High-thermal-conductivity and high-electric-conductivity silver adhesive for LED packaging and preparation method thereof

Abstract

The invention discloses a high thermal conductivity and electric conductivity silver adhesive for LED packaging, which is prepared from the following components in parts by weight: 100 parts of bisphenol A epoxy resin, 10 to 20 parts of benzoxazine resin, 0.5 to 2 parts of 2, 5-dimethoxyphenylethylamine, 150 to 250 parts of flaky micron silver powder, 30 to 120 parts of flaky nano silver powder, 15 to 30 parts of latent curing agent and 1 to 5 parts of curing accelerator. The invention further discloses a preparation method of the high-thermal-conductivity and high-electric-conductivity silver adhesive. The epoxy resin and the benzoxazine resin are compounded, the 2, 5-dimethoxyphenylethylamine is added, and the flaky nano silver powder and the flaky micron silver powder are compounded, so that the electric conduction (heat conduction) network of the silver powder in the base adhesive is synergistically improved, the heat resistance and moisture resistance and the linear shrinkage rate are excellent, and meanwhile, the electric conduction (heat conduction) network of the silver powder in the base adhesive is improved. The raw material cost of the existing conductive silver adhesive is effectively reduced; and the silver colloid with low silver content also improves the product stability of the silver colloid system, optimizes the bonding strength and toughness of the silver colloid, and greatly widens the application range of the silver colloid.

Description

Technical Field

[0001] This invention belongs to the field of electronic materials technology, specifically relating to a high thermal conductivity silver paste for LED packaging and its preparation method. Background Technology

[0002] Conductive silver paste is a core material for LED packaging, responsible for chip bonding, circuit interconnection, and heat dissipation. Its performance directly affects the efficiency and reliability of the device. In the LED industry, the requirements for conductive silver paste are good conductivity, heat resistance, high shear strength, and strong adhesion. Existing conductive silver pastes are typically composed of a polymer matrix, conductive fillers, and additives. The typical polymer matrix is ​​epoxy resin, and the conductive fillers include silver powder, copper powder, aluminum powder, carbon black, etc. Additives include curing agents, etc. Among them, silver powder, due to its high electrical and thermal conductivity, is the main filler in conductive pastes.

[0003] Currently, the conductivity of conductive silver paste used in LED packaging has been increased to 10 by optimizing the size, morphology, and high fill rate of silver particles. -4 ~10 -5 With a silver content of S / cm and a thermal conductivity exceeding 20 W / mK, it meets the requirements of high-power LEDs. However, due to its excessively high silver content, typically 600-800% of the base adhesive, the material cost accounts for more than 30% of the total packaging cost, limiting its widespread adoption in low- to mid-range lighting applications. Furthermore, silver ions are prone to migration under humid or electric field conditions, causing short circuits or resistance drift, significantly reducing the stability and lifespan of LED devices. In addition, the significant difference in thermal expansion coefficients between the conductive silver paste and the LED chip leads to interface delamination after thermal cycling, resulting in a substantial decrease in adhesive strength. In summary, existing conductive silver pastes for LED packaging suffer from high cost, poor stability, and inadequate interfacial adhesion. Summary of the Invention

[0004] This invention aims to at least partially solve one of the technical problems in the related art. Therefore, the main objective of this invention is to provide a high thermal and electrical conductivity silver paste for LED packaging, thereby addressing the problems of high cost, poor stability, and poor adhesion between interfaces in existing conductive silver pastes for LED packaging.

[0005] The objective of this invention is achieved through the following technical solution: In a first aspect, the present invention provides a high thermal and electrical conductivity silver paste for LED packaging, comprising the following components by weight: 100 parts of bisphenol A epoxy resin, 10-20 parts of benzoxazine resin, 0.5-2 parts of 2,5-dimethoxyphenylethylamine, 150-250 parts of flake-shaped micron silver powder, 30-120 parts of flake-shaped nano silver powder, 15-30 parts of latent curing agent, and 1-5 parts of curing accelerator.

