CN114752332B

CN114752332B - Wide-temperature-zone anisotropic conductive adhesive based on liquid metal and preparation method thereof

Info

Publication number: CN114752332B
Application number: CN202210364699.4A
Authority: CN
Inventors: 刘娜娜; 任龙; 杜轶; 孙洁
Original assignee: Ningbo Xihan Technology Co ltd
Current assignee: Ningbo Xihan Technology Co ltd
Priority date: 2022-04-08
Filing date: 2022-04-08
Publication date: 2023-07-14
Anticipated expiration: 2042-04-08
Also published as: CN114752332A

Abstract

The invention relates to a wide-temperature-range anisotropic conductive adhesive based on liquid metal, which comprises the following raw materials: the modified PS microsphere comprises base material resin and conductive filler, wherein the conductive filler is prepared by coating modified liquid metal on the surface of the modified PS microsphere, and a modifier of the modified liquid metal comprises a surfactant and/or a sulfur-containing compound; the modified PS microsphere has a core-shell structure with PS as a core and a polymer of an unsaturated thiourea compound as a shell. The conductive filler is prepared by coating modified liquid metal on the surface of the modified PS microsphere, and the surface of the modified liquid metal is provided with a layer of oxide film and a layer of modifier film, so that the modified liquid metal has lower melting point and better wettability, and the conductive filler is more uniformly dispersed in the base material resin; the modified PS microsphere is a hard core-soft shell structure which takes PS as a core and takes a polymer of an unsaturated thiourea compound as a shell, and the microsphere still maintains good toughness at low temperature, is not easy to crack or collapse under stress, so that the conductive adhesive can be applied at wider temperature.

Description

Wide-temperature-zone anisotropic conductive adhesive based on liquid metal and preparation method thereof

Technical Field

The invention belongs to the technical field of conductive adhesive, and particularly relates to a wide-temperature-range anisotropic conductive adhesive based on liquid metal and a preparation method thereof.

Background

With the innovation and development of the electronic industry, anisotropic Conductive Adhesives (ACAs) are favored by people due to their better creep resistance and low-temperature processability, and are widely applied in the fields of electronic components, optical devices, flexible printing, displays and the like. Anisotropic Conductive Adhesives (ACAs) are a type of microelectronic interconnect material that is electrically conductive only in the vertical direction and insulating in the horizontal direction under pressure or heat, and comprise a polymer composite material that contains a uniformly dispersed conductive material. The conductive material plays a role in providing carriers, and the content, the dispersion state and the property characteristics of the conductive material determine the electrical properties of the material; the high molecular polymer provides the material with processability, strength, heat resistance, adhesion, compression resistance, etc., which also indirectly have an effect on electrical properties.

The conventional conductive materials are solid metal gold, silver and copper, which are gradually replaced by liquid metal due to the disadvantages of high cost and incomplete flexible packaging, for example, patent CN201910103418.8 discloses a preparation method of anisotropic conductive adhesive based on liquid metal, wherein the anisotropic conductive adhesive prepared by combining low-melting-point liquid metal and adhesive is easy to process and form, has good conductive anisotropy and excellent adhesion, and the preparation method comprises the following steps: (1) preparing liquid metal anisotropic conductive adhesive: dispersing liquid metal in the adhesive to obtain a mixture of liquid metal particles and the adhesive, removing bubbles, and storing for later use; (2) a using method of the liquid metal anisotropic conductive adhesive: and coating the mixture of the liquid metal particles with bubbles removed and the adhesive on a matrix, and then placing the other matrix on the mixture, and curing and forming to obtain the liquid metal conductive adhesive. The patent CN201810907262.4 discloses a ready-to-use middle-low temperature curing liquid metal conductive adhesive and a preparation method thereof, wherein the conductive adhesive comprises liquid metal, matrix resin, a curing agent, a diluent and a functional additive, and the functional additive is one or more of an accelerator, a coupling agent and a defoaming agent; the liquid metal is one of gallium-based alloy, bismuth-based alloy, indium-based alloy or tin-based alloy, and the liquid metal is liquid at the temperature of 5-232 ℃. The technology utilizes the free deformability of the liquid metal flowing according to the need under the influence of an external field or force to realize flexible contact, but the liquid metal has higher surface tension and lower viscosity, if enough conductive performance is obtained, enough pressure needs to be applied during solidification to increase the contact area between the liquid metal and a conductive electrode, and the liquid metal is not provided with a supporting framework, so that the liquid metal can be deformed severely due to the application of larger pressure, the conductive adhesive is conducted transversely, even the liquid metal is separated out from the conductive adhesive system, and the conductive adhesive loses or loses the conductive function.

