A low-temperature curing copper-silver composite paste for TGV interconnects and its preparation method

Abstract

This invention relates to the field of electronic materials technology and discloses a low-temperature curing copper-silver composite paste for TGV interconnects and multilayer RDL fabrication and its preparation method. The aim is to address how to suppress the destructive effect of intrinsic copper oxidation on the conductive network during TGV via metallization in an air atmosphere at 200-300°C. This is achieved by using a dense silver layer to coat copper powder to form silver-coated copper composite particles, suppressing the oxidation of the copper core during the heating process. The low-temperature sintering activity of nano-silver powder forms conductive silver bridges before the silver layer dehumidifies, connecting adjacent silver-coated copper particles. A high-temperature resistant resin with a glass transition temperature higher than 260°C after curing is selected as the binder. After curing, the resin is distributed in a discontinuous island-like pattern between the particles, applying compressive stress to enhance contact and simultaneously resisting multilayer wiring processes. The synergistic effect of these three stages allows the sintering reaction to form a stable conductive network in an air atmosphere at 200-300°C, and it is compatible with photosensitive polyimide insulating layers, making it suitable for additive manufacturing of multilayer RDLs for glass via circuit boards.

Description

Technical Field

[0001] This invention relates to the field of electronic materials technology, and in particular to a low-temperature curing copper-silver composite paste for TGV interconnects and its preparation method. Background Technology

[0002] Through-Glass Vias (TGV) are considered a key next-generation 3D integration technology to replace silicon interposers and organic packaging substrates due to the advantages of glass materials such as low dielectric constant, low loss factor, low cost, and large size availability. For TGV technology to achieve industrial application, the manufacturing problems of through-hole metallization and multilayer redistribution layers (RDLs) need to be solved. The current mainstream is to use photosensitive polyimide (PI) as the insulating dielectric layer and form fine lines through photolithography. Traditional PI systems require temperatures above 300°C to be fully imidized, while some commercially available low-temperature curing PIs can reduce the curing temperature to around 200°C. Therefore, the TGV metallization process usually requires completion in the range of 200-300°C. At the same time, in order to reduce equipment costs and simplify the process, the feasibility of air atmosphere sintering needs to be explored.

[0003] To strike a balance between cost and oxidation resistance, existing technologies have proposed a scheme for preparing conductive pastes using silver-coated copper powder. Chinese Patent Publication No. CN114437509A discloses a conductive resin composition and a conductive layer and circuit board using the conductive resin composition. By physically blocking oxygen through the silver layer, it attempts to achieve low-temperature sintering of copper-based pastes in air. However, the academic paper "Low-temperaturesintering of Cu@Ag microparticles in air for recyclable printed electronics" published in Journal of Materials Chemistry C in 2024 confirms that the silver layer in silver-coated copper powder undergoes thermodynamically driven dewetting above 250°C, resulting in the exposure of the copper core. Meanwhile, the oxidation rate of copper in air accelerates sharply at 200-300°C, rapidly forming an insulating oxide layer, causing the resistivity to increase rather than decrease after sintering. Summary of the Invention

[0004] The technical problem to be solved by this invention is: how to suppress the destructive effect of intrinsic oxidation of copper on the conductive network when metallizing TGV vias in an air atmosphere at 200-300℃, so as to obtain a stable low-resistance interconnect. To this end, we propose a low-temperature curing copper-silver composite paste for TGV interconnects and its preparation method.

[0005] To achieve the above objectives, this application adopts the following technical solution: a low-temperature curing copper-silver composite paste for TGV interconnect, comprising, by weight, the following components: 50-90 parts of silver-coated copper powder, 10-30 parts of silver powder, 2-8 parts of resin, 1-3 parts of curing agent, 5-20 parts of solvent, and 0.5-2.0 parts of functional additives; the silver-coated copper powder is a composite powder with pure copper powder as the core and a dense silver layer coated on the surface, the silver coating thickness is less than 100 nm, the silver coating accounts for 8%-15% of the total mass of the silver-coated copper powder, the median particle size of the silver-coated copper powder is 0.5-5 µm, the median particle size of the silver powder is 0.05-0.3 µm, and the resin is a high-temperature resistant resin with a glass transition temperature greater than 260 °C after curing.

[0006] Preferably, the resin is selected from one or more of cyanate ester resins and mixed resins of cyanate ester resins and epoxy resins.

[0007] Preferably, the curing agent is selected from one or more of imidazole curing agents, tertiary amine curing agents, Lewis acid curing agents, and transition metal complexes.

[0008] Preferably, the solvent is selected from one or more of ethylene glycol ethyl ether acetate, diethylene glycol ethyl ether acetate, and terpineol.

[0009] Preferably, the thickness of the silver coating layer is 20-80 nm.

[0010] Preferably, the median particle size of the silver powder is 0.1-0.2µm.

[0011] Preferably, the functional additive includes a dispersant and a coupling agent, wherein the dispersant is selected from the BYK series and the Solsperse series, and the coupling agent is the silane coupling agent KH-550.

[0012] A method for preparing a low-temperature curing copper-silver composite slurry includes the following steps: S1: Mixing resin with a first-part solvent and stirring to dissolve, obtaining a resin solution; mixing a curing agent with a second-part solvent and stirring to dissolve, obtaining a curing agent solution; mixing the resin solution and the curing agent solution and stirring to mix evenly, obtaining a bonding system; S2: Adding silver-coated copper powder, silver powder and functional additives to the bonding system, mixing and stirring, obtaining a primary slurry; S3: Grinding and dispersing the primary slurry using a three-roll mill, controlling the fineness of the slurry after grinding to ≤10µm; S4: Filtering the ground slurry and collecting the filtrate, thus obtaining the low-temperature curing copper-silver composite slurry.

