A sintering process of an ultra-thin ceramic substrate

Abstract

This invention provides a sintering process for ultrathin ceramic substrates, comprising the following steps: A) dispersing alumina powder, sintering aid, dispersant, and solvent through ball milling in a first stage, followed by adding a binder and plasticizer and dispersing through ball milling in a second stage to obtain a slurry; the sintering aid includes SiO2, MgO, and CaO; the mass of the sintering aid is 0.3~0.8% of the mass of the alumina powder; B) casting the slurry into a gasket green; C) slicing the gasket green and sintering it at 1500~1530℃ to obtain a gasket sheet; D) stacking the gasket sheet with the ultrathin ceramic green and firing it to obtain an ultrathin ceramic substrate. The method of this invention can avoid problems such as pitting, dents, and bulges on the surface of the ultrathin ceramic substrate. The gasket sheets in this invention are recyclable, saving costs.

Description

Technical Field

[0001] This invention belongs to the field of functional ceramic materials technology, and in particular relates to a sintering process for an ultrathin ceramic substrate. Background Technology

[0002] To meet the demands of modern communication and wireless technology, electronic components are evolving towards miniaturization, high performance, and multifunctionality. Alumina ceramic substrates are widely used in this field due to their advantages, including high-frequency dielectric constant, low dielectric loss, good insulation properties, high thermal conductivity, and a coefficient of linear expansion similar to that of the components. Therefore, ceramic substrates are also gradually developing towards ultra-thin designs.

[0003] Currently, the common sintering methods in ceramic substrate production lines are to use smaller particle size sand for bonding or to use spacer green blanks to be stacked alternately for sintering. Small particle size sand for bonding is expensive and difficult to remove later; spacer green blanks are prone to causing defects such as bulges in the middle of the product surface; resulting in severe deformation of ultra-thin substrates during sintering, and problems such as pitting, dents and bulges on the surface are likely to appear. Summary of the Invention

[0004] The purpose of this invention is to provide a sintering process for ultrathin ceramic substrates. The sintering process of this invention can improve the surface quality of ultrathin ceramic substrates and avoid problems such as pitting, dents, and bulges on the surface of ultrathin ceramic substrates.

[0005] This invention provides a sintering process for ultrathin ceramic substrates, comprising the following steps:

[0006] A) Alumina powder, sintering aid, dispersant and solvent are dispersed by ball milling in one stage, and then binder and plasticizer are added and dispersed by ball milling in two stages to obtain slurry;

[0007] The sintering aids include SiO2, MgO, and CaO; the mass of the sintering aids is 0.3~0.8% of the mass of the alumina powder.

[0008] B) The slurry is cast into a blank to obtain a gasket.

[0009] C) The gasket green blank is sliced ​​and sintered at 1500~1530℃ to obtain the gasket cooked sheet;

[0010] D) The gasket sheet and the ultrathin ceramic green body are stacked and fired to obtain an ultrathin ceramic substrate.

[0011] Preferably, the alumina powder has a D50 of 2.5~3μm; and the mass fraction of the alumina powder in the slurry is 60~70%.

[0012] Preferably, the dispersant includes one or more of castor oil, Span 80, and dispersant AKM-0531; the mass of the dispersant is 1 to 1.5% of the mass of the alumina powder.

[0013] Preferably, the binder comprises polyvinyl butyral; the mass of the binder is 2-5% of the mass of the alumina powder.

[0014] Preferably, the plasticizer includes dioctyl ester, or a mixture of dioctyl ester and polyethylene glycol; the mass of the plasticizer is 0.76 to 1.9% of the mass of the alumina powder.

[0015] Preferably, the thickness of the gasket blank is 0.2~0.4mm.

[0016] Preferably, the sintering time in step C) is 2 to 4 hours.

[0017] Preferably, in step D), a strip-shaped support sheet is further provided between the gasket sheets;

[0018] The strip-shaped support sheet is a strip-shaped gasket sheet.

[0019] Preferably, the strip-shaped support sheet is placed around the ultrathin ceramic green body.

[0020] Preferably, the firing temperature in step D) is 1400~1510℃.

