WO2020093556A1 - Anisotropic conductive adhesive and conducting film thereof - Google Patents

Abstract

The present invention provides an anisotropic conductive adhesive and a conducting film thereof. The conductive adhesive uses a thermosetting acrylate system as a basis, and comprises an acrylate monomer, a radical initiator, a film-forming resin, a carboxyl or hydroxy containing rubber, a silane coupling agent, an anti-ageing agent, carbon nano tube modified polystyrene beads and a solvent. The present invention provides an anisotropic conductive adhesive having high reaction speed and short solidifying time.

Description

Anisotropic conductive adhesive and conductive film Technical field

The present invention relates to the field of semiconductor technology, and in particular, to a conductive adhesive and its conductive film for electrical connection between semiconductor electronic components.

Background technique

It is known that the development of semiconductor electronic components is becoming more and more miniaturized and refined. Correspondingly, the electrical connection between small-sized semiconductor devices also poses huge challenges for the conductive adhesive used to connect and conduct circuits.

Among them, it is not only required that the conductive adhesive has high adhesion and reliability, but also to accurately turn on the micro circuit, especially to realize the anisotropic conduction of the micro circuit, such as the vertical conduction of the upper and lower circuits, and the horizontal guarantee of insulation , That is, anisotropic conductive adhesive.

At the same time, in addition to improving the performance of the conductive adhesive itself, the application process must also be able to meet the requirements of the production process. The most important point is that the anisotropic conductive adhesive needs to cure in a very short time, usually less than 15s, to complete the bonding of the circuit board, thereby improving production efficiency and increasing output.

In this regard, the anisotropic conductive adhesives commonly used in the industry can be divided into two major categories from the main components: the first category is a system of thermosetting epoxy resin mixed with conductive gold balls; the second category is a thermosetting acrylic resin Mixed conductive gold ball system.

There are still many problems in the actual development and application of these two types of conductive adhesives, which are mainly summarized in the following aspects:

First, the curing time is too long, and the curing temperature is too high, these two problems are particularly prominent for the anisotropic conductive adhesive of the epoxy system;

Second, the bonding strength is not enough. It is not enough to just increase the degree of adhesion inside the glue. It is also necessary to consider how to increase the adhesion at the interface of the glued substrate;

Third, the conductive particles used are mainly gold balls, that is, the surface of the resin beads is coated with a layer of gold. On the one hand, the technology of gold plating is difficult, the process of producing gold balls is complicated, on the other hand, the price of gold balls is very high. Not conducive to reducing production costs.

Therefore, it is indeed necessary to develop a new type of anisotropic conductive adhesive to overcome the defects in the prior art.

technical problem

One aspect of the present invention is to provide an anisotropic conductive adhesive with a fast reaction speed and a short curing time.

Technical solution

The technical scheme adopted by the present invention is as follows:

An anisotropic conductive adhesive (ACF) based on a thermally cured acrylate system. The acrylate system includes the following components in mass ratio: 5% to 40% of acrylate monomer, 0.5 to 10% of free radical initiator, 5% to 40% of film-forming resin, 5% to 40 % Rubber with carboxyl group or hydroxyl group, 0.1 ~ 5% silane coupling agent, 0.1 ~ 5% anti-aging agent, 1% ~ 10% conductive ball and remaining solvent.

Further, in various embodiments, the acrylate monomers include methyl acrylate, methyl methacrylate, isobutyl acrylate, bisphenol A epoxy acrylate, ethyl acrylate, ethylene glycol diacrylate Combination of monofunctional groups, difunctional groups and multifunctional groups such as esters, trifluoroethyl methacrylate, ethoxy diethylene glycol acrylate, pentaerythritol tetraacrylate, pentaerythritol triacrylate, trimethylolpropane triacrylate, Wherein the monofunctional and bifunctional acrylate monomers account for the main part, and the multifunctional acrylate monomers are the accessory part to increase the degree of crosslinking.

Further, in various embodiments, the acrylate monomer includes one of methyl methacrylate, ethylene glycol diacrylate, and pentaerythritol triacrylate.

