KR20090115516A - Anisotropic Conductive Film Having A Optimum Elastic Restitution Property And Circuit Board Using The Same - Google Patents

Abstract

PURPOSE: An anisotropic conductive film is provided to maintain excellent indentation characteristic when the pressure after compression is removed, and to realize high adhesive property and electricity reliability. CONSTITUTION: An anisotropic conductive film includes a thermoplastic resin, an epoxy-based thermosetting resin, a hardener, conductive particles and a release film. An elastic recovery index(ε) represented by the formula: ε =(L2/L1) has a value satisfying 0.05<=ε<=0.15. In chemical formula, L1 is the length extended when the anisotropic conductor film is drawn by 2 kgf/cm^2 tensile force before hardening; and L2 is the length shortened when 2 kgf/cm^2 tensile force is removed.

Description

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 to connect 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 with elastic recovery characteristics 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 various applications from large panels for notebook PCs, monitors, and TVs to medium and small panels for mobile devices such as mobile phones, PDAs (Personal Digital Assistants), and games. Driver IC implementation is adopted. Driver IC mounting in LCDs uses an OLB (Outer Lead Bonding) method or a printed circuit board that converts the driver IC into a Tape Carrier Package (TCP) or a Chip On Film (COF) and adheres it 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. Also, it will be readily appreciated that the objects and advantages of the present invention may be realized by the means and combinations thereof indicated in the claims.

The anisotropic conductive film according to the present invention is composed of a thermoplastic resin for forming a film, an epoxy-based thermosetting resin used as a binder, a curing agent, a conductive particle, and a release film. The anisotropic conductive film is interposed between circuit members opposing to each other and then opposed by thermal compression. The circuit members to be bonded together are electrically connected to each other.

In addition, the base resin (particularly, thermosetting resin) of the anisotropic conductive film has a predetermined elastic recovery force due to the characteristics 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 pressurized, the main compression is performed while the conductive particles are interposed between the electrodes of the circuit member (see Fig. 2). After the pressing is completed, as shown in FIG. 3, 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 characteristics of the anisotropic conductive film to exhibit excellent connection reliability even after the main compression by the elastic recovery index (ε) represented by the following formula (1).

ε = (L ₂ / L ₁ )

(L ₁ : length that is increased when the anisotropic conductive film is pulled with a tensile force of 2kgf / ㎠ before curing, L ₂ : length is reduced when the tension of 2kgf / ㎠ is removed)

Epoxy-based anisotropic conductive film according to the invention is characterized in that the elastic recovery index (ε) has a value of 0.05 ≤ ε ≤ 0.15.

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 figure, the same reference numerals indicate 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 composed of a thermoplastic resin for forming a film, a thermosetting resin as a binder, a curing agent, conductive particles, a release film, and other additives.

Examples of the thermoplastic resin include polyvinyl butyral, polyvinyl formal, polyvinyl acetal, polyamide, phenoxy resin, poly monkeyphone, styrene-butadiene-styrene block copolymer, carboxylated styrene-ethylene-butylene-styrene A block copolymer, polyacrylate resin, etc. can be used 30 to 60 weight%.

As the thermosetting resin, an epoxy resin is preferable, and in particular, a bisphenol type epoxy resin, a novolak type epoxy resin, a biphenyl type epoxy resin, a dicyclopentadiene type epoxy resin, a naphthalene type epoxy resin, or the like may be used alone or in combination. 30 to 70% by weight can be used.

As said hardening | curing agent, the hardening | curing agent for epoxy resins is preferable, In particular, it is preferable to use the latent hardening | curing agent which is excellent in storage stability and fast hardening rate. Specifically, imidazole type (imidazole, 2-ethyl imidazole, 2-phenyl-4-methyl imidazole, 2-dodecyl imidazole, 2-phenyl imidazole, 2-phenyl-4-methyl imidazole, 4 0.1 to 10% by weight of -methyl imidazole, etc.), a hydrazide system, a boron trifluoride-amine complex, a sulfonium salt, an amineimide, a salt of a polyamine, and dicyandiamide.

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 has an elastic recovery index described in detail below by changing the type or content of the thermoplastic resin, the type or content of the thermosetting resin, the type or content of the curing agent, and the type of the additive. ) Can be adjusted in various ways.