[0006] In some specific embodiments, the epoxy equivalent of the bisphenol A epoxy resin is 300-500, and the benzoxazine resin is a bisphenol A benzoxazine resin.

[0007] In some specific embodiments, the average particle size of the flake-shaped micron silver powder ranges from 2 to 5 μm; the average particle size of the flake-shaped nano silver powder ranges from 15 to 30 nm.

[0008] In some specific embodiments, the flake-shaped micron-sized silver powder is modified by the following method: The flake-shaped silver powder is immersed in a 1-3 wt.% citric acid aqueous solution, ultrasonically dispersed for 5-15 min, and centrifuged and dried. Then, the surface is sprayed with a 0.5-1.5 wt.% KH-550 ethanol solution while stirring at 25-45℃ for 1-1.5 h. Finally, it is dried at 60-80℃ to obtain the modified flake-shaped silver powder.

[0009] In some specific embodiments, the latent curing agent is an acid anhydride curing agent, which is one or more of tetrahydrophthalic anhydride, methyltetrahydrophthalic anhydride, and hexahydrophthalic anhydride.

[0010] In some specific embodiments, the curing accelerator comprises microencapsulated 2-ethyl-4-methylimidazole.

[0011] Secondly, based on the same inventive concept, the present invention also provides a method for preparing a high thermal and electrical conductivity silver paste for LED packaging, comprising the following steps: 1) According to the formula requirements, bisphenol A epoxy resin, benzoxazine resin and 2,5-dimethoxyphenylethylamine are stirred to form a mixture. The mixture is mechanically stirred at 500-1000 r / min for 5-15 min at a temperature of 30-60℃ to obtain the mixed base material. 2) Add flake-shaped nano silver powder and flake-shaped micron silver powder to the mixed base material in sequence. After each addition, stir at 80-120℃ for 5-15 minutes, with a rotation speed of 300-800 r / min and a revolution speed of 800-1500 r / min. Cool to 40-60℃ and discharge to obtain the premixed silver paste. 3) Add latent curing agent and curing accelerator to the premixed silver paste in sequence. After mechanical dispersion, disperse by three-roll milling 3-5 times. Then remove impurities and uneven large particles from the silver paste with a 500-mesh sieve to obtain high thermal and electrical conductivity silver paste.

[0012] Compared with the prior art, the present invention has at least the following advantages: The high thermal and electrical conductivity silver paste for LED packaging provided by this invention utilizes a compound of epoxy resin and benzoxazine resin, along with the addition of 2,5-dimethoxyphenylethylamine. The epoxy resin, benzoxazine resin, and 2,5-dimethoxyphenylethylamine form a three-dimensional network structure, effectively improving the heat resistance of the conductive silver paste and significantly reducing its curing linear shrinkage. Simultaneously, the introduction of 2,5-dimethoxyphenylethylamine also significantly reduces the hygroscopicity of the conductive silver paste. In summary, by using a compound of epoxy resin and benzoxazine resin, and adding 2,5-dimethoxyphenylethylamine, the problems of poor adhesion, poor stability, and short service life of conductive silver paste caused by the poor heat resistance, high hygroscopicity, and high curing shrinkage of existing epoxy resins can be improved.

[0013] 2) The flake-shaped micron silver powder used in this application is coated with citric acid and then surface-modified with a silane coupling agent. This not only effectively improves its dispersion performance in the conductive silver paste base, but also introduces active groups that can adsorb onto the polar groups of the resin, forming conductive channels. The introduced flake-shaped nano-silver powder can fill the gaps between the flake-shaped micron silver powder, allowing previously non-contacting adjacent flake-shaped micron silver powder to come into contact, increasing the conductive pathway. Furthermore, when the flake-shaped nano-silver powder is cured at a temperature of 100-130℃, it can partially melt, forming sintering necks between flake-shaped nano-silver powder and between flake-shaped micron silver powder, thus forming conductive channels and effectively improving the conductivity and stability of the high thermal conductivity and conductive silver paste. In other words, by using a combination of flake-shaped nano-silver powder and flake-shaped micron silver powder, the entire system can achieve a low volume resistivity while reducing the amount of silver powder added, meeting the performance requirements of existing LED packaging.

