High-temperature sintering type alumina ceramic large-aperture hole filling near-zero shrinkage silver paste, and preparation method and application thereof

Abstract

This invention belongs to the field of conductive silver paste for via filling, and discloses a high-temperature sintered alumina ceramic large-diameter via near-zero shrinkage silver paste, its preparation method, and its application. The silver paste comprises 82-90% conductive silver powder, 3-5% lead-free high-temperature glass powder, 0.5-1% functional additives, 5-11% organic carrier, and 0.5-1% anti-shrinkage modifier; the silver paste has a thixotropic index of 5.0-6.0 at 25℃ and a viscosity of 180,000-220,000 mPa·s. This invention achieves a near-zero shrinkage solution for high-frequency PCB via metallization through close-packed, zero-gap particle stacking, three-dimensional skeleton full-domain support, and rigid interface without displacement constraints, coupled with 100-500μm large-diameter printing vias and extreme micro-shrinkage control at 800-900℃ high-temperature sintering. This results in a sintering linear shrinkage rate ≤0.1%, 100% hole regularity, zero collapse / zero cracking / zero interface deformation.

Description

Technical Field

[0001] This invention belongs to the field of conductive silver paste for pore filling, and discloses a high-temperature sintered alumina ceramic large-pore near-zero shrinkage silver paste, its preparation method and application. Background Technology

[0002] With the rapid iteration of high-frequency communication and third-generation semiconductor technologies, 96% alumina ceramics, due to their high insulation, high temperature resistance, and high stability, have become the core substrate for high-frequency PCBs and ceramic-based electronic devices. Through-hole filling silver paste is the core material for interlayer electrical interconnection, and its shrinkage rate, density, and solderability directly determine the reliability of high-frequency devices. Existing filling silver pastes are generally suitable for co-fired systems of LTCC green ceramics, with pore sizes ≤200μm and sintering linear shrinkage rates ≥3%. Under large-pore-size (100-500μm) conditions, collapse, shrinkage, voids, and soldering failures occur frequently. High-temperature silver pastes lack specific rheology and shrinkage matching designs and cannot simultaneously meet the exclusive requirements of high-frequency PCBs, which require large pore sizes, 800-900℃ high-temperature sintering, high density, strong solderability, and zero shrinkage. Summary of the Invention

[0003] Addressing the core industry pain points of high shrinkage, collapse, cracking, and pore deformation during high-temperature sintering of 100-500μm large-pore alumina ceramics at 800-900℃, this invention provides a near-zero shrinkage silver paste for high-temperature sintering of large-pore alumina ceramics, its preparation method, and applications. This invention achieves near-zero shrinkage through four key technologies: close-packed particles with zero gaps, three-dimensional skeleton support across the entire domain, rigid interface without displacement constraints, and extreme micro-control of shrinkage during 100-500μm large-pore printing and sintering at 800-900℃. This results in a sintering linear shrinkage rate of ≤0.1% (near-zero shrinkage), 100% pore regularity, and zero collapse / zero cracking / zero interface deformation, eliminating all shrinkage-induced defects at their source and providing a near-zero shrinkage solution for high-frequency PCB through-hole metallization.

[0004] To achieve the above objectives, the present invention adopts the following solution:

[0005] A high-temperature sintered alumina ceramic large-pore near-zero shrinkage filling silver paste, with a thixotropic index of 5.5, is composed of the following components by mass percentage: 82%-90% conductive silver powder, 3%-5% lead-free high-temperature glass powder, 5%-11% organic carrier, 0.5%-1% functional additives, and 0.5%-1% anti-shrinkage modifier.

[0006] The thixotropic index of the silver paste used in this invention is 5.0~6.0, which far exceeds the industry standard (≤4.8). The 10s filling and forming rate reaches 98%, completely solving the problems of sagging and uneven filling. The volume change rate after drying is ≤0.05%, laying the foundation for near-zero shrinkage. It also solves the problem of defect-free pore walls after sintering, and solves the pain points of pore collapse and incomplete filling.

[0007] Based on the above, the ultimate anti-shrinkage effect is achieved by further combining multiple components such as conductive silver powder, lead-free high-temperature glass powder, solder affinity additives and anti-shrinkage modifiers.

[0008] Specifically, the conductive silver powder has a tap density ≥88%, including spherical silver powder, nano silver powder, and flake silver powder in a mass ratio of 6~7:2~3:1~1.5; the surface of the conductive silver powder is coated with oleic acid and KH570 silane coupling agent, and the molar ratio of conductive silver powder, oleic acid, and KH570 silane coupling agent is 99:0.75:0.25;

[0009] The lead-free high-temperature glass powder has a particle size D50 of 2~3.5μm, a softening temperature controlled at 630~750℃, and a stable coefficient of thermal expansion at (7.8~8.3)×10. -6 / ℃, the composition by mass percentage is: Bi2O3 55%~60%, B2O3 10%~12%, Al2O3 5%~8%, SiO2 8%~10%, CaO 3%~5%, ZnO 4%~7%;

[0010] Functional additives include solder affinity additives and silane coupling agents;

[0011] The anti-shrinkage modifier includes any one or more of SiO2, ZrO2, and Al2O3, with a particle size range of 0.3~0.5μm, of which the mass content of 0.3μm is not less than 96%.

[0012] The above-mentioned filling silver paste of the present invention is specially designed for printing filling with large pore diameter of 100-500μm and high temperature sintering of 800-900℃, eliminating the risk of collapse and shrinkage from the raw material end, while strengthening the welding bond.

