A method for preparing a hermetic ceramic base

Abstract

This invention relates to the field of special ceramic product manufacturing technology, specifically to a method for preparing an airtight ceramic base, comprising: a co-fired ceramic substrate, wherein the co-fired ceramic substrate is provided with a dense support layer, an interconnected functional layer, and a cavity sealing layer sequentially from bottom to top; the dense support layer is a high-purity alumina dense ceramic layer with a thickness ≥0.2mm; the interconnected functional layer is an integral sintered layer composed of a multi-layered stacked alumina ceramic dielectric layer and an embedded tungsten metallized three-dimensional interconnected structure; the cavity sealing layer is an alumina ceramic layer with a concave cavity structure, and the edge of the concave cavity is provided with an annular stress buffer groove. The airtight ceramic base of this invention, through structural innovation and synergistic optimization of the manufacturing process, adopts a three-layer integral co-fired ceramic substrate structure of the same material, combined with a rounded corner annular stress buffer groove design at the cavity edge, solving the problems of sintering warping, interlayer delamination, and stress concentration cracking.

Description

Technical Field

[0001] This invention relates to the field of special ceramic product manufacturing technology, specifically a method for preparing an airtight ceramic base. Background Technology

[0002] Hermetic ceramic substrates are core packaging substrates made using high-temperature co-fired ceramic processes, which combine electrical interconnection, structural support, and hermetic protection functions. They are key basic components in fields such as automotive-grade MEMS inertial sensors, radio frequency communication devices, aerospace high-reliability electronic equipment, and optoelectronic devices. Their core performance indicator is the helium mass spectrometry leak detection rate, which directly determines the long-term reliability, environmental adaptability, and service life of the packaged devices.

[0003] However, traditional ceramic substrates have significant drawbacks: First, poor thermal compatibility with the substrate. They often use ceramic green bodies with varying alumina contents, layered and co-fired, resulting in significant differences in sintering shrinkage and thermal expansion coefficients between layers. After high-temperature co-firing, defects such as warping, interlayer delamination, and microcracks easily occur, forming continuous gas permeation channels. This leads to substandard initial airtightness and a continuously increasing leakage rate over long-term use. Second, insufficient interfacial bonding. Ceramic metallization processes often use pure tungsten or pure molybdenum slurries, lacking a wetting phase with the alumina ceramic substrate. This results in low interfacial bonding strength, making them prone to interfacial cracking and metallization layer delamination under automotive-grade wide-temperature-range cycling and vibration / impact conditions (-40℃-125℃), directly compromising the airtight structure. Third, stress concentration in the cavity. The concave cavity edge of the base has a right-angle structure and no stress relief design. During sintering, sealing, and high and low temperature cycling, stress concentration is prone to occur at the cavity edge, causing ceramic cracking, which is the core cause of device failure in automotive-grade scenarios. Fourth, the airtight protection range is limited, only protecting the upper surface sealing pads and the inner wall of the cavity, without providing full-area protection for the sides, bottom, and interlayer interface edges of the substrate. In salt spray and high humidity and heat environments, it is easy to form penetration and corrosion channels, which cannot meet the service life requirement of more than 10 years. Fifth, the sintering process is simple, mostly using single-stage isothermal sintering, which cannot take into account both the uniformity of ceramic grains and the density of the matrix. It is prone to abnormal grain growth and insufficient density, resulting in increased gas permeability of the matrix and failing to achieve ultimate airtight protection.

[0004] In summary, a method for preparing an airtight ceramic substrate is needed to solve the above problems. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing an airtight ceramic substrate to solve the problems mentioned in the background art.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] This invention proposes an airtight ceramic base, comprising:

[0008] A co-fired ceramic matrix, wherein the co-fired ceramic matrix is ​​provided with a dense support layer, an interconnected functional layer and a cavity sealing layer from bottom to top;

[0009] The dense support layer is a high-purity alumina dense ceramic layer with a thickness ≥0.2mm; the interconnection functional layer is an integral sintered layer composed of a multi-layer stacked alumina ceramic dielectric layer and an embedded tungsten metallized three-dimensional interconnection structure; the cavity sealing layer is an alumina ceramic layer with a concave cavity structure, and the edge of the concave cavity is provided with an annular stress buffer groove.

[0010] An interface metallization layer is provided, which covers the entire surface of the co-fired ceramic substrate and the inner wall of the concave cavity. The interface metallization layer is provided with a molybdenum-manganese wetting bonding layer, a tungsten-molybdenum conductive transition layer, and a nickel-gold protective sealing layer from the inside to the outside.

[0011] A global barrier layer is provided, which covers the surface of the interface metallization layer and the sides and bottom of the co-fired ceramic substrate. The global barrier layer is provided with an alumina nano-matching layer, a silicon nitride dense barrier layer and a solder sealant layer from the inside to the outside.

[0012] Preferably, the dense support layer, interconnection functional layer, and cavity sealing layer are all made by co-firing high-purity alumina powder with an alumina mass fraction of 99.7% with a composite sintering aid with a magnesium oxide mass fraction of 0.15% and a yttrium oxide mass fraction of 0.15%, with a sintering density ≥99.8%, an average grain size of 1.5μm-2μm, and an overall flatness ≤0.002mm / 100mm.

