Aluminum nitride thin film circuit substrate and method for manufacturing the same

Abstract

The application discloses an aluminum nitride film circuit substrate and a preparation method thereof, and relates to the technical field of aluminum nitride substrates.The application is characterized by the following steps: a titanium film is plated on the surface of an aluminum nitride ceramic substrate by magnetron sputtering, and then a copper film is plated on the surface of the titanium film by magnetron sputtering; and a nickel film is plated on the surface of the copper film by a chemical plating method to prepare the aluminum nitride film circuit substrate.Through the titanium-copper gradient dynamic transition technology, a gradient alloy layer is formed to reduce the interface stress; the titanium and the surface of the aluminum nitride are combined through a chemical bond to form a dense transition layer, thereby relieving the difference in the thermal expansion coefficient; the copper enhances the conductive performance of the surface of the aluminum nitride ceramic substrate; the titanium compensates for the interface defects of the mismatch between the copper and the aluminum nitride ceramic lattice; the chemical nickel plating enhances the hardness and corrosion resistance of the aluminum nitride ceramic substrate, and the aluminum nitride film substrate is endowed with weldability and bondability.

Description

Technical Field

[0001] This invention relates to the field of aluminum nitride substrate technology, specifically to an aluminum nitride thin-film circuit substrate and its preparation method. Background Technology

[0002] In recent years, copper thin-film circuit boards (DPCs) with semiconductor components mounted on a metal layer have been wildly popular. However, with the rapid development of miniaturization and integration of power devices, more stringent requirements have been placed on the heat dissipation performance and temperature resistance reliability of thin-film circuits. At the same time, requirements have also been placed on the substrate structure design and manufacturing process. Aluminum nitride ceramic is currently the ceramic with the highest thermal conductivity on the market, which is 5 to 8 times higher than that of alumina. Therefore, DPC substrates based on aluminum nitride are ideal substrates for high heat dissipation packaging.

[0003] The main preparation method of DPC is to achieve metallization of the ceramic substrate surface by magnetron sputtering or vapor deposition of seed layers such as copper / titanium copper / titanium tungsten on a ceramic substrate, followed by electroplating to thicken the substrate. Due to the lattice mismatch between copper and aluminum nitride, the coating of copper thin film circuit substrate has poor adhesion and poor heat resistance. In application scenarios above 200°C, the coating is prone to blistering or even peeling, which can no longer meet the needs of many high-temperature commercial applications. There is an urgent need to develop a new type of thin film circuit substrate to solve the above problems. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a method for preparing aluminum nitride thin-film circuit substrates, which features strong metal layer adhesion, high thermal conductivity, and long-term application at temperatures above 200°C without failure, thus meeting the requirements for high-temperature applications in the field of thin-film circuits and other electronic information technologies.

[0005] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a method for preparing an aluminum nitride thin film circuit substrate, comprising the following steps:

[0006] S1: Preparation of titanium-copper seed layer

[0007] An aluminum nitride ceramic substrate is taken and magnetron sputtering is performed to deposit a copper layer and a titanium layer sequentially on the surface of the aluminum nitride ceramic substrate to form a titanium-copper seed layer, thus obtaining aluminum nitride ceramic substrate A.

[0008] S2: Electroless nickel plating

[0009] Take the aluminum nitride ceramic substrate A obtained in S1, place it in a chemical nickel plating solution, and perform chemical nickel plating on the surface of the titanium-copper seed layer to form a nickel layer, thus obtaining a composite aluminum nitride ceramic substrate.

[0010] The above-mentioned technical effects are as follows: By chemically plating nickel, the aluminum nitride ceramic substrate has higher bonding strength and high temperature resistance, and also endows the aluminum nitride ceramic substrate with solderability and bonding properties; since the chemical bonding ability of nickel and titanium is significantly better than that of nickel and copper, copper is sputtered first and then titanium is sputtered during the magnetron sputtering process. Titanium compensates for the interface defects of lattice mismatch between copper and aluminum nitride, thereby improving the mechanical properties and chemical bonding stability of the aluminum nitride ceramic substrate.

[0011] S3: Vacuum sintering

[0012] The composite aluminum nitride ceramic substrate obtained in S2 was vacuum sintered and cooled to room temperature in the furnace to form a thin film, thus obtaining the composite aluminum nitride ceramic substrate B.