[0013] Specifically, the conductive silver powder is a gradient blend of spherical silver powder, nano silver powder, and flake silver powder, which is then modified with oleic acid and KH570 silane coupling agent to achieve close-packed, zero-gap particle packing with a tap density of ≥88% (definition and calculation formula below). This completely eliminates shrinkage space at the microscale, laying the core physical foundation for a sintering shrinkage rate of ≤0.1%. Under synergistic effect, the silver powder couples with the glass powder and the anti-shrinkage skeleton to form a continuous and dense conductive network without discontinuities or voids, thus preventing micro-shrinkage.

[0014] Key definitions and calculation formulas

[0015] In this invention, "tap density" is defined as the ratio of the actual tap density of silver powder to the theoretical density of silver, reflecting the packing density of the silver powder. The calculation formula is: Tap density = ρtheoretical silver / ρtap density × 100% where:

[0016] ρ_tap: The actual density of silver powder after tapping treatment (g / cm³).

[0017] Theoretical density of silver (ρ): The theoretical density of silver, taken as 10.49 g / cm³. 3 ;

[0018] The tap density of the silver powder compounded in this invention is ≥88%. For example, the tap density is 9.23 g / cm³. 3 The corresponding tap density is: (10.49 / 9.23)×100%≈88%.

[0019] The conductive silver powder surface is coated with oleic acid and KH570 silane coupling agent. Oleic acid solves the problems of silver nanoparticle agglomeration and flake-like silver powder stacking, ensuring the basic dispersibility of silver powder in the organic carrier. Compared with other silane coupling agents, KH-570 coupling agent has the following advantages: it forms Si-O-Al chemical bonds more fully with the ceramic pore walls, improves interfacial wettability, leaves no residue after sintering, and does not affect the dual modification treatment of silver layer densification and conductive network.

[0020] The surface is treated with a dual modification of oleic acid and KH-570 silane coupling agent, which greatly improves the dispersibility of silver powder and the wettability of ceramic pore walls. This ensures uniform flow and no agglomeration or clogging during the printing and filling process. It also allows for rapid melting and fusion after high-temperature sintering at 800-900℃, forming a continuous and dense conductive network. After filling, there are no breaks, voids, or significant volume compression space in the pores, achieving "near-zero shrinkage space" at the microscopic particle scale.

[0021] Furthermore, the method for coating the conductive silver powder surface with oleic acid and silane coupling agent includes the following steps: the conductive silver powder, oleic acid and silane coupling agent are mixed in a V-type mixer at a speed of 200~300 r / min for at least 60 min;

[0022] And / or, the parameters of each component of the silver powder are as follows:

[0023] .

[0024] The main function of the aforementioned lead-free high-temperature glass powder is to provide rigid interfacial constraint and synergistically lock in zero shrinkage. Its thermal expansion coefficient deviation from that of 96% alumina ceramic (96% refers to the alumina content in the ceramic, commonly known as 96 ceramic) is ≤0.3×10⁻⁶. -6 The temperature matching is high, which completely eliminates the internal stress caused by thermal mismatch during sintering and avoids problems such as substrate warping and through-hole cracking.

[0025] The glass powder has a particle size of D50 of 2~3.5μm. It can slowly and uniformly melt within the sintering range of 800-900℃, and spread as an ultrathin uniform layer of 50-100nm along the ceramic pore wall and the entire area of ​​the silver powder skeleton, forming a "rigid interface constraint film". This film completely fixes the silver powder particles and the anti-shrinkage skeleton to the inner side of the ceramic pore wall, restricting the high-temperature micro-migration and micro-aggregation of silver powder particles at the interface scale, completely eliminating local micro-shrinkage, and achieving overall displacement-free and shrinkage-free silver layer.

[0026] The trace ZnO modifier in the glass powder can further optimize solder affinity, eliminate solder detachment, cold solder joints, and tin shrinkage. At the same time, it is lead-free and environmentally friendly, fully compliant with RoHS environmental standards for electronic components, and suitable for the environmental requirements of high-end high-frequency PCBs.

[0027] The organic carrier is used to provide suitable rheological properties and viscosity for the filling silver paste. It can be an additive composed of commonly used components in the art (such as solvents, resins and leveling agents, defoamers, dispersants, etc.). In this invention, the organic carrier is used to ensure that the thixotropic index of the silver paste is 5.0-6.0 at 25°C and the viscosity is controlled at 80000-220000 mPa·s (test conditions: 25°C, 10 rpm).

[0028] Furthermore, the organic carrier includes an organic solvent and a thixotropic agent, wherein the organic solvent includes diethylene glycol ethyl ether and terpineol in a mass ratio of 6.5:3.5, and the thixotropic agent includes ethyl cellulose, E-51 resin and BYK™ BM-50 modified aliphatic polyamide wax in a mass ratio of 1.1:0.5:0.8; the mass amount of the thixotropic agent is 2.0~3.0% of the total mass of the silver paste.

[0029] Furthermore, the thixotropic agents include 1.1% ethyl cellulose (by weight of the silver paste), 0.5% epoxy resin E-51 (by weight of the silver paste), and 0.8% BYK™ BM-50 modified aliphatic polyamide wax (by weight of the silver paste).

[0030] And / or, the organic carrier also includes additives, which consist of modified fumed silica, polycarboxylate dispersants, and polyacrylate leveling agents.

