Anisotropic conductive film containing microencapsulated radical accelerators

Abstract

The application relates to the field of microelectronic packaging, and specifically discloses an anisotropic conductive film containing microencapsulated radical accelerators, which is prepared by curing an adhesive, and the adhesive is prepared from raw materials containing the following components by weight: 35-50 parts of film-forming resin, 3-8 parts of toughening elastomer, 13-35 parts of acrylate prepolymer, 3-5 parts of acrylate active diluent, 1-3 parts of difunctional acrylate, 2-4 parts of phosphoric acid acrylate, 1-3 parts of silane coupling agent, 2-5 parts of organic peroxide curing agent, 0.5-3 parts of microencapsulated curing accelerator, 0.0001-0.0004 parts of hydroquinone, 3-7 parts of fumed nano-silicon dioxide, 4-6 parts of conductive microspheres, and 200-300 parts of ethyl acetate; the adhesive has the advantages of rapid curing under low-temperature conditions and good stability under normal-temperature conditions.

Description

Technical Field

[0001] The present invention relates to the field of microelectronic packaging, and more particularly to an anisotropic conductive film containing a microencapsulated free radical accelerator. Background Art

[0002] Anisotropic conductive film uses conductive ions to connect the electrodes between the IC chip and the substrate to make them conductive, while avoiding short circuits between adjacent electrodes and achieving the purpose of conductivity only in the Z-axis direction.

[0003] Anisotropic conductive film is a single-component, fast-curing film adhesive. It needs to cure within 5-10 seconds at 140-160°C, and the adhesive must be stored at room temperature for 2-4 weeks without pre-curing. Therefore, there is a conflict between the curing speed of the anisotropic conductive film and the stability of the adhesive.

[0004] The curing conditions of ordinary epoxy resin adhesives are 180-200℃ and 10-20s, which means that epoxy resin adhesives cannot meet the curing conditions specified by the anisotropic conductive film. The curing conditions of simple acrylate free radicals are 150-160℃ and 10-15s. Although it can meet the curing conditions specified by the anisotropic conductive film, the room temperature stability is not satisfactory.

[0005] Therefore, there is an urgent need to provide an anisotropic conductive film that has the advantages of rapid curing under low temperature conditions and good storage stability of the adhesive under room temperature conditions. Summary of the Invention

[0006] In order to prepare an anisotropic conductive film with the advantages of rapid curing under low temperature conditions and good storage stability of the adhesive under room temperature conditions, the present application provides an anisotropic conductive film containing a microencapsulated free radical accelerator.

[0007] The present application provides an anisotropic conductive film containing a microencapsulated free radical accelerator, which adopts the following technical solution: an anisotropic conductive film containing a microencapsulated free radical accelerator, the anisotropic conductive film is made by curing an adhesive, and the adhesive is made of the following raw materials in parts by weight: 35-50 parts of a film-forming resin, 3-8 parts of a toughening elastomer, 13-35 parts of an acrylate prepolymer, 3-5 parts of an acrylate reactive diluent, 1-3 parts of a bifunctional acrylate, 2-4 parts of a phosphate acrylate, 1-3 parts of a silane coupling agent, 2-5 parts of an organic peroxide curing agent, 0.5-3 parts of a microencapsulated curing accelerator, 0.0001-0.0004 parts of hydroquinone, 3-7 parts of fumed nanosilica, 4-6 parts of conductive microspheres, and 203-300 parts of ethyl acetate.

[0008] By adopting the above technical solution, the organic peroxide curing agent is matched with the microencapsulated curing accelerator. During the storage of the adhesive, since the curing accelerator is coated with the microcapsules, the curing accelerator will not come into contact with the organic peroxide curing agent. During the storage of the adhesive at room temperature, no pre-curing will occur, and the adhesive has good stability. After being stored for a period of time, it still has good adhesion to the substrate.

[0009] When the adhesive is hot-pressed, the microcapsule wall material on the surface of the curing accelerator is destroyed by the action of temperature and pressure. The curing accelerator flows out of the microcapsule and gradually comes into contact with the organic peroxide curing agent, thereby promoting the decomposition of the curing agent and improving the curing efficiency. This enables the adhesive to achieve low-temperature rapid curing in a short time, meeting the curing requirements of the anisotropic conductive film.

[0010] Preferably, the acrylate prepolymer is made of the following raw materials in parts by weight: 3-10 parts of epoxy acrylate and 10-25 parts of polyurethane acrylate.

[0011] By adopting the above technical solution, epoxy acrylate, polyurethane acrylate, bifunctional acrylate and phosphate acrylate are combined, which not only makes the adhesive have better adhesion, but also can improve the hardness, wear resistance and weather resistance of the anisotropic conductive film.

[0012] Preferably, the organic peroxide curing agent is selected from one or more of cumene hydroperoxide, tert-amyl hydroperoxide, di-tert-butyl peroxide, diisopropyl peroxide, tert-butyl peracetate, di-tert-amyl peroxide, tert-butyl perbenzoate, tert-amyl perbenzoate, 2,2-di(tert-butylperoxy)butane, tert-butyl permaleate, tert-butyl peroxy-3,3,5-trimethylhexanoate, 1,1-di(tert-butylperoxy)cyclohexane, 1,1-di-tert-butylperoxy-3,3,5-trimethylcyclohexane, tert-butyl peroxyisobutyrate, tert-amyl peroxy-2-ethylhexanoate, tert-butyl peroxy-2-ethylhexanoate, benzoyl peroxide, and lauroyl peroxide.