[0013] Preferably, the mass ratio of the resin to the first solvent is 1:1 to 1:5, and the mass ratio of the curing agent to the second solvent is 1:3 to 1:15.

[0014] The application of a low-temperature curing copper-silver composite paste in TGV interconnects includes filling the TGV vias of a glass substrate with the low-temperature curing copper-silver composite paste and curing it at 200-300°C in an air atmosphere to form vertical interconnect channels.

[0015] The application of a low-temperature curing copper-silver composite paste in the manufacture of redistribution layers is characterized by using photosensitive polyimide as the insulating dielectric layer and printing the low-temperature curing copper-silver composite paste as the conductive layer to prepare single-layer or multi-layer redistribution layer circuits with glass vias.

[0016] The technical effects and advantages of this invention are as follows:

[0017] This invention addresses the kinetic competition between oxidation and sintering in copper-based slurries during low-temperature air sintering by constructing a three-stage process: first, physically isolating the silver layer; then, pre-sintering the nano-silver bridges; and finally, shrinking and compressing the resin. Specifically, silver-coated copper powder serves as the main conductive phase, and its dense silver layer effectively blocks oxygen in the early stages of sintering, inhibiting copper core oxidation. The compounded nano-silver powder forms conductive silver bridges between the silver-coated copper particles, compensating for potential localized conductivity interruptions after the silver layer is dehumidified. Simultaneously, a high-temperature resistant resin with a high glass transition temperature is used. After curing, it is distributed in a discontinuous island-like morphology between the conductive particles, neither blocking direct metal contact nor hindering interparticle bonding through the compressive stress generated by curing shrinkage. Compared with existing technologies, this invention does not require a reducing atmosphere protection, and after curing at 200-300℃ in air, the through-hole resistance is less than 5mΩ, the adhesion reaches grade 5B, and the resistance change rate after 500 thermal cycles is less than 5%. Furthermore, it is fully compatible with the multiple curing process of photosensitive polyimide insulating layers, reducing equipment costs while ensuring long-term reliability. Attached Figure Description

[0018] The disclosure of this invention is illustrated with reference to the accompanying drawings. It should be understood that the drawings are for illustrative purposes only and are not intended to limit the scope of protection of this invention. In the drawings, the same reference numerals are used to refer to the same parts:

[0019] Figure 1 This invention relates to a glass-through-hole double-sided single-layer redistribution layer circuit board.

[0020] Figure 2 This invention relates to a glass through-hole double-sided multilayer redistribution layer circuit board.

[0021] Figure 3 This is a low-magnification SEM image of the cross-section of the TGV through-hole after the slurry of the present invention has been filled;

[0022] Figure 4 This is a high-magnification SEM image of the cross-section of the slurry after filling the TGV through-holes according to the present invention;

[0023] Figure 5This is a curve showing the relationship between the number of thermal cycles and the rate of change of electrical resistance in this invention.

[0024] Legend:

[0025] 1. Conductive layer; 2. Insulating dielectric layer. Detailed Implementation

[0026] It is readily understood that, based on the technical solution of this invention, those skilled in the art can propose various interchangeable structural methods and implementations without altering the essential spirit of the invention. Therefore, the following detailed embodiments and accompanying drawings are merely illustrative examples of the technical solution of this invention and should not be considered as the entirety of the invention or as limitations or restrictions on the technical solution of this invention.

[0027] The present invention provides a technical solution: a low-temperature curing copper-silver composite paste, characterized in that, by weight, it is composed of the following components: 50-90 parts silver-coated copper powder, 10-30 parts silver powder, 2-8 parts resin, 1-3 parts curing agent, 5-20 parts solvent, and 0.5-2.0 parts functional additives.

[0028] The silver-coated copper powder is a composite powder with pure copper powder as the core and a dense silver layer on the surface. Compared with alloy powders such as copper-nickel alloys, pure copper has a lower volume resistivity and can obtain better electrical conductivity after sintering.

[0029] The silver coating is a dense nanoscale silver layer with a thickness of <100nm, more preferably 20-80nm, and the silver coating accounts for 8%-15% of the total mass of the silver-coated copper powder.

[0030] The median particle size (D50) of silver-coated copper powder is 0.5-5 µm, and the tap density is >3.5 g / cm³. 3 The selection of this particle size range is based on a comprehensive consideration of TGV through-hole filling and printing processes. TGV pore size is usually 30-120µm. The particle size in the slurry needs to be much smaller than the pore size to ensure smooth filling and avoid clogging. At the same time, if the particle size is too small, the specific surface area is too large, which makes it easy to agglomerate and requires more binder, which is not conducive to the formation of a continuous metal conductive network.

[0031] The silver-coated copper powder can be prepared using chemical plating methods known in the art. For example, after pretreatment such as degreasing and pickling to remove the surface oxide layer of pure copper powder, it is immersed in a plating solution containing silver ammonia complex or silver salt. Under the action of a reducing agent, silver ions are reduced and deposited on the surface of the copper powder to form a silver coating layer. By adjusting the concentration of the plating solution, the reaction temperature, the time, and the stirring rate, a silver layer of the required thickness and density can be obtained.