[0031] To further enhance conductivity and anti-aging properties, functional additives also include antioxidants, specifically 0.5% lead-free antioxidants and light stabilizers by weight of the silver paste. These lead-free antioxidants and light stabilizers are commonly used substances in the field of conductive grouting materials. The aim is to inhibit silver ion migration and prevent conductive failure caused by photoaging. For products that are not immediately sintered after drying, the powder surface modification and solder affinity are completed at low temperatures. During high-temperature sintering at 800~900℃, complete thermal decomposition leaves no residue and does not affect the conductivity of the silver layer or the reliability of the weld.

[0032] To further enhance the welding bond strength and improve the weld peel strength, the solder affinity additive is 0.3% of the silver paste mass of silane coupling agent, more preferably KH570 silane coupling agent.

[0033] Furthermore, the anti-shrinkage modifier includes nano-ZrO2 and Al2O3 in a mass ratio of 6~7:3~4, or nano-SiO2 and Al2O3 in a mass ratio of 6~7:3~4.

[0034] This invention also provides a method for preparing the above-mentioned high-temperature sintered alumina ceramic large-pore near-zero shrinkage silver paste, comprising the following steps:

[0035] First, place conductive silver powder, lead-free high-temperature glass powder, functional additives, and anti-shrinkage modifier into a mixer and mix them evenly, controlling the mixer speed to 900~1000r / min;

[0036] Then, the mixed materials are slowly added to the organic carrier while stirring. The stirring speed is 250~300 r / min and the stirring time is 45~60 min to form a preliminary slurry without dry powder agglomeration.

[0037] Finally, the initial slurry is transferred to a three-roll mill and ground repeatedly 4-5 times, controlling the grinding gap to 1-10μm, until the slurry particle fineness is ≤5μm and there are no agglomerated particles; after grinding, defoaming is performed.

[0038] Furthermore, vacuum degassing is employed, including the following steps: placing the ground slurry in a vacuum degassing machine with a vacuum degree of -0.096~0.098MPa and a degassing time of 18-20min.

[0039] This invention also provides a method for sintering through-hole printing, comprising the following steps: screen printing is used to pour the high-temperature sintering alumina ceramic large-diameter near-zero shrinkage silver paste as described above, followed by leveling and drying (the purpose of drying is to evaporate the solvent and form a dry film; the drying temperature can be a temperature commonly used in the art, such as 100℃, 120℃, 150℃, etc., or within a certain temperature range, such as 100~150℃); after drying, under an air atmosphere, an ultra-slow gradient segmented heating is used, with the heating rate precisely controlled as follows: heating to 370~400℃ at 2-3℃ / min, holding at this temperature until all organic phases are completely decomposed without residue, generally 10~15min (preferably 12min), then heating to 800~900℃ at 4-6℃ / min, holding at this temperature for 28~30min; finally, natural cooling with the furnace.

[0040] First, heat the temperature to 370~400℃ (preferably 380℃±5℃) and hold it until all organic phases are completely decomposed without residue (preferably 12min) to avoid the gas impact caused by the rapid decomposition of organic phases at high temperature, which would lead to loose silver layer structure and local micro-shrinkage.

[0041] The sintering process is highly compatible with the shrinkage-resistant structure of the formulation. Combined with the full-domain support of the three-dimensional skeleton and the displacement-free fixation of the interface constraint film, the near-zero shrinkage performance of the silver paste can be fully utilized. This means that the sintering linear shrinkage rate is ≤0.1% with a higher success rate, and the through holes are free from any collapse, cracking, or substrate warping, with 100% hole regularity.

[0042] Compared with the prior art, the present invention has achieved the following beneficial effects:

[0043] 1. Excellent slurry filling and printing characteristics, with uniform and defect-free filling: Optimized rheological formula, fineness ≤5.5μm, viscosity 180000-220000mPa·s, thixotropic index 5.0-6.0.

[0044] 2. Printing is non-clogging and non-sagging. The 100-500μm full-diameter range is fully filled in one go after pore filling. The pore shape is 100% regular. There are no air bubbles, voids, local material shortages, cracks, substrate warping, shrinkage, serrated edge deformation or any other defects in the pores.

[0045] 3. A three-dimensional anti-shrinkage skeleton consisting of ternary silver powder with equal volumetric close packing (bulk density ≥88%) + coverage ≥95% + thermal expansion deviation ≤0.3×10 -6 A rigid interface constraint film with a temperature of / ℃, combined with an extreme shrinkage control process of stepped slow drying + ultra-slow gradient heating, achieves a linear shrinkage rate of ≤0.1% after high-temperature sintering at 800-900℃, which is an industry breakthrough indicator in the field of 100-500μm large-pore alumina ceramic filling silver paste.

[0046] 4. Significantly improved welding performance and extremely strong adhesion: Modified lead-free glass powder + composite welding enhancer + solder affinity additive form a strong three-in-one bonding layer. The lead-free solder has excellent wettability, and the weld peel strength is ≥9N / mm, far exceeding the level of conventional products below 6N / mm; it can withstand more than 5 lead-free reflow solderings at 260℃.

[0047] 5. After high temperature and high humidity aging (85℃ / 85%RH, 1000h) and cold and hot cycle testing (-40℃~125℃, 500 times), the welding performance showed no decline, no detachment, and no false welds, demonstrating excellent reliability.

[0048] 6. High-frequency application adaptability: The dense and continuous filling body and tight interface bonding eliminate signal scattering caused by pores and impurities, resulting in low dielectric loss and fully meeting the signal transmission requirements of high-frequency PCBs such as 5G and millimeter wave; it is resistant to high temperature and humidity, and resists silver migration, extending the service life of high-frequency devices.

