Low-temperature silver paste suitable for hole filling process and preparation method of low-temperature silver paste

Abstract

The invention discloses low-temperature silver paste and a preparation method thereof. The conductive silver paste comprises the following components in parts by weight: 7-12 parts of matrix resin, 1-2.5 parts of a curing agent, 1-2.5 parts of a dispersing agent, 0.5-1.5 parts of a coupling agent, 75-85 parts of conductive silver powder and 3-6 parts of a thixotropic anti-settling agent, the matrix resin is low-viscosity liquid epoxy resin, and the viscosity of the matrix resin is 200-1000 cP; the curing agent is a latent epoxy curing agent, and the deblocking temperature of the curing agent does not exceed 90 DEG C; the dispersing agent is a hyperbranched polymer type dispersing agent; the conductive silver powder is a combination of micron-sized flaky silver powder and submicron-sized spherical silver powder; the thixotropic anti-settling agent is a uniform mixture formed by grinding and dispersing matrix resin, a dispersing agent, high-conductivity carbon black and expanded graphite powder. The low-temperature silver paste has the beneficial effects that poor conductivity caused by grouting defects is prevented, and the low-temperature silver paste has excellent grouting quality, so that the prepared low-temperature silver paste has excellent conductivity and can still keep a stable state under the condition of high silver powder filling amount.

Description

Technical Field

[0001] The present invention relates to a silver paste and a preparation method thereof, in particular to a low-temperature silver paste suitable for a hole filling process and a preparation method thereof, belonging to the technical field of paste preparation. Background Art

[0002] With the increasing integration of electronic products, the wiring density of circuit boards and electronic components has gradually increased. To optimize the design of traditional circuit boards, accommodate more complex and compact circuit layouts, reduce signal transmission loss or interference, and improve signal integrity, via technology has emerged. Via technology uses structures such as through-holes, blind vias, and buried vias, plating a conductive layer or filling the holes with conductive materials to electrically connect different layers of circuit boards or functional structures. It has become a key process in electronics manufacturing.

[0003] Low-temperature silver paste has excellent properties such as good conductivity, simple application process, and low curing temperature. It does not cause thermal damage to substrates that are not resistant to high temperatures during the curing process. Therefore, it has been used in the filling of conductive holes in polymer substrates such as epoxy resin, polycarbonate, and polyimide. For example, multi-layer FPCs form inter-layer conduction through filling holes, and 5G mobile phone shell antennas and internal circuit boards form signal connections through filling holes.

[0004] However, existing low-temperature silver pastes are mostly designed to form thin-film conductive circuits with a thickness of less than 20μm through a printing process, and are not fully suitable for use in conductive holes with a higher thickness. Volatile solvents are present in their components to adjust viscosity and fluidity. During heating and curing, the solvents evaporate, causing defects such as bubbles, depressions, and shrinkage cavities. Using reactive active diluents can alleviate the above problems, but active diluents usually have a low molecular weight and remain volatile before reacting with the low-temperature silver paste matrix resin and curing agent during the curing temperature increase process, making it impossible to completely avoid the occurrence of filling defects. In addition, due to the large amount of silver powder filled, low-temperature silver pastes are usually added with thixotropic anti-settling agents to prevent the silver powder from settling. However, traditional thixotropic anti-settling agents such as fumed silica, organic bentonite, and polyamide wax are difficult to disperse in the silver paste system and are non-conductive, thereby damaging the uniformity and conductivity of the low-temperature silver paste and affecting the conduction of the filling circuit. Therefore, how to prepare a low-temperature silver paste suitable for the filling process has become a technical problem that needs to be solved urgently. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a low-temperature silver paste suitable for the hole filling process and a preparation method thereof, which can effectively solve the problems of poor adaptability, insufficient hole filling quality, conductivity and other performance of the existing low-temperature silver paste hole filling process.

[0006] In order to solve the above technical problems, the low-temperature silver paste suitable for the hole filling process of the present invention comprises the following components in parts by weight: Base resin: 7-12 parts Curing agent: 1-2.5 parts Dispersant: 1-2.5 parts Coupling agent: 0.5-1.5 parts Conductive silver powder: 75-85 parts Thixotropic anti-settling agent: 3-6 parts The matrix resin is a low-viscosity liquid epoxy resin with a viscosity of 200 to 1000 cP; the curing agent is a latent epoxy curing agent with a deblocking temperature not exceeding 90°C; the dispersant is a hyperbranched polymer dispersant; the conductive silver powder is a combination of micron-sized flaky silver powder and submicron-sized spherical silver powder; and the thixotropic anti-settling agent is a uniform mixture formed by grinding and dispersing the matrix resin, dispersant, highly conductive carbon black and expanded graphite powder.

