Preparation method of ceramic packaging base

Abstract

The invention relates to the technical field of electronic packaging, in particular to a preparation method of a ceramic packaging base. The ceramic packaging base is prepared from the following raw materials in parts by weight: 80-120 parts of aluminum oxide ceramic powder, 5-8 parts of a heat conducting agent, 4-6 parts of modified titanium nitride, 3-5 parts of yttrium oxide, 2-4 parts of silicon carbide, 3-5 parts of titanium dioxide, 60-90 parts of an organic solvent, 1.5-2.5 parts of sodium polyacrylate, 4-6 parts of polyvinyl butyral and 5-8 parts of a plasticizer; the prepared ceramic packaging base not only has outstanding wear resistance and corrosion resistance, but also has excellent heat conduction performance, the service life of the ceramic packaging base is prolonged to a certain extent, meanwhile, the quality of the ceramic packaging base is guaranteed, and the packaging reliability of electronic devices is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of electronic packaging, and in particular to a method for preparing a ceramic packaging base. Background Art

[0002] As an important component of electronic devices, the performance of the ceramic package base directly affects the reliability and service life of electronic devices. In fields such as 5G communications, artificial intelligence, and big data centers, the integration and power density of electronic devices are constantly improving, which places higher demands on the performance of the ceramic package base. On the one hand, electronic devices generate a lot of heat during operation, and the base needs to have good thermal conductivity to dissipate the heat in a timely manner to avoid device performance degradation or even damage due to overheating. On the other hand, during the assembly and long-term use of electronic devices, the base will be subject to mechanical friction and wear, so it needs to have excellent wear resistance. In addition, good corrosion resistance and mechanical properties are also key to ensuring the stable operation of the ceramic package base in complex environments.

[0003] However, traditional methods for preparing ceramic package bases have many shortcomings. In terms of thermal conductivity, conventional thermal conductive agents have weak bonding with the ceramic matrix, making it difficult to form an effective heat conduction channel, resulting in low heat conduction efficiency. In terms of wear resistance, ordinary wear-resistant agents have poor dispersibility and cannot fully exert their reinforcing effect, and the surface of the base is prone to wear. In terms of corrosion resistance and mechanical properties, due to limitations in raw materials and processes, the base has poor performance stability when facing acid and alkali corrosion and mechanical stress. These problems have seriously restricted the application and development of ceramic package bases in the field of high-end electronics. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for preparing a ceramic package base. The prepared ceramic package base not only has outstanding wear resistance and corrosion resistance, but also has excellent thermal conductivity. To a certain extent, it extends the service life of the ceramic package base while also ensuring its quality, thereby improving the reliability of electronic device packaging.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] A method for preparing a ceramic package base comprises the following steps:

[0007] Step 1: Weigh 80-120 parts of alumina ceramic powder, 5-8 parts of thermal conductor, 4-6 parts of modified titanium nitride, 3-5 parts of yttrium oxide, 2-4 parts of silicon carbide, 3-5 parts of titanium dioxide, 60-90 parts of organic solvent and 1.5-2.5 parts of sodium polyacrylate respectively, mix the above raw materials and then perform ultrasonic dispersion; after uniform dispersion, add 4-6 parts of polyvinyl butyral and 5-8 parts of plasticizer, stir mechanically and then perform degassing treatment, and store the obtained mixed slurry for future use;

[0008] Step 2: The mixed slurry obtained in step 1 is tape-cast on a polyester film through a tape casting machine to obtain a ceramic green body; the obtained ceramic green body is then subjected to punching, via hole filling, lamination, printing of metal slurry and sintering to obtain a ceramic packaging base.

[0009] Furthermore, the preparation method of the thermal conductor is as follows: boron nitride with a thickness of 2 to 8 nm and a diameter of 0.8 to 1.8 μm is ultrasonically dispersed in toluene at a solid-liquid ratio of 0.05 to 0.1 g / mL, methyl methacrylate with a mass of 0.6 to 0.8 times that of boron nitride and azobisisobutyronitrile with a mass of 0.1 to 0.15 times that of boron nitride are added, the mixture is mixed and stirred evenly, and the temperature is raised to 80 to 90° C., and then the mixture is kept warm and stirred under the protection of nitrogen for 6 to 10 hours; after the reaction is completed, the reaction product is subjected to solid-liquid separation, the obtained solid filter material is washed with petroleum ether 3 to 5 times and then transferred to a drying oven, and dried at a temperature of 70 to 80° C. for 10 to 14 hours to obtain the thermal conductor.