[0049] 7. Strong process versatility and suitable for mass production: The preparation process is simple, requiring no special equipment. The printing and filling process is compatible with conventional production lines. Segmented sintering in an air atmosphere is sufficient, requiring no inert protection. The production cost is low, and the stability of large-scale production is strong. Attached Figure Description

[0050] Figure 1 This is a 500x metallographic microscopic image of the cross-section of the through hole after sintering the silver paste in Embodiment 1 of the present invention (ceramic pore diameter 200μm).

[0051] Figure 2 This is a metallographic microscopic image of the cross-section of the through hole after sintering silver paste with a pore diameter of 200 μm in ceramic according to the method of Example 3 of the present invention, magnified 500 times. Detailed Implementation

[0052] To further understand the purpose, content, and advantages of this invention, specific embodiments of the invention are described in detail below. However, these embodiments are not limited to the examples described below and should be freely combined according to actual circumstances. The endpoints and values ​​of the ranges disclosed herein are not limited to the precise ranges and values. For numerical ranges, endpoint values ​​of various ranges, endpoint values ​​of various ranges and individual point values, and individual point values ​​can be combined to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0053] In this invention, both the antioxidant and the light stabilizer can be those commonly used in the art. In the embodiments of this invention, the antioxidant specifically selected is BASF: Irganox® 1010, and the light stabilizer is BASF: Tinuvin® 770.

[0054] This invention provides a high-temperature sintered alumina ceramic large-pore near-zero shrinkage silver paste, wherein the large pore size refers to 100-500μm, and the sintering temperature is 800-900℃. The paste is characterized by comprising the following weight components: 82-90 parts conductive silver powder, 3-5 parts lead-free high-temperature glass powder, 0.5-1 part functional additives, 5-11 parts organic carrier, and 0.5-1 part anti-shrinkage modifier.

[0055] The silver paste has a thixotropic index of 5.0-6.0 at 25℃ and a viscosity controlled at 180,000-220,000 mPa·s.

[0056] The conductive silver powder has a tap density ≥88%, including spherical silver powder, nano silver powder, and flake silver powder in a mass ratio of 6~7:2~3:1~1.5; the surface of the conductive silver powder is coated with oleic acid and KH570 silane coupling agent, and the mass ratio of conductive silver powder, oleic acid, and KH570 silane coupling agent is 99:0.75:0.25; experimental verification shows that KH570 silane coupling agent is more convenient to use and has a better adhesion effect compared with other coupling agents.

[0057] The lead-free high-temperature glass powder has a particle size D50 of 2~3.5μm, a softening temperature controlled at 630~750℃, and a stable coefficient of thermal expansion at (7.8~8.3)×10. -6 / ℃, the composition by mass percentage is: Bi2O3 55%~60%, B2O3 10%~12%, Al2O3 5%~8%, SiO2 8%~10%, CaO 3%~5%, ZnO 4%~7%;

[0058] Functional additives include solder affinity additives and silane coupling agents;

[0059] The anti-shrinkage modifier includes any one or more of SiO2, ZrO2, and Al2O3, with a particle size range of 0.3~0.5μm, of which the mass content of 0.3μm is not less than 96%.

[0060] The filling silver paste provided in the above embodiments achieves synergistic effects through four key technologies: densely packed particles with zero gaps, three-dimensional skeleton full-domain support, rigid interface without displacement constraints, large-diameter printing and filling of 100-500μm holes, and extreme micro-shrinkage control at a high-temperature sintering temperature of 800-900℃. These technologies are deeply coupled and work together to achieve a sintering linear shrinkage rate of ≤0.1% (nearly zero shrinkage), 100% hole regularity, and zero collapse / zero cracking / zero interface deformation. This eliminates all defects caused by shrinkage at the source, providing absolute structural assurance for ultra-high filling density, high weld peel strength, and low through-hole resistivity. All core performance characteristics far exceed the existing technology level, fully meeting the extremely stringent requirements for alumina ceramic through-hole metallization in 5G / millimeter-wave high-frequency PCBs. The technological advantages are groundbreaking in the industry.

[0061] In some preferred embodiments, the method for coating the conductive silver powder surface with oleic acid and silane coupling agent includes the following steps: the conductive silver powder, oleic acid and silane coupling agent are mixed in a V-type mixer at a mixing speed of 200~300 r / min for at least 60 min;

[0062] And / or, spherical silver powder D50=2~3μm, tap density 6.0~7.0g / cm³; nano silver powder D50=0.05~0.1μm, tap density 5.0~6.0g / cm³; flake silver powder D50=0.8~1μm, tap density 5.5~6.5g / cm³.

[0063] In some other preferred embodiments, the organic carrier comprises an organic solvent and a thixotropic agent, wherein the organic solvent comprises diethylene glycol ethyl ether and terpineol in a mass ratio of 6.5:3.5, and the thixotropic agent comprises ethyl cellulose, E-51 resin and BYK™ BM-50 modified aliphatic polyamide wax in a mass ratio of 1.1:0.5:0.8; the mass amount of the thixotropic agent is 2.0 to 3.0% of the total mass of the silver paste.

[0064] In a more preferred embodiment, the organic carrier further includes an additive composed of modified fumed silica, a polycarboxylate dispersant, and a polyacrylate leveling agent.

[0065] In some other preferred embodiments, the functional additives further include antioxidants, which include 0.5% by weight of lead-free antioxidants and light stabilizers from the silver paste.

