WO2003000816A1 - Anisotropic conductive adhesives having enhanced viscosity and bonding methods and integrated circuit packages using the same - Google Patents

Anisotropic conductive adhesives having enhanced viscosity and bonding methods and integrated circuit packages using the same Download PDF

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Publication number
WO2003000816A1
WO2003000816A1 PCT/KR2002/001198 KR0201198W WO03000816A1 WO 2003000816 A1 WO2003000816 A1 WO 2003000816A1 KR 0201198 W KR0201198 W KR 0201198W WO 03000816 A1 WO03000816 A1 WO 03000816A1
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WO
WIPO (PCT)
Prior art keywords
anisotropic conductive
resin
conductive adhesive
substrate
adhesive
Prior art date
Application number
PCT/KR2002/001198
Other languages
French (fr)
Inventor
Jin-Sang Hwang
Myung-Jin Yim
Original Assignee
Telephus, Inc.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from KR1020020017406A external-priority patent/KR20030001231A/en
Application filed by Telephus, Inc. filed Critical Telephus, Inc.
Publication of WO2003000816A1 publication Critical patent/WO2003000816A1/en

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L24/00—Arrangements for connecting or disconnecting semiconductor or solid-state bodies; Methods or apparatus related thereto
    • H01L24/80—Methods for connecting semiconductor or other solid state bodies using means for bonding being attached to, or being formed on, the surface to be connected
    • H01L24/83—Methods for connecting semiconductor or other solid state bodies using means for bonding being attached to, or being formed on, the surface to be connected using a layer connector
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09J—ADHESIVES; NON-MECHANICAL ASPECTS OF ADHESIVE PROCESSES IN GENERAL; ADHESIVE PROCESSES NOT PROVIDED FOR ELSEWHERE; USE OF MATERIALS AS ADHESIVES
    • C09J163/00—Adhesives based on epoxy resins; Adhesives based on derivatives of epoxy resins
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09J—ADHESIVES; NON-MECHANICAL ASPECTS OF ADHESIVE PROCESSES IN GENERAL; ADHESIVE PROCESSES NOT PROVIDED FOR ELSEWHERE; USE OF MATERIALS AS ADHESIVES
    • C09J5/00—Adhesive processes in general; Adhesive processes not provided for elsewhere, e.g. relating to primers
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09J—ADHESIVES; NON-MECHANICAL ASPECTS OF ADHESIVE PROCESSES IN GENERAL; ADHESIVE PROCESSES NOT PROVIDED FOR ELSEWHERE; USE OF MATERIALS AS ADHESIVES
    • C09J9/00—Adhesives characterised by their physical nature or the effects produced, e.g. glue sticks
    • C09J9/02—Electrically-conducting adhesives
    • H—ELECTRICITY
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    • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
    • H01B1/00—Conductors or conductive bodies characterised by the conductive materials; Selection of materials as conductors
    • H01B1/20—Conductive material dispersed in non-conductive organic material
    • H01B1/22—Conductive material dispersed in non-conductive organic material the conductive material comprising metals or alloys
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    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
    • H05K3/00—Apparatus or processes for manufacturing printed circuits
    • H05K3/30—Assembling printed circuits with electric components, e.g. with resistor
    • H05K3/32—Assembling printed circuits with electric components, e.g. with resistor electrically connecting electric components or wires to printed circuits
    • H05K3/321—Assembling printed circuits with electric components, e.g. with resistor electrically connecting electric components or wires to printed circuits by conductive adhesives
    • H05K3/323—Assembling printed circuits with electric components, e.g. with resistor electrically connecting electric components or wires to printed circuits by conductive adhesives by applying an anisotropic conductive adhesive layer over an array of pads
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
    • C08L63/00—Compositions of epoxy resins; Compositions of derivatives of epoxy resins
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    • H01L2224/83851—Bonding techniques using a polymer adhesive, e.g. an adhesive based on silicone, epoxy, polyimide, polyester being an anisotropic conductive adhesive
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    • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
    • H05K2201/00—Indexing scheme relating to printed circuits covered by H05K1/00
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    • H05K3/00—Apparatus or processes for manufacturing printed circuits
    • H05K3/36—Assembling printed circuits with other printed circuits
    • H05K3/361—Assembling flexible printed circuits with other printed circuits

Definitions

  • the present invention relates to an anisotropic conductive adhesive, a bonding method using the adhesive, and an integrated circuit package using the adhesive, and more particularly, to an anisotropic conductive adhesive available in the manufacture of a module for a flat panel display, such as a liquid crystal display panel (LCD), plasma display panel (PDP), electroluminescent display (ELD), etc., and available in bonding micro circuits to package a semiconductor, a bonding method using the anisotropic conductive adhesive, and an integrated circuit package obtained using the bonding method. More particularly, the present invention directs to methods of flip-chip bonding and chip-scale packaging of a semiconductor.
  • LCD liquid crystal display panel
  • PDP plasma display panel
  • ELD electroluminescent display
  • Japanese Patent Laid-open No. 8-20629 discloses an epoxy resin composition prepared by mixing a resin mixture, which includes an epoxy resin containing a non-cross-linked, thermoplastic elastomer component, an epoxy resin containing a cross-linked rubber component, and a solid epoxy resin having a softening point of 50°C or greater, with a urea-based hardener for expoxy resin and a latent catalyst which is stable at 40°C and is activated at 80°C or less.
  • U.S. Patent No. 6,020,059 discloses an anisotropic conductive adhesive containing a film-forming resin and conductive particles and having a melting viscosity greater than 100 poises at 150°C.
  • U.S. Patent No. 5,543,486 discloses an epoxy resin composition containing an epoxy resin having more than two epoxy groups in one molecule, a solid-dispersing, amine adduct-type latent hardener, and a metal alkoxide as the essential components.
  • Most conventional anisotropic conductive adhesives suggested so far use a thermocurable epoxy resin or a modified epoxy resin alone or a mixture of a variety of types of thermoplastic resins as a polymeric resin.
  • conductive particles for the conventional anisotropic conductive adhesives nickel or a gold and nickel-coated composite has been mostly used.
  • additives including a hardener for the thermocurable resin, an adhesion imparting agent, an anti-oxidant, a coupling agent, etc. has been used.
  • FIGS. 1A and 1 B are sectional views illustrating a process of bonding circuits using an anisotropic conductive adhesive in the manufacture of a module for a general flat panel display or in the packaging of a semiconductor.
  • FIG. 1A is a cross-sectional view after the anisotropic conductive additive is applied to a substrate 60 with a lower circuit 50 on its top surface and before an IC circuit 10 is bound to the substrate 60.
  • FIG. 1 B is a cross-sectional view after an upper circuit 20 on the IC chip 10 is connected to the lower circuit 50 on the substrate 60 by heating and pressing.
  • Conductive particles 30 contained in the anisotropic conductive adhesive are immobilized between the upper circuit 20 and the lower circuit 50 by heating and pressing, as shown in FIG. 1 B.
  • the upper circuit 20 and the lower circuit 50 are electrically connected by the conductive particles 30 and are insulated from and bound to each other by an adhesive resin 40 constituting the anisotropic conductive adhesive.
  • the bonding of the upper circuit 20 and the lower circuit 50 using the anisotropic conducrive adhesive is a high-temperature process performed at 150-250°C. Therefore, a change in the fluidity of the adhesive resin 40 from a time point of heating the adhesive resin 40 to a time point at which the adhesive resin 40 is completely cured considerably affects the connection reliability of the upper circuit 20 and the lower circuit 50.
  • FIG. 2 is a graph of a viscosity variation pattern of the adhesive resin over heating time when bonding circuits at a high temperature using a conventional anisotropic conductive adhesive.
  • FIG. 2 in the interval of state A appearing immediately after heating, viscosity increases.
  • the temperature of the adhesive resin contained in the anisotropic conductive adhesive rises in the initial stage of bonding, a curing reaction is initiated, and viscosity gradually increases with increasing heating time.
  • the curing reaction of the adhesive resin constituting the anisotropic conductive adhesive become active, and viscosity increases with respect to heating time at a faster rate than in the interval of state A.
  • the interval of state C the curing reaction of the adhesive resin constituting the anisotropic conductive adhesive is accelerated, and viscosity tends to suddenly increase with respect to heating time.
  • FIG. 3 is an optical microscopic photograph showing a state of circuits 80 bound together using a conventional anisotropic conductive adhesive 70.