[0013] By adopting the above technical solution, the adhesive can be cured quickly during curing, thereby improving the curing efficiency, and the organic peroxide curing agent can be dispersed more evenly in the adhesive, further promoting the curing of the adhesive.

[0014] Preferably, the core material of the microencapsulated curing accelerator is selected from one or more of tertiary amines, cyclopentane salts, isooctanoates, thiols, and organometallic compounds.

[0015] By adopting the above technical solution, when tertiary amines, cyclopentane salts, isooctanoates, thiols, and organometallic compounds are released from the microcapsules and gradually come into contact with the organic peroxide curing agent, a redox initiation system is generated between the core material and the organic peroxide curing agent, so that the tertiary amines, cyclopentane salts, isooctanoates, thiols, and organometallic compounds can accelerate the organic peroxide curing agent to form free radicals. The free radicals open the double bonds in the resin, forming a chain reaction, thereby accelerating the curing of the adhesive.

[0016] Preferably, the wall material of the microencapsulated curing accelerator is one or more of gelatin, chitosan, melamine formaldehyde resin, and gum arabic.

[0017] By adopting the above technical solution, gelatin, chitosan, gum arabic, and melamine formaldehyde resin are used as wall materials, which can improve the coating density of the core material, and the wall material has good adhesion, which can improve the bonding stability of the wall material to the core material; when the adhesive is prepared, the damage to the wall material of the microencapsulated curing accelerator by the stirring operation is reduced, so that when the adhesive is placed at room temperature, the wall material can better protect the core material and prevent the core material from contacting the organic peroxide curing agent, thereby making the adhesive have good storage stability when placed at room temperature.

[0018] Gelatin, chitosan, melamine formaldehyde resin, and gum arabic have good strength as wall materials. When the microencapsulated curing accelerator is squeezed by the external environment, the wall material of the microencapsulated curing accelerator is easily destroyed, thereby facilitating the release of the core material in the microencapsulated curing accelerator into the adhesive and contacting with the organic peroxide curing agent, thereby promoting rapid curing of the adhesive under low temperature conditions.

[0019] Gelatin, chitosan, melamine formaldehyde resin, and gum arabic as wall materials can improve the compatibility of microencapsulated curing accelerators with resins, acrylates and other raw materials, so that the adhesive still has good stability when placed for a long time at room temperature and is not prone to pre-curing or delamination.

[0020] Preferably, the film-forming resin is selected from one or more of phenoxy resin, polyurethane, acrylic resin, and polyester resin.

[0021] By adopting the above technical solution, the adhesive can be quickly cured into an anisotropic conductive film, and the water resistance, heat resistance and wear resistance of the anisotropic conductive film are improved, while the anisotropic conductive film has better hardness and fullness.

[0022] Preferably, the toughening elastomer is selected from one or more of nitrile rubber, core-shell rubber, and acrylic block copolymer rubber.

[0023] By adopting the above technical solution, the anisotropic conductive film has better elastic properties, further improving the oil resistance, wear resistance and heat resistance of the anisotropic conductive film, and at the same time improving the bonding strength of the adhesive.

[0024] Preferably, the diluent is selected from one or more of isobornyl (meth)acrylate, tetrahydrofuranyl methacrylate, ethoxyphenyl methacrylate, and n-butyl methacrylate.

[0025] By adopting the above technical solution, the huge non-polar side groups on the (meth)acrylate isobornyl ester polymer chain weaken the interaction force between the molecular chains, reduce the viscosity of the polymer solution, and improve the compatibility between the resin and the solvent; tetrahydrofuran methacrylate has good wettability; ethoxyphenyl methacrylate and n-butyl methacrylate have a good dilution effect; not only does the adhesive have good stability, but it also promotes the flow of the adhesive during hot pressing, making it easier for the microencapsulated curing accelerator inside the adhesive to be more evenly dispersed in the adhesive, thereby facilitating more even contact between the accelerator and the curing agent after release, and at the same time facilitating more even contact between the curing agent and the resin, so that the adhesive can be quickly cured under low temperature conditions.

[0026] Preferably, the microencapsulated curing accelerator is prepared by the following method:

[0027] Ⅰ. Weigh and dissolve the wall material to obtain a solution, and emulsify the core material in the solution to obtain an emulsion;

[0028] Ⅱ. Adding the nano thermal conductive filler to the emulsion and stirring to prepare a mixed emulsion, wherein the weight ratio of the nano thermal conductive filler to the emulsion is 0.024-0.08:1;

[0029] Ⅲ The mixed emulsion is subjected to coagulation, gelation, solidification and drying to obtain a finished product.

[0030] By adopting the above technical solution, nano thermally conductive fillers, wall materials, and core materials are coordinated, and the better viscosity of the wall material is utilized to compound the nano thermally conductive fillers in the wall material, and the wall material coating structure on the surface of the microencapsulated curing accelerator is loaded with nano thermally conductive fillers; when the adhesive is hot-pressed, the better thermal conductivity of the nano thermally conductive fillers is utilized to further destroy the microcapsule membrane structure on the surface of the microencapsulated curing accelerator, thereby facilitating the release of the core material in the microencapsulated curing accelerator into the adhesive, and promoting the rapid curing of the adhesive under low temperature conditions.