[0014] 3) This application uses epoxy resin and benzoxazine resin to compound the product, and adds 2,5-dimethoxyphenylethylamine. It also combines the use of flake-shaped nano silver powder and flake-shaped micron silver powder to compound the product. This synergistically improves the electrical (thermal) conductivity pathway of silver powder in the base adhesive. When preparing the same amount of conductive silver paste, the amount of silver powder added can be reduced, which reduces the price of conductive silver paste by 150-200%, effectively reducing the raw material cost of existing conductive silver paste. In addition, the low silver content of the silver paste can also improve the product stability of the silver paste system, optimize the bonding strength and toughness of the silver paste, and greatly broaden the application range of silver paste. Detailed Implementation

[0015] The present invention will be further described in detail below with reference to specific embodiments. The following embodiments are merely descriptive and not limiting, and should not be used to limit the scope of protection of the present invention.

[0016] When a quantity, concentration, or other value or parameter is described as a range, preferred range, or preferred upper and lower limits, it should be understood that it is equivalent to specifically disclosing any range by combining any pair of upper or preferred values ​​with any lower or preferred values, regardless of whether the range is specifically disclosed. Unless otherwise stated, the numerical range values ​​listed herein include the endpoints of the range and all integers and fractions within that range.

[0017] Unless otherwise stated, all percentages, parts, ratios, etc. in this document are by weight.

[0018] The materials, methods, and embodiments described herein are exemplary and should not be construed as limiting unless otherwise stated.

[0019] This invention provides a general and / or specific description of the materials and experimental methods used in the experiments. Unless otherwise specified, all experimental or testing methods are conventional methods; all reagents or instruments used, unless otherwise specified, are commercially available conventional products prepared or used using conventional methods.

[0020] In the following embodiments, the bisphenol A epoxy resin is a liquid bisphenol A epoxy resin with an epoxy equivalent of 300-500; the benzoxazine resin is PBR-2000, purchased from Zibo Keerben Polymer New Materials Co., Ltd.; the average particle size range of the flake-shaped micron silver powder is 2-5 μm; and the average particle size range of the flake-shaped nano silver powder is 15-30 nm. In the following embodiments, the curing accelerator comprises microencapsulated 2-ethyl-4-methylimidazole, with an optimal curing temperature range of 80-120 degrees Celsius; in order to complete the reaction and achieve the highest glass transition temperature (Tg) and optimal mechanical properties, post-curing is typically performed at a temperature 20-30°C higher than the curing temperature. Example 1

[0021] This embodiment discloses a method for preparing a high thermal and electrical conductivity silver paste for LED packaging, comprising the following steps: 1) According to the formula requirements, 100 parts by weight of bisphenol A epoxy resin, 10 parts by weight of benzoxazine resin and 1 part by weight of 2,5-dimethoxyphenylethylamine are stirred to form a mixture. The mixture is mechanically stirred at 800 r / min for 10 min at a temperature of 45℃ to obtain the mixed base material. 2) Add 50 parts by weight of flake nano silver powder and 150 parts by weight of flake micron silver powder to the mixed base material in sequence. After each addition, stir at 100°C for 10 minutes, with a rotation speed of 500 r / min and a revolution speed of 1000 r / min. Cool to 50°C and discharge to obtain the premixed silver paste. 3) Add 20 parts by weight of latent curing agent and 1 part by weight of curing accelerator to the premixed silver paste in sequence. After mechanical dispersion, disperse by three-roll milling 5 times. Then remove impurities and uneven large particles from the silver paste with a 500-mesh sieve to obtain high thermal and electrical conductivity silver paste.

