Ternary carbide additive-based high-thermal-conductivity silicon nitride ceramic and preparation method thereof

Abstract

The invention discloses high-thermal-conductivity silicon nitride ceramic based on a ternary carbide additive and a preparation method of the high-thermal-conductivity silicon nitride ceramic, and belongs to the technical field of ceramic products. Ternary layered ceramic Al3BC3 is used as a multifunctional sintering aid to be applied to preparation of the high-thermal-conductivity silicon nitride ceramic, on one hand, active components (B, C and Al) generated by decomposition of Al3BC3 in the sintering process and silicon nitride lattice oxygen are subjected to a redox reaction, dual deep purification of grain boundaries and crystal lattices is achieved, and the phonon scattering center is fundamentally reduced; and on the other hand, a transitional liquid phase formed by the material and an oxide in the system is used as an efficient substance transmission medium in the middle stage of sintering to promote densification, and is converted into a high-melting-point crystal phase (such as AlN and BN) through phase change in the later stage, harmful glass phase residues are avoided, and finally, the high density and the excellent mechanical property (the bending strength is greater than or equal to 700 MPa) of the material are ensured, and meanwhile, the material has good application prospects. The technical bottleneck that the thermal conductivity breaks through 95 W / (m.K) is achieved, and the key technical problem that the thermal conductivity and the mechanical property of a traditional additive system are difficult to collaboratively optimize is solved.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of ceramic products, in particular to high-thermal-conductivity silicon nitride ceramics based on ternary carbide additives and a preparation method thereof. BACKGROUND

[0002] With the rapid development of power devices in the direction of high power and high integration, the heat generated by the chip during operation increases sharply. If the heat is not removed in time, it will seriously affect the working reliability of the chip, and even cause the failure of the device. In order to ensure the stability and reliability of high-power devices, the electronic packaging industry puts forward higher requirements on the heat dissipation capacity and mechanical properties of ceramic substrates for power device packaging.

[0003] Silicon nitride ceramics have excellent properties such as good insulation, low thermal expansion coefficient, high chemical stability, etc. In particular, the theoretical thermal conductivity of its single crystal is as high as 400 W / (m·K), which is more than 10 times that of commercial alumina ceramic substrates, and its bending strength is more than twice that of aluminum nitride ceramic substrates. Based on the above excellent properties, silicon nitride ceramics are considered as ideal candidates for new generation of high-end electronic device heat dissipation substrates and packaging materials. However, although the theoretical value of the intrinsic thermal conductivity of silicon nitride ceramics is as high as 400 W / (m·K), the thermal conductivity of the actual sintered body is often significantly lower than this value, which seriously limits its large-scale application in the field of high thermal conductivity. SUMMARY

[0004] The application applies ternary layered ceramic Al3BC3 as a multifunctional sintering aid in the preparation of high-thermal-conductivity silicon nitride ceramics. On the one hand, the active components (B, C, Al) produced by the decomposition of Al3BC3 in the sintering process have an oxidation-reduction reaction with the lattice oxygen of silicon nitride, realizing the double-depth purification of the grain boundary and the lattice, and fundamentally reducing the phonon scattering center. On the other hand, the transition liquid phase formed by the oxides in the system not only acts as an efficient mass transfer medium to promote densification in the middle stage of sintering, but also is converted into high-melting-point crystal phases (such as AlN and BN) in the later stage to avoid the residual of harmful glass phases. Finally, while ensuring high density and excellent mechanical properties (bending strength ≥ 700 MPa) of the material, the thermal conductivity breaks through the technical bottleneck of 95 W / (m·K), solving the key technical problem of the difficulty in synergistic optimization between thermal conductivity and mechanical properties in the traditional additive system.

[0005] A high-thermal-conductivity silicon nitride ceramic based on ternary carbide additives and a preparation method thereof, characterized by the following steps: S1, put the components silicon nitride powder, Al3BC3 powder, AlN powder, sintering aid into a ball mill for ball milling, ball mill until all particle sizes are <0.5 μm, prepare a mixed powder, in the mixed powder, the mass fraction of silicon nitride powder is 85-96 parts, the mass fraction of Al3BC3 powder is 0.5-4 parts, the mass fraction of AlN powder is 0.5-2 parts, and the mass fraction of sintering aid is 0.5-3 parts.

[0006] S2, place the mixed powder in a forming die, cold isostatic pressing or dry pressing forming, to prepare a ceramic green body.

[0007] S3, degreasing the ceramic green body.

[0008] S4, high temperature sintering of the degreased ceramic green body, the sintering method is gas pressure sintering, hot pressing sintering or discharge plasma sintering.

[0009] Further, in the silicon nitride powder of step S1, the content of α-phase silicon nitride powder is ≥85%.

