of an anisotropic conductive film, since the carrier film (separator) on the surface is peeled off after temporary pressure bonding, reflected light (9) at the interface of the upper surface of the adhesive resin and conductive particles in the adhesive resin The reflected light at the point also becomes noise, which causes the accuracy of recognition of the transparent electrode pattern to deteriorate.

[0009]

SUMMARY OF THE INVENTION The present invention has been made as a result of various studies in view of such conventional drawbacks, and an object of the present invention is to cope with fine circuit connection and to improve position. An object of the present invention is to provide an anisotropic conductive film having high recognition property and high connection reliability.

[0010]

That is, the present invention provides an anisotropic conductive film in which conductive particles are dispersed in an insulating adhesive resin, the transparent electrode having the insulating adhesive resin formed on glass. To the insulating adhesive resin, the average particle diameter of the insulating adhesive resin is 0.10 or more.
~ 1.0 μm, oxide having a specific surface area of 10 to 20 m ² / g
Particles are dispersed in 0.1-5.0% by weight, film
And a total light transmittance of 40 to 70% .

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below.

FIG. 1 is a schematic sectional view of an anisotropic conductive film according to the present invention. FIG. 2 is a schematic cross-sectional view for explaining a connecting method using an anisotropic conductive film, and FIG.
It is a schematic cross section for explaining the recognizability of a circuit terminal.

As shown in FIG. 1, the anisotropic conductive film of the present invention comprises conductive particles (2) dispersed in an insulating adhesive (1) having a refractive index difference from that of a transparent electrode on a glass substrate.
Further, oxide particles having a refractive index difference with the insulating adhesive (3)
The feature is that they are dispersed.

Due to the recent high definition display, the input and output terminals are becoming ultra finer, and it becomes more and more difficult to recognize the transparent ITO electrode pattern formed on the glass, and the recognition time and the recognition device price increase. The tendency is getting stronger. As measures against this, it has been proposed to add dyes and pigments to the resin, but due to problems such as heat resistance and reliability deterioration due to ionic impurities, it is the current situation that it is not sufficient. . Further, even in such ultra-fine structure, there is a high demand for high reliability, and improvement of the shape and elastic modulus of the resin and the conductive particles, reduction of connection resistance, reduction of aggregation, etc. is being advanced.

As described above, in the case of the connection in the LCD panel, when the TCP (4) and the LCD glass (5) are connected using the anisotropic conductive film as shown in FIG. 2, the circuit terminal (6) becomes conductive. The particles make mechanical contact and a stable electrical connection can be obtained between the top and bottom. At this time, if the anisotropic conductive film of the present invention is used, the transparent electrode (10) on the glass substrate can be easily recognized as shown in FIG. Further, by optimizing the specifications of the conductive particles between the terminals, the conductive particles are uniformly dispersed, and a large number of conductive particles contributing to the connection can be added while maintaining the insulating property between the circuit terminals. As a result, it becomes possible to connect fine circuit terminals to each other, which was difficult to connect with the conventional anisotropic conductive film, and it is possible to achieve both high connection reliability and good pattern recognition.

The particle size of the conductive particles in the present invention is not particularly limited, but is preferably 2 to 10 μm on average.
Is better. If it is smaller than 2 μm, it is possible to mix a large number of conductive particles in order to obtain high connection reliability in fine circuit connection, but it is not possible to uniformly coat the polymer core material with metal without agglomeration. It is extremely difficult with the current technology, and it is actually difficult to stably connect fine circuits. On the other hand, if it is larger than 10 μm, it is possible to apply the metal coating uniformly without agglomeration, but when connecting a fine circuit, the electrical insulation between the terminals cannot be maintained, so that the number of particles cannot be maintained. Cannot be added in a large amount, and there is a limit to improvement in connection reliability. For example, in the connection between a liquid crystal display panel and an FPC (flexible circuit board), which is a main application of the anisotropic conductive film, particularly in connection with an extremely fine pitch circuit having a pitch of about 50 μm, an average particle size of about 3 to 5 μm is desirable. Needless to say, it is preferable that the particle size distribution is sharp, and it is more preferable that the average particle size is within ± 10%.

