Conductive adhesive and preparation method thereof

Abstract

The invention discloses a low-temperature conductive adhesive which is prepared from the following raw materials in parts by weight: 70-80 parts of silver powder, 20-30 parts of a resin matrix, 1-10 parts of a curing agent, 0.1-0.5 part of a silane coupling agent, 0.1-0.5 part of a stabilizer and 0.1-0.5 part of metal salt. The organic metal salt is introduced into the resin matrix, so that the contact resistance of the colloid can be reduced, and a relatively low contact resistance increasing rate can be maintained after damp-heat aging. The composition of the epoxy resin, the acrylate and the modified epoxy acrylic resin is adopted, the sum of the weight of the epoxy resin and the acrylate is smaller than or equal to the weight of the modified epoxy acrylic resin, and low-temperature curing can be achieved. The conductive adhesive can be cured for 20-40 minutes at the temperature of 60-80 DEG C, the elongation at break of the obtained conductive adhesive can reach 8% or above, and the conductive adhesive has relatively stable and relatively small contact resistance before and after damp-heat aging, and is particularly suitable for the field of electronics with relatively high requirements on contact resistance.

Description

Technical Field

[0001] The present invention relates to the field of adhesives, and particularly to a low-temperature conductive adhesive and a preparation method thereof. Background Art

[0002] With the development of science and technology, electronic chips are more and more widely used. The colloid applied to electronic chips needs to have high conductivity. And with the wide application of electronic chips, the use in high-temperature and high-humidity environments puts forward higher requirements for the aging performance and conductive performance of electronic adhesives. The existing conductive adhesives have a large contact resistance, and after damp-heat aging, the resistivity will also increase significantly. Therefore, it is crucial to develop a conductive adhesive with good conductivity and resistance to damp-heat aging.

[0003] Chinese invention patent CN104356970A discloses a UV-curable conductive adhesive with high conductivity. A small amount of spherical nano-silver powder is used to fill the gaps between flaky nano-silver powders, so that the originally non-contact adjacent flaky nano-silver powders are in contact with each other, increasing the conductive path and reducing the volume resistivity of the conductive adhesive system. However, there are still gaps in the colloid and the resistivity is relatively high. Chinese invention patent CN119505176A discloses a modified epoxy acrylate, a preparation method thereof, a conductive adhesive, a preparation method thereof and an application. The modified epoxy acrylate adopted has a long-chain structure, so that the cured modified epoxy acrylate can have excellent flexibility. The prepared conductive adhesive has excellent properties such as low-temperature curing, flexibility, damp-heat resistance, high bonding strength, good conductive performance, and low stress. However, the temperature and humidity resistance to damp-heat still cannot meet the requirements. Summary of the Invention

[0004] In order to develop a conductive adhesive with good conductivity and resistance to damp-heat aging, the first aspect of the present invention provides a low-temperature conductive adhesive. The preparation raw materials in parts by weight include 70-80 parts of silver powder, 20-30 parts of resin matrix, 1-10 parts of curing agent, 0.1-0.5 part of silane coupling agent, 0.1-0.5 part of stabilizer, and 0.1-0.5 part of metal salt, and the metal salt is an organometallic salt.

[0005] As an implementation manner, the resin matrix includes modified epoxy acrylate resin, acrylate and epoxy resin; the sum of the weights of the acrylate and epoxy resin ≤ the weight of the modified epoxy acrylate resin.

[0006] During the experiment, the inventor found that by using a combination of epoxy resin, acrylate, and modified epoxy acrylate, and when the sum of the weights of the epoxy resin and acrylate is ≤ the weight of the modified epoxy acrylate, a low-temperature conductive adhesive can be obtained, which can achieve low-temperature curing and has a stable and small contact resistance before and after damp heat aging. The possible reason is speculated as follows: At the preferred weight ratio, grafting of epoxy and acrylate can be achieved, and the cross-linked network of the formed colloid has a low contact resistance. When the epoxy resin exceeds the preferred weight ratio, the contact resistance increases and the conductivity decreases after damp heat aging.

[0007] As an embodiment, the silver powder includes flaky silver powder and spherical silver powder. The D50 particle size of the flaky silver powder is 1 - 10 μm, and the D50 particle size of the spherical silver powder is 500 - 900 nm.

[0008] As an embodiment, the D50 particle size of the spherical silver powder is 800 nm.