Further, in various embodiments, the conductive spheres include polystyrene beads modified with carbon nanotubes, the surface of which is uniformly coated with the carbon nanotubes. By adjusting the particle size of the polystyrene pellets, conductive pellets with different particle diameters can be prepared, which fully utilizes the conductivity of the carbon nanotubes, and at the same time greatly reduces the cost compared to the gold-plated pellets.

Further, in different embodiments, wherein the radical initiator includes an organic peroxide, the organic peroxide can exist stably under normal temperature and low temperature conditions below 60 ° C without decomposing into free radicals; and At 120 ℃ -150 ℃, it will quickly decompose into free radicals.

Further, in various embodiments, the peroxide includes methylcyclohexanone peroxide, dibenzoyl peroxide, t-butyl toluene peroxide, t-butyl peroxybenzoate, and laurel peroxide One of acyl and stearoyl peroxide. Among them, dibenzoyl peroxide and lauroyl peroxide are preferred, but not limited to.

Further, in various embodiments, the film-forming resin includes phenoxy resin, urea resin, polyimide resin, polyvinyl methylal, xylene resin, polyamide resin, polyester resin, and poly One of ethylene butyral, and the molecular weight of the selected resin is between 10,000 and 100,000.

Further, if the selected resin can contain more hydroxyl groups or carboxyl groups, it is more suitable, which is conducive to improving the adhesion of the adhesive; at the same time, the selected resin must have sufficient heat resistance, when the temperature changes, it has more Small volume change rate. Phenoxy resins with molecular weights between 20,000 and 60,000 are preferred here.

Further, in different embodiments, wherein the carboxyl / hydroxyl-containing rubber includes carboxyl / hydroxyl-containing acrylic rubber and / or carboxyl-terminal nitrile rubber, the performance parameter requirement is that the molecular weight is between 100000-1000000, Glass transition temperature Tg <0 ° C. Among them, the more hydroxyl group / carboxyl group content in the selected rubber is better, which is beneficial to increase the adhesion; in addition, the acid value can be preferentially selected according to the acid value> 10mgKOH / g rubber.

Further, in different embodiments, the ratio of the carboxyl group / hydroxyl group-containing rubber to the phenoxy resin in the film-forming resin is preferably 1: 1, but it is not limited thereto.

Further, in various embodiments, the silane coupling agent includes vinyl silane, amino silane, methacryloxy silane, A151 (vinyl triethoxy silane), A171 (vinyl trimethoxy) Silane), A172 (vinyl tri (β-methoxyethoxy) silane), 2,3 epoxypropyl propyl trimethoxy silane, amino functional group tri methoxy silane and (3-aminopropyl) tri One of ethoxysilane. Specifically, it is preferably (3-aminopropyl) triethoxysilane, but is not limited thereto.

Further, in various embodiments, the anti-aging stabilizer includes one of amines, phenols, sulfides, and phosphites. Specifically, an amine anti-aging agent is preferred, which may be N-phenyl-2-naphthylamine, but is not limited thereto.

Further, in different embodiments, wherein the solvent, the main selection principle is to have good solubility in the polymer resin and rubber used, which includes methyl ethyl ketone, n-butyl glycidyl ether, toluene and dichloromethane One of methane. Specifically, it is preferably an epoxy-containing n-butyl glycidyl ether, because it has an epoxy group, and the residual solvent can also react with the system to solidify.

Further, another aspect of the present invention is to provide a conductive film, which includes a release film. The anisotropic conductive adhesive according to the present invention is attached to the release film.

