Conductive adhesive and preparation method thereof

Abstract

The present invention discloses a low-temperature conductive adhesive, which is prepared by weight using raw materials including 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. The present invention introduces an organic metal salt into the resin matrix to reduce the contact resistance of the colloid, and after wet heat aging, maintains a lower contact resistance increase rate. The present invention adopts a combination of epoxy resin, acrylate and modified epoxy acrylic resin, and the weight of epoxy resin and acrylate is less than or equal to the weight of modified epoxy acrylic resin, so that low-temperature curing can be achieved. The present invention can achieve 60-80 ° C, 20-40 min curing, and the conductive adhesive elongation at break obtained can reach more than 8%, and before and after wet heat aging, there is a more stable and relatively small contact resistance, which is particularly suitable for the electronic field with high requirements for contact resistance.

Description

Technical Field

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

[0002] With the advancement of science and technology, the application of electronic chips is becoming increasingly widespread. The colloids used in electronic chips need to have high electrical conductivity. Furthermore, the widespread use of electronic chips in high-temperature and high-humidity environments places higher demands on the aging and electrical conductivity of electronic adhesives. Existing conductive adhesives have high contact resistance, and after wet-heat aging, the resistivity increases significantly. Therefore, the development of a conductive adhesive with good conductivity and resistance to wet-heat aging is crucial.

[0003] Chinese invention patent CN104356970A discloses a highly conductive UV-curable conductive adhesive. This adhesive uses a small amount of spherical nano-silver powder to fill the gaps between flaky nano-silver powders, allowing previously non-contacting adjacent flaky nano-silver powders to contact each other. This increases the conductive path and reduces the volume resistivity of the conductive adhesive system. However, voids still exist within the adhesive, resulting in a high resistivity. Chinese invention patent CN119505176A discloses a modified epoxy acrylate, its preparation method, a conductive adhesive, its preparation method, and its application. The modified epoxy acrylate has a long chain structure, which imparts excellent flexibility to the cured modified epoxy acrylate. The resulting conductive adhesive exhibits excellent properties, including low-temperature curing, flexibility, moisture and heat resistance, high adhesion, good conductivity, and low stress. However, its moisture and heat resistance still fails to meet the required temperature and humidity requirements. Summary of the Invention

[0004] In order to develop a conductive adhesive with good conductivity and resistance to moisture and heat aging, the first aspect of the present invention provides a low-temperature conductive adhesive. The raw materials for preparation include, by weight, 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.

[0005] As an embodiment, the resin matrix includes modified epoxy acrylic resin, acrylate and epoxy resin; the sum of the weights of the acrylate and epoxy resin is less than or equal to the weight of the modified epoxy acrylic resin.

[0006] During the experiment, the inventors discovered that by using a combination of epoxy resin, acrylate and modified epoxy acrylate resin, where the sum of the weights of the epoxy resin and acrylate is ≤ the weight of the modified epoxy acrylate resin, a low-temperature conductive adhesive can be obtained. This adhesive can achieve low-temperature curing and has stable and low contact resistance before and after wet-heat aging. The inventors speculate that the possible reason is that: at the preferred weight ratio, the grafting of epoxy and acrylate can be achieved, and the cross-linked network of the colloid formed has a low contact resistance. When the epoxy resin exceeds the preferred weight ratio, the contact resistance increases and the conductivity decreases after wet-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 the flaky silver powder I with a D50 particle size of 5-10 μm, the flaky silver powder II with a D50 particle size of 1-3 μm and the 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 the flaky silver powder I with a D50 particle size of 5-10 μm, the flaky silver powder II with a D50 particle size of 1-3 μm, and the 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 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. The reason is that the flaky silver powder and the spherical silver powder are overlapped, which can reduce the contact resistance of the low-temperature conductive adhesive. In addition, the addition of small-particle silver micropowder can fill the gaps between the flaky silver powder and the spherical silver powder, reduce the resistance increase caused by air pores, and further improve the conductive effect.

[0014] As an embodiment, 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.

[0015] As an embodiment, the functionality of the organic metal salt is 2.

