KR100979728B1 - Anisotropic conductive film having a optimum elastic restitution property and circuit board using the same - Google Patents

Abstract

The present invention relates to an acrylate-based anisotropic conductive film, characterized in that the elastic recovery index (ε) defined by the following formula has a value between 0.04≤ε≤0.15.

ε = (L ₂ / L ₁ )

(L ₁ : length of stretching when pulling the anisotropic conductive film 60% to 80% of the curing proceeds with a tensile force of 5kgf / ㎠, L ₂ : length to decrease when removing the tensile force of 5kgf / ㎠)

Elastic recovery, anisotropic conductive film, ACF

Description

Anisotropic conductive film with controlled elastic recovery characteristics and circuit connection structure using same {ANISOTROPIC CONDUCTIVE FILM HAVING A OPTIMUM ELASTIC RESTITUTION PROPERTY AND CIRCUIT BOARD USING THE SAME}

The present invention relates to an anisotropic conductive film used for connecting circuit boards or electronic components such as IC chips and wiring boards, and a circuit connection structure using the same, and more particularly, to an anisotropic conductive film in which elastic recovery characteristics are controlled. It is about.

In order to electrically connect circuit boards or electronic components, such as an IC chip, and a circuit board, the anisotropic conductive film in which the electroconductive particle is disperse | distributed to the adhesive agent is used. In this case, the anisotropic conductive film is disposed between the electrodes facing each other, and the electrodes are connected by heating and pressurization, and then electrically connected by making the conductive in the pressing direction. Such anisotropic conductive film is typically used for packaging LCD panels, printed circuit boards (PCBs), and driver ICs in LCD modules.

Currently, LCDs are applied to a wide range of applications from large panels for notebook PCs, monitors, and TVs to medium and small panels for mobile devices such as mobile phones, personal digital assistants, and games. Driver IC mounting is adopted. Driver IC mounting in LCDs uses an outer lead bonding (OLB) method or a printed circuit board (PCB) in which a driver IC is formed into a tape carrier package (TCP) or a chip on film (COF) and bonded to the LCD panel. PCB: PCB type is attached to the printed circuit board. In addition, in small and medium-sized LCDs such as mobile phones, a COG (Chip On Glass) method in which a driver IC is directly mounted on an LCD panel by an anisotropic conductive film is adopted.

As described above, connection reliability between the circuit boards and electronic components such as IC chips and the circuit board using an anisotropic conductive film is the most problematic. That is, in the anisotropic conductive film, excellent conduction reliability is required along with high adhesiveness.

The connection reliability of the anisotropic conductive film is mainly observed through the indentation characteristic, which indicates that the conductive particles of the anisotropic conductive film interposed between the members to be pressed are pressed between the electrodes of the members to be bonded. Therefore, good indentation characteristics indicate that the conductive particles are well pressed between the electrodes, so that the electrical connection characteristics in the pressing direction are excellent, and bad indentation characteristics indicate that the conductive particles are not sufficiently pressed between the electrodes, resulting in poor electrical connection. Indicates.

Until now, indentation properties of anisotropic conductive films have been reported to be closely related to the curing rate of anisotropic conductive films. However, in this crimping, the indentation characteristics were good, but immediately after the crimping, the anisotropic conductive film may be elastically recovered, and the indentation characteristics may deteriorate again.

That is, the anisotropic conductive film excellent in curing rate and elastic modulus can guarantee the superiority of the basic indentation characteristics, but does not guarantee the superiority of the indentation characteristics after the main compression.

Therefore, an object of the present invention is to provide an anisotropic conductive film that can maintain excellent indentation properties even after the main compression.

Other objects and advantages of the present invention can be understood by the following description, and will be more clearly understood by the embodiments of the present invention. It will also be readily apparent that the objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.

The anisotropic conductive film according to the present invention is composed of a thermoplastic resin for forming a film, an acrylate-based thermosetting monomer used as a binder, a curing initiator, conductive particles, and a release film, and is interposed between circuit members opposing to each other. By doing so, the opposing circuit members are not only bonded to each other but also electrically connected.

In addition, the base resin (particularly, the thermosetting monomer) of the anisotropic conductive film has a predetermined elastic recovery force due to the properties of the resin itself. Therefore, after the anisotropic conductive film is compressed between the circuit members, the elastic recovery force may cause the electrode between the circuit members to be lifted up, resulting in poor indentation characteristics.

Problems of indentation characteristics due to the elastic recovery force of the anisotropic conductive film are well shown in FIGS. 1 and 2. Fig. 1 is a circuit connection state diagram before the pressure after the main compression is removed, and Fig. 2 is a circuit connection state diagram after the pressure after the main compression is removed.