[0007] The low-viscosity liquid epoxy resin is a combination of one or more of tetrahydrophthalic acid bisglycidyl ester, hexahydrophthalic acid bisglycidyl ester, 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexylcarboxylate or bis((3,4-epoxycyclohexyl)methyl)adipate.

[0008] The latent epoxy curing agent is a combination of one or more of Ajinomoto PN-23, Ajinomoto PN-23J, Ajinomoto PN-40J, Shikoku Chemical 2E4MZ, Shikoku Chemical 2E4MZCN, Fujicure FXR-1020, Fujicure FXR-1061, Fujicure FXR-1081 or Fujicure FXR-1121.

[0009] The hyperbranched polymer dispersant is one of BYK-9076, BYK-9077, DISPERBYK-2152, DISPERBYK-2155, DISPERBYK-2200, DISPERBYK-2205 or Silok 7631.

[0010] The coupling agent is a combination of one or more of silane coupling agent KH-151, silane coupling agent KH-171, silane coupling agent KH-172, silane coupling agent KH-560, silane coupling agent KH-570, titanate coupling agent KR-TTS, titanate coupling agent KR-12, titanate coupling agent KR-38S, titanate coupling agent KR-138S or titanate coupling agent KR-238S.

[0011] In terms of weight ratio, the ratio of micron-sized flaky silver powder to submicron-sized spherical silver powder in the conductive silver powder is 3 to 6:1.

[0012] The particle size of the micron-sized flaky silver powder is 2.0 to 4.0 μm, and the tap density is 4.5 to 5.5 g / cm3; the particle size of the submicron-sized spherical silver powder is 0.3 to 0.6 μm, and the tap density is 5.0 to 6.0 g / cm3.

[0013] The highly conductive carbon black in the thixotropic anti-settling agent is one of CABOT VXC-72, CABOT VXC-72R, CABOTBP2000, CHEZACARB AC80, Ketjenblack EC300J or Ketjenblack EC600JD.

[0014] The mesh number of the expanded graphite powder in the thixotropic anti-settling agent is 50-150 meshes.

[0015] Calculated by weight, the ratio of the base resin, the dispersant, the high-conductive carbon black and the expanded graphite powder in the thixotropic anti-settling agent is 1:0.3-0.7:0.8-1.5:0.2-0.6.

[0016] A method for preparing a low-temperature silver paste suitable for a hole filling process comprises the following steps: (1) Preparation of thixotropic anti-settling agent: The base resin, dispersant, highly conductive carbon black and expanded graphite powder required for preparing the thixotropic anti-settling agent are weighed in proportion by weight, the base resin and dispersant are first poured into a sand mill, and pre-mixed at a speed of 800-1500 rpm for 20-45 minutes; then, grinding zirconium beads and expanded graphite powder are added thereto, and grinding is carried out at a speed of 1500-3000 rpm for 1.5-3 hours; after the grinding is completed, highly conductive carbon black is added thereto, and the whole is ground at a speed of 1500-3000 rpm for 1-2.5 hours; after the whole grinding is completed, impurities, large particles of powder and grinding zirconium beads are filtered out using a 200-500 mesh filter to obtain a thixotropic anti-settling agent; (2) Preparation of silver paste carrier: Weigh the base resin, curing agent, dispersant, coupling agent and thixotropic anti-settling agent prepared in step (1) required for preparing low-temperature silver paste according to the weight ratio, and evenly mix the above components in a planetary disperser at a speed of 800-1500 rpm for 30-60 min to obtain a silver paste carrier; (3) Preparation of low-temperature silver paste: The silver paste carrier and the conductive silver powder prepared in step (2) were weighed according to the weight ratio, and the above components were uniformly mixed in a planetary disperser at a dispersion speed of 1200-1800 rpm for 30-60 min. The mixture was then placed in a three-roll grinder for grinding until the fineness was less than 5 μm, and then the mixture was discharged. Impurities were filtered out using a 400-800 mesh filter to obtain a low-temperature silver paste.

