A method for manufacturing a multilayer aluminum nitride substrate

Abstract

The application discloses a preparation method of a multilayer aluminum nitride substrate and relates to the technical field of aluminum nitride substrate production.The method comprises the following steps: flow casting, i.e., casting ceramic slurry into green ceramic sheets, punching the green ceramic sheets, and forming required connecting through holes on the green ceramic sheets; hole filling and circuit printing, i.e., filling the connecting through holes with conductive slurry and printing circuits on the surfaces of the green ceramic sheets; lamination and laminating, i.e., laminating the green ceramic sheets and then performing static pressure lamination to combine the green ceramic sheets into a multilayer substrate green body; glue removal, i.e., placing the multilayer substrate green body in a glue removal furnace to gradually decompose and remove the binder and plasticizer; high-temperature co-firing, i.e., transferring the multilayer substrate green body to a high-temperature sintering furnace to perform sintering and form a multilayer aluminum nitride substrate; and substrate processing, i.e., performing contour machining, polishing and electroplating on the multilayer aluminum nitride substrate.The application realizes the gradual and complete decomposition and removal of organic matters such as the binder and the plasticizer, ensures the compactness of the multilayer aluminum nitride substrate, and thus reduces the product defect rate.

Description

Technical Field

[0001] This invention relates to the field of aluminum nitride substrate manufacturing technology, specifically a method for preparing multilayer aluminum nitride substrates. Background Technology

[0002] With the rapid development of microelectronics technology, devices are required to evolve towards higher capacity, higher density, higher speed, and higher power output. Increasingly complex devices place increasingly stringent demands on the heat dissipation of substrates and packaging materials. Traditional resin substrates and alumina ceramic substrates have a maximum thermal conductivity of only around 30 W / (m·K), far from meeting the heat dissipation requirements of today's devices. In contrast, aluminum nitride ceramics possess excellent thermal conductivity, a thermal expansion coefficient close to that of silicon, good insulation properties, moderate dielectric constant and dielectric loss, good mechanical properties at both room and high temperatures, and are non-toxic. Therefore, they have broad application prospects as substrate materials for integrated circuits and high-power devices, as well as electronic packaging materials.

[0003] However, existing aluminum nitride substrates, due to their high organic carrier content and complex decomposition kinetics, are prone to cracking, blistering, or even delamination inside the multilayer substrate green blank if the heating rate is not properly controlled or the atmosphere switching is not precise during the debinding process. Furthermore, if the carbon residue generated by thermal decomposition is not completely removed, it will reduce the metal oxides in the conductive paste during the subsequent high-temperature sintering stage, leading to increased resistivity and decreased adhesion of the metal lines, or the formation of closed pores that severely degrade the thermal conductivity and insulation properties of the aluminum nitride substrate. Therefore, we propose a more convenient method for preparing multilayer aluminum nitride substrates to meet the application requirements. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing a multilayer aluminum nitride substrate to solve the problems mentioned in the background art.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] A method for preparing a multilayer aluminum nitride substrate includes the following steps:

[0007] Step 1: Casting and forming. High-purity aluminum nitride powder, sintering aid, dispersant, binder and plasticizer are mixed in a preset ratio to prepare a uniform ceramic slurry. The ceramic slurry is cast into a green ceramic sheet of the required thickness using a casting machine. After drying, the green ceramic sheet is punched according to the design size, and the required connecting through holes are formed on the green ceramic sheet using laser drilling.

[0008] Step 2: Filling and Printing Circuits. Use conductive paste to fill the connecting vias and print circuits on the surface of the green ceramic sheet.

[0009] Step 3: Stacking and lamination. The printed circuit green ceramic sheets are precisely stacked in the design order so that the circuits on each green ceramic sheet are electrically connected through the conductive paste in the connecting through holes. Static pressure lamination is performed under the set temperature and pressure to firmly bond the green ceramic sheets into a whole multilayer substrate green blank.