[0010] Furthermore, the ultrasonic power during ultrasonic dispersion is set to 350-450 W, and the ultrasonic dispersion time is set to 30-40 min.

[0011] Furthermore, the preparation method of the modified titanium nitride is as follows: tetrabutyl titanate is added to ethanol at a dosage ratio of 5 to 15 g / L, and then ethylenediamine (1.5 to 2 times the mass of tetrabutyl titanate) and an initiator (0.2 to 0.3 times the mass of initiator) are added, mixed and stirred evenly, and then acidified carbon nanotubes (the mass of which is equal to that of ethylenediamine) are added. After uniform dispersion, the temperature is raised to 65 to 80° C. and the reaction is carried out under the protection of a nitrogen atmosphere for 8 to 12 hours. After the reaction is completed, the reaction product is subjected to solid-liquid separation, and the obtained solid filter material is washed alternately with deionized water and ethanol for 3 to 5 times and then vacuum dried to obtain the modified titanium nitride.

[0012] Furthermore, the initiator is selected from any one of azobisisobutyronitrile and benzoyl peroxide.

[0013] Furthermore, the preparation method of the acidified carbon nanotubes is: adding carbon nanotubes into a mixed acid solution of concentrated sulfuric acid and concentrated nitric acid in a volume ratio of 3:1 at a solid-liquid ratio of 20-50 g / L, and ultrasonically treating at a temperature of 40-60° C. for 2-3 hours to obtain the acidified carbon nanotubes.

[0014] Furthermore, the vacuum drying temperature is set to 60-80° C., and the drying time is set to 12-24 hours.

[0015] Furthermore, the organic solvent is selected from any one of xylene, ethanol, toluene, and isopropanol.

[0016] Furthermore, the plasticizer is selected from any one of dibutyl phthalate and dioctyl phthalate.

[0017] Furthermore, in step 2, the sintering temperature is set to 1500-1650° C., and the sintering time is set to 3-5 hours.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] 1. Azobisisobutyronitrile can trigger a free radical polymerization reaction on the carbon-carbon double bonds of methyl methacrylate, forming polymethyl acrylate (PMA) molecular chains. The resulting PMA molecular chains are adsorbed on the surface of the boron nitride nanosheets through physical entanglement, π-π stacking interactions, hydrogen bonding, and other interactions. During mixing with the ceramic matrix and high-temperature sintering, the ester groups on the PMA molecular chains undergo an ester exchange reaction with metal oxides (such as aluminum oxide) in the ceramic matrix, firmly bonding the boron nitride nanosheets to the ceramic package base and forming a continuous and efficient thermal conductivity network within it. The resulting ceramic package base not only exhibits excellent thermal conductivity but also exceptional wear resistance. This, to a certain extent, addresses the problem of poor heat dissipation in conventional package bases, which can affect the performance of electronic components. This ensures timely heat dissipation of electronic chips during long-term stable operation, extending their service life while also ensuring their quality.

[0020] 2. Under the action of an initiator, tetrabutyl titanate and ethylenediamine react chemically to form a titanium nitride precursor. Acidification of the carbon nanotubes with a mixed acid solution introduces oxygen-containing functional groups onto their surfaces. These oxygen-containing functional groups react chemically with the titanium nitride precursor, successfully "grafting" titanium nitride onto the surface of the carbon nanotubes. Furthermore, the free radicals generated by the initiator can trigger interactions between carbon atoms on the carbon nanotubes and the titanium nitride precursor to form chemical bonds, further enhancing the grafting effect of titanium nitride onto the carbon nanotubes. Modified titanium nitride, used as a raw material for ceramic packaging bases, can effectively improve not only their wear and corrosion resistance, but also their mechanical properties, effectively extending the service life of the ceramic packaging base and enhancing the reliability of electronic device packaging. DETAILED DESCRIPTION