Further, another aspect of the present invention is to provide a method for preparing the conductive film according to the present invention, including the following steps:

The film-forming resin is dispersed into the solvent at a predetermined concentration, and then the silane coupling agent, anti-aging agent, rubber, and acrylate monomer are sequentially added at a predetermined ratio to perform the steps of mixing, stirring, and defoaming To get pre-mixed rubber material;

After the pre-mixed rubber material is cooled, a predetermined amount of the free radical initiator is added to perform the rubber-mixing, stirring and defoaming steps to obtain a medium-mixed rubber material;

Disperse the conductive balls in the medium-mixed rubber material at a predetermined ratio, and perform the steps of mixing, stirring and defoaming again to obtain a final mixed rubber material;

The final mixed rubber material is coated on a release film with a thickness of 10 to 100 um and dried, to obtain the anisotropic conductive film according to the present invention.

Further, in different embodiments, the material of the release film includes one of PET, PTFT, or a composite film material.

Further, in different embodiments, the coating method of the final mixed glue material includes one of film forming methods such as knife coating, spin coating, and screen printing.

Further, in different embodiments, the drying treatment method is to heat it at 50 to 100 ° C. for 3 min to 15 min, or use an infrared lamp drying process; the specific may be determined according to actual needs and is not limited.

Beneficial effect

The invention relates to an anisotropic conductive adhesive, which adopts free radical polymerized acrylate system, which has fast reaction speed and short curing time. Further, by incorporating carboxyl-terminated nitrile rubber and acrylic rubber into the acrylate system, the adhesive force at the bonding interface is increased, thereby greatly improving the bonding strength.

In addition, it uses small balls modified with carbon nanotubes on the surface to replace the existing conductive gold balls. While obtaining the same effect, it also greatly reduces its overall production cost.

BRIEF DESCRIPTION

In order to more clearly explain the technical solutions in the embodiments of the present invention, the drawings required in the description of the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present invention. For those skilled in the art, without paying any creative work, other drawings can be obtained based on these drawings.

FIG. 1 is a schematic layout diagram of a test structure for testing the conduction resistance and insulation resistance of an anisotropic conductive adhesive according to the present invention.

Embodiments of the invention

The technical solution of an anisotropic conductive adhesive and its conductive film according to the present invention will be described in further detail below with reference to the accompanying drawings and embodiments.

An embodiment of the present invention provides an anisotropic conductive adhesive, which is mainly based on a thermally cured acrylate system, which contains at least (A) acrylate monomer, (B) free radical initiator, (C) Film-forming resin, (D) rubber with carboxyl or hydroxyl groups, (E) silane-based coupling agent, (F) anti-aging agent, (G) carbon nanotube modified polystyrene beads, and (H ) Solvent.

Among them, as the (A) acrylate monomer, the added mass ratio is 5% to 40%. Specifically, methyl acrylate, methyl methacrylate, isobutyl acrylate, bisphenol A epoxy acrylate, ethyl acrylate, ethylene glycol diacrylate, trifluoroethyl methacrylate, ethoxy acrylate The combination of monofunctional groups, difunctional groups and multifunctional groups such as diethylene glycol esters, pentaerythritol tetraacrylate, pentaerythritol triacrylate, trimethylolpropane triacrylate, etc., where monofunctional and bifunctional acrylate monomers account for The main part, the multifunctional acrylate monomer accounts for a small part, which is used to increase the degree of crosslinking. Among them, one of methyl methacrylate, ethylene glycol diacrylate, and pentaerythritol triacrylate is preferred.

Among them, as the (B) free radical initiator, the mass ratio is 0.5 to 10%. The main choices are organic peroxides, such as methylcyclohexanone peroxide, dibenzoyl peroxide, t-butyl toluene peroxide, t-butyl peroxybenzoate, lauroyl peroxide, stearoyl peroxide and many more. The main selection principle is that the peroxide can exist stably under normal temperature and low temperature conditions, and will not decompose into free radicals, but will decompose into free radicals rapidly under high temperature (120 ℃ -150 ℃). Among them, one of dibenzoyl peroxide and lauroyl peroxide is preferably selected.

Among them, as the (C) film-forming resin, a mass ratio of 5% to 40% is added. Specifically, you can choose phenoxy resin, urea resin, polyimide resin, polyvinyl methylal, xylene resin, polyamide resin, polyester resin, polyethylene butyral. The molecular weight of these resins is preferably located at 10000 -100000. If the selected resin can contain more hydroxyl groups or carboxyl groups, it is more suitable, which is conducive to improving the adhesion of the adhesive; at the same time, the selected resin must have sufficient heat resistance and a small temperature change For volume change rate, phenoxy resin with molecular weight between 20,000 and 60,000 is preferred here.