[0013] Preferably, the thickness of the alumina ceramic dielectric layer of the interconnecting functional layer is 0.05mm-0.1mm, and the number of stacked layers is 2-8. The line width and line spacing of the embedded tungsten metallized three-dimensional interconnect structure are both ≥0.05mm. The interlayer vias are filled with high-purity tungsten slurry with a tungsten mass fraction of 98%, and the inner wall of the vias is provided with a continuous tungsten metallization layer that connects with the interface metallization layer.

[0014] Preferably, the concave cavity depth of the cavity sealing layer is 0.1mm-0.5mm, the width of the annular stress buffer groove is 0.2mm-0.3mm, and the depth is 30%-40% of the thickness of the cavity sealing layer. The upper surface of the cavity sealing layer is provided with a continuous annular sealing pad, and the width of the annular sealing pad is ≥0.3mm.

[0015] Based on the hermetic ceramic base, this invention also proposes a method for preparing the hermetic ceramic base, comprising the following steps:

[0016] S1. Prepare a ceramic green body strip with a dense support layer, an interconnected functional layer, and a cavity sealing layer. Complete the punching, filling, pattern printing, cavity and stress buffer groove processing of each green body strip. Stack and position them in sequence to obtain a ceramic green body preform.

[0017] S2. After the ceramic green body is subjected to warm isostatic pressing, the integrated densification sintering is completed by a stepped glue removal and two-stage high-temperature co-firing process to obtain a co-fired ceramic matrix.

[0018] S3. After precision grinding of the surface of the co-fired ceramic substrate, an interface metallization layer is prepared by thick film printing and high-temperature sintering process, and an all-area barrier layer is prepared by atomic layer deposition process to obtain an airtight ceramic substrate.

[0019] Preferably, the preparation process of the ceramic green body preform in step S1 includes the following steps:

[0020] A1. Ceramic green belt casting: High-purity alumina powder, composite sintering aid, organic binder, plasticizer, and anhydrous ethanol solvent are mixed in a mass ratio of 100:0.3:9:3:28 and ball-milled to obtain a ceramic slurry with a solid content ≥58%. The green belts of corresponding thicknesses, including a dense support layer, an interconnected functional layer, and a cavity sealing layer, are then formed by casting process.

[0021] A2. Interconnect functional layer processing: Laser punching is used to complete the through-hole processing of the green strip of the interconnect functional layer, high-purity tungsten paste is used to complete the vacuum filling of the through-hole, and screen printing is used to complete the patterned tungsten metallization wiring printing with a printing thickness of 15μm-20μm;

[0022] A3. Cavity sealing layer processing: The concave cavity and annular stress buffer groove are processed by laser engraving with a dimensional tolerance of ≤ ±0.02mm. The annular sealing pad is graphicly printed by screen printing.

[0023] A4. Green Blank Stacking and Positioning: The green blanks are stacked in the order of dense support layer, interconnected functional layer, and cavity sealing layer. Positioning pins are used to achieve precise alignment with an alignment accuracy of ≤ ±0.01mm.

[0024] Preferably, the integral sintering process of the ceramic green body in step S2 includes the following steps:

[0025] B1. Warm isostatic pressing pretreatment: After vacuum sealing the stacked ceramic green preform, place it in a warm isostatic press and hold it under pressure at 50℃ and 25MPa for 15min.

[0026] B2. Stepped debinding pre-sintering: The pretreated green preform is placed in a nitrogen atmosphere debinding furnace, heated to 600℃ at a heating rate of 2℃ / min, held for 120min to complete debinding, and then heated to 1100℃ at a heating rate of 3℃ / min, held for 60min to complete pre-sintering.

[0027] B3. Two-stage high-temperature co-firing: The pre-sintered green body is placed in a tungsten mesh sintering furnace in a hydrogen atmosphere and heated to 1550°C at a heating rate of 5°C / min. The temperature is held for 90 min to complete grain control. The temperature is then raised to 1600°C and held for 120 min to complete densification co-firing. The temperature is then lowered to room temperature at a cooling rate of 3°C / min to obtain the co-fired ceramic matrix.

[0028] Preferably, the preparation process of the interface metallization layer in step S3 includes the following steps:

[0029] C1. Surface pretreatment of the substrate: The co-fired ceramic substrate is surface-processed by double-sided grinding to control the surface roughness to ≤0.2μm. After ultrasonic cleaning, it is dried for later use.

[0030] C2. Thick film printing and sintering: Molybdenum-manganese paste, tungsten-molybdenum paste, and nickel paste are sequentially printed on all surfaces, inner walls of concave cavities, and inner walls of through holes of the co-fired ceramic substrate. After each layer is printed, it is dried at 120°C for 15 minutes. After all printing is completed, it is placed in a hydrogen atmosphere sintering furnace and held at 1400°C for 60 minutes to complete sintering.

[0031] C3. Surface gold plating treatment: A dense gold layer is prepared on the surface of the nickel layer using an electroplating process to complete the preparation of the interface metallization layer.