The composition of the conductive particles in the present invention is not particularly limited, but considering the connection of fine circuits and long-term connection reliability, it is preferable that the surface of the polymer core material is coated with gold, nickel or the like. Also, for example, although there is no particular limitation on the thickness of the film, if it is too thin, the conductivity becomes unstable, and if it is too thick, it becomes difficult to deform the particles or aggregates. . In the method of forming the coating, the adhesion between the coating and the polymer core material that serves as the central core
It is needless to say that it is better to be formed uniformly in consideration of conductivity and the like, and electroless plating which has been conventionally used is preferable. Here, the polymer core material is not particularly limited in composition and the like, and for example, it is selected from polymers such as epoxy resin, urethane resin, melamine resin, phenol resin, acrylic resin, polyester resin, styrene resin, and styrene-butadiene copolymer. These may be used alone or in combination of two or more. The compounding amount with respect to the insulating adhesive is not particularly limited, but is preferably 0.5 to 10% by volume. If the blending amount is smaller than this, the connection area is reduced and the connection reliability is reduced. On the contrary, if the blending amount is large, the insulating property between adjacent terminals is reduced and a short circuit occurs.

The insulating adhesive resin used in the present invention is
A transparent electrode formed on glass, that is, a material having a refractive index difference of 0.3 or more with respect to the refractive index of ITO of 1.95 is basically thermoplasticity, thermosetting property, photocurability, etc. There is no limit. For example, styrene-butadiene resin, styrene resin, ethylene vinyl acetate resin, acrylonitrile-butadiene rubber, silicon resin, acrylic resin, epoxy resin, urethane resin, phenol resin, amide resin, acrylate resin including epoxy methacrylate resin, etc. may be mentioned. Therefore, two or more resins may be combined if necessary. Further, a tackifier, a cross-linking agent, an antiaging agent, a coupling agent and the like may be used in combination. When the difference in refractive index is less than 0.3, the contrast between the patterned transparent electrode and the insulating adhesive interface is low, and the recognizability is poor. For example, in general, even epoxy resin has a refractive index of 1.1 to 1.6.
Although it can be designed up to this point, in consideration of recognizability, it is necessary to make the refractive index 1.1 to 1.4 type obtained with an aliphatic or alicyclic epoxy. An alicyclic epoxy that can obtain a refractive index of 1.3 to 1.4 is preferable for connection reliability.

Further, it is desirable to reduce the total light transmittance as a measure for improving the recognizability. This is because the reflective effect is aimed at by an insulating adhesive that covers the transparent glass and the transparent electrode. Specifically, the total light transmittance is most preferably 40 to 70%. This is because the recognition device generally recognizes the transparent electrode through the glass as shown in FIG. 3, and further recognizes the TCP electrode from the driving circuit, so that it becomes difficult when the ratio is less than 40%.
Also, in the range of more than 70%, the reflection effect cannot be expected and the recognizability cannot be improved. As a result of diligent studies to suppress the above range, basically, since the internal haze is increased to a transparent resin, the refractive index difference with respect to the insulating adhesive resin is 0.
The object was achieved by adding 0.1 to 5.0% by weight of an oxide having an average particle size of 5 or more and having an average particle size of 0.10 to 1.0 μm and a specific surface area of 10 to 20 m ² / g.

The oxide is not particularly limited as long as it has a sufficient insulating property. However, in order to increase the internal haze that scatters light, the refractive index difference from the resin is set to 0.
It is desirable to take 5 or more. This is because if it is less than 0.5, the effect is low and the addition amount must be increased, resulting in too low a total light transmittance. Refractive index iron oxide: 2.5
-2.75, cerium oxide: 2.1-2.2, bismuth oxide 2.3-2.45, cadmium oxide 2.0-2.3.
, Etc., but the particle size can be controlled, and it is widely used in cosmetics, etc., so the refractive index is 2.05, which can be obtained at a low price.
Most preferred is zinc oxide having a viscosity of up to 2.25 and titanium oxide having a density of 2.5 to 2.8.

