WO2022002278A1

WO2022002278A1 - Conductive microsphere for anisotropic conductive adhesive film and preparation method therefor

Info

Publication number: WO2022002278A1
Application number: PCT/CN2021/109952
Authority: WO
Inventors: 张竞; 郑国栋; 郑争
Original assignee: 台州天舒新材料科技有限公司
Priority date: 2020-06-30
Filing date: 2021-08-01
Publication date: 2022-01-06
Also published as: CN111718444A

Abstract

The present invention belongs to the field of conductive material preparation, and particularly relates to a conductive microsphere for an anisotropic conductive adhesive/film. A "core-shell" microsphere is made by using a monodisperse and highly cross-linked microsphere as a core base sphere, and then grafting a linear polymer onto the surface of the base sphere to form a soft-shell outer layer; and then, a "core-shell" conductive microsphere is made by means of the electroless plating of metals (nickel or silver) and the secondary electrochemical plating of gold on the surface of the microsphere. The invention effectively solves the problem that an existing ordinary conductive microsphere is broken under a large attaching pressure range, which causes a decrease in the number of effective conductive microspheres between electrodes and an increase in the contact resistance.

Description

A kind of conductive microsphere for anisotropic conductive adhesive film and preparation method thereof

technical field

The present invention is to provide a method for making high-conductivity microspheres and a method for preparing anisotropic conductive adhesive/film. The conductive microspheres are made of hard-core-soft-shell microspheres composed of a highly cross-linked polydivinylbenzene hard core and a linear polymer soft shell, which are then coated with a conductive metal layer on the surface. The degree of cross-linking of polydivinylbenzene hard core microspheres is more than 30%, and it does not deform under hot pressing conditions, while the linear polymer soft shell softens and deforms under hot pressing conditions, and the thickness of the soft shell layer is about the diameter of the core. 8%-20%. The toughness of the hard core makes the microspheres less likely to be broken under hot pressing, which not only ensures the number of effective conductive microspheres, but also increases the pressure operating range for hot pressing. The outer layer of the soft shell microspheres is deformed under hot pressing to form a large contact area with the electrode, which greatly increases the contact conductivity.

Background technique

Using resin microspheres as the base material, conductive microspheres formed by electroless plating of conductive metal materials, and anisotropic conductive materials mixed with binder resins are the mainstream direction of microelectronic circuit connection today. Anisotropic conductive materials are widely used in the packaging of microelectronic devices, such as LCD TV screens, personal computers, cameras, and mobile phones.

technical problem

The anisotropic conductive adhesive/film usually needs to apply a certain pressure and temperature during the application process to ensure low contact resistance and fast curing of the adhesive. The temperature will soften the polymer microspheres in the conductive microspheres, and the degree of softening is related to the temperature. When bonding is performed under pressure, the conductive microspheres are deformed while achieving a large contact area and low contact resistance. However, the application of excessive pressure will cause some of the conductive microspheres to rupture, and the conductive microspheres will lose their conductivity. Especially in the case of uneven distribution of microsphere particles, the breakage rate of conductive microspheres will be higher. In the actual bonding process, it is necessary to find a balance point from the high bonding pressure to obtain a large contact area and a low bonding force to reduce the breakage rate of the microspheres, which increases the difficulty of the bonding operation. Especially when bonding different electronic circuits, the number of electrodes and electrode area may be different, and the number of conductive microspheres between electrodes will be very different. This directly changes the pressure on each conductive microsphere, making it extremely difficult to control the optimum pressure for the fit. In addition, even with the best bonding pressure, the conductive microspheres still have a certain breakage rate. This reduces the number of effective conductive microspheres between electrodes and increases the contact resistance.

technical solutions

Aiming at the above-mentioned defects of the conductive microspheres, the present invention provides a new method for producing "core-shell type" conductive microspheres. There is a lot of tolerance for different fitting pressures. That is, the contact resistance of the conductive microspheres can be kept consistent in a wide range of bonding pressure. Under relatively high bonding pressure, the conductive microspheres do not break, and the effective number of conductive microspheres is maintained.

beneficial effect

The high cross-linked polymer core microspheres in the present invention are measured by hot pressing, and the microspheres are not damaged under the pressure of ^{150 C o} and 80 kg/cm ^{2 .} Each conductive microsphere between the electrodes plays a conductive role, and the number of effective conductive microsphere particles is maintained at a high level. The outer layer of the soft shell is softened under hot pressing conditions, and the area in contact with the electrode is significantly increased, which effectively improves the conductivity of a single conductive microsphere.