[0032] Preferably, the preparation process of the global barrier layer in step S3 includes the following steps:

[0033] D1. Atomic Layer Deposition of the Underlying Matching Layer: The ceramic substrate with the prepared interface metallization layer is placed in an atomic layer deposition apparatus, and an alumina nano-matching layer is deposited at 150°C with a deposition thickness of 1μm-1.5μm.

[0034] D2. Atomic layer deposition barrier layer: A dense silicon nitride barrier layer is deposited on the surface of the alumina nano-matching layer at a deposition temperature of 150℃ and a deposition thickness of 1.5μm-2μm.

[0035] D3. Preparation of the sealing adapter layer: A nickel-gold gradient sealing adapter layer is prepared on the silicon nitride barrier layer on the surface of the annular sealing pad. The nickel layer thickness is 2μm-3μm and the gold layer thickness is 0.8μm-1.2μm.

[0036] Preferably, the manganese mass fraction in the molybdenum-manganese slurry is 12%-15%, the bonding strength between the sintered interface metallization layer and the ceramic substrate is ≥45MPa, the pinhole rate of the global barrier layer prepared by atomic layer deposition is 0, and the leak rate detected by helium mass spectrometry is ≤1×10⁻⁶. -10 Pa·m 3 / s.

[0037] Compared with existing technologies, the beneficial effects of this invention are as follows: The airtight ceramic substrate of this invention, through structural innovation and synergistic optimization of the manufacturing process, adopts a three-layer integrated co-fired ceramic substrate structure of the same material, combined with a rounded-corner annular stress buffer groove design at the cavity edge, solving the problems of sintering warping, interlayer delamination, and stress concentration cracking. The substrate sintering density is ≥99.8%, and the thermal cycling cracking rate at the cavity edge is reduced to 0. A gradient metallization system with a molybdenum-manganese wetting bonding layer as the core is used to improve the interfacial bonding strength between the ceramic and the metallization layer, achieving an interfacial bonding strength ≥45MPa. After 200 cycles of high and low temperature cycling from -40℃ to 125℃, there is no delamination or cracking, and the airtight performance remains unchanged. An innovative atomic layer deposition global barrier layer is introduced to achieve airtight protection across the entire surface of the ceramic substrate without dead angles, with a pinhole rate of 0 and an initial helium mass spectrometry leak rate ≤1×10⁻¹⁰ Pa·m. 3 / s, it can maintain high airtightness even after long-term humid heat aging; through stepped debinding and two-stage high-temperature co-firing process, it achieves precise control of ceramic grain size and matrix densification. After sintering, the overall flatness of the matrix is ​​≤0.002mm / 100mm. The dimensional accuracy is suitable for high-precision sealing and bonding processes, and it can be widely used in high-reliability electronic packaging scenarios such as automotive-grade MEMS inertial navigation, RF communication, and aerospace, meeting the long-term use requirements in extreme environments. Detailed Implementation

[0038] Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0039] I. Materials:

[0040] Unless otherwise specified, the raw materials used in the airtight ceramic base proposed in this invention are all commercially available products that meet electronic-grade industry standards, as detailed below:

[0041] Ceramic matrix raw materials: electronic grade high-purity alumina powder, purity ≥99.99%, median particle size D50=0.3μm-0.5μm; electronic grade magnesium oxide powder, purity ≥99.95%; electronic grade yttrium oxide powder, purity ≥99.95%; organic binder is polyvinyl butyral (PVB); plasticizer is dibutyl phthalate (DBP); anhydrous ethanol solvent, purity ≥99.5%.

[0042] Metallization raw materials: Electronic-grade high-purity tungsten paste, tungsten mass fraction 98%, suitable for HTCC co-firing process; molybdenum-manganese paste, molybdenum mass fraction 80%-85%, manganese mass fraction 12%-15%, balance is borosilicate glass phase binder; tungsten-molybdenum paste, tungsten mass fraction 10%-15%, molybdenum mass fraction 85%-90%; electronic-grade nickel paste, nickel mass fraction ≥99.9%; potassium gold cyanide electroplating solution, gold mass concentration 10g / L, conforming to electronic-grade electroplating standards.

[0043] Atomic layer deposition raw materials: Trimethylaluminum (TMA), purity ≥99.999%; Deionized water, resistivity ≥18.2 MΩ·cm; Dichlorosilane (DCS), purity ≥99.999%; High-purity ammonia, purity ≥99.999%.

[0044] The core structure and parameter range of the airtight ceramic base of the present invention are as follows:

[0045] The co-fired ceramic matrix is ​​provided with a dense support layer, an interconnected functional layer, and a cavity sealing layer from bottom to top.

[0046] The thickness of the dense support layer is ≥0.2mm; the thickness of the single layer of the alumina ceramic dielectric layer of the interconnect functional layer is 0.05mm-0.1mm, with 2-8 layers; the line width and line spacing of the embedded tungsten metallized three-dimensional interconnect structure are both ≥0.05mm; the depth of the concave cavity of the cavity sealing layer is 0.1mm-0.5mm, the edge of the concave cavity is provided with a rounded annular stress buffer groove, the width of the annular stress buffer groove is 0.2mm-0.3mm, and the depth is 30%-40% of the thickness of the cavity sealing layer; the upper surface of the cavity sealing layer is provided with a continuous annular sealing pad with a width ≥0.3mm;

[0047] The co-fired ceramic matrix is ​​made by co-firing high-purity alumina powder with an alumina mass fraction of 99.7% with a composite sintering aid with a magnesium oxide mass fraction of 0.15% and a yttrium oxide mass fraction of 0.15%. The sintering density is ≥99.8%, the average grain size is 1.5μm-2μm, and the overall flatness is ≤0.002mm / 100mm.