[0010] Step 4: Adhesive Removal. The multilayer substrate green sheet is placed in an adhesive removal furnace and heated slowly to gradually decompose and remove the adhesive and plasticizer from the green ceramic sheet. This includes the following sub-steps:

[0011] N1. Low-temperature volatilization removal: The laminated multilayer substrate preform is placed in a descaling furnace. First, under the protection of an inert atmosphere with an inert gas, it is heated from room temperature to 250℃-350℃ at a heating rate of 0.5℃ / min-1.5℃ / min. After reaching the specified temperature, it is held for 30 minutes to 90 minutes to remove the plasticizer in the multilayer substrate preform.

[0012] N2, adhesive pyrolysis and decomposition: After low-temperature volatilization and removal, the inert atmosphere in the adhesive removal furnace is switched to one of high-purity nitrogen and nitrogen-hydrogen mixture, the gas flow rate is increased to 800 sccm-1500 sccm, and the temperature is heated from 250℃-350℃ to 450℃-500℃ at an extremely slow heating rate of 0.1℃ / min-0.5℃ / min, so that the adhesive undergoes slow thermal decomposition under the inert atmosphere;

[0013] N3, micro-oxidation to remove carbon and residues: After reaching 450℃-500℃, hold for 60 minutes-180 minutes. During this holding period, oxygen is introduced into the debinding furnace to form a micro-oxidation atmosphere to thoroughly remove carbon residues generated during pyrolysis.

[0014] N4 atmosphere purification: After the carbon residue is removed, stop the oxygen supply, maintain the inert atmosphere in the debinding furnace, and raise the furnace temperature from 450℃-500℃ to 600℃-800℃ at a heating rate of 0.5℃ / min-1.0℃ / min, and hold at this temperature for 30 minutes-60 minutes.

[0015] Step 5: High-temperature co-firing. The multilayer substrate green blank that has been debonded is transferred to a high-temperature sintering furnace for sintering to form a multilayer aluminum nitride substrate.

[0016] Step 6: Substrate processing. The sintered multilayer aluminum nitride substrate is shaped and polished, and then electroplated to improve solderability and oxidation resistance.

[0017] Furthermore, the adhesive is an acrylic resin system, the plasticizer is a phthalate compound, and the conductive paste is a tungsten paste or a molybdenum-manganese paste.

[0018] Furthermore, in step three, the lamination and stacking are carried out using either isostatic pressing or hot pressing, with a lamination temperature of 60℃-100℃, a pressure of 5MPa-20MPa, and a holding time of 10 minutes-60 minutes.

[0019] Furthermore, in sub-step N1, the inert gas first introduced is argon, with a gas flow rate of 10 mL / min·cm²-50 mL / min·cm², and the vacuum degree is controlled at 10 Pa-100 Pa.

[0020] Furthermore, in step five, the sintering temperature for high-temperature co-firing is 1600℃-1800℃, the sintering time is 2 hours-6 hours, the sintering atmosphere is high-purity nitrogen, and the nitrogen flow rate is 5L / min·cm²-20L / min·cm².

[0021] Furthermore, in step six, the substrate processing includes performing three-dimensional precision machining on the sintered substrate, grinding and polishing to the target thickness and surface roughness, and then conducting strength, roughness, thermal conductivity, and warpage performance tests.

[0022] Compared with the prior art, the beneficial effects of the present invention are:

[0023] This method for preparing multilayer aluminum nitride substrates achieves the gradual and thorough decomposition and removal of organic substances such as plasticizers and binders through multi-stage, extremely slow heating rates and switching of inert atmospheres at different stages. This avoids internal and external pressure differences and damage to the green substrate caused by excessively rapid volatilization. Furthermore, a trace amount of oxygen is specifically introduced to remove carbon residues, preventing carbon from reducing circuits or forming pores during high-temperature sintering. This ensures the density of the multilayer aluminum nitride substrate, thereby reducing the product defect rate and improving the quality and consistency of the final product.