  • state A as shown in FIG. 2, which corresponds to the initial stage of bonding where the adhesive resin contained in the anisotropic conductive adhesive has a great fluidity, is sustained for a long time, so that the adhesive resin of the anisotropic conductive adhesive 70 is not retained between the circuits 80 to be connected and flows down to form voids 90 resulting from bubbles present in a region between the circuits 80 unfilled with the adhesive resin. Due to the presence of the voids 90 between the connected circuits 80, insulating resistance, connection resistance, and adhesive force between the circuits 80 are lowered, thereby degrading reliability of the device.
  • an anisotropic conductive adhesive comprising: an adhesive composition including an epoxy-based base resin, a hardener, and conductive particles; and a viscosity enhancer of 5-95% by weight based on the total amount of the anisotropic conductive adhesive for adjusting the fluidity of the adhesive composition.
  • the anisotropic conductive adhesive comprises an inorganic material.
  • the inorganic material may be selected from the group consisting of alumina, silicon carbide, silica, copper oxide, titanium dioxide, and a mixture of at least two of these materials.
  • the inorganic material is in a granular form having an average particle size of 0.1-5 microns and is contained in an amount of 5-60% by weight based on the total amount of the anisotropic conductive adhesive.
  • the viscosity enhancer comprises a radical curable resin and a radical initiator.
  • the radical curable resin may comprise an acrylic monomer or methacrylic monomer having a C ⁇ -C 20 main chain, an acrylic oligomer or methacrylic oligomer having a C 2 ⁇ -C ⁇ oo main chain, a thermocurable resin including a reactive acrylic or methacrylic unit, a thermoplastic resin including a reactive acrylic or methacrylic unit, or a mixture of these materials
  • the radical initiator comprises a peroxide initiator, an azo initiator, or a mixture of these materials.
  • the radical initiator comprises cumil peroxyoctoate, acetyl peroxide, t-butyl peroxybenzoate, dicumil peroxide, azobisisobutyronitril, or a mixture of these materials.
  • the UV initiator is formed of a material responsive to light of a UV wavelength of 200-400 nm.
  • the UV initiator may comprise 2,2-dimethoxy-2-phenylacetophenone, 1 -hydroxy- cyclohexyl-penylketone, para-phenylbenzophenone, benzyldimethylketal, or a mixture of these materials.
  • the anisotropic conductive adhesive according to the present invention may further comprise a conductive impurity ion of 1-100 ppm.
  • the conductive impurity ion may be selected from the group consisting of Na + , K ⁇ and cr.
  • the base resin may be selected from the group consisting of bisphenol-A type epoxy resin, bisphenol-F type epoxy resin, phenol nobolak type epoxy resin, cresol nobolak type epoxy resin, dimeric modified epoxy resin, rubber modified epoxy resin, urethane modified epoxy resin, bromated epoxy resin, melamine resin, urethane resin, polyimide resin, polyamide resin, polyethylene resin, polypropylene resin, styrene resin, styrene-butadiene resin, phenol resin, formaldehyde resin, silicon resin, acrylate resin, or a mixture of these resins.
  • the hardener is selected from the group consisting of imidazole derivatives, amine derivatives, amide derivatives, acidic anhydrides, phenol derivatives, and a mixture of at least two of these materials.
  • the conductive particles comprises pure nickel particles or composite particles obtained by sequentially coating the surface of polymeric beads with nickel and gold.
  • the adhesive composition further comprises an adhesion imparting agent selected from the group consisting of rosin resin, terpene resin, and cumarone-indene resin.
  • the adhesive composition further comprises a coupling agent for dispersing and stabilizing the conductive particles.
  • the coupling agent may comprise a silane derivative.
  • an integrated circuit package comprising: a first substrate on which a first circuit including a first electrode is implemented; a second substrate on which a second circuit including a second electrode disposed to face the first substrate is implemented; and an anisotropic conductive adhesive applied between the first and second substrates to bond the same together while the first and second electrodes are in contact to be electrically connected, wherein the anisotropic conductive adhesive comprises a resin, a hardener, conductive particles dispersed in the resin, and a viscosity enhancer for increasing the viscosity of the resin.
  • the viscosity enhancer comprises an inorganic material selected from the group consisting of silica, silicon carbide, alumina, and a mixture of at least two of the materials and is contained in an amount of 5-60% by weight based on the total amount of the anisotropic conductive adhesive.
  • the first substrate is a component of a liquid crystal display (LCD), for example, a glass substrate or a flexible printed circuit board (FPC).
  • LCD liquid crystal display
  • FPC flexible printed circuit board
  • a method for bonding a first substrate with a first circuit having a first electrode, and a second substrate with a second circuit having a second electrode comprising applying an anisotropic conductive adhesive to the first substrate.
  • the applied anisotropic conductive adhesive is pre-pressed against the first substrate at a temperature of 60-100°C.
  • the first and second substrates are aligned such that the first and second circuits face each other.
  • the first and second substrates are bound together by pressing the first and second substrates against each other such that the first and second electrodes are electrically connected.
  • the bonding method according to the present invention further comprises: aligning a third substrate on the first substrate against which the anisotropic conductive adhesive has been pre-pressed; and pre-pressing the third substrate against the first substrate by applying a pressure of 0.1-1 MP at a temperature 60-100°C.
  • FIG. 1A is a cross-sectional view after an anisotropic conductive additive is applied to a substrate before an IC circuit is bound to the substrate in the manufacture of a module of a conventional flat panel display or in the packaging of a semiconductor;
  • FIG. 1 B is a cross-sectional view after an upper circuit on the IC chip is connected to a lower circuit on the substrate by heating and pressing;
  • FIG. 2 is a graph of a viscosity variation pattern of an adhesive resin over heating time when bonding circuits at a high temperature using a conventional anisotropic conductive adhesive;
  • FIG. 3 is an optical microscopic photograph showing a state of the circuits bound together using a conventional anisotropic conductive adhesive
  • FIG. 4 is a flowchart illustrating a first embodiment of a method for preparing an anisotropic conductive adhesive according to the present invention
  • FIG. 5 is a flowchart illustrating a second embodiment of the method for preparing the anisotropic conductive adhesive according to the present invention
  • FIG. 6 is a flowchart illustrating a third embodiment of the method for preparing the anisotropic conductive adhesive according to the present invention
  • FIG. 7 is a graph showing a viscosity variation pattern of an adhesive resin with respect to heating time when micro circuits are bound at a high temperature using an anisotropic conductive adhesive according to the present invention
  • FIG. 8 is an optical microscopic photograph showing the state of the connection of circuits when an example of the anisotropic conductive adhesive according to the present invention is applied;
  • FIG. 1 1 is a graph comparatively showing the change in connection resistance over time when a conventional anisotropic conductive adhesive and a variety of anisotropic conductive adhesives prepared according to the present invention with different compositions by different methods are applied to bond circuits;
  • FIG. 12 is a flowchart illustrating a preferred embodiment of a bonding method using an anisotropic conductive adhesive according to the present invention.
  • an inorganic viscosity enhancer is incorporated as a component of an anisotropic conductive adhesive to adjust the fluidity of an adhesive resin.
  • a viscosity enhancer composed of a radical curable resin and radical initiator is incorporated as a component of the anisotropic conductive adhesive to the fluidity of an adhesive resin.
  • a radical initiator which is highly reactive at a comparatively low temperature of about 100-150°C is used to increase the rate of curing reaction.
  • a viscosity enhancer composed of a UV-curable resin and UV initiator is incorporated as a component of the anisotropic conductive adhesive to the fluidity of an adhesive resin. In this case, UV of an appropriate wavelength for curing is radiated in the preparation of the anisotropic conductive adhesive to partially or entirely cure the UV curable resin. Alternatively, heating may be performed while the UV radiation to induce the curing reaction.
  • the fluidity of the adhesive composition can be reduced in an initial attachment process, which is performed at a comparatively high temperature, thereby preventing formation of voids between connected circuits in a resultant final circuit construct to ensure the reliability of the connected circuits.
  • an anisotropic conductive adhesive includes the following basic components: (a) an adhesive composition comprising an epoxy-based base resin, a hardener, and conductive particles, and (b) a viscosity enhancer for adjusting the fluidity of the adhesive composition.