[0048] An interface metallization layer covers the entire surface of the co-fired ceramic substrate and the inner wall of the concave cavity. From the inside out, it is provided with a molybdenum-manganese wetting bonding layer, a tungsten-molybdenum conductive transition layer, and a nickel-gold protective sealing layer. The mass fraction of manganese in the molybdenum-manganese slurry is 12%-15%, and the bonding strength between the sintered interface metallization layer and the ceramic substrate is ≥45MPa.

[0049] A global barrier layer covers the surface of the interface metallization layer and the sides and bottom of the co-fired ceramic substrate. From the inside out, it consists of an alumina nano-matching layer, a silicon nitride dense barrier layer, and a solder mask layer. The alumina nano-matching layer has a deposition thickness of 1 μm-1.5 μm, the silicon nitride dense barrier layer has a deposition thickness of 1.5 μm-2 μm, the nickel layer of the solder mask layer has a thickness of 2 μm-3 μm, and the gold layer has a thickness of 0.8 μm-1.2 μm. The global barrier layer prepared by atomic layer deposition has a pinhole rate of 0 and a leak rate detected by helium mass spectrometry ≤1×10⁻⁶. -10 Pa·m 3 / s.

[0050] II. Process:

[0051] Based on the above structure and raw materials, this invention also proposes a method for preparing an airtight ceramic substrate, specifically including the following steps:

[0052] S1. Prepare a ceramic green body strip with a dense support layer, an interconnected functional layer, and a cavity sealing layer. Complete the punching, filling, pattern printing, cavity and stress buffer groove processing of each green body strip. Stack and position them in sequence to obtain a ceramic green body preform.

[0053] S2. After the ceramic green body is subjected to warm isostatic pressing, the integrated densification sintering is completed by a stepped glue removal and two-stage high-temperature co-firing process to obtain a co-fired ceramic matrix.

[0054] S3. After precision grinding of the surface of the co-fired ceramic substrate, an interface metallization layer is prepared by thick film printing and high temperature sintering process, and an all-domain barrier layer is prepared by atomic layer deposition process to obtain an airtight ceramic substrate.

[0055] The preparation process of the ceramic green body in step S1 includes the following steps:

[0056] A1. Ceramic green belt casting: High-purity alumina powder, composite sintering aid, organic binder, plasticizer, and anhydrous ethanol solvent are mixed in a mass ratio of 100:0.3:9:3:28 and subjected to planetary ball milling for 24 hours to obtain a ceramic slurry with a solid content ≥58%. The slurry viscosity is controlled between 3000 mPa·s and 5000 mPa·s. Green belts of corresponding thicknesses for dense support layer, interconnected functional layer, and cavity sealing layer are then formed using a casting process. The thickness tolerance of the green belt is ≤±5%.

[0057] A2. Interconnect Functional Layer Processing: Through-hole processing of the green strip of the interconnect functional layer is completed by ultraviolet laser punching, with a through-hole diameter of 0.08mm-0.1mm. High-purity tungsten paste is used to complete the vacuum filling of the through-holes, with a filling density of ≥99%. High-precision screen printing is used to complete the patterned tungsten metallization wiring printing, with a printing thickness of 15μm-20μm and a printing alignment accuracy of ≤±0.005mm.

[0058] A3. Cavity sealing layer processing: The concave cavity and annular stress buffer groove are processed by ultraviolet laser engraving with a dimensional tolerance of ≤ ±0.02mm. The annular sealing pad and chip bonding pad are patterned by screen printing.

[0059] A4. Green Blank Stacking and Positioning: The green blanks are stacked in the order of dense support layer, interconnected functional layer, and cavity sealing layer. High-precision positioning pins are used to achieve accurate alignment with an alignment accuracy of ≤ ±0.01mm.

[0060] The integral sintering process of the ceramic green body in step S2 includes the following steps:

[0061] B1. Warm isostatic pressing pretreatment: After the stacked ceramic green body is vacuum sealed with an aluminum-plastic composite film, it is placed in a warm isostatic press and held at 50℃ and 25MPa for 15 minutes to ensure that the green body layers are tightly bonded and there are no delamination gaps.

[0062] B2. Stepped debinding pre-sintering: The pretreated green body is placed in a nitrogen atmosphere debinding furnace and heated to 600℃ at a heating rate of 2℃ / min. It is held for 120min to complete the decomposition and removal of organic binders. Then, the temperature is increased to 1100℃ at a heating rate of 3℃ / min and held for 60min to complete the pre-sintering. This allows the green body to obtain initial strength and avoids deformation during high-temperature sintering.

