Method for improving flatness of DCB ceramic chip and reducing DCB sintering bubbles

Abstract

The invention discloses a method for improving the flatness of a DCB ceramic chip and reducing DCB sintering bubbles, and relates to the technical field of ceramic preparation. The preparation method comprises the following steps: 1, pre-grinding powder, and spray-drying; preparing slurry from the raw material, and carrying out curtain coating, drying and punch forming to form a green sheet; 2, powder is applied to the surface of the green body piece, the green body piece is transferred to a kiln to be sintered, and a DCB ceramic piece is obtained; powder coating slurry is used in the powder coating process; in the raw materials of the powder coating slurry, the ratio of water to glue to aluminum oxide powder is (10-15) L: (0.5-1.5) L: (1-1.5) Kg. The DCB ceramic chip prepared by the method has high flatness and low bubble rate.

Description

Technical Field

[0001] This invention relates to the field of ceramic preparation technology, specifically a method for improving the flatness of DCB ceramic sheets and reducing DCB sintering bubbles. Background Technology

[0002] DCB technology, also known as direct copper plating, involves directly bonding copper onto ceramics using an oxygen-containing eutectic solution. The basic principle is to introduce an appropriate amount of oxygen between the copper and ceramics before or during the bonding process. Within a certain high-temperature range, copper and oxygen form a Cu-O eutectic solution. DCB technology utilizes this eutectic solution to react chemically with the ceramic substrate to generate CuAlO2 or CuAl2O4 phases, while simultaneously wetting copper foil to achieve bonding between the ceramic substrate and the copper plate, resulting in a DCB ceramic sheet.

[0003] However, the bonding process between the ceramic substrate and the copper plate requires extremely high surface flatness of the ceramic. If the ceramic surface is uneven, the eutectic liquid flow will be obstructed, leading to poor bonding and the formation of bubbles during the calcination stage, affecting the performance of the DCB ceramic sheet. Existing technologies for preparing DCB ceramic sheets have certain limitations: on the one hand, the ceramic green body is not treated for surface flatness before sintering, resulting in an irregular surface morphology and poor surface flatness of the subsequently produced ceramic sheet; on the other hand, due to insufficient surface flatness, the flow of the Cu-O eutectic liquid formed between the copper and ceramic is obstructed during the subsequent copper plating process, preventing uniform wetting of the ceramic sheet surface. This leads to poor bonding between the copper and the ceramic substrate, ultimately generating a large number of bubbles during sintering, severely affecting the product quality and performance of the DCB ceramic sheet.

[0004] Therefore, it is of great significance to propose a method to improve the flatness of DCB ceramic tiles and reduce DCB sintering bubbles. Summary of the Invention

[0005] The purpose of this invention is to provide a method for improving the flatness of DCB ceramic tiles and reducing DCB sintering bubbles, so as to solve the problems mentioned in the prior art.

[0006] To achieve the above objectives, the present invention provides the following technical solution: A method for improving the flatness of DCB ceramic tiles and reducing DCB sintering bubbles includes the following steps: Step 1: Pre-grind the powder and spray dry it; use it to prepare a slurry, cast it, dry it, press it into shape, and form a green sheet; Step 2: Apply powder to the surface of the green ceramic sheet and transfer it to a kiln for sintering to obtain DCB ceramic sheet.

[0007] In a more optimized manner, a powdering slurry is used during the powdering process; the ratio of water: glue: alumina powder in the raw materials of the powdering slurry is 10~15L:0.5~1.5L:1~1.5Kg.

[0008] In a more optimized manner, the process parameters for powder application are: feeding belt speed of 500~1000mm / min, atomization pressure of 0.08~0.12MPa, main spray pressure of 0.08~0.12MPa, and discharge pressure of 0.1~0.2MPa.

[0009] In a more optimized manner, the powder application process employs segmented drying, with a temperature gradient of 190℃-200℃-210℃, and each segment maintaining the temperature for 25~35 minutes.