[0021] This invention provides a sintering process for an ultrathin ceramic substrate, comprising the following steps: A) dispersing alumina powder, sintering aid, dispersant, and solvent in a first-stage ball mill, followed by adding a binder and plasticizer and dispersing in a second-stage ball mill to obtain a slurry; the sintering aid includes SiO2, MgO, and CaO; the mass of the sintering aid is 0.3~0.8% of the mass of the alumina powder; B) casting the slurry to obtain a spacer green; C) slicing the spacer green and sintering it at 1500~1530℃ to obtain a spacer finished sheet; D) stacking the spacer finished sheet with the ultrathin ceramic green and firing it to obtain an ultrathin ceramic substrate. This invention involves adding a specific amount of sintering aid to the gasket green body and sintering it to obtain a matured sheet. This matured sheet is used for firing ultra-thin ceramic green bodies, which can avoid problems such as pitting, dents, and bulges on the surface of ultra-thin ceramic substrates. Furthermore, this invention also provides a strip-shaped support sheet between the matured gasket sheet and the ultra-thin ceramic green body to prevent the green body from breaking due to excessive pressure after glue removal. The matured gasket sheet in this invention can be recycled and reused, saving costs. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0023] Figure 1 The appearance morphology of the gasket sheet prepared in Example 1 of this invention under light;

[0024] Figure 2 This is the appearance of one of the ultrathin ceramic substrates after the gasket sheet and the ultrathin ceramic substrate are sintered in Embodiment 1 of the present invention. The middle part is the ultrathin ceramic substrate with a smooth and defect-free surface.

[0025] Figure 3 This is the appearance of one of the ultrathin ceramic substrates in Embodiment 2 of the present invention, with a smooth and defect-free surface;

[0026] Figure 4 As a comparative example of the present invention, after the gasket sheet and the ultra-thin ceramic substrate are sintered, the appearance of one of the gasket sheets is shown, with water stain-like spots appearing on its surface.

[0027] Figure 5 The image shows the appearance of one of the ultrathin ceramic substrates after the gasket sheet and the ultrathin ceramic substrate are sintered in Comparative Example 1 of the present invention. The gasket and the ultrathin ceramic substrate are stuck together and cannot be separated.

[0028] Figure 6 The image shows the appearance of one of the ultrathin ceramic substrates after the gasket sheet and the ultrathin ceramic substrate were sintered in Comparative Example 1 of the present invention. The surface of the substrate has obvious pits.

[0029] Figure 7 This is the appearance of one of the ultrathin ceramic substrates after the gasket sheet and ultrathin ceramic substrate were sintered in Comparative Example 2 of the present invention. Due to the difficulty in removing adhesive, it was severely cracked.

[0030] Figure 8 This is the appearance of one of the ultrathin ceramic substrates after the gasket sheet and the ultrathin ceramic substrate are sintered in Comparative Example 3 of the present invention. The middle part is the ultrathin ceramic substrate, and its surface is obviously wrinkled.

[0031] Figure 9 This is the appearance of one of the ultrathin ceramic substrates after the gasket sheet and the ultrathin ceramic substrate are sintered in Comparative Example 3 of the present invention. The middle part is the ultrathin ceramic substrate, and its surface is obviously wrinkled.

[0032] Figure 10 The image shows the appearance of one of the ultra-thin ceramic substrates after the gasket sheet and the ultra-thin ceramic substrate are sintered in Comparative Example 4 of the present invention. The gasket and the ultra-thin ceramic substrate are bonded together and inseparable.

[0033] Figure 11 This is a schematic diagram showing the stacking order of the gasket sheet, strip support sheet, and ultra-thin ceramic green body in this invention. Detailed Implementation

[0034] This invention provides a sintering process for ultrathin ceramic substrates, comprising the following steps:

[0035] A) Alumina powder, sintering aid, dispersant and solvent are dispersed by ball milling in one stage, and then binder and plasticizer are added for ball milling in two stages to obtain slurry;

[0036] The sintering aids include SiO2, MgO, and CaO; the mass of the sintering aids is 0.3~0.8% of the mass of the alumina powder.

[0037] B) The slurry is cast into a blank to obtain a gasket.

[0038] C) The gasket green blank is sliced ​​and sintered at 1500~1530℃ to obtain the gasket cooked sheet;

[0039] D) The gasket sheet and the ultrathin ceramic green body are stacked and fired to obtain an ultrathin ceramic substrate.

[0040] In this invention, the particle size D50 of the alumina powder is preferably 2.5~3.0μm, and the mass fraction of the alumina powder in the slurry is preferably 60~70%, more preferably 63~68%, such as 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, preferably a range of values ​​with any of the above values ​​as the upper or lower limit.