[0022] The latent curing agent is methyltetrahydrophthalic anhydride, and the curing accelerator is methylimidazole. Example 2

[0023] This embodiment discloses a method for preparing a high thermal and electrical conductivity silver paste for LED packaging, comprising the following steps: 1) According to the formula requirements, 100 parts by weight of bisphenol A epoxy resin, 15 parts by weight of benzoxazine resin and 1.0 parts by weight of 2,5-dimethoxyphenylethylamine are stirred to form a mixture. The mixture is mechanically stirred at 800 r / min for 10 min at a temperature of 45℃ to obtain the mixed base material. 2) Add 90 parts by weight of flake nano silver powder and 200 parts by weight of flake micron silver powder to the mixed base material in sequence. After each addition, stir at 100°C for 10 minutes, with a rotation speed of 500 r / min and a revolution speed of 1000 r / min. Cool to 50°C and discharge to obtain the premixed silver paste. 3) Add 25 parts by weight of latent curing agent and 3 parts by weight of curing accelerator to the premixed silver paste in sequence. After mechanical dispersion, grind and disperse it 5 times with a three-roll mill. Then remove impurities and uneven large particles from the silver paste with a 500-mesh sieve to obtain high thermal and electrical conductivity silver paste.

[0024] The latent curing agent is methyltetrahydrophthalic anhydride, and the curing accelerator is methylimidazole. Example 3

[0025] This embodiment discloses a method for preparing a high thermal and electrical conductivity silver paste for LED packaging, comprising the following steps: 1) According to the formula requirements, 100 parts by weight of bisphenol A epoxy resin, 20 parts by weight of benzoxazine resin and 1.5 parts by weight of 2,5-dimethoxyphenylethylamine are stirred to form a mixture. The mixture is mechanically stirred at 1000 r / min for 15 min at 50℃ to obtain the mixed base material. 2) Add 100 parts by weight of flake nano silver powder and 250 parts by weight of flake micron silver powder to the mixed base material in sequence. After each addition, stir at 100°C for 15 minutes, with a rotation speed of 800 r / min and a revolution speed of 1500 r / min. Cool to 50°C and discharge to obtain the premixed silver paste. 3) Add 30 parts by weight of latent curing agent and 3 parts by weight of curing accelerator to the premixed silver paste in sequence. After mechanical dispersion, disperse by three-roll milling 5 times. Then remove impurities and uneven large particles from the silver paste with a 500-mesh sieve to obtain high thermal and electrical conductivity silver paste.

[0026] The latent curing agent is methyltetrahydrophthalic anhydride, and the curing accelerator is methylimidazole. Example 4

[0027] This embodiment discloses a method for preparing a high thermal and electrical conductivity silver paste for LED packaging. The composition and proportions are basically the same as in Example 2, except that the flake-shaped micron silver powder used is modified flake-shaped micron silver powder. The flake-shaped micron silver powder is modified as follows: the flake-shaped micron silver powder is immersed in a 2 wt.% citric acid aqueous solution, ultrasonically dispersed for 10 min, and centrifuged and dried. Then, a 1.0 wt.% KH-550 ethanol solution is sprayed onto the surface, while stirring is maintained at 30°C for 1 h. Finally, it is dried at 60°C to obtain the modified flake-shaped micron silver powder. The preparation steps and process parameters are the same as in Example 2. Comparative Example 1

[0028] This comparative example provides a method for preparing a high thermal and electrical conductivity silver paste for LED packaging. Its components and proportions are basically the same as in Example 2, except that it does not contain benzoxazine resin and 2,5-dimethoxyphenylethylamine, but only bisphenol A epoxy resin base. Specifically: 1) According to the formula requirements, 100 parts by weight of bisphenol A epoxy resin were mechanically stirred at 800 r / min for 10 min at a temperature of 45℃ to obtain bisphenol A epoxy resin base material. The remaining preparation steps and process parameters are the same as in Example 2. Comparative Example 2

[0029] This comparative example provides a method for preparing a high thermal and electrical conductivity silver paste for LED packaging, which is basically the same as Example 2 in terms of composition and proportions, except that it does not contain 2,5-dimethoxyphenylethylamine. Specifically: 1) According to the formula requirements, 100 parts by weight of bisphenol A epoxy resin and 15 parts by weight of benzoxazine resin are stirred to form a mixture. The mixture is mechanically stirred at 800 r / min for 10 min at a temperature of 45℃ to obtain the mixed base material. The remaining preparation steps and process parameters are the same as in Example 2. Comparative Example 3