[0010] In a more optimized manner, the alumina powder is composed of coarse-grained alumina powder and fine-grained alumina powder in a mass ratio of 0.6~0.8Kg:0.4~0.7Kg, wherein the coarse-grained alumina powder has a particle size of 8~10μm and the fine-grained alumina powder has a particle size of 5~7μm.

[0011] More preferably, the adhesive is composed of polyvinyl alcohol and modified polyvinyl alcohol in a volume ratio of 0.3~0.8L:0.2~0.7L, and the modified polyvinyl alcohol is prepared by: Step 1: Add polyvinyl alcohol to deionized water and stir until homogeneous. Then add polypropylene glycol, ammonium persulfate and glycerol in sequence. Set the temperature to 70~90℃ and react for 3~5 hours to obtain polyether modified polyvinyl alcohol. Step 2: Add 1-2 parts of glass powder and 0.5-1 parts of nano silica to 7-8 parts of polyether modified polyvinyl alcohol in sequence, mix, ultrasonically disperse for 20-30 minutes, then heat to 60-65℃ and stir for 10-20 minutes to obtain modified polyvinyl alcohol.

[0012] In a more optimized manner, the raw materials for the polyether-modified polyvinyl alcohol contain, by weight, 6-8 parts polyvinyl alcohol, 2-4 parts polypropylene glycol, 0.2-0.5 parts ammonium persulfate, and 0.1-0.3 parts glycerol.

[0013] In a more optimized manner, the raw materials for the modified polyvinyl alcohol comprise, by weight, 1-2 parts glass powder, 0.5-1 parts nano-silica, and 7-8 parts polyether-modified polyvinyl alcohol.

[0014] In a more optimized manner, in step 1, the raw materials of the slurry are composed of the following components by weight: 90-110 parts alumina powder, 4-6 parts polyvinyl alcohol, 2-4 parts glycerol, 0.5-1.5 parts fish oil dispersant, and 30-40 parts ethanol aqueous solution.

[0015] Ideally, the sintering temperature is 1800~1900℃ and the sintering time is 2~4 hours.

[0016] Compared with the prior art, the beneficial effects of the present invention are: This invention utilizes the synergistic design of alumina powder and adhesive in the powder coating slurry to prepare DCB ceramic tiles. Firstly, the powder in the powder coating slurry is a blend of alumina powders with different particle sizes. The coarse-particle-size powder constructs a uniform supporting framework, while the fine-particle-size powder fills the gaps in the framework, resulting in a dense and smooth insulating layer after powder coating. This prevents localized pressure deformation due to uneven powder distribution during green body stacking and ensures the regularity of the green body surface morphology. Meanwhile, the adhesive in the powder coating component adopts a composite system of basic polyvinyl alcohol and modified polyvinyl alcohol. The basic polyvinyl alcohol provides basic adhesive function to ensure that the powder coating can be firmly adhered to the surface of the green body, avoiding peeling and powdering after coating, and providing a stable coating base for the subsequent stacking process. The modified polyvinyl alcohol is first grafted with polypropylene glycol to introduce polyether segments. The flowability of the polyether segments enhances the coating ability of alumina powder, preventing powder agglomeration that leads to particle protrusion and uneven distribution. At the same time, it lowers the glass transition temperature of the adhesive. Then, glycerol is embedded in the system. In the subsequent drying and heat treatment process, it plays a plasticizing role, weakens the shrinkage stress of the binder, reduces the risk of coating cracking and lifting, and ensures the smoothness of the green body surface after coating. Furthermore, a compound of glass powder and nano-silica is added to the modified polyvinyl alcohol. The glass powder melts at a lower temperature to form a liquid phase, filling the internal pores of the powder coating and densifying the isolation layer. At the same time, the liquid phase can form a good interfacial bond with the alumina powder and the surface of the green sheet, allowing the green sheet to resist shrinkage deformation during stacking and subsequent sintering, maintaining the flatness of the green sheet and ceramic sheet surface. Nano-silica has an ultra-large specific surface area, which can adsorb the volatiles generated by the decomposition of the adhesive at high temperature, preventing them from agglomerating and forming bubbles during sintering. At the same time, nano-silica can form continuous exhaust channels inside, allowing the volatiles to be discharged during sintering and preventing the formation of closed-cell bubbles. Furthermore, the flatness optimization of the powder coating can indirectly improve the fluidity of the Cu-O eutectic liquid in the subsequent copper cladding process, allowing it to uniformly wet the ceramic sheet surface, ensuring good bonding between copper and ceramic substrate, reducing bubble generation at the bonding stage, and resulting in DCB ceramic sheets with high flatness and low bubble rate. Attached Figure Description

