Degreasing method of silicon nitride ceramic substrate

Abstract

The invention discloses a degreasing method of a silicon nitride ceramic substrate, which belongs to the field of advanced ceramic preparation, and comprises the following steps: in a silicon nitride green body pre-degassing stage, heating to 140-160 DEG C; in the silicon nitride green body pre-decomposition stage, the temperature is increased to 230-270 DEG C, and N2 is added; in the oxygenolysis and catalytic chain scission stage of the silicon nitride green body, the temperature is raised to 350-400 DEG C, and the volume ratio of N2 to O2 is 97: 3-90: 10; in the inert purification and structure relaxation stage of the silicon nitride green body, the temperature is increased to 450-600 DEG C, and N2 is added; in a silicon nitride green body cooling stage, cooling to 180-220 DEG C, and adding N2; the temperature rise rate gt of the silicon nitride green body inert purification and structure relaxation stage; the heating rate gt of the silicon nitride green body in the pre-decomposition stage; the temperature rise rate gt of the oxygenolysis and catalytic chain scission stage of the silicon nitride green body; the temperature rise rate in the oxygenolysis and catalytic chain scission stages of the silicon nitride green body is increased. According to the method, the degreasing time is shortened by 40% or above, the warping rate of the green body is reduced to be smaller than or equal to 1%, the single-stack stacking amount is increased to be larger than or equal to 30 pieces, and the production efficiency and the product quality are remarkably improved.

Description

Technical Field

[0001] This invention relates to the field of advanced ceramic preparation, and in particular to a method for degreasing silicon nitride ceramic substrates. Background Technology

[0002] Silicon nitride ceramics are ideal materials for next-generation high-performance electronic packaging substrates, with significant comprehensive performance advantages: high thermal conductivity (up to 90 W / m·K) and a coefficient of thermal expansion (~3.2×10⁻⁶). -6 It has good compatibility with silicon chips (at / ℃), excellent mechanical strength (bending strength >800 MPa), and stable dielectric properties.

[0003] In order to obtain good rheological properties and green strength, a large amount of organic binder (usually accounting for 10-15% of the total mass of the green body) needs to be introduced during the molding process of silicon nitride ceramics.

[0004] The purpose of the degreasing process is to completely remove these organic substances before sintering without damaging the integrity of the green body structure.

[0005] Traditional degreasing processes generally employ a single linear temperature rise curve and an inert atmosphere (such as N2). This traditional method has the following drawbacks: (1) Imbalance between thermodynamics and mass transfer process: The linear heating mode ignores the differences in decomposition kinetics of organic compounds with different molecular weights; the thermal decomposition temperature windows of low molecular weight plasticizers and high molecular weight polymers are different, and a single heating rate cannot achieve efficient and sequential decomposition, resulting in either the rapid escape of low-temperature volatiles causing cracking, or the polymer chains leaving carbon traces due to insufficient thermal decomposition.

[0006] (2) Single atmosphere control: Although the inert atmosphere throughout the process can prevent oxidation, it lacks the catalytic effect on the decomposition of high molecular organic matter and cannot effectively deal with the free carbon generated by pyrolysis; these residual carbons will hinder densification in subsequent sintering, form pores, and deteriorate thermal and electrical properties.

[0007] (3) The contradiction between heat transfer and stress: When the stacking density of billets is increased to improve production efficiency, the uniformity of the temperature field in the furnace becomes worse (usually >±10℃ in traditional processes); the temperature gradient between billets and inside billets induces uneven thermal expansion and contraction, generating huge internal stress, which directly manifests as billet warping, deformation or even cracking, seriously limiting the single furnace capacity and product yield.

[0008] CN119775029A discloses a debinding process for a high thermal conductivity silicon nitride substrate, which employs multi-stage heating, but only uses simple N2 protection for atmosphere control and lacks targeted catalysis and purification methods; CN119797935A discloses a high-density, high thermal conductivity silicon nitride ceramic and its preparation method and application. This method focuses on vacuum debinding, which is beneficial for the removal of small molecules, but for thick-walled or highly stacked blanks, it is easy to cause "bubbling" defects due to excessive internal gas pressure.