[0013] S4: Chemical Etching

[0014] A photosensitive film is deposited on the surface of the composite aluminum nitride ceramic substrate B obtained in S3, and then exposed, developed, and chemically etched to form a thin film circuit, thus obtaining an aluminum nitride thin film circuit substrate.

[0015] Furthermore, in step S1, the copper layer has a thickness of 50nm to 800nm, and the titanium layer has a thickness of 20 to 300nm.

[0016] Furthermore, in step S1, the cleaning process is as follows: at a temperature of 35℃~65℃, clean with 3%~15% NaOH solution for 10~20 minutes; the drying process is as follows: under a nitrogen atmosphere oven, dry at a temperature of 80~100℃ for 10~30 minutes.

[0017] Furthermore, in step S2, the electroless nickel plating solution comprises the following components by mass: 5%–15% nickel sulfate heptahydrate (NiSO4·7H2O), 2%–8% sodium hypophosphite (NaH2PO2·H2O), 1%–5.5% sodium acetate trihydrate (NaC2H3O2), 3%–7% sodium citrate (Na3C6H5O7·2H2O), and the remainder is pure water.

[0018] Furthermore, the pH of the electroless nickel plating solution is 4–5.5.

[0019] The above-mentioned technical effects are as follows: Nickel sulfate is the main salt in the plating solution, providing nickel ions for the plating solution; sodium hypophosphite is a commonly used reducing agent for chemical nickel plating; the synergistic effect of sodium citrate and sodium acetate trihydrate forms a stable complex, inhibiting the hydrolysis of nickel ions; the dense and non-porous characteristics of the nickel layer increase the corrosion resistance of the aluminum nitride thin film substrate.

[0020] Furthermore, in step S2, ultrasonic-assisted dispersion is used during the electroless nickel plating process, with a frequency of 20–50 Hz; the nickel plating temperature is 60–85 °C; and the drying process conditions are: drying at 60–80 °C for 5–15 min.

[0021] Furthermore, in step S2, the thickness of the nickel layer is 2–20 μm.

[0022] Furthermore, in step S3, the sintering process conditions are: vacuum degree < 0.01 Pa, heating to 650-900℃ at a rate of 10℃ / min to 25℃ / min, and holding at that temperature for 2-5 hours.

[0023] Furthermore, in step S4, the etching solution used for chemical etching includes the following components by mass: 1% to 7% of a fluorine-containing compound, 10% to 25% of nickel stripping powder, 1% to 5% of a corrosion inhibitor, and the balance being pure water.

[0024] Furthermore, the fluorinated compound is hydrofluoric acid.

[0025] Furthermore, the nickel removal powder comprises the following components by mass: 45-50% sodium nitrate (NaNO3), 25-30% sodium chloride (NaCl), and 10-25% sodium hydroxide (NaOH).

[0026] Furthermore, the corrosion inhibitor is thiourea.

[0027] Furthermore, in step S4, the chemical etching pressure is 0.2–0.5 MPa.

[0028] The above-mentioned technical effects are as follows: Adding nickel removal powder to the chemical etching solution dissolves the nickel oxide layer through a chemical reaction, restoring the surface of the ceramic substrate to the active state of metallic nickel, providing a clean substrate for metal layer patterning, and ensuring precise etching. Sodium nitrate acts as a strong oxidant, and sodium chloride ionizes into sodium ions and chloride ions in the solution, enhancing conductivity and thus improving nickel removal efficiency. Sodium hydroxide can neutralize acidic substances in the solution, maintain the chemical stability of the solution, and ensure that the nickel removal reaction proceeds in the expected direction.

[0029] Furthermore, the process for step S1 is as follows:

[0030] First, the aluminum nitride ceramic substrate was cleaned in NaOH solution, dried in a nitrogen atmosphere oven, and then heat-treated. Next, copper and titanium were sequentially sputtered using DC magnetron sputtering at a target power of 100–150 W, a substrate negative bias of -90 V to -70 V, an argon flow rate of 30–40 sccm, a working pressure of 0.3–0.5 Pa, and a deposition time of 20–30 min. The copper target power was gradually decreased and the titanium target power increased through dynamic transition. The copper sputtering power was reduced from 100–150 W to 0 W, while the titanium sputtering power was increased from 0 W to 100–150 W. After turning off the copper target, sputtering continued for 10–30 min at a titanium target power of 100–150 W. Finally, the substrate was heat-treated to obtain aluminum nitride ceramic substrate A.