[0024] At the same time, it enables each layer of green ceramic tiles to bond firmly without significant deformation or misalignment, ensuring the alignment accuracy between layers and the strength of the multi-layer substrate green body. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the preparation method of the present invention. Detailed Implementation

[0026] 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.

[0027] like Figure 1As shown, the present invention provides a method for preparing a multilayer aluminum nitride substrate, comprising the following steps:

[0028] Step 1: Casting and forming. High-purity aluminum nitride powder, sintering aid, dispersant, binder and plasticizer are mixed in a preset ratio to prepare a uniform ceramic slurry. The ceramic slurry is cast into a green ceramic sheet of the required thickness using a casting machine. After drying, the green ceramic sheet is punched according to the design size, and the required connecting through holes are formed on the green ceramic sheet using laser drilling.

[0029] In this specific embodiment, preferably, the adhesive is an acrylic resin system and the plasticizer is a phthalate compound.

[0030] Step 2: Hole filling and circuit printing. Use conductive paste to fill the connecting vias and print circuits on the surface of the green ceramic sheet. The conductive paste is tungsten paste or molybdenum-manganese paste.

[0031] Step 3: Stacking and lamination. The printed circuit green ceramic sheets are precisely stacked in the design order, so that the circuits on each layer of green ceramic sheets are electrically connected through the conductive paste in the connecting through holes. Static pressure lamination is performed under the set temperature and pressure to firmly bond the green ceramic sheets into a whole multilayer substrate green blank.

[0032] The lamination and stacking are carried out using either isostatic pressing or hot pressing. The lamination temperature is 60℃-100℃, the pressure is 5MPa-20MPa, and the holding time is 10 minutes-60 minutes.

[0033] Step 4: Debonding and removal. Place the multilayer substrate green blank in a debonding furnace and slowly heat it up to allow the adhesive and plasticizer in the green ceramic sheet to gradually decompose and be removed.

[0034] The glue removal process includes the following sub-steps:

[0035] N1. Low-temperature volatilization removal: The laminated multilayer substrate preform is placed in a descaling furnace. First, under the protection of an inert atmosphere with an inert gas, it is heated from room temperature to 250℃-350℃ at a heating rate of 0.5℃ / min-1.5℃ / min. After reaching the specified temperature, it is held for 30 minutes to 90 minutes to remove the plasticizer in the multilayer substrate preform.

[0036] Preferably, in this specific embodiment, sub-step N1 involves heating from room temperature to 300°C at a heating rate of 1.0°C / min, and holding at that temperature for 60 minutes to remove the plasticizer from the green substrate. Alternatively, sub-step N1 involves heating from room temperature to 320°C at a heating rate of 0.8°C / min, and holding at that temperature for 90 minutes to remove the plasticizer from the green substrate.

[0037] N2, adhesive pyrolysis and decomposition: After low-temperature volatilization and removal, the inert atmosphere in the adhesive removal furnace is switched to one of high-purity nitrogen and nitrogen-hydrogen mixture, the gas flow rate is increased to 800 sccm-1500 sccm, and the temperature is heated from 250℃-350℃ to 450℃-500℃ at an extremely slow heating rate of 0.1℃ / min-0.5℃ / min, so that the adhesive undergoes slow thermal decomposition under the inert atmosphere;

[0038] Preferably, in this specific embodiment, sub-step N2 involves heating to 450°C-500°C at a rate of 0.3°C / min and holding at that temperature for approximately 120 minutes to allow the adhesive to thermally decompose under a controlled atmosphere. Alternatively, sub-step N2 involves heating to 450°C-500°C at a rate of 0.2°C / min and holding at that temperature for approximately 100 minutes to allow the adhesive to thermally decompose under a controlled atmosphere.

[0039] N3, micro-oxidation to remove carbon and residues: After reaching 450℃-500℃, hold for 60 minutes-180 minutes. During this holding period, oxygen is introduced into the debinding furnace to form a micro-oxidation atmosphere to thoroughly remove carbon residues generated during pyrolysis.