[0009] As an embodiment, the flaky silver powder includes flaky silver powder I with a D50 particle size of 5 - 10 μm and flaky silver powder II with a D50 particle size of 1 - 3 μm.

[0010] As an embodiment, the silver powder is a combination of flaky silver powder I with a D50 particle size of 5 - 10 μm, flaky silver powder II with a D50 particle size of 1 - 3 μm, and spherical silver powder with a D50 particle size of 800 nm.

[0011] As an embodiment, the weight ratio of flaky silver powder I with a D50 particle size of 5 - 10 μm, flaky silver powder II with a D50 particle size of 1 - 3 μm, and spherical silver powder with a D50 particle size of 800 nm is (60 - 70):(5 - 15):(1 - 10).

[0012] As an embodiment, the weight ratio of flaky silver powder I with a D50 particle size of 5 - 10 μm, flaky silver powder II with a D50 particle size of 1 - 3 μm, and spherical silver powder with a D50 particle size of 800 nm is 65:10:5.

[0013] This application uses a combination of flaky silver powder with a D50 particle size of 5 - 10 μm, silver micro-powder with a D50 particle size of 1 - 3 μm, and spherical silver powder with a D50 particle size of 800 nm, which can further improve the conductivity of the low-temperature conductive adhesive. The reason is that the lap joint of the flaky silver powder and the spherical silver powder can reduce the contact resistance of the low-temperature conductive adhesive, and adding silver micro-powder with a small particle size can fill the gaps between the flaky silver powder and the spherical silver powder, reducing the increase in resistance caused by air pores and further improving the conductive effect.

[0014] As an implementation manner, the organometallic salt includes at least one of potassium acrylate, zinc acrylate, calcium acrylate, (meth)acrylate potassium salt, (meth)acrylate zinc salt or (meth)acrylate calcium salt.

[0015] As an implementation manner, the functionality of the organometallic salt is 2.

[0016] During the experiment, the inventors found that introducing an organometallic salt into the resin matrix can reduce the contact resistance of the colloid, and maintain a low contact resistance increase rate after damp heat aging. The reason may be that the organometallic salt can have a coupling effect with the resin matrix, and the organic molecular structure can react chemically with the resin matrix. On the basis of reducing the contact resistance, the stability of the structure is maintained, and it is not easily degraded under damp heat aging conditions, and the contact resistance does not change significantly.

[0017] As an implementation manner, the silane coupling agent is an amino-containing silane coupling agent, and the amino-containing silane coupling agent includes at least one of γ-glycidoxypropyltrimethoxysilane, secondary amino silane coupling agent, ureidopropyltrimethoxysilane, bis(γ-trimethoxysilylpropyl)amine or N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane.

[0018] As an implementation manner, the amino-containing silane coupling agent is γ-glycidoxypropyltrimethoxysilane.

[0019] As an implementation manner, the models of the amino-containing silane coupling agent include at least one of Momentive Y-9669, A-Link15, A-1524 CF, A-1120J or A-1170.

[0020] As an implementation manner, the curing agent includes at least one of modified amine curing agents, thiols or modified imidazoles.

[0021] As an implementation manner, the curing agent is a modified amine curing agent.

[0022] As an implementation manner, the modified amine curing agent is a polyester latent curing agent.

[0023] As an implementation manner, the stabilizer is an acidic stabilizer, and the acidic stabilizer includes at least one of salicylic acid, barbituric acid or boric acid.

[0024] As an implementation manner, the stabilizer is barbituric acid.

[0025] The present invention uses an amino-containing silane coupling agent and a polyester latent curing agent, which can cure the colloid at low temperature. The combined use of the amino-containing silane coupling agent and the polyester latent curing agent can optimize the reaction activity of the curing agent, enabling the reaction and curing between the metal salt and the resin matrix at a relatively low temperature. The elongation at break of the product can reach more than 8%, and the change in mechanical properties after damp heat aging is relatively small. The present invention can be cured at 60 - 80 °C and is applied to electronic products to avoid the influence of the high-temperature curing environment on the internal quality of electronic products.

[0026] As an embodiment, the modified epoxy acrylate resin includes at least one of an aliphatic polyurethane-modified epoxy acrylate resin, a polyester-modified epoxy acrylate resin, a polybutadiene-grafted epoxy acrylate resin, or an organosilicon-modified epoxy acrylate resin.