Among them, as (D) rubber with carboxyl groups / hydroxyl groups, the mass ratio is 5% to 40%. Specifically, acrylic rubber with carboxyl groups / hydroxyl groups and / or nitrile rubber with carboxyl groups at the ends can be selected. The performance parameters are required to have a molecular weight between 100000-1000000 and a glass transition temperature Tg <0 ° C. Among them, the more hydroxy / carboxyl content in the selected rubber, the better, which is beneficial to increase the adhesion. According to the acid value, the acid value can be selected preferentially> 10mgKOH / g rubber. Further, the preferred ratio of the rubber with carboxyl groups / hydroxyl groups to the phenoxy resin is 1: 1.

Among them, as the (E) silane-based coupling agent, a mass ratio of 0.1 to 5% is added. Specifically, vinyl silane, amino silane, methacryloxy silane, A151 (vinyl triethoxy silane), A171 (vinyl trimethoxy silane), A172 (vinyl tri (β-methoxy) (Ethoxy) silane), 2,3 epoxypropylpropyl trimethoxysilane, amino functional trimethoxysilane, (3-aminopropyl) triethoxysilane, (3-aminopropyl) is preferred here ) Triethoxysilane.

Among them, as (F) anti-aging stabilizer, add a mass ratio of 0.1 to 5%. Specifically, amines, phenols, sulfides, phosphites, etc. can be selected, and amine anti-aging agents are preferred here. N-phenyl-2-naphthylamine is used in this patent.

Among them, as (G) carbon nanotube modified polystyrene beads, the mass ratio is 1% to 10%. Wherein, the surface of the polystyrene beads is uniformly coated with carbon nanotubes, and then by adjusting the particle size of the polystyrene beads, conductive beads with different particle diameters can be prepared, thereby making full use of the carbon nanotubes. Conductivity greatly reduces costs.

Among them, as the (H) solvent, it is the balance. The main selection principle is to have good solubility in the polymer resin and rubber used. Among them, methyl ethyl ketone, n-butyl glycidyl ether, toluene, and methylene chloride can be used. N-butyl glycidyl ether with epoxy groups is preferred here, because it has epoxy groups, and the residual solvent can also react with the system to solidify.

Further, another aspect of the present invention is to provide a conductive film, which includes a release film. The anisotropic conductive adhesive according to the present invention is attached to the release film.

Further, another embodiment of the present invention provides a method for preparing the conductive film according to the present invention, which includes the following steps:

Step1: Firstly disperse the selected predetermined amount of phenoxy resin in the solvent at a predetermined concentration, and then add the silane coupling agent, anti-aging agent, rubber and acrylate monomers in a predetermined ratio in order to mix the glue , Mixing and defoaming processes to obtain pre-mixed rubber materials; wait for the pre-mixed rubber materials to cool, then add the free radical initiator, intermittent, multiple times of mixing, stirring and de-foaming processes, for example, parameter settings It can be 2000 rpm, pressure adjusted to 30Kpa and time 1min, homogenization operation, after cooling, recirculation 3 times, control the homogenization temperature <40 ℃; and then the carbon nanotube modified polystyrene beads (CNT Ball) is dispersed in the mixed rubber material at a predetermined ratio, and the mixing, stirring and defoaming processes are performed again to ensure full mixing.

Step2: Apply the defoamed glue from step 1 on the 10 ~ 100um thick release film, and apply and dry it. The release film can be made of PET, PTFT or its composite film, and can be processed. The coating can be formed by scraping, spin coating, screen printing and other processes, and the drying can be heated at 50 ~ 100 ℃ for 3min ~ 15min, or using infrared lamp drying process.

Step3: Cut the large ACF film produced in step 2 to obtain ACF films of different widths, such as 1.2mm width, as required.