Generally, the conductive microspheres are deformed into ellipses under hot pressing, and the contact area with the electrodes increases, but they cannot form a completely flat contact like soft spheres, and the conductivity of each conductive microsphere cannot be maximized. The increased pressure can increase the conductivity of the single conductive microspheres. However, it will cause the microspheres to rupture, which will damage the conductivity. The results confirmed that the water conducting microspheres pressure exceeds ^2:00 30kg / cm, breakage of the microspheres is significantly increased. Therefore, for ordinary conductive microspheres, the bonding pressure has become an operation that cannot do both. Furthermore, where the effective conductive particles are too low, the only way to increase the overall conductivity is to increase the concentration of conductive microspheres, with the consequence of increasing the risk of short circuits in the horizontal (XY) direction.

Description of drawings

No accompanying drawings.

BEST MODE FOR CARRYING OUT THE INVENTION

实施例Example 11 。.

(1) Microsphere initiator.

The 2.5-micron microspheres copolymerized with 25% hydroxyethyl methacrylate and 75% divinylbenzene were used as the starting microspheres (the microspheres were TS025HM microspheres provided by Taizhou Tianshu New Material Technology Co., Ltd., the particle size distribution of the microspheres was The coefficient of variation was 3.0%). 20 g of TS025HM microspheres and 9.5 g of triethylamine were added to a 500 ml round bottom flask containing 200 ml of tetrahydrofuran. Under electromagnetic stirring, 20 g of 2-bromopropionyl bromide was added dropwise to the above mixture, and the reaction continued for 12 hours. Filter, wash thoroughly with tetrahydrofuran and methanol. After vacuum drying at 100°C for two hours, the initiator microspheres were obtained. The microspheres were analyzed by infrared spectroscopy, and the hydroxyl groups on the surface of the microspheres were completely converted into 2-bromopropionate groups.

(2) Core-shell microspheres.

20.0 g of the microsphere initiator and 19.0 g of methyl methacrylate were added to a 1000 ml round bottom flask containing 550 ml of tetrahydrofuran (solution A) and deoxygenated with nitrogen. Add 1.8 g of CuBr and 3.2 g of MeCyclam to a 500-ml round-bottom flask (solution B) containing 150 ml of tetrahydrofuran, and deoxygenate with nitrogen. Add 4.0 g of glycidyl methacrylate to a 500 ml round bottom flask containing 250 ml of tetrahydrofuran (solution C) and deoxygenate with nitrogen. Solution B was transferred into solution A with a syringe and magnetically stirred for 10 hours at room temperature. Then use a syringe to transfer solution C into solutions A-B and stir magnetically for 5 hours at room temperature. Filter, wash thoroughly with tetrahydrofuran and methanol. After vacuum drying at 100°C for two hours, 34.1 g of core-shell microspheres were obtained. The particle size of the microspheres was 3.0 microns, and the coefficient of variation of the particle size distribution was 3.5%.

(3) Polyamine surface modification.

The above-mentioned 3.0-micron core-shell microspheres were used as starting microspheres. 30g core-shell microspheres and 3.7 g of tris(2-aminoethyl)amine were added to a 500 ml round bottom flask containing 250 ml of DMF. Under magnetic stirring, the solution was heated to 105°C and the reaction was continued for 5 hours. After cooling, filter and rinse thoroughly with deionized water. The polyamine-modified microspheres were dried under vacuum at 100°C for two hours. The microspheres were analyzed by infrared spectroscopy, and the glycidyl ester groups on the surface of the microspheres were completely converted into amine groups.

(4) The microsphere surface carrier is activated in the catalyst.

30 g of the polyamine-modified core-shell microspheres obtained by the above-mentioned polyamine surface modification reaction were added to a 5000 ml round-bottomed flask containing 1000 ml of distilled water. Under magnetic stirring, the solution was heated to 60°C and 1000ml of 0.05% (NH)2PdCl4 solution was added. The reaction continued for 30 minutes. After cooling, filter and rinse thoroughly with deionized water.

The above-mentioned palladium salt-loaded microspheres were added to a 5000 ml round bottom flask containing 1000 ml of distilled water. Under magnetic stirring, the solution was heated to 60°C, 2000 ml of 10% dimethylamine borane (DMAB) was added, and the reaction was continued for 20 minutes. After cooling, filter and rinse thoroughly with deionized water. Palladium-activated microspheres were obtained.