[0030] This comparative example provides a method for preparing a high thermal and electrical conductivity silver paste for LED packaging, which is basically the same as Example 2. Its components and proportions are basically the same as those in Example 2, except that it does not contain benzoxazine resin. Specifically: 1) According to the formula requirements, 100 parts by weight of bisphenol A epoxy resin and 1.0 parts by weight of 2,5-dimethoxyphenylethylamine are stirred to form a mixture. The mixture is mechanically stirred at 800 r / min for 10 min at a temperature of 45°C to obtain a mixed base material. The remaining preparation steps and process parameters are the same as in Example 2. Comparative Example 4

[0031] This comparative example provides a method for preparing a high thermal and electrical conductivity silver paste for LED packaging, which is basically the same as Example 2, except that spherical silver nanoparticles with a particle size of 15-30 nm are used; the preparation steps and parameters of steps 1), 2) and 3) are the same as those of Example 2. Comparative Example 5

[0032] This comparative example provides a method for preparing a high thermal and electrical conductivity silver paste for LED packaging, which is basically the same as Comparative Example 1, except that the filling amount of flake-shaped micron-sized silver powder and flake-shaped nano-sized silver powder is increased to 580 parts by weight. Specifically: 180 parts by weight of flake nano silver powder and 400 parts by weight of flake micron silver powder were added to the mixed base material in sequence. After each addition, the mixture was stirred at 100°C for 10 minutes, with a rotation speed of 500 r / min and a revolution speed of 1000 r / min. The mixture was then cooled to 50°C and discharged to obtain the premixed silver paste. The preparation steps and process parameters of steps 1) and 3) are the same as those in Example 2. Performance testing:

[0033] This application uses Examples 2 and 4 as examples. The high thermal conductivity and conductive silver paste prepared in Examples 2, 4, and Comparative Examples 1-5 were baked at 100°C for 30 minutes and then cured at 130°C for 60 minutes. The preparation and testing methods for the shear strength test were carried out in accordance with GB / T 7124-1986 standard. The volume resistivity was tested using the four-probe method after preparing conductive paste samples according to the length, width, and thickness of the glass sheet. The thermal conductivity was tested using a QTM-500 thermal conductivity meter.

[0034] Table 1 Performance test results of the high thermal conductivity and electrical conductivity adhesives in each embodiment

[0035] The data in the table shows that the high thermal and electrical conductivity silver paste provided in this application has excellent volume resistivity, shear strength, and thermal conductivity, which can meet the requirements of high-power LED packaging. A comparison of Comparative Examples 1, 2, 3, and Example 2 shows that the addition of benzoxazine resin and 2,5-dimethoxyphenylethylamine to the bisphenol A epoxy resin in this application can significantly improve the volume resistivity, shear strength, and thermal conductivity of the high thermal and electrical conductivity silver paste. A comparison between Comparative Example 4 and Example 2 shows that the specific particle size of the flake-shaped silver nanoparticles in this application can effectively improve the volume resistivity and thermal conductivity of the silver paste. This is mainly because the small-particle-size flake-shaped silver nanoparticles can be partially melted at a curing temperature of 120-160°C to form… Sintering necks form conductive (thermal) network pathways, thereby improving the volume resistivity and thermal conductivity of the silver paste. However, when using spherical silver nanoparticles of the same particle size, at a curing temperature of 100-130°C, they cannot be partially melted or the number of sintered necks formed is too small, resulting in insufficient conductive (thermal) network pathways between the silver nanoparticles and micron-sized silver powders, thus failing to effectively improve the volume resistivity and thermal conductivity. A comparison of Comparative Example 5 and Example 2 shows that, if only bisphenol A epoxy resin is used in this application, the volume resistivity of the silver paste needs to be increased to 10. -4 With a filler content on the order of Ω·m and 580 parts of bisphenol A epoxy resin, the cost of this conductive silver paste is reduced by 200% compared to the applied conductive silver paste, giving it a competitive edge in the market. Data from Examples 2 and 4 show that the electrical and thermal conductivity of this conductive silver paste are further improved by modifying the flake-shaped micron-sized silver powder.