[0010] Further, in the silicon nitride powder of step S1, the oxygen content is ≤2%.

[0011] Further, the dry pressing forming pressure of step S2 is 150-250 MPa, and the pressure holding time is 10-30 s.

[0012] Further, the cold isostatic pressing forming pressure of step S2 is 200-400 MPa, and the pressure holding time is 2-5 min.

[0013] Further, the degreasing temperature of step S3 is 500-700℃, the holding time is 2-10 h, and the degreasing atmosphere is air or nitrogen.

[0014] Further, the sintering pressure of the gas pressure sintering of step S4 is 2-5 MPa, the sintering temperature is 1650-1850℃, and the holding time is 1-5 h.

[0015] Further, the sintering pressure of the hot pressing sintering of step S4 is 20-50 MPa, the sintering temperature is 1650-1850℃, and the holding time is 2-6 h.

[0016] Further, the sintering pressure of the discharge plasma sintering of step S4 is 30-60 MPa, the sintering temperature is 1650-1850℃, and the holding time is 5-20 min. DETAILED DESCRIPTION

[0017] The following examples are provided to better enable those skilled in the art to further understand and practice the application, and are not intended to limit the scope of the application in any way. Any product derived from the application or any combination of the application with other prior art teachings that is not expressly disclosed herein is intended to be within the scope of the application.

[0018] Example 1, ceramic formulation design is 94wt% silicon nitride powder, 1wt% Al3BC3 powder, 1wt% AlN powder, 4wt% Yb2O3 powder. Mixed in a planetary ball mill at 400r / min, mixing time 12h, wherein the mass ratio of raw materials: anhydrous ethanol: ball milling beads is 1:3:6. Then the slurry is dried in a 100℃ drying box for 12h, and sieved through a 150 mesh screen to obtain the mixed powder. The mixed powder is cold isostatic pressed, the forming pressure is 250MPa, and the holding pressure is 3min to obtain the ceramic green body. Then the sample is subjected to degassing treatment, and is kept at 550℃ in air for 4h. Then it is sintered by gas pressure sintering, the sintering temperature is 1750℃, the holding time is 5h, and the sintering pressure is 3MPa. The silicon nitride ceramic prepared in this embodiment has a density of 99%, a thermal conductivity of 88 W / (m·K), and a bending strength of 804MPa.

[0019] Example 2, ceramic formulation design is 91wt% silicon nitride powder, 3wt% Al3BC3 powder, 1wt% AlN powder, 5wt% Y2O3 powder. Mixed in a planetary ball mill at 500r / min, mixing time 18h, wherein the mass ratio of raw materials: anhydrous ethanol: ball milling beads is 1:4:9. Then the slurry is dried in a 80℃ drying box for 24h, and sieved through a 120 mesh screen to obtain the mixed powder. Then it is sintered by spark plasma sintering, the sintering temperature is 1800℃, the holding time is 10min, and the sintering pressure is 40MPa. The silicon nitride ceramic prepared in this embodiment has a density of 99.4%, a thermal conductivity of 98 W / (m·K), and a bending strength of 726MPa.

[0020] Example 3, ceramic formulation design is 92wt% silicon nitride powder, 2wt% Al3BC3 powder, 1.5wt% AlN powder, 4.5wt% Sm2O3 powder. Mixed in a planetary ball mill at 300r / min, mixing time 20h, wherein the mass ratio of raw materials: anhydrous ethanol: ball milling beads is 1:2:5. Then the slurry is dried in a 90℃ drying box for 18h, and sieved through a 200 mesh screen to obtain the mixed powder. Then it is sintered by hot-pressing sintering, the sintering temperature is 1700℃, the holding time is 3h, and the sintering pressure is 30MPa. The silicon nitride ceramic prepared in this embodiment has a density of 99.3%, a thermal conductivity of 95 W / (m·K), and a bending strength of 754MPa.

[0021] Comparative Example 1, ceramic formula designed as 92wt% silicon nitride powder, 2wt% Al2O3 powder, 1.5wt% AlN powder, 4.5wt% Y2O3 powder. Mixed in a planetary ball mill at 350r / min, mixing time 24h, wherein the mass ratio of raw materials: anhydrous ethanol: ball milling beads is 1:3:4. Then the slurry is dried in a 100℃ drying box for 20h, and sieved through a 150 mesh screen to obtain the mixed powder. Then it is sintered by hot-press sintering, sintering temperature is 1750℃, holding time is 2h, sintering pressure is 40MPa. The silicon nitride ceramic prepared in this example has a density of 98.5%, a thermal conductivity of 78 W / (m·K), and a bending strength of 762MPa.