[0031] Furthermore, the rate of the dynamic transition is 7.5–15 W / min, and the time is 10–15 min.

[0032] Furthermore, the heat treatment process is as follows: heating to 600-700℃, holding at that temperature for 1-2 hours, and cooling to room temperature at a rate of 10-20℃ / min.

[0033] The above-mentioned technical effects are as follows: NaOH solution is used for surface cleaning, which decomposes organic contaminants such as grease and fingerprints on the ceramic substrate surface through saponification, providing a clean surface for subsequent metal bonding processes and preventing impurities from affecting the adhesion of the coating; the aluminum nitride ceramic substrate undergoes heat treatment, releasing residual stress and improving the surface flatness; a gradient alloy layer is formed through gradient dynamic transition technology to reduce interfacial stress; the seed layer and the aluminum nitride surface are chemically bonded to form a dense transition layer, mitigating the difference in thermal expansion coefficients; copper atoms coated on the surface of the aluminum nitride ceramic substrate enhance its conductivity; heat treatment after magnetron sputtering promotes titanium-copper interface diffusion, reduces grain boundary defects, and improves its conductivity and mechanical strength.

[0034] Furthermore, the electroless nickel plating solution also includes 1% to 4% aluminum oxide (Al2O3).

[0035] The above-mentioned technical effects are as follows: Adding aluminum oxide to the electroless nickel plating solution, as an alumina filler to increase thermal conductivity, can significantly improve hardness and wear resistance, increase the nickel plating rate, and at the same time increase the thermal conductivity of aluminum nitride thin film circuit boards.

[0036] The photosensitive film is evenly applied by a laminating machine, and pressure control and temperature regulation ensure that there are no bubbles or wrinkles, providing physical support for high-resolution graphics. Through the synergistic effect of exposure and development, non-circuit areas are precisely removed, significantly improving resolution. The oxidation-reduction reaction of chemical solution and metal is used to selectively remove exposed metal, improving etching uniformity and reducing surface roughness.

[0037] Compared with the prior art, the beneficial effects of the present invention are:

[0038] 1. The aluminum nitride thin film circuit board of the present invention uses a mixture of nickel, copper and phosphorus elements to reduce the melting point of nickel and promote rapid diffusion and solidification, while the titanium base layer improves the bonding strength. It does not produce molten liquid and avoids the problem of uneven molding caused by cooling flow and shrinkage.

[0039] 2. The aluminum nitride thin film circuit board of the present invention is simple to operate by chemical nickel plating, with uniform plating and corrosion resistance; it meets the requirements of electrofusion connection, has a uniform surface and high thermal conductivity; it can match the current carrying capacity requirements of thin film substrates and has high circuit accuracy.

[0040] 3. The aluminum nitride thin film circuit board of the present invention, by adding thermally conductive filler and adding aluminum oxide to the nickel plating solution, not only improves the hardness and wear resistance, but also increases the chemical nickel plating rate, and at the same time increases the thermal conductivity of the aluminum nitride thin film board.

[0041] 4. The aluminum nitride thin film circuit board of the present invention has a simple manufacturing process. The substrate has nickel properties and can directly bond functional components or further gold / silver plating processes to meet the packaging requirements of the substrate. Attached Figure Description

[0042] Figure 1 This is a flowchart of the present invention;

[0043] Figure 2 This is a surface view of the aluminum nitride thin film circuit substrate of Embodiment 1 of the present invention;

[0044] Figure 3 This is a cross-sectional SEM image of the aluminum nitride thin film circuit substrate of Embodiment 1 of the present invention; Detailed Implementation

[0045] The technical solutions in the embodiments of the present invention will be clearly and completely described below. 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.

[0046] In the following specific implementation:

[0047] The nickel removal powder comprises the following components by weight: 50% sodium nitrate (NaNO3), 25% sodium chloride (NaCl), and 25% sodium hydroxide (NaOH);

[0048] The fluorinated compound is hydrofluoric acid;

[0049] The corrosion inhibitor is thiourea;

[0050] Alumina, with a particle size of 30nm, model number DK410-1;

[0051] Example 1: A method for preparing an aluminum nitride thin-film circuit substrate, the preparation process is as follows:

[0052] Step 1: Preparation of the titanium-copper seed layer

[0053] A 0.638 mm aluminum nitride ceramic substrate was cleaned with 12% NaOH solution at 50 °C for 13 min, and then placed in a nitrogen atmosphere oven and dried at 95 °C for 15 min. After removal, a copper layer and a titanium layer were sequentially deposited on the surface of the aluminum nitride ceramic by magnetron sputtering to form a titanium-copper seed layer. The target power was 150 W, the substrate negative bias was -90 V, the argon flow rate was 32 sccm, the working pressure was 0.3 Pa, and the deposition time was 20 min. The copper layer thickness was 360 nm and the titanium layer thickness was 50 nm, resulting in aluminum nitride ceramic substrate a.