(5) Electroless nickel plating on the surface.

40 g of the palladium-activated microspheres obtained by the above reaction were added to a 5000 ml round bottom flask containing 1000 ml of electroless nickel plating solution for thin plating. The solution was heated to 90°C under magnetic stirring. The reaction continued for 120 minutes. After cooling, filter and rinse thoroughly with deionized water. 50 g of nickel-plated microspheres were obtained, and the nickel-plated layer was about 80 nanometers.

The composition of the thin electroless copper plating solution is: 20g nickel sulfate, 25g sodium hypophosphite, 15g sodium acetate, 15ml additives, pH value is 4.5.

(6) Barrel gold plating.

50 g of nickel-plated core-shell microspheres obtained by the above-mentioned thin plating method were added to a four-liter small barrel plating device, the rotating speed was 20/min, the current was 10 ampere, and the electrolysis was performed for 4.5 hours. Nickel/gold plated microspheres were obtained. The gold coating is about 70 nm. The gold plating solution is an ordinary plating solution.

本发明的实施方式。Embodiments of the present invention.

实施例Example 22 。.

The other steps are the same as in Example 1, except that:

(1) Microsphere initiator.

The 2.9-micron microspheres polymerized with 65% divinylbenzene were used as the starting microspheres (the numbered TS0029-Y microspheres were provided by Taizhou Tianshu New Material Technology Co., Ltd., and the particle size distribution coefficient of variation of the microspheres was 2.6%). (A) 20 g of TS0029-Y microspheres and 2.0 g of sodium borohydride were added to a 500 ml round-bottomed flask containing 200 ml of tetrahydrofuran, ice bath. 20 ml of _{a tetrahydrofuran solution containing 8.0 BF 3} g was added dropwise to the above solution, and the reaction was continued for 3 hours at room temperature under electromagnetic stirring. Then, add 20ml of ice water to adjust the pH to 8, and then add 20ml of 35% hydrogen peroxide. Filter, wash thoroughly with tetrahydrofuran and methanol. After drying under vacuum at 100°C for two hours, hydroxylated microspheres were obtained. (B) 20g of above-mentioned hydroxylated microspheres and 9.5g of triethylamine were added to a 500ml round-bottomed flask containing 200ml of tetrahydrofuran and under electromagnetic stirring, 20g of 2-bromopropionyl bromide was added dropwise to the above-mentioned mixed solution, The reaction continued for 12 hours. Filter, wash thoroughly with tetrahydrofuran and methanol. After vacuum drying at 100°C for two hours, the initiator microspheres were obtained. The microspheres were analyzed by infrared spectroscopy, and the hydroxyl groups on the surface of the microspheres were completely converted into 2-bromopropionate groups.

实施例Example 33 。.

The other steps are the same as in Example 1, except that:

(1) Microsphere initiator.

The 3.0-micron microspheres copolymerized with 25% chloromethylstyrene and 75% divinylbenzene were used as the starting microspheres, and the particle size distribution coefficient of variation of the microspheres was 2.8% (the microspheres were provided by Taizhou Tianshu New Material Technology Co., Ltd. TS003CI microspheres).

(2) Core-shell microspheres

Add 20.0 g of microsphere initiator and 19.0 g of methylstyrene to a 1000 ml round bottom flask (solution A) containing 550 ml of tetrahydrofuran and deoxygenate with nitrogen. Add 1.8 g of CuBr and 4.0 g of bipy to a 500-ml round-bottom flask (solution B) containing 150 ml of tetrahydrofuran, deoxygenated with nitrogen,. Add 4.0 g of chloromethylstyrene to a 500 ml round bottom flask containing 250 ml of tetrahydrofuran (solution C) and deoxygenate with nitrogen. Transfer solution B into solution A with a syringe and stir magnetically for 10 hours at room temperature. Then use a syringe to transfer solution C into solutions A-B and stir magnetically for 5 hours at room temperature. Filter, wash thoroughly with tetrahydrofuran and methanol. After vacuum drying at 100°C for two hours, 34.1 g of core-shell microspheres were obtained. The particle size of the microspheres was 3.6 microns, and the coefficient of variation of the particle size distribution was 2.9%.

工业实用性。Industrial applicability.

With the advancement of the microelectronics industry, integrated circuits are miniaturized. The wiring technology of electronic devices relies more on high-performance anisotropic conductive adhesives/films. Compared with the prior art, the advantages of the present invention are:

1. The soft-shell and hard-core conductive microspheres of the present invention can maximize the contact area of the conductive microspheres and improve the conductivity under the condition of hot pressing.