[0021] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0022] Example 1

[0023] A method for preparing a ceramic package base comprises the following steps:

[0024] Step 1: Weigh 80 parts of alumina ceramic powder, 5 parts of thermal conductor, 4 parts of modified titanium nitride, 3 parts of yttrium oxide, 2 parts of silicon carbide, 3 parts of titanium dioxide, 60 parts of xylene, and 1.5 parts of sodium polyacrylate, respectively, and mix the above raw materials and then perform ultrasonic dispersion; after uniform dispersion, add 4 parts of polyvinyl butyral and 5 parts of dibutyl phthalate, stir mechanically and then degas, and store the obtained mixed slurry for future use;

[0025] Step 2: The mixed slurry obtained in step 1 is cast on a polyester film through a casting machine to obtain a ceramic green body; the obtained ceramic green body is then subjected to punching, via hole filling, lamination, printing of metal slurry and sintering to obtain a ceramic packaging base; wherein the sintering temperature is set to 1500°C and the sintering time is set to 5h.

[0026] The preparation method of the thermal conductor is as follows: boron nitride with a thickness of 2 nm and a diameter of 0.8 μm is ultrasonically dispersed in toluene at a solid-liquid ratio of 0.05 g / mL, methyl methacrylate with a mass of 0.6 times that of boron nitride and azobisisobutyronitrile with a mass of 0.1 times that of boron nitride are added, the mixture is stirred evenly, the temperature is raised to 80°C, and then the mixture is kept warm and stirred for 10 hours under the protection of nitrogen; after the reaction is completed, the reaction product is separated into solid and liquid, the obtained solid filter material is washed three times with petroleum ether and then transferred to a drying oven, and dried at a temperature of 70°C for 14 hours to obtain the thermal conductor; wherein the ultrasonic power during ultrasonic dispersion is set to 350 W, and the ultrasonic dispersion time is set to 40 minutes.

[0027] The preparation method of modified titanium nitride is as follows: tetrabutyl titanate is added to ethanol at a dosage ratio of 5g / L, and then ethylenediamine (1.5 times the mass of tetrabutyl titanate) and azobisisobutyronitrile (0.2 times the mass of azobisisobutyronitrile) are added, and the mixture is stirred evenly. After the mixture is evenly dispersed, the temperature is raised to 65°C, and the mixture is kept warm for 8 hours under the protection of a nitrogen atmosphere. After the reaction is completed, the reaction product is subjected to solid-liquid separation, and the obtained solid filter material is washed alternately with deionized water and ethanol three times and then vacuum dried to obtain modified titanium nitride. The vacuum drying temperature is set to 60°C and the drying time is set to 24 hours.

[0028] The preparation method of acidified carbon nanotubes is as follows: carbon nanotubes are put into a mixed acid solution of concentrated sulfuric acid and concentrated nitric acid in a volume ratio of 3:1 at a solid-liquid ratio of 20g / L, and the acidified carbon nanotubes are obtained after ultrasonic treatment at a temperature of 40°C for 3h.

[0029] Example 2

[0030] A method for preparing a ceramic package base comprises the following steps:

[0031] Step 1: Weigh 100 parts of alumina ceramic powder, 6 parts of thermal conductor, 5 parts of modified titanium nitride, 4 parts of yttrium oxide, 3 parts of silicon carbide, 4 parts of titanium dioxide, 80 parts of xylene, and 2 parts of sodium polyacrylate, respectively, mix the above raw materials, and then ultrasonically disperse them; after uniform dispersion, add 5 parts of polyvinyl butyral and 6 parts of dioctyl phthalate, stir mechanically, and then degas. The resulting mixed slurry is stored for future use;

[0032] Step 2: The mixed slurry obtained in step 1 is cast on a polyester film through a casting machine to obtain a ceramic green body; the obtained ceramic green body is then subjected to punching, via hole filling, lamination and printing of metal slurry and sintering to obtain a ceramic packaging base; wherein the sintering temperature is set to 1600°C and the sintering time is set to 4 hours.