[0054] Step 2: Electroless Nickel Plating

[0055] An aluminum nitride ceramic substrate a was placed in a chemical nickel plating solution, and nickel was chemically plated on the surface of the titanium-copper seed layer to form a nickel layer. The nickel plating was carried out at 75°C for 30 min, followed by drying in a nitrogen atmosphere oven at 70°C for 7 min to obtain a composite aluminum nitride ceramic substrate. The chemical nickel plating solution consisted of 10% NiSO4·7H2O, 3% NaH2PO2·H2O, 2% NaC2H3O2, 3% Na3C6H5O7·2H2O, with the remainder being pure water and a pH of 4.2. The nickel layer thickness was 4.3 μm.

[0056] Step 3: Vacuum sintering

[0057] The composite aluminum nitride ceramic substrate obtained in step two was vacuum sintered at a vacuum degree of 0.001 Pa, a heating rate of 15 °C / min, heated to 700 °C, held for 3 h, and then cooled to room temperature in the furnace to obtain composite aluminum nitride ceramic substrate b.

[0058] Step 4: Chemical Etching

[0059] A photosensitive film is deposited on the surface of a composite aluminum nitride ceramic substrate b, exposed, developed, and chemically etched to form a thin film circuit. The etching pressure is 0.3 MPa. The remaining photosensitive film is removed to obtain an aluminum nitride thin film circuit substrate. Figure 2 This is a view of the substrate surface. Figure 3 The image shows the cross-sectional SEM morphology of the substrate. The chemical etching solution consists of 2% fluorine-containing compound, 13% nickel stripping powder, 5% etching inhibitor, and the remainder is water.

[0060] Example 2: A method for preparing an aluminum nitride thin-film circuit substrate, the preparation process is as follows:

[0061] Step 1: Preparation of the titanium-copper seed layer

[0062] A 0.635 mm thick aluminum nitride ceramic substrate was cleaned with 12% NaOH solution at 55°C for 15 min, then placed in a nitrogen atmosphere oven and dried at 90°C for 18 min. After removal, magnetron sputtering was performed to sequentially deposit a copper layer and a titanium layer on the aluminum nitride ceramic surface, forming a titanium-copper seed metal layer. The copper target power was 120 W, the substrate negative bias was -80 V, the argon flow rate was 35 sccm, the working pressure was 0.4 Pa, and the deposition time was 25 min. The copper content was reduced through dynamic transition. The target power was gradually increased for titanium target power, while the copper sputtering power was reduced from 120W to 0W and the titanium sputtering power was increased from 0W to 120W. After the copper target was turned off, sputtering continued for 20 minutes at a titanium target power of 120W. The dynamic transition rate was 10W / min and the time was 12 minutes. Heat treatment was performed by heating to 650℃ and holding for 1.5 hours. The temperature was then reduced to room temperature at a rate of 15℃ / min. The copper layer thickness was 350nm and the titanium layer thickness was 60nm, resulting in aluminum nitride ceramic substrate a.

[0063] Step 2: Electroless Nickel Plating

[0064] An aluminum nitride ceramic substrate a was placed in a chemical nickel plating solution, and nickel was chemically plated onto the surface of the titanium-copper seed layer to form a nickel layer. The nickel plating was carried out at 70°C for 30 min, followed by drying in a nitrogen atmosphere oven at 70°C for 7 min to obtain a composite aluminum nitride ceramic substrate. The chemical nickel plating solution consisted of the following components: 12% NiSO4·7H2O, 3% NaH2PO2·H2O, 2% Al2O3, 2.5% NaC2H3O2, 4% Na3C6H5O7·2H2O, with the remainder being pure water; the pH was 4.5; and the nickel layer thickness was 4.3 μm.