Referring to the drawings, when the anisotropic conductive film is interposed between the circuit members facing each other, and heated and pressed, the main compression is performed while the conductive particles are interposed between the electrodes of the circuit member (see FIG. 1). After the pressing is completed, as shown in FIG. 2, when the pressure applied to the circuit member disappears, elastic recovery force in the direction of the arrow is generated on the anisotropic conductive film, and the electrode is excited between the electrodes.

Therefore, in order to maintain the indentation characteristics excellent after the main compression, the elastic recovery characteristics of the anisotropic conductive film should be adjusted to an optimal state.

The present inventors have shown the elastic recovery index (ε) represented by the following equation for the elastic recovery characteristics of the anisotropic conductive film to exhibit excellent connection reliability even after the main compression.

ε = (L ₂ / L ₁ )

(L ₁ : length of stretching when pulling the anisotropic conductive film 60% to 80% of the curing proceeds with a tensile force of 5kgf / ㎠, L ₂ : length to decrease when removing the tensile force of 5kgf / ㎠)

The acrylate-based anisotropic conductive film according to the present invention is characterized in that the elastic recovery index (ε) before curing has a value of 0.04 ≦ ε ≦ 0.15.
The present invention also provides a circuit connection structure electrically connected as well as mechanically by thermocompression bonding between the first circuit member and the second circuit member via the anisotropic conductive film. Here, the first circuit member may be a COF or TCP, and the second circuit member may be a glass substrate or a printed circuit board.

The anisotropic conductive film according to the present invention maintains excellent indentation properties even after the pressure is removed after the main compression. Therefore, in the electrical connection between the boards or electronic components such as IC chips and the circuit board, high adhesion and conduction reliability can be realized.

Hereinafter, the present invention will be described in detail with reference to the drawings. In each of the drawings, the same reference numerals denote the same or equivalent components.

3 illustrates a state in which the anisotropic conductive film 10 according to the present invention is interposed between circuit boards 20 and 30 facing each other.

The anisotropic conductive film 10 is made of a thermoplastic resin for forming a film, a binder, an acrylate-based thermosetting monomer, a curing initiator, conductive particles, and a release film, and other additives may be included as necessary.
Examples of the thermoplastic resin include polyvinyl butyral, polyvinyl formal, polyvinyl acetal, polyamide, phenoxy resin, styrene-butadiene-styrene block copolymer, carboxylated styrene-ethylene-butylene-styrene block copolymer, Polyacrylate resin etc. can be used individually or in mixture of 2 or more types. At this time, the thermoplastic resin is preferably contained 30 to 60% by weight.

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As the thermosetting monomer, a radical polymerizable resin having a functional group that is polymerized by a radical such as an acrylic monomer or a methacryl monomer may be used. Specifically, methyl acrylate, ethyl acrylate, iso amyl acrylate, and lauryl acrylate. , Stearyl acrylate, butoxy ethyl acrylate, ethoxy diethylene glycol acrylate, methoxy triethylene glycol acrylate, methoxy polystyrene glycol acrylate, methoxy dipropylene glycol acrylate, phenoxy ethyl acrylate , Phenoxy polystyrene glycol acrylate, isobornyl acrylate, 2-hydroxy ethyl acrylate, 2-hydroxy propyl acrylate, methyl methacrylate, isobutyl methacrylate, tridecyl methacrylate, methoxy Diethylene glycol methacrylate, Methoxy polystyrene glycol methacrylate, perryl methacrylate, perryl acrylate, isobutyl acrylate, isobornyl methacrylate, methoxy triethylene glycol methacrylate, etc., alone or in combination of two or more Can be used. At this time, the thermosetting monomer is preferably contained 30 to 70% by weight.

As the curing initiator, an azo compound or an organic peroxide may be used. Specifically, dicumyl peroxide, t-butyl-cumylperoxide, and bis (alpha-thi-butylperoxyiso) Propyl) benzene, 2,5-di (thi-butylperoxy) -2,5-dimethylhexane, 2,5-di (thi-butylperoxy) -2,5-dimethylhexine-3, diterbutylper Oxide (diterbutylperoxide), 1,1-di-terbutyl peroxycyclohexane, isopropyl cumylterbutyl peroxide, bis (alpha-teramyl peroxy isopropyl) benzene can be used alone or in combination of two or more have. At this time, the curing initiator is preferably contained 0.1 to 10% by weight.

As the conductive particles, in the case of an anisotropic conductive film of an OLB method or a COG method, a gold-nickel coated polymer ball or a gold coated nickel ball may be used, and in the case of a PCB type anisotropic conductive film, a nickel ball may be used. .