[0017] Compared with the prior art, the present invention has the following beneficial effects: The present invention avoids the hole filling defects such as bubbles, depressions, shrinkage holes and the like caused by the volatilization of various solvents in the curing process of the existing low-temperature silver paste through the design of components and the improvement of the preparation method, thereby preventing poor conductivity caused by the hole filling defects and having excellent hole filling quality. In particular, a carbon-based conductive powder is used, which is combined with a matrix resin and a dispersant, and a thixotropic anti-settling agent with conductivity, good dispersibility and anti-settling effect is first prepared by grinding and dispersing, and then added to the silver paste system. The problems of poor dispersibility and damage to conductivity of traditional thixotropic anti-settling agents are overcome, so that the low-temperature silver paste prepared therefrom has excellent conductivity and can still maintain a stable state under a high silver powder filling amount. DETAILED DESCRIPTION

[0018] The low-temperature silver paste suitable for the hole filling process and the preparation method thereof of the present invention will be further described in detail below in conjunction with specific embodiments.

[0019] The low-temperature silver paste suitable for the hole filling process of the present invention comprises the following components in parts by weight: base resin: 7 to 12 parts, curing agent: 1 to 2.5 parts, dispersant: 1 to 2.5 parts, coupling agent: 0.5 to 1.5 parts, conductive silver powder: 75 to 85 parts, and thixotropic anti-settling agent: 3 to 6 parts, wherein the base resin is a low-viscosity liquid epoxy resin with a viscosity of 200 to 1000 cP; the curing agent is a latent epoxy curing agent with a deblocking temperature not exceeding 90°C; the dispersant is a hyperbranched polymer type Dispersant; the conductive silver powder is a combination of micron-sized flaky silver powder and submicron-sized spherical silver powder, and the ratio of micron-sized flaky silver powder to submicron-sized spherical silver powder in the conductive silver powder is 3 to 6:1 in parts by weight; the thixotropic anti-settling agent is a uniform mixture formed by grinding and dispersing a base resin, a dispersant, highly conductive carbon black and expanded graphite powder, the base resin in the thixotropic anti-settling agent being of the same type as the base resin in the aforementioned low-temperature silver paste, and the dispersant in the thixotropic anti-settling agent being of the same type as the dispersant in the aforementioned low-temperature silver paste.

[0020] Preferably, the low-viscosity liquid epoxy resin is a combination of one or more of tetrahydrophthalic acid bisglycidyl ester (common brand: Huntsman CY183, viscosity 500-1000 cP), hexahydrophthalic acid bisglycidyl ester (common brand: Huntsman CY184, viscosity 300-900 cP), 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexylcarboxylate (common brand: CELLOXIDE 2021P, DOW UVR-6110, Huntsman CY179, viscosity 200-300 cP) or bis((3,4-epoxycyclohexyl)methyl)adipate (common brand: DOW UVR-6128, viscosity 400-800 cP). Low-viscosity liquid epoxy resin is used as the matrix resin. Compared with conventional epoxy resins such as bisphenol A and bisphenol F, it has better wettability for silver powder, which is conducive to the dispersion and filling of silver powder in the matrix resin. The silver paste prepared after adding silver powder has lower viscosity and good fluidity, thus avoiding the addition of volatile solvents or active diluents used to reduce viscosity, and preventing filling defects caused by solvent volatilization and silver paste volume shrinkage during the curing process.

[0021] Preferably, the latent epoxy curing agent is a combination of one or more of Ajinomoto PN-23, Ajinomoto PN-23J, Ajinomoto PN-40J, Shikoku Chemical 2E4MZ, Shikoku Chemical 2E4MZCN, Fujicure FXR-1020, Fujicure FXR-1061, Fujicure FXR-1081 or Fujicure FXR-1121.

[0022] Preferably, the hyperbranched polymer dispersant is one of BYK-9076, BYK-9077, DISPERBYK-2152, DISPERBYK-2155, DISPERBYK-2200, DISPERBYK-2205 or Silok 7631.

[0023] The silane coupling agent is a combination of one or more of silane coupling agent KH-151, silane coupling agent KH-171, silane coupling agent KH-172, silane coupling agent KH-560, silane coupling agent KH-570, titanate coupling agent KR-TTS, titanate coupling agent KR-12, titanate coupling agent KR-38S, titanate coupling agent KR-138S or titanate coupling agent KR-238S.

[0024] Preferably, the particle size of the micron-sized flaky silver powder is 2.0-4.0 μm, and the tap density is 4.5-5.5 g / cm3; the particle size of the submicron-sized spherical silver powder is 0.3-0.6 μm, and the tap density is 5.0-6.0 g / cm3.