[0017] Figure 1 The DCB ceramic sheet prepared in Example 1 of this invention; Figure 2 This is an electron microscope image of the DCB ceramic sheet prepared in Example 1 of the present invention after copper plating; Figure 3The DCB ceramic sheet prepared in Comparative Example 1 of this invention; Figure 4 This is an electron microscope image of the DCB ceramic sheet prepared in Comparative Example 1 of this invention after copper coating; Figure 5 The image shows the roughness data of the long side of the DCB ceramic sheet prepared in Example 1 and Comparative Example 1 of this invention. Figure 6 The image shows the short-side roughness data of the DCB ceramic tiles prepared in Example 1 and Comparative Example 1 of this invention. Figure 7 The image shows the intermediate roughness data of the DCB ceramic sheets prepared in Example 1 and Comparative Example 1 of this invention. Detailed Implementation

[0018] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. 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.

[0019] In the following embodiments, the parts are by weight. It should be noted that there are no special restrictions on the purchase manufacturers of all the raw materials involved in this invention. Exemplary examples include: polyvinyl alcohol (CAS: 9002-89-5, model: PVA-1788, degree of polymerization 1700), polypropylene glycol (CAS: 25322-69-4, molecular weight 3000), ammonium persulfate (CAS: 7727-54-0), glycerol (CAS: 56-81-5), glass powder (particle size 3μm), and nano silica (CAS: 7631-86-9, particle size 20nm).

[0020] Pre-preparation: Green sheet slurry: 100 parts of alumina powder (D50=1.0μm) were added to 35 parts of ethanol aqueous solution (deionized water: ethanol volume ratio = 1:1) containing 5 parts of polyvinyl alcohol, 3 parts of glycerol and 1 part of fish oil dispersant. The mixture was ball-milled for 24 hours and degassed to obtain a uniform green sheet slurry.

[0021] Example 1: A method for improving the flatness of DCB ceramic tiles and reducing DCB sintering bubbles, the specific steps of which are as follows: I. Preparation of modified polyvinyl alcohol: Step 1: Add 7 parts of polyvinyl alcohol to 90 parts of deionized water and stir well. Then add 3 parts of polypropylene glycol, 0.4 parts of ammonium persulfate and 0.2 parts of glycerol in sequence. Set the temperature to 80℃ and react for 4 hours to obtain polyether modified polyvinyl alcohol. Step 2: Add 1.5 parts of glass powder and 0.7 parts of nano silica to 7.5 parts of polyether modified polyvinyl alcohol in sequence, mix, ultrasonically disperse for 25 min, then heat to 62℃ and stir for 15 min to obtain modified polyvinyl alcohol.

[0022] II. Preparation of the coating slurry: Mix 0.7 kg of alumina powder with a particle size of 9 μm and 0.6 kg of alumina powder with a particle size of 6 μm, then add 0.7 L of polyvinyl alcohol and 0.6 L of modified polyvinyl alcohol in sequence, stir evenly, then add 13 L of deionized water and continue stirring to obtain the coating slurry.

[0023] III. Preparation of DCB ceramic tiles: Step 1: The green sheet slurry is cast, dried, and stamped to form green sheets; Step 2: Apply powder to the surface of the green sheet. Set the feeding speed of the powder slurry to 750 mm / min and then apply it to the surface of the green sheet. The coating process parameters are: atomization pressure: 0.1 MPa, main spray pressure: 0.1 MPa, discharge pressure: 0.15 MPa. Set the temperature gradient to 190℃-200℃-210℃ for segmented drying. The temperature holding time for each segment is 30 min. Collect the material and transfer it to the kiln for sintering. Set the sintering temperature to 1850℃ and sinter for 3 hours to obtain DCB ceramic tiles.