[0041] 1. In this invention, the sintering aid preferably comprises SiO2, MgO, and CaO, wherein the mass ratio of SiO2, MgO, and CaO is preferably (8~15):(3~8):1, more preferably (10~12):(4~7):1, and most preferably (10~11):(5~6):1. The mass of the sintering aid is 0.3~0.8% of the mass of the alumina powder, more preferably 0.4~0.7%, such as 0.3%, 0.4%, 0.5%, 0. The preferred values ​​are 0.6%, 0.7%, and 0.8%, with any of these values ​​serving as the upper or lower limit. According to experimental results, when the sintering aid is insufficient, the porosity of the sintered gasket is high. When the sintered gasket and the ceramic green body are sintered at high temperatures, the sintering aid in the ultrathin ceramic green body forms a liquid phase at high temperatures. Due to capillary action or concentration difference, this liquid phase penetrates into the gasket, leading to adhesion. Conversely, when the sintering aid is excessive, the porosity of the sintered gasket is low, hindering the removal of binder from the ultrathin ceramic green body, resulting in breakage. Controlling the sintering aid dosage within the range of 0.3% to 0.8% results in a smooth, defect-free surface on the ultrathin ceramic substrate.

[0042] In this invention, the dispersant is preferably one or more of castor oil, Span 80 (S-80), and dispersant AKM-0531; the mass of the dispersant is 1 to 1.5% of the mass of the alumina powder, more preferably 1.2 to 1.4%, such as 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, preferably a range of values ​​with any of the above values ​​as the upper or lower limit.

[0043] In this invention, the solvent is preferably one or more of ethyl acetate, ethanol and n-butanol.

[0044] In this invention, the ball milling dispersion time is preferably 8 to 16 hours, more preferably 10 to 12 hours.

[0045] In this invention, the binder is preferably polyvinyl butyral (PVB); the mass of the binder is 2-5% of the mass of the alumina powder, more preferably 3-4%.

[0046] In this invention, the plasticizer is preferably dioctyl ester, or a mixture of dioctyl ester and polyethylene glycol; the mass of the plasticizer is 0.76~1.9% of the mass of the alumina powder, more preferably 0.8~1.5%, such as 0.76%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, preferably a range of values ​​with any of the above values ​​as the upper or lower limit.

[0047] In this invention, the two-stage ball milling time is preferably 16 to 24 hours, more preferably 18 to 20 hours.

[0048] After obtaining the slurry, the present invention casts the slurry into a gasket green strip.

[0049] In this invention, the casting process can be a commonly used casting process in the art, and will not be described in detail here.

[0050] This invention slices the raw ceramic blank into pieces as needed. For example, it can cut the pieces into sheets similar in size and shape to the ultra-thin ceramic blank, serving as the finished blank spacer, or cut them into strips as support strips. This invention does not have specific limitations on the dimensions of the support strips, as long as they provide support and create a certain space between the ultra-thin ceramic blank and the finished blank spacer. Specifically, in this invention, the raw ceramic blank can be sintered at 1500-1530℃ to determine the shrinkage rate. Then, the specific dimensions are determined based on the shrinkage rate, ensuring that "the side length of the ceramic blank + the width of the support strip × 2" is slightly larger than the corresponding side length of the finished blank spacer. Specifically, in embodiments of this invention, a support strip with a width of 2mm can be used.

[0051] This invention involves sintering sliced ​​green blanks to obtain sintered gasket sheets.

[0052] In this invention, the sintering temperature is preferably 1500~1530℃, more preferably 1505~1525℃, such as 1500℃, 1505℃, 1510℃, 1515℃, 1520℃, 1525℃, 1530℃, preferably within a range where any of the above values ​​are the upper or lower limits. With the addition of certain sintering aids, the sintering temperature of the gasket also needs further control. If the sintering temperature is too low, the gasket will not be ceramicized, and the liquid phase in the ultrathin ceramic green body will permeate into the gasket, causing it to stick together. If the sintering temperature is too high, the sintering aids in the gasket will form a solid solution with alumina at high temperature. This solid solution has a low melting point and melts and precipitates during the firing process of the ultrathin ceramic green body, also causing it to stick together. When the sintering temperature of the gasket is 1500~1530℃, the resulting ultrathin ceramic substrate is free of adhesion. The sintering time is preferably 2~4 hours, more preferably 2.5~3 hours.