[0040] In this specific embodiment, the oxygen content introduced into the debinding furnace is 1.5 vol.

[0041] N4. After the atmosphere is purified and carbon residue is removed, stop the oxygen supply and maintain an inert atmosphere in the debinding furnace. Raise the furnace temperature from 450℃-500℃ to 600℃-800℃ at a heating rate of 0.5℃ / min-1.0℃ / min, and hold at this temperature for 30-60 minutes.

[0042] In this specific embodiment, preferably, the furnace temperature is maintained at 700°C for 50 minutes. Alternatively, the furnace temperature is maintained at 750°C for 30 minutes.

[0043] Step 5: High-temperature co-firing. The multilayer substrate green blank that has been debonded is transferred to a high-temperature sintering furnace for sintering to form a dense multilayer aluminum nitride substrate.

[0044] The high-temperature co-firing sintering temperature is 1600℃-1800℃, the sintering time is 2 hours-6 hours, the sintering atmosphere is high-purity nitrogen, and the nitrogen flow rate is 5L / min·cm²-20L / min·cm².

[0045] In this specific embodiment, preferably, sintering is carried out at 1700°C for 4 hours, and the nitrogen flow rate is controlled at 10L / min·cm².

[0046] Step Six: Substrate Processing. The sintered multilayer aluminum nitride substrate undergoes shaping and polishing, followed by electroplating to improve solderability and oxidation resistance. Simultaneously, various performance tests are performed. More specifically, substrate processing includes three-dimensional precision machining of the sintered substrate, grinding and polishing to the target thickness and surface roughness, and subsequently, strength, roughness, thermal conductivity, and warpage performance tests.

[0047] in:

[0048] Warpage test: The warpage of the multilayer aluminum nitride substrate after ceramic bonding is measured using a parallel plate warpage tester. The standard spacing of the parallel plates = the standard thickness of the multilayer aluminum nitride substrate + the allowable warpage value (1.8‰).

[0049] Roughness test: The roughness of the multilayer aluminum nitride substrate was measured using a roughness tester.

[0050] Strength test: The multilayer aluminum nitride substrate was laser-scribed into a small board with a specification of 24mm×40mm, and then the strength of the multilayer aluminum nitride substrate was determined by fracture extrusion test using an electronic universal testing machine.

[0051] Thermal conductivity: Using an LFA467 thermal conductivity tester (10mm×2.0mm sample), the acceptable thermal conductivity range is ≥170W / (m·K).

[0052] The warpage test, roughness test, strength test, and thermal conductivity test were all performed on more than 10 multilayer aluminum nitride substrates, and the average value of the test results was taken.

[0053] By employing a multi-stage, extremely slow heating rate and switching inert atmospheres at different stages, the plasticizers, binders, and other organic substances are decomposed and removed gradually and completely. This avoids internal and external pressure differences and damage to the multilayer substrate green body caused by excessively rapid volatilization. Furthermore, a trace amount of oxygen is specifically introduced to remove carbon residue, preventing carbon from reducing circuitry or forming pores during high-temperature sintering. This ensures the density of the multilayer aluminum nitride substrate, thereby reducing the product defect rate and improving the quality and consistency of the final product. Simultaneously, it allows each layer of green ceramic sheet to bond firmly without significant deformation or misalignment, ensuring interlayer alignment accuracy and the strength of the multilayer substrate green body.

[0054] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended embodiments and their equivalents.