Patent CN201910540529.5 discloses an anisotropic conductive adhesive based on particle matrix coated with liquid metal and a preparation method thereof, wherein the liquid metal is coated on the surface of the particle matrix to form a core-shell structure with the particle matrix as a core and the liquid metal coating as a shell, a conductive filler with the surface coated with the liquid metal is mixed into an adhesive by a mechanical stirring method, and the obtained mixture of the liquid metal coating particles and the adhesive is subjected to bubble removal and stored for standby; and coating the mixture of the bubble-removed liquid metal coating particles and the adhesive on the surface of the substrate with the electrode, and placing the other substrate with the electrode on the mixture to form a sandwich structure. The technology is to coat liquid metal on the organic particles to strengthen the strength of the liquid metal, so that the liquid metal cannot be transversely conducted due to severe deformation caused by stress, or the conductive adhesive is separated out to lose or lose the conductive function. The problems of high surface tension and poor wettability of polymer particles exist in the liquid metal, the low Wen Shouli is easy to fall off from the surfaces of the particles, the low-temperature polymer particles are brittle and easy to crack under stress, the maximum contact between the liquid metal and an electrode can not be realized, the problems of transverse conduction or precipitation still exist, and the reliability of the conductive adhesive is seriously reduced. In summary, there is a need to develop a liquid metal conductive paste that can be flexibly packaged and has good reliability at low temperature.

Disclosure of Invention

In order to solve the technical problems, the invention provides the wide-temperature-range anisotropic conductive adhesive based on the liquid metal and the preparation method thereof, wherein the conductive filler is a microsphere coated with the modified liquid metal, the surface of the modified liquid metal is provided with a layer of oxide film and a layer of modifier film, the oxide film can enable the liquid metal to have extremely small particle size under ultrasound, the modifier enables the liquid metal with small particle size not to be easily aggregated into large liquid drops, the melting point of the surface modified liquid metal is lower, the surface modified liquid metal still has fluidity at lower temperature, and meanwhile, the wettability of the surface modified liquid metal is better, so that the conductive filler is dispersed in the base material resin more uniformly; the modified PS microsphere has a hard core-soft shell core-shell structure with PS as a core and an unsaturated thiourea compound as a shell, has good compatibility with modified liquid metal, still keeps good toughness at low temperature, is difficult to crack or collapse under stress, and ensures that the conductive adhesive is applicable to wider temperature.

In order to achieve the above object, the following scheme is adopted:

an anisotropic conductive adhesive based on a wide temperature range of liquid metal, wherein the conductive adhesive comprises the following raw materials: the conductive filler is prepared by coating modified liquid metal on the surface of modified PS microspheres, wherein a modifier of the modified liquid metal comprises a surfactant and/or a sulfur-containing compound; the modified PS microsphere has a core-shell structure with PS as a core and a polymer of an unsaturated thiourea compound as a shell.

Further, the conductive adhesive comprises the following raw materials in parts by weight: 100 parts of base material resin and 15-25 parts of conductive filler, wherein the mass ratio of the modified PS microspheres to the modified liquid metal in the conductive filler is 100:3-6.

Further, in the modified liquid metal, the modifier is used in an amount of 13-17wt% of the liquid metal.

The sulfur-containing compound is at least one selected from ethyl 3-mercaptopropionate, (methylthio) ethyl acetate, methyl 4-mercaptobutyrate, methyl 3-methylthiopropionate, ethyl 2-mercaptopropionate, isopropyl thioglycolate and methyl 2- (methylthio) propionate; the surfactant is at least one selected from carboxylate surfactant, sulfate surfactant, sulfonate surfactant, phosphate surfactant and alcohol ether surfactant; preferably, the surfactant is an alcohol ether surfactant, and specifically is at least one selected from fatty alcohol polyoxyethylene ether (AEO), n-decyl alcohol polyoxyethylene ether, polyoxyethylene glyceryl ether, polyoxyethylene lauryl ether and polyoxyethylene stearyl ether.