Hereinafter, the elastic recovery index (ε) is introduced as an index indicating the elastic recovery characteristics of the epoxy-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. do. Using the anisotropic conductive film plate thus prepared to produce a specimen 13 having a thickness d = 5mm and the length ℓ = 20mm as shown in (c) of FIG. Both ends of the specimen are bitten by the jig of the UTM apparatus shown in FIG. 5 (d) and then pulled so that the crosshead speed is 100 mm / min. At this time, when the stress reaches 2kgf / ㎠, the tension of the specimen is stopped, the applied stress is removed. Here, the tensile force of 2kgf / ㎠ 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 using the UTM device until the stress becomes 2 kgf / cm 2, the length of the anisotropic conductive film is increased by L ₁ as shown in FIG. 4. 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 expressed by Equation 2 below.

ε = (L ₂ / L ₁ )

(Wherein L ₁ : length increased when the anisotropic conductive film is pulled with a tensile force of 2kgf / ㎠ before curing, L ₂ : length reduced when the tensile force of 2kgf / ㎠ is removed)

Epoxy-based anisotropic conductive film according to the invention is characterized in that the elastic recovery index (ε) is 0.05 or more, 0.15 or less.

At this time, when the elastic recovery index (ε) of the anisotropic conductive film is less than 0.05, the elastic recovery force of the anisotropic conductive film is too weak, so that the conductive particles and the circuit member contract and expand with each other in a high temperature and high humidity environment, and are not synchronized with the adhesive resin. Interfacial peeling occurs or connection resistance rises. 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 main compression, the elastic recovery index (ε) of the anisotropic conductive film before curing should have a value of 0.05 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 resin, the curing agent, 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 comprising a thermoplastic resin for film formation, an epoxy 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. At this time, the organic solvent used 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 hot air drying for 70 minutes and 10 minutes. At this time, by changing the type and amount of the thermoplastic resin, thermosetting resin, curing agent, additives, etc. constituting the anisotropic conductive film, an anisotropic conductive film having various elastic recovery index (ε) was prepared as in the following Examples and Comparative Examples. .

[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, the circuit was heated and pressurized for 10 seconds at a temperature of 180 ° C. and 2 MPa to 4 MPa using a heating bar 41 on a COF or TCP 22 through a buffer 42 made of 0.15T Teflon sheet. Manufacture connection structure.

At this time, the anisotropic conductive film used for the circuit connection structure has a different elastic recovery index (ε = (L ₂ / L ₁ ), where L ₁ : 2kgf of the anisotropic conductive film before curing as shown in the following Examples and Comparative Examples L ₂ : length that is reduced when the tension of 2 kgf / cm 2 is removed. 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? Of 0.05 (L ₁ = 50 mm, L ₂ = 2.5 mm) was produced, and the anisotropic conductive film was applied to the circuit connection structure assembly.

Example  2

An anisotropic conductive film having an elastic recovery index? Of 0.1 (L ₁ = 35 mm, L ₂ = 3.5 mm) was produced, and the anisotropic conductive film was applied to the circuit connection structure assembly.

Example  3

An anisotropic conductive film having an elastic recovery index (ε) of 0.15 (L ₁ = 40 mm, L ₂ = 6.0 mm) was produced, and the anisotropic conductive film was applied to the circuit connection structure assembly.

Comparative example  One

An anisotropic conductive film having an elastic recovery index (ε) of 0.03 (L ₁ = 40 mm, L ₂ = 1.2 mm) was produced, and the anisotropic conductive film was applied to the circuit connection structure assembly.

Comparative example  2

An anisotropic conductive film having an elastic recovery index? Of 0.04 (L ₁ = 45 mm, L ₂ = 1.8 mm) was produced, and the anisotropic conductive film was applied to the circuit connection structure assembly.

Comparative example  3

An anisotropic conductive film having an elastic recovery index (ε) of 0.16 (L ₁ = 35 mm, L ₂ = 5.6 mm) was produced, and the anisotropic conductive film was applied to the circuit connection structure assembly.