[0031] When the adhesive is subjected to heat pressing, the microencapsulated curing accelerator is subjected to pressure, and the nano-thermal conductive filler further promotes the destruction of the microcapsule membrane structure, thereby quickly releasing the core material of the microencapsulated curing accelerator and allowing the adhesive to cure quickly under low temperature conditions.

[0032] Preferably, the nano thermal conductive filler is composed of aluminum nitride whiskers and nano boron nitride in a weight ratio of 1:0.6-1.5.

[0033] By adopting the above technical solution, aluminum nitride whiskers and nano-boron nitride are combined, and the fibrous whisker structure of the aluminum nitride whiskers is combined with the nano-boron nitride particle structure, so that the nano-boron nitride can be loaded into the three-dimensional network structure formed by the aluminum nitride whiskers; when the adhesive is subjected to hot pressing, the connectivity effect of the aluminum nitride whisker fibers is utilized to achieve uniform heat conduction, and the good thermal conductivity of the nano-boron nitride further promotes the destruction of the microcapsule membrane structure on the surface of the microencapsulated curing accelerator; during hot pressing, the needle-like structure of the whiskers can promote the release of the core material in the microencapsulated curing accelerator, so that the adhesive can be quickly cured under low temperature conditions.

[0034] In summary, this application has the following beneficial effects:

[0035] 1. The organic peroxide curing agent is matched with the microencapsulated curing accelerator. During the storage of the adhesive, since the curing accelerator is coated by the microcapsule, the curing accelerator will not come into contact with the organic peroxide curing agent. During the storage of the adhesive at room temperature, pre-curing will not occur and the stability is good.

[0036] 2. When the adhesive is hot-pressed, the microcapsule wall material on the surface of the curing accelerator is destroyed by the action of temperature and pressure. The curing accelerator flows out of the microcapsule and gradually comes into contact with the organic peroxide curing agent, thereby promoting the decomposition of the curing agent, improving the curing efficiency, and enabling the adhesive to achieve low-temperature rapid curing, meeting the curing requirements of the anisotropic conductive film.

[0037] 3. Gelatin, chitosan, gum arabic, and melamine formaldehyde resin are used as wall materials to increase the density of the core material's coating. The wall materials have good adhesion and can improve the bonding stability of the wall materials to the core materials. During the preparation of the adhesive, the damage to the wall materials of the microencapsulated curing accelerator caused by the stirring operation is reduced, thereby making the adhesive have better storage stability under room temperature conditions.

[0038] 4. Gelatin, chitosan, melamine formaldehyde resin, and gum arabic as wall materials can improve the compatibility of microencapsulated curing accelerators with resins, acrylates and other raw materials, so that the adhesive can still have good stability when placed for a long time at room temperature and is not prone to pre-curing or stratification. DETAILED DESCRIPTION

[0039] The present application is further described in detail below with reference to the embodiments.

[0040] Preparation Example of Microencapsulated Curing Accelerator

[0041] Among the following raw materials, N,N-dimethyl-p-toluidine was purchased from Yueyang Jiazhiyuan Biotechnology Co., Ltd.; aluminum nitride whiskers were purchased from Shanghai Gerunya Nanomaterials Co., Ltd.; nano-boron nitride was purchased from Guangzhou Hongwu Materials Technology Co., Ltd.; other raw materials were commercially available.

[0042] Preparation Example 1: A microencapsulated curing accelerator was prepared by the following method:

[0043] I. Dissolution: Weigh 2 g of gelatin and place it in 98 g of water. Stir and dissolve in a constant temperature water bath at 50°C to prepare a gelatin solution. Weigh 5 g of gum arabic and place it in 95 g of water. Stir and dissolve in a constant temperature water bath at 50°C to prepare a gum arabic solution. II. Emulsification: Weigh 3 g of N,N-dimethyl-p-toluidine and place it in 49 ml of the gelatin solution. Homogenize and emulsify at 14,500 rpm for 3 minutes. Then, add 48 ml of the gum arabic solution and stir at 500 rpm for 40 minutes to prepare a mixed emulsion.

[0044] III. Coagulation: Add 10% glacial acetic acid solution to the mixed emulsion at a rate of 30 drops / min using a peristaltic pump within 30 minutes, adjust the pH of the mixed emulsion to 3.5, and stir continuously at a speed of 500 rpm during the addition of glacial acetic acid. Continue stirring for 20 minutes after the addition of glacial acetic acid. Coagulation is formed between the wall materials and adsorbed on the oil surface to obtain a coagulated liquid;

[0045] IV. Gelation: The coagulation solution was cooled naturally to room temperature, then placed in an ice water bath to cool to 4°C and allowed to stand for 40 min to obtain a gel solution;

[0046] V. Curing: Add 1 mol / L sodium hydroxide solution to the gel solution to adjust the pH to 8.5, then add 2.2 ml of 20% glutaraldehyde solution at a rate of 30 drops / min. Stir continuously at 350 rpm during the addition process. Cured microspheres are obtained by low-temperature curing.