  • Suitable base resins for the anisotropic conductive adhesive according to the present invention include, for example, bisphenol-A type epoxy resin, bisphenol-F type epoxy resin, phenol nobolak type epoxy resin, cresol nobolak type epoxy resin, dimeric modified epoxy resin, rubber modified epoxy resin, urethane modified epoxy resin, bromated epoxy resin, melamine resin, urethane resin, polyimide resin, polyamide resin, polyethylene resin, polypropylene resins, styrene resin, styrene-butadiene resin, phenol resin, formaldehyde resin, silicon resin, acrylate resin, or a mixture of these resins.
  • Suitable hardeners for the anisotropic conductive adhesive according to the present invention include, for example, imidazole derivatives, such as 2-methyl imidazole, 2-ethyl imidazole, and 1 -cyanoethyl-2-methyl imidazole, amide derivatives, such as dicyandiamide, amine derivatives, acidic anhydrides, or phenol derivatives.
  • imidazole derivatives such as 2-methyl imidazole, 2-ethyl imidazole, and 1 -cyanoethyl-2-methyl imidazole
  • amide derivatives such as dicyandiamide
  • amine derivatives such as dicyandiamide
  • acidic anhydrides or phenol derivatives.
  • phenol derivatives phenol derivatives.
  • one compound selected from the above-listed hardeners may be used alone, or at least two compounds among the hardeners may be used in a mixed form.
  • the hardener may be encapsulated into a microcapsule with a thermo
  • Suitable conductive particles for the anisotropic conductive adhesive according to the present invention include pure nickel particles or composite particles obtained by sequentially coating the surface of polymeric beads with nickel and gold to a thickness of about 500A each.
  • the composite particles have a gravity of 1-3. This level of gravity is similar to that of the adhesive composition of the anisotropic conductive adhesive according to the present invention, and thus dispersion stability is better than using pure nickel particles. In addition, due to their particle sizes that are almost uniform, advantageously, there is no deviation in electrical conductivity between individual circuits connected with each other.
  • the viscosity enhancer for the anisotropic conductive adhesive which is used to adjust the fluidity of the adhesive composition
  • an inorganic material, a radical curable resin and radical initiator, or a UV-curable resin and UV initiator can be used.
  • the viscosity enhancer is contained in an amount of 5-95% by weight based on the total amount of the anisotrotropic conductive adhesive.
  • An inorganic material having thixotropic behavior may be used as the viscosity enhancer.
  • Suitable inorganic materials for the anisotropic conductive adhesive according to the present invention include, for example, aluminum oxide (AI 2 O 3 ), silicon carbide (SiC), silica (SiO 2 ), copper oxide (CuO), or titanium dioxide (TiO 2 ).
  • One material selected from the listed materials may be used alone. Alternatively, at least two of the materials may be used in a mixed form.
  • the inorganic materials are in a granular form of an average particle size of 0.1-5 microns.
  • silica is used in an amount of 5-60% by weight based on the total amount of the anisotropic conductive adhesive.
  • an increase in the viscosity of the anisotropic conductive adhesive and characteristics improvements in terms of thermal expansion coefficient and glass transition temperature are expected.
  • Suitable radical initiators include a peroxide initiator, an azo initiator, or a mixture of these materials, and more particularly, cumil peroxyoctoate, acetyl peroxide, t-butyl peroxybenzoate, dicumil peroxide, azobisisobutyronitril, or a mixture of these materials.
  • suitable UV curable resins include a multi-functional monomer selected from the group consisting of dipentaerythritol hexaacrylate, methyleneglycol bisacrylate, trimethylolpropane triacrylate, ethyleneglycol diacrylate, and pentaerythritol triacrylate, a multi-functional oligomer selected from the group consisting of epoxy acrylate, urethane acrylate, and polyester acrylate, a reactive acrylate polymer, or a mixture of these materials.
  • Any UV initiator capable of inducing a photoreaction with a UV wavelength preferably a UV wavelength of 200-400nm, may be used.
  • Suitable UV initiators include, for example, 2,2-dimethoxy-2-phenylacetophenone, 1 -hydroxy-cyclohexyl-penylketone, para-phenylbenzophenone, benzyldimethylketal, or a mixture of these materials.
  • a mixture of at least two photoinitiators having a reactivity with respect to different wavelengths is used, deviations in characteristics of the anisotropic conductive adhesive depending on different preparation conditions can be reduced.
  • a benzophenone photosensitizer, or an anti-polymerization agent such as hydroquinone monoethylether may be additionally used.
  • the anisotropic conductive adhesive according to the present invention may further include conductive impurity ions if necessary.
  • the addition of the conductive impurity ions can prevent the connected circuits from corrosion.
  • conductive impurity ions cations or anions, for example, Na + , K*, and Cl " , may be used.
  • the conductive impurity ions are contained in an amount of, preferably 1-100 ppm, and more preferably less than 10 ppm. The components and composition of the anisotropic conductive adhesive are adjusted in consideration of the amount of the conductive impurity ions.
  • FIG. 4 is a flowchart illustrating a first embodiment of a method for preparing the anisotropic conductive adhesive according to the present invention.
  • FIG. 5 is a flowchart illustrating a second embodiment of the method for preparing the anisotropic conductive adhesive according to the present invention.
  • anisotripic conductive adhesives according to the present invention and a variety of characteristics measured for the resulting anisotripic conductive adhesives will be described in greater detail with reference to the following examples.
  • An anisotropic conductive adhesive with the composition of Table 1 was prepared in a film form, and the characteristics of the anisotropic conductive adhesive were measured.
  • the anisotropic conductive adhesive with the above composition was processed into a film without additional thermal treatment and applied for circuit connections, and the characteristics of the anisotropic conductive adhesive were determined.
  • FIG. 9 is an optical microscopic photograph showing a state of the connection of circuits 280 when the anisotropic conductive adhesive 270 according to the present invention with the composition of Table 2 is applied.
  • the anisotropic conductive adhesive 270 prepared in this example to contain the radical curable resin and the radical initiator as a viscosity enhancer according to the present invention, voids are almost not generated.
  • adhesive force and connection resistance were measured in the same manner as used in Example 1. As a result, the adhesive force between the circuits was 910 g/cm, and the connection resistance was 0.7 ⁇ .
  • UV light of an appropriate wavelength in the range of 200-400 nm was radiated and then the anisotrpic conductive adhesive was processed into a film.
  • the appropriate wavelength of UV for curing was determined in consideration of the absorptive wavelength range of the UV initiator.
  • FIG. 12 is a flowchart illustrating a preferred embodiment of a bonding method using an anisotropic conductive adhesive according to the present invention.
  • a substrate with a first circuit having a first electrode, a chip having a second circuit having a second electrode, which are to be bound together, and the anisotropic conductive adhesive are prepared.
  • the anisotropic conductive adhesive any anisotropic conductive adhesive having a different composition described above according to the present invention is prepared (Step 510).
  • the anisotropic conductive adhesive is applied to the prepared substrate
  • a plurality of FPCs are bound on one glass substrate.
  • a step of aligning a new FPC on the pre-pressed substrate and pre-pressing the new FPC may be further included. The same conditions as in
  • Step 530 of FIG. 12 can be applied. However, the pre-pressing duration can be reduced if necessary.

Abstract

An anisotropic conductive adhesive containing a viscosity enhancer for adjusting the fluidity of an adhesive composition, a bonding method using the anisotropic conductive adhesive, and an integrated circuit package using the method are provided. The anisotropic conductive adhesive contains: an adhesive composition including an epoxy-based base resin, a hardener, and conductive particles; and a viscosity enhancer for adjusting the fluidity of the adhesive composition. The adhesive enhancer includes an inorganic material, a radical curable resin and a radical initiator, or a UV-curable resin and a UV initiator.

Description

ANISOTROPIC CONDUCTIVE ADHESIVES HAVING ENHANCED VISCOSITY
AND BONDING METHODS AND INTEGRATED CIRCUIT PACKAGES USING THE SAME
Technical Field
The present invention relates to an anisotropic conductive adhesive, a bonding method using the adhesive, and an integrated circuit package using the adhesive, and more particularly, to an anisotropic conductive adhesive available in the manufacture of a module for a flat panel display, such as a liquid crystal display panel (LCD), plasma display panel (PDP), electroluminescent display (ELD), etc., and available in bonding micro circuits to package a semiconductor, a bonding method using the anisotropic conductive adhesive, and an integrated circuit package obtained using the bonding method. More particularly, the present invention directs to methods of flip-chip bonding and chip-scale packaging of a semiconductor.