[0024] Example 2: A method for improving the flatness of DCB ceramic tiles and reducing DCB sintering bubbles, the specific steps of which are as follows: I. Preparation of modified polyvinyl alcohol: Step 1: Add 6 parts of polyvinyl alcohol to 80 parts of deionized water and stir well. Then add 2 parts of polypropylene glycol, 0.2 parts of ammonium persulfate and 0.1 parts of glycerol in sequence. Set the temperature to 70℃ and react for 3 hours to obtain polyether modified polyvinyl alcohol. Step 2: Add 1 part glass powder and 0.5 parts nano silica to 7 parts polyether modified polyvinyl alcohol in sequence, mix and ultrasonically disperse for 20 min, then heat to 60℃ and stir for 10 min to obtain modified polyvinyl alcohol.

[0025] II. Preparation of the coating slurry: Mix 0.7 kg of alumina powder with a particle size of 8 μm and 0.6 kg of alumina powder with a particle size of 5 μm, then add 0.7 L of polyvinyl alcohol and 0.6 L of modified polyvinyl alcohol in sequence, stir evenly, then add 13 L of deionized water and continue stirring to obtain the coating slurry.

[0026] III. Preparation of DCB ceramic tiles: Step 1: The green sheet slurry is cast, dried, and stamped to form green sheets; Step 2: Apply powder to the surface of the green sheet. Set the feeding speed of the powder slurry to 750 mm / min, and then apply it to the surface of the green sheet. The coating process parameters are: atomization pressure: 0.08 MPa, main spray pressure: 0.08 MPa, discharge pressure: 0.1 MPa. Set the temperature gradient to 190℃-200℃-210℃ for segmented drying. The temperature holding time for each segment is 25 min. Collect the material and transfer it to the kiln for sintering. Set the sintering temperature to 1800℃ and sinter for 2 hours to obtain DCB ceramic tiles.

[0027] Example 3: A method for improving the flatness of DCB ceramic tiles and reducing DCB sintering bubbles, the specific steps of which are as follows: I. Preparation of modified polyvinyl alcohol: Step 1: Add 8 parts of polyvinyl alcohol to 100 parts of deionized water and stir well. Then add 4 parts of polypropylene glycol, 0.5 parts of ammonium persulfate and 0.3 parts of glycerol in sequence. Set the temperature to 90℃ and react for 5 hours to obtain polyether modified polyvinyl alcohol. Step 2: Add 2 parts of glass powder and 1 part of nano silica to 8 parts of polyether modified polyvinyl alcohol in sequence, mix with ultrasonic dispersion for 30 min, then heat to 65℃ and stir for 20 min to obtain modified polyvinyl alcohol.

[0028] II. Preparation of the coating slurry: Mix 0.7 kg of alumina powder with a particle size of 10 μm and 0.6 kg of alumina powder with a particle size of 7 μm, then add 0.7 L of polyvinyl alcohol and 0.6 L of modified polyvinyl alcohol in sequence, stir evenly, then add 13 L of deionized water and continue stirring to obtain the coating slurry.

[0029] III. Preparation of DCB ceramic tiles: Step 1: The green sheet slurry is cast, dried, and stamped to form green sheets; Step 2: Apply powder to the surface of the green sheet. Set the feeding speed of the powder slurry to 750 mm / min, and then apply it to the surface of the green sheet. The coating process parameters are: atomization pressure of 0.12 MPa, main spray pressure of 0.12 MPa, and discharge pressure of 0.2 MPa. Set the temperature gradient to 190℃-200℃-210℃ for segmented drying. The temperature holding time for each segment is 35 min. Collect the material and transfer it to a kiln for sintering. Set the sintering temperature to 1900℃ and sinter for 4 hours to obtain DCB ceramic tiles.

[0030] Comparative Example 1: Based on Example 1, the process for preparing DCB ceramic tiles was adjusted, omitting the powder coating process. The specific steps are as follows: Preparation of DCB ceramic tiles: Step 1: The green sheet slurry is cast, dried, and stamped to form green sheets; Step 2: Transfer the green ceramic pieces to a kiln for sintering. Set the sintering temperature to 1850℃ and sinter for 3 hours to obtain DCB ceramic pieces.