[0066] And / or, the solder affinity additive is 0.3% of the mass of the silver paste as a silane coupling agent (more preferably KH570 silane coupling agent).

[0067] In some other preferred embodiments, the anti-shrinkage modifier includes nano-ZrO2 and Al2O3 in a mass ratio of 6~7:3~4, or nano-SiO2 and Al2O3 in a mass ratio of 6~7:3~4.

[0068] An example of a method for preparing near-zero shrinkage silver paste for large-pore filling of high-temperature sintered alumina ceramics was also provided, including the following steps:

[0069] First, place conductive silver powder, lead-free high-temperature glass powder, functional additives, and anti-shrinkage modifier into a mixer and mix them evenly, controlling the mixer speed to 900~1000r / min;

[0070] Then, the mixed materials are slowly added to the organic carrier while stirring. The stirring speed is 250~300 r / min and the stirring time is 45~60 min to form a preliminary slurry without dry powder agglomeration.

[0071] Finally, the initial slurry is transferred to a three-roll mill and ground repeatedly 4-5 times, controlling the grinding gap to 1-10μm, until the slurry particle fineness is ≤5μm and there are no agglomerated particles; after grinding, defoaming is performed.

[0072] In some preferred embodiments, vacuum degassing is employed, including the following steps: placing the ground slurry in a vacuum degassing machine with a vacuum degree of -0.096~0.098MPa and a degassing time of 18-20min.

[0073] An embodiment of a pore-filling printing and sintering method is also provided, comprising the following steps: The high-temperature sintering alumina ceramic with large pores and near-zero shrinkage silver paste provided in the above embodiment is screen-printed and poured in. After leveling, it is dried (the purpose of drying is to evaporate the solvent and form a dry film; the drying temperature can be a temperature commonly used in the art, such as 100℃, 120℃, 150℃, etc. in some embodiments, or within a certain temperature range, such as 100~150℃, or gradient drying, such as drying at 120℃ for 3 minutes, then drying at 150℃ for 6 minutes); after drying, the temperature is increased in an air atmosphere using an ultra-slow gradient segmented heating method, with the heating rate precisely controlled as follows: heating to 370~400℃ at 2-3℃ / min, holding at the temperature until all organic phases are completely decomposed without residue (preferred embodiment, holding at the temperature for 12 minutes), then heating to 800~900℃ at 4-6℃ / min, holding at the temperature for 28 minutes; finally, it is naturally cooled with the furnace.

[0074] The sintering process is highly compatible with the shrinkage-resistant structure of the formulation. Combined with the full-domain support of the three-dimensional skeleton and the displacement-free fixation of the interface constraint film, the near-zero shrinkage performance of the silver paste can be fully utilized. This means that the sintering linear shrinkage rate is ≤0.1% with a higher success rate, and the through holes are free from any collapse, cracking, or substrate warping, with 100% hole regularity.

[0075] The present invention will be further explained below with reference to more specific and preferred embodiments:

[0076] Example 1:

[0077] By weight percentage: 90% double-modified compound conductive silver powder, 3% lead-free high-temperature glass powder, 6% organic carrier, 0.5% functional additives, and 0.5% anti-shrinkage modifier.

[0078] The conductive silver powder is a mixture of spherical silver powder (D50 = 2.5 μm), nano-silver powder (D50 = 0.050 μm), and flake silver powder (D50 = 1 μm) in a mass ratio of 7:2:1. It is then modified by coating with oleic acid and KH570 at a ratio of 99:0.75:0.25. The coating method includes the following steps: the conductive silver powder, oleic acid, and silane coupling agent are mixed in a V-type mixer at a speed of 200-300 r / min for at least 60 min.

[0079] Lead-free high-temperature glass powder has a D50 of 2.5 μm, a softening temperature of 690℃, and a coefficient of thermal expansion of 8.0 × 10⁻⁶. -6 / ℃, the lead-free high-temperature glass powder composition is Bi2O3 60%, B2O3 12%, Al2O3 8%, SiO2 10%, CaO 4%, ZnO 6%.

[0080] The organic carrier accounts for 6% of the total mass of the silver paste, of which the organic solvent is a compound of diethylene glycol ethyl ether and terpineol in a mass ratio of 6.5:3.5 (accounting for 3.4% of the total mass of the silver paste); the total content of thixotropic agents is 2.4% of the total mass of the silver paste (1.1% ethyl cellulose, 0.5% E-51 epoxy resin, and 0.8% BYK™ BM-50 modified aliphatic polyamide wax); the additives (0.2% of the total mass of the silver paste) are 0.08% modified fumed silica, 0.06% polycarboxylate dispersant, and 0.06% polyacrylate leveling agent.

[0081] The functional additives are KH570 0.3%, antioxidant 1010 0.1%, and light stabilizer 770 0.1%.

[0082] The anti-shrinkage modifier has a particle size range of 0.3~0.5μm, specifically 0.3μm, and is a mixture of 96% SiO2 and Al2O3 in a 7:3 ratio.

[0083] The preparation method includes the following steps:

[0084] 1. Preparation of organic carrier: Weigh diethylene glycol butyl ether and terpineol compounded organic solvent according to the formula, add ethyl cellulose, E-51 epoxy resin, BYK™ BM-50, modified aliphatic polyamide wax, modified fumed silica, polycarboxylate dispersant, and polyacrylate leveling agent. Stir at 80℃ for 60 min at a speed of 500 r / min until the components are completely dissolved and uniform. After cooling, filter for later use to ensure that the carrier viscosity is suitable for subsequent filling and printing requirements.