[0025] Preferably, the highly conductive carbon black in the thixotropic anti-settling agent is one of CABOT VXC-72, CABOT VXC-72R, CABOTBP2000, CHEZACARB AC80, Ketjenblack EC300J or Ketjenblack EC600JD.

[0026] Preferably, the mesh size of the expanded graphite powder in the thixotropic anti-settling agent is 50-150 meshes.

[0027] Preferably, the ratio of the base resin, dispersant, highly conductive carbon black and expanded graphite powder in the thixotropic anti-settling agent is 1:0.3-0.7:0.8-1.5:0.2-0.6 in parts by weight.

[0028] The effects are verified by the following specific examples and comparative examples; Example 1

[0029] The low-temperature silver paste suitable for the hole filling process of this embodiment is prepared by the following steps: (1) Preparation of thixotropic anti-settling agent: The invention discloses a method for preparing a thixotropic anti-settling agent, comprising weighing 10 parts of a low-viscosity liquid epoxy resin Huntsman CY179, 5 parts of a hyperbranched polymer dispersant BYK-9076, 10.5 parts of a highly conductive carbon black CABOT VXC-72R, and 4.5 parts of 120-mesh expanded graphite powder, required for preparing a thixotropic anti-settling agent. The low-viscosity liquid epoxy resin Huntsman CY179 and the hyperbranched polymer dispersant BYK-9076 are first poured into a sand mill and pre-mixed at a speed of 1200 rpm for 30 minutes. Then, grinding zirconium beads and 120-mesh expanded graphite powder are added thereto, and the mixture is ground at a speed of 2500 rpm for 2 hours. After the grinding, the highly conductive carbon black CABOT VXC-72R is added thereto, and the mixture is ground as a whole at a speed of 2500 rpm for 1.5 hours. After the grinding, a 400-mesh filter is used to remove impurities, large-particle powder, and the grinding zirconium beads to obtain a thixotropic anti-settling agent.

[0030] (2) Preparation of silver paste carrier: 8 parts by weight of low-viscosity liquid epoxy resin Huntsman CY179, 1.2 parts of latent epoxy curing agent Fujicure FXR-1020, 2 parts of hyperbranched polymer dispersant BYK-9076, 1 part of silane coupling agent KH-560 and 5 parts of thixotropic anti-settling agent prepared in step (1) required for preparing low-temperature silver paste were weighed, and the above components were uniformly mixed in a planetary disperser at a speed of 1200 rpm for 45 minutes to obtain a silver paste carrier; (3) Preparation of low-temperature silver paste: In parts by weight, 17.2 parts of the silver paste carrier prepared in step (2), 66.2 parts of micron-sized flaky silver powder (average particle size 2.8 μm, tap density 5.1 g / cm3) and 16.6 parts of submicron-sized spherical silver powder (average particle size 0.5 μm, tap density 5.7 g / cm3) were weighed, and the above components were uniformly mixed in a planetary disperser at a dispersion speed of 1500 rpm for 45 min. The mixture was then placed in a three-roll grinder for grinding until the fineness was less than 5 μm, and then the mixture was discharged. Impurities were filtered out using a 600-mesh filter to obtain the low-temperature silver paste suitable for the hole filling process of the present invention. Example 2

[0031] The low-temperature silver paste suitable for the hole filling process of this embodiment is prepared by the following steps: (1) Preparation of thixotropic anti-settling agent: The invention discloses a method for preparing a thixotropic anti-settling agent, comprising weighing 10 parts of a low-viscosity liquid epoxy resin Huntsman CY179, 5 parts of a hyperbranched polymer dispersant BYK-9076, 10.5 parts of a highly conductive carbon black CABOT VXC-72R, and 4.5 parts of 120-mesh expanded graphite powder, required for preparing a thixotropic anti-settling agent. The low-viscosity liquid epoxy resin Huntsman CY179 and the hyperbranched polymer dispersant BYK-9076 are first poured into a sand mill and pre-mixed at a speed of 1200 rpm for 30 minutes. Then, grinding zirconium beads and 120-mesh expanded graphite powder are added thereto, and the mixture is ground at a speed of 2500 rpm for 2 hours. After the grinding, the highly conductive carbon black CABOT VXC-72R is added thereto, and the mixture is ground as a whole at a speed of 2500 rpm for 1.5 hours. After the grinding, a 400-mesh filter is used to remove impurities, large-particle powder, and the grinding zirconium beads to obtain a thixotropic anti-settling agent.