Background Art
As one prior art related to an anisotropic conductive adhesive, Japanese Patent Laid-open No. 8-20629 discloses an epoxy resin composition prepared by mixing a resin mixture, which includes an epoxy resin containing a non-cross-linked, thermoplastic elastomer component, an epoxy resin containing a cross-linked rubber component, and a solid epoxy resin having a softening point of 50°C or greater, with a urea-based hardener for expoxy resin and a latent catalyst which is stable at 40°C and is activated at 80°C or less. U.S. Patent No. 6,020,059 discloses an anisotropic conductive adhesive containing a film-forming resin and conductive particles and having a melting viscosity greater than 100 poises at 150°C. U.S. Patent No. 5,543,486 discloses an epoxy resin composition containing an epoxy resin having more than two epoxy groups in one molecule, a solid-dispersing, amine adduct-type latent hardener, and a metal alkoxide as the essential components. Most conventional anisotropic conductive adhesives suggested so far use a thermocurable epoxy resin or a modified epoxy resin alone or a mixture of a variety of types of thermoplastic resins as a polymeric resin. As conductive particles for the conventional anisotropic conductive adhesives, nickel or a gold and nickel-coated composite has been mostly used. In addition, a variety of additives, including a hardener for the thermocurable resin, an adhesion imparting agent, an anti-oxidant, a coupling agent, etc. has been used.
FIGS. 1A and 1 B are sectional views illustrating a process of bonding circuits using an anisotropic conductive adhesive in the manufacture of a module for a general flat panel display or in the packaging of a semiconductor. In particular, FIG. 1A is a cross-sectional view after the anisotropic conductive additive is applied to a substrate 60 with a lower circuit 50 on its top surface and before an IC circuit 10 is bound to the substrate 60. FIG. 1 B is a cross-sectional view after an upper circuit 20 on the IC chip 10 is connected to the lower circuit 50 on the substrate 60 by heating and pressing.
Conductive particles 30 contained in the anisotropic conductive adhesive are immobilized between the upper circuit 20 and the lower circuit 50 by heating and pressing, as shown in FIG. 1 B. The upper circuit 20 and the lower circuit 50 are electrically connected by the conductive particles 30 and are insulated from and bound to each other by an adhesive resin 40 constituting the anisotropic conductive adhesive.
The bonding of the upper circuit 20 and the lower circuit 50 using the anisotropic conducrive adhesive is a high-temperature process performed at 150-250°C. Therefore, a change in the fluidity of the adhesive resin 40 from a time point of heating the adhesive resin 40 to a time point at which the adhesive resin 40 is completely cured considerably affects the connection reliability of the upper circuit 20 and the lower circuit 50.
FIG. 2 is a graph of a viscosity variation pattern of the adhesive resin over heating time when bonding circuits at a high temperature using a conventional anisotropic conductive adhesive. In FIG. 2, in the interval of state A appearing immediately after heating, viscosity increases. As the temperature of the adhesive resin contained in the anisotropic conductive adhesive rises in the initial stage of bonding, a curing reaction is initiated, and viscosity gradually increases with increasing heating time. In the interval of state B, the curing reaction of the adhesive resin constituting the anisotropic conductive adhesive become active, and viscosity increases with respect to heating time at a faster rate than in the interval of state A. In the interval of state C, the curing reaction of the adhesive resin constituting the anisotropic conductive adhesive is accelerated, and viscosity tends to suddenly increase with respect to heating time.
FIG. 3 is an optical microscopic photograph showing a state of circuits 80 bound together using a conventional anisotropic conductive adhesive 70. As shown in FIG. 3, as a result of the bonding of the circuits 80 using the conventional anisotropic conductive adhesive 70, state A as shown in FIG. 2, which corresponds to the initial stage of bonding where the adhesive resin contained in the anisotropic conductive adhesive has a great fluidity, is sustained for a long time, so that the adhesive resin of the anisotropic conductive adhesive 70 is not retained between the circuits 80 to be connected and flows down to form voids 90 resulting from bubbles present in a region between the circuits 80 unfilled with the adhesive resin. Due to the presence of the voids 90 between the connected circuits 80, insulating resistance, connection resistance, and adhesive force between the circuits 80 are lowered, thereby degrading reliability of the device.
Disclosure of the Invention
To solve the above problems, it is a first object of the present invention to provide an anisotropic conductive adhesive with the composition capable of adjusting the fluidity of an adhesive composition in the initial stage of bonding of micro circuits to prevent formation of voids between the micro circuits to be connected.
It is a second object of the present invention to provide an integrated circuit package fabricated using the anisotropic conductive adhesive, in which formation of voids is suppressed to provide satisfactory conductivity and adhesion between micro circuits.
It is a third object of the present invention to provide a method for bonding micro circuits using the anisotropic conductive adhesive in the manufacture of a module for a flat panel display or in the packaging of a semiconductor, in which formation of voids is suppressed to provide satisfactory conductivity and adhesion between the connected micro circuits.
To achieve the first object of the present invention, there is an anisotropic conductive adhesive comprising: an adhesive composition including an epoxy-based base resin, a hardener, and conductive particles; and a viscosity enhancer of 5-95% by weight based on the total amount of the anisotropic conductive adhesive for adjusting the fluidity of the adhesive composition.
Preferably, the anisotropic conductive adhesive comprises an inorganic material. Here, the inorganic material may be selected from the group consisting of alumina, silicon carbide, silica, copper oxide, titanium dioxide, and a mixture of at least two of these materials. Preferably, the inorganic material is in a granular form having an average particle size of 0.1-5 microns and is contained in an amount of 5-60% by weight based on the total amount of the anisotropic conductive adhesive.
In the anisotropic conductive adhesive, preferably, the viscosity enhancer comprises a radical curable resin and a radical initiator. In this case, the radical curable resin may comprise an acrylic monomer or methacrylic monomer having a Cι-C20 main chain, an acrylic oligomer or methacrylic oligomer having a C2ι-Cιoo main chain, a thermocurable resin including a reactive acrylic or methacrylic unit, a thermoplastic resin including a reactive acrylic or methacrylic unit, or a mixture of these materials, and the radical initiator comprises a peroxide initiator, an azo initiator, or a mixture of these materials. Preferably, the radical initiator comprises cumil peroxyoctoate, acetyl peroxide, t-butyl peroxybenzoate, dicumil peroxide, azobisisobutyronitril, or a mixture of these materials.
In the anisotropic conductive adhesive, alternatively, the viscosity enhancer may comprise a UV-curable resin and a UV initiator. In this case, the UV-curable resin may comprise a multi-functional monomer selected from the group consisting of dipentaerythritol hexaacrylate, methyleneglycol bisacrylate, trimethylolpropane triacrylate, ethyleneglycol diacrylate, and pentaerythritol triacrylate, a multi-functional oligomer selected from the group consisting of epoxy acrylate, urethane acrylate, and polyester acrylate, a reactive acrylate polymer, or a mixture of these materials.
Preferably, the UV initiator is formed of a material responsive to light of a UV wavelength of 200-400 nm. For example, the UV initiator may comprise 2,2-dimethoxy-2-phenylacetophenone, 1 -hydroxy- cyclohexyl-penylketone, para-phenylbenzophenone, benzyldimethylketal, or a mixture of these materials. The anisotropic conductive adhesive according to the present invention may further comprise a conductive impurity ion of 1-100 ppm. In this case, the conductive impurity ion may be selected from the group consisting of Na+, K\ and cr.
In the anisotropic conductive adhesive according to the present invention, the base resin may be selected from the group consisting of bisphenol-A type epoxy resin, bisphenol-F type epoxy resin, phenol nobolak type epoxy resin, cresol nobolak type epoxy resin, dimeric modified epoxy resin, rubber modified epoxy resin, urethane modified epoxy resin, bromated epoxy resin, melamine resin, urethane resin, polyimide resin, polyamide resin, polyethylene resin, polypropylene resin, styrene resin, styrene-butadiene resin, phenol resin, formaldehyde resin, silicon resin, acrylate resin, or a mixture of these resins.
Preferably, the hardener is selected from the group consisting of imidazole derivatives, amine derivatives, amide derivatives, acidic anhydrides, phenol derivatives, and a mixture of at least two of these materials. Preferably, the conductive particles comprises pure nickel particles or composite particles obtained by sequentially coating the surface of polymeric beads with nickel and gold.
