High-thermal-conductivity spherical low-radioactivity alpha-Al2O3 powder as well as preparation method and application thereof

Abstract

The invention provides high-thermal-conductivity spherical low-radioactivity alpha-Al2O3 powder as well as a preparation method and application thereof, and relates to the field of materials. The method comprises the following steps: spheroidizing an aluminum oxide raw material by using a flame melting method or a combustion synthesis method to obtain spherical aluminum oxide with the particle size D50 of 0.5-70 microns; uniformly mixing the spherical aluminum oxide with a composite mineralizing agent, adding a dispersing agent solution, and uniformly mixing, so as to obtain a premix; and finally, calcining, grinding and purifying the premix in sequence to obtain a target product.

Description

Technical Field

[0001] This invention relates to the field of materials, specifically to a high thermal conductivity spherical low radioactivity α-Al2O3 powder, its preparation method, and its applications. Background Technology

[0002] With the rapid development of AI servers, autonomous driving, 5G, and the Internet of Things, the demand for High-Bandwidth Memory (HBM) chips, a new type of GPU / CPU memory chip, is gradually increasing and has become a hot topic in the industry recently. HBM uses 2.5D chip packaging technology, employing MUF and POP packaging processes during production. It stacks many DDR memory chips together and packages them with the GPU to achieve a large-capacity, high-bandwidth DDR array. However, more memory units mean a significant increase in GPU power consumption, posing a pressing heat dissipation problem, while simultaneously ensuring the stability and accuracy of signal transmission. As a crucial component of the chip, epoxy molding compound (EMC) serves to protect the chip, handle part of its heat dissipation, and maintain low radioactivity to avoid emitting alpha particles that could cause "soft errors" affecting signal accuracy. Inorganic fillers account for 80-90% of EMC, playing a vital role in achieving high thermal conductivity and low radioactivity.

[0003] The theoretical thermal conductivity of commonly used spherical silicon micropowder is only 1 W / mK, far from meeting the heat dissipation requirements of chips. Conventional spherical alumina has a theoretical thermal conductivity of 30 W / mK and is chemically stable; however, it contains hundreds or even thousands of ppb of radioactive elements such as uranium (U) and thorium (Th), and due to its low α-phase content, its thermal conductivity often deviates significantly from the theoretical value. Therefore, low-radioactivity spherical alumina products with high α-phase content can be used as an inorganic filler with higher thermal conductivity in memory chip packaging.

[0004] Patent CN102249276A describes a preferred Bayer process for preparing aluminum hydroxide: Aluminum hydroxide, used as a seed crystal, is added to a sodium aluminate solution produced by the Bayer process. The mixture is stirred and precipitated at 30-90°C to obtain gibbsite crystals. The raw material can be surface-treated with silane coupling agents, titanate coupling agents, and ≤0.5% fatty acid (stearic acid). The aluminum hydroxide powder is then sprayed into a flame, and the powder is collected to obtain a low-radioactivity spherical alumina product with a uranium (U) content ≤10 ppb, preferably ≤8 ppb. This method can only achieve a uranium (U) content of ≤8 ppb, while current memory chips require a uranium (U) content of at least ≤5 ppb.

[0005] Patent CN 101528604 B describes a process where aluminum or alumina powder is spherically shaped, and then the powder is passed through temperature ranges of 550–900°C and 950–1500°C to increase the α-phase content. After cooling and collection, the target product is obtained. The spherical alumina produced has a sphericity of ≥0.93 and an α-phase content of ≥95%. However, in Examples 1-5 of the patent, the residence time of the material at 550–900°C is shorter than that at 950–1500°C. This results in material accumulation at 950–1500°C, potentially causing agglomeration or uneven heating. Summary of the Invention

[0006] The purpose of this invention is to design a high thermal conductivity, spherical, low-radioactivity α-Al₂O₃ powder and its preparation method. Using hydrated industrial alumina or angular α-Al₂O₃ as raw materials, the invention employs processes such as spheroidization, dispersant pretreatment, phase transformation, purification, and deagglomeration to obtain α-Al₂O₃ powder with adjustable particle size (0.5–70 μm), uranium (U) content ≤5 ppb, high sphericity ≥0.95, high α-phase content ≥95%, low viscosity, high flowability, and high thermal conductivity. This powder can meet the heat dissipation and signal transmission requirements of memory chips. Furthermore, it features a simple process, environmental friendliness, and ease of industrial production.