[0032] (2) Preparation of silver paste carrier: 9 parts by weight of Huntsman CY179, a low-viscosity liquid epoxy resin, 1.4 parts of Fujicure FXR-1081, 2 parts of BYK-9076, a hyperbranched polymer dispersant, 1 part of KH-570, a silane coupling agent, and 5 parts of the thixotropic anti-settling agent prepared in step (1) required for preparing a low-temperature silver paste were weighed, and the above components were uniformly mixed in a planetary disperser at a speed of 1200 rpm for 45 min to obtain a silver paste carrier; (3) Preparation of low-temperature silver paste: In parts by weight, 18.4 parts of the silver paste carrier prepared in step (2), 65.3 parts of micron-sized flaky silver powder (average particle size 2.8 μm, tap density 5.1 g / cm3) and 16.3 parts of submicron-sized spherical silver powder (average particle size 0.5 μm, tap density 5.7 g / cm3) were weighed, and the above components were uniformly mixed in a planetary disperser at a dispersion speed of 1500 rpm for 45 min. The mixture was then placed in a three-roll grinder for grinding until the fineness was less than 5 μm, and then the mixture was discharged. Impurities were filtered out using a 600-mesh filter to obtain the low-temperature silver paste suitable for the hole filling process of the present invention. Example 3

[0033] The low-temperature silver paste suitable for the hole filling process of this embodiment is prepared by the following steps: (1) Preparation of thixotropic anti-settling agent: The invention discloses a method for preparing a thixotropic anti-settling agent, comprising weighing 10 parts of a low-viscosity liquid epoxy resin Huntsman CY184, 5 parts of a hyperbranched polymer dispersant DISPERBYK-2152, 12 parts of a highly conductive carbon black Ketjenblack EC300J, and 3 parts of 120-mesh expanded graphite powder, required for preparing a thixotropic anti-settling agent. The low-viscosity liquid epoxy resin Huntsman CY184 and the hyperbranched polymer dispersant DISPERBYK-2152 are first poured into a sand mill and pre-mixed at a rotation speed of 1200 rpm for 30 minutes. Then, grinding zirconium beads and 120-mesh expanded graphite powder are added thereto, and the mixture is ground at a rotation speed of 2500 rpm for 2 hours. After the grinding is completed, the highly conductive carbon black Ketjenblack EC300J is added thereto, and the whole mixture is ground at a rotation speed of 2500 rpm for 1.5 hours. After the whole grinding is completed, a 400-mesh filter is used to filter out impurities, large-particle powder, and the grinding zirconium beads to obtain a thixotropic anti-settling agent.

[0034] (2) Preparation of silver paste carrier: 10 parts by weight of Huntsman CY184, a low-viscosity liquid epoxy resin, 2 parts of a latent epoxy curing agent, Ajinomoto PN-23J, 1.5 parts of a hyperbranched polymer dispersant, DISPERBYK-2152, 1 part of a titanate coupling agent, KR-TTS, and 5 parts of a thixotropic anti-settling agent prepared in step (1) required for preparing a low-temperature silver paste were weighed, and the above components were uniformly mixed in a planetary disperser at a speed of 1200 rpm for 45 min to obtain a silver paste carrier; (3) Preparation of low-temperature silver paste: In parts by weight, 19.5 parts of the silver paste carrier prepared in step (2), 67.1 parts of micron-sized flaky silver powder (average particle size 2.8 μm, tap density 5.1 g / cm3) and 13.4 parts of submicron-sized spherical silver powder (average particle size 0.5 μm, tap density 5.7 g / cm3) were weighed, and the above components were uniformly mixed in a planetary disperser at a dispersion speed of 1500 rpm for 45 min. The mixture was then placed in a three-roll grinder for grinding until the fineness was less than 5 μm, and then the mixture was discharged. Impurities were filtered out using a 600-mesh filter to obtain the low-temperature silver paste suitable for the hole filling process of the present invention. Example 4

[0035] The low-temperature silver paste suitable for the hole filling process of this embodiment is prepared by the following steps: (1) Preparation of thixotropic anti-settling agent: The invention discloses a method for preparing a thixotropic anti-settling agent, comprising weighing 10 parts of a low-viscosity liquid epoxy resin Huntsman CY184, 5 parts of a hyperbranched polymer dispersant DISPERBYK-2152, 12 parts of a highly conductive carbon black Ketjenblack EC300J, and 3 parts of 120-mesh expanded graphite powder, required for preparing a thixotropic anti-settling agent. The low-viscosity liquid epoxy resin Huntsman CY184 and the hyperbranched polymer dispersant DISPERBYK-2152 are first poured into a sand mill and pre-mixed at a rotation speed of 1200 rpm for 30 minutes. Then, grinding zirconium beads and 120-mesh expanded graphite powder are added thereto, and the mixture is ground at a rotation speed of 2500 rpm for 2 hours. After the grinding is completed, the highly conductive carbon black Ketjenblack EC300J is added thereto, and the whole mixture is ground at a rotation speed of 2500 rpm for 1.5 hours. After the whole grinding is completed, a 400-mesh filter is used to filter out impurities, large-particle powder, and the grinding zirconium beads to obtain a thixotropic anti-settling agent.