[0065] Step 3: Vacuum sintering

[0066] The composite aluminum nitride ceramic substrate obtained in step two was subjected to vacuum sintering at a vacuum degree of 0.005 Pa, a heating rate of 20 °C / min, and a temperature of 700 °C. The temperature was held for 4 hours and then cooled to room temperature in the furnace to obtain composite aluminum nitride ceramic substrate b.

[0067] Step 4: Chemical Etching

[0068] A photosensitive film is deposited on the surface of a composite aluminum nitride ceramic substrate b, exposed, developed, and chemically etched to form a thin film circuit. The etching pressure is 0.4 MPa. The remaining photosensitive film is removed to obtain an aluminum nitride thin film circuit substrate. The chemical etching solution consists of 5% fluorine-containing compound, 15% nickel stripping powder, 5% corrosion inhibitor, and the balance is water.

[0069] Example 3: A method for preparing an aluminum nitride thin-film circuit substrate, the preparation process is as follows:

[0070] Step 1: Preparation of the titanium-copper seed layer

[0071] A 0.645 mm thick aluminum nitride ceramic substrate was cleaned with 14% NaOH solution at 60 °C for 18 min, then placed in a nitrogen atmosphere oven and dried at 95 °C for 25 min. The substrate was then removed and subjected to magnetron sputtering to deposit a copper layer and a titanium layer sequentially on the aluminum nitride ceramic surface, forming a titanium-copper seed layer. The copper target power was 100 W, the substrate negative bias was -70 V, the argon flow rate was 30 sccm, the working pressure was 0.5 Pa, and the deposition time was 28 min. The copper target power was gradually decreased and the titanium target power gradually increased through dynamic transition. The copper sputtering power decreased from 100 W to 0 W, and the titanium sputtering power increased from 0 W to 100 W. After turning off the copper target, sputtering continued for 10 min at a titanium target power of 100 W. The dynamic transition rate was 15 W / min for 15 min. Heat treatment was performed at 700 °C for 2 h, followed by cooling to room temperature at a rate of 20 °C / min. The copper layer thickness was 500 nm, and the titanium layer thickness was 150 nm, resulting in aluminum nitride ceramic substrate a.

[0072] Step 2: Electroless Nickel Plating

[0073] An aluminum nitride ceramic substrate a was placed in a chemical nickel plating solution, and nickel was chemically plated onto the surface of the titanium-copper seed layer to form a nickel layer. The nickel plating was carried out at 75°C for 30 min, followed by drying in a nitrogen atmosphere oven at 70°C for 7 min to obtain a composite aluminum nitride ceramic substrate. The chemical nickel plating solution consisted of the following components: 14% NiSO4·7H2O, 7% NaH2PO2·H2O, 4% Al2O3, 4% NaC2H3O2, 6% Na3C6H5O7·2H2O, with the remainder being pure water; the pH was 5.0; and the nickel layer thickness was 4.3 μm.

[0074] Step 3: Vacuum sintering

[0075] The composite aluminum nitride ceramic substrate obtained in step two was vacuum sintered at a vacuum degree of 0.001 Pa, a heating rate of 15 °C / min, and heated to 700 °C. The temperature was held for 3 hours and then cooled to room temperature in the furnace to obtain composite aluminum nitride ceramic substrate b.

[0076] Step 4: Chemical Etching

[0077] A photosensitive film is deposited on the surface of a composite aluminum nitride ceramic substrate b, exposed, developed, and chemically etched to form a thin film circuit. The etching pressure is 0.3 MPa. The remaining photosensitive film is removed to obtain an aluminum nitride thin film circuit substrate. The etching solution used for chemical etching consists of: 4% fluorine-containing compound, 24% nickel stripping powder, 5% corrosion inhibitor, and the balance is water.

[0078] Comparative Example 1: A method for preparing an aluminum nitride thin-film circuit substrate, the preparation process of which is as follows:

[0079] Step 1: Preparation of the titanium-copper seed layer

[0080] A 0.644 mm thick aluminum nitride ceramic substrate was cleaned with 13% NaOH solution at 60°C for 18 min, and then dried in a nitrogen atmosphere oven at 95°C for 25 min. After removal, chromium, nickel, and copper seed metal layers were sequentially deposited on its surface using magnetron sputtering. The chromium target power was 110 W, the substrate negative bias was -70 V, the argon flow rate was 30 sccm, the working pressure was 0.5 Pa, and the deposition time was 28 min. The chromium target power was gradually decreased and the nickel target power gradually increased through a dynamic transition, with the chromium sputtering power decreasing from 110 W to 0 W and the nickel sputtering power increasing from 0 W to 110 W. After shutting off the chromium target, sputtering continued for 10 minutes at a nickel target power of 110W. The nickel target power was gradually reduced and the copper target power was gradually increased through dynamic transition. The nickel sputtering power was reduced from 110W to 0W, and the copper sputtering power was increased from 0W to 110W. After shutting off the nickel target, sputtering continued for 10 minutes at a copper target power of 110W. The dynamic transition rate was 15W / min and the time was 15min. Heat treatment was performed by heating to 700℃ and holding for 2 hours. The temperature was then reduced to room temperature at a rate of 20℃ / min. The copper layer thickness was 450nm and the titanium layer thickness was 120nm, resulting in an aluminum nitride ceramic substrate a.

[0081] Step 2: Electroless Nickel Plating

[0082] An aluminum nitride ceramic substrate a was placed in a chemical nickel plating solution to form a nickel layer. The nickel plating was performed at 75°C for 30 minutes. After the nickel plating was completed, the substrate was dried at 70°C under a nitrogen atmosphere for 7 minutes to obtain a composite aluminum nitride ceramic substrate. The chemical nickel plating solution consisted of the following components: 10% NiSO4·7H2O, 3% NaH2PO2·H2O, 2% NaC2H3O2, 3% Na3C6H5O7·2H2O, with the remainder being pure water; the pH was 4.2; and the nickel layer thickness was 4.3 μm.

[0083] Step 3: Vacuum sintering

[0084] The composite aluminum nitride ceramic substrate obtained in step two was vacuum sintered at a vacuum degree of 0.001 Pa, a heating rate of 15 °C / min, heated to 700 °C, held for 3 h, and then cooled to room temperature in the furnace to obtain composite aluminum nitride ceramic substrate b.

[0085] Step 4: Chemical Etching

[0086] A photosensitive film is deposited on the surface of a composite aluminum nitride ceramic substrate b, exposed, developed, and chemically etched to form a thin film circuit. The etching pressure is 0.3 MPa. The remaining photosensitive film is removed to obtain an aluminum nitride thin film circuit substrate. The chemical etching solution consists of 4% fluorine-containing compound, 24% nickel stripping powder, 5% corrosion inhibitor, and the balance is water.

[0087] Comparative Example 2: A method for preparing an aluminum nitride thin-film circuit substrate, the preparation process of which is as follows:

[0088] Step 1: Preparation of the titanium-copper seed layer

[0089] A 0.638 mm thick aluminum nitride ceramic substrate was cleaned with 12% NaOH solution at 50 °C for 13 min, and then dried in a nitrogen atmosphere oven at 95 °C for 15 min. The substrate was then removed, and copper and titanium seed metal layers were sequentially deposited on its surface using magnetron sputtering. The copper target power was 150 W, the substrate negative bias was -90 V, the argon flow rate was 32 sccm, the working pressure was 0.3 Pa, and the deposition time was 20 min. The copper target power was gradually decreased and the titanium target power was gradually increased through dynamic transition. The copper sputtering power decreased from 150 W to 0 W, and the titanium sputtering power increased from 0 W to 150 W. After turning off the copper target, sputtering continued for 10 min at a titanium target power of 150 W. The dynamic transition rate was 7.6 W / min, and the time was 12 min. The substrate was then heat-treated to 600 °C and held for 1 h. It was then cooled to room temperature at a rate of 10 °C / min. The copper layer thickness was 440 nm, and the titanium layer thickness was 110 nm, resulting in aluminum nitride ceramic substrate a.

[0090] Step 2: Electroplating nickel onto aluminum nitride ceramic substrate

[0091] Take an aluminum nitride ceramic substrate a, and plate it with nickel using electroplating at a current density of 0.5 A / dm³. 2 The nickel plating solution was prepared at 50℃ for 30 minutes, followed by rinsing with deionized water and drying at 70℃ under nitrogen atmosphere for 7 minutes to obtain a composite aluminum nitride ceramic substrate. The nickel plating solution consisted of 14% NiSO4·7H2O, 7% Ni(NH2SO3)2, 4% H3BO3, 6% NiCl2·6H2O, 8% Na2SO4, with the remainder being pure water; the pH was 5.0; and the nickel layer thickness was 4.3 μm.