[0007] The objective of this invention can be achieved through the following technical solutions:

[0008] A method for preparing highly thermally conductive spherical low-radioactivity α-Al2O3 powder, the method comprising the following steps:

[0009] (1) Spheroidization: Alumina raw materials are spheroidized by flame melting or combustion synthesis to obtain spherical alumina with a particle size D50 of 0.5 to 70 μm;

[0010] (2) Pretreatment: Mix spherical alumina with composite mineralizer, then add dispersant solution and mix well to obtain premix;

[0011] The composite mineralizer is at least two of the following: acidic reagent, ammonium fluoride, ammonium chloride, aluminum fluoride, and magnesium oxide.

[0012] The dispersant is a silane coupling agent and / or a silane ether;

[0013] (3) The target product can be obtained by calcining, grinding and purifying the premixed material in sequence.

[0014] In the technical solution of the present invention: the alumina raw material in step (2) is alumina, boehmite or angular α-Al2O3, with a D50 between 0.5 and 80 μm and a U content ≤ 5 ppb.

[0015] In the technical solution of the present invention: the composite mineralizer in step (2) is an acidic reagent, ammonium fluoride and magnesium oxide in a mass ratio of 1:0.01~8:0.01~3; preferably: the composite mineralizer in step (2) is an acidic reagent, ammonium fluoride and magnesium oxide in a mass ratio of 1:0.05~4.5:0.02~0.3.

[0016] In the technical solution of this invention: the acidic reagent mentioned in step (2) is boric acid.

[0017] In the technical solution of this invention: the mass ratio between spherical alumina and composite mineralizer in step (2) is 1:0.001 to 0.01.

[0018] In the technical solution of the present invention: the dispersant mentioned in step (2) is methyltrimethoxysilane or hexamethyldisiloxane.

[0019] In the technical solution of the present invention: the mass ratio between spherical alumina and dispersant in step (2) is 1:0.001 to 0.01; preferably: the mass ratio between spherical alumina and dispersant in step (2) is 1:0.001 to 0.005.

[0020] In the technical solution of the present invention: the calcination temperature in step (3) is 1200~1300℃, the heating rate is 5~10℃ / min, and the holding time is 6~8h.

[0021] A high thermal conductivity spherical low radioactivity α-Al2O3 powder was prepared by the above method. The powder has a U content ≤5ppb, a D50 of 0.6-70μm, and a thermal conductivity of 1.53-1.94W / m·K.

[0022] In the technical solution of this invention, the application of the high thermal conductivity spherical low radioactivity α-Al2O3 powder obtained by the method in memory chip packaging.

[0023] In the technical solution of this invention, after spherical alumina is obtained by sphericalization of high thermal conductivity spherical low radioactivity α-Al2O3 powder, spherical low radioactivity α-Al2O3 powder with high dispersion and high α phase content is obtained under the combined action of mineralizer and dispersant at high temperature. This not only solves the problem of low α phase content in spherical alumina, but also avoids product sticking during phase transformation, which would cause a decrease in product flowability and other properties.

[0024] Methods for testing thermal conductivity:

[0025] Weighing: Weigh out 70g of the compounded spherical alumina powder, 10g of vinyl silicone oil, 0.25g of hydrogen-containing silicone oil, 0.02g of inhibitor, and 0.15g of platinum catalyst. Add the weighed silicone oil, inhibitor, and catalyst to the spherical alumina powder, stir evenly, and solidify into samples approximately 3mm in diameter. Thermal conductivity is tested using a DRL-3 thermal conductivity tester at a pressure of 50N and a temperature difference of 40℃.

[0026] The beneficial effects of this invention are:

[0027] The product of this invention has the characteristics of high thermal conductivity, low radioactivity, and high fluidity. It can effectively reduce "soft errors" while improving the heat dissipation capacity of the device, and can be widely used in storage-related packaging materials and substrates. Attached Figure Description

[0028] Figure 1 The XRD pattern of the product in Example 1 is shown.