Preferably, the adhesive composition further comprises an adhesion imparting agent selected from the group consisting of rosin resin, terpene resin, and cumarone-indene resin. Preferably, the adhesive composition further comprises a coupling agent for dispersing and stabilizing the conductive particles. In this case, the coupling agent may comprise a silane derivative.
To achieve the second object of the present invention, there is provided an integrated circuit package comprising: a first substrate on which a first circuit including a first electrode is implemented; a second substrate on which a second circuit including a second electrode disposed to face the first substrate is implemented; and an anisotropic conductive adhesive applied between the first and second substrates to bond the same together while the first and second electrodes are in contact to be electrically connected, wherein the anisotropic conductive adhesive comprises a resin, a hardener, conductive particles dispersed in the resin, and a viscosity enhancer for increasing the viscosity of the resin.
Preferably, the viscosity enhancer comprises an inorganic material selected from the group consisting of silica, silicon carbide, alumina, and a mixture of at least two of the materials and is contained in an amount of 5-60% by weight based on the total amount of the anisotropic conductive adhesive. Preferably, the first substrate is a component of a liquid crystal display (LCD), for example, a glass substrate or a flexible printed circuit board (FPC).
To achieve the third object of the present invention, there is provided a method for bonding a first substrate with a first circuit having a first electrode, and a second substrate with a second circuit having a second electrode, the method comprising applying an anisotropic conductive adhesive to the first substrate. Next, the applied anisotropic conductive adhesive is pre-pressed against the first substrate at a temperature of 60-100°C. The first and second substrates are aligned such that the first and second circuits face each other. The first and second substrates are bound together by pressing the first and second substrates against each other such that the first and second electrodes are electrically connected.
In pre-pressing the applied anisotropic conductive adhesive against the first substrate a pressure of 0.1-1 MPa may be applied, and in bonding the first and second substrates a pressure of 1-5 MPa may be applied at a temperature of 130-250°C to bond the first and second substrates. Preferably, the bonding method according to the present invention further comprises: aligning a third substrate on the first substrate against which the anisotropic conductive adhesive has been pre-pressed; and pre-pressing the third substrate against the first substrate by applying a pressure of 0.1-1 MP at a temperature 60-100°C.
The anisotropic conductive adhesive according to the present invention includes a viscosity enhancer to adjust the fluidity of the adhesive composition. Therefore, the anisotropic conductive adhesive can be retained between micro circuits to be connected even under high-temperature bonding conditions, thereby preventing generation of voids between the micro circuits. In addition, strong adhesive force and satisfactory bonding reliability, insulating resistance, and connection resistance are ensured.
Brief Description of the Drawings FIG. 1A is a cross-sectional view after an anisotropic conductive additive is applied to a substrate before an IC circuit is bound to the substrate in the manufacture of a module of a conventional flat panel display or in the packaging of a semiconductor;
FIG. 1 B is a cross-sectional view after an upper circuit on the IC chip is connected to a lower circuit on the substrate by heating and pressing;
FIG. 2 is a graph of a viscosity variation pattern of an adhesive resin over heating time when bonding circuits at a high temperature using a conventional anisotropic conductive adhesive;
FIG. 3 is an optical microscopic photograph showing a state of the circuits bound together using a conventional anisotropic conductive adhesive;
FIG. 4 is a flowchart illustrating a first embodiment of a method for preparing an anisotropic conductive adhesive according to the present invention;
FIG. 5 is a flowchart illustrating a second embodiment of the method for preparing the anisotropic conductive adhesive according to the present invention; FIG. 6 is a flowchart illustrating a third embodiment of the method for preparing the anisotropic conductive adhesive according to the present invention; FIG. 7 is a graph showing a viscosity variation pattern of an adhesive resin with respect to heating time when micro circuits are bound at a high temperature using an anisotropic conductive adhesive according to the present invention;
FIG. 8 is an optical microscopic photograph showing the state of the connection of circuits when an example of the anisotropic conductive adhesive according to the present invention is applied;
FIG. 9 is an optical microscopic photograph showing a state of the connection of circuits when another example of the anisotropic conductive adhesive according to the present invention is applied; FIG. 10 is an optical microscopic photograph showing a state of the connection of circuits when still another example of the anisotropic conductive adhesive according to the present invention is applied;
FIG. 1 1 is a graph comparatively showing the change in connection resistance over time when a conventional anisotropic conductive adhesive and a variety of anisotropic conductive adhesives prepared according to the present invention with different compositions by different methods are applied to bond circuits; and
FIG. 12 is a flowchart illustrating a preferred embodiment of a bonding method using an anisotropic conductive adhesive according to the present invention.
Best mode for carrying out the Invention
The technical spirit of the present invention can be summarized with the following three features. First, an inorganic viscosity enhancer is incorporated as a component of an anisotropic conductive adhesive to adjust the fluidity of an adhesive resin.
Second, a viscosity enhancer composed of a radical curable resin and radical initiator is incorporated as a component of the anisotropic conductive adhesive to the fluidity of an adhesive resin. A radical initiator which is highly reactive at a comparatively low temperature of about 100-150°C is used to increase the rate of curing reaction. Third, a viscosity enhancer composed of a UV-curable resin and UV initiator is incorporated as a component of the anisotropic conductive adhesive to the fluidity of an adhesive resin. In this case, UV of an appropriate wavelength for curing is radiated in the preparation of the anisotropic conductive adhesive to partially or entirely cure the UV curable resin. Alternatively, heating may be performed while the UV radiation to induce the curing reaction.
Due to the above-listed three features, the fluidity of the adhesive composition can be reduced in an initial attachment process, which is performed at a comparatively high temperature, thereby preventing formation of voids between connected circuits in a resultant final circuit construct to ensure the reliability of the connected circuits.
In particular, an anisotropic conductive adhesive according to the present invention includes the following basic components: (a) an adhesive composition comprising an epoxy-based base resin, a hardener, and conductive particles, and (b) a viscosity enhancer for adjusting the fluidity of the adhesive composition.
Suitable base resins for the anisotropic conductive adhesive according to the present invention include, for example, bisphenol-A type epoxy resin, bisphenol-F type epoxy resin, phenol nobolak type epoxy resin, cresol nobolak type epoxy resin, dimeric modified epoxy resin, rubber modified epoxy resin, urethane modified epoxy resin, bromated epoxy resin, melamine resin, urethane resin, polyimide resin, polyamide resin, polyethylene resin, polypropylene resins, styrene resin, styrene-butadiene resin, phenol resin, formaldehyde resin, silicon resin, acrylate resin, or a mixture of these resins.
Suitable hardeners for the anisotropic conductive adhesive according to the present invention include, for example, imidazole derivatives, such as 2-methyl imidazole, 2-ethyl imidazole, and 1 -cyanoethyl-2-methyl imidazole, amide derivatives, such as dicyandiamide, amine derivatives, acidic anhydrides, or phenol derivatives. To improve the adhesive characteristics of the anisotropic conductive adhesive, one compound selected from the above-listed hardeners may be used alone, or at least two compounds among the hardeners may be used in a mixed form. To improve the storage stability at room temperature, the hardener may be encapsulated into a microcapsule with a thermocurable resin or thermoplastic resin.
Suitable conductive particles for the anisotropic conductive adhesive according to the present invention include pure nickel particles or composite particles obtained by sequentially coating the surface of polymeric beads with nickel and gold to a thickness of about 500A each.
The composite particles have a gravity of 1-3. This level of gravity is similar to that of the adhesive composition of the anisotropic conductive adhesive according to the present invention, and thus dispersion stability is better than using pure nickel particles. In addition, due to their particle sizes that are almost uniform, advantageously, there is no deviation in electrical conductivity between individual circuits connected with each other.
As the viscosity enhancer for the anisotropic conductive adhesive according to the present invention, which is used to adjust the fluidity of the adhesive composition, an inorganic material, a radical curable resin and radical initiator, or a UV-curable resin and UV initiator, can be used. Preferably, the viscosity enhancer is contained in an amount of 5-95% by weight based on the total amount of the anisotrotropic conductive adhesive.