The dispersion medium of the modifier is low-carbon alcohol; the low-carbon alcohol is at least one selected from methanol, ethanol, propanol, butanol, isobutanol and n-pentanol. The low carbon alcohol is used as a dispersing agent, so that the modifier can uniformly coat the liquid metal to form smaller liquid drops.

Preferably, the modifier is an alcohol ether surfactant and a sulfur-containing compound according to the mass ratio of 1:3-7. The dosage of the low-carbon alcohol of the dispersion medium is 10-20 times of the mass of the modifier.

The liquid metal is an alloy of gallium and other metals, and the other metals are at least one of indium, tin, zinc, bismuth, lead, magnesium, aluminum, iron, manganese, titanium and vanadium; the alloy has a gallium content of 50-70wt%.

The particle size of the modified liquid metal is 50-110nm.

The particle size of the modified PS microsphere is 1-5 mu m.

The modified PS microsphere is of a hard core-soft shell core-shell structure which is prepared by seed emulsion polymerization and takes polystyrene as a core and takes a polymer of an unsaturated thiourea compound as a shell, and the weight ratio of a styrene monomer to the unsaturated thiourea compound is 1:1-1.25; preferably, the unsaturated thiourea compound is at least one selected from allyl thiourea, 1-methallyl-3-methyl-2-thiourea, 4-propenyl thiocarbamide and N-allyl-N' -2-hydroxyethyl thiourea.

The modified PS microsphere is prepared by a method comprising the following steps:

1) Adding styrene, water and ethanol into a reaction kettle under the nitrogen atmosphere to obtain a mixture, stirring the mixture to be uniform, heating the mixture and keeping the temperature constant, dropwise adding an aqueous solution of an initiator to perform polymerization reaction, and naturally cooling the mixture to room temperature after the reaction is finished to obtain PS seed microsphere emulsion for later use;

2) And heating the PS seed microsphere emulsion in a nitrogen atmosphere, keeping the temperature, adding an unsaturated thiourea compound and an initiator, stirring uniformly, carrying out constant-temperature polymerization reaction, naturally cooling to room temperature after the reaction is finished, carrying out suction filtration by using a microporous filter membrane, washing until the conductivity is not changed, and carrying out vacuum drying to obtain the modified PS microsphere.

The concentration of styrene in the mixture in the step 1) is 0.7-0.9mol/L, the volume ratio of water to ethanol is 6-9:1, the initiator is commonly used in the field and comprises at least one of potassium persulfate, sodium persulfate and ammonium persulfate, the dosage of the initiator is 0.05-0.18wt% of styrene, the concentration of an aqueous solution of the initiator is 15-30wt%, the temperature is raised to 60-90 ℃, and the polymerization time is 12-36h;

the initiator in the step 2) comprises but is not limited to azodiisobutyronitrile, the temperature is raised to 60-90 ℃, the addition amount of the initiator is 0.2-0.5wt% of unsaturated thiourea compounds, the constant temperature polymerization reaction time is 10-24h, the microporous filter membrane is firstly subjected to suction filtration by a filter membrane with the thickness of 1-10 mu m, the filtrate is reserved, then subjected to suction filtration by a filter membrane with the thickness of 1-5 mu m, the filter residue is reserved, and the vacuum drying temperature is 50-80 ℃.

The conductive filler is prepared by a method comprising the following steps:

s1, heating a reactor containing gallium in a water bath under an inert atmosphere, keeping the temperature constant until the gallium is completely changed into a liquid state, continuously keeping the temperature constant, adding other metals, stirring until the gallium is completely melted into the liquid state, and naturally cooling to room temperature for later use;

s2, adding the mixture obtained in the step S1 into a reaction tank provided with an aeration device, and performing aeration treatment;

s3, adding the mixture obtained in the step S2 into an ultrasonic device containing a modifier for ultrasonic treatment to obtain modified liquid metal;

s4, adding modified PS microspheres into the modified liquid metal in the step S3, and performing ultrasonic treatment to obtain the conductive filler.