[0009] The above background information is provided to facilitate understanding of the present invention and is not intended to be publicly known technology disclosed to the general public prior to the application of this invention. Summary of the Invention

[0010] To address the aforementioned shortcomings, this invention provides a degreasing method for silicon nitride ceramic substrates, which achieves rapid, thorough, and non-destructive removal of organic matter, while significantly reducing the warpage of the blank and greatly increasing the single-furnace stacking capacity, thereby breaking through the bottleneck of high-yield and high-quality silicon nitride substrate manufacturing.

[0011] This invention is particularly suitable for applications such as electronic packaging and high-power semiconductor modules, which have extremely high requirements for substrate flatness, density, and reliability.

[0012] This invention successfully solves the fundamental contradictions in traditional degreasing processes by constructing a precise temporal synergy between temperature, atmosphere, and pressure, supplemented by advanced temperature field homogenization technology. It not only achieves efficient, low-stress, and residue-free degreasing, but also breaks through the bottleneck of high-stack production, providing a practical and highly competitive technical solution for the low-cost, high-performance, and large-scale manufacturing of silicon nitride ceramic substrates.

[0013] The technical solution is: a method for degreasing a silicon nitride ceramic substrate, comprising the following steps: During the pre-degassing stage of silicon nitride green blank, the temperature is increased from room temperature to 140℃~160℃, and vacuum is pumped out, maintaining a vacuum degree of 5Pa~20Pa. During the pre-decomposition stage of silicon nitride green blank, the temperature was increased to 230℃~270℃, and the atmosphere and flow rate were N2, 5 L / min ~10 L / min; the O2 content was ≤200ppm. Oxidative decomposition and catalytic chain scission stage of silicon nitride green blank: temperature: heated to 350℃~400℃; atmosphere and flow rate: N2 and O2 mixed gas, 8 L / min ~12 L / min; N2 volume: O2 volume is 97:3~90:10; infrared temperature difference alarm threshold 3℃~7℃. Inert purification and structural relaxation stage of silicon nitride green blank, temperature is raised to 450℃~600℃, atmosphere and flow rate: N2, 10L / min ~20 L / min, O2 content ≤10ppm; During the cooling stage of silicon nitride green blank, the temperature is cooled to 180℃~220℃, the cooling rate is 2℃ / min~5℃ / min, the atmosphere and flow rate are N2, 5 L / min~15 L / min, and the pressure is controlled at ±30Pa~80 Pa. The heating rate during the inert purification and structural relaxation stage of silicon nitride green blanks is greater than that during the pre-decomposition stage of silicon nitride green blanks, which in turn is greater than that during the oxidative decomposition and catalytic chain scission stage of silicon nitride green blanks. During the pre-decomposition stage to the cooling stage of the silicon nitride green billet, the pressure regulation strategy is a stepped pressure regulation.

[0014] Furthermore, the silicon nitride green blank stacking quantity is ≥30 wafers / stack.

[0015] Furthermore, the total degreasing time is <35h, of which the degreasing time is 2h~4h in the pre-degassing stage of silicon nitride green blank; 6h~10h in the pre-decomposition stage of silicon nitride green blank; 8h~12h in the oxidative decomposition and catalytic chain breaking stage of silicon nitride green blank; and 6h~10h in the inert purification and structural relaxation stage of silicon nitride green blank.

[0016] Furthermore, in the pre-degassing stage of silicon nitride green billet, the holding time is 1h~2h; in the pre-decomposition stage of silicon nitride green billet, the holding time is 2h~4h; in the oxidation decomposition and catalytic chain breaking stage of silicon nitride green billet, the holding time is 4h~6h; and in the inert purification and structural relaxation stage of silicon nitride green billet, the holding time is 2h~4h.

[0017] Furthermore, the N2 volume to O2 volume ratio is 95:5.

[0018] Furthermore, in the pre-degassing stage of silicon nitride green billet, the heating rate is 0.6℃ / min ~ 1.0℃ / min; in the pre-decomposition stage of silicon nitride green billet, the heating rate is 0.25℃ / min ~ 0.5℃ / min; in the oxidation decomposition and catalytic chain scission stage of silicon nitride green billet, the heating rate is 0.1℃ / min ~ 0.2℃ / min; and in the inert purification and structural relaxation stage of silicon nitride green billet, the heating rate is 2℃ / min ~ 5℃ / min.