[0022] Comparative Example 2, ceramic formula designed as 93wt% silicon nitride powder, 5wt% Al2O3 powder, 3wt% Yb2O3 powder. Mixed in a planetary ball mill at 500r / min, mixing time 15h, wherein the mass ratio of raw materials: anhydrous ethanol: ball milling beads is 1:4:8. Then the slurry is dried in a 95℃ drying box for 15h, and sieved through a 120 mesh screen to obtain the mixed powder. Then it is sintered by spark plasma sintering, sintering temperature is 1780℃, holding time is 15min, sintering pressure is 50MPa. The silicon nitride ceramic prepared in this example has a density of 98%, a thermal conductivity of 74 W / (m·K), and a bending strength of 685MPa. Item Formulation Sintering method Sintering temperature / °C Density / % Thermal conductivity / W / (m·K) Bending strength / MPa Example 1 94wt% Si3N4- 1wt% Al3BC3- 1wt% AlN- 4wt% Yb2O3 GPS 1750 99 88 804 Example 2 91 wt% Si3N4- 3 wt% Al3BC3- 1 wt% AlN- 5 wt% Y2O3 SPS 1800 99.4 98 726 Example 3 92wt% Si3N4 - 2wt% Al3BC3 - 1.5wt% AlN - 4.5wt% Sm2O3 HP 1700 99.3 95 754 Comparative Example 1 92wt% Si3N4 - 2wt% AI2O3 - 1.5wt% AlN - 4.5wt% Y2O3 HP 1750 98.5 78 762 Comparative Example 2 93wt% Si3N4 - 5wt% Al2O3 - 3wt% Yb2O3 SPS 1780 98 74 685 As can be seen from the data of the above examples and comparative examples, the thermal conductivity of Si3N4 ceramic added with Al3BC3 reaches 98 W / (m·K), and the bending strength is ensured to be above 700MPa, realizing the preparation of silicon nitride ceramic with both ultra-high thermal conductivity and excellent mechanical properties, and providing a theoretical basis for its application in the field of semiconductor high-power devices, etc.

Claims

1. A high-thermal-conductivity silicon nitride ceramic based on ternary carbide additive and a preparation method thereof, characterized in that the steps are as follows: S1. Put the components, silicon nitride powder, Al3BC3 powder, AlN powder, and sintering aid, into a ball mill for ball milling until all the particle sizes are <0.5 μm to prepare a mixed powder, wherein the mass fraction of the silicon nitride powder is 85-96 parts, the mass fraction of the Al3BC3 powder is 0.5-4 parts, the mass fraction of the AlN powder is 0.5-2 parts, and the mass fraction of the sintering aid is 0.5-3 parts; S2. Put the mixed powder into a forming mold for cold isostatic pressing or dry pressing to prepare a ceramic green body; S3. Perform degreasing on the ceramic green body; S4. Perform high-temperature sintering on the degreased ceramic green body, and the sintering mode is gas pressure sintering, hot-pressing sintering, or discharge plasma sintering.

2. The high thermal conductivity silicon nitride ceramic based on ternary carbide additive according to claim 1, and a method for manufacturing the same, characterized by: In the silicon nitride powder of step S1, the content of α-phase silicon nitride powder is ≥85%.

3. The high thermal conductivity silicon nitride ceramic based on ternary carbide additive according to claim 1, wherein: In the silicon nitride powder of step S1, the oxygen content is ≤2%.

4. The high thermal conductivity silicon nitride ceramic based on ternary carbide additive according to claim 1, wherein: In step S2, the dry pressing pressure is 150-250 MPa, and the pressure holding time is 10-30 s.

5. The high thermal conductivity silicon nitride ceramic based on ternary carbide additive according to claim 1, wherein: In step S2, the cold isostatic pressing pressure is 200-400 MPa, and the pressure holding time is 2-5 min.

6. The high thermal conductivity silicon nitride ceramic based on ternary carbide additive according to claim 1, wherein: In step S3, the degreasing temperature is 500-700 ℃, the holding time is 2-10 h, and the degreasing atmosphere is air or nitrogen.

7. The high thermal conductivity silicon nitride ceramic based on ternary carbide additive according to claim 1, wherein: In step S4, the sintering pressure of the gas pressure sintering is 2-5 MPa, the sintering temperature is 1650-1850 ℃, and the holding time is 1-5 h.

8. The high thermal conductivity silicon nitride ceramic based on ternary carbide additive according to claim 1, wherein: In step S4, the sintering pressure of the hot-pressing sintering is 20-50 MPa, the sintering temperature is 1650-1850 ℃, and the holding time is 2-6 h.

9. The high thermal conductivity silicon nitride ceramic based on ternary carbide additive according to claim 1, wherein: In step S4, the sintering pressure of the discharge plasma sintering is 30-60 MPa, the sintering temperature is 1650-1850 ℃, and the holding time is 5-20 min.