[0031] Comparative Example 2: Based on Example 1, the modified polyvinyl alcohol component in the powder coating slurry was adjusted, and glycerol was not added. This was used to prepare DCB ceramic tiles. The rest remained the same as in Example 1. The specific steps are as follows: I. Preparation of modified polyvinyl alcohol: Step 1: Add 7 parts of polyvinyl alcohol to 90 parts of deionized water and stir well. Then add 3 parts of polypropylene glycol and 0.4 parts of ammonium persulfate in sequence. Set the temperature to 80℃ and react for 4 hours to obtain polyether modified polyvinyl alcohol. Step 2: Add 1.5 parts of glass powder and 0.7 parts of nano silica to 7.5 parts of polyether modified polyvinyl alcohol in sequence, mix, ultrasonically disperse for 25 min, then heat to 62℃ and stir for 15 min to obtain modified polyvinyl alcohol.

[0032] II. Preparation of the coating slurry: Mix 0.7 kg of alumina powder with a particle size of 9 μm and 0.6 kg of alumina powder with a particle size of 6 μm, then add 0.7 L of polyvinyl alcohol and 0.6 L of modified polyvinyl alcohol in sequence, stir evenly, then add 13 L of deionized water and continue stirring to obtain the coating slurry.

[0033] III. Preparation of DCB ceramic tiles: Step 1: The green sheet slurry is cast, dried, and stamped to form green sheets; Step 2: Apply powder to the surface of the green sheet. Set the feeding speed of the powder slurry to 750 mm / min and then apply it to the surface of the green sheet. The coating process parameters are: atomization pressure: 0.1 MPa, main spray pressure: 0.1 MPa, discharge pressure: 0.15 MPa. Set the temperature gradient to 190℃-200℃-210℃ for segmented drying. The temperature holding time for each segment is 30 min. Collect the material and transfer it to the kiln for sintering. Set the sintering temperature to 1850℃ and sinter for 3 hours to obtain DCB ceramic tiles.

[0034] Comparative Example 3: Based on Example 1, the modified polyvinyl alcohol component in the powder coating slurry was adjusted, and glass powder was not added. This was used to prepare DCB ceramic tiles. The rest remained the same as in Example 1. The specific steps are as follows: I. Preparation of modified polyvinyl alcohol: Step 1: Add 7 parts of polyvinyl alcohol to 90 parts of deionized water and stir well. Then add 3 parts of polypropylene glycol, 0.4 parts of ammonium persulfate and 0.2 parts of glycerol in sequence. Set the temperature to 80℃ and react for 4 hours to obtain polyether modified polyvinyl alcohol. Step 2: Add 0.7 parts of nano silica to 7.5 parts of polyether modified polyvinyl alcohol, mix, ultrasonically disperse for 25 min, then heat to 62℃ and stir for 15 min to obtain modified polyvinyl alcohol.

[0035] II. Preparation of the coating slurry: Mix 0.7 kg of alumina powder with a particle size of 9 μm and 0.6 kg of alumina powder with a particle size of 6 μm, then add 0.7 L of polyvinyl alcohol and 0.6 L of modified polyvinyl alcohol in sequence, stir evenly, then add 13 L of deionized water and continue stirring to obtain the coating slurry.

[0036] III. Preparation of DCB ceramic tiles: Step 1: The green sheet slurry is cast, dried, and stamped to form green sheets; Step 2: Apply powder to the surface of the green sheet. Set the feeding speed of the powder slurry to 750 mm / min and then apply it to the surface of the green sheet. The coating process parameters are: atomization pressure: 0.1 MPa, main spray pressure: 0.1 MPa, discharge pressure: 0.15 MPa. Set the temperature gradient to 190℃-200℃-210℃ for segmented drying. The temperature holding time for each segment is 30 min. Collect the material and transfer it to the kiln for sintering. Set the sintering temperature to 1850℃ and sinter for 3 hours to obtain DCB ceramic tiles.