[0016] During the experiment, the inventors found that introducing organic metal salts into the resin matrix can reduce the contact resistance of the colloid and maintain a low contact resistance increase rate after wet heat aging. The reason may be that the organic metal salts can produce a coupling effect with the resin matrix, and the organic molecular structure can chemically react with the resin matrix. On the basis of reducing the contact resistance, the stability of the structure is maintained. Under wet heat aging conditions, it is not easy to degrade, and the contact resistance will not change significantly.

[0017] As an embodiment, 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, a secondary amino silane coupling agent, ureidopropyltrimethoxysilane, di(γ-trimethoxysilylpropyl)amine or N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane.

[0018] As an embodiment, the amino-containing silane coupling agent is γ-glycidyloxypropyltrimethoxysilane.

[0019] As an embodiment, the model of the amino-containing silane coupling agent includes at least one of Maitu Y-9669, A-Link15, A-1524 CF, A-1120J or A-1170.

[0020] As an embodiment, the curing agent includes at least one of a modified amine curing agent, a thiol or a modified imidazole.

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

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

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

[0024] In one embodiment, the stabilizer is barbituric acid.

[0025] The present invention utilizes an amino-containing silane coupling agent and a polyester latent curing agent to cure the colloid at low temperatures. The combination of the amino-containing silane coupling agent and the polyester latent curing agent optimizes the curing agent's reactivity, allowing the metal salt and the resin matrix to react and cure at lower temperatures. The product's elongation at break can reach over 8%, and mechanical properties show minimal change after wet-heat aging. The present invention can cure at 60-80°C and is applicable to electronic products, avoiding the impact of high-temperature curing environments on the internal quality of electronic products.

[0026] As an embodiment, the modified epoxy acrylic resin includes at least one of an aliphatic polyurethane-modified epoxy acrylic resin, a polyester-modified epoxy acrylic resin, a polybutadiene-grafted epoxy acrylic resin, or an organosilicon-modified epoxy acrylic 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 epoxy resin model includes at least one of Aidico EP-4040L, EPR-4030, EP-49-10P2 or Shanghai Huayi EBA-30D.

[0029] A second aspect of the present invention provides a method for preparing a low-temperature conductive adhesive, comprising the following steps:

[0030] S1: Mix the resin matrix and stabilizer and stir evenly;

[0031] S2: Add curing agent, silane coupling agent and metal salt, mix well and grind;

[0032] S3: After grinding, add silver powder and mix well to obtain low-temperature conductive adhesive.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] (1) The low-temperature conductive adhesive of the present invention introduces an organic metal salt into the resin matrix, which can reduce the contact resistance of the adhesive and maintain a low contact resistance increase rate after wet-heat aging.

[0035] (2) The low-temperature conductive adhesive of the present invention adopts a combination of epoxy resin, acrylate and modified epoxy acrylate resin, and the sum of the weights of epoxy resin and acrylate is ≤ the weight of modified epoxy acrylate resin, so as to obtain a low-temperature conductive adhesive, which can achieve low-temperature curing and has stable and low contact resistance before and after wet-heat aging.

[0036] (3) The low-temperature conductive adhesive of the present invention adopts 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.

[0037] (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 temperatures. When used in electronic products, it can avoid the impact of high-temperature curing environment on the internal quality of electronic products.

[0038] (5) The low-temperature conductive adhesive of the present invention can be cured at 60-80°C for 20-40 minutes. The resulting conductive adhesive has an elongation at break of more than 8%, and has a relatively stable and small contact resistance before and after wet-heat aging. The bonding surface can cover a size of (0.1×0.1mm)-(20×20mm), and is particularly suitable for the electronic field with high requirements for contact resistance. DETAILED DESCRIPTION

[0039] A low-temperature conductive adhesive is prepared from raw materials including silver powder, a resin matrix, a curing agent, a silane coupling agent, a stabilizer, and a metal salt. The specific amounts added in parts by weight for Examples 1-6 are shown in Table 1. The specific amounts added for Comparative Examples 1-6 are shown in Table 2.