An inorganic material having thixotropic behavior may be used as the viscosity enhancer. Suitable inorganic materials for the anisotropic conductive adhesive according to the present invention include, for example, aluminum oxide (AI2O3), silicon carbide (SiC), silica (SiO2), copper oxide (CuO), or titanium dioxide (TiO2). One material selected from the listed materials may be used alone. Alternatively, at least two of the materials may be used in a mixed form. Preferably, the inorganic materials are in a granular form of an average particle size of 0.1-5 microns. Preferably, as the inorganic material, silica is used in an amount of 5-60% by weight based on the total amount of the anisotropic conductive adhesive. In this case, an increase in the viscosity of the anisotropic conductive adhesive and characteristics improvements in terms of thermal expansion coefficient and glass transition temperature are expected.
When the radical curable resin and radical initiator are used as the viscosity enhancer, suitable radical curable resins include, for example, an acrylic monomer or methacrylic monomer having a d-C20 main chain, an acrylic oligomer or methacrylic oligomer having a C2ι-Cιo0 main chain, a thermocurable resin including a reactive acrylic or methacrylic unit, a thermoplastic resin including a reactive acrylic or methacrylic unit, or a mixture of these materials. Any organic compound capable of producing radicals may be used as the radical initiator. Suitable radical initiators include a peroxide initiator, an azo initiator, or a mixture of these materials, and more particularly, cumil peroxyoctoate, acetyl peroxide, t-butyl peroxybenzoate, dicumil peroxide, azobisisobutyronitril, or a mixture of these materials.
When the UV curable resin and UV initiator are used as the viscosity enhancer, suitable UV curable resins include a multi-functional monomer selected from the group consisting of dipentaerythritol hexaacrylate, methyleneglycol bisacrylate, trimethylolpropane triacrylate, ethyleneglycol diacrylate, and pentaerythritol triacrylate, a multi-functional oligomer selected from the group consisting of epoxy acrylate, urethane acrylate, and polyester acrylate, a reactive acrylate polymer, or a mixture of these materials. Any UV initiator capable of inducing a photoreaction with a UV wavelength, preferably a UV wavelength of 200-400nm, may be used. Suitable UV initiators include, for example, 2,2-dimethoxy-2-phenylacetophenone, 1 -hydroxy-cyclohexyl-penylketone, para-phenylbenzophenone, benzyldimethylketal, or a mixture of these materials. When a mixture of at least two photoinitiators having a reactivity with respect to different wavelengths is used, deviations in characteristics of the anisotropic conductive adhesive depending on different preparation conditions can be reduced.. To improve the characteristics of the UV curable resin, a benzophenone photosensitizer, or an anti-polymerization agent such as hydroquinone monoethylether may be additionally used.
The anisotropic conductive adhesive according to the present invention may further include conductive impurity ions if necessary. The addition of the conductive impurity ions can prevent the connected circuits from corrosion. As the conductive impurity ions, cations or anions, for example, Na+, K*, and Cl", may be used. The conductive impurity ions are contained in an amount of, preferably 1-100 ppm, and more preferably less than 10 ppm. The components and composition of the anisotropic conductive adhesive are adjusted in consideration of the amount of the conductive impurity ions. If necessary, the anisotropic conductive adhesive according to the present invention may further include an adhesion imparting agent, such as rosin resin, terpene resin, or cumarone-indene resin. Suitable resins for the adhesion imparting agent have a glass transition temperature lower than or equal to room temperature. The adhesive composition for the anisotropic conductive adhesive according to the present invention may further include a coupling agent for dispersing and stabilizing the conductive particles. Suitable coupling agent includes a variety of silane derivatives, for example, 3-glycidyloxypropyltrimethoxysilane, or 3-glycidyloxypropylmethyl- diethoxysilane. To improve the physical properties of the anisotropic conductive adhesive according to the present invention, a variety of additives other than the components described above may be used. For example, an acrylic or silicon-based dispersing agent, a silicon-based anti-foaming agent, an anti-oxidant, etc. can be used. When the anisotropic conductive adhesive according to the present invention is processed as a film, a smoothening agent may be used for easy shaping of the film.
The anisotropic conductive adhesive according to the present invention may be prepared as a film or paste.
FIG. 4 is a flowchart illustrating a first embodiment of a method for preparing the anisotropic conductive adhesive according to the present invention.
Referring to FIG. 4, the first embodiment of the method for preparation of the anisotropic conductive adhesive involves preparing an adhesive composition containing a base resin (Step S10). As described above, the adhesive composition includes the base resin, which contains epoxy resin as a base material, a hardener, and conductive particles. To prepare the adhesive composition in step S10, the base resin, which contains a thermocurable resin alone or a thermoplastic resin-added thermocurable resin, is prepared (Step S12). Next, the conductive particles are mixed with the base resin (Step S14), and the hardener is added to the mixture (Step S16). Next, to the adhesive composition prepared in step S10, a viscosity enhancer is added to adjust the fluidity of the adhesive composition (Step S20). As described above, the viscosity enhancer may comprise an inorganic material having thixotropic behavior. Next, additives such as a coupling agent may be mixed with the mixture if necessary (Step S30). In the preparation of the anisotropic conductive adhesive according to the first embodiment of the present invention, the sequence of the steps can be changed without going beyond the technical scope of the present invention.
FIG. 5 is a flowchart illustrating a second embodiment of the method for preparing the anisotropic conductive adhesive according to the present invention.
The method for preparing the anisotropic conductive adhesive according to the second embodiment of the present invention involves preparing an adhesive composition containing a base resin in the same manner as described with reference to FIG. 4 (Step S110). The adhesive composition is prepared through preparation of a base resin (Step S112), mixing of conductive particles (S114), and addition of a hardener (Step S116). Next, a viscosity enhancer for adjusting the fluidity of the adhesive composition is added to the adhesive composition prepared in Step S110 (Step S120). The viscosity enhancer may be composed of a radical curable resin and radical initiator. Detailed descriptions of these materials for the viscosity enhancer will be omitted here since they have been described above. Additives such as a coupling agent may be further added if necessary (Step S130). The fluidity of the adhesive composition is adjusted by heating the mixture (Step S140). In Step S140 of the fluidity adjustment, the mixture is heated to a temperature of 100-150°C. The initial viscosity of the anisotropic conductive adhesive is increased by the heating. Here, the heating is performed until at least a portion of, preferably 1-70%, the radical curable resin is cured. In the preparation of the anisotropic conductive adhesive according to the second embodiment of the present invention, the sequence of the steps can be changed without going beyond the technical scope of the present invention. FIG. 6 is a flowchart illustrating a third embodiment of the method for preparing the anisotropic conductive adhesive according to the present invention.
The method for preparing the anisotropic conductive adhesive according to the third embodiment of the present invention involves preparing an adhesive composition containing a base resin in the same manner as described with reference to FIG. 4 (Step S210). The adhesive composition is prepared through preparation of a base resin (Step S212), mixing of conductive particles (S214), and addition of a hardener (Step S216). Next, a viscosity enhancer for adjusting the fluidity of the adhesive composition is added to the adhesive composition prepared in Step S210 (Step S220). The viscosity enhancer may be composed of a UV-curable resin and UV initiator. Detailed descriptions of these materials for the viscosity enhancer will be omitted here since they have been described above. Additives such as a coupling agent may be further added if necessary (Step S230). The fluidity of the adhesive composition is adjusted by UV irradiation of the mixture (Step S240). In Step S240 of the fluidity adjustment, detailed conditions for the UV irradiation are the same as described above. The initial viscosity of the anisotropic conductive adhesive is increased by the UV irradiation. Here, the UV irradiation is continued until at least a portion of, preferably 1-70%, the UV curable resin is cured. In the preparation of the anisotropic conductive adhesive according to the third embodiment of the present invention, the sequence of the steps can be changed without going beyond the technical scope of the present invention.
FIG. 7 is a graph showing a viscosity variation pattern of the adhesive resin with respect to heating time when micro circuits are bound at a high temperature using an anisotropic conductive adhesive according to the present invention. As shown in FIG. 7, since the anisotropic conductive adhesive according to the present invention includes the viscosity enhancer to increase the viscosity and lower the fluidity of the adhesive composition, the anisotropic conductive adhesive used to bond micro circuits does not undergo the interval of State A, as shown in FIG. 2. Therefore, in the bonding of the micro circuits using the anisotropic conductive adhesive according to the present invention, time consumption is reduced by the interval of State A, and a pattern of viscosity changing as in the interval of State B appears in the initial stage of bonding. In other words, when micro circuits are connected using an anisotropic conductive adhesive according to the present invention, the fluidity of the adhesive resin is reduced in the initial, high-temperature stage of bonding to such a degree that the adhesive resin can be retained between the micro circuits to be connected for a period of sufficient time for curing. Therefore, there is no generation of voids between the micro circuits due to lack of sufficient adhesive resin.