[0032] The median particle size D50 of the silver powder is 0.05-0.3µm, more preferably 0.1-0.2µm, and the morphology of the silver powder can be spherical or near-spherical, with a tap density >3.6g / cm³. 3 .

[0033] Nanoscale silver powder has high surface energy and its sintering initiation temperature can be as low as 200℃. It can complete sintering in the temperature range before the silver layer of silver-coated copper powder has dehumidified, forming a conductive silver bridge to connect adjacent silver-coated copper particles.

[0034] If the silver powder particle size is too large, its sintering temperature needs to be raised to above 300℃, which makes it impossible to sinter effectively before the silver layer is dehumidified. Once the silver layer is dehumidified above 250℃, the copper core will be exposed and oxidized, which will lead to an increase in resistivity. If the silver powder particle size is too small, the particle surface energy is extremely high, making it very easy to agglomerate and difficult to disperse evenly. The sintering behavior of the agglomerates is similar to that of large particles, which also makes it impossible to achieve low-temperature rapid sintering. Furthermore, poor dispersion will lead to uneven local sintering, affecting the consistency of the conductive network.

[0035] The adhesive system of the present invention consists of two parts: a resin and a curing agent, wherein the resin is selected from one or a combination of cyanate ester resin, a mixed resin system of cyanate ester resin and epoxy resin.

[0036] The glass transition temperature of the cured resin is >260℃ and the initial thermal decomposition temperature is >400℃, to ensure that it does not soften or deform during sintering at 200-300℃, maintains structural stability under subsequent thermal cycling conditions, and does not decompose to produce gas or residues.

[0037] It should be noted that when using a mixture of cyanate ester and epoxy resin, the proportion of cyanate ester in the mixture should be high enough to ensure that the glass transition temperature of the cured system is >260℃.

[0038] The curing agent is selected from catalysts or curing agents that can promote the curing of cyanate ester resins, including one or more of imidazoles, tertiary amines, Lewis acids, transition metal complexes, and organotin compounds.

[0039] The imidazole curing agent is selected from one or more of 2-ethyl-4-methylimidazolium, 1-benzyl-2-methylimidazolium, and 1-cyanoethyl-2-ethyl-4-methylimidazolium, wherein 2-ethyl-4-methylimidazolium can effectively promote the co-curing reaction between cyanate ester and epoxy.

[0040] The tertiary amine curing agent is selected from one or more of triethylamine, triethanolamine, and benzyl dimethylamine;

[0041] The Lewis acid curing agent is selected from boron trifluoride (BF3) and its complexes, boron trichloride (BCl3) and its complexes, preferably boron trifluoride monoethylamine complex.

[0042] The transition metal complex is selected from, for example, zinc acetylacetonate or cobalt acetylacetonate.

[0043] After curing, the adhesive is distributed in a discontinuous island-like form between the conductive particles, without blocking the direct contact between the metal particles. At the same time, the volume shrinkage during the curing process applies compressive stress to the particles, enhancing the contact between the particles and reducing the contact resistance.

[0044] The solvent is selected from high-boiling-point organic solvents commonly used in the field of electronic pastes, including one or more of ethylene glycol ethyl ether acetate, diethylene glycol ethyl ether acetate, and terpineol.

[0045] The functional additives include dispersants and coupling agents;

[0046] The dispersant is a polymeric type, selected from commonly used dispersants in the field such as the BYK series and Solsperse series, and is used to promote the uniform dispersion of silver-coated copper powder and silver powder in the binder system and prevent particle agglomeration; the coupling agent is silane coupling agent KH-550.

[0047] This invention also provides a method for preparing a low-temperature curing copper-silver composite paste, specifically including the following steps:

[0048] S1: Add the resin and the first part of the organic solvent to the mixing container at a mass ratio of 1:1-1:5, and stir at 500-1500 r / min for 10-30 minutes to fully dissolve or disperse the resin and obtain a uniform resin solution; add the curing agent and the remaining organic solvent to another container at a mass ratio of 1:3-1:15, and stir at 500-1000 r / min for 5-15 minutes to fully dissolve the curing agent and obtain a curing agent solution; mix the resin solution and the curing agent solution, and stir at 800-1500 r / min for 10-30 minutes to fully mix and obtain a bonding system.

[0049] S2: Slowly add the silver-coated copper powder, silver powder, and functional additives to the bonding system prepared in step S1. Mix using a planetary mixer or high-speed disperser at a speed of 800-2000 r / min for 20-60 minutes. During the mixing process, vacuum can be applied to -0.06 MPa to -0.09 MPa as needed to eliminate air bubbles in the slurry. The entire process is carried out at room temperature. If necessary, cooling measures should be taken to control the temperature to not exceed 40°C to avoid premature curing of the resin. After mixing, a uniform primary copper-silver paste is obtained.

[0050] S3: The primary copper-silver paste obtained in step S2 is ground and dispersed using a three-roll mill. The roller gap of the three-roll mill is set to 5-20µm, and adjusted gradually from large to small. The number of grinding passes is 3-5. After each grinding pass, the fineness of the paste can be checked with a scraper fineness gauge until the fineness is ≤10µm.

[0051] S4: The ground slurry is filtered through a 200-400 mesh stainless steel mesh or a stainless steel filter element to remove undispersed agglomerated particles and impurities that may fall off the grinding roller; the slurry collected after filtration is the copper-silver composite slurry of the present invention.