[0040] Table 1

[0041]

[0042] Table 2

[0043]

[0044] The flaky silver powder I was purchased from Kunming Norman Electronics, with the brand name APS-05F;

[0045] The flake silver powder II was purchased from Metalor, brand C0083P;

[0046] The spherical silver powder was purchased from Kunming Norman Electronics, brand APS-0140H;

[0047] The modified epoxy acrylic resins of Examples 1-3 and Comparative Examples 1-6 were purchased from Sartomer with the brand name SR2003;

[0048] The modified epoxy acrylic resin of Examples 4-6 was purchased from Changxing, with the brand name 6235;

[0049] The epoxy resins of Examples 1-3 and Comparative Examples 1-6 were purchased from Shanghai Huayi with the brand name EBA-30D;

[0050] The epoxy resins in Examples 4-6 were purchased from Aidico, with the brand name EP-4040L.

[0051] The acrylate was purchased from Sartomer with the brand name SR238;

[0052] The curing agent was purchased from Aidico, brand EH-5057PK;

[0053] The silane coupling agent of Examples 1-3 and Comparative Examples 1-6 was purchased from Momentive, with the brand name Y-9669;

[0054] The silane coupling agent of Examples 4-6 was purchased from Momentive, with the brand name A-Link 15;

[0055] The metal salts of Examples 1-3 and Comparative Examples 1-6 were purchased from Crayville, brand Dymalink 633;

[0056] The metal salts of Examples 4-6 were purchased from Cray Valley with the brand name Dymalink 708.

[0057] A method for preparing a low-temperature conductive adhesive comprises the following steps:

[0058] S1: Mix the resin matrix and stabilizer and stir evenly;

[0059] S2: Add curing agent, silane coupling agent and metal salt, mix and stir evenly, and grind to a particle size of <5μm;

[0060] S3: After grinding, add silver powder and mix well to obtain low-temperature conductive adhesive.

[0061] Performance Testing

[0062] 1. Elongation at break: The low-temperature conductive adhesives prepared in the examples and comparative examples were made into four dumbbell-shaped samples and tested using an electronic universal testing machine at 25°C according to GBT1040 standard.

[0063] 2. Contact resistance: The contact resistance is measured after curing at 60°C for 40 minutes at a temperature of 85°C and 85% humidity for 500 hours at a temperature of 85°C and 85% humidity, respectively. The contact resistance is measured after ...

[0064] Resistance growth rate = (R2-R1) / R1×100%.

[0065] The test results are shown in Table 3.

[0066] Table 3

[0067]

[0068] Comparing Examples 1-3 of the present invention with Comparative Examples 4-6, the contact resistance of Comparative Examples 4-6 without adding metal salt is large and the conductivity is poor.

[0069] Comparing Examples 1-3 of the present invention with Comparative Examples 1-3, the weight sum of the epoxy resin and the acrylate in Comparative Examples 1-3 is greater than the ratio of the modified epoxy propylene resin. The electrical properties before and after wet heat aging differ significantly, increasing from 11.3Ω to 13.5Ω, and the elongation at break decreasing from 9.3% to 6.2%.

Claims

1. A conductive adhesive, characterized in that: The raw materials prepared include, by weight, 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 includes modified epoxy acrylic resin, acrylate and epoxy resin; the sum of the weight of the acrylate and epoxy resin = the weight of the modified epoxy acrylic resin; The acrylate includes at least one of isobornyl (meth)acrylate, acryloylmorpholine, 1,6-hexanediol diacrylate or ethoxylated bisphenol A dimethacrylate; The silver powder includes flake silver powder and spherical silver powder. The D50 particle size of the flake silver powder is 1-10 μm, and the D50 particle size of the spherical silver powder is 500-900 nm. The flake silver powder includes flake silver powder I with a D50 particle size of 5-10 μm and flake silver powder II with a D50 particle size of 1-3 μm. The organic metal salt includes at least one of potassium acrylate, zinc acrylate, calcium acrylate, potassium methacrylate, zinc methacrylate or calcium methacrylate; The modified epoxy acrylic resin includes at least one of an aliphatic polyurethane-modified epoxy acrylic resin, a polyester-modified epoxy acrylic resin, a polybutadiene-grafted epoxy acrylic resin, and an organosilicon-modified epoxy acrylic resin; The curing agent is a modified amine curing agent.

2. 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 ureapropyltrimethoxysilane, di(γ-trimethoxysilylpropyl)amine or N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane.

3. 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.

4. A method for preparing the conductive adhesive according to any one of claims 1 to 3, 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 well and grind; S3: After grinding, add silver powder and mix well to obtain conductive adhesive.

Images