[0047] VI. Post-drying treatment: the solidified microspheres were washed with water three times, filtered, and then freeze-dried in a vacuum for 24 hours to obtain the finished product.

[0048] Preparation Example 2: This preparation example differs from Preparation Example 1 in that:

[0049] II. Emulsification: Weigh 3 g of N, N-dimethyl-p-toluidine and place it in 49 ml of gelatin solution, homogenize and emulsify at 14,500 rpm for 3 minutes, then add 48 ml of gum arabic solution and stir at 500 rpm for 40 minutes to prepare an emulsion; weigh 5 g of nano-thermal conductive filler and add it to the emulsion, stir and mix at 15,000 rpm for 8 minutes to prepare a mixed emulsion; the nano-thermal conductive filler is composed of aluminum nitride whiskers and nano-boron nitride in a weight ratio of 1:1, the aluminum nitride whiskers are 15-25 nm in length, and the nano-boron nitride particle size is 3-5 nm.

[0050] Preparation Example 3: This preparation example differs from Preparation Example 2 in that:

[0051] 2.4 g of nano thermal conductive filler was weighed and added to the emulsion, and stirred at 15000 rpm for 8 minutes to prepare a mixed emulsion; the nano thermal conductive filler consisted of aluminum nitride whiskers and nano boron nitride in a weight ratio of 1:0.6.

[0052] Preparation Example 4: This preparation example differs from Preparation Example 2 in that:

[0053] 8 g of nano thermal conductive filler was weighed and added to the emulsion, and stirred at 15000 rpm for 8 minutes to prepare a mixed emulsion; the nano thermal conductive filler consisted of aluminum nitride whiskers and nano boron nitride in a weight ratio of 1:1.5.

[0054] Preparation Example 5: This preparation example differs from Preparation Example 2 in that:

[0055] The nano-boron nitride was pretreated as follows: 0.5 kg of boron nitride powder was weighed and added to 1 kg of 1% gelatin solution at a rate of 50 g / min. During the addition process, the mixture was continuously stirred and mixed at a speed of 2500 rpm to obtain a mixture; after the mixture was dried, it was ground to 3-5 nm to obtain nano-boron nitride.

[0056] Preparation example of conductive microspheres

[0057] The polystyrene microspheres in the following raw materials were purchased from Zhongke Leiming (Beijing) Technology Co., Ltd. 250nm; other raw materials were commonly available on the market.

[0058] Preparation Example 6: Conductive microspheres were prepared by the following method:

[0059] 20 g of polystyrene microspheres and 20 g of dichloroethane were mixed, ultrasonically dispersed at 20 kHz for 30 minutes, and then stirred and swelled at 300 rpm for 1 hour to prepare swollen polystyrene microspheres; 20 g of methylal was added to a three-necked flask equipped with a stirrer, a dropping funnel, a thermometer, and a condenser equipped with a calcium chloride drying tube, and 35 g of sulfuryl chloride was added dropwise at 25° C. within 1 hour, and the mixture was reacted for 1 hour to obtain a mixed solution after the reaction; the mixed solution was poured into the above-mentioned swollen polystyrene microspheres, stirred at 300 rpm for 3 hours, and then 8 g of anhydrous zinc chloride powder was added to the above-mentioned reaction system, and stirred at 40° C. for 8 hours; then the mixture was centrifuged and washed to obtain chloromethylated polystyrene microspheres.

[0060] Chloromethylated polystyrene microspheres were added to a three-necked flask containing 100 ml of 5% NaOH solution. 40 g of 2,3-dimercaptopropanol was added with Bu4NOH as a catalyst. Under N2 protection, the mixture was stirred at 60°C for 48 h, centrifuged and washed to obtain thiolated polystyrene microspheres.

[0061] The thiolated polystyrene microspheres were dispersed in 200 ml of potassium tetrachloroaurate solution containing 0.01 mol / L gold ions and adsorbed for 1 hour by ultrasonic stirring. The polystyrene microspheres with gold ions adsorbed on the surface were obtained by centrifugation and washing.

[0062] The polystyrene microspheres with gold ions adsorbed on the surface are added to a 10% hydrazine solution and ultrasonically stirred for 15 minutes to reduce the gold ions adsorbed on the surface of the microspheres to elemental gold with catalytic activity; the polystyrene microspheres with elemental gold adsorbed on the surface are directly added to a cyanide-free gold plating solution, ultrasonically stirred at 80°C for 2 hours, and then centrifuged, washed, and vacuum dried. The finished product has a particle size of 5um.

[0063] The cyanide-free gold plating solution contains: 0.0125 mol / L potassium tetrachloroaurate, 0.1 mol / L sodium thiosulfate, 0.1 mol / L sodium sulfite, 0.05 mol / L ammonium chloride, 0.1 mol / L thiourea, 100 mg / L sodium benzenesulfonate, 10 mg / L lead acetate, and the balance is water. The pH is adjusted to 6.0 with 10% by mass ammonia water or 10% by mass sulfuric acid.

[0064] Example

[0065] The following raw materials are all commercially available.