[0027] As an embodiment, the acrylate includes at least one of isobornyl (meth)acrylate, acryloylmorpholine, 1,6-hexanediol diacrylate, or ethoxylated bisphenol A dimethacrylate.

[0028] As an embodiment, the epoxy resin is a polyether-modified epoxy resin, and the models of the epoxy resin include at least one of Adeka EP-4040L, EPR-4030, EP-49-10P2, or Shanghai Huayi EBA-30D.

[0029] The second aspect of the present invention provides a preparation method of a low-temperature conductive adhesive, including the following steps: S1: Mix and stir the resin matrix and the stabilizer evenly. S2: Add the curing agent, the silane coupling agent, and the metal salt, mix and stir evenly, and grind. S3: After grinding, add silver powder and mix and stir evenly to obtain the low-temperature conductive adhesive.

[0030] Compared with the prior art, the present invention has the following beneficial effects: (1) For the low-temperature conductive adhesive of the present invention, introducing an organometallic salt into the resin matrix can reduce the contact resistance of the colloid, and maintain a relatively low increase rate of the contact resistance after damp heat aging.

[0031] (2) For the low-temperature conductive adhesive of the present invention, by using a combination of an epoxy resin, an acrylate, and a modified epoxy acrylate resin, and the sum of the weights of the epoxy resin and the acrylate ≤ the weight of the modified epoxy acrylate resin, a low-temperature conductive adhesive can be obtained, which can achieve low-temperature curing and has a stable and relatively small contact resistance before and after damp heat aging.

[0032] (3) The low-temperature conductive adhesive of the present invention uses a combination of flaky silver powder with a D50 particle size of 5-10 μm, silver micropowder with a D50 particle size of 1-3 μm, and spherical silver powder with a D50 particle size of 800 nm, which can further improve the conductive performance of the low-temperature conductive adhesive.

[0033] (4) The low-temperature conductive adhesive of the present invention uses an amino-containing silane coupling agent and a polyester latent curing agent, which can cure the colloid at low temperature. When applied to electronic products, it can avoid the influence of the high-temperature curing environment on the internal quality of electronic products.

[0034] (5) The low-temperature conductive adhesive of the present invention can be cured at 60-80 °C for 20-40 min. The obtained conductive adhesive has an elongation at break of more than 8%. Before and after damp heat aging, it has a relatively stable and small contact resistance. The bonding surface can cover a size of (0.1×0.1 mm)-(20×20 mm), and it is particularly suitable for the electronic field with high requirements for contact resistance. Specific Embodiments

[0035] A low-temperature conductive adhesive, the preparation raw materials include silver powder, resin matrix, curing agent, silane coupling agent, stabilizer, and metal salt. By weight, the specific addition amounts of Examples 1-6 are shown in Table 1. The specific addition amounts of Comparative Examples 1-6 are shown in Table 2.

[0036] Table 1

[0037] Table 2

[0038] The flaky silver powder I is purchased from Kunming Norman Electronics, and the product number is APS-05F; The flaky silver powder II is purchased from metalor, and the product number is C0083P; The spherical silver powder is purchased from Kunming Norman Electronics, and the product number is APS-0140H; The modified epoxy acrylate resin of Examples 1-3 and Comparative Examples 1-6 is purchased from Sartomer, and the product number is SR2003; The modified epoxy acrylate resin of Examples 4-6 is purchased from Changxing, and the product number is 6235; The epoxy resin of Examples 1-3 and Comparative Examples 1-6 is purchased from Shanghai Huayi, and the product number is EBA-30D; The epoxy resin of Examples 4-6 is purchased from ADEKA, and the product number is EP-4040L; The acrylate is purchased from Sartomer, and the product number is SR238; The curing agent is purchased from ADEKA, and the product number is EH-5057PK; For the silane coupling agents in Examples 1-3 and Comparative Examples 1-6, they were purchased from Momentive, with the product number Y-9669; For the silane coupling agents in Examples 4-6, they were purchased from Momentive, with the product number A-Link 15; For the metal salts in Examples 1-3 and Comparative Examples 1-6, they were purchased from Cray Valley, with the product number Dymalink633; For the metal salts in Examples 4-6, they were purchased from Cray Valley, with the product number Dymalink 708.