[0052] The present invention will be further illustrated by specific embodiments below, but the present invention is not limited to these embodiments. In addition, the raw materials used in the embodiments are all commercially available industrial products, and the parts mentioned are all parts by weight.

[0053] Example 1

[0054] This embodiment provides a low-temperature curing copper-silver composite slurry, comprising 65 parts silver-coated copper powder, 20 parts silver powder, 5 parts cyanate ester resin, 1 part 2-ethyl-4-methylimidazolium, 8 parts ethylene glycol ethyl ether acetate, 0.8 parts BYK-111, and 0.2 parts KH-550; wherein the core of the silver-coated copper powder is pure copper, the silver coating thickness is 50 nm, the silver content is 12%, and the median particle size is 2 µm; the median particle size of the silver powder is 0.2 µm; and the glass transition temperature of the cyanate ester resin after curing is 280 °C.

[0055] This embodiment also provides a method for preparing a low-temperature curing copper-silver composite paste, including the following steps:

[0056] S1: Add 5 parts of cyanate ester resin and 5 parts of ethylene glycol ethyl ether acetate to a mixing container, and stir at 1000 r / min for 20 minutes to fully dissolve the resin and obtain a resin solution; add 1 part of 2-ethyl-4-methylimidazole and 3 parts of ethylene glycol ethyl ether acetate to another container, and stir at 800 r / min for 10 minutes to fully dissolve the curing agent and obtain a curing agent solution; mix the resin solution and the curing agent solution, and stir at 1200 r / min for 15 minutes to fully mix and homogeneously obtain a bonding system;

[0057] S2: Weigh 65 parts of silver-coated copper powder, 20 parts of silver powder, 0.8 parts of BYK-111 dispersant and 0.2 parts of KH-550 coupling agent according to the formula, slowly add them to the bonding system, mix them with a planetary mixer at a speed of 1500 r / min for 40 minutes, and at the same time, evacuate to -0.08 MPa to eliminate air bubbles in the slurry to obtain primary copper-silver paste;

[0058] S3: The primary copper-silver paste is ground and dispersed using a three-roll mill. The first pass has a roller gap of 20µm, the second pass has a roller gap of 15µm, the third pass has a roller gap of 10µm, and the fourth pass has a roller gap of 5µm. The paste is ground for a total of 4 passes. After grinding, a sample is taken and tested with a scraper fineness meter. The fineness is ≤8µm.

[0059] S4: Filter the ground slurry through a 300-mesh stainless steel mesh to remove undispersed agglomerated particles, collect the filtrate, and obtain the copper-silver composite slurry of this embodiment.

[0060] After sintering, the resistivity of the copper-silver paste was measured to be 5 µΩ·cm using the four-probe method.

[0061] Example 2

[0062] This embodiment provides a low-temperature curing copper-silver composite paste, which differs from Embodiment 1 in that the amounts of silver-coated copper powder and silver powder are adjusted, including 55 parts of silver-coated copper powder and 25 parts of silver powder.

[0063] Example 3

[0064] This embodiment provides a low-temperature curing copper-silver composite paste, which differs from Embodiment 1 in that the amounts of silver-coated copper powder and silver powder are adjusted, including 75 parts of silver-coated copper powder and 15 parts of silver powder.

[0065] Example 4

[0066] This embodiment provides a low-temperature curing copper-silver composite paste, which differs from Embodiment 1 in that its components, by weight, include 70 parts of silver-coated copper powder, 20 parts of silver powder, 2 parts of cyanate ester resin, 1 part of 2-ethyl-4-methylimidazole, 5 parts of ethylene glycol ethyl ether acetate, 0.8 parts of BYK-111, and 0.2 parts of KH-550.

[0067] Example 5

[0068] This embodiment provides a low-temperature curing copper-silver composite slurry, which differs from Embodiment 1 in that its components, by weight, include 60 parts of silver-coated copper powder, 18 parts of silver powder, 8 parts of cyanate ester resin, 2 parts of 2-ethyl-4-methylimidazole, 14 parts of ethylene glycol ethyl ether acetate, 0.8 parts of BYK-111, and 0.2 parts of KH-550.

[0069] Example 6

[0070] This embodiment provides a low-temperature curing copper-silver composite paste, which differs from Embodiment 1 in that its components, by weight, include 65 parts of silver-coated copper powder, 20 parts of silver powder, 5 parts of cyanate ester resin, 1 part of 2-ethyl-4-methylimidazole, 15 parts of ethylene glycol ethyl ether acetate, 0.8 parts of BYK-111, and 0.2 parts of KH-550; the preparation method is the same as in Embodiment 1, wherein the ratio of curing agent to solvent in S1 is adjusted to 1:10.

[0071] Example 7

[0072] This embodiment provides a low-temperature curing copper-silver composite slurry, which differs from Embodiment 1 in that its components, by weight, include 65 parts of silver-coated copper powder, 20 parts of silver powder, 2 parts of cyanate ester resin, 1 part of 2-ethyl-4-methylimidazole, 13 parts of ethylene glycol ethyl ether acetate, 0.8 parts of BYK-111, and 0.2 parts of KH-550; the preparation method is the same as in Embodiment 1, wherein the ratio of resin to solvent in S1 is adjusted to 1:5.