[0033] The preparation method of the thermal conductor is as follows: boron nitride with a thickness of 5 nm and a diameter of 1 μm is ultrasonically dispersed in toluene at a solid-liquid ratio of 0.08 g / mL, methyl methacrylate with a mass of 0.7 times that of boron nitride and azobisisobutyronitrile with a mass of 0.1 times that of boron nitride are added, the mixture is stirred evenly, the temperature is raised to 85°C, and then the mixture is kept warm and stirred for 8 hours under the protection of nitrogen; after the reaction is completed, the reaction product is separated into solid and liquid, the obtained solid filter material is washed 5 times with petroleum ether and then transferred to a drying oven, and dried at a temperature of 75°C for 12 hours to obtain the thermal conductor; wherein, the ultrasonic power during ultrasonic dispersion is set to 400 W, and the ultrasonic dispersion time is set to 35 minutes.

[0034] The preparation method of modified titanium nitride is as follows: tetrabutyl titanate is added to ethanol at a dosage ratio of 10 g / L, and then ethylenediamine (2 times the mass of tetrabutyl titanate) and benzoyl peroxide (0.25 times the mass of benzoyl peroxide) are added, and the mixture is stirred evenly. After the mixture is evenly dispersed, the temperature is raised to 75° C. and the mixture is kept warm for 10 hours under the protection of a nitrogen atmosphere. After the reaction is completed, the reaction product is subjected to solid-liquid separation, and the obtained solid filter material is washed alternately with deionized water and ethanol for 5 times and then vacuum dried to obtain modified titanium nitride. The vacuum drying temperature is set to 70° C. and the drying time is set to 20 hours.

[0035] The preparation method of acidified carbon nanotubes is as follows: carbon nanotubes are added into a mixed acid solution of concentrated sulfuric acid and concentrated nitric acid in a volume ratio of 3:1 at a solid-liquid ratio of 30g / L, and then ultrasonically treated at a temperature of 50°C for 3h to obtain acidified carbon nanotubes.

[0036] Example 3

[0037] A method for preparing a ceramic package base comprises the following steps:

[0038] Step 1: Weigh 120 parts of alumina ceramic powder, 8 parts of thermal conductor, 6 parts of modified titanium nitride, 5 parts of yttrium oxide, 4 parts of silicon carbide, 5 parts of titanium dioxide, 90 parts of xylene, and 2.5 parts of sodium polyacrylate, respectively, and mix the above raw materials and then perform ultrasonic dispersion; after uniform dispersion, add 6 parts of polyvinyl butyral and 8 parts of dibutyl phthalate, stir mechanically and then degas, and store the resulting mixed slurry for future use;

[0039] Step 2: The mixed slurry obtained in step 1 is cast on a polyester film through a casting machine to obtain a ceramic green body; the obtained ceramic green body is then subjected to punching, via hole filling, lamination and printing of metal slurry and sintering to obtain a ceramic packaging base; wherein the sintering temperature is set to 1650°C and the sintering time is set to 3h.

[0040] The preparation method of the thermal conductor is as follows: boron nitride with a thickness of 8 nm and a diameter of 1.8 μm is ultrasonically dispersed in toluene at a solid-liquid ratio of 0.1 g / mL, methyl methacrylate with a mass of 0.8 times that of boron nitride and azobisisobutyronitrile with a mass of 0.15 times that of boron nitride are added, the mixture is stirred evenly, the temperature is raised to 90°C, and then the mixture is kept warm and stirred for 6 hours under the protection of nitrogen; after the reaction is completed, the reaction product is separated into solid and liquid, the obtained solid filter material is washed with petroleum ether 5 times and then transferred to a drying oven, and dried at a temperature of 80°C for 10 hours to obtain the thermal conductor; wherein, the ultrasonic power during ultrasonic dispersion is set to 450 W, and the ultrasonic dispersion time is set to 30 minutes.

[0041] The preparation method of modified titanium nitride is as follows: tetrabutyl titanate is added to ethanol at a dosage ratio of 15g / L, and then ethylenediamine (2 times the mass of tetrabutyl titanate) and azobisisobutyronitrile (0.3 times the mass of azobisisobutyronitrile) are added, and the mixture is stirred evenly. After the mixture is evenly dispersed, the temperature is raised to 80°C, and the mixture is kept warm for 8 hours under the protection of a nitrogen atmosphere. After the reaction is completed, the reaction product is subjected to solid-liquid separation, and the obtained solid filter material is washed alternately with deionized water and ethanol for 5 times and then vacuum dried to obtain modified titanium nitride. The vacuum drying temperature is set to 80°C and the drying time is set to 12 hours.