In addition, a silane coupling agent (adhesion enhancer), an adhesion imparting agent, or the like may additionally be used as an additive.

The anisotropic conductive film having the above-described configuration may be described in detail below by changing the type or content of the thermoplastic resin, the type or content of the thermosetting monomer, the type or content of the curing initiator, and the type of the additive. ε) can be adjusted in various ways.

Hereinafter, the elastic recovery index ε is introduced as an index indicating the elastic recovery characteristics of the acrylate-based anisotropic conductive film.

Figure 4 is a graph showing the change in length according to the stress of the anisotropic conductive film, Figure 5 is a test flow chart for performing a tensile strength test of the anisotropic conductive film.

First, as shown in FIG. 5 (a), a plurality of anisotropic conductive films before curing are prepared, and after laminating them, a compression roller is passed through to produce an anisotropic conductive film plate having a thickness (t) of 1 mm as shown in FIG. 5 (b). do. Using the anisotropic conductive film plate thus produced, as shown in Figure 5 (c) to prepare a specimen 13 having a thickness (d) 5mm, length (l) 20mm. Then, the specimen is placed in an oven and heated at a temperature of 160 ° C to 180 ° C for 8 seconds to 15 seconds to advance the curing so that the curing rate is 60% to 80%. Both ends of the specimens undergoing hardening 60% to 80% are bitten by the jig of the UTM apparatus shown in FIG. 5 (d) and then pulled so that the crosshead speed becomes 100 mm / min. At this time, when the stress reaches 5kgf / ㎠, the tension of the specimen is stopped, the applied stress is removed. Here, the tensile force of 5kgf / ㎠ is selected from the value less than the maximum tensile force that causes the fracture of the anisotropic conductive film specimen.

As such, when a tensile force is applied to both ends of the anisotropic conductive film having a curing rate of 60% to 80% using a UTM device until the stress becomes 5 kgf / cm 2, the length of the anisotropic conductive film is L ₁ as shown in FIG. 4. Increases. Then, when the stress applied to both ends of the anisotropic conductive film is removed, the length of the anisotropic conductive film is again reduced by L ₂ .

At this time, the elastic recovery index (ε) representing the elastic recovery characteristics of the anisotropic conductive film is defined as in the following equation.

ε = (L ₂ / L ₁ )

(L ₁ : length of stretching when pulling the anisotropic conductive film 60% to 80% of the curing proceeds with a tensile force of 5kgf / ㎠, L ₂ : length to decrease when removing the tensile force of 5kgf / ㎠)

The acrylate-based anisotropic conductive film according to the present invention is characterized in that the elastic recovery index (ε) is 0.04 or more and 0.15 or less.

At this time, if the elastic recovery index (ε) of the anisotropic conductive film is less than 0.04, the elastic recovery power of the anisotropic conductive film is so weak that when the conductive particles and the circuit member shrink and expand each other in a high temperature and high humidity environment, it is incompatible with the adhesive resin. As a result, warpage phenomenon occurs in which interfacial peeling occurs. On the other hand, if the elastic recovery index (ε) of the anisotropic conductive film exceeds 0.15, the elastic recovery force of the anisotropic conductive film is so strong that rebounding in the opposite direction to the bonding direction (or pressing direction) occurs after the main compression. This will cause poor indentation properties.

Therefore, in order to maintain excellent connection reliability even after the present compression, the elastic recovery index (ε) of the anisotropic conductive film that has undergone 60% to 80% of hardening should have a value of 0.04 or more and 0.15 or less.

The elastic recovery index (ε) can be adjusted by changing the type and amount of the thermoplastic resin, the thermosetting monomer, the curing initiator and the additive constituting the anisotropic conductive film.

Hereinafter, a plurality of anisotropic conductive films having various elastic recovery index (ε) were prepared, and the indentation characteristics and the connection resistance characteristics of the anisotropic conductive films thus prepared were measured and summarized in a table.

[Production of Anisotropic Conductive Film]

An adhesive composition containing a thermoplastic resin for film formation, an acrylate thermosetting resin as a binder, a curing agent, and various additives is dissolved or dispersed in an organic solvent, and conductive particles are dispersed to prepare a solution for film coating. The organic solvent used at this time is preferable because the mixed solvent of an aromatic hydrocarbon type and an oxygen type improves the solubility of a material. Subsequently, this solution is apply | coated to the transparent PET film which surface-treated the single side | surface using a pottery tool, and the anisotropic conductive film before hardening is obtained by 70 degreeC and hot air drying for 10 minutes. At this time, by changing the type and amount of the thermoplastic resin, thermosetting monomer, curing initiator, additives, etc. constituting the anisotropic conductive film appropriately to prepare an anisotropic conductive film having a variety of elastic recovery index (ε) as shown in the following Examples and Comparative Examples It was.