[0073] Example 8

[0074] This embodiment provides a low-temperature curing copper-silver composite paste, which differs from Embodiment 1 in that its components, by weight, include 65 parts of silver-coated copper powder, 20 parts of silver powder, 4 parts of cyanate ester resin, 1 part of 2-ethyl-4-methylimidazole, 19 parts of ethylene glycol ethyl ether acetate, 0.8 parts of BYK-111, and 0.2 parts of KH-550; the preparation method is the same as in Embodiment 1, wherein the ratio of curing agent to solvent in S1 is adjusted to 1:15.

[0075] Comparative Example 1

[0076] This comparative example adopts the high resin content scheme in the prior art disclosed in CN114437509A. For effective comparison, this comparative example increases the resin content while maintaining a similar amount of silver-coated copper powder and silver powder as in Example 1. Specifically, it includes 50 parts of silver-coated copper powder, 15 parts of silver powder, 25 parts of cyanate ester resin, 5 parts of 2-ethyl-4-methylimidazole, 30 parts of ethylene glycol ethyl ether acetate, 1 part of BYK-111, and 0.5 parts of KH-550. The preparation method is the same as in Example 1, except that the mixing time in S2 is extended to 60 minutes to ensure uniformity.

[0077] Comparative Example 2

[0078] This comparative example provides a low-temperature curing copper-silver composite slurry, which differs from Example 1 in that it does not contain nano-silver powder. Its components, by weight, include 85 parts silver-coated copper powder, 5 parts cyanate ester resin, 1 part 2-ethyl-4-methylimidazolium, 8 parts ethylene glycol ethyl ether acetate, 0.8 parts BYK-111, and 0.2 parts KH-550. The specifications of the silver-coated copper powder are the same as those in Example 1.

[0079] Comparative Example 3

[0080] This comparative example provides a low-temperature curing copper-silver composite paste, which differs from Example 1 in that pure copper powder is used instead of silver-coated copper powder. Its components, by weight, specifically include 65 parts pure copper powder, 20 parts silver powder, 5 parts cyanate ester resin, 1 part 2-ethyl-4-methylimidazolium curing agent, 8 parts ethylene glycol ethyl ether acetate, 0.8 parts BYK-111 and 0.2 parts KH-550.

[0081] Comparative Example 4

[0082] This comparative example provides a low-temperature curing copper-silver composite slurry, which differs from Example 1 in that it uses bisphenol A epoxy resin instead of cyanate ester resin. Its components, by weight, specifically include 65 parts of silver-coated copper powder, 20 parts of silver powder, 5 parts of bisphenol A epoxy resin, 1 part of 2-ethyl-4-methylimidazolium, 8 parts of ethylene glycol ethyl ether acetate, 0.8 parts of BYK-111, and 0.2 parts of KH-550.

[0083] The present invention also provides an application of a low-temperature curing copper-silver composite paste in the manufacture of glass through-hole circuit boards, specifically by applying the copper-silver composite paste prepared in the aforementioned embodiments and comparative examples to the manufacture of TGV circuit boards, further illustrating the technical solution and technical effects of the present invention.

[0084] The application methods described in this section also constitute part of the invention, but it does not mean that the invention can only be implemented in the following ways. Those skilled in the art can make adaptive adjustments to the process parameters according to actual needs.

[0085] Select a glass substrate suitable for the TGV process, such as borosilicate glass, quartz glass or aluminosilicate glass. The thickness can be selected according to the actual application requirements, usually 100-1000µm.

[0086] TGV vias are fabricated on the substrate according to design requirements. The aperture is usually 30-120µm and the depth-to-diameter ratio can be 5:1-20:1.

[0087] The vias can be fabricated using methods known in the art, such as laser-induced etching, photolithography of photosensitive glass, or plasma etching. The specific process parameters are determined based on the glass type and via size, and will not be elaborated here.

[0088] This invention uses a 425µm thick borosilicate glass substrate and employs laser-induced etching to prepare TGV vias with a diameter of 45µm. The copper-silver composite pastes prepared in the above embodiments and comparative examples are used to fill the TGV vias. The via plugging process uses vacuum-assisted printing to ensure that the paste fills the high aspect ratio vias without voids. The specific steps are as follows:

[0089] C11: Place the TGV substrate on the worktable of the vacuum plugging equipment, and place a breathable polytetrafluoroethylene porous membrane with a pore size of 10µm under the substrate as a vacuum buffer layer. Connect the vacuum extraction hole under the porous membrane.

[0090] C12: Turn on the vacuum pump and evacuate the system to below 100Pa, hold for 2 minutes to allow the air in the through hole to be fully expelled;

[0091] C13: Under vacuum conditions, the paste is applied to the surface of the TGV substrate using screen printing. The paste is drawn into the through holes by vacuum negative pressure. A 325-mesh stainless steel screen can be used to control the filling area during printing.

[0092] C14: After filling with slurry, continue to evacuate for 2 minutes to further remove any remaining air bubbles in the holes. Turn off the vacuum, remove the substrate, and gently remove any excess slurry from the surface with a scraper or a lint-free cloth.

[0093] The plugged TGV substrate is placed in an air atmosphere furnace for drying and sintering. To ensure that the nano-silver powder is fully sintered to form silver bridges and that the resin system is completely cured without thermal decomposition, the present invention employs the following sintering steps:

[0094] C21: Heat from room temperature to 150-180℃ at a rate of 3-5℃ / min and hold for 30-60 minutes. The main purpose is to evaporate the solvent and at the same time soften and flow the resin to further fill the gaps between the particles.