[0042] The preparation method of acidified carbon nanotubes is as follows: carbon nanotubes are added into a mixed acid solution of concentrated sulfuric acid and concentrated nitric acid in a volume ratio of 3:1 at a solid-liquid ratio of 50g / L, and then ultrasonically treated at a temperature of 60°C for 2h to obtain acidified carbon nanotubes.

[0043] Comparative Example 1: The difference between this comparative example and Example 1 is that this comparative example uses an equal amount of boron nitride instead of the thermal conductor.

[0044] Comparative Example 2: This comparative example differs from Example 1 in that an equal amount of titanium nitride is used in this comparative example instead of modified titanium nitride.

[0045] Performance test: The following tests were performed on the relevant performance of the ceramic package base samples prepared in Examples 1 to 3 and Comparative Examples 1 to 2:

[0046] 1. Determination of thermal conductivity: The tape-cast ceramic green body is punched and cut into thin slices, which are sintered in a kiln to a thickness of 0.2 to 0.3 mm. The thermal conductivity of the ceramic body is measured using the guarded hot plate method.

[0047] 2. Porcelain body strength: The tape-cast ceramic green body is laminated to a thickness of 3 cm, then cut into 4*55 cm cuboids. After sintering in a kiln, the three-point bending strength of the ceramic body is tested.

[0048] 3. Wear resistance test: Taber abrasion tester (model: Taber 5135) was used to test in accordance with ASTM D4060. The ceramic package base sample was fixed on the test bench, and a CS-10 rubber grinding wheel was selected. A load of 500g was applied and the sample was rotated at a speed of 60r / min for 1000 revolutions. After the test, a laser confocal microscope (model: Leica TCS SP8) was used to measure the wear depth of the sample surface. Five different positions (avoiding special areas such as holes) were selected on the surface of the ceramic package base sample for measurement. Each position was measured three times, and the average value was taken as the wear depth of the position. The average value of the five positions was then calculated as the wear depth result of the sample. The measurement accuracy was ±0.2μm.

[0049] 4. Corrosion Resistance Test: Ceramic package base samples were immersed in 5wt% HCl solution and 5wt% NaOH solution, respectively, with the solution volume being 10 times the sample volume, for 24 hours at room temperature. After immersion, the samples were removed, rinsed with water, and dried in a 100°C oven for 2 hours. An electronic balance with an accuracy of 0.0001g (model: Sartorius ME204E) was used to measure the mass of the samples before and after immersion. The mass loss rate was calculated according to the formula: Mass Loss Rate = (Mass Before Immersion - Mass After Immersion) / Mass Before Immersion × 100%. Three parallel experiments were performed for each sample, and the average value was taken as the mass loss rate result.

[0050] The test data obtained above are recorded in the following table:

[0051]

[0052]

[0053] Comparing and analyzing the relevant data in the table shows that the ceramic package base prepared by the present invention not only has outstanding wear and corrosion resistance, but also has excellent thermal conductivity. This significantly extends the service life of the ceramic package base while also ensuring its quality and improving the reliability of electronic device packaging. This demonstrates that the method for preparing the ceramic package base provided by the present invention has a broader market prospect and is more suitable for promotion.

[0054] Throughout this specification, references to terms such as "one embodiment," "example," or "specific example" indicate that the specific features, structures, materials, or characteristics described in conjunction with that embodiment or example are included in at least one embodiment or example of the present invention. In this specification, schematic representations of these terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

[0055] The preferred embodiments of the present invention disclosed above are intended only to help illustrate the present invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the present invention to the specific embodiments described. Obviously, many modifications and variations are possible based on the content of this specification. These embodiments are selected and described in detail in this specification to better explain the principles and practical applications of the present invention, thereby enabling those skilled in the art to better understand and utilize the present invention. The present invention is limited only by the claims and their full scope and equivalents.