[Circuit Connection Structure]

FIG. 6 illustrates an OLB method or a PCB method connection process of bonding COF or TCP to a glass substrate or a PCB substrate through an anisotropic conductive film.

As shown in the figure, the anisotropic conductive films 10 prepared above are placed on a glass substrate or a PCB substrate 31 and pressurized at a pressure of 1 MPa to 3.5 MPa for 0.5 seconds to 3 seconds in a temperature range of 65 ° C. to 90 ° C. The COF or TCP 22 is disposed on the anisotropic conductive film. Subsequently, 8 seconds to 15 seconds under the conditions of 160 ° C to 190 ° C and 2 MPa to 4 MPa by using a heating bar 41 on the COF or TCP 22 through a buffer 42 made of 0.15T Teflon sheet. Heat and press to fabricate the circuit connection structure.

At this time, the anisotropic conductive film used in the circuit connection structure has a different elastic recovery index (ε) [ε = (L ₂ / L ₁ ), where L ₁ : hardening 60% as shown in the following Examples and Comparative Examples ˜80% of the length of the anisotropic conductive film stretched when pulled with a tensile force of 5kgf / ㎠, L ₂ : the length is reduced when removing the tensile force of the 5kgf / ㎠).

At this time, ten identical samples were produced for each Example and Comparative Example, the indentation characteristic and the connection resistance were measured about each, the average value was calculated | required, and it was put together in the table.

Example  One

An anisotropic conductive film having an elastic recovery index (ε) of 0.04 (L ₁ = 17 mm, L ₂ = 0.68 mm) was produced, and the anisotropic conductive film was applied to the circuit connection structure.

Example  2

An anisotropic conductive film having an elastic recovery index? Of 0.10 (L ₁ = 20 mm, L ₂ = 2 mm) was produced, and the anisotropic conductive film was applied to the circuit connection structure.

Example  3

An anisotropic conductive film having an elastic recovery index (ε) of 0.15 (L ₁ = 24 mm, L ₂ = 3.6 mm) was produced, and the anisotropic conductive film was applied to the circuit connection structure.

Comparative example  One

An anisotropic conductive film having an elastic recovery index? Of 0.02 (L ₁ = 15 mm, L ₂ = 0.3 mm) was produced, and the anisotropic conductive film was applied to the circuit connection structure.

Comparative example  2

An anisotropic conductive film having an elastic recovery index (ε) of 0.17 (L ₁ = 30 mm, L ₂ = 5.1 mm) was fabricated, and the anisotropic conductive film was applied to the circuit connection structure.

Comparative example  3

An anisotropic conductive film having an elastic recovery index? Of 0.20 (L ₁ = 35 mm, L ₂ = 7 mm) was produced, and the anisotropic conductive film was applied to the circuit connection structure.

(1) indentation characteristics and (2) conduction reliability tests were performed on the circuit connection structure via the anisotropic conductive film produced through the above-described Examples and Comparative Examples, and the results are shown in Table 1.

(1) indentation test

When the electrode of the glass substrate bonded to the chip is an ITO transparent electrode, the conductive ball pressing phenomenon was observed through an optical microscope, and in the case of a chromium electrode, the DIC indentation was observed using a differential interference microscope.

At this time, if the deformation of the conductive ball is observed in the ITO transparent electrode, ○, if there is no deformation of the conductive ball, it is indicated by ×, and if the protrusion of the conductive ball is observed in the chromium electrode, ○, there is no protrusion of the conductive ball. In the case, X was indicated.

(2) conduction reliability test

The resistance after the aging for 500 hours at the temperature of 85 ° C. and the 85% relative humidity (Ω _a ) and the initial resistance before aging (Ω _i ) were measured using a multimeter, respectively.

At this time, when the resistance value ( _a ) after aging and the initial resistance value ( _i ) before aging were both less than 5 kV, it was represented as (circle), x when 5 kW or more, and "OPEN" when measurement was impossible.

Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Challenge ○ ○ ○ × ○ ○ DIC Indentation ○ ○ ○ × ○ × Ω _i [Ω] 0.3 0.3 0.4 2.7 0.7 4.7 Ω _a [Ω] 1.3 1.2 1.3 19 7.5 27 Continuity reliability ○ ○ ○ × × ×

As can be seen from Table 1, all of the anisotropic conductive films of Examples 1 to 3 exhibited excellent indentation phenomenon and conduction reliability. On the other hand, the anisotropic conductive films of Comparative Example 1 and Comparative Example 3 exhibited poor indentation characteristics as well as poor conduction after aging. In Comparative Example 2, the indentation characteristics were good, but the resistance value after aging was 5 times or more than the initial resistance value before aging.