[0063] B3. Two-stage high-temperature co-firing: The pre-sintered green body is placed in a tungsten mesh sintering furnace in a hydrogen atmosphere and heated to 1550℃ at a heating rate of 5℃ / min. It is held for 90min to complete grain regulation, suppress abnormal grain growth, and obtain a uniform and fine grain structure. The temperature is then increased to 1600℃ and held for 120min to complete densification co-firing. Subsequently, the temperature is uniformly reduced to room temperature at a cooling rate of 3℃ / min to obtain the co-fired ceramic matrix.

[0064] The preparation process of the interface metallization layer in step S3 includes the following steps:

[0065] C1. Surface pretreatment of the substrate: The co-fired ceramic substrate is precision machined on both the upper and lower surfaces using a double-sided grinding process, with the surface roughness controlled to be ≤0.2μm and the flatness ≤0.002mm / 100mm. Then, it is ultrasonically cleaned with anhydrous ethanol and deionized water for 15min each, and dried in an oven at 120℃ for later use.

[0066] C2. Thick film printing and sintering: Molybdenum-manganese paste, tungsten-molybdenum paste, and nickel paste are sequentially printed on the entire surface of the co-fired ceramic substrate, the inner wall of the concave cavity, and the inner wall of the through hole. After each layer is printed, it is dried at 120℃ for 15 minutes. After all the printing is completed, it is placed in a hydrogen atmosphere sintering furnace and held at 1400℃ for 60 minutes to complete the sintering, so as to achieve the metallurgical bonding between the metallization layer and the ceramic substrate.

[0067] C3. Surface gold plating treatment: A dense gold layer is prepared on the nickel layer surface using a high-speed electroplating process with a current density of 0.3A / dm² and an electroplating time of 60s to complete the preparation of the interface metallization layer.

[0068] The preparation process of the global barrier layer in step S3 includes the following steps:

[0069] D1. Atomic Layer Deposition (ALD) Underlying Matching Layer: The ceramic substrate with the prepared interface metallization layer is placed in a plasma-enhanced atomic layer deposition (ALD) apparatus at 150°C and a vacuum degree of 1×10⁻ ...�. 3 Under the condition of Pa, an alumina nano-matching layer was deposited, with a single cycle deposition thickness of 0.1 nm and a total deposition thickness of 1 μm-1.5 μm;

[0070] D2. Atomic layer deposition barrier layer: A dense silicon nitride barrier layer is deposited on the surface of the alumina nano-matching layer at a deposition temperature of 150℃, a single-cycle deposition thickness of 0.08nm, and a total deposition thickness of 1.5μm-2μm.

[0071] D3. Preparation of the sealing adapter layer: The annular sealing pad area is exposed by photolithography. A nickel-gold gradient sealing adapter layer is prepared on the silicon nitride barrier layer on the surface of the annular sealing pad. The nickel layer is prepared by electroplating and has a thickness of 2μm-3μm, and the gold layer is prepared by immersion gold and has a thickness of 0.8μm-1.2μm.

[0072] Example 1: In this example, an airtight ceramic base is prepared according to the following process. The core structure and process parameters are as follows:

[0073] Co-fired ceramic substrate: dense support layer thickness 0.3mm; interconnect functional layer alumina ceramic dielectric layer single layer thickness 0.08mm, stacked in 4 layers, embedded tungsten metallized wiring line width and spacing 0.08mm; cavity sealing layer concave cavity depth 0.3mm, annular stress buffer groove width 0.25mm, depth 35% of cavity sealing layer thickness, annular sealing pad width 0.4mm;

[0074] Raw material ratio: The mass ratio of high-purity alumina powder, composite sintering aid, organic binder, plasticizer, and anhydrous ethanol solvent is 100:0.3:9:3:28. The composite sintering aid contains 0.15% magnesium oxide and 0.15% yttrium oxide. The molybdenum-manganese slurry contains 13% manganese.

[0075] Process parameters: Two-stage co-firing process: 1550℃ for 90 min, 1600℃ for 120 min; Alumina nano-matching layer deposition thickness 1.2 μm, silicon nitride dense barrier layer deposition thickness 1.8 μm; Solder sealant layer: nickel layer thickness 2.5 μm, gold layer thickness 1.0 μm.

[0076] The remaining raw materials, structure, and process steps are consistent with the aforementioned specific implementation method.

[0077] Example 2: In this example, the number of interconnect functional layer alumina ceramic dielectric layers is 2, and the remaining structure, raw material ratio, and process parameters are the same as in Example 1.

[0078] Example 3: In this example, the number of interconnect functional layer alumina ceramic dielectric layers is 8, and the remaining structure, raw material ratio, and process parameters are the same as in Example 1.

[0079] Example 4: In this example, the depth of the concave cavity in the cavity sealing layer is 0.1 mm, and the rest of the structure, raw material ratio, and process parameters are the same as in Example 1.

[0080] Example 5: In this example, the depth of the concave cavity in the cavity sealing layer is 0.5 mm, and the rest of the structure, raw material ratio, and process parameters are the same as in Example 1.

[0081] Example 6: In this example, the densification sintering temperature in the two-stage high-temperature co-firing process is 1580℃, and the remaining structure, raw material ratio, and process parameters are the same as in Example 1.