[0036] In addition, this application further tests the heat resistance storage and heat and moisture resistance properties of the high thermal conductivity and electrical conductivity silver pastes prepared in Example 2 and Comparative Examples 1-4: Heat resistance storage test: The high temperature storage performance of conductive silver paste is to simulate the heat resistance performance of LED in actual application. The conductive silver paste sample is made into a volume resistivity test sample and a shear strength test sample, and the sample is stored at 150℃ for 1000h. Heat and moisture resistance test: The conductive silver paste sample was made into a volume resistivity test sample and a shear strength test sample. The sample was placed in a high and low temperature test chamber and stored at 85℃ and 85%RH for 1000h. The changes in its volume resistivity and shear strength were measured.

[0037]

[0038] As can be seen from the data in the table, the high thermal and electrical conductivity silver paste for LED packaging provided in this application has excellent heat storage performance, as well as heat and moisture resistance, and excellent overall performance.

[0039] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be covered within the scope of the claims and specification of the present invention.

Claims

1. A high thermal and electrical conductivity silver paste for LED packaging, characterized in that, The product comprises the following components by weight: 100 parts of bisphenol A epoxy resin, 10-20 parts of benzoxazine resin, 0.5-2 parts of 2,5-dimethoxyphenylethylamine, 150-250 parts of flake-shaped micron silver powder, 30-120 parts of flake-shaped nano silver powder, 15-30 parts of latent curing agent, and 1-5 parts of curing accelerator.

2. The high thermal and electrical conductivity silver paste for LED packaging according to claim 1, characterized in that, The bisphenol A epoxy resin has an epoxy equivalent of 300-500, and the benzoxazine resin is a bisphenol A benzoxazine resin.

3. The high thermal and electrical conductivity silver paste for LED packaging according to claim 1, characterized in that, The average particle size of the sheet-like micron silver powder ranges from 2 to 5 μm; the average particle size of the sheet-like nano silver powder ranges from 15 to 30 nm.

4. The high thermal and electrical conductivity silver paste for LED packaging according to claim 1, characterized in that, The flake-shaped micron-sized silver powder is modified by the following method: The flake-shaped silver powder is immersed in a 1-3 wt.% citric acid aqueous solution, ultrasonically dispersed for 5-15 min, and centrifuged and dried. Then, the surface is sprayed with a 0.5-1.5 wt.% KH-550 ethanol solution while stirring at 25-45℃ for 1-1.5 h. Finally, it is dried at 60-80℃ to obtain the modified flake-shaped silver powder.

5. The high thermal and electrical conductivity silver paste for LED packaging according to claim 4, characterized in that, The latent curing agent is an acid anhydride curing agent, which is one or more of tetrahydrophthalic anhydride, methyltetrahydrophthalic anhydride, and hexahydrophthalic anhydride.

6. The high thermal and electrical conductivity silver paste for LED packaging according to claim 1, characterized in that, The curing accelerator includes microencapsulated 2-ethyl-4-methylimidazole.

7. A method for preparing a high thermal and electrical conductivity silver paste for LED packaging according to any one of claims 1-6, characterized in that, Includes the following steps: 1) According to the formula requirements, bisphenol A epoxy resin, benzoxazine resin and 2,5-dimethoxyphenylethylamine are stirred to form a mixture. The mixture is mechanically stirred at 500-1000 r / min for 5-15 min at a temperature of 30-60℃ to obtain the mixed base material. 2) Add flake-shaped nano silver powder and flake-shaped micron silver powder to the mixed base material in sequence. After each addition, stir at 80-120℃ for 5-15 minutes, with a rotation speed of 300-800 r / min and a revolution speed of 800-1500 r / min. Cool to 40-60℃ and discharge to obtain the premixed silver paste. 3) Add latent curing agent and curing accelerator to the premixed silver paste in sequence. After mechanical dispersion, disperse by three-roll milling 3-5 times. Then remove impurities and uneven large particles from the silver paste with a 500-mesh sieve to obtain high thermal and electrical conductivity silver paste.

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