[0029] Figure 2 The XRD pattern of Comparative Example 1 product is shown. Detailed Implementation

[0030] The present invention will be further described below with reference to embodiments, but the scope of protection of the present invention is not limited thereto:

[0031] Spherical alumina semi-finished products with a sphericity ≥ 0.95 are produced by sphericification using flame melting technology.

[0032] Example 1

[0033] Alumina (raw material D50 between 0.5 and 80 μm, U content 4.8 ppb) was spheroidized at a feed rate of 100 kg / h and a temperature of 2100℃ using flame melting technology. Spherical alumina with D50 = 0.5 μm and U content 4.8 ppb (sphericity ≥ 0.95) was selected.

[0034] The composite mineralizer is boric acid, ammonium fluoride, and magnesium oxide in a mass ratio of 1:0.16:0.02. The composite mineralizer is pretreated in a ball mill for 1 hour. Then, spherical alumina is added and mixed with the composite mineralizer. The amount of mineralizer added is 0.3% wt of the spherical alumina. Finally, methyltrimethoxysilane (methyltrimethoxysilane is added in the form of hydrolysate, which consists of water and methyltrimethoxysilane in a mass ratio of 2:1) is added at a mass ratio of 0.3% wt of the spherical alumina. The mixture is then dispersed for another 10 minutes to obtain premix M1.

[0035] Premix M1 was calcined in a sagger at a maximum temperature of 1250℃, a heating rate of 7℃ / min, and a holding time of 8h. The cooled product A was then ground in a ball mill for 6h, purified with deionized water, and dried to obtain the final product. XRD patterns showed that the diffraction peaks at 2θ = 25.56°, 35.13°, 37.75°, and 43.33° were sharp, consistent with the characteristic peaks of α-Al₂O₃ (PDF#74-0323), and without impurity peaks, indicating good α-phase crystallinity of the product.

[0036] The sieve test showed no obvious agglomeration of the product, with zero residue on the sieve. The product had a U content of 1.5 ppb, a particle size D50 of 0.8 μm, and a thermal conductivity of 1.68 W / m·K.

[0037] Example 2

[0038] Alumina (raw material D50 between 0.5 and 80 μm, U content 4.8 ppb) was spheroidized at a feed rate of 100 kg / h and a temperature of 2100℃ using flame melting technology. Spherical alumina with D50 = 0.5 μm and U content 4.8 ppb (sphericity ≥ 0.95) was selected.

[0039] The composite mineralizer is boric acid, ammonium fluoride, and magnesium oxide in a mass ratio of 1:4.5:0.3. The composite mineralizer is pretreated in a ball mill for 1 hour. Then, spherical alumina is added and mixed with the composite mineralizer. The amount of mineralizer added is 0.1% wt of the spherical alumina. Finally, methyltrimethoxysilane (methyltrimethoxysilane is added in the form of hydrolysate, which consists of water and methyltrimethoxysilane in a mass ratio of 2:1) is added at a amount of 0.5% wt of the spherical alumina. The mixture is then dispersed for another 10 minutes to obtain premix M1.

[0040] Premix M1 was calcined in a crucible at a maximum temperature of 1250℃, a heating rate of 7℃ / min, and a holding time of 8h. The cooled product A was then ground in a ball mill for 6h, purified with deionized water, and dried to obtain the final product. XRD patterns showed sharp diffraction peaks at 2θ = 25.56°, 35.13°, 37.75°, and 43.33°, consistent with the characteristic peaks of α-Al₂O₃ (PDF#74-0323) and free of impurities, indicating good α-phase crystallinity. Sieving revealed no obvious agglomeration, with the residue content below 100ppm. The final product had a U content of 2.3ppb, a particle size D50 of 0.7μm, and a thermal conductivity of 1.53W / m·K.

[0041] Example 3

[0042] Alumina (raw material D50 between 0.5 and 80 μm, U content 3.2 ppb) was spheroidized at a feed rate of 100 kg / h and a temperature of 2100℃ using flame melting technology. Spherical alumina with D50 = 40 μm and U content 3.2 ppb (sphericity ≥ 0.95) was selected.

