Anti-migration conductive silver adhesive and preparation method thereof

Abstract

The invention belongs to the technical field of electronic packaging materials, and relates to an anti-migration conductive silver adhesive and a preparation method thereof, and the anti-migration conductive silver adhesive comprises the following components by weight: 70-90% of silver powder; 6%-15% of a resin matrix; 1.5%-5% of a curing agent; 2%-15% of a diluent; and 0.5%-3% of a sulfur-containing silane coupling agent. The sulfur-containing silane coupling agent forms a strong chemical bond with silver through sulfydryl of the sulfur-containing silane coupling agent, and a hydrophobic membrane is formed through hydrolytic condensation, so that a dual inhibition mechanism on silver migration is realized; the performance is excellent; the electrochemical migration failure life in a high-temperature and high-humidity environment is prolonged; the sulfur-containing silane coupling agent is added on the basis of an existing conductive silver adhesive formula, complex pretreatment or synthesis steps are not needed, the conductive silver adhesive is suitable for industrial large-scale production, precious metal such as palladium is not introduced, and the cost advantage is obvious; and the compatibility is good.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electronic packaging materials, and in particular to an anti-migration conductive silver adhesive and a preparation method thereof. BACKGROUND

[0002] As a kind of key electronic packaging material, conductive adhesive is mainly composed of conductive filler, resin matrix, curing agent and diluent, etc., and has both conductivity and adhesive strength after curing. Among them, silver is the first choice for conductive filler due to its excellent conductivity and chemical stability. Compared with traditional tin-based solder, the curing temperature of conductive silver adhesive is usually lower than 180℃, which has the advantages of low energy consumption and small thermal stress, and is widely used in microelectronic assembly, chip mounting and other fields.

[0003] However, with the development of electronic devices towards miniaturization and high power density, the spacing between lines and electrodes is continuously reduced. In a silver conductor under direct current voltage in a high humidity environment, silver atoms will ionize and move towards the anode under the driving of the electric field, forming dendrites and causing insulation resistance to drop or even short circuit, which is called "silver migration". Silver is the most migratory element among all metals, which seriously restricts the application of conductive silver adhesive in high reliability and high density electronic devices.

[0004] To solve the problem of silver migration, the prior art has proposed various solutions, but all have deficiencies. For example, although the use of silver-plated copper powder as filler can inhibit migration to a certain extent, the preparation process is complex, and copper is easy to oxidize, resulting in unstable conductivity; adding noble metals such as palladium powder can improve the anti-migration property by forming an alloy or passivation film, but the cost is high and the nano powder is easy to agglomerate; adding organic modifiers (such as epoxy chloropropane modified hydroxyl betaine) to adsorb silver ions involves multi-step synthesis and purification, which is not conducive to industrial production.

[0005] Therefore, it is a technical problem to be solved in the field to develop a high-performance conductive silver adhesive with simple process, low cost and effective inhibition of silver migration. SUMMARY

[0006] To solve the above technical problems, on the one hand, the present application provides an anti-migration conductive silver adhesive, which comprises the following components by weight percentage: 70% to 90% of silver powder; 6% to 15% of resin matrix; 1.5% to 5% of curing agent; 2% to 15% of diluent; 0.5% to 3% of sulfur-containing silane coupling agent.

[0007] Preferably, the silver powder has a particle size of 0.1-10 μm and a shape of one or more combinations of spherical, near-spherical, microcrystalline, flaky or rod-like.

[0008] Preferably, the resin matrix is one or more combinations of bisphenol A type epoxy resin, bisphenol F type epoxy resin, phenolic epoxy resin or acrylic resin.

[0009] Preferably, the curing agent is one or more combinations of imidazole type curing agent, amine type curing agent or acid anhydride type curing agent.

[0010] Preferably, the diluent is one or more combinations of propylene oxide propylene ether, diglycidyl ether, butyl glycidyl ether, octyl glycidyl ether, benzyl glycidyl ether or 1,4-butanediol diglycidyl ether.