[0037] Comparative Example 4: Based on Example 1, the modified polyvinyl alcohol component in the powder coating slurry was adjusted, and nano-silica was not added. This was used to prepare DCB ceramic tiles. The rest remained the same as in Example 1. The specific steps are as follows: I. Preparation of modified polyvinyl alcohol: Step 1: Add 7 parts of polyvinyl alcohol to 90 parts of deionized water and stir well. Then add 3 parts of polypropylene glycol, 0.4 parts of ammonium persulfate and 0.2 parts of glycerol in sequence. Set the temperature to 80℃ and react for 4 hours to obtain polyether modified polyvinyl alcohol. Step 2: Add 1.5 parts of glass powder to 7.5 parts of polyether-modified polyvinyl alcohol, mix, ultrasonically disperse for 25 minutes, then heat to 62°C and stir for 15 minutes to obtain modified polyvinyl alcohol.

[0038] II. Preparation of the coating slurry: Mix 0.7 kg of alumina powder with a particle size of 9 μm and 0.6 kg of alumina powder with a particle size of 6 μm, then add 0.7 L of polyvinyl alcohol and 0.6 L of modified polyvinyl alcohol in sequence, stir evenly, then add 13 L of deionized water and continue stirring to obtain the coating slurry.

[0039] III. Preparation of DCB ceramic tiles: Step 1: The green sheet slurry is cast, dried, and stamped to form green sheets; Step 2: Apply powder to the surface of the green sheet. Set the feeding speed of the powder slurry to 750 mm / min and then apply it to the surface of the green sheet. The coating process parameters are: atomization pressure: 0.1 MPa, main spray pressure: 0.1 MPa, discharge pressure: 0.15 MPa. Set the temperature gradient to 190℃-200℃-210℃ for segmented drying. The temperature holding time for each segment is 30 min. Collect the material and transfer it to the kiln for sintering. Set the sintering temperature to 1850℃ and sinter for 3 hours to obtain DCB ceramic tiles.

[0040] Comparative Example 5: Based on Example 1, only basic polyvinyl alcohol was used to prepare DCB ceramic tiles, and the rest remained the same as in Example 1. The specific steps are as follows: 1. Preparation of the coating slurry: Mix 0.7 kg of alumina powder with a particle size of 9 μm and 0.6 kg of alumina powder with a particle size of 6 μm, add 1.3 L of polyvinyl alcohol, stir evenly, then add 13 L of deionized water and continue stirring to obtain the coating slurry.

[0041] II. Preparation of DCB ceramic tiles: Step 1: The green sheet slurry is cast, dried, and stamped to form green sheets; Step 2: Apply powder to the surface of the green sheet. Set the feeding speed of the powder slurry to 750 mm / min and then apply it to the surface of the green sheet. The coating process parameters are: atomization pressure: 0.1 MPa, main spray pressure: 0.1 MPa, discharge pressure: 0.15 MPa. Set the temperature gradient to 190℃-200℃-210℃ for segmented drying. The temperature holding time for each segment is 30 min. Collect the material and transfer it to the kiln for sintering. Set the sintering temperature to 1850℃ and sinter for 3 hours to obtain DCB ceramic tiles.

[0042] Comparative Example 6: Based on Example 1, the particle size of alumina powder in the powder coating slurry was adjusted to 27 μm, while the rest remained the same as in Example 1. The specific steps are as follows: I. Preparation of modified polyvinyl alcohol: Step 1: Add 7 parts of polyvinyl alcohol to 90 parts of deionized water and stir well. Then add 3 parts of polypropylene glycol, 0.4 parts of ammonium persulfate and 0.2 parts of glycerol in sequence. Set the temperature to 80℃ and react for 4 hours to obtain polyether modified polyvinyl alcohol. Step 2: Add 1.5 parts of glass powder and 0.7 parts of nano silica to 7.5 parts of polyether modified polyvinyl alcohol in sequence, mix, ultrasonically disperse for 25 min, then heat to 62℃ and stir for 15 min to obtain modified polyvinyl alcohol.