[0082] Example 7: In this example, the densification sintering temperature in the two-stage high-temperature co-firing process is 1620℃, and the remaining structure, raw material ratio, and process parameters are the same as in Example 1.

[0083] Comparative Example 1: In this comparative example, the concave cavity edge of the cavity sealing layer is not provided with an annular stress buffer groove, and the rest of the structure, raw material ratio, and process parameters are the same as in Example 1.

[0084] Comparative Example 2: In this comparative example, the composite sintering aid contained 0.3% magnesium oxide and 0.3% yttrium oxide by mass, with a total addition of 0.6%. The remaining structure, raw material ratio, and process parameters were the same as in Example 1.

[0085] Comparative Example 3: In this comparative example, no molybdenum-manganese wetting bonding layer was provided in the interface metallization layer. Tungsten-molybdenum paste was directly printed on the surface of the ceramic substrate. The remaining structure, raw material ratio, and process parameters were the same as in Example 1.

[0086] Comparative Example 4: In this comparative example, no full-area barrier layer was prepared, but the remaining structure, raw material ratio, and process parameters were the same as in Example 1.

[0087] Comparative Example 5: In this comparative example, the high-temperature co-firing process adopts single-stage sintering, directly raising the temperature to 1600℃ at a heating rate of 5℃ / min, holding for 210min, and eliminating the 1550℃ grain control section. The remaining structure, raw material ratio, and process parameters are consistent with those of Example 1.

[0088] Comparative Example 6: In this comparative example, the interconnecting functional layer is made of ceramic green body with 95% alumina mass fraction. The sintering shrinkage rate and thermal expansion coefficient of the dense support layer and cavity sealing layer with 99.7% alumina material do not match, so the two cannot be co-fired synchronously. The remaining structure, raw material ratio and process parameters are the same as in Example 1.

[0089] Comparative Example 7: In this comparative example, the mass fraction of manganese in the molybdenum-manganese slurry is 10%, and the remaining structure, raw material ratio, and process parameters are the same as in Example 1.

[0090] III. Performance Testing:

[0091] The following performance tests were performed on the hermetic ceramic substrates prepared in Examples 1-7 and Comparative Examples 1-7:

[0092] a. Matrix density: Tested according to GB / T2413-2008 "Determination of density and porosity of precision ceramics - Archimedes method";

[0093] b. Helium mass spectrometry leak detection rate: According to method 1014.2 of GJB548B-2005 "Test methods and environmental test methods for microelectronic devices", the initial leak rate and the leak rate after 200 cycles of high and low temperature (-40℃ to 125℃) were detected using a helium mass spectrometer leak detector.

[0094] c. Interface bond strength: Tested according to GB / T4907-2002 "Test method for the bond strength of ceramic materials and metals - tensile method";

[0095] d. Flatness: Measured using a laser flatness tester according to GB / T2529-2012 "Alumina Ceramic Substrates for Electronic Ceramics";

[0096] e. Crack rate at the cavity edge: Take 50 samples from the same batch, and after 200 cycles of high and low temperature, observe the cracking at the cavity edge using a metallographic microscope and count the crack rate.

[0097] f. Average grain size: Detected using the scanning electron microscope (SEM) statistical method according to GB / T6569-2006 "Test Method for Bending Strength of Fine Ceramics".

[0098] The performance test data of Examples 1-7 and Comparative Examples 1-7 are shown in Tables 1 and 2:

[0099] Table 1: Performance Data Table of Examples

[0100]

[0101] Table 2: Comparative Performance Data Table

[0102]

[0103] IV. Analysis Conclusion:

[0104] As shown in Table 1, the hermetic ceramic substrates prepared in Examples 1-7 of this invention exhibit significantly better performance indicators than the comparative examples, with matrix density ≥99.8% and initial helium mass spectrometry leak rates ≤1×10⁻⁶. -10 Pa·m 3 / s, after 200 high and low temperature cycles, the airtightness performance has not significantly decreased, the interface bonding strength is ≥45MPa, and the cavity edge cracking rate is 0, which fully meets the requirements for high-reliability electronic packaging.

[0105] As shown in Table 2, Comparative Example 1, which did not have an annular stress buffer groove, had a 100% cracking rate at the cavity edge after high and low temperature cycling, and the leakage rate soared by 3 orders of magnitude. This verifies that the annular stress buffer groove design of the present invention can effectively release the stress at the cavity edge and avoid thermal cycling cracking. It is the core structural design for maintaining long-term airtightness.

[0106] As shown in Table 2, the amount of composite sintering aid added in Comparative Example 2 exceeded the limit of the present invention, resulting in abnormal growth of ceramic grains, a significant decrease in matrix density, excessive flatness, increased cracking rate after thermal cycling, and a significant decrease in air tightness. This verifies the scientific nature of the amount of composite sintering aid added in the present invention, which can achieve precise control of grain size and synergy with high matrix density.

[0107] As shown in Table 2, in Comparative Example 3, without the molybdenum-manganese wetting bonding layer, the interfacial bonding strength between the ceramic and the metallized layer decreased to 22 MPa, a decrease of 54% compared to Example 1. After thermal cycling, the interface delaminated, and the leakage rate increased significantly. This verifies that the molybdenum-manganese wetting bonding layer of the present invention can achieve metallurgical bonding between the ceramic and the metallized layer, which is the key to improving the interfacial bonding force and maintaining the airtight performance after thermal cycling.