Further, the following will list different examples and their experimental results to further describe the performance of the anisotropic conductive adhesive according to the present invention.

Examples	1	2	3	4	5	6	7
Methyl methacrylate	18.5	18.5	18.5	18.5	18.5	18.5	18.5
Ethylene glycol dimethacrylate	18.5	18.5	18.5	18.5	18.5	18.5	18.5
Pentaerythritol triacrylate	5	5	5	5	5	5	5
Dibenzoyl peroxide	1.2	1.2	1.2	1.2	1.2	1.2	1.2
Lauroyl peroxide	0.4	0.4	0.4	0.4	0.4	0.4	0.4
Phenoxy resin	40	30	25	20	40	30	20
Carboxyl-terminated nitrile rubber	20	30	30	40	A	A	A
Acrylic rubber (containing carboxyl group)	A	A	A	A	20	30	40
Coupling agent	5	5	5	5	5	5	5
Anti-aging agent	2	2	2	2	2	2	2
N-butyl glycidyl ether	5ml / 1g resin or rubber	5ml / 1g resin or rubber	5ml / 1g resin or rubber	5ml / 1g resin or rubber	5ml / 1g resin	5ml / 1g resin	5ml / 1g resin
Conductive ball	3	3	3	3	3	3	3
Degree of epoxy curing	> 90%	> 90%	> 90%	> 90%	> 90%	> 90%	> 90%
Bonding strength (N / m)	100	1100	500	150	700	1200	900
On-resistance (ohm) -20 ℃, 100h	0.4	0.4	0.4	0.2	0.2	0.2	0.2
On-resistance (ohm) 85 ℃ / 85% RH, 500h	6.2	6.4	6.5	6.1	3.5	4.0	4.5
Insulation resistance (ohm)	> 105	> 105	> 105	> 105	> 105	> 105	> 105

Among them, the test method of the above-mentioned adhesive strength is that the anisotropic conductive adhesive film in each embodiment column in the above list is attached to the connection point of the PCBA circuit board, the conductive film length is 42mm, the width is 2mm, Press (pressure 0.3 Mpa, temperature 120 ℃, time 2s), tear off the release film (PET material), paste COF on it, and then pass this pressure (pressure 0.3 Mpa, temperature 180 ℃, time 10s) For sample preparation, use a tensile machine, perpendicular to the PCBA board, and pull the COF upward at 90 degrees to determine the bonding strength.

Among them, the above-mentioned test method for conducting impedance and insulation impedance is to adopt the layout structure as shown in FIG. 1, and stick the anisotropic conductive adhesive film in each embodiment column in the above list on it. Specifically, for the insulation resistance, the conductive glue is directly pasted, and the insulation resistance is tested by the four-probe method after the hot pressing process described above; and for the conduction resistance, it is necessary to stick ITO glass on the glue. Verify whether the upper and lower continuity, also use the four-probe method to test.

It can be seen from the above test results that for the phenoxy resin and nitrile rubber system, it can be seen that the ratio of the two has little effect on the electrical conductivity, but has a greater effect on the adhesion, and it can be concluded from the experimental results that the benzene When the ratio of oxygen resin to nitrile rubber is 1: 1, the adhesion reaches the medium maximum; and for phenoxy resin with acrylic rubber system, it can be seen that the ratio of the two has little effect on the electrical conductivity, but it has a greater effect on the adhesion Through the experimental results, it can be concluded that when the ratio of phenoxy resin and acrylic rubber is 1: 1, the adhesive force reaches the maximum.

Further, during the experiment, it was found that the phenoxy resin + nitrile rubber system has a hard texture, and the adhesion during pre-pressing is too weak, which is not conducive to the alignment of PCBA and COF, while the phenoxy resin + acrylic rubber system When slightly melted and softened, it has a certain adhesion, which is conducive to the alignment of PCBA and COF and achieves preliminary adhesion. From this aspect, the performance of acrylic rubber is better than that of nitrile rubber.