[0019] Furthermore, the stepped pressure regulation is as follows: during the pre-decomposition stage of silicon nitride green blank, the environment is normal pressure or slightly positive pressure; during the oxidation decomposition and catalytic chain breaking stage of silicon nitride green blank, the environment is slightly negative pressure -10 Pa to -20 Pa; during the inert purification and structural relaxation stage of silicon nitride green blank, the environment is normal pressure or slightly positive pressure.

[0020] Furthermore, the silicon nitride green blank is a cast silicon nitride green blank with a diameter of 0.4 mm to 1.0 mm.

[0021] Furthermore, the warpage of the silicon nitride ceramic substrate formed after the silicon nitride green stage is ≤1%.

[0022] Invention principle: In this invention, the pre-degassing stage and the pre-decomposition stage of the silicon nitride green blank are designed to allow low molecular weight plasticizers (such as dibutyl phthalate) and some solvents to slowly evaporate, avoiding cracking of the green blank due to a sudden increase in vapor pressure. This stage mainly involves physical desorption and oligomer melting. The slow heating conforms to the Arrhenius equation, controlling the reaction rate within a safe range. Atmosphere strategy: maintain a static or low flow rate (≤ 10 L / min) N2 environment. Its function is to provide inert protection and to act as a carrier gas to dilute and carry away organic molecules that volatilize at low temperatures.

[0023] In this invention, the oxidation decomposition and catalytic chain scission stage of silicon nitride green body aims to provide sufficient reaction time and energy for the main chain scission of polymers (such as PVB and acrylic resin). The atmosphere strategy is switched to an N2 / O2 mixed gas; the introduction of trace amounts of oxygen acts as a catalyst, significantly reducing the activation energy of the polymer and promoting its oxidative decomposition to generate small molecule gases such as CO2 and H2O, rather than stable residual carbon. The pressure strategy involves applying a slight negative pressure of -10 to -20 Pa. This negative pressure environment generates a directional airflow, powerfully extracting decomposition products and preventing them from re-condensing or forming blockages in the pores of the green body. The synergistic effect of "slow heating + catalytic oxygen + slight negative pressure" constitutes the core of this stage; slow heating ensures a thorough reaction; catalytic oxygen ensures the decomposition path leads to gaseous products; and slight negative pressure accelerates product removal—all three are indispensable.

[0024] In this invention, the purpose of the inert purification and structural relaxation stage of the silicon nitride green body is to decompose any remaining, most stable hydrocarbons or oxygen-containing carbides. Atmosphere strategy: Switch back to a high-flow-rate pure N2 atmosphere; the high-velocity inert gas acts as a "flushing" agent, completely removing trace amounts of CO and other gases that may have been generated in the previous stage, ensuring a pure furnace atmosphere; Pressure strategy: Restore to atmospheric pressure or slightly positive pressure (≤ +50 Pa); This helps to counteract the shrinkage stress caused by the weakening of the skeletal structure after the removal of organic matter from the green body, promoting structural relaxation and reducing permanent deformation.

[0025] In this invention, a stepped pressure regulation is adopted: the pressure control is matched with the temperature-atmosphere stage, namely "normal pressure / slight positive pressure → slight negative pressure → normal pressure / slight positive pressure"; this stepped change ensures the optimal mass transfer conditions at each stage, while avoiding the impact on the porous preform caused by sudden pressure changes.

[0026] Invention effects: This invention achieves rapid, thorough, and non-damaging removal of organic matter through precise and coordinated control of the three elements of temperature, atmosphere, and pressure, while significantly reducing the warpage of the blank and greatly increasing the stacking capacity of a single furnace, thereby breaking through the bottleneck of high-yield and high-quality silicon nitride substrate manufacturing.