[0108] As shown in Table 2, in Comparative Example 4, no full-area barrier layer was prepared, and the initial leakage rate had already increased. After thermal cycling, water vapor and corrosive gases penetrated from the side and bottom of the ceramic substrate, and the leakage rate increased significantly. This verifies that the full-area barrier layer of the present invention can achieve airtight protection without dead corners on the entire surface, and significantly improve the long-term reliability of the device.

[0109] As shown in Table 2, Comparative Example 5 adopted a single-stage sintering process and eliminated the grain control stage, which resulted in abnormal growth of ceramic grains, decreased density, serious exceedance of flatness, and increased cracking rate after thermal cycling. This verifies that the dual-stage high-temperature co-firing process of the present invention can take into account both grain uniformity and matrix density, and is the core process for obtaining a high flatness and high density ceramic matrix.

[0110] As shown in Table 2, the interconnecting functional layer of Comparative Example 6 uses a 95% alumina green strip, which is not compatible with the substrate material. The difference in sintering shrinkage rate leads to severe warping and deformation, exceeding the flatness standard, microcracks appearing between layers, and a significant decrease in airtightness. This verifies that the design of the entire substrate being made of the same material can solve the thermal matching problem and avoid sintering delamination and warping.

[0111] As shown in Table 2, the manganese content in the molybdenum-manganese slurry of Comparative Example 7 was lower than the lower limit specified in this invention, resulting in insufficient wetting effect, a significant decrease in interfacial bonding strength, interfacial cracking after thermal cycling, and a decline in airtightness. This verifies the rationality of the manganese content range of this invention, which is the key to ensuring interfacial wetting and bonding strength.

[0112] Based on the performance data in Tables 1 and 2, it can be seen that all performance indicators in Example 1 have reached the optimal level. This invention solves the problems of sintering warping, poor interfacial bonding, stress concentration cracking, and insufficient long-term airtightness of existing airtight ceramic bases through the synergistic effect of structural design, raw material ratio, and preparation process. Therefore, Example 1 is the optimal implementation scheme of this invention.

[0113] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. An airtight ceramic base, characterized in that, include: A co-fired ceramic matrix, wherein the co-fired ceramic matrix is ​​provided with a dense support layer, an interconnected functional layer and a cavity sealing layer from bottom to top; The dense support layer is a high-purity alumina dense ceramic layer with a thickness ≥0.2mm; the interconnection functional layer is an integral sintered layer composed of a multi-layer stacked alumina ceramic dielectric layer and an embedded tungsten metallized three-dimensional interconnection structure; the cavity sealing layer is an alumina ceramic layer with a concave cavity structure, and the edge of the concave cavity is provided with an annular stress buffer groove. An interface metallization layer is provided, which covers the entire surface of the co-fired ceramic substrate and the inner wall of the concave cavity. The interface metallization layer is provided with a molybdenum-manganese wetting bonding layer, a tungsten-molybdenum conductive transition layer, and a nickel-gold protective sealing layer from the inside to the outside. A global barrier layer is provided, which covers the surface of the interface metallization layer and the sides and bottom of the co-fired ceramic substrate. The global barrier layer is provided with an alumina nano-matching layer, a silicon nitride dense barrier layer and a solder sealant layer from the inside to the outside.

2. The airtight ceramic base according to claim 1, characterized in that, The dense support layer, interconnected functional layer, and cavity sealing layer are all made by co-firing high-purity alumina powder with an alumina mass fraction of 99.7% with a composite sintering aid with a magnesium oxide mass fraction of 0.15% and a yttrium oxide mass fraction of 0.15%. The sintering density is ≥99.8%, the average grain size is 1.5μm-2μm, and the overall flatness is ≤0.002mm / 100mm.

3. The airtight ceramic base according to claim 2, characterized in that, The thickness of the alumina ceramic dielectric layer of the interconnecting functional layer is 0.05mm-0.1mm, and the number of stacked layers is 2-8. The line width and line spacing of the embedded tungsten metallized three-dimensional interconnecting structure are both ≥0.05mm. The interlayer vias are filled with high-purity tungsten slurry with a tungsten mass fraction of 98%, and the inner wall of the vias is provided with a continuous tungsten metallization layer that connects with the interface metallization layer.

4. The airtight ceramic base according to claim 3, characterized in that, The concave cavity depth of the cavity sealing layer is 0.1mm-0.5mm, the width of the annular stress buffer groove is 0.2mm-0.3mm, and the depth is 30%-40% of the thickness of the cavity sealing layer. The upper surface of the cavity sealing layer is provided with a continuous annular sealing pad, and the width of the annular sealing pad is ≥0.3mm.