Next, the average particle size is 0.10 to 1.0.
μm is preferred. This is because the light source of the recognition device generally uses a wavelength of 0.4 to 0.8 μm, which is a visible light region in many cases. Therefore, when the average particle size is less than 0.10, the transmittance is caused by the light diffusion phenomenon. Is greatly increased and the reflection effect is reduced. On the other hand, the addition of those in the range of more than 1.0 affects the uniform dispersion of the conductive particles contributing to the connection and reduces the number of the conductive particles existing in the connection area on the electrode.

Further, the specific surface area is preferably 10 to 20 m ² / g. This is because the air adsorbed on the surface of the particles has a scattering effect. When it is less than 10, the wettability of the resin is deteriorated, while when it exceeds 20, conversely, a problem occurs in reliability due to the effect of bubbles after thermocompression bonding. Because it comes.

[0023]

EXAMPLES Examples according to the present invention and comparative examples according to the conventional method will be shown below.

[Example 1] Epoxy resin (Epicoat 8
28, Yuka Shell Epoxy Co., Ltd.) 25 parts by weight, polyvinyl butyral resin (S-REC BM-S, Sekisui Chemical Co., Ltd.) 25 parts by weight, imidazole-based latent curing agent (Nova Cure HX-3721, Asahi Kasei Co., Ltd.) )) Adhesive mixed with 50 parts by weight is prepared. In this, a polystyrene resin was used as a core material, nickel of 0.1 μm thickness was electroless plated, and further 0.1 μm of gold coating was formed by electroless plating. A distribution with an average particle size of 5 μm and a maximum particle size of 6 μm was obtained. 2% by volume of the conductive particles are dispersed, and 0.5% by weight of zinc oxide having an average particle size of 0.4 μm, a specific surface area of 12 m ² / g and a refractive index of 2.1 is further blended, and then the carrier film (polyester) is coated. The coated and dried product was slit into a 2 mm width to prepare an anisotropic conductive film. The total light transmittance of the produced anisotropic conductive film was 65%.

A circuit width of 0.06 is obtained by using this anisotropic conductive film.
mm, circuit pitch 0.10 mm, 200 terminals transparent electrode (ITO sheet resistance value 10Ω / □) placed on the circuit terminal part of the glass substrate, 70 ℃, 5kg / cm ² , 2s
Temporary compression was performed by heating and pressing under the condition of ec. After that, peel off the carrier film on the surface, circuit width 0.04mm,
Aligned with TCP having a circuit pitch of 0.10 mm and 200 terminals, 175 ° C., 30 kg / cm ² , 15
It was heated and pressed under the condition of sec to perform crimp connection. A TCP mounting device manufactured by Hitachi Electronics Engineering was used for connection. The TCP used here is made of a polyimide base material of 75 μm and a copper foil of 18 μm, and the surface thereof is Sn-plated after circuit processing.

At the time of connection, there was no stoppage of equipment due to defective recognition of transparent electrodes. Also, the TC of the connected sample
Measure the connection resistance between adjacent terminals of P (measurement current 1μA)
As a result, it was good that there was little variation of 1Ω or less between all terminals. Insulation resistance between terminals is 10 between all terminals
^{It was 10} Ω or more (50 v, 30 sec), which was good. In addition, this sample was subjected to a high temperature and high humidity treatment tester (85 ° C, 8
5% RH) and observed changes in connection resistance and insulation resistance between adjacent terminals. As a result, even after 1000 hours of treatment, the increase in connection resistance from the initial stage was 2Ω or less at all terminals, and the insulation resistance was 10 ¹⁰ Good connectivity with Ω or more was obtained.

[Example 2] The same adhesive resin as that of Example 1 in which conductive particles were dispersed was prepared, and further, an average particle diameter of 0.2 µm, a specific surface area of 15 m ² / g and a refractive index of 2 were prepared. ．
0.7mm by weight of titanium oxide of No. 6 was blended, coated on a carrier film (polyester) and dried, then 2mm
An anisotropic conductive film was produced by slitting the film in the width. The total light transmittance of the produced anisotropic conductive film was 60%.