Therefore, when the anisotropic conductive film is cured 60% to 80% has the same elastic recovery index (0.04≤ε≤0.15) as in Examples 1 to 3, it can be confirmed that the connection reliability of the anisotropic conductive film is excellent. .

The following drawings, which are attached to this specification, illustrate exemplary embodiments of the present invention, and together with the detailed description of the present invention, serve to further understand the technical spirit of the present invention. It should not be construed as limited to.

1 is a circuit connection state diagram before the pressure is removed after the main compression.

2 is a circuit connection state diagram after the pressure after the main compression is removed.

3 is a state diagram in which an anisotropic conductive film is interposed between opposing circuit members.

Figure 4 is a graph showing the change in length according to the stress of the anisotropic conductive film.

5 is a test flow chart for performing a tensile strength test for an anisotropic conductive film before curing.

6 is a connection process diagram for bonding COF or TCP to a glass substrate or a PCB via an anisotropic conductive film.

<Explanation of symbols for the main parts of the drawings>

10: anisotropic conductive film 31: glass substrate or PCB

22: COF or TCP 41: Heating bar

42: cushioning material

Claims (10)

In the anisotropic conductive film comprising a thermoplastic resin for forming a film, an acrylate-based thermosetting monomer, a curing initiator, conductive particles and a release film as a binder, Anisotropic conductive film, characterized in that the elastic recovery index (ε) defined as follows has a value between 0.04≤ε≤0.15. ε = (L ₂ / L ₁ ) (L ₁ : length of stretching when pulling the anisotropic conductive film 60% to 80% of the curing proceeds with a tensile force of 5kgf / ㎠, L ₂ : length to decrease when removing the tensile force of 5kgf / ㎠) The method of claim 1, As said acrylate-type thermosetting monomer, the radically polymerizable resin which has a functional group superposing | polymerizing with the radical containing an acryl-type monomer and a methacryl-type monomer is used. The method of claim 2, As said thermosetting monomer, methyl acrylate, ethyl acrylate, iso amyl acrylate, lauryl acrylate, stearyl acrylate, butoxy ethyl acrylate, ethoxy diethylene glycol acrylate, methoxy triethylene glycol acrylate , Methoxy polystyrene glycol acrylate, methoxy dipropylene glycol acrylate, phenoxy ethyl acrylate, phenoxy polystyrene glycol acrylate, isobornyl acrylate, 2-hydroxy ethyl acrylate, 2-hydroxy Propyl acrylate, methyl methacrylate, isobutyl methacrylate, tridecyl methacrylate, methoxy diethylene glycol methacrylate, methoxy polystyrene glycol methacrylate, perryl methacrylate, perryl acrylate , Isobutyl acrylate, isobonyl meta An anisotropic conductive film, characterized in that acrylate and methoxy triethylene glycol methacrylate are used alone or in combination of two or more thereof. The method of claim 2, The curing initiator is an anisotropic conductive film, characterized in that an azo compound or an organic peroxide is used. The method of claim 4, wherein As said curing initiator, dicumyl peroxide, thi-butyl- cumyl peroxide, bis (alpha- thi- butyl peroxy isopropyl) benzene, 2, 5- di (thi-butyl peroxy) -2, 5- dimethyl Hexane, 2,5-di (thi-butylperoxy) -2,5-dimethylhexine-3, diterbutylperoxide, 1,1-di-terbutylperoxycyclohexane, isopropylcumylterbutylperoxide And bis (alpha-teramylperoxyisopropyl) benzene are used singly or in admixture of two or more thereof. The method of claim 4, wherein Examples of the thermoplastic resin include polyvinyl butyral, polyvinyl formal, polyvinyl acetal, polyamide, phenoxy resin, styrene-butadiene-styrene block copolymer, and carboxylated styrene-ethylene-butylene-styrene block copolymer. And polyacrylate resins are used alone or in combination of two or more. The method of claim 6, As the conductive particles, gold-nickel coated polymer balls, gold coated nickel balls or nickel balls are used, characterized in that the anisotropic conductive film. A circuit connection structure electrically and mechanically connected between a first circuit member and a second circuit member by thermocompression bonding through the anisotropic conductive film of any one of claims 1 to 7. The method of claim 8, And the first circuit member is COF or TCP, and the second circuit member is a glass substrate. The method of claim 8, Wherein said first circuit member is a COF or TCP and said second circuit member is a printed circuit board.

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