[0066] Example 1: Anisotropic conductive film containing microencapsulated free radical accelerator

[0067] The anisotropic conductive film is prepared by curing an adhesive, which is made of the following raw materials in parts by weight: 50g of phenoxy resin of model YP-50, 3g of nitrile rubber, 10g of epoxy acrylic resin of model CN151, 20g of polyurethane acrylate of model GU-9400Y, 5g of tetrahydrofuran methacrylate, 3g of 1,6-hexanediol diacrylate, 3g of phosphate acrylate, 3g of propyl methacrylate trimethoxysilane, 5g of conductive microspheres prepared in Preparation Example 6, 0.0004g of hydroquinone, 5g of fumed nano-silica of P25, 3g of benzoyl peroxide, 0.5g of microencapsulated N,N-dimethyl-p-toluidine prepared in Preparation Example 1, and 300g of ethyl acetate.

[0068] The preparation method of anisotropic conductive film is as follows:

[0069] Phenoxy resin, nitrile rubber, and 1 / 2 of the total amount of ethyl acetate are mixed, and then epoxy acrylic resin, polyurethane acrylate, tetrahydrofuran methacrylate, 1,6-hexanediol diacrylate, and phosphate acrylate are added in sequence and stirred evenly to prepare a premixed adhesive; composite conductive microspheres, fumed nanosilica, benzoyl peroxide, microencapsulated N,N-dimethyl-p-toluidine are mixed with the remaining ethyl acetate, stirred evenly, and then mixed with the premixed adhesive and stirred at 1000 rpm for 20 minutes to prepare an adhesive; the adhesive is coated and dried to form a film to obtain an anisotropic conductive film with a thickness of 25 μm.

[0070] Example 2: This example differs from Example 1 in that:

[0071] The microencapsulated N,N-dimethyl-p-toluidine prepared in Preparation Example 1 was replaced with an equal mass of microencapsulated cobalt isooctanoate in the raw materials; wherein the microencapsulated cobalt isooctanoate was prepared by the method of Preparation Example 1, except that an equal mass of N,N-dimethyl-p-toluidine in Preparation Example 1 was replaced with cobalt isooctanoate.

[0072] Example 3: This example differs from Example 1 in that:

[0073] The benzoyl peroxide in the raw material is replaced by an equal mass of dicumyl peroxide.

[0074] Example 4: This example differs from Example 1 in that:

[0075] 35g acrylic resin, 3g core-shell rubber, 3g epoxy acrylic resin model CN151, 10g polyurethane acrylate model GU-9400Y, 3g ethoxyphenyl methacrylate, 1g 1,6-hexanediol diacrylate, 2g phosphate acrylate, 2.5g vinyltrimethoxysilane, 4g 5um composite conductive microspheres, 3g P25 fumed nanosilica, 2g benzoyl peroxide, 1g microencapsulated N,N-dimethyl-p-toluidine prepared in Preparation 1, and 200g ethyl acetate.

[0076] Example 5: This example differs from Example 1 in that:

[0077] The microencapsulated N,N-dimethyl-p-toluidine prepared in Preparation Example 2 was used as the raw material to replace the microencapsulated N,N-dimethyl-p-toluidine prepared in Preparation Example 1.

[0078] Example 6: This example differs from Example 1 in that:

[0079] The microencapsulated N,N-dimethyl-p-toluidine prepared in Preparation Example 3 was used as the raw material to replace the microencapsulated N,N-dimethyl-p-toluidine prepared in Preparation Example 1.

[0080] Example 7: This example differs from Example 1 in that:

[0081] The microencapsulated N,N-dimethyl-p-toluidine prepared in Preparation Example 4 was used as the raw material to replace the microencapsulated N,N-dimethyl-p-toluidine prepared in Preparation Example 1.

[0082] Example 8: This example differs from Example 1 in that:

[0083] The microencapsulated N,N-dimethyl-p-toluidine prepared in Preparation Example 5 was used as the raw material to replace the microencapsulated N,N-dimethyl-p-toluidine prepared in Preparation Example 1.

[0084] Example 9: The difference between this example and example 1 is that

[0085] The polyurethane acrylate is replaced by epoxy acrylate of equal mass in the acrylate raw material.

[0086] Example 10: This example differs from Example 1 in that:

[0087] During the preparation of microencapsulated N,N-dimethyl-p-toluidine, the gum arabic solution is replaced by a gelatin solution of equal mass, and the mass fraction of the gelatin solution is 2%.

[0088] Example 11: This example differs from Example 5 in that:

[0089] The aluminum nitride whiskers are replaced by nano boron nitride of equal mass in the raw material of the nano thermal conductive filler.

[0090] Comparative Example

[0091] Comparative Example 1: The difference between this comparative example and Example 1 is that:

[0092] The microencapsulated N,N-dimethyl-p-toluidine prepared in Preparation Example 1 was not added to the raw materials.

[0093] Comparative Example 2: This comparative example differs from Example 1 in that:

[0094] The microencapsulated N,N-dimethyl-p-toluidine was replaced with an equal mass of N,N-dimethyl-p-toluidine in the raw materials.