The heating in the step S1 is heating to the melting point of gallium;

the aeration device in the step S2 is not particularly limited, and a common bubble type aeration device is adopted, wherein the aeration treatment is continuous aeration, and the aeration time is 20-45min;

the ultrasonic frequency in the step S3 is 40-100KHZ, and the ultrasonic time is 1-3h;

and step S4, the ultrasonic frequency is 30-70KHZ, and the ultrasonic time is 20-50min.

The type of the base resin comprises thermosetting resin or thermoplastic resin, and specifically at least one of epoxy resins, epoxy acrylates, polyesters, polyurethanes, phenolic resins and polyacrylic acids.

Preferably, the base resin is an epoxy resin, more preferably the base resin comprises 100 parts bisphenol a epoxy resin, 3-10 parts latent curing agent, 1-3 parts curing accelerator, 10-15 parts non-reactive diluent.

The bisphenol A type epoxy resin is at least one selected from E-51, E-44 and E-42.

The latent curing agent comprises at least one of imidazole derivatives and dicyandiamide compounds, and is specifically selected from at least one of dicyandiamide, 2-methylimidazole and 2-ethyl-4-methylimidazole; the curing accelerator is at least one selected from triethylamine and triethanolamine; the non-reactive diluent is at least one selected from acetone, cyclohexanone, n-butanol, dibutyl phthalate and dioctyl phthalate.

A preparation method of anisotropic conductive adhesive based on liquid metal wide temperature range comprises the following steps:

and uniformly mixing the base material resin and the conductive filler to obtain the anisotropic conductive adhesive.

An application of anisotropic conductive adhesive based on liquid metal wide temperature range comprises the following steps: the anisotropic conductive adhesive is coated with a film having a thickness of 2 to 100 μm, preferably 70 to 100 μm, and cured under hot press conditions.

Compared with the prior art, the invention has the beneficial effects that:

the conductive filler is prepared by coating modified liquid metal on the surface of the modified PS microsphere, wherein the surface of the modified liquid metal is provided with a layer of oxide film and a layer of modifier film, the oxide film can enable the liquid metal to have extremely small particle size under ultrasonic, and the modifier enables the liquid metal with small particle size not to be easily aggregated into large liquid drops; the modified PS microsphere has a hard core-soft shell core-shell structure with PS as a core and a polymer of an unsaturated thiourea compound as a shell, has good compatibility with modified liquid metal, still keeps good toughness at low temperature, is difficult to crack or collapse under stress, and ensures that the conductive adhesive is applicable to wider temperature.

Drawings

FIG. 1 is a TEM image of the modified liquid metal prepared in step S3 of preparation example A1;

fig. 2 is an SEM image of the modified liquid metal prepared in step S3 of preparation example A1.

Detailed Description

The invention is further illustrated below in connection with specific examples, but is not limited to the disclosure. Unless otherwise specified, "parts" are parts by weight in the examples of the present invention. All reagents used are those commercially available in the art.

Preparation of modified PS microspheres

Preparation example B1

1) Adding 100 parts of styrene into a reaction kettle containing water and ethanol mixed solution prepared according to the volume ratio of 9:1 in a nitrogen atmosphere, stirring uniformly, preparing styrene dispersion liquid with the concentration of 0.85mol/L, heating to 75 ℃, keeping the temperature constant, dropwise adding initiator solution with the concentration of 15wt% dissolved with 0.18 part of ammonium persulfate for polymerization reaction for 12 hours, and naturally cooling to room temperature after the reaction is finished to obtain PS seed microsphere emulsion for later use;

2) Heating the PS seed microsphere emulsion to 80 ℃ under nitrogen atmosphere and keeping the temperature, adding 100 parts of allylthiourea and 0.5 part of azodiisobutyronitrile, stirring uniformly, performing constant-temperature polymerization reaction for 20 hours, naturally cooling to room temperature after the reaction is finished, performing suction filtration by using a5 mu m microporous filter membrane, retaining filtrate, performing suction filtration by using a2 mu m filter membrane, retaining filter residues, washing with deionized water until the conductivity is not changed, and performing vacuum drying at 50 ℃ to obtain the modified PS microsphere.