[0036] (2) Preparation of silver paste carrier: Weigh 11 parts by weight of Huntsman CY184, a low-viscosity liquid epoxy resin, 2.2 parts of a latent epoxy curing agent, Ajinomoto PN-40J, 1.5 parts of a hyperbranched polymer dispersant, DISPERBYK-2152, 1 part of a titanate coupling agent, KR-138S, and 5 parts of a thixotropic anti-settling agent prepared in step (1) required for preparing a low-temperature silver paste, and uniformly mix the above components in a planetary disperser at a speed of 1200 rpm for 45 minutes to obtain a silver paste carrier; (3) Preparation of low-temperature silver paste: In parts by weight, 20.7 parts of the silver paste carrier prepared in step (2), 66.1 parts of micron-sized flaky silver powder (average particle size 2.8 μm, tap density 5.1 g / cm3) and 13.2 parts of submicron-sized spherical silver powder (average particle size 0.5 μm, tap density 5.7 g / cm3) were weighed and uniformly mixed in a planetary disperser at a dispersion speed of 1500 rpm for 45 min. The mixture was then placed in a three-roll mill for grinding until the fineness was less than 5 μm and then discharged. Impurities were filtered out using a 600-mesh filter to obtain the low-temperature silver paste suitable for the hole filling process of the present invention.

[0037] Comparative Example 1 Based on Example 1, the base resin and dispersant in the thixotropic anti-settling agent were transferred to the base resin and dispersant of the silver paste, respectively. The highly conductive carbon black and expanded graphite powder in the thixotropic anti-settling agent were replaced with a conventional thixotropic anti-settling agent, and a volatile solvent was added to adjust the viscosity. A low-temperature silver paste was prepared using conventional epoxy resin E51, the volatile solvent ethylene glycol butyl ether acetate, and the thixotropic anti-settling agent fumed silica. The preparation was carried out by the following steps: (1) Preparation of silver paste carrier: Weigh 9.7 parts (8 parts original + 1.7 parts transferred from the thixotropic anti-settling agent in Example 1) of epoxy resin E51, 1.2 parts of latent epoxy curing agent Fujicure FXR-1020, 2.8 parts (2 parts original + 0.8 parts transferred from the thixotropic anti-settling agent in Example 1) of hyperbranched polymer dispersant BYK-9076, 1 part of silane coupling agent KH-560, and 2.5 parts (replacing the high conductive carbon black and expanded graphite powder in the thixotropic anti-settling agent in Example 1, a total of 2.5 parts) of thixotropic anti-settling agent fumed silica, and mix the above components uniformly in a planetary disperser at a speed of 1200 rpm for 45 minutes to obtain a silver paste carrier; (2) Preparation of low-temperature silver paste: In parts by weight, 17.2 parts of the silver paste carrier prepared in step (1), 66.2 parts of micron-sized flaky silver powder (average particle size 2.8 μm, tap density 5.1 g / cm3) and 16.6 parts of submicron-sized spherical silver powder (average particle size 0.5 μm, tap density 5.7 g / cm3) were weighed, and 10 parts of volatile solvent ethylene glycol butyl ether acetate were added to adjust the viscosity. The above components were uniformly mixed in a planetary disperser at a dispersion speed of 1500 rpm for 45 min, and then placed in a three-roll grinder for grinding. After grinding to a fineness of less than 5 μm, the material was discharged, and then impurities were filtered out using a 600-mesh filter to obtain the low-temperature silver paste prepared in Comparative Example 1.