[0095] Performance testing

[0096] 1. Peel strength test

[0097] Sample preparation: The anisotropic conductive films prepared in Examples 1-10 and Comparative Examples 1-2 were respectively used to connect a flexible circuit board and a glass substrate; the flexible circuit board was a copper circuit board with a width of 1.3 cm, a distance between the center lines of two adjacent electrodes on the flexible circuit board of 200 μm, an electrode width of 100 μm, and a thickness of 35 μm; the glass substrate had a thickness of 1.1 cm, a surface resistance of 10 Ω / □, a distance between the center lines of two adjacent electrodes of 200 μm, and an electrode width of 100 μm; during the preparation process: the adhesives prepared in Examples 1-10 and Comparative Examples 1-2 were respectively applied between the flexible circuit board and the glass substrate, and a hot press was used (the hot press was purchased from Shenzhen PowerDe Automation Precision Equipment Co., Ltd., model (PW-M1005)) at a temperature of 150° C. and a pressure of 3 MPa for 5 s. After the adhesive was cured, an anisotropic conductive film was formed, and the thickness of the anisotropic conductive film was 25 μm.

[0098] The test steps are as follows: bend the end of the flexible circuit board that is not bonded with the adhesive 90° and fix it with a chuck, fix the side of the glass substrate that is not bonded with the adhesive with a chuck, accurately position the sample between the chucks to ensure that the applied tension is evenly distributed over the width of the sample, separate the upper and lower chucks at a separation speed of 25mm / min, and the universal tensile testing machine automatically records the separation rate of the chucks and the force exerted when the chucks are separated until the flexible circuit board is peeled off; for each sample, determine the maximum peel force from the relationship curve between peel force and peel length, in N, and calculate the peel force as the maximum peel force divided by the corresponding width. Calculate the corresponding peel strength value (peel strength is abbreviated as strength) in N / m and record it as the initial bonding data.

[0099] 2. Preparation of resistance test samples: The anisotropic conductive films prepared in Examples 1-10 and Comparative Examples 1-2 were respectively used to connect a flexible circuit board and a glass substrate; the distance between the center lines of two adjacent electrodes on the flexible circuit board was 600 μm, the electrode width was 300 μm, and the thickness was 35 μm, and some electrodes had 4 probe test points; the glass substrate was 1.1 cm thick, had a surface resistance of 10 Ω / □, and was a full ITO substrate; during the preparation process: the adhesives prepared in Examples 1-10 and Comparative Examples 1-2 were respectively applied between the flexible circuit board and the glass substrate, and a hot press was used (the hot press was purchased from Shenzhen PowerDe Automation Precision Equipment Co., Ltd., model PW-M1005) at a temperature of 150°C and a pressure of 3 MPa for 5 seconds. After the adhesive was cured, an anisotropic conductive film was formed, and the thickness of the anisotropic conductive film was 25 μm.

[0100] A four-probe resistance tester (purchased from Hebei Deke Machinery Technology Co., Ltd.) was used to detect the resistance value, which was recorded as the initial bonding data.

[0101] 3. Reliability test

[0102] The specimens were prepared using the specimen preparation method described in the peel strength test, and then placed in a constant temperature and humidity chamber at a temperature of 85°C and a humidity of 85% for 240 h. The specimens were removed and the peel strength of the treated specimens was tested according to the test steps described in the peel strength test, and the data was recorded. The specimens were prepared using the specimen preparation method described in the resistance test, and then placed in a constant temperature and humidity chamber at a temperature of 85°C and a humidity of 85% for 240 h. The specimens were removed and the resistance of the treated specimens was tested using the testing instrument described in the resistance test, and the data was recorded, as shown in Table 1.

[0103] 4. Storage stability test

[0104] Adhesives were prepared using the preparation methods of Examples 1-10 and Comparative Examples 1-2. The prepared adhesives were placed in an environment at 25°C and a relative humidity of 60% for 14 days, and then samples were prepared using the sample preparation method in the peel strength test. The peel strength of the samples was then tested according to the test steps in the peel strength test. The prepared adhesives were placed in an environment at 25°C and a relative humidity of 60% for 14 days, and then samples were prepared using the sample preparation method in the resistance test. The resistance of the samples was tested using the detection instrument in the resistance test, and the data was recorded.

[0105] Table 1 Performance test table

[0106]

[0107]

[0108] Combining Example 1 and Examples 2-4 with Table 1, it can be seen that the anisotropic conductive film has good peel strength and low resistance regardless of initial bonding, storage in a hot and humid environment for 240 hours after sample bonding, or bonding after the adhesive is placed at room temperature for 14 days. This shows that the organic peroxide curing agent is combined with the microencapsulated curing accelerator. When subjected to hot pressing, the microcapsule wall material on the surface of the curing accelerator is destroyed by the effects of temperature and pressure, and the curing accelerator flows out of the microcapsule and gradually contacts the organic peroxide curing agent, thereby promoting the decomposition of the curing agent, improving the curing efficiency, and enabling the adhesive to achieve low-temperature rapid curing in a short time. During the storage of the adhesive, the isolation effect of the microcapsules prevents the curing accelerator from contacting the curing agent, making it difficult for the adhesive to pre-cure during storage, and having good stability. At the same time, after being stored for a period of time, it still has good bonding strength when bonding to the substrate.

[0109] Combining Example 1 and Examples 5-8 with Table 1, it can be seen that the addition of nano-thermal conductive fillers to the adhesive raw materials of Examples 5-7 slightly improves the peel strength compared to Example 1, indicating that the appropriate addition of nano-thermal conductive fillers can improve the peel strength of the anisotropic conductive film and appropriately reduce the resistance value, thereby making the anisotropic conductive film have better bonding strength.