Comparative example  4

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

Comparative example  5

An anisotropic conductive film having an elastic recovery index? Of 0.20 (L ₁ = 25 mm, L ₂ = 5.0 mm) was produced, and the anisotropic conductive film was applied to the circuit connection structure assembly.

Comparative example  6

An anisotropic conductive film having an elastic recovery index? Of 0.30 (L ₁ = 20 mm, L ₂ = 6.0 mm) was produced, and the anisotropic conductive film was applied to the circuit connection structure assembly.

Comparative example  7

An anisotropic conductive film having an elastic recovery index? Of 0.40 (L ₁ = 30 mm, L ₂ = 12 mm) was produced, and the anisotropic conductive film was applied to the circuit connection structure assembly.

The circuit connection structure via the anisotropic conductive film produced through the above-described Examples and Comparative Examples was subjected to (1) indentation characteristics and (2) conduction reliability test as shown below, 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 derivation 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), * 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 Comparative Example 4 Comparative Example 5 Comparative Example 6 Comparative Example 7 Challenge ○ ○ ○ × ○ ○ ○ ○ × × DIC Indentation ○ ○ ○ × ○ ○ × ○ × × Ω _i [Ω] 0.3 0.4 0.3 3.8 0.6 0.5 2.4 0.5 3.2 5.2 Ω _a [Ω] 1.2 1.3 1.3 OPEN 10 8 24 12.0 OPEN OPEN Continuity reliability ○ ○ ○ OPEN × × × × OPEN OPEN

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, Comparative Example 4, Comparative Example 6 and Comparative Example 7 not only had poor indentation characteristics but also showed poor conduction after aging. Moreover, although the indentation characteristic was favorable in Comparative Example 2, Comparative Example 3, and Comparative Example 5, the resistance value after aging was 5 times or more than the initial resistance value before aging.

Therefore, when the epoxy-based anisotropic conductive film has the same elastic recovery index (0.05≤ε≤0.15) as in Example 1 to Example 3, it can be confirmed that the connection reliability is excellent.

The following drawings attached to this specification are illustrative of the preferred embodiments of the present invention, and together with the detailed description of the invention to serve to further understand the technical spirit of the present invention, the present invention is a matter described in such drawings 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 (8)

In the anisotropic conductive film comprising a thermoplastic resin for forming a film, an epoxy-based thermosetting resin, a curing agent, conductive particles and a release film as a binder, Anisotropic conductive film, characterized in that the elastic recovery index (ε) defined as below has a value between 0.05≤ε≤0.15. ε = (L ₂ / L ₁ ) (Wherein L ₁ : length increased when the anisotropic conductive film is pulled with a tensile force of 2kgf / ㎠ before curing, L ₂ : length reduced when the tensile force of 2kgf / ㎠ is removed) The method of claim 1, The epoxy-based thermosetting resin is a bisphenol-type epoxy resin, a novolak-type epoxy resin, a biphenyl-type epoxy resin, a dicyclopentadiene-type epoxy resin, naphthalene-type epoxy resin, or the like, using anisotropically characterized by Conductive film. The method of claim 2, The curing agent is imidazole-based (imidazole, 2-ethyl imidazole, 2-phenyl-4-methyl imidazole, 2-dodecyl imidazole, 2-phenyl imidazole, 2-phenyl-4-methyl imidazole, 4 -Methyl imidazole), a hydrazide system, a boron trifluoride-amine complex, a sulfonium salt, an amineimide, a salt of a polyamine, an anisotropic conductive film characterized by using a latent curing agent for epoxy resins. The method of claim 3, wherein The thermoplastic resin is polyvinyl butyral, polyvinyl formal, polyvinyl acetal, polyamide, phenoxy resin, poly monkeyphone, styrene-butadiene-styrene block copolymer, carboxylated styrene-ethylene-butylene-styrene Block copolymer, an anisotropic conductive film comprising a polyacrylate resin. The method of claim 4, wherein The conductive particles, gold-nickel coated polymer ball, gold-coated nickel film and nickel anisotropic conductive film comprising a nickel ball. A circuit connecting 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 5. The method of claim 6, And the first circuit member is COF or TCP, and the second circuit member is a glass substrate. The method of claim 6, Wherein said first circuit member is a COF or TCP and said second circuit member is a printed circuit board.

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