[0043] The composite mineralizer is boric acid, ammonium fluoride, and magnesium oxide in a mass ratio of 1:0.16:0.02. The composite mineralizer is pretreated in a ball mill for 1 hour. Then, spherical alumina is added and mixed with the composite mineralizer. The amount of mineralizer added is 0.5% wt of the spherical alumina. Finally, methyltrimethoxysilane (methyltrimethoxysilane is added in the form of hydrolysate, which consists of water and methyltrimethoxysilane in a mass ratio of 2:1) is added at a amount of 0.2% wt of the spherical alumina. The mixture is then dispersed for another 10 minutes to obtain premix M1.

[0044] Premix M1 was calcined in a sagger at a maximum temperature of 1250℃, a heating rate of 7℃ / min, and a holding time of 8h. The cooled product A was then ground in a ball mill for 6h, purified with deionized water, and dried to obtain the final product. XRD patterns showed sharp diffraction peaks at 2θ = 25.56°, 35.13°, 37.75°, and 43.33°, consistent with the characteristic peaks of α-Al₂O₃ (PDF#74-0323) and without impurities, indicating good α-phase crystallinity. Sieving revealed no obvious agglomeration, with the residue content below 100ppm. The product had a U content of 3.0ppb, a particle size D50 of 42μm, and a thermal conductivity of 1.82W / m·K.

[0045] Example 4

[0046] Alumina (raw material D50 between 0.5 and 80 μm, U content of 2.8 ppb) was spheroidized at a feed rate of 100 kg / h and a temperature of 2100℃ using flame melting technology. Spherical alumina with D50 = 70 μm and U content of 2.8 ppb (sphericity ≥ 0.95) was selected.

[0047] The composite mineralizer is boric acid, ammonium fluoride, and magnesium oxide in a mass ratio of 1:4.5:0.3. The composite mineralizer is pretreated in a ball mill for 1 hour. Then, spherical alumina is added and mixed with the composite mineralizer. The amount of mineralizer added is 1% wt of the spherical alumina. Finally, methyltrimethoxysilane (methyltrimethoxysilane is added in the form of hydrolysate, which consists of water and methyltrimethoxysilane in a mass ratio of 2:1) is added at a amount of 0.1% wt of the spherical alumina. The mixture is then dispersed for another 10 minutes to obtain premix M1.

[0048] Premix M1 was calcined in a crucible at a maximum temperature of 1250℃, a heating rate of 7℃ / min, and a holding time of 8h. The cooled product A was then ground in a ball mill for 6h, purified with deionized water, and dried to obtain the final product. XRD patterns showed sharp diffraction peaks at 2θ = 25.56°, 35.13°, 37.75°, and 43.33°, consistent with the characteristic peaks of α-Al₂O₃ (PDF#74-0323) and free of impurities, indicating good α-phase crystallinity. Sieving revealed no obvious agglomeration, with the residue content below 100ppm. The product had a U content of 2.6ppb, a particle size D50 of 72μm, and a thermal conductivity of 1.94W / m·K.

[0049] Comparative Example 1

[0050] Alumina (raw material D50 between 0.5 and 80 μm, U content of 4.8 ppb) was spheroidized using flame melting technology at a feed rate of 100 kg / h and a temperature of 2100℃. Spherical alumina with D50 = 0.5 μm and U content of 4.8 ppb was selected.

[0051] The product was obtained after purification and drying with deionized water. A sample with D50 = 0.5 μm was selected. The XRD pattern showed that the diffraction peaks of this sample were not as sharp as those in Example 1, and impurity peaks were present, indicating that the α-phase content of the product was relatively low and that the product contained other crystalline phases. Sieving revealed no obvious agglomeration of the material, and the amount of material remaining on the sieve was almost zero.

[0052] Comparative Example 2

[0053] Alumina (raw material D50 between 0.5 and 80 μm, U content 4.8 ppb) was spheroidized at a feed rate of 100 kg / h and a temperature of 2100℃ using flame melting technology. Spherical alumina with D50 = 0.5 μm and U content 4.8 ppb (sphericity ≥ 0.95) was selected.

[0054] The sample with D50 = 0.5 μm was selected and calcined in a crucible at a maximum temperature of 1250℃, a heating rate of 7℃ / min, and a holding time of 8h. After cooling, product A was ground in a ball mill for 6h, purified with deionized water, and dried to obtain the final product. XRD patterns showed sharp diffraction peaks at 2θ = 25.56°, 35.13°, 37.75°, and 43.33°, consistent with the characteristic peaks of α-Al₂O₃ (PDF#74-0323) and without impurities, indicating good α-phase crystallinity. However, sieve analysis revealed significant agglomeration, with the sieve residue exceeding 1000 ppm.