2. Compared with ordinary conductive microspheres, the conductive microspheres are not broken under hot pressing conditions. Maintain the effective number of conductive microspheres and improve the conductivity.

3. The soft-shell and hard-core conductive microspheres provided by the present invention can meet the further miniaturization circuit connection requirements of integrated circuits and electronic devices.

Sequence Listing Free Content

none.

Claims

A conductive microsphere for anisotropic conductive adhesive/film, characterized in that the inner layer of the conductive microsphere is a highly cross-linked polymer hard core microsphere, and the outer layer is a linear polymer soft shell, and The surface layer of the outer layer is coated with copper, silver, nickel or gold as a conductive metal layer, wherein the cross-linking degree of the inner layer hard core microspheres is more than 30%; the particle size of the inner layer hard core microspheres is 1 micron ~10 microns, and the thickness of the outer soft shell layer is 8%-20% of the diameter of the inner hard core microspheres.
The conductive microsphere for anisotropic conductive adhesive/film according to claim 1, wherein the inner layer is a highly cross-linked polymer hard core microsphere, and the copolymer consists of two It is polymerized from vinylbenzene, styrene, chloromethylstyrene, hydroxyethyl (meth)acrylate or maleic anhydride monomers.
The conductive microsphere for anisotropic conductive adhesive/film according to claim 1, wherein the surface of the inner hard core microsphere is modified as an initiator of atom transfer polymerization.
The conductive microsphere for anisotropic conductive adhesive/film according to claim 1, wherein the outer layer is a linear or low cross-linked polymer soft shell produced by atom transfer polymerization , the polymer composition includes styrene, methylstyrene, methoxystyrene, chloromethylstyrene, hydroxystyrene, carboxystyrene, aldehyde styrene, (meth)acrylic acid, (meth)acrylic acid methyl ester, ethyl (meth)acrylate, butyl (meth)acrylate, hydroxyethyl (meth)acrylate, glycidyl (meth)acrylate or (meth)acrylate (dimethyl) amine) ethyl ester.
The conductive microsphere for anisotropic conductive adhesive/film according to claim 1, wherein the outer layer comprises a hydroxyl group, a carboxyl group, an amine group, an aldehyde group, an epoxy group, a phenol group or a Anhydride functional groups.
The conductive microsphere for anisotropic conductive adhesive/film according to claim 1, wherein the outer layer is polystyrene or polystyrene derivatives, poly(meth)acrylate Or poly(meth)acrylate derivatives or their block copolymers.
A kind of conductive microspheres for anisotropic conductive adhesive/film according to claim 1, characterized in that, the inner layer hard core microspheres are selected from polymer microspheres with a cross-linking degree of more than 30%, The degree of crosslinking is in the range of 30%-95%.
The conductive microsphere for anisotropic conductive adhesive/film according to claim 1, wherein the particle size of the inner layer hard core microsphere is 2-6 micrometers.
The conductive microsphere for anisotropic conductive adhesive/film according to claim 1, wherein the particle size distribution variation coefficient of the conductive microsphere is less than 10%.
A kind of preparation method of conductive microspheres for anisotropic conductive adhesive/film according to any one of claims 1-9, is characterized in that, mainly comprises the following steps:

(1) Preparation of initiator microspheres,

(2) Preparation of core-shell microspheres,

(3) Preparation of polyamine surface-modified microspheres,

Polymer microspheres with functional groups that can react with polyamine molecules react with polyamines to achieve amine group-modified microsphere surfaces. Polyamine molecules are derived from ethylenediamine, propylenediamine, diethyltriamine, triethyltetramine amine, tetraethylpentamine, tris(2-aminoethyl)amine and low molecular weight polyethyleneimine (PEI),

(4) Preparation of activated microspheres,

The polyamine-modified microspheres interact with platinum, palladium, and tin salts, and the salts are reduced to platinum, palladium, tin or mixed metal-loaded activated base spheres by a reducing agent.

(5) Preparation of conductive microspheres

(5.1) The electroless plating surface is plated with a thin metal layer, and the initial thickness of the conductive microspheres plated with copper, silver and nickel is 50 nanometers to 150 nanometers;

(5.2) Electroless metal plating thick layer or electric barrel plating metal thick layer, the thickness of the copper, silver, nickel or gold plated conductive microspheres is 80 nanometers to 150 nanometers.