Preparation example B2

The remainder was the same as in preparation example B1 except that the amount of allylthiourea used in step 2) was 125 parts.

Comparative preparation B1

The remainder was the same as in preparation example B1 except that 100 parts of the styrene monomer in step 1) was replaced with 100 parts of allylthiourea.

Comparative preparation B2

The remainder was the same as in preparation example B1 except that 100 parts of allylthiourea was replaced with 100 parts of styrene monomer in step 2).

Preparation of conductive filler

Preparation example A1

S1, heating a reactor containing 70 parts of gallium to the melting point of gallium in a water bath under an inert atmosphere, keeping the temperature until the gallium is completely liquid, adding 19 parts of indium and 11 parts of tin, stirring until the gallium is completely melted into liquid, and naturally cooling to room temperature for later use;

s2, adding the mixture obtained in the step S1 into a reaction tank provided with a bubble type aeration device, and continuously aerating for 30min;

s3, adding the mixture obtained in the step S2 into a dispersion liquid containing 170 parts of modifier, wherein the modifier in the dispersion liquid is 17 parts, the modifier is formed by mixing polyoxyethylene glyceryl ether and 3-mercaptopropionic acid ethyl ester according to the weight ratio of 1:7, the dispersion medium is ethanol, and carrying out 80KHZ ultrasonic treatment on the mixture for 3 hours to obtain modified liquid metal;

s4, adding the modified PS microspheres prepared in the preparation example B1 into the modified liquid metal in the step S3, and performing ultrasonic treatment at 40KHZ for 30min to obtain the conductive filler.

Preparation example A2

The rest is the same as preparation A1, except that the modifier is mixed by polyoxyethylene glyceryl ether and 3-mercaptopropionic acid ethyl ester according to the weight ratio of 1:3.

Preparation example A3

The remainder was the same as in preparation A1 except that the modifier was ethyl 3-mercaptopropionate in its entirety.

Preparation example A4

The other components are the same as in preparation A1 except that all the modifiers are polyoxyethylene glyceryl ether.

Preparation example A5

The remainder was the same as in preparation A1 except that the amount of the modifier was 13 parts.

Preparation example A6

The remainder was the same as in preparation A1 except that the aeration treatment in step S2 was not performed.

Preparation example A7

The remainder was the same as in preparation A1, except that the modified PS microspheres were prepared in preparation B2.

Comparative preparation A1

The remainder was the same as in preparation A1, except that modified PS microspheres were prepared in comparative preparation B1.

Comparative preparation A2

The remainder was the same as in preparation A1, except that the modified PS microspheres were prepared in comparative preparation B2.

Preparation of conductive adhesive

Examples 1 to 7, comparative examples 1 to 2

Taking 100 parts of base resin and 25 parts of preparation examples A1-7, and uniformly mixing the conductive fillers correspondingly prepared in comparative preparation examples A1-2 to obtain conductive adhesive, wherein the base resin is prepared by mixing the following components in parts by weight:

100 parts of bisphenol A type epoxy resin, 3-10 parts of latent curing agent, 1-3 parts of curing accelerator and 10-15 parts of non-reactive diluent.

Example 8

The rest was the same as in example 1, except that the amount of the conductive filler prepared in preparation example A1 was 15 parts.

Application examples and comparative application examples

The conductive pastes prepared in the above examples and comparative examples were coated with 80 μm film thickness, and pre-cured: heating to 100deg.C, hot pressing for 15s, and solidifying under 1.5MPa; and (3) secondary curing at 120 ℃ for 3 hours.

Conducting resin prepared by the application example and the comparative application example is respectively subjected to the following performance tests at-20 ℃ and room temperature:

conductive properties: the device is Beijing Dahua electronic DH1790-5 DC POWER SUPPLY, and EPS4 and Ji Shili 2400 Sourcemeter of Puxi industry Co., ltd, respectively testing the z-direction resistance and the x-y-direction resistance of the non-bending conductive adhesive, and the z-direction resistance and the x-y-direction resistance of the conductive adhesive when bending 135 degrees; the test of conductivity mainly adopts a four-probe test method, wherein 4 probes are connected to the surface of conductive adhesive, a proper small current of 150mA is provided for two probes at the outer side by a constant current source, then the voltage between the two probes at the middle is measured, the resistance of the conductive adhesive is obtained according to ohm law, different positions are found on the conductive adhesive, the test is carried out for 3 times, and the average value is obtained.