[0038] Comparative Example 2 Based on Example 1, the base resin and dispersant in the thixotropic anti-settling agent were transferred to the base resin and dispersant of the silver paste, respectively. The highly conductive carbon black and expanded graphite powder in the thixotropic anti-settling agent were replaced with a conventional thixotropic anti-settling agent, and a reactive diluent was added to adjust the viscosity. A low-temperature silver paste was prepared using conventional epoxy resin E51, reactive diluent AGE, and thixotropic anti-settling agent fumed silica, and the preparation was carried out by the following steps: (1) Preparation of silver paste carrier: Weigh 9.7 parts (8 parts original + 1.7 parts transferred from the thixotropic anti-settling agent in Example 1) of epoxy resin E51, 1.2 parts of latent epoxy curing agent Fujicure FXR-1020, 2.8 parts (2 parts original + 0.8 parts transferred from the thixotropic anti-settling agent in Example 1) of hyperbranched polymer dispersant BYK-9076, 1 part of silane coupling agent KH-560, and 2.5 parts (replacing the high conductive carbon black and expanded graphite powder in the thixotropic anti-settling agent in Example 1, a total of 2.5 parts) of thixotropic anti-settling agent fumed silica, and mix the above components uniformly in a planetary disperser at a speed of 1200 rpm for 45 minutes to obtain a silver paste carrier; (2) Preparation of low-temperature silver paste: In parts by weight, 17.2 parts of the silver paste carrier prepared in step (1), 66.2 parts of micron-sized flaky silver powder (average particle size 2.8 μm, tap density 5.1 g / cm3) and 16.6 parts of submicron-sized spherical silver powder (average particle size 0.5 μm, tap density 5.7 g / cm3) were weighed, and 10 parts of active diluent AGE were added to adjust the viscosity. The above components were uniformly mixed in a planetary disperser at a dispersion speed of 1500 rpm for 45 min, and then placed in a three-roll grinder for grinding. After grinding to a fineness of less than 5 μm, the material was discharged, and then impurities were filtered out using a 600-mesh filter to obtain the low-temperature silver paste prepared in Comparative Example 2.

[0039] The viscosity of the low-temperature silver paste prepared in Examples 1 to 4 and Comparative Examples 1 to 2 was tested using a Brookfield viscometer, and the paste was placed at room temperature for 72 hours to observe whether stratification, sedimentation, and other state changes occurred. The low-temperature silver paste prepared in Examples 1 to 4 and Comparative Examples 1 to 2 was printed on a polycarbonate sheet by screen printing to test the volume resistivity and adhesion. The low-temperature silver paste prepared in Examples 1 to 4 and Comparative Examples 1 to 2 was filled into through holes prepared in a polycarbonate substrate by dispensing, with a hole diameter of 0.2 mm and a hole depth of 0.5 mm, to test the hole filling quality. The curing temperature was 90°C and the curing time was 60 minutes. After curing was completed, the volume resistivity was tested using a four-probe tester, the adhesion was tested using the hundred-grid method, the silver paste filled with the hole was sliced, and the hole filling quality was observed under a metallographic microscope.

[0040] The test results are shown in Table 1: Table 1

[0041] It can be seen from the above test results that the low-temperature silver paste prepared in Examples 1 to 4 of the present invention is specifically designed for via filling applications through improvements in components and preparation methods. It has a stable storage state, low resistivity after curing, and high via filling quality. It is suitable for via filling and conduction scenarios of various electronic components and circuit boards under low-temperature curing conditions. It effectively improves the shortcomings of existing low-temperature silver pastes such as insufficient conductivity and many via filling defects caused by the volatilization of solvents during the curing process and the addition of non-conductive and difficult-to-disperse thixotropic anti-settling agents. It has broad application prospects.

Claims

1. A low-temperature silver paste suitable for hole filling process, characterized in that: In parts by weight, it comprises the following components: Base resin: 7-12 parts Curing agent: 1-2.5 parts Dispersant: 1-2.5 parts Coupling agent: 0.5-1.5 parts Conductive silver powder: 75-85 parts Thixotropic anti-settling agent: 3-6 parts The matrix resin is a low-viscosity liquid epoxy resin with a viscosity of 200 to 1000 cP; the curing agent is a latent epoxy curing agent with a deblocking temperature not exceeding 90°C; the dispersant is a hyperbranched polymer dispersant; the conductive silver powder is a combination of micron-sized flaky silver powder and submicron-sized spherical silver powder; and the thixotropic anti-settling agent is a uniform mixture formed by grinding and dispersing the matrix resin, dispersant, highly conductive carbon black and expanded graphite powder.

2. The low-temperature silver paste suitable for hole filling process according to claim 1, characterized in that: The low-viscosity liquid epoxy resin is a combination of one or more of tetrahydrophthalic acid bisglycidyl ester, hexahydrophthalic acid bisglycidyl ester, 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexylcarboxylate or bis((3,4-epoxycyclohexyl)methyl)adipate.