A sample of this anisotropic conductive film was prepared in the same manner as in Example 1 and evaluated. There was no defective recognition of the transparent electrode, the connection resistance value between adjacent terminals was good, with a small variation of 1Ω or less between all terminals, and the insulation resistance value was 10 ¹⁰ Ω or more between all terminals. Even after 1000 hours of high temperature and high humidity treatment (85 ° C, 85% RH), the increase in connection resistance was 3Ω or less at all terminals, and the insulation resistance was 10 ¹⁰ Ω.
Good connectivity was obtained as described above.

Comparative Example 1 An anisotropic conductive film exactly the same as in Example 1 was prepared except that zinc oxide was not added. The total light transmittance of the produced anisotropic conductive film is 80%.
Met. Using this, the same TCP and glass connection sample as in the example was prepared and evaluated. In this case, a recognition failure of the transparent electrode occurred when connecting, and the alignment had to be performed manually. However, the connection resistance between adjacent terminals after connection is 1 for all terminals.
The resistance was good, with less variation of Ω or less, and the insulation resistance value was 10 ¹⁰ Ω or more across all terminals. Also,
After 1000 hours of high temperature and high humidity treatment (85 ℃, 85% RH)
In addition, a good connection was obtained with an increase in connection resistance value of 3Ω or less for all terminals and an insulation resistance value of 10 ¹⁰ Ω or more.

[0030]

By using the anisotropic conductive film of the present invention, the transparent electrode on the glass substrate can be easily recognized in the connection in the LCD panel, and the connection by the conductive particles between the terminals is not affected. Therefore, in the conventional anisotropic conductive film, it is possible to connect fine circuit terminals to each other, which is difficult to connect due to short circuit between terminals, and it is possible to achieve both high connection reliability and good pattern recognition.

[Brief description of drawings]

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

FIG. 2 is a schematic cross-sectional view for explaining a connecting method using an anisotropic conductive film.

FIG. 3 is a schematic cross-sectional view for explaining the recognizability of circuit terminals.

[Explanation of symbols]

1. Insulating adhesive resin 2. Conductive particles 3. Oxide particles 4. TCP 5. LCD glass 6. Circuit terminal 7. Light reflected at the interface between glass and insulating adhesive resin 8. Light reflected at the interface between the transparent electrode and the adhesive resin 9. Light reflected from the adhesive resin upper surface Ten. Transparent electrode

─────────────────────────────────────────────────── --- Continuation of the front page (56) Reference JP-A-7-90236 (JP, A) JP-A-7-133466 (JP, A) JP-A-8-319467 (JP, A) JP-A-6- 240217 (JP, A) JP 3-166284 (JP, A) JP 8-315946 (JP, A) JP 62-243668 (JP, A) JP 51-135938 (JP, A) JP-A-60-84718 (JP, A) JP-A-60-115678 (JP, A) Plastics Data Book, Industrial Investigation Committee, December 1, 1999, 36 (58) Fields investigated (Int.Cl. ⁷ , DB name) C09J 4/00-201/10 H01B 1/00-5/16 H01R 11/00-11/32

Claims (3)

(57) [Claims] 1. An anisotropic conductive film having conductive particles dispersed in an insulating adhesive resin, wherein the insulating adhesive resin has a refractive index difference of 0.3 or more with respect to a transparent electrode formed on glass. it is those having, and the difference in refractive index between the insulating adhesive insulating adhesive resin in the resin is 0.5 or more flat
Uniform particle size 0.10-1.0 μm, specific surface area 10-20
0.1 to 5.0% by weight of m ² / g oxide particles are dispersed.
And the total light transmittance of the film is 40 to 70% . Wherein the zinc oxide particles are oxidized, the anisotropic conductive film of claim 1 Symbol mounting, characterized in that in which the titanium oxide particles were individually or in combination. 3. The conductive particles are those having a metal film made of nickel and gold on the surface of a central core made of a polymer core material, or made of metal particles, and having an average particle diameter of 2 to 10 μm. The anisotropic conductive film according to claim 1 or 2, which is characterized in that.