[0039] A preparation method of a low-temperature conductive adhesive includes the following steps: S1: Mix and stir the resin matrix and the stabilizer evenly; S2: Add the curing agent, the silane coupling agent and the metal salt, mix and stir evenly, and after grinding, the particle size < 5 μm; S3: After grinding, add silver powder and mix and stir evenly to obtain the low-temperature conductive adhesive.

[0040] Performance testing 1. Elongation at break: Make 4 dumbbell-shaped samples from the low-temperature conductive adhesives prepared in the examples and comparative examples, and refer to the GBT1040 standard to conduct tests using an electronic universal testing machine at 25 °C.

[0041] 2. Contact resistance: Drop the glue symmetrically and evenly on the ITO conductive glass surface with a spacing of 20 mm. The diameter of the dropped glue is 1.5 mm. The ITO conductive glass surface is an indium tin oxide coating with a coating thickness of 50 μm. After curing at 60 °C for 40 min, test the resistance and record it as R1; after 500 h under double 85 (85 °C, 85% humidity), test the resistance and record it as R2.

[0042] Resistance growth rate = (R2 - R1) / R1 × 100%.

[0043] The test results are shown in Table 3.

[0044] Table 3

[0045] When comparing Examples 1-3 of the present invention with Comparative Examples 4-6, in Comparative Examples 4-6, without adding metal salts, the contact resistance is relatively large and the conductivity is poor.

[0046] When comparing Examples 1-3 of the present invention with Comparative Examples 1-3, in Comparative Examples 1-3, the sum of the weights of epoxy resin and acrylate is greater than the proportion of the modified epoxy propylene resin, and the electrical properties vary greatly before and after damp heat aging, rising from 11.3 Ω to 13.5 Ω, and the elongation at break decreases from 9.3% to 6.2%.

Claims

1. A conductive adhesive, characterized in that: The raw materials prepared include 70-80 parts of silver powder, 20-30 parts of resin matrix, 1-10 parts of curing agent, 0.1-0.5 parts of silane coupling agent, 0.1-0.5 parts of stabilizer, and 0.1-0.5 parts of metal salt, wherein the metal salt is an organic metal salt; The resin matrix comprises modified epoxy acrylic resin, acrylate and epoxy resin; the sum of the weights of the acrylate and the epoxy resin is less than or equal to the weight of the modified epoxy acrylic resin.

2. The conductive adhesive according to claim 1, characterized in that: The silver powder includes flaky silver powder and spherical silver powder. The D50 particle size of the flaky silver powder is 1-10 μm, and the D50 particle size of the spherical silver powder is 500-900 nm.

3. The conductive adhesive according to claim 2, characterized in that: The flaky silver powder includes flaky silver powder I with a D50 particle size of 5-10 μm and flaky silver powder II with a D50 particle size of 1-3 μm.

4. The conductive adhesive according to claim 1, characterized in that: The organic metal salt includes at least one of potassium acrylate, zinc acrylate, calcium acrylate, potassium (meth)acrylate, zinc (meth)acrylate or calcium (meth)acrylate.

5. The conductive adhesive according to claim 1, characterized in that: The silane coupling agent is an amino-containing silane coupling agent, and the amino-containing silane coupling agent includes at least one of γ-glycidyloxypropyltrimethoxysilane, secondary amino silane coupling agent, ureidopropyltrimethoxysilane, di(γ-trimethoxysilylpropyl)amine or N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane.

6. The conductive adhesive according to claim 1, characterized in that: The curing agent includes at least one of a modified amine curing agent, a thiol or a modified imidazole.

7. The conductive adhesive according to claim 1, characterized in that: The stabilizer is an acidic stabilizer, and the acidic stabilizer includes at least one of salicylic acid, barbituric acid or boric acid.

8. The conductive adhesive according to claim 1, characterized in that: The modified epoxy acrylic resin includes at least one of an epoxy acrylic resin modified by aliphatic polyurethane, an epoxy acrylic resin modified by polyester, an epoxy acrylic resin grafted by polybutadiene, or an epoxy acrylic resin modified by silicone.

9. A method for preparing the conductive adhesive according to any one of claims 1 to 8, characterized in that: The following steps are involved: S1: Mix the resin matrix and stabilizer and stir evenly; S2: Add curing agent, silane coupling agent and metal salt, mix and stir evenly, and grind; S3: After grinding, add silver powder and mix well to obtain conductive glue.

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