[0011] Preferably, the sulfur-containing silane coupling agent is one or more combinations of 3-mercaptopropyl trimethoxysilane, 3-mercaptopropyl triethoxysilane, 3-mercaptopropyl dimethoxysilane, 3-thiocyanatopropyl triethoxysilane, bis-[3-(triethoxysil)propyl]-disulfide, bis-(3-(triethoxysil)-propyl)-tetrasulfide or mercaptopropyl ethoxyl bis-undecylsilane.

[0012] In another aspect, the present application also provides a method for preparing the above-mentioned anti-migration conductive silver paste, comprising the following steps: Step one, preparation of the organic carrier: the resin matrix, curing agent, diluent and sulfur-containing silane coupling agent are mixed according to the proportions, and stirred uniformly to obtain the organic carrier; Step two, preparation of the conductive silver paste: the silver powder is mixed with the organic carrier prepared in step one according to the proportions, and stirred uniformly to obtain the anti-migration conductive silver paste.

[0013] In another aspect, the present application also provides an electronic component packaged or bonded using the above-mentioned anti-migration conductive silver paste.

[0014] In another aspect, the present application also provides the use of a sulfur-containing silane coupling agent in the preparation of the anti-migration conductive silver paste, wherein the addition amount of the sulfur-containing silane coupling agent is 0.5%-3% of the total weight of the conductive silver paste, and the sulfur-containing silane coupling agent is used to inhibit silver migration by chemically bonding with the silver powder through its mercapto group and forming a hydrophobic film through its hydrolytic condensation.

[0015] In another aspect, the present application also provides an anti-migration conductive silver paste using alkyl mercaptan as the anti-migration agent, wherein the addition amount of the alkyl mercaptan is 0.1%-2% of the total weight of the conductive silver paste, and the alkyl mercaptan is preferably selected from 1-octane mercaptan or 1-dodecane mercaptan.

[0016] Compared with the prior art, the present application has the following beneficial effects: (1) High efficiency anti-migration: sulfur-containing silane coupling agent forms a strong chemical bond with silver through its mercapto group (chemical passivation) and forms a hydrophobic film through hydrolysis condensation (physical shielding), realizing a double inhibition mechanism of silver migration, solving the problem from the root.

[0017] (2) Excellent performance: on the basis of maintaining the original conductivity and bonding strength of the conductive silver adhesive, the electrochemical migration failure life in high temperature and high humidity environment is significantly improved, and the failure life can be increased by nearly 10 times.

[0018] (3) Simple process and low cost: the scheme directly adds commercially available sulfur-containing silane coupling agent to the existing conductive silver adhesive formula, without complex pretreatment or synthesis steps, the process is simple, suitable for large-scale industrial production, and no noble metal such as palladium is introduced, and the cost advantage is obvious.

[0019] (4) Good compatibility: the curing process of the conductive silver adhesive is compatible with the traditional epoxy resin system, and does not affect the subsequent welding, packaging and other electronic manufacturing processes. BRIEF DESCRIPTION OF DRAWINGS

[0020] In order to more clearly illustrate the scheme in the present application, the drawings needed in the description of the embodiments of the present application will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present application, and those skilled in the art can obtain other drawings according to these drawings without creative labor.

[0021] Figure 1 is a process flow chart for preparing the anti-migration conductive silver adhesive of the present application. DETAILED DESCRIPTION

[0022] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present application belongs; the terms used in the specification of the application are only for the purpose of describing specific embodiments and are not intended to limit the present application; the specification, claims and above description of the drawings of the present application The terms "include" and "have" and any variations thereof in the specification and claims and above description of the drawings are intended to cover non-exclusive inclusion. The terms "first", "second" and the like in the specification and claims or above description of the drawings are used to distinguish different objects, not to describe a particular order.

[0023] Reference herein to "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the application. The appearances of the phrase in various places in the specification are not necessarily all referring to the same embodiment, nor are they necessarily mutually exclusive of one another. As will be apparent to those of ordinary skill in the art, embodiments described herein can be combinable with other embodiments.