[0043] II. Preparation of the coating slurry: Add 1.3 kg of alumina powder with a particle size of 27 μm to 0.7 L of polyvinyl alcohol and 0.6 L of modified polyvinyl alcohol, stir evenly, then add 13 L of deionized water and continue stirring to obtain the coating slurry.

[0044] III. Preparation of DCB ceramic tiles: Step 1: The green sheet slurry is cast, dried, and stamped to form green sheets; Step 2: Apply powder to the surface of the green sheet. Set the feeding speed of the powder slurry to 750 mm / min and then apply it to the surface of the green sheet. The coating process parameters are: atomization pressure: 0.1 MPa, main spray pressure: 0.1 MPa, discharge pressure: 0.15 MPa. Set the temperature gradient to 190℃-200℃-210℃ for segmented drying. The temperature holding time for each segment is 30 min. Collect the material and transfer it to the kiln for sintering. Set the sintering temperature to 1850℃ and sinter for 3 hours to obtain DCB ceramic tiles.

[0045] Performance testing: Roughness test: The roughness of the DCB ceramic tiles prepared in Example 1 and Comparative Example 6 was tested. Test points were selected on surfaces A and B of the DCB ceramic tiles, and the undulation value Ra was measured and recorded using a roughness tester. Bubble rate detection: The DCB ceramic sheets prepared in Examples 1-3 and Comparative Examples 1-6 were coated with copper. Under a hydrogen atmosphere, the temperature was set to 1080℃ and held for 60 minutes. A pressure of 0.2MPa was applied to coat the surface of the DCB ceramic sheets with copper. At least 5 fields of view were randomly selected, and the percentage of bubble area to the total interface area was calculated using image analysis software. The average value was taken as the bubble rate of the sample.

[0046] Table 1: Surface roughness test data of DCB ceramic tiles

[0047] Table 2: Bubble Rate Test Data for Copper-Clad DCB Ceramic Sheets

[0048] Conclusion: As can be seen from the data in Table 1, the roughness of the DCB ceramic sheet prepared in Example 1 is significantly lower than that in Comparative Example 1, indicating that the powder coating process can significantly reduce the roughness of the obtained DCB ceramic sheet. Furthermore, the data in Table 2 shows that the bubble rate of the DCB ceramic sheets in Examples 1-3 after copper plating is better than that of the comparative examples. This may be because the modified polyvinyl alcohol, through the polyether modification of polypropylene glycol and ammonium persulfate, improves the dispersibility and film-forming properties of the adhesive, glycerol further optimizes its toughness, and the introduction of glass powder and nano-silica enhances the interfacial bonding force between the adhesive and alumina powder. This not only improves the density and flatness of the green sheet, but also reduces the porosity and interlayer voids of the green sheet. Combined with the powder coating process, the generation of bubbles is effectively suppressed during sintering and copper plating.

[0049] Comparing Example 1 with Comparative Examples 1-6, it can be seen that Comparative Example 1, without the powder coating process, leads to severe adhesion and deformation during green body sintering, significantly increasing the roughness and bubble rate of the ceramic slabs; Comparative Example 2, without the addition of glycerol, experiences increased shrinkage stress during powder coating drying, resulting in an increased bubble rate in the ceramic slabs; Comparative Example 3, lacking glass powder, has insufficient powder density, failing to effectively resist shrinkage deformation during green body sintering, leading to an increased bubble rate; Comparative Example 4, without the addition of nano-silica, cannot effectively expel the volatiles generated by the decomposition of the adhesive at high temperatures, significantly increasing the bubble rate in the ceramic slabs; Comparative Example 5, using only basic polyvinyl alcohol, lacks crack resistance and densification capabilities in the powder coating slurry, resulting in an increased bubble rate in the ceramic slabs; Comparative Example 6, using a single coarse-grained alumina powder with a particle size of 27 μm, fails to form a dense isolation layer, resulting in a significant increase in the surface undulation value of the ceramic slabs and an increased bubble rate. In summary, the powder coating process between green body stages, along with the use of alumina powders of different particle sizes and a modified polyvinyl alcohol composite system, can effectively ensure the high flatness and low bubble rate of DCB ceramic tiles. The synergistic effect of these three factors can meet the performance requirements of the green body sintering and copper plating processes.