[0027] By precisely and synergistically controlling the three key elements of temperature, atmosphere, and pressure in a specific time sequence, this invention achieves the following significant advancements: (1) A qualitative leap in degreasing efficiency: Through catalytic oxidation and enhanced mass transfer, the total degreasing time is reduced by more than 40% (from over 48 hours in the traditional process to 28-32 hours), directly reducing energy consumption and production costs; (2) Significantly improved billet quality: Low warpage: The billet warpage rate is stably controlled at ≤1%, far lower than the ≥2% of the traditional process; this is attributed to precise temperature field control (±3℃) and a matching stress management strategy; Defect-free: Effectively eliminates carbon residue, blistering, cracking, etc. Common defects; the relative density of the substrate after sintering can reach over 99.5%, with uniform performance; (3) Significant breakthrough in production capacity: the stacking quantity has been increased from ≤10 pieces / stack in traditional processes to ≥30 pieces / stack, and even stable production of 45 pieces / stack can be achieved under optimized conditions, with the single furnace processing capacity increased by more than 3 times, laying the foundation for large-scale manufacturing; (4) Strong process universality and reliability: this collaborative control strategy shows good adaptability to different green blank thicknesses (such as 0.4mm to 1.0mm) and binder systems, requiring only fine-tuning of parameters, demonstrating strong potential for industrial application. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the process curve of Embodiment 1 of the present invention. Detailed Implementation

[0029] The technical solution of the present invention will be described in detail below with specific embodiments. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention and not for limiting the claims of the present invention.

[0030] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "longitudinal," "lateral," "horizontal," "inner," "outer," "front," "rear," "top," and "bottom," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of this invention is in use. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0031] In the description of this invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set up," "open," "installed," "connected," and "communicate" should be interpreted broadly. For example, they can refer to fixed connection, detachable connection, or integral connection; they can refer to direct connection or indirect connection through an intermediate medium; and they can refer to the connection within two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0032] Unless otherwise specified, all inventions are existing technologies.

[0033] Unless otherwise specified, all materials involved in this invention are purchased from the market.

[0034] In the following examples and comparative examples, the silicon nitride green blank is a cast silicon nitride green blank.

[0035] Example 1 The process in this embodiment is as follows: Figure 1 , Figure 1 It comprehensively demonstrates the synergistic relationship between temperature, atmosphere, and pressure changes over time.

[0036] A method for degreasing a silicon nitride ceramic substrate includes the following steps: During the pre-degassing stage, the temperature was increased from room temperature to 150℃ at a rate of 0.8℃ / min. Vacuum was pumped out, and the vacuum level was maintained at 10Pa for 1.5 hours.

[0037] Pre-decomposition stage: Temperature: 150℃ to 250℃, heating rate: 0.3℃ / min, atmosphere and flow rate: N2, 8L / min; O2 content ≤100ppm, holding time 3h, atmospheric pressure environment.

[0038] Oxidative decomposition and catalytic chain scission stage: Temperature: 250℃ to 380℃, heating rate: 0.15℃ / min, atmosphere and flow rate: N2 and O2 mixed gas, 12 L / min, N2 volume: O2 volume = 95:5; micro negative pressure environment -10 Pa ~ -20 Pa, infrared temperature difference alarm threshold 5℃, heat preservation time 5h.

[0039] Inert purification and structural relaxation stage: temperature rises from 380℃ to 550℃ at a rate of 2℃ / min, with an atmosphere and flow rate of N2 at 15 L / min and an O2 content ≤1ppm. The holding time is 3 hours under normal pressure.

[0040] During the cooling phase, the temperature was reduced from 550℃ to 200℃ at a rate of 1.5℃ / min. The atmosphere and flow rate were N2, 10 L / min, and the pressure was controlled at ±50Pa.

[0041] In this embodiment, the stacking amount of silicon nitride green blanks is shown in Table 1 below, and the thickness of the silicon nitride green blanks is 0.6 mm.

[0042] The uniformity of the temperature field was tested, and the results are shown in Table 1 below.

[0043] The properties of the silicon nitride ceramic substrate formed after degreasing are shown in Table 1 below.

[0044] Example 2 The difference from Example 1 is that in this example, the stacking amount is as shown in Table 1 below, the flow rate of the N2 and O2 mixed gas during the debinding stage is 15 L / min, and the negative pressure during the oxidation decomposition and catalytic chain scission stage is -18 Pa.