From the conductivity result, the resistance of the nitrile rubber system is higher than that of the acrylic rubber system. From this aspect, the performance of the acrylic rubber is better than that of the nitrile rubber. Furthermore, the selected carbon nanotube spheres have excellent conductivity, and the density can be controlled by choosing an appropriate ratio to achieve anisotropic conductivity, which has excellent reliability and can completely replace expensive gold spheres.

The technical scope of the present invention is not limited to the content in the above description. Those skilled in the art can make various modifications and modifications to the above embodiments without departing from the technical idea of the present invention, and these modifications and modifications should belong to Within the scope of the invention.

Claims (10)

1. An anisotropic conductive adhesive based on a heat-cured acrylate system; wherein the acrylate system includes the following components in mass ratio:

   5% ~ 40% acrylate monomer;

   0.5 ~ 10% free radical initiator;

   5% ~ 40% film-forming resin;

   5% ~ 40% rubber with carboxyl group or hydroxyl group;

   0.1 ~ 5% silane coupling agent;

   0.1 ~ 5% anti-aging agent;

   1% ~ 10% conductive ball; and

   Remaining solvent;

   The acrylate monomers include methyl acrylate, methyl methacrylate, isobutyl acrylate, bisphenol A epoxy acrylate, ethyl acrylate, ethylene glycol diacrylate, trifluoroethyl methacrylate , Ethoxy diethylene glycol acrylate, pentaerythritol tetraacrylate, pentaerythritol triacrylate and trimethylolpropane triacrylate and other monofunctional groups, bifunctional groups and a combination of multifunctional groups, wherein the monofunctional and bifunctional groups The acrylate monomer accounts for the main part, and the multifunctional acrylate monomer is an auxiliary part for increasing the degree of crosslinking.
2.  The anisotropic conductive adhesive according to claim 1, wherein the acrylate monomer includes at least one of methyl methacrylate, ethylene glycol diacrylate, and pentaerythritol triacrylate.
3.  The anisotropic conductive adhesive according to claim 1, wherein the conductive ball comprises polystyrene beads modified with carbon nanotubes, and the surface thereof is uniformly coated with the carbon nanotubes.
4.  An anisotropic conductive adhesive according to claim 1, wherein the radical initiator includes methylcyclohexanone peroxide, dibenzoyl peroxide, tert-butyl toluene peroxide, peroxide One of tert-butyl benzoate, lauroyl peroxide and stearoyl peroxide.
5.  An anisotropic conductive adhesive according to claim 1, wherein the film-forming resin comprises phenoxy resin, urea resin, polyimide resin, polyvinyl methylal, xylene resin, poly One of amide resin, polyester resin and polyethylene butyral, and the molecular weight of the selected resin is between 10,000 and 100,000.
6.  An anisotropic conductive adhesive according to claim 1, wherein the rubber with carboxyl / hydroxyl groups includes acrylic rubber with carboxyl / hydroxyl groups and / or nitrile rubber with carboxyl end groups, wherein the required performance parameters Including molecular weight between 100000-1000000, glass transition temperature Tg <0 ℃ and acid value > 10mgKOH / g.
7.  An anisotropic conductive adhesive according to claim 1, wherein the silane-based coupling agent includes vinyl silane, amino silane, methacryloxy silane, A151 (vinyl triethoxy silane ), A171 (vinyl trimethoxysilane), A172 (vinyl tri (β-methoxyethoxy) silane), 2,3 epoxypropylpropyl trimethoxysilane, amino functional trimethoxysilane and One of (3-aminopropyl) triethoxysilane.
8.  An anisotropic conductive adhesive according to claim 1, wherein the anti-aging stabilizer includes an anti-aging agent among amines, phenols, sulfides and phosphites.
9.  An anisotropic conductive adhesive according to claim 1, wherein the solvent includes one of methyl ethyl ketone, n-butyl glycidyl ether, toluene and methylene chloride.
10.  A conductive film comprising a release film, wherein the anisotropic conductive adhesive according to claim 1 is attached to the release film.