[0095] C22: Heat to 230-250℃ at 2-3℃ / min and hold for 60-90 minutes. This corresponds to the rapid sintering stage of the nano silver powder and is also the stage when the resin begins to solidify. The holding time must ensure that the nano silver powder is fully sintered to form a conductive silver bridge.

[0096] C23: Heat to 270-300℃ at 2-3℃ / min and hold for 30-60 minutes, corresponding to the complete curing stage of the resin. At the same time, the silver layer of the silver-coated copper powder may be locally dehydrated. The holding time should not be too long to avoid excessive oxidation. Cool to room temperature with the furnace.

[0097] The sintering process is carried out in an air atmosphere without any protective gas. After sintering, the substrate surface can be lightly polished as needed to remove any surface residues and expose the conductive pillars in the filling holes.

[0098] After the vias are filled, a photosensitive PI (Polyimide) insulating dielectric is applied to both the front and back surfaces of the glass TGV. Then, blind holes and circuit slots that connect to the conductors inside the TGV are etched on the insulating layer using photolithography or laser etching, serving as a template for the printed circuit.

[0099] Then, conductive copper-silver paste is printed into the aforementioned front-side filler circuit template. Printing can be done using a screen printing process to accurately print the paste into the circuit template. After drying and curing, the first RDL layer circuit is prepared.

[0100] Then, the photosensitive PI (Polyimide) insulating dielectric coating is repeated, and blind vias and circuit grooves are prepared using photolithography as templates for filling circuits. Then, conductive copper silver paste is printed into the above-mentioned front-side filling circuit template to prepare the second layer RDL circuit.

[0101] Following the coating, photolithography, and filling steps described above, a multilayer RDL circuit is sequentially fabricated. Alternatively, the RDL circuit can be fabricated simultaneously on the other side of the glass substrate, as needed. After the multilayer RDL circuit fabrication is completed, subsequent packaging processes such as surface passivation and ball bonding are performed to obtain the TGV circuit board. Figure 1 and Figure 2 As shown.

[0102] To verify the actual effect of the slurry of the present invention in TGV interconnect, test samples were made from the slurries prepared in the aforementioned embodiments and comparative examples, and the following performance tests were conducted to further demonstrate the technical advantages of the present invention.

[0103] Experimental Example 1

[0104] To verify the filling effect of the slurry of the present invention in TGV through-holes, the slurry prepared in Example 1 was selected, and TGV through-holes were filled, sintered, and RDL insulating layer was coated according to the above method. The microstructure of the sample was characterized by scanning electron microscopy (SEM).

[0105] Specifically, the copper-silver composite paste prepared in Example 1 was filled into TGV vias with a thickness of 425µm and a pore size of 45µm. The temperature was increased to 150℃ at 5℃ / min and held for 30 minutes, then increased to 250℃ at 3℃ / min and held for 60 minutes, and finally increased to 280℃ at 3℃ / min and held for 30 minutes, followed by furnace cooling. A photosensitive polyimide insulating layer with a thickness of about 10µm was coated on the surface of the sintered substrate. After pre-baking, exposure, and development, blind holes and circuit grooves for interconnecting with the TGV internal conductor were etched on the insulating layer as templates for printing the circuit. The substrate was cured at 250℃ for 60 minutes, and the paste was precisely printed into the circuit template. Then, it was dried and cured to prepare the first RDL layer circuit. After grinding and polishing, it was sputter-coated with gold for later use.

[0106] The cross-section of the sample was observed using a field emission scanning electron microscope (FET), with an operating voltage of 5 kV and a working distance of 8 mm. The results are shown in [Figure number missing]. Figure 3 and Figure 4 As shown.

[0107] from Figure 3It is evident that the slurry completely fills the through-holes, with no voids, cracks, or insufficient filling, indicating that the slurry has good wettability to the glass during the sintering process.

[0108] from Figure 4 As can be seen, the silver-coated copper particles are interconnected to form a framework, and a large number of nanoscale sintered necks are visible in the interparticle gaps, tightly connecting adjacent silver-coated copper particles. The size of these silver bridges is about 0.1-0.3µm, which is consistent with the particle size of the nano-silver powder used, confirming that the nano-silver powder was fully sintered during the 250℃ sintering process, forming the expected conductive bridging structure. At the same time, discontinuous island-like resin filling morphology is visible in the interparticle gaps, which does not block the direct contact between metal particles.

[0109] Experiment Example 2

[0110] To verify the conductivity of the slurry provided by the present invention, slurries prepared in Examples 1-8 and Comparative Examples 1-4 were selected, filled with TGV through holes, and their resistance values ​​were measured.

[0111] The copper-silver composite pastes prepared in Examples 1-8 and Comparative Examples 1-4 were respectively filled into the TGV vias according to the above method. The glass substrate used was borosilicate glass with a thickness of 425µm and a pore diameter of 45µm. The vias were arranged in an array. Each test chip was designed with 20 independent via chain structures. Three test chips were filled with each paste as parallel samples.

[0112] The filled substrate is heated to 150°C at 5°C / min and held for 30 minutes, then heated to 250°C at 3°C / min and held for 60 minutes, and then heated to 280°C at 3°C / min and held for 30 minutes. After cooling in the furnace, the substrate surface is lightly polished to remove surface residues and expose the conductive pillars in the filling holes.