[0045] The uniformity of the temperature field was tested, and the results are shown in Table 1 below.

[0046] The properties of the silicon nitride ceramic substrate formed after degreasing are shown in Table 1 below.

[0047] Example 3 The difference from Example 1 is that in this example, the stacking amount is as shown in Table 1 below, the green body thickness is 1.0 mm, the heating rate of the oxidation decomposition and catalytic chain scission stage is 0.5 °C / min, and the holding time is 4 h.

[0048] The uniformity of the temperature field was tested, and the results are shown in Table 1 below.

[0049] The properties of the silicon nitride ceramic substrate formed after degreasing are shown in Table 1 below.

[0050] Comparative Example 1 A degreasing method for silicon nitride ceramic substrates, wherein the green blank of silicon nitride ceramic substrates is degreased under the following conditions: the temperature is raised from room temperature to 600°C at a rate of 2°C / min, and held for 2 hours. The stacking amount is shown in Table 1 below, and the thickness of the green blank of silicon nitride ceramic substrates is 0.6 mm.

[0051] The uniformity of the temperature field was tested, and the results are shown in Table 1 below.

[0052] The properties of the silicon nitride ceramic substrate formed after degreasing are shown in Table 1 below.

[0053] Comparative Example 2 Compared with Example 1, the difference is that the degreasing process is carried out in an atmosphere of N2 throughout, with no O2 introduced and no negative pressure.

[0054] The uniformity of the temperature field was tested, and the results are shown in Table 1 below.

[0055] The properties of the silicon nitride ceramic substrate formed after degreasing are shown in Table 1 below.

[0056] Comparative Example 3 Compared with Example 1, the difference is that the micro-negative pressure environment is replaced with an atmospheric pressure environment in the oxidative decomposition and catalytic chain breaking stage.

[0057] The uniformity of the temperature field was tested, and the results are shown in Table 1 below.

[0058] The properties of the silicon nitride ceramic substrate formed after degreasing are shown in Table 1 below.

[0059] Comparative Example 4 Compared with Example 1, the difference is that in the oxidative decomposition and catalytic chain scission stage, the N2 volume: O2 volume = 98:2.

[0060] The uniformity of the temperature field was tested, and the results are shown in Table 1 below.

[0061] The properties of the silicon nitride ceramic substrate formed after degreasing are shown in Table 1 below.

[0062] Table 1 Table 1 shows that although the warpage rate of Comparative Example 2 is acceptable, the billet has serious internal defects, resulting in a low pass rate. Although the warpage rate and defect situation of Comparative Examples 3 and 4 are worse than those of Comparative Example 1, they are still not as good as Examples 1-3 of the present invention, demonstrating the necessity of the temperature-atmosphere-pressure coordinated control of the present invention.

[0063] The temperature field uniformity of Comparative Example 1 was poor (±15℃), resulting in incomplete decomposition of organic matter and concentration of internal stress.

[0064] Comparative Example 2 lacks O2 catalysis, resulting in slow and incomplete decomposition of polymers. The generated large molecular gases cannot be discharged in time, leading to bubbling. Although the warping is slightly improved, the product qualification rate is extremely low.

[0065] In Comparative Example 3, the lack of micro-negative pressure resulted in the retention of decomposition gases in the pores of the billet, leading to localized pressure buildup and bubbling, while also increasing carbon residue. The prolonged degreasing time and increased warpage rate demonstrate that micro-negative pressure is crucial for mass transfer efficiency.

[0066] In Comparative Example 4, insufficient oxygen content led to incomplete oxidative cracking of the polymer, increased residual carbon, and a significantly prolonged degreasing time. Although pressure control was good, insufficient atmospheric catalysis affected the overall decomposition efficiency and quality.