[0055] Comparative Example 3

[0056] Alumina (raw material D50 between 0.5 and 80 μm, U content 4.8 ppb) was spheroidized at a feed rate of 100 kg / h and a temperature of 2100℃ using flame melting technology. Spherical alumina with D50 = 0.5 μm and U content 4.8 ppb (sphericity ≥ 0.95) was selected.

[0057] The sample with D50 = 0.5 μm was selected, and ammonium fluoride and magnesium oxide were used as composite mineralizers. The mass ratio of ammonium fluoride to magnesium oxide was 8:1. The sample was pretreated in a ball mill for 1 hour. Spherical alumina was added, and the ratio of spherical alumina to mineralizer was 0.1% wt, to obtain premix M1.

[0058] Premix M1 was placed in a sagger and calcined at a maximum temperature of 1250℃, a heating rate of 7℃ / min, and a holding time of 8h. The cooled product A was then ground in a ball mill for 6h, purified with deionized water, and dried to obtain the final product. XRD patterns showed sharp diffraction peaks at 2θ = 25.56°, 35.13°, 37.75°, and 43.33°, consistent with the characteristic peaks of α-Al₂O₃ (PDF#74-0323) and free of impurities, indicating good α-phase crystallinity. However, sieve analysis revealed severe caking, requiring additional dispersion processing before use.

Claims

1. A method for preparing highly thermally conductive spherical low-radioactivity α-Al₂O₃ powder, characterized in that: The preparation method includes the following steps: (1) Spheroidization: Alumina raw materials are spheroidized by flame melting or combustion synthesis to obtain spherical alumina with a particle size D50 of 0.5 to 70 μm; (2) Pretreatment: Mix spherical alumina with composite mineralizer, then add dispersant solution and mix well to obtain premix; The composite mineralizer is at least two of the following: acidic reagent, ammonium fluoride, ammonium chloride, aluminum fluoride, and magnesium oxide. The dispersant is a silane coupling agent and / or a silane ether; (3) The target product can be obtained by calcining, grinding and purifying the premixed material in sequence.

2. The preparation method according to claim 1, characterized in that: In step (2), the alumina raw material is industrial alumina, boehmite or angular α-Al2O3, with a D50 between 0.5 and 80 μm and a U content ≤ 5 ppb.

3. The preparation method according to claim 1, characterized in that: In step (2), the composite mineralizer is an acidic reagent, ammonium fluoride and magnesium oxide in a mass ratio of 1:0.01 to 8:0.01 to 3; preferably, in step (2), the composite mineralizer is an acidic reagent, ammonium fluoride and magnesium oxide in a mass ratio of 1:0.05 to 4.5:0.02 to 0.

3.

4. The preparation method according to claim 3, characterized in that: The acidic reagent mentioned in step (2) is boric acid.

5. The preparation method according to claim 1, characterized in that: In step (2), the mass ratio between spherical alumina and composite mineralizer is 1:0.001 to 0.

01.

6. The preparation method according to claim 1, characterized in that: The dispersant mentioned in step (2) is methyltrimethoxysilane or hexamethyldisiloxane.

7. The preparation method according to claim 6, characterized in that: In step (2), the mass ratio between spherical alumina and dispersant is 1:0.001 to 0.01; preferably, the mass ratio between spherical alumina and dispersant in step (2) is 1:0.001 to 0.

005.

8. The preparation method according to claim 1, characterized in that: In step (3), the calcination temperature is 1200-1300℃, the heating rate is 5-10℃ / min, and the holding time is 6-8h.

9. A highly thermally conductive, spherical, low-radioactivity α-Al₂O₃ powder, characterized in that: The powder is prepared by the method described in any one of claims 1 to 8, and has a U content ≤ 5 ppb, a D50 of 0.6 to 70 μm, and a thermal conductivity of 1.53 to 1.94 W / m·K.

10. The application of the high thermal conductivity spherical low radioactivity α-Al2O3 powder prepared by the method of claim 1 in memory chip packaging.

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