[0110] Combining Example 1 and Examples 9-10 and Table 1, it can be seen that in Example 9, the polyurethane acrylate is replaced with epoxy acrylate of equal mass in the acrylate raw material. Compared with Example 1, the peel strength of the anisotropic conductive film prepared in Example 9 is lower than that in Example 1; this indicates that the combination of epoxy acrylate, polyurethane acrylate, bifunctional acrylate, and phosphate acrylate can make the anisotropic conductive film have better adhesion and can also improve the weather resistance of the anisotropic conductive film.

[0111] In the preparation process of microencapsulated N,N-dimethyl-p-toluidine in Example 10, the gum arabic solution was replaced by gelatin solution of equal mass, and the mass fraction of the gelatin solution was 2%. Compared with Example 1, the peel strength and resistance value did not change much.

[0112] Combining Example 1 and Comparative Examples 1-2 with Table 1, it can be seen that the microencapsulated N,N-dimethyl-p-toluidine prepared in Preparation Example 1 was not added to the raw materials of Comparative Example 1. Compared with Example 1, the peel strength of the anisotropic conductive film prepared in Comparative Example 1 was lower than that of Example 1, whether it was the initial bonding immediately after the adhesive was prepared, or after the bonding was placed in a hot and humid environment for 240 hours, or after the adhesive was placed at room temperature for 14 days. This indicates that the anisotropic conductive film without the addition of a accelerator had an insufficient reaction speed during hot pressing and a low curing rate, resulting in insufficient peel strength. After the adhesive was placed in a hot and humid environment for 240 hours or at room temperature for 14 days, the resistance of Comparative Example 1 was greater than that of Example 1. The absence of a accelerator in the adhesive can easily affect the performance of the finished anisotropic conductive film.

[0113] In Comparative Example 2, a non-microencapsulated curing accelerator is added. Before the adhesive is coated, the accelerator easily promotes the reaction of the curing agent to solidify the resin, thereby affecting the fluidity of the adhesive, resulting in insufficient explosion of the conductive microspheres and high resistance. During the storage process at room temperature, the adhesive is prone to pre-curing due to the lack of microencapsulation treatment. Therefore, during bonding, the fluidity of the adhesive further deteriorates, resulting in no conduction between the upper and lower electrodes, and the peel strength of the adhesive is also greatly reduced.

[0114] 5. Preparation of curing speed test specimens: The anisotropic conductive films prepared in Examples 1, 5-8, and 11 were respectively used to connect a flexible circuit board and a glass substrate; the flexible circuit board was a copper circuit board having a width of 1.3 cm, a distance between the centerlines of two adjacent electrodes on the flexible circuit board of 200 μm, an electrode width of 100 μm, and a thickness of 35 μm; the glass substrate had a thickness of 1.1 cm, a surface resistance of 10 Ω / □, a distance between the centerlines of two adjacent electrodes of 200 μm, and an electrode width of 100 μm. During the preparation process: the adhesives prepared in Examples 1, 5-8, and 11 were respectively applied between the flexible circuit board and the glass substrate, and hot pressed for 5 seconds at a temperature of 140° C. and a pressure of 3 MPa using a hot press (the hot press was purchased from Shenzhen PowerDe Automation Precision Equipment Co., Ltd., model PW-M1005). After the adhesive was cured, an anisotropic conductive film was formed. The thickness of the anisotropic conductive film was 25 μm, and the peel strength of the anisotropic conductive film was tested.

[0115] Adhesives were prepared using the preparation methods of Examples 1, 5-8, and 11, respectively. The adhesives were placed at 25°C and a relative humidity of 60% for 14 days, and then the adhesives were coated between a flexible circuit board and a glass substrate. The flexible circuit board and the glass substrate had the same specifications as the above-mentioned samples. A hot press (the hot press was purchased from Shenzhen Baode Automation Precision Equipment Co., Ltd., model PW-M1005) was used at a temperature of 140°C and a pressure of 3 MPa for 5 seconds. After the adhesive was cured, an anisotropic conductive film was formed. The thickness of the anisotropic conductive film was 25 μm, and the peel strength was recorded.

[0116] Table 2 Curing speed test table

[0117]

[0118]

[0119] Combining Example 1 and Examples 5-7 and Table 2, it can be seen that the addition of nano-thermal conductive fillers to the raw materials of Examples 5-7 and hot pressing at 140°C still make the adhesive have a high peel strength, and after being placed for a long time, the anisotropic conductive film still has good peel strength; this shows that when the adhesive is subjected to hot pressing, the interconnection effect of the aluminum nitride whisker fibers is utilized to achieve uniform heat conduction, and the good thermal conductivity of nano-boron nitride further promotes the destruction of the microcapsule membrane structure on the surface of the microencapsulated curing accelerator, improves the release of the core material in the microencapsulated curing accelerator during hot pressing, accelerates the release of the accelerator, thereby accelerating the contact between the accelerator and the organic peroxide curing agent, and further enables the adhesive to achieve rapid curing under low temperature conditions.