[0024] For those skilled in the art to better understand the technical scheme of the present application, the technical scheme in the embodiments of the present application will be described clearly and completely in conjunction with the drawings.

[0025] Example 1 (comparative example) In this embodiment, a conductive silver adhesive without sulfur-containing silane coupling agent is prepared as a performance comparison benchmark.

[0026] Prepare the organic carrier: take 55 g of bisphenol A type epoxy resin, 15 g of imidazole curing agent, 30 g of diglycidyl ether diluent, and place them in a beaker. Stir mechanically at a speed of 500 rpm for 30 minutes until the mixture is uniform. A transparent and uniform organic carrier is obtained.

[0027] Prepare the conductive silver adhesive: take 40 g of flaky silver powder (average particle size 2 μm) and 10 g of the above organic carrier. Use a non-invasive planetary mixer to mix the flaky silver powder and the organic carrier uniformly, ensuring that the silver powder is fully infiltrated and mixed uniformly with the organic carrier. Conductive silver adhesive 1 is obtained.

[0028] Example 2 Figure 1 is a flow chart of the method for preparing the anti-migration conductive silver adhesive of the present application. As shown in Figure 1 the method for preparing the anti-migration conductive silver adhesive comprises the following steps: S1, preparation of the organic carrier: mix the resin matrix, curing agent, diluent and sulfur-containing silane coupling agent in the specified proportions, and stir until uniform to obtain the organic carrier; S2, preparation of the conductive silver adhesive: mix the silver powder with the organic carrier prepared in step 1 in the specified proportions, and stir until uniform to obtain the anti-migration high-performance conductive silver adhesive.

[0029] In specific implementation, the present embodiment provides a method for preparing an anti-migration conductive silver adhesive containing 3-mercaptopropyl trimethoxysilane.

[0030] Prepare the organic carrier: take 55 g of bisphenol A type epoxy resin, 15 g of imidazole curing agent, 30 g of diglycidyl ether diluent, and place them in a beaker. Stir mechanically at a speed of 500 rpm for 30 minutes until the mixture is uniform. A transparent and uniform organic carrier is obtained.

[0031] Preparation of conductive silver paste: 40 g of flaky silver powder (average particle size 2 μm) and 10 g of the above organic vehicle were weighed and mixed uniformly using a non-intrusive planetary mixer to ensure that the silver powder was fully infiltrated and mixed uniformly with the organic vehicle, to obtain conductive silver paste 2.

[0032] Example 3 In this example, a migration-resistant conductive silver paste containing 3-mercaptopropyltrimethoxysilane was prepared.

[0033] Preparation of organic vehicle: 55 g of bisphenol A type epoxy resin, 15 g of imidazole curing agent, 28 g of diglycidyl ether diluent, and 2 g of 3-mercaptopropyltrimethoxysilane were weighed, and the remaining steps were the same as in Example 2.

[0034] Preparation of conductive silver paste: the same silver powder and mixing process as in Example 2 were used to obtain conductive silver paste 3.

[0035] Example 4 In this example, a migration-resistant conductive silver paste containing 3-mercaptopropyltrimethoxysilane was prepared.

[0036] Preparation of organic vehicle: 55 g of bisphenol A type epoxy resin, 15 g of imidazole curing agent, 28 g of diglycidyl ether diluent, and 2 g of 3-mercaptopropyltrimethoxysilane were weighed, and the remaining steps were the same as in Example 2.

[0037] Preparation of conductive silver paste: the same silver powder and mixing process as in Example 2 were used to obtain conductive silver paste 3.

[0038] Example 5 (performance test) In this example, the migration-resistant conductive silver paste prepared in Examples 1-4 above was tested for silver migration resistance, including the following steps: 1. Sample preparation: each conductive silver paste was printed on an alumina ceramic substrate using screen printing to form two parallel electrode patterns with dimensions of 20 mm x 4 mm x 0.1 mm and a spacing of 0.5 mm.

[0039] 2. Curing: the printed substrate was placed in a 160°C air oven and cured for 2 hours.