TABLE 1

From the above-listed conductive property test results, it can be seen that the conductive paste containing the conductive filler prepared by coating the modified liquid metal on the surface of the modified PS microsphere according to the present invention is applicable to a wider temperature range.

The foregoing detailed description is directed to one of the possible embodiments of the present invention, which is not intended to limit the scope of the invention, but is to be accorded the full scope of all such equivalents and modifications so as not to depart from the scope of the invention.

Claims

1. An anisotropic conductive adhesive based on a wide temperature range of liquid metal, wherein the conductive adhesive comprises the following raw materials: 100 parts of base material resin and 15-25 parts of conductive filler, wherein the conductive filler is prepared by coating modified liquid metal on the surface of modified PS microspheres, and the modifier of the modified liquid metal comprises a surfactant and/or a sulfur-containing compound; the modified PS microsphere has a core-shell structure with PS as a core and a polymer of an unsaturated thiourea compound as a shell; in the conductive filler, the mass ratio of the modified PS microspheres to the modified liquid metal is 100:3-6, and in the preparation raw materials of the modified PS microspheres, the weight ratio of the styrene monomer to the unsaturated thiourea compound is 1:1-1.25; the sulfur-containing compound is at least one selected from ethyl 3-mercaptopropionate, ethyl methylthioacetate, methyl 4-mercaptobutyrate, methyl 3-methylthiopropionate, ethyl 2-mercaptopropionate, isopropyl thioglycolate and methyl 2- (methylthio) propionate; the surfactant is selected from alcohol ether surfactants.

2. The wide temperature range anisotropic conductive adhesive based on liquid metal according to claim 1, wherein the particle size of the modified liquid metal is 50-110nm, and the modifier is used in an amount of 13-17wt% of the liquid metal; the particle size of the modified PS microsphere is 1-5 mu m.

3. The wide temperature range anisotropic conductive adhesive based on liquid metal as claimed in claim 1, wherein the surfactant is an alcohol ether surfactant selected from at least one of fatty alcohol polyoxyethylene ether and polyoxyethylene glyceryl ether; the unsaturated thiourea compound is at least one selected from allyl thiourea, 1-methallyl-3-methyl-2-thiourea, 4-propenyl thiocarbamide and N-allyl-N' -2-hydroxyethyl thiourea.

4. The wide temperature range anisotropic conductive adhesive based on liquid metal according to claim 3, wherein the fatty alcohol-polyoxyethylene ether is at least one selected from polyoxyethylene lauryl ether and polyoxyethylene stearyl ether.

5. The wide temperature range anisotropic conductive adhesive based on liquid metal as claimed in claim 3, wherein the modifier is an alcohol ether surfactant and a sulfur-containing compound according to a mass ratio of 1:3-7.

6. The wide temperature range anisotropic conductive paste according to claim 1, wherein the liquid metal is an alloy of gallium and other metals selected from at least one of indium, tin, zinc, bismuth, lead, magnesium, aluminum, iron, manganese, titanium, vanadium; the alloy has a gallium content of 50-70wt%.

7. The liquid metal wide temperature range based anisotropic conductive paste according to claim 1, wherein the modified PS microspheres are prepared by a method comprising the steps of:

8. The wide temperature range anisotropic conductive paste according to claim 1, wherein the conductive filler is prepared by a method comprising the steps of:

9. The method for preparing the wide temperature range anisotropic conductive adhesive based on the liquid metal as claimed in any one of claims 1 to 8, comprising the following steps:

10. The method for using the wide temperature range anisotropic conductive adhesive based on liquid metal according to any one of claims 1 to 8, comprising the following steps: and (3) coating the anisotropic conductive adhesive, wherein the film thickness is 2-100 mu m, and curing under the hot-pressing condition.

11. Use according to claim 10, characterized in that the film thickness is 70-100 μm.