[0085] 2. Premixing: Place the double-modified compound conductive silver powder, lead-free high-temperature glass powder, functional additives, and anti-shrinkage modifier into a high-speed mixer and mix at 900 r / min for 25 min to achieve uniform dispersion of solid components without agglomeration or segregation;

[0086] 3. Grinding and dispersing: After mixing and stirring the premixed material with the organic carrier, transfer it to a three-roll mill and grind it repeatedly 4 times, controlling the grinding gap to 3-5μm, until the fineness of the slurry particles is ≤5μm, the slurry viscosity is stable at 180000-22000mPa·s (25℃, 10rpm), and the thixotropic index meets the standard;

[0087] 4. Vacuum degassing: Place the ground slurry in a vacuum degassing machine with a vacuum degree of -0.096MPa for 18 minutes to completely remove internal air bubbles and avoid pinholes and voids after filling, thus obtaining the finished silver paste.

[0088] The application method is as follows:

[0089] Substrate: 96% Al2O3 ceramic, with 200μm pore size; a 250-mesh stainless steel screen printing and squeegee filling process was used, with a squeegee angle of 50° and a squeegee speed of 60mm / s. After filling, the material was leveled at room temperature for 5 minutes, dried at 150℃ for 5 minutes to remove solvent, and then sintered using a gradient heating method: first, holding at 380℃ for 10 minutes, then increasing to 900℃ and holding for 25 minutes, followed by natural cooling to room temperature. The same method was used, but the pore size was changed to 500μm.

[0090] Example 2

[0091] Silver paste formulation: 86% of the surface of the compounded conductive silver powder (spherical silver powder D50=2.5μm, nano silver powder D50=0.050μm, flake silver powder D50=1μm, mass ratio 6.0:2.5:1.5) after double modification treatment with oleic acid and silane coupling agent, 4% lead-free high-temperature glass powder, 8.5% organic carrier, 0.75% functional additives, and 0.75% anti-shrinkage modifier.

[0092] Conductive silver powder: Spherical silver powder, nano silver powder and flake silver powder are compounded in a mass ratio of 6:2.5:1.5, and modified by coating with oleic acid and KH570 in a ratio of 99:0.75:0.25. The coating method is the same as in Example 1.

[0093] Lead-free high-temperature glass powder: D50=2.8μm, softening temperature 710℃, coefficient of thermal expansion 8.1×10⁻⁶ -6 / ℃, with the following composition: Bi2O3 58%, B2O3 12%, Al2O3 8%, SiO2 10%, CaO 5%, ZnO 7%.

[0094] Organic carrier: The organic solvent is a mixture of diethylene glycol ethyl ether and terpineol in a mass ratio of 6.5:3.5; the total thixotropic agent content is 2.4% (ethyl cellulose 1.1%, E-51 epoxy resin 0.5%, BYK™ BM-50 modified aliphatic polyamide wax 0.8%); the additives are modified fumed silica 0.10%, polycarboxylate dispersant 0.08%, and polyacrylate leveling agent 0.07%.

[0095] The functional additives are KH570 0.3%, antioxidant 1010 0.225%, and light stabilizer 770 0.225%.

[0096] The anti-shrinkage modifier is a mixture of 0.3μm ZrO2 (96% by weight) and Al2O3 in a mass ratio of 7:3.

[0097] The preparation process is the same as in Example 1.

[0098] Substrate: 96% Al2O3 ceramic, with a through-hole diameter of 300μm; the printing and filling process is carried out using a 250-mesh stainless steel screen, with a squeegee angle of 50° and a squeegee speed of 60mm / s. After filling the holes, the material is leveled at room temperature for 5 minutes, dried at 150℃ for 5 minutes to remove the solvent, and then sintered by gradient heating. The material is first held at 380℃ for 10 minutes, then heated to 880℃ and held for 25 minutes, and then naturally cooled to room temperature.

[0099] Example 3

[0100] Silver paste formulation: 82% of the surface of the compounded conductive silver powder is double-modified with oleic acid and silane coupling agent (spherical silver powder D50=2.5μm, nano silver powder D50=0.050μm, flake silver powder D50=1μm, mass ratio 6.0:3.0:1.0), 5% lead-free high-temperature glass powder, 11% organic carrier, 1% functional additives, and 1% anti-shrinkage modifier;

[0101] Conductive silver powder: Spherical silver powder, nano silver powder and flake silver powder are compounded in a mass ratio of 6:3:1 and modified by coating with oleic acid and KH570 in a ratio of 99:0.75:0.25.

[0102] Lead-free high-temperature glass powder: D50=3.2μm, softening temperature 730℃, coefficient of thermal expansion 8.2×10⁻⁶ -6 The composition at / ℃ is Bi2O3 59%, B2O3 11%, Al2O3 8%, SiO2 10%, CaO 5%, and ZnO 7%.

[0103] Organic carrier: The organic solvent is a mixture of diethylene glycol ethyl ether and terpineol in a mass ratio of 6.5:3.5, and the total thixotropic agent content is 2.4% (ethyl cellulose 1.1%, E-51 epoxy resin 0.5%, BYK™ BM-50 modified aliphatic polyamide wax 0.8%).

[0104] The additives are 0.12% modified fumed silica, 0.09% polycarboxylate dispersant, and 0.09% polyacrylate leveling agent.

[0105] The functional additives are KH570 0.3%, antioxidant 1010 0.35%, and light stabilizer 770 0.35%.