Claims

1. A method for preparing a ceramic package base, characterized in that: The following steps are involved: Step 1: Weigh 80-120 parts of alumina ceramic powder, 5-8 parts of thermal conductor, 4-6 parts of modified titanium nitride, 3-5 parts of yttrium oxide, 2-4 parts of silicon carbide, 3-5 parts of titanium dioxide, 60-90 parts of organic solvent and 1.5-2.5 parts of sodium polyacrylate, respectively, by weight, mix the above raw materials and then perform ultrasonic dispersion; After being evenly dispersed, add 4 to 6 parts of polyvinyl butyral and 5 to 8 parts of plasticizer, stir mechanically and then degas. The resulting mixed slurry is stored for future use. Step 2: The mixed slurry obtained in step 1 is tape-cast on a polyester film through a tape casting machine to obtain a ceramic green body; the obtained ceramic green body is then subjected to punching, via hole filling, lamination, printing of metal slurry and sintering to obtain a ceramic packaging base.

2. The method for preparing a ceramic package base according to claim 1, wherein: The preparation method of the thermal conductor comprises the following steps: ultrasonically dispersing boron nitride with a thickness of 2 to 8 nm and a diameter of 0.8 to 1.8 μm in toluene at a solid-liquid ratio of 0.05 to 0.1 g / mL, adding methyl methacrylate and azobisisobutyronitrile in an amount of 0.6 to 0.8 times the mass of the boron nitride, respectively, and stirring the mixture uniformly, heating the mixture to 80 to 90° C., and then stirring the mixture under nitrogen protection for 6 to 10 hours. After the reaction is completed, solid-liquid separation is performed on the reaction product, and the obtained solid filter material is washed with petroleum ether for 3 to 5 times, then transferred to a drying oven, and dried at 70 to 80° C. for 10 to 14 hours to obtain the thermal conductor.

3. The method for preparing a ceramic package base according to claim 2, wherein: The ultrasonic power during ultrasonic dispersion was set to 350-450 W, and the ultrasonic dispersion time was set to 30-40 min.

4. The method for preparing a ceramic package base according to claim 1, wherein: The modified titanium nitride preparation method comprises the following steps: adding tetrabutyl titanate into ethanol at a dosage ratio of 5 to 15 g / L, then adding ethylenediamine (1.5 to 2 times the mass of the tetrabutyl titanate) and an initiator (0.2 to 0.3 times the mass of the initiator), mixing and stirring uniformly, adding acidified carbon nanotubes (the mass of which is equal to the mass of the ethylenediamine), raising the temperature to 65 to 80° C. after uniform dispersion, and reacting under the protection of a nitrogen atmosphere for 8 to 12 hours; after the reaction is completed, performing solid-liquid separation on the reaction product, and washing the obtained solid filter material with deionized water and ethanol alternately for 3 to 5 times and then vacuum drying to obtain the modified titanium nitride.

5. The method for preparing a ceramic package base according to claim 4, wherein: The initiator is selected from any one of azobisisobutyronitrile and benzoyl peroxide.

6. The method for preparing a ceramic package base according to claim 4, wherein: The preparation method of the acidified carbon nanotubes is as follows: carbon nanotubes are added into a mixed acid solution of concentrated sulfuric acid and concentrated nitric acid in a volume ratio of 3:1 at a solid-liquid ratio of 20-50 g / L, and the acidified carbon nanotubes are obtained after ultrasonic treatment at a temperature of 40-60° C. for 2-3 hours.

7. The method for preparing a ceramic package base according to claim 4, wherein: The vacuum drying temperature is set to 60-80° C., and the drying time is set to 12-24 hours.

8. The method for preparing a ceramic package base according to claim 1, wherein: The organic solvent is selected from any one of xylene, ethanol, toluene and isopropanol.

9. The method for preparing a ceramic package base according to claim 1, wherein: The plasticizer is selected from any one of dibutyl phthalate and dioctyl phthalate.

10. The method for preparing a ceramic package base according to claim 1, wherein: In step 2, the sintering temperature is set to 1500-1650° C., and the sintering time is set to 3-5 hours.

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