[0050] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

Claims

1. A method for improving the flatness of DCB ceramic tiles and reducing sintering bubbles in DCB, characterized in that: Includes the following steps: Step 1: Pre-grind the powder and spray dry it; use it to prepare a slurry, cast it, dry it, press it into shape, and form a green sheet; Step 2: Apply powder to the surface of the green ceramic sheet and transfer it to a kiln for sintering to obtain DCB ceramic sheet.

2. The method for improving the flatness of DCB ceramic tiles and reducing DCB sintering bubbles according to claim 1, characterized in that: During the powder application process, a powder slurry is used; the raw materials of the powder slurry contain water: glue: alumina powder in a ratio of 10~15L:0.5~1.5L:1~1.5Kg.

3. The method for improving the flatness of DCB ceramic tiles and reducing DCB sintering bubbles according to claim 1, characterized in that: The process parameters for powder application are as follows: feeding belt speed is 500~1000mm / min, atomization pressure is 0.08~0.12MPa, main spray pressure is 0.08~0.12MPa, and discharge pressure is 0.1~0.2MPa.

4. The method for improving the flatness of DCB ceramic tiles and reducing DCB sintering bubbles according to claim 1, characterized in that: During the powder application process, segmented drying is employed, with a temperature gradient of 190℃-200℃-210℃, and each segment maintaining the temperature for 25~35 minutes.

5. The method for improving the flatness of DCB ceramic tiles and reducing DCB sintering bubbles according to claim 2, characterized in that: The alumina powder is composed of coarse-grained alumina powder and fine-grained alumina powder in a mass ratio of 0.6~0.8Kg:0.4~0.7Kg. The coarse-grained alumina powder has a particle size of 8~10μm, and the fine-grained alumina powder has a particle size of 5~7μm.

6. The method for improving the flatness of DCB ceramic tiles and reducing DCB sintering bubbles according to claim 2, characterized in that: The adhesive is composed of polyvinyl alcohol and modified polyvinyl alcohol in a volume ratio of 0.3~0.8L:0.2~0.7L, and the modified polyvinyl alcohol is prepared by: Step 1: Add polyvinyl alcohol to deionized water and stir until homogeneous. Then add polypropylene glycol, ammonium persulfate and glycerol in sequence. Set the temperature to 70~90℃ and react for 3~5 hours to obtain polyether modified polyvinyl alcohol. Step 2: Add 1-2 parts of glass powder and 0.5-1 parts of nano silica to 7-8 parts of polyether modified polyvinyl alcohol in sequence, mix, ultrasonically disperse for 20-30 minutes, then heat to 60-65℃ and stir for 10-20 minutes to obtain modified polyvinyl alcohol.

7. The method for improving the flatness of DCB ceramic tiles and reducing DCB sintering bubbles according to claim 6, characterized in that: The raw materials for the polyether-modified polyvinyl alcohol comprise, by weight, 6-8 parts polyvinyl alcohol, 2-4 parts polypropylene glycol, 0.2-0.5 parts ammonium persulfate, and 0.1-0.3 parts glycerol.

8. The method for improving the flatness of DCB ceramic tiles and reducing DCB sintering bubbles according to claim 6, characterized in that: The raw materials for the modified polyvinyl alcohol comprise, by weight, 1-2 parts glass powder, 0.5-1 parts nano silica, and 7-8 parts polyether-modified polyvinyl alcohol.

9. The method for improving the flatness of DCB ceramic tiles and reducing DCB sintering bubbles according to claim 1, characterized in that: In step 1, the raw materials of the slurry are composed of the following components by weight: 90-110 parts alumina powder, 4-6 parts polyvinyl alcohol, 2-4 parts glycerol, 0.5-1.5 parts fish oil dispersant, and 30-40 parts ethanol aqueous solution.

10. The method for improving the flatness of DCB ceramic tiles and reducing DCB sintering bubbles according to claim 1, characterized in that: The sintering temperature is 1800~1900℃, and the sintering time is 2~4 hours.

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