[0040] 3. Test conditions: the cured sample was placed on a heating platform at 120°C, and a humidifier was used to control the relative humidity of the environment to be above 85%. A direct current bias of 10V was applied to the two parallel electrodes.

[0041] 4. Failure judgment and recording: the leakage current between the two electrodes was monitored in real time using a digital source meter. When the leakage current value reached 1 mA, it was determined that electrochemical migration failure had occurred, and the time elapsed from the application of voltage to failure was recorded, defined as the electrochemical migration failure life.

[0042] The test results are shown in Table 1: Table 1 Result analysis: According to the test results, the comparative example (silver paste 1) without adding sulfur-containing silane coupling agent has a very short failure life of only 5 minutes. The examples (silver pastes 2, 3 and 4) of the present application with 2% to 3% sulfur-containing silane coupling agent added have significantly prolonged electrochemical migration failure life, reaching more than 46 minutes, which is more than 9 times that of the comparative example. This fully proves that the sulfur-containing silane coupling agent added in the present application has an extremely significant effect on inhibiting silver migration.

[0043] Example 6 (alternative example) This example shows the application of an alternative to the sulfur-containing silane coupling agent, i.e. alkyl mercaptan.

[0044] Preparation of organic carrier: 55 g of phenolic epoxy resin, 16 g of acid anhydride curing agent, 28.5 g of benzyl glycidyl ether diluent and 0.5 g of 1-dodecanethiol are weighed and mixed uniformly.

[0045] Preparation of conductive silver paste: 40 g of flaky silver powder (average particle size 2 μm) and 10 g of the above organic carrier are weighed and mixed uniformly to obtain a conductive silver paste. This silver paste can also obtain anti-migration performance superior to that of the comparative example through the bonding of mercapto groups and silver and the hydrophobic effect of the alkyl long chain.

[0046] Under the concept of the present application, the function of the sulfur-containing silane coupling agent can be realized by other compounds containing mercapto groups (-SH). For example, alkyl mercaptans (such as 1-octanethiol, 1-dodecanethiol, etc.) can be used as alternative components. The mercapto groups of alkyl mercaptans can also form firm Ag-S bonds with the surface of silver, and the alkyl long chains can build a dense hydrophobic monolayer on the surface of silver powder, thereby playing a role in inhibiting silver migration. The addition amount of alkyl mercaptan can be adjusted in the range of 0.1% to 2%.

[0047] Example 7 (alternative example) This example is based on Example 6 and combines the advantages of short-chain and long-chain alkyl mercaptans, aiming to achieve the synergistic effect of rapid adsorption and long-term stable protection.

[0048] Preparation of organic carrier: 60 g of phenolic epoxy resin, 16 g of acid anhydride curing agent and 22.5 g of benzyl glycidyl ether are mixed by adding 0.5 g of 1-octanethiol (short chain, rapid effect) and 1.0 g of 1-dodecanethiol (long chain, stable hydrophobicity) and stirring for 45 minutes.

[0049] Preparation of conductive silver paste: 40 g of flaky silver powder (average particle size 2 μm) and 10 g of the above organic carrier are weighed and mixed uniformly to obtain a conductive silver paste.

[0050] Performance characteristics: The mixed mercaptan system can theoretically form a tighter mixed monolayer. The short-chain mercaptan quickly occupies the active sites on the silver surface, and the long-chain mercaptan fills and enhances the hydrophobicity. It is expected to obtain better comprehensive migration resistance than a single mercaptan.

[0051] Example 8 (alternative embodiment) This example is based on Example 6, and introduces an auxiliary antioxidant on the basis of the alkyl mercaptan to cope with more severe oxidative environments and provide multiple protection.

[0052] Organic carrier preparation: In 52 grams of bisphenol F type epoxy resin, 14 grams of modified amine curing agent, and 33.5 grams of diglycidyl ether diluent, 1.0 gram of 1-octane mercaptan and 0.5 gram of hindered phenolic antioxidant (such as Irganox 1010) are added. Mechanical stirring for 40 minutes makes it completely dissolved and dispersed.