Claims

1. A method for preparing a multilayer aluminum nitride substrate, characterized in that, Includes the following steps: Step 1: Casting and forming. High-purity aluminum nitride powder, sintering aid, dispersant, binder and plasticizer are mixed in a preset ratio to prepare a uniform ceramic slurry. The ceramic slurry is cast into a green ceramic sheet of the required thickness using a casting machine. After drying, the green ceramic sheet is punched according to the design size, and the required connecting through holes are formed on the green ceramic sheet using laser drilling. Step 2: Filling and Printing Circuits. Use conductive paste to fill the connecting vias and print circuits on the surface of the green ceramic sheet. Step 3: Stacking and lamination. The printed circuit green ceramic sheets are precisely stacked in the design order so that the circuits on each green ceramic sheet are electrically connected through the conductive paste in the connecting through holes. Static pressure lamination is performed under the set temperature and pressure to firmly bond the green ceramic sheets into a whole multilayer substrate green blank. Step 4: Adhesive Removal. The multilayer substrate green sheet is placed in an adhesive removal furnace and heated slowly to gradually decompose and remove the adhesive and plasticizer from the green ceramic sheet. This includes the following sub-steps: N1. Low-temperature volatilization removal: The laminated multilayer substrate preform is placed in a descaling furnace. First, under the protection of an inert atmosphere with an inert gas, it is heated from room temperature to 250℃-350℃ at a heating rate of 0.5℃ / min-1.5℃ / min. After reaching the specified temperature, it is held for 30 minutes to 90 minutes to remove the plasticizer in the multilayer substrate preform. N2, adhesive pyrolysis and decomposition: After low-temperature volatilization and removal, the inert atmosphere in the adhesive removal furnace is switched to one of high-purity nitrogen and nitrogen-hydrogen mixture, the gas flow rate is increased to 800 sccm-1500 sccm, and the temperature is heated from 250℃-350℃ to 450℃-500℃ at an extremely slow heating rate of 0.1℃ / min-0.5℃ / min, so that the adhesive undergoes slow thermal decomposition under the inert atmosphere; N3, micro-oxidation to remove carbon and residues: After reaching 450℃-500℃, hold for 60 minutes-180 minutes. During this holding period, oxygen is introduced into the debinding furnace to form a micro-oxidation atmosphere to thoroughly remove carbon residues generated during pyrolysis. N4 atmosphere purification: After the carbon residue is removed, stop the oxygen supply, maintain the inert atmosphere in the debinding furnace, and raise the furnace temperature from 450℃-500℃ to 600℃-800℃ at a heating rate of 0.5℃ / min-1.0℃ / min, and hold at this temperature for 30 minutes-60 minutes. Step 5: High-temperature co-firing. The multilayer substrate green blank that has been debonded is transferred to a high-temperature sintering furnace for sintering to form a multilayer aluminum nitride substrate. Step 6: Substrate processing. The sintered multilayer aluminum nitride substrate is shaped and polished, and then electroplated to improve solderability and oxidation resistance.

2. The method for preparing a multilayer aluminum nitride substrate according to claim 1, characterized in that: The adhesive is an acrylic resin system, the plasticizer is a phthalate compound, and the conductive paste is a tungsten paste or a molybdenum-manganese paste.

3. The method for preparing a multilayer aluminum nitride substrate according to claim 1, characterized in that: In step three, the lamination and stacking are carried out using either isostatic pressing or hot pressing, with a lamination temperature of 60℃-100℃, a pressure of 5MPa-20MPa, and a holding time of 10 minutes-60 minutes.

4. The method for preparing a multilayer aluminum nitride substrate according to claim 1, characterized in that: In sub-step N1, the first inert gas introduced is argon, with a gas flow rate of 10 mL / min·cm²-50 mL / min·cm², and the vacuum degree is controlled at 10 Pa-100 Pa.

5. The method for preparing a multilayer aluminum nitride substrate according to claim 1, characterized in that: In step five, the sintering temperature for high-temperature co-firing is 1600℃-1800℃, the sintering time is 2 hours-6 hours, the sintering atmosphere is high-purity nitrogen, and the nitrogen flow rate is 5L / min·cm²-20L / min·cm².

6. The method for preparing a multilayer aluminum nitride substrate according to claim 1, characterized in that: In step six, the substrate processing includes three-dimensional precision machining of the sintered substrate, grinding and polishing to the target thickness and surface roughness, followed by strength, roughness, thermal conductivity and warpage performance tests.

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