[0106] The anti-shrinkage modifier is a mixture of 0.3μm SiO2 (96%) and Al2O3 in a 7:3 ratio.

[0107] The preparation process is the same as in Example 1.

[0108] Substrate: 96% Al2O3 ceramic, with a through-hole diameter of 100μm; the printing and filling process is carried out using a 250-mesh stainless steel screen, with a squeegee angle of 50° and a squeegee speed of 60mm / s. After filling the holes, the surface is leveled at room temperature for 5 minutes, dried at 150℃ for 5 minutes to remove the solvent, and then sintered by gradient heating. First, the temperature is increased to 380℃ and held for 10 minutes, then the temperature is increased to 820℃ and held for 25 minutes, and then naturally cooled to room temperature.

[0109] Comparative Example 1

[0110] Commercially available conventional filling silver paste (sintering temperature 850℃, no shrinkage, high thixotropic optimized design) was selected, and the same 200μm pore size 96% alumina ceramic substrate was used. Filling and sintering were completed according to the manufacturer's recommended process as a control.

[0111] Comparative Example 2

[0112] A single spherical silver powder with a particle size D50 of 2.5 μm and a tap density of (6.0-7.0) g / cm was used to replace the gradient compounded silver powder. No anti-shrinkage modifier was added. The other formulation components, proportions, preparation and sintering processes were the same as in Example 1, serving as a single variable control.

[0113] Performance test results:

[0114] .

[0115] Test conclusion:

[0116] The embodiments of this invention target the full pore size range of 100-500μm and high-temperature sintering conditions of 800-900℃. For the first time in the industry, it achieves a near-zero shrinkage effect with a linear shrinkage rate of ≤0.1% during sintering. At the same time, it achieves a silver powder bulk density of ≥88%, a shrinkage-resistant skeleton coverage of ≥95%, and a green body volume change rate of ≤0.05% after drying. There are no shrinkage-inducing factors throughout the entire process, and the final technical effect of 100% pore regularity, zero collapse, and zero cracking is achieved.

[0117] Comparative Example 1, lacking any anti-shrinkage design, experienced a shrinkage rate of 3.8%, resulting in severe pore deformation. Comparative Example 2, lacking ternary close-packed silver powder and a global three-dimensional framework, exhibited a shrinkage rate of 2.9% and localized microcracks.

[0118] In addition, based on Example 1, a silver powder gradation screening test was also conducted. The substrate was 96% Al2O3 ceramic with a pore size of 200 μm, as detailed in Table 1.

[0119] Table 1. Silver powder gradation screening test data (performance comparison of different ratios)

[0120] .

[0121] Based on Example 1, a screening test was conducted to determine the amount of oleic acid used. The substrate was 96% Al2O3 ceramic with a pore size of 200 μm, as detailed in Table 2.

[0122] Table 2: Screening test data for oleic acid dosage (silver powder: oleic acid mass ratio)

[0123] .

[0124] Based on Example 1, the following experiments were also conducted, as detailed in Tables 3 and 4. Except for the limiting conditions in the tables, the other experiments were the same as in Example 1:

[0125] Table 3

[0126] .

[0127] Table 4

[0128] .

[0129] The three-dimensional skeleton coverage of experimental group 3 was 95%, and the porosity of the pore walls was 100%, which completely eliminated the porosity in the large-diameter pores. When the mass ratio of SiO2:Al2O3 was 7:3~4, the performance was comparable to that of 7:3. The same applies when all or part of SiO2 is replaced with ZrO2.

[0130] The coefficient of thermal expansion differs from that of alumina ceramics by only 0.3 × 10⁻⁶. -6 / ℃, solving the problems of substrate warping and via cracking; after sintering, the density reaches 96%, with no voids or cracks, meeting the metallization requirements of high-frequency PCBs.

[0131] As can be seen from Figures 1 and 2:

[0132] (1) The white conductive silver paste area is completely filled inside the black 96% alumina ceramic through hole. There are no voids, bubbles, or missing materials in the hole. The filling fullness reaches 100%, which reflects the excellent filling performance of the high thixotropic organic carrier and gradient compound silver powder system of the present invention under the large pore size (100-500μm) pore filling process. It can avoid defects such as local looseness and uneven filling.

[0133] (2) The interface between the silver paste filling area and the ceramic pore wall is clear and tightly bonded, with no delamination, peeling and cracks, which proves that the silver powder modified by oleic acid + KH-570 coupling agent formed a stable chemical bond with the ceramic pore wall. At the same time, the lead-free high temperature glass powder fully wets the silver powder and ceramic substrate during the sintering process at 800-900℃, forming a "glass-silver-ceramic" three-layer bond, which significantly improves the interface bonding strength.

[0134] (3) After sintering, the cross-section of the through hole maintains a regular rectangular shape with straight edges and no shrinkage, expansion or collapse deformation. This directly verifies that under the synergistic effect of the anti-shrinkage modifier and the gradient compounded silver powder, the linear shrinkage rate of sintering is ≤0.1%, which completely solves the industry pain point of easy collapse and cracking after large-diameter pore filling.

[0135] (4) The silver paste sintered body has a uniform and dense texture with no obvious micropores and loose particles, indicating that the silver powder is fully melted and fused during the high-temperature sintering process to form a continuous and dense conductive network. The filling density is ≥96%, which provides structural protection for low through-hole resistivity and high weld peel strength.

[0136] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the technical scope disclosed in the present invention, based on the technical solution and concept of the present invention, should be covered within the scope of protection of the present invention. It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present invention can be combined with each other.