[0053] After obtaining the gasket sheet, the present invention stacks the gasket sheet with an ultra-thin ceramic green body, as follows: Figure 11As shown, the bottom layer consists of a pre-cast spacer sheet, the surrounding area consists of strip-shaped support sheets, and the center layer is an ultra-thin ceramic green body. When stacking, another pre-cast spacer sheet is added on top, as shown in the diagram, and this process is repeated. Preferably, the present invention places the ultra-thin ceramic green body and the strip-shaped support sheets between the pre-cast spacer sheets. The strip-shaped support sheets are placed around the ultra-thin ceramic green body to prevent damage to the green body due to excessive pressure after glue removal. More preferably, thicker pre-cast spacer sheets, such as those with a thickness of 0.3~0.5mm, are placed at the top and bottom of the stack. The slightly thicker pre-cast spacer sheet at the bottom can prevent defects such as pits and dents caused by unevenness of the firing plate surface. The slightly thicker pre-cast spacer sheet at the top can utilize gravity to reduce the warping of the ceramic substrate. Thinner pre-cast spacer sheets, such as those with a thickness of 0.1~0.2mm, are placed in the middle of the stack; the thinner the sheet, the better for glue removal. The stacked ultra-thin ceramic substrates are then fired to obtain the ultra-thin ceramic substrate.

[0054] In this invention, the firing temperature is preferably 1400~1510℃, more preferably 1450~1480℃, such as 1400℃, 1410℃, 1420℃, 1430℃, 1440℃, 1450℃, 1460℃, 1470℃, 1480℃, 1490℃, 1500℃, 1510℃, preferably a range of values ​​with any of the above as the upper or lower limit, and the firing time is preferably 1~2 hours.

[0055] This invention provides a sintering process for an ultrathin ceramic substrate, comprising the following steps: A) dispersing alumina powder, sintering aid, dispersant, and solvent in a first-stage ball mill, followed by adding a binder and plasticizer and dispersing in a second-stage ball mill to obtain a slurry; the sintering aid includes SiO2, MgO, and CaO; the mass of the sintering aid is 0.3~0.8% of the mass of the alumina powder; B) casting the slurry to obtain a spacer green; C) slicing the spacer green and sintering it at 1500~1510℃ to obtain a spacer finished sheet; D) stacking the spacer finished sheet with the ultrathin ceramic green and firing it to obtain an ultrathin ceramic substrate. This invention involves adding a specific amount of sintering aid to the gasket green body and sintering it to obtain a matured sheet. This matured sheet is used for firing ultra-thin ceramic green bodies, which can avoid problems such as pitting, dents, and bulges on the surface of ultra-thin ceramic substrates. Furthermore, this invention also provides a strip-shaped support sheet between the matured gasket sheet and the ultra-thin ceramic green body to prevent the green body from breaking due to excessive pressure after glue removal. The matured gasket sheet in this invention can be recycled and reused, saving costs.

[0056] To further illustrate the present invention, the sintering process of an ultrathin ceramic substrate provided by the present invention will be described in detail below with reference to embodiments, but it should not be construed as a limitation on the scope of protection of the present invention.

[0057] Example 1

[0058] ① Using alumina powder as 100% by mass, alumina powder (D50=2.7 μm) + 0.3% sintering aid (SiO2, MgO, CaO mass ratio of 11:5:1) + 1.2% dispersant (castor oil) + solvent (ethyl acetate: ethanol: n-butanol mass ratio of 7:2:1) was ball-milled and dispersed for 8 hours.

[0059] ② Add binder PVB (5%) and plasticizer dioctyl ester (1.9%), and disperse in two stages of ball milling for 16 hours to obtain slurry.

[0060] ③ The slurry is cast into shape, and the thickness of the green body is 0.2 mm and 0.4 mm respectively.

[0061] ③ Cut the cast tape into slices of 100×110mm and fire them at 1510℃ for 2 hours.

[0062] ④ The above-mentioned gaskets and ultra-thin ceramic substrates are placed in a cycle of “cooked sheet - (ceramic green body - surrounding support sheet) - cooked sheet - (ceramic green body - surrounding support sheet) - cooked sheet”, with 0.4mm gaskets placed at the top and bottom, and 0.2mm gaskets placed in the middle, for a total of 11 pieces stacked together, and fired at 1485℃ for 2 hours.

[0063] The firing result is as follows Figure 1 and Figure 2 As shown, by Figures 1-2 It can be seen that the gasket is normal under light and can be reused. The gasket can be easily separated from the ceramic substrate, and the surface of the ultra-thin ceramic substrate is smooth and without defects.

[0064] Example 2

[0065] ① Using alumina powder as 100% by mass, alumina powder (D50=2.7 μm) + 0.3% sintering aid (SiO2, MgO, CaO mass ratio of 11:5:1) + 1.2% dispersant (castor oil) + solvent (ethyl acetate: ethanol: n-butanol mass ratio of 7:2:1) was ball-milled and dispersed for 8 hours.

[0066] ② Add binder PVB (5%) and plasticizer dioctyl ester (1.9%), and disperse by ball milling for 16 hours.