[0120] Combining Example 1 and Example 8 and Table 2, it can be seen that the initial bonding peel strength and the peel strength after 14 days of placement in Example 8 are both greater than those in Example 1, and greater than those in Example 5; this indicates that after the boron nitride powder is treated with the gelatin solution, the compatibility of nano-boron nitride with the wall material can be improved, thereby improving the compatibility of the microencapsulated curing accelerator with other raw materials of the adhesive, and improving the density of the microencapsulated coating, so that the microencapsulated curing accelerator still has a good coating effect on the accelerator after long-term placement, avoiding the release of the accelerator into the adhesive during storage, thereby improving the storage stability of the adhesive.

[0121] Combining Example 5 and Example 11 and Table 2, it can be seen that in Example 11, the aluminum nitride whiskers are replaced with nano-boron nitride of equal mass in the raw material of the nano-thermal conductive filler. Compared with Example 5, the initial bonding peel strength of Example 11 is less than the initial bonding peel strength of Example 5, and the peel strength of Example 11 after 14 days of storage is still less than that of Example 5; this shows that the aluminum nitride whiskers and nano-boron nitride cooperate with each other, and the heat transfer of the aluminum nitride whisker filament structure is combined with the heat conduction of the nano-boron nitride, so that the microencapsulated curing accelerator can still achieve rapid curing under low temperature conditions; pure nano-boron nitride is not easy to transfer heat, which easily affects the destruction of the microcapsule structure on the surface of the microencapsulated curing accelerator.

[0122] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make non-creative modifications to the present embodiment as needed, but as long as they are within the scope of the claims of the present application, they are protected by the patent law.

Claims

1. An anisotropic conductive film containing a microencapsulated free radical accelerator, characterized in that: The anisotropic conductive film is prepared by curing an adhesive. The adhesive is prepared from the following raw materials in parts by weight: 35-50 parts of a film-forming resin, 3-8 parts of a toughening elastomer, 13-35 parts of an acrylate prepolymer, 3-5 parts of an acrylate reactive diluent, 1-3 parts of a bifunctional acrylate, 2-4 parts of a phosphate acrylate, 1-3 parts of a silane coupling agent, 2-5 parts of an organic peroxide curing agent, 0.5-3 parts of a microencapsulated curing accelerator, 0.0001-0.0004 parts of hydroquinone, 3-7 parts of fumed nano-silica, 4-6 parts of conductive microspheres, and 200-300 parts of ethyl acetate. The acrylate prepolymer is prepared from the following raw materials in parts by weight: 3-10 parts of epoxy acrylate and 10-25 parts of polyurethane acrylate. The microencapsulated curing accelerator is prepared by the following method: Ⅰ. Weigh and dissolve the wall material to obtain a solution, and emulsify the core material in the solution to obtain an emulsion; II. Adding a nano thermally conductive filler to an emulsion and stirring to prepare a mixed emulsion, wherein the weight ratio of the nano thermally conductive filler to the emulsion is 0.024-0.08:1; the nano thermally conductive filler comprises aluminum nitride whiskers and nano boron nitride at a weight ratio of 1:0.6-1.5; the aluminum nitride whiskers are 15-25 nm in length, and the nano boron nitride particle size is 3-5 nm; Ⅲ The mixed emulsion is subjected to coagulation, gelation, solidification and drying to obtain a finished product.

2. The anisotropic conductive film containing a microencapsulated free radical accelerator according to claim 1, characterized in that: The organic peroxide curing agent is selected from one or more of cumene hydroperoxide, tert-amyl hydroperoxide, di-tert-butyl peroxide, diisopropyl benzene peroxide, tert-butyl peracetate, di-tert-amyl peroxide, tert-butyl perbenzoate, tert-amyl perbenzoate, 2,2-di(tert-butylperoxy)butane, tert-butyl permaleate, tert-butyl peroxy-3,3,5-trimethylhexanoate, 1,1-di(tert-butylperoxy)cyclohexane, 1,1-di-tert-butylperoxy-3,3,5-trimethylcyclohexane, tert-butyl peroxyisobutyrate, tert-amyl peroxy-2-ethylhexanoate, tert-butyl peroxy-2-ethylhexanoate, benzoyl peroxide, and lauroyl peroxide.

3. The anisotropic conductive film containing a microencapsulated free radical accelerator according to claim 1, characterized in that: The core material of the microencapsulated curing accelerator is selected from one or more of tertiary amines, cyclopentane salts, isooctanoates, thiols, and organic metal compounds.

4. The anisotropic conductive film containing a microencapsulated free radical accelerator according to claim 1, characterized in that: The wall material of the microencapsulated curing accelerator is selected from one or more of gelatin, chitosan, melamine formaldehyde resin, and gum arabic.

5. The anisotropic conductive film containing a microencapsulated free radical accelerator according to claim 1, characterized in that: The film-forming resin is selected from one or more of phenoxy resin, polyurethane, acrylic resin, and polyester resin.

6. The anisotropic conductive film containing a microencapsulated free radical accelerator according to claim 1, characterized in that: The toughening elastomer is selected from one or more of nitrile rubber, core-shell rubber, and acrylic block copolymer rubber.

7. The anisotropic conductive film containing a microencapsulated free radical accelerator according to claim 1, characterized in that: The diluent is selected from one or more of isobornyl (meth)acrylate, tetrahydrofuran methacrylate, ethoxyphenyl methacrylate, and n-butyl methacrylate.

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