To bond circuits using the anisotropic conductive adhesive according to the present invention, a bonding temperature is set to be in the range of 100-300°C and a pressure of about 0.5-5 MPa is applied for 5-60 seconds. This method results in reliable bonding between the circuits. Preferably, a pressure of 2-5 MPa is applied for 10-30 seconds at a bonding temperature of 150-250°C. When the circuits are bound under these conditions, most excellent adhesion and connection resistance and insulating resistance characteristics are ensured.
The preparation of anisotripic conductive adhesives according to the present invention and a variety of characteristics measured for the resulting anisotripic conductive adhesives will be described in greater detail with reference to the following examples.
Example 1
An anisotropic conductive adhesive with the composition of Table 1 was prepared in a film form, and the characteristics of the anisotropic conductive adhesive were measured.
Table 1
Figure imgf000017_0001
Figure imgf000018_0001
Circuits of a 80-micro pitch were bound by applying a pressure of 3 MPa at a temperature of 180°C, and a state of the circuit connection was observed using an optical microscope. FIG. 8 is an optical microscopic photograph showing the state of the connection of circuits 180 when the anisotropic conductive adhesive 170 according to the present invention with the composition of Table 1 is applied. As is apparent from the photograph of FIG. 8, for the anisotropic conductive adhesive 170 containing the inorganic viscosity enhancer according to the present invention, the number of voids 190 unfilled with the adhesive resin is markedly reduced, compared to the case of using the conventional anisotropic conductive adhesive 70 shown in FIG. 3.
For the circuits bound together by the anisotropic conductive adhesive having the composition of Table 1 , connection resistance was measured at 25°C using a 4-probe method, and 90° delamination force was measured at a rate of 50 mm/min and 25°C. As a result, the adhesive force between the circuits was 850 g/cm, and the connection resistance was 0.8 Ω . For a reliability test, a variation in connection resistance of the connected circuits were observed in a thermohydrostat at 85°C and 85%-humidity for 2000 hours. The result is shown in FIG. 11. Comparing to the conventional anisotropic conductive adhesive containing no viscosity enhancer, the anisotropic conductive adhesive prepared in Example 1 shows excellent characteristics. Example 2
An anisotropic conductive adhesive with the composition of Table 2 was prepared in a film form, and the characteristics of the anisotropic conductive adhesive were measured.
Table 2
Figure imgf000019_0001
The anisotropic conductive adhesive with the above composition was processed into a film without additional thermal treatment and applied for circuit connections, and the characteristics of the anisotropic conductive adhesive were determined.
FIG. 9 is an optical microscopic photograph showing a state of the connection of circuits 280 when the anisotropic conductive adhesive 270 according to the present invention with the composition of Table 2 is applied. As is apparent from the photograph of FIG. 9, with the anisotropic conductive adhesive 270 prepared in this example to contain the radical curable resin and the radical initiator as a viscosity enhancer according to the present invention, voids are almost not generated. For the circuits bound together by the anisotropic conductive adhesive having the composition of Table 2, adhesive force and connection resistance were measured in the same manner as used in Example 1. As a result, the adhesive force between the circuits was 910 g/cm, and the connection resistance was 0.7 Ω . A variation in the connection resistance over time was observed in a thermohydrostat under the same conditions applied as in Example 1. The result is shown in FIG. 11. Comparing to the conventional anisotropic conductive adhesive containing no viscosity enhancer, the anisotropic conductive adhesive prepared in Example 2 shows excellent characteristics.
Example 3
An anisotropic conductive adhesive was prepared with the composition of
Table 2. In the preparation of the anisotropic conductive adhesive, an additional thermal process was performed at 120°C in consideration of the initiation temperature of the radical initiator, and the anisotropic conductive adhesive was processed into a film.
Adhesive force and connection resistance were measured in the same manner as used in Example 1. As a result, the adhesive force between the circuits was 1023 g/cm, and the connection resistance was 0.8 Ω . A variation in the connection resistance over time was observed in a thermohydrostat under the same conditions applied as in Example 1. The result is shown in FIG. 11. Comparing to the conventional anisotropic conductive adhesive containing no viscosity enhancer, the anisotropic conductive adhesive prepared in Example 3 shows excellent characteristics.
Example 4
An anisotropic conductive adhesive with the composition of Table 3 was prepared in a film form, and the characteristics of the anisotropic conductive adhesive were measured. Table 3
Figure imgf000021_0001
In the preparation of the anisotropic conductive adhesive with the composition of Table 3, UV light of an appropriate wavelength in the range of 200-400 nm was radiated and then the anisotrpic conductive adhesive was processed into a film. Here, the appropriate wavelength of UV for curing was determined in consideration of the absorptive wavelength range of the UV initiator.
FIG. 10 is an optical microscopic photograph showing a state of the connection of circuits 380 when the anisotropic conductive adhesive 370 according to the present invention with the composition of Table 3 is applied. As is apparent from the photograph of FIG. 10, with the anisotropic conductive adhesive 370 prepared in this example to contain the UV-curable resin and the radical initiator as a viscosity enhancer according to the present invention, no void is generated.
For the circuits bound together by the anisotropic conductive adhesive having the composition of Table 3, adhesive force and connection resistance were measured in the same manner as used in Example 1. As a result, the adhesive force between the circuits was 955 g/cm, and the connection resistance was 0.7 Ω . A variation in the connection resistance over time was observed in a thermohydrostat under the same conditions applied as in Example 1. The result is shown in FIG. 11. Comparing to the conventional anisotropic conductive adhesive containing no viscosity enhancer, the anisotropic conductive adhesive prepared in Example 4 shows excellent characteristics.
Example 5
An anisotropic conductive adhesive with the composition of Table 4 was prepared, and the characteristics of the anisotropic conductive adhesive were measured.
Table 4
Figure imgf000022_0001
After the preparation of the anisotropic conductive adhesive with the composition of Table 4, the anisotropic conductive adhesive was processed in a paste form. For the circuits bound together by the resulting anisotropic conductive adhesive, adhesive force and connection resistance were measured in the same manner as used in Example 1. As a result, the adhesive force between the circuits was 972 g/cm, and the connection resistance was 0.9 Ω . A variation in the connection resistance over time was observed in a thermohydrostat under the same conditions applied as in Example 1. The result is shown in FIG. 11. Comparing to the conventional anisotropic conductive adhesive containing no viscosity enhancer, the anisotropic conductive adhesive prepared in Example 5 shows excellent characteristics.
FIG. 12 is a flowchart illustrating a preferred embodiment of a bonding method using an anisotropic conductive adhesive according to the present invention. Referring to FIG. 12, a substrate with a first circuit having a first electrode, a chip having a second circuit having a second electrode, which are to be bound together, and the anisotropic conductive adhesive are prepared. As the anisotropic conductive adhesive, any anisotropic conductive adhesive having a different composition described above according to the present invention is prepared (Step 510). The anisotropic conductive adhesive is applied to the prepared substrate
(Step 520). Here, the anisotropic conductive adhesive used may be in a film or paste form. When a film type anisotropic conductive adhesive is used, the anisotropic conductive adhesive with a non-adhesive release film, for example, made of polyethylene terephthalate, attached to its top surface is applied on the substrate. When a paste type anisotropic conductive adhesive is used, the anisotropic conductive adhesive is directly applied to a desired position on the substrate.
Next, the applied anisotropic conductive adhesive is pre-pressed against the substrate (Step 530). This pre-pressing step is more effective when a film type anisotropic conductive adhesive is applied, and can be omitted when a paste type anisotropic conductive adhesive is applied. In particular, the anisotropic conductive adhesive applied to the substrate with the release film on its top surface is pressed using a heat head at a temperature of about 60-100°C and a pressure of about 0.1-1 MPa for about 0.5-5 seconds. Next, the release film attached to the surface of the anisotropic conductive adhesive is removed.
Next, the substrate and the chip are aligned such that the first circuit and the second circuit are face each other (Step S540). Next, the substrate and the chip are bound together by applying a pressure such that the first and second electrodes are electrically connected (Step 550). In this main bonding process, the substrate and the chip are pressed using the heat head at a temperature of about 130-250°C and a pressure of about 1-5 MPa for about 10-120 seconds. Here, the temperature and pressure for the main bonding can be appropriated adjusted in consideration of mutual dependency.