5. A method for preparing an airtight ceramic substrate according to any one of claims 1-4, characterized in that, Includes the following steps: S1. Prepare a ceramic green body strip with a dense support layer, an interconnected functional layer, and a cavity sealing layer. Complete the punching, filling, pattern printing, cavity and stress buffer groove processing of each green body strip. Stack and position them in sequence to obtain a ceramic green body preform. S2. After the ceramic green body is subjected to warm isostatic pressing, the integrated densification sintering is completed by a stepped glue removal and two-stage high-temperature co-firing process to obtain a co-fired ceramic matrix. S3. After precision grinding of the surface of the co-fired ceramic substrate, an interface metallization layer is prepared by thick film printing and high-temperature sintering process, and an all-area barrier layer is prepared by atomic layer deposition process to obtain an airtight ceramic substrate.

6. The method for preparing an airtight ceramic substrate according to claim 5, characterized in that, The preparation process of the ceramic green body preform in step S1 is as follows: A1. Ceramic green belt casting: High-purity alumina powder, composite sintering aid, organic binder, plasticizer, and anhydrous ethanol solvent are mixed in a mass ratio of 100:0.3:9:3:28 and ball-milled to obtain a ceramic slurry with a solid content ≥58%. The green belts of corresponding thicknesses, including a dense support layer, an interconnected functional layer, and a cavity sealing layer, are then formed by casting process. A2. Interconnect functional layer processing: Laser punching is used to complete the through-hole processing of the green strip of the interconnect functional layer, high-purity tungsten paste is used to complete the vacuum filling of the through-hole, and screen printing is used to complete the patterned tungsten metallization wiring printing with a printing thickness of 15μm-20μm; A3. Cavity sealing layer processing: The concave cavity and annular stress buffer groove are processed by laser engraving with a dimensional tolerance of ≤ ±0.02mm. The annular sealing pad is graphicly printed by screen printing. A4. Green Blank Stacking and Positioning: The green blanks are stacked in the order of dense support layer, interconnected functional layer, and cavity sealing layer. Positioning pins are used to achieve precise alignment with an alignment accuracy of ≤ ±0.01mm.

7. The method for preparing an airtight ceramic substrate according to claim 6, characterized in that, The integral sintering process of the ceramic green body in step S2 is as follows: B1. Warm isostatic pressing pretreatment: After vacuum sealing the stacked ceramic green preform, place it in a warm isostatic press and hold it under pressure at 50℃ and 25MPa for 15min. B2. Stepped debinding pre-sintering: The pretreated green preform is placed in a nitrogen atmosphere debinding furnace, heated to 600℃ at a heating rate of 2℃ / min, held for 120min to complete debinding, and then heated to 1100℃ at a heating rate of 3℃ / min, held for 60min to complete pre-sintering. B3. Two-stage high-temperature co-firing: The pre-sintered green body is placed in a tungsten mesh sintering furnace in a hydrogen atmosphere and heated to 1550°C at a heating rate of 5°C / min. The temperature is held for 90 min to complete grain control. The temperature is then raised to 1600°C and held for 120 min to complete densification co-firing. The temperature is then lowered to room temperature at a cooling rate of 3°C / min to obtain the co-fired ceramic matrix.

8. The method for preparing an airtight ceramic substrate according to claim 7, characterized in that, The preparation process of the interface metallization layer in step S3 is as follows: C1. Surface pretreatment of the substrate: The co-fired ceramic substrate is surface-processed by double-sided grinding to control the surface roughness to ≤0.2μm. After ultrasonic cleaning, it is dried for later use. C2. Thick film printing and sintering: Molybdenum-manganese paste, tungsten-molybdenum paste, and nickel paste are sequentially printed on all surfaces, inner walls of concave cavities, and inner walls of through holes of the co-fired ceramic substrate. After each layer is printed, it is dried at 120°C for 15 minutes. After all printing is completed, it is placed in a hydrogen atmosphere sintering furnace and held at 1400°C for 60 minutes to complete sintering. C3. Surface gold plating treatment: A dense gold layer is prepared on the surface of the nickel layer using an electroplating process to complete the preparation of the interface metallization layer.

9. The method for preparing an airtight ceramic substrate according to claim 8, characterized in that, The preparation process of the global barrier layer in step S3 is as follows: D1. Atomic Layer Deposition of the Underlying Matching Layer: The ceramic substrate with the prepared interface metallization layer is placed in an atomic layer deposition apparatus, and an alumina nano-matching layer is deposited at 150°C with a deposition thickness of 1μm-1.5μm. D2. Atomic layer deposition barrier layer: A dense silicon nitride barrier layer is deposited on the surface of the alumina nano-matching layer at a deposition temperature of 150℃ and a deposition thickness of 1.5μm-2μm. D3. Preparation of the sealing adapter layer: A nickel-gold gradient sealing adapter layer is prepared on the silicon nitride barrier layer on the surface of the annular sealing pad. The nickel layer thickness is 2μm-3μm and the gold layer thickness is 0.8μm-1.2μm.

10. The method for preparing an airtight ceramic substrate according to claim 9, characterized in that, The manganese mass fraction in the molybdenum-manganese slurry is 12%-15%, the bonding strength between the sintered interface metallization layer and the ceramic substrate is ≥45MPa, the pinhole rate of the global barrier layer prepared by atomic layer deposition is 0, and the leak rate detected by helium mass spectrometry is ≤1×10⁻⁶. -10 Pa·m 3 / s.

Images