3. The low-temperature silver paste suitable for hole filling process according to claim 1 or 2, characterized in that: The latent epoxy curing agent is a combination of one or more of Ajinomoto PN-23, Ajinomoto PN-23J, Ajinomoto PN-40J, Shikoku Chemical 2E4MZ, Shikoku Chemical 2E4MZCN, Fujicure FXR-1020, Fujicure FXR-1061, Fujicure FXR-1081 or Fujicure FXR-1121.

4. The low-temperature silver paste suitable for hole filling process according to claim 3, characterized in that: The hyperbranched polymer dispersant is one of BYK-9076, BYK-9077, DISPERBYK-2152, DISPERBYK-2155, DISPERBYK-2200, DISPERBYK-2205 or Silok 7631.

5. The low-temperature silver paste suitable for hole filling process according to claim 1, 2 or 4, characterized in that: The coupling agent is a combination of one or more of silane coupling agent KH-151, silane coupling agent KH-171, silane coupling agent KH-172, silane coupling agent KH-560, silane coupling agent KH-570, titanate coupling agent KR-TTS, titanate coupling agent KR-12, titanate coupling agent KR-38S, titanate coupling agent KR-138S or titanate coupling agent KR-238S.

6. The low-temperature silver paste suitable for hole filling process according to claim 5, characterized in that: In terms of weight ratio, the ratio of micron-sized flaky silver powder to submicron-sized spherical silver powder in the conductive silver powder is 3 to 6:

1.

7. The low-temperature silver paste suitable for hole filling process according to claim 1, 2, 4 or 6, characterized in that: The particle size of the micron-sized flaky silver powder is 2.0 to 4.0 μm, and the tap density is 4.5 to 5.5 g / cm3; the particle size of the submicron-sized spherical silver powder is 0.3 to 0.6 μm, and the tap density is 5.0 to 6.0 g / cm3.

8. The low-temperature silver paste suitable for hole filling process according to claim 7, characterized in that: The highly conductive carbon black in the thixotropic anti-settling agent is one of CABOT VXC-72, CABOT VXC-72R, CABOT BP2000, CHEZACARB AC80, Ketjenblack EC300J or Ketjenblack EC600JD.

9. The low-temperature silver paste suitable for hole filling process according to claim 8, characterized in that: The mesh number of the expanded graphite powder in the thixotropic anti-settling agent is 50-150 meshes.

10. The low-temperature silver paste suitable for hole filling process according to claim 9, characterized in that: In terms of weight ratio, the ratio of base resin, dispersant, high conductive carbon black and expanded graphite powder in the thixotropic anti-settling agent is 1:0.3-0.7:0.8-1.5:0.2-0.6; A method for preparing a low-temperature silver paste suitable for a hole filling process, characterized by comprising the following steps: (1) Preparation of thixotropic anti-settling agent: The base resin, dispersant, highly conductive carbon black and expanded graphite powder required for preparing the thixotropic anti-settling agent are weighed in proportion by weight, the base resin and dispersant are first poured into a sand mill, and pre-mixed at a speed of 800-1500 rpm for 20-45 minutes; then, grinding zirconium beads and expanded graphite powder are added thereto, and grinding is carried out at a speed of 1500-3000 rpm for 1.5-3 hours; after the grinding is completed, highly conductive carbon black is added thereto, and the whole is ground at a speed of 1500-3000 rpm for 1-2.5 hours; after the whole grinding is completed, impurities, large particles of powder and grinding zirconium beads are filtered out using a 200-500 mesh filter to obtain a thixotropic anti-settling agent; (2) Preparation of silver paste carrier: Weigh the base resin, curing agent, dispersant, coupling agent and thixotropic anti-settling agent prepared in step (1) required for preparing low-temperature silver paste according to the weight ratio, and evenly mix the above components in a planetary disperser at a speed of 800-1500 rpm for 30-60 min to obtain a silver paste carrier; (3) Preparation of low-temperature silver paste: The silver paste carrier and the conductive silver powder prepared in step (2) were weighed according to the weight ratio, and the above components were uniformly mixed in a planetary disperser at a dispersion speed of 1200-1800 rpm for 30-60 min. The mixture was then placed in a three-roll grinder for grinding until the fineness was less than 5 μm, and then the mixture was discharged. Impurities were filtered out using a 400-800 mesh filter to obtain a low-temperature silver paste.

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