In the bonding method according to the present invention, the substrate may be implemented with a printed circuit board (PCB) or a component of a liquid crystal display panel, such as a glass substrate or flexible printed circuit board
(FPC).
In the manufacture of a TFT-LCD, a plurality of FPCs are bound on one glass substrate. In this case, after step 530 of pre-pressing the applied anisotropic conductive adhesive against substrate, as illustrated in the flowchart of FIG. 12, a step of aligning a new FPC on the pre-pressed substrate and pre-pressing the new FPC may be further included. The same conditions as in
Step 530 of FIG. 12 can be applied. However, the pre-pressing duration can be reduced if necessary.
While the anisotropic conductive adhesive and the method for preparing the same according to the present invention have been described with reference to preferred embodiments thereof, various changes in form and details may be made therein without departing from the sprit and scope of the present invention.
The above-described preferred embodiments and drawings are for illustrative purposes and are not intended to limit the scope of the invention. It will be understood by those skilled in the art that the present invention described above can be changed in a variety of ways by substitution and modification without going beyond the sprit and scope of the invention as defined by the appended claims or within the range of equality thereto.
Industrial Applicability
The anisotropic conductive adhesive according to the present invention includes a viscosity enhancer to adjust the fluidity of the adhesive composition.
Therefore, when bonding micro circuits using the anisotropic conductive adhesive according to the present invention, the fluidity of the anisotropic conductive adhesive is reduced in the initial stage of a heating and pressing process. As a result, the anisotropic conductive adhesive can be retained between the micro circuits even under high-temperature bonding conditions, thereby preventing generation of voids between the micro circuits. In addition, strong adhesive force and satisfactory bonding reliability, insulating resistance, and connection resistance are ensured.

Claims

What is claimed is:
1. An anisotropic conductive adhesive comprising: an adhesive composition including an epoxy-based base resin, a hardener, and conductive particles; and a viscosity enhancer of 5-95% by weight based on the total amount of the anisotropic conductive adhesive for adjusting the fluidity of the adhesive composition.
2. The anisotropic conductive adhesive of claim 1 , wherein the viscosity enhancer comprises an inorganic material selected from the group consisting of alumina, silicon carbide, silica, copper oxide, titanium dioxide, and a mixture of at least two of these materials.
3. The anisotropic conductive adhesive of claim 2, wherein the inorganic material is in a granular form having an average particle size of 0.1-5 microns and is contained in an amount of 5-60% by weight based on the total amount of the anisotropic conductive adhesive.
4. The anisotropic conductive adhesive of claim 1 , wherein the viscosity enhancer comprises a radical curable resin and a radical initiator.
5. The anisotropic conductive adhesive of claim 4, wherein the radical curable resin comprises an acrylic monomer or methacrylic monomer having a d-C20 main chain, an acrylic oligomer or methacrylic oligomer having a C21-C100 main chain, a thermocurable resin including a reactive acrylic or methacrylic unit, a thermoplastic resin including a reactive acrylic or methacrylic unit, or a mixture of these materials, and the radical initiator comprises a peroxide initiator, an azo initiator, or a mixture of these materials.
6. The anisotropic conductive adhesive of claim 4, wherein the radical initiator comprises cumil peroxyoctoate, acetyl peroxide, t-butyl peroxybenzoate, dicumil peroxide, azobisisobutyronitril, or a mixture of these materials.
7. The anisotropic conductive adhesive of claim 1 , wherein the viscosity enhancer comprises a UV-curable resin and a UV initiator.
8. The anisotropic conductive adhesive of claim 7, wherein the UV-curable resin comprises a multi-functional monomer selected from the group consisting of dipentaerythritol hexaacrylate, methyleneglycol bisacrylate, trimethylolpropane triacrylate, ethyleneglycol diacrylate, and pentaerythritol triacrylate, a multi-functional oligomer selected from the group consisting of epoxy acrylate, urethane acrylate, and polyester acrylate, a reactive acrylate polymer, or a mixture of these materials.
9. The anisotropic conductive adhesive of claim 7, wherein the UV initiator comprises 2,2-dimethoxy-2-phenylacetophenone,
1 -hydroxy-cyclohexyl-penylketone, para-phenylbenzophenone, benzyldimethylketal, or a mixture of these materials.
10. The anisotropic conductive adhesive of claim 1 , further comprising a conductive impurity ion of 1-100 ppm.
11. The anisotropic conductive adhesive of claim 10, wherein the conductive impurity ion is selected from the group consisting of Na+, K*, and CL.
12. The anisotropic conductive adhesive of claim 1 , wherein the base resin is selected from the group consisting of bisphenol-A type epoxy resin, bisphenol-F type epoxy resin, phenol nobolak type epoxy resin, cresol nobolak type epoxy resin, dimeric modified epoxy resin, rubber modified epoxy resin, urethane modified epoxy resin, bromated epoxy resin, melamine resin, urethane resin, polyimide resin, polyamide resin, polyethylene resin, polypropylene resin, styrene resin, styrene-butadiene resin, phenol resin, formaldehyde resin, silicon resin, acrylate resin, or a mixture of these resins.
13. The anisotropic conductive adhesive of claim 1 , wherein the hardener is selected from the group consisting of imidazole derivatives, amine derivatives, amide derivatives, acidic anhydrides, phenol derivatives, and a mixture of at least two of these materials.
14. The anisotripic conductive adhesive of claim 1 , wherein the conductive particles comprises pure nickel particles or composite particles obtained by sequentially coating the surface of polymeric beads with nickel and gold.
15. The anisotropic conductive adhesive of claim 1 , wherein the adhesive composition further comprises an adhesion imparting agent selected from the group consisting of rosin resin, terpene resin, and cumarone-indene resin.
16. The anisotropic conductive adhesive of claim 1 , wherein the adhesive composition further comprises a coupling agent for dispersing and stabilizing the conductive particles.
17. The anisotropic conductive adhesive of claim 16, wherein the coupling agent comprises a silane derivative.
18. An integrated circuit package comprising: a first substrate on which a first circuit including a first electrode is implemented; a second substrate on which a second circuit including a second electrode disposed to face the first substrate is implemented; and an anisotropic conductive adhesive applied between the first and second substrates to bond the same together while the first and second electrodes are in contact to be electrically connected, wherein the anisotropic conductive adhesive comprises a resin, a hardener, conductive particles dispersed in the resin, and a viscosity enhancer for increasing the viscosity of the resin.
19. The integrated circuit package of claim 18, wherein the rein is an epoxy-based thermocurable resin, and the viscosity enhancer comprises an inorganic material selected from the group consisting of silica, silicon carbide, alumina, and a mixture of at least two of the materials and is contained in an amount of 5-60% by weight based on the total amount of the anisotropic conductive adhesive.
20. The integrated circuit package of claim 18, wherein the first substrate is a glass substrate or a flexible printed circuit board (FPC).
21. A method for bonding a first substrate with a first circuit having a first electrode, and a second substrate with a second circuit having a second electrode, the method comprising: applying an anisotropic conductive adhesive to the first substrate; pre-pressing the applied anisotropic conductive adhesive against the first substrate; aligning the first and second substrates such that the first and second circuits face each other; bonding the first and second substrates by pressing the first and second substrates against each other such that the first and second electrodes are electrically connected.
22. The method of claim 21 , wherein the anisotropic conductive adhesive comprises an epoxy-based thermocurable resin, a hardener, conductive particles dispersed in the resin, and a viscosity enhancer of 5-60% by weight based on the total amount of the anisotropic conductive adhesive for increasing the viscosity of the resin, the viscosity enhancer selected from the group consisting of silica, silicon carbide, alumina, and a mixture of at least two of these materials.
23. The method of claim 21 , wherein, in pre-pressing the applied anisotropic conductive adhesive against the first substrate a pressure of 0.1-1 MPa is applied, and in bonding the first and second substrates a pressure of 1-5 MPa is applied at a temperature of 130-250°C to bond the first and second substrates.
24. The method of claim 21 , wherein the first substrate is a glass substrate or a flexible printed circuit board (FPC).
25. The method of claim 21 , further comprising: aligning a third substrate on the first substrate against which the anisotropic conductive adhesive has been pre-pressed; and pre-pressing the third substrate against the first substrate by applying a pressure of 0.1-1 MP at a temperature 60-100°C.
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