Claims

1. A high-temperature sintered alumina ceramic large-pore near-zero shrinkage silver paste, wherein the large pore size refers to 100-500 μm, and the sintering temperature is 800-900℃, characterized in that: It comprises the following components by weight: 82-90% conductive silver powder, 3-5% lead-free high-temperature glass powder, 0.5-1% functional additives, 5-11% organic carrier, and 0.5-1% anti-shrinkage modifier; The silver paste has a thixotropic index of 5.0-6.0 at 25℃ and a viscosity controlled at 180,000-220,000 mPa·s. The conductive silver powder has a tap density ≥88%, including spherical silver powder, nano silver powder and flake silver powder in a mass ratio of 6~7:2~3:1~1.5; the surface of the conductive silver powder is coated with oleic acid and KH570 silane coupling agent, and the molar ratio of conductive silver powder, oleic acid and KH570 silane coupling agent is 99:0.75:0.25; The lead-free high-temperature glass powder has a particle size D50 of 2~3.5μm, a softening temperature controlled at 630~750℃, and a stable coefficient of thermal expansion at (7.8~8.3)×10. -6 / ℃, the composition by mass percentage is: Bi2O3 55%~60%, B2O3 10%~12%, Al2O3 5%~8%, SiO2 8%~10%, CaO 3%~5%, ZnO 4%~7%; Functional additives include solder affinity additives and silane coupling agents; The anti-shrinkage modifier includes SiO2, as well as ZrO2 and / or Al2O3, with a particle size range of 0.3~0.5μm, wherein the mass content of 0.3μm particles is not less than 96% of the mass of the anti-shrinkage modifier.

2. The high-temperature sintered alumina ceramic large-pore near-zero shrinkage silver paste according to claim 1, characterized in that: The method for coating conductive silver powder with oleic acid and silane coupling agent includes the following steps: conductive silver powder, oleic acid and silane coupling agent are mixed in a V-type mixer at a speed of 200~300 r / min for at least 60 min; And / or, spherical silver powder D50=2~3μm, tap density 6.0~7.0g / cm³; nano silver powder D50=0.05~0.1μm, tap density 5.0~6.0g / cm³; flake silver powder D50=0.8~1μm, tap density 5.5~6.5g / cm³.

3. The high-temperature sintered alumina ceramic large-pore near-zero shrinkage silver paste according to claim 1, characterized in that: The organic carrier includes an organic solvent and a thixotropic agent. The organic solvent includes diethylene glycol ethyl ether and terpineol in a mass ratio of 6.5:3.

5. The thixotropic agent includes ethyl cellulose, E-51 resin and BYK™ BM-50 modified aliphatic polyamide wax in a mass ratio of 1.1:0.5:0.

8. The mass amount of the thixotropic agent is 2.0~3.0% of the total mass of the silver paste.

4. The high-temperature sintered alumina ceramic large-pore near-zero shrinkage silver paste according to claim 3, characterized in that: The organic carrier also includes additives, which consist of modified fumed silica, polycarboxylate dispersant and polyacrylate leveling agent.

5. The high-temperature sintered alumina ceramic large-pore near-zero shrinkage silver paste according to claim 1, characterized in that: The functional additives also include antioxidants, which include 0.5% lead-free antioxidants and light stabilizers by weight of the silver paste. And / or, the solder affinity additive is 0.3% of the silver paste mass of a silane coupling agent.

6. The high-temperature sintered alumina ceramic large-pore near-zero shrinkage silver paste according to claim 1, characterized in that: The solder affinity additive is 0.3% of KH570 silane coupling agent by weight of silver paste.

7. The high-temperature sintered alumina ceramic large-pore near-zero shrinkage silver paste according to claim 1, characterized in that: The anti-shrinkage modifier includes nano ZrO2 and Al2O3 in a mass ratio of 6~7:3~4, or nano SiO2 and Al2O3 in a mass ratio of 6~7:3~4.

8. The method for preparing near-zero shrinkage silver paste for large-pore alumina ceramics according to any one of claims 1 to 7, comprising the following steps: First, place conductive silver powder, lead-free high-temperature glass powder, functional additives, and anti-shrinkage modifier into a mixer and mix them evenly, controlling the mixer speed to 900~1000 r / min; Then, the mixed materials are slowly added to the organic carrier while stirring. The stirring speed is 250~300 r / min and the stirring time is 45~60 min to form a preliminary slurry without dry powder agglomeration. Finally, the initial slurry is transferred to a three-roll mill and ground repeatedly 4-5 times, controlling the grinding gap to 1-10μm, until the slurry particle fineness is ≤5μm and there are no agglomerated particles; after grinding, defoaming is performed.

9. The method for preparing near-zero shrinkage silver paste for large-pore alumina ceramics according to claim 8, characterized in that, Vacuum degassing is employed, including the following steps: the ground slurry is placed in a vacuum degassing machine with a vacuum degree of -0.096~0.098MPa and a degassing time of 18-20min.

10. A method for sintering by printing through a hole, comprising the following steps: screen printing a near-zero shrinkage silver paste for large-diameter pores of high-temperature sintered alumina ceramic as described in any one of claims 1 to 7, leveling it, and then drying it; after drying, using an ultra-slow gradient segmented heating in an air atmosphere, with the heating rate precisely controlled as follows: heating to 370~400℃ at 2-3℃ / min, holding it until all organic phases are completely decomposed without residue, then heating to 800~900℃ at 4-6℃ / min, holding it for 28~30min; and finally cooling it naturally in the furnace.

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