[0113] The via resistance was measured using a four-probe method combined with a via chain structure. The prepared test chip was placed on the probe stage, and a resistance meter was used to connect the lead electrodes at both ends of the via chain. A constant current of 1mA was applied, and the voltage drop across the via chain was measured. The total resistance value was calculated, and the average via resistance was obtained by dividing the total resistance value by the number of vias in series, 20. Each sample was measured three times and the average value was taken. The standard deviation was calculated, and the results are shown in Table 1 below.

[0114]

[0115] Table 1

[0116] The data in Table 1 show that the through-hole resistance of Examples 1-8 is all below 5mΩ and the standard deviation is small, indicating that the slurry of the present invention can form a stable low-resistance conductive network under different formulations.

[0117] The resistance value of Comparative Example 1 is as high as 25.6 mΩ, which is much higher than that of the Example. This indicates that the high resin content leads to the discontinuity of the conductive network and the increase in resistance. After curing, the resin becomes a continuous phase, and the conductive particles are dispersed in the resin matrix to form a resin-based composite material structure. It is impossible to form a continuous metal conductive network, which leads to an order of magnitude increase in resistivity.

[0118] Comparative Example 2 has a resistance of 18.2 mΩ. Without nano silver powder, the conductivity is achieved solely through direct contact between silver-coated copper particles. As the temperature rises above 250°C, the silver layer dehydrates, exposing the copper core and causing oxidation. The resulting oxide layer blocks the conductive path, leading to a significant increase in resistance.

[0119] Comparative Example 3 has the highest resistance. The pure copper powder has no silver layer protection on its surface. During the air sintering process at 200-300℃, it is rapidly oxidized to form Cu2O and CuO. The particles are blocked by the insulating oxide layer and cannot form an effective conductive network.

[0120] Although the resistance of Comparative Example 4 was lower than that of Comparative Examples 1 and 2, it was still higher than that of the Example. When the bisphenol A epoxy resin was sintered at 280°C, it was in a highly elastic state or even softened and flowed, which could not apply stable compressive stress to the conductive particles, resulting in increased contact resistance between particles. At the same time, the resin may be locally deformed, which would damage the stability of the conductive network.

[0121] Experimental Example 3

[0122] To verify the adhesion between the conductive lines formed by different pastes on the glass substrate and the substrate, pastes prepared in Examples 1, 4, 5, Comparative Examples 1, 2, and 4 were selected as test objects for cross-cut adhesion testing. The preparation steps were the same as in Experiment 1.

[0123] According to GB / T 9286-2021 "Cross-cut Test for Paints and Varnishes", a 100-square test was conducted. A cross-cutting tool was used to make perpendicular, intersecting cuts along the sintered lines, forming 10×10 squares, each 1mm×1mm in size. The chips were gently brushed away with a soft brush. 3M 600 tape was then firmly applied to the cut area, pressing it flat with a finger to ensure good contact. After 5 minutes, the tape was smoothly peeled off at an angle of approximately 60° within 0.5-1 second. The extent of square detachment was observed under a magnifying glass and graded according to the standard.

[0124] Among them, 5B indicates that the cut edge is completely smooth with no chips falling off; 4B indicates that small pieces have fallen off the cut edge, with an area of ​​<5%; 3B indicates that there are flaky chips on the cut edge, with an area of ​​5%-15%; 2B indicates that the cut edge has partially or completely fallen off in large fragments, with an area of ​​15%-35%; 1B indicates that the cut edge has fallen off in large fragments, with an area of ​​35%-65%; 0B indicates that the area of ​​chipping off is >65%.

[0125] The test results are shown in Table 2.

[0126]

[0127] Table 2

[0128] According to the data in Table 2, Examples 1, 4 and 5 all showed good adhesion performance. In Comparative Example 1, although the resin itself has a certain adhesion to the glass, the direct contact between the metal particles and the glass is blocked. When the tape is torn, the stress is concentrated at the interface between the resin and the glass or the resin cohesive layer, resulting in small pieces falling off.

[0129] In Comparative Example 2, the sintered body with slightly higher porosity was missing the nano-silver powder, and the contact between particles was not as dense as in Example 1. When the tape was torn, local stress concentration caused a small amount of edge detachment. In Comparative Example 4, the bisphenol A epoxy resin was in a highly elastic state or even softened during the sintering process at 280°C. The compressive stress generated by curing shrinkage was insufficient, and the resin may undergo thermal decomposition or interfacial debonding, resulting in loose contact between the metal particles and the glass. When the tape was torn, the conductive layer was easily peeled off from the glass surface, resulting in large-area detachment.

[0130] Experiment Example 4

[0131] To verify the long-term reliability of TGV interconnect structures prepared with different slurries under temperature cycling conditions, thermal cycling tests were conducted on the slurries prepared in Examples 1, 5, 1, 2, and 4.

[0132] The test sample preparation was consistent with that of Experiment 2. Following JESD22-A104 standard, the samples were cycled from -55℃ to 125℃, with each temperature held for 15 minutes, for a total of 500 cycles. The resistance of the through-hole chain was measured after every 100 cycles, and the rate of change of resistance was calculated.

[0133]

[0134] In the formula, R0 is the initial resistance, R n The resistance after the nth cycle is given. Each sample was measured three times, and the arithmetic mean was taken. The results are shown in [the table below]. Figure 5 As shown.