[0067] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for degreasing a silicon nitride ceramic substrate, characterized in that, Includes the following steps: During the pre-degassing stage of silicon nitride green blank, the temperature is increased from room temperature to 140℃~160℃, and vacuum is pumped out, maintaining a vacuum degree of 5Pa~20Pa. During the pre-decomposition stage of silicon nitride green blank, the temperature was increased to 230℃~270℃, and the atmosphere and flow rate were: N2, 5 L / min ~10 L / min; O2 content ≤200ppm. Oxidative decomposition and catalytic chain scission stage of silicon nitride green blank: temperature: heated to 350℃~400℃; atmosphere and flow rate: N2 and O2 mixed gas, 8 L / min ~12 L / min; N2 volume: O2 volume is 97:3~90:10; infrared temperature difference alarm threshold 3℃~7℃. Inert purification and structural relaxation stage of silicon nitride green blank, temperature is raised to 450℃~600℃, atmosphere and flow rate: N2, 10 L / min~20 L / min, O2 content ≤10ppm; During the cooling stage of silicon nitride green blank, the temperature is cooled to 180℃~220℃, the cooling rate is 2℃ / min~5℃ / min, the atmosphere and flow rate are N2, 5 L / min~15 L / min, and the pressure is controlled at ±30Pa~80 Pa. The heating rate during the inert purification and structural relaxation stage of silicon nitride green blanks is greater than that during the pre-decomposition stage of silicon nitride green blanks, which in turn is greater than that during the oxidative decomposition and catalytic chain scission stage of silicon nitride green blanks. During the pre-decomposition stage to the cooling stage of the silicon nitride green billet, the pressure regulation strategy is a stepped pressure regulation.

2. The degreasing method for silicon nitride ceramic substrates according to claim 1, characterized in that, The stacking density of silicon nitride green blanks is ≥30 wafers / stack.

3. The degreasing method for silicon nitride ceramic substrates according to claim 1, characterized in that, The total degreasing time is <35h, of which the degreasing time is 2~4h in the pre-degassing stage of silicon nitride green blank; 6~10h in the pre-decomposition stage of silicon nitride green blank; 8~12h in the oxidative decomposition and catalytic chain breaking stage of silicon nitride green blank; and 6~10h in the inert purification and structural relaxation stage of silicon nitride green blank.

4. The degreasing method for silicon nitride ceramic substrates according to claim 1, characterized in that, In the pre-degassing stage of silicon nitride green billet, the holding time is 1~2h; in the pre-decomposition stage of silicon nitride green billet, the holding time is 2~4h; in the oxidation decomposition and catalytic chain breaking stage of silicon nitride green billet, the holding time is 4~6h; in the inert purification and structural relaxation stage of silicon nitride green billet, the holding time is 2~4h.

5. The degreasing method for silicon nitride ceramic substrates according to claim 1, characterized in that, The volume ratio of N2 to O2 is 95:

5.

6. The degreasing method for silicon nitride ceramic substrates according to claim 1, characterized in that, During the pre-degassing stage of silicon nitride green billet, the heating rate is 0.6℃ / min ~ 1.0℃ / min; during the pre-decomposition stage of silicon nitride green billet, the heating rate is 0.25℃ / min ~ 0.5℃ / min; during the oxidation decomposition and catalytic chain scission stage of silicon nitride green billet, the heating rate is 0.1℃ / min ~ 0.2℃ / min; during the inert purification and structural relaxation stage of silicon nitride green billet, the heating rate is 2℃ / min ~ 5℃ / min.

7. The degreasing method for silicon nitride ceramic substrates according to claim 1, characterized in that, The stepped pressure regulation is as follows: during the pre-decomposition stage of silicon nitride green blank, the environment is normal pressure or slightly positive pressure 0Pa~20Pa; during the oxidation decomposition and catalytic chain breaking stage of silicon nitride green blank, the environment is slightly negative pressure -10Pa~-20Pa; during the inert purification and structural relaxation stage of silicon nitride green blank, the environment is normal pressure or slightly positive pressure 0Pa~20Pa.

8. The degreasing method for silicon nitride ceramic substrates according to claim 1, characterized in that, The silicon nitride green blank is a cast silicon nitride green blank with a diameter of 0.4 mm to 1.0 mm.

9. The degreasing method for silicon nitride ceramic substrates according to claim 1, characterized in that, The warpage of the silicon nitride ceramic substrate formed after the cooling stage of the silicon nitride green is ≤1%.

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