[0067] ③ Casting, with green body thicknesses of 0.2mm and 0.4mm respectively.

[0068] ④ Cut the cast tape into slices of 100×110mm and fire them at 1517℃ for 2 hours.

[0069] ⑤ The above-mentioned gaskets and ultra-thin ceramic substrates are placed in a cycle in the order of "cooked sheet - (ceramic green body - surrounding support sheet) - cooked sheet - (ceramic green body - surrounding support sheet) - cooked sheet". Among them, 0.4mm gaskets are placed at the top and bottom, and 0.2mm gaskets are placed in the middle. A total of 11 pieces are stacked together and fired at 1485℃ for 2 hours.

[0070] The firing result is as follows Figure 3 As shown, by Figure 3 It can be seen that the gasket and the ultrathin ceramic substrate can be easily separated. The surface of the ultrathin ceramic substrate is smooth and without defects.

[0071] Comparative Example 1

[0072] The ultrathin ceramic substrate was prepared according to the method in Example 1, except that no sintering aid was added in Comparative Example 1.

[0073] The firing result is as follows Figures 4-6 As shown, by Figures 4-6 It can be seen that when the gasket is viewed under light, water stain-like spots appear, the gasket is stuck to the ceramic substrate and cannot be separated, and obvious pits appear on the surface of the ceramic substrate.

[0074] Comparative Example 2

[0075] The ultrathin ceramic substrate was prepared according to the method in Example 1, except that 1% of sintering aid was added in Comparative Example 2.

[0076] The firing result is as follows Figure 7 As shown, by Figure 7 It can be seen that the ceramic substrate cracked severely due to difficulties in removing the adhesive.

[0077] Comparative Example 3

[0078] The ultrathin ceramic substrate was prepared according to the method in Example 1, except that the firing temperature of the gasket green blank in step ④ of Comparative Example 3 was 1414℃.

[0079] The firing result is as follows Figures 8-9 As shown, by Figures 8-9 It is evident that the gasket is inextricably bonded to the ultrathin ceramic substrate. The surface of the ultrathin ceramic substrate shows obvious wrinkling.

[0080] Comparative Example 4

[0081] The ultrathin ceramic substrate was prepared according to the method in Example 1, except that the firing temperature of the gasket green blank in step ④ of Comparative Example 3 was 1535°C.

[0082] The firing result is as follows Figure 10 As shown, by Figure 10 It can be seen that the gasket and the ultra-thin ceramic substrate are inseparable.

[0083] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A sintering process for an ultrathin ceramic substrate, comprising the following steps: A) Alumina powder, sintering aid, dispersant and solvent are dispersed by ball milling in one stage, and then binder and plasticizer are added and dispersed by ball milling in two stages to obtain slurry; The sintering aids include SiO2, MgO, and CaO; the mass of the sintering aids is 0.3~0.8% of the mass of the alumina powder. B) The slurry is cast into a blank to obtain a gasket. C) The gasket green blank is sliced ​​and sintered at 1500~1530℃ to obtain the gasket cooked sheet; D) The gasket sheet and the ultra-thin ceramic green body are stacked and fired to obtain an ultra-thin ceramic substrate; the firing temperature in step D) is 1400~1510℃.

2. The sintering process according to claim 1, characterized in that The alumina powder has a D50 of 2.5~3μm; the mass fraction of the alumina powder in the slurry is 60~70%.

3. The sintering process of claim 1, wherein, The dispersant includes one or more of castor oil, Span 80, and dispersant AKM-0531; the mass of the dispersant is 1 to 1.5% of the mass of the alumina powder.

4. The sintering process according to claim 1, characterized in that, The binder comprises polyvinyl butyral; the mass of the binder is 2-5% of the mass of the alumina powder.

5. The sintering process according to claim 1, characterized in that, The plasticizer includes dioctyl ester, or a mixture of dioctyl ester and polyethylene glycol; the mass of the plasticizer is 0.76 to 1.9% of the mass of the alumina powder.

6. The sintering process according to claim 1, characterized in that, The thickness of the gasket blank is 0.2~0.4mm.

7. The sintering process according to claim 1, characterized in that, The sintering time in step C) is 2 to 4 hours.

8. The sintering process according to claim 1, characterized in that, In step D), a strip-shaped support sheet is also provided between the gasket sheets; The strip-shaped support sheet is a strip-shaped gasket sheet.

9. The sintering process according to claim 8, characterized in that, The strip-shaped support sheet is placed around the ultrathin ceramic green body.

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