[0053] Conductive silver paste preparation: 40g of flaky silver powder (average particle size 2μm) and 10g of the above organic carrier are weighed and mixed uniformly to obtain a conductive silver paste.

[0054] Performance characteristics: The addition of antioxidants can capture free radicals that may be generated under high temperature or light conditions, reducing the aging of the organic carrier itself, and indirectly protecting the silver-mercaptan interface. This complements the direct passivation effect of mercaptan, and is expected to exhibit superior durability under extreme working conditions (such as high temperature and humidity and bias).

[0055] Obviously, the above-described embodiments are only a part of the embodiments of the present application, and are not all the embodiments. The preferred embodiments of the present application are given in the drawings, but do not limit the patent scope of the present application. The present application can be realized in many different forms, and conversely, the purpose of providing these embodiments is to make the disclosure of the present application more thorough and comprehensive. Although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments, or make equivalent substitutions for some of the technical features. Any equivalent structure made by using the contents of the present application specification and drawings, directly or indirectly applied to other related technical fields, is also within the patent protection scope of the present application.

Claims

1. A type of anti-migration conductive silver paste, characterized in that, By weight percentage, it includes the following components: 70%–90% silver powder; 6%–15% resin matrix; 1.5% to 5% curing agent; 2%–15% diluent; 0.5% to 3% sulfur-containing silane coupling agent.

2. The anti-migration conductive silver paste according to claim 1, characterized in that, The silver powder has a particle size of 0.1 to 10 μm and a shape that is one or more combinations of spherical, near-spherical, microcrystalline, flake, or rod-shaped.

3. The anti-migration conductive silver paste according to claim 1, characterized in that, The resin matrix is ​​one or more combinations of bisphenol A type epoxy resin, bisphenol F type epoxy resin, phenolic epoxy resin or acrylic resin.

4. The anti-migration conductive silver paste according to claim 1, characterized in that, The curing agent is one or more combinations of imidazole curing agents, amine curing agents, or acid anhydride curing agents.

5. The anti-migration conductive silver paste according to claim 1, characterized in that, The diluent is one or a combination of propylene oxide ether, diglycidyl ether, butyl glycidyl ether, octyl glycidyl ether, benzyl glycidyl ether, or 1,4-butanediol diglycidyl ether.

6. The anti-migration conductive silver paste according to any one of claims 1 to 5, characterized in that, The sulfur-containing silane coupling agent is one or more combinations of 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 3-mercaptopropyldimethoxysilane, 3-thiocyanopropyltriethoxysilane, bis-[3-(triethoxysilane)propyl]-disulfide, bis-(3-(triethoxysilane)propyl)-tetrasulfide, or mercaptopropylethoxydiundecylsilane.

7. A method for preparing the anti-migration conductive silver paste as described in any one of claims 1 to 6, characterized in that, Includes the following steps: Step 1: Preparation of organic carrier: Mix the resin matrix, curing agent, diluent and sulfur-containing silane coupling agent according to the formula, stir evenly to obtain organic carrier; Step 2: Preparation of conductive silver paste: Mix the silver powder with the organic carrier obtained in Step 1 according to the specified ratio, stir evenly, and obtain the anti-migration conductive silver paste.

8. An electronic component, characterized in that, Encapsulation or bonding is performed using the anti-migration conductive silver paste as described in any one of claims 1 to 6.

9. The application of a sulfur-containing silane coupling agent in the preparation of conductive silver paste with anti-silver migration properties, characterized in that, The amount of the sulfur-containing silane coupling agent added is 0.5% to 3% of the total weight of the conductive silver paste, and it is used to inhibit silver migration by chemically bonding its thiol groups with silver powder and forming a hydrophobic film through hydrolysis and condensation.

10. A type of anti-migration conductive silver paste, characterized in that, Alkyl thiols are used as anti-migration agents, and the amount of alkyl thiols added is 0.1% to 2% of the total weight of the conductive silver paste. The alkyl thiols are preferably 1-octanethiol or 1-dodecanethiol.

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