[0135] from Figure 5 As can be seen, the resistance change rate of Examples 1 and 5 after 500 thermal cycles was lower than that of the comparative examples, while the resistance change rate of Comparative Example 4 reached 35.8% after 500 cycles, almost failing.

[0136] In Comparative Example 1, the expansion and contraction rates of the resin differed significantly from those of the metal during thermal cycling. Repeated stress caused the resin and metal interfaces to debond, resulting in microcracks inside the resin layer. This loosened the contact between the conductive particles, causing the resistance to gradually increase. After 500 cycles, the resistance change rate reached 22.3%.

[0137] In Comparative Example 2, no silver nanoparticles were used to form a silver bridge. The conductive network relied entirely on the direct contact between the silver-coated copper particles. As thermal cycling proceeded, the silver layer may have dehumidified rapidly under repeated thermal stress, exposing the copper core to oxidation. The thickening of the oxide layer led to an increase in contact resistance. At the same time, the lack of parallel pathways for silver bridges meant that local contact failures could not be compensated, and the rate of change in resistance rapidly increased to 18.6%.

[0138] Although the bisphenol A epoxy resin in Comparative Example 4 did not reach its glass transition temperature in the high-temperature section of thermal cycling, it softened during the sintering process. After curing, the compressive stress of the resin was insufficient, and the initial contact between particles was weak. In subsequent thermal cycles, the resin could not effectively constrain the movement of particles. Repeated thermal stress caused relative slippage of particles and separation of contact points, resulting in a sharp increase in resistance. After 500 cycles, the change rate reached 35.8%, indicating almost complete failure.

[0139] The technical scope of this invention is not limited to the content described above. Those skilled in the art can make various modifications and variations to the above embodiments without departing from the technical concept of this invention, and all such modifications and variations should fall within the protection scope of this invention.

Claims

1. A low-temperature curing copper-silver composite paste, characterized in that, By weight, it consists of the following components: 50-90 parts silver-coated copper powder, 10-30 parts silver powder, 2-8 parts resin, 1-3 parts curing agent, 5-20 parts solvent and 0.5-2.0 parts functional additives; The silver-coated copper powder is a composite powder with pure copper powder as the core and a dense silver layer on the surface. The thickness of the silver coating layer is less than 100 nm, and the silver coating layer accounts for 8%-15% of the total mass of the silver-coated copper powder. The median particle size of the silver-coated copper powder is 0.5-5 µm, and the median particle size of the silver powder is 0.05-0.3 µm. The resin is a high-temperature resistant resin with a glass transition temperature greater than 260°C after curing.

2. The low-temperature curing copper-silver composite paste according to claim 1, characterized in that: The resin is selected from one or more of cyanate ester resins and mixed resins of cyanate ester resins and epoxy resins.

3. The low-temperature curing copper-silver composite paste according to claim 1, characterized in that: The curing agent is selected from one or more of imidazole curing agents, tertiary amine curing agents, Lewis acid curing agents, and transition metal complexes.

4. The low-temperature curing copper-silver composite paste according to claim 1, characterized in that: The solvent is selected from one or more of ethylene glycol ethyl ether acetate, diethylene glycol ethyl ether acetate, and terpineol.

5. The low-temperature curing copper-silver composite paste according to claim 1, characterized in that: The thickness of the silver coating is 20-80 nm.

6. The low-temperature curing copper-silver composite paste according to claim 1, characterized in that: The median particle size of the silver powder is 0.1-0.2µm.

7. The low-temperature curing copper-silver composite paste according to claim 1, characterized in that: The functional additives include dispersants and coupling agents. The dispersant is selected from the BYK series and the Solsperse series, and the coupling agent is the silane coupling agent KH-550.

8. A method for preparing a low-temperature curing copper-silver composite paste as described in any one of claims 1-7, characterized in that, Includes the following steps: S1: Mix the resin with the first part of the solvent, stir and dissolve to obtain a resin solution; mix the curing agent with the second part of the solvent, stir and dissolve to obtain a curing agent solution; The resin solution and the curing agent solution are mixed and stirred until homogeneous to obtain the bonding system; S2: Add silver-coated copper powder, silver powder and functional additives to the bonding system, mix and stir to obtain a primary slurry; S3: The primary slurry is ground and dispersed using a three-roll mill to control the fineness of the slurry after grinding to ≤10µm; S4: Filter the ground slurry and collect the filtrate to obtain the low-temperature curing copper-silver composite slurry.

9. The method for preparing a low-temperature curing copper-silver composite paste according to claim 8, characterized in that: In S1, the mass ratio of the resin to the first solvent is 1:1 to 1:5, and the mass ratio of the curing agent to the second solvent is 1:3 to 1:

15.

10. An application of the low-temperature curing copper-silver composite paste as described in any one of claims 1-7 in TGV interconnects, characterized in that: The application involves filling a low-temperature curing copper-silver composite paste into TGV vias in a glass substrate using a vacuum-assisted process, and then curing it at 200-300°C in an air atmosphere to form vertical interconnect channels.

11. The application of a low-temperature curing copper-silver composite paste as described in any one of claims 1-7 in the manufacture of redistribution layers, characterized in that, A single-layer or multi-layer rewiring layer circuit with glass vias is prepared by using photosensitive polyimide as the insulating dielectric layer and printing the low-temperature curing copper-silver composite paste as the conductive layer.

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