[0092] Step 3: Vacuum sintering

[0093] The composite aluminum nitride ceramic substrate obtained in step two was vacuum sintered at a vacuum degree of 0.001 Pa, a heating rate of 15 °C / min, and heated to 700 °C. The temperature was held for 3 hours and then cooled to room temperature in the furnace to obtain composite aluminum nitride ceramic substrate b.

[0094] Step 4: Pattern Etching of Aluminum Nitride Thin Film Substrate

[0095] A photosensitive film is deposited on the surface of a composite aluminum nitride ceramic substrate b, exposed, developed, and chemically etched to form a thin film circuit. The etching pressure is 0.3 MPa. The remaining photosensitive film is removed to obtain an aluminum nitride thin film circuit substrate. The chemical etching solution consists of 2% fluorine-containing compound, 13% nickel stripping powder, 5% corrosion inhibitor, and the balance is water.

[0096] Comparative Example 3: A method for preparing an aluminum nitride thin-film circuit substrate, the preparation process of which is as follows:

[0097] Step 1: Preparation of the titanium-copper seed layer

[0098] A 0.635 mm thick aluminum nitride ceramic substrate was cleaned at 60°C with 13% NaOH solution for 14 min, and then dried at 96°C in a nitrogen atmosphere oven for 16 min. The substrate was then removed, and copper and titanium seed metal layers were deposited on its surface using magnetron sputtering. The copper target power was 140 W, the substrate negative bias was -80 V, the argon flow rate was 31 sccm, the working pressure was 0.3 Pa, and the deposition time was 20 min. The titanium target was then turned off, and sputtering continued at 150 W for 10 min. The substrate was then heat-treated to 600°C and held for 1 h. It was then cooled to room temperature at a rate of 10°C / min. The copper layer thickness was 350 nm, and the titanium layer thickness was 60 nm, resulting in aluminum nitride ceramic substrate a.

[0099] Step 2: Electroless Nickel Plating

[0100] An aluminum nitride ceramic substrate a was placed in a chemical nickel plating solution, and nickel was chemically plated onto the surface of the titanium-copper seed layer to form a nickel layer. The nickel plating was carried out at 75°C for 30 min, followed by drying at 70°C under a nitrogen atmosphere for 7 min to obtain a composite aluminum nitride ceramic substrate. The chemical nickel plating solution consisted of the following components: 11% NiSO4·7H2O, 4% NaH2PO2·H2O, 3% Al2O3, 2% NaC2H3O2, 3% Na3C6H5O7·2H2O, with the remainder being pure water; the pH was 4.2; and the nickel layer thickness was 4.5 μm.

[0101] Step 3: Vacuum sintering

[0102] The composite aluminum nitride ceramic substrate obtained in step two was vacuum sintered at a vacuum degree of 0.001 Pa, a heating rate of 15 °C / min, and heated to 700 °C. The temperature was held for 3 hours and then cooled to room temperature in the furnace to obtain composite aluminum nitride ceramic substrate b.

[0103] Step 4: Chemical Etching

[0104] A photosensitive film is deposited on the surface of a composite aluminum nitride ceramic substrate b, exposed, developed, and chemically etched to form a thin film circuit. The etching pressure is 0.3 MPa. The remaining photosensitive film is removed to obtain an aluminum nitride thin film circuit substrate. The chemical etching solution consists of 2% fluorine-containing compound, 13% nickel stripping powder, 5% corrosion inhibitor, and the balance is water.

[0105] Comparative Example 4: A method for preparing an aluminum nitride thin-film circuit substrate, the preparation process of which is as follows:

[0106] Step 1: Electroless Nickel Plating

[0107] A 0.633 mm thick aluminum nitride ceramic substrate was cleaned with a 13% NaOH solution at 60°C for 14 min, dried in a nitrogen atmosphere oven at 96°C for 16 min, removed, and placed in a chemical nickel plating solution for chemical nickel plating to form a nickel layer. The nickel plating was then carried out at 75°C for 30 min, followed by drying in a nitrogen atmosphere oven at 70°C for 7 min to obtain a composite aluminum nitride ceramic substrate. The chemical nickel plating solution consisted of 10% NiSO4·7H2O, 3% NaH2PO2·H2O, 2% NaC2H3O2, 3% Na3C6H5O7·2H2O, with the remainder being pure water, and a pH of 4.2. The nickel layer thickness was 4.3 μm.

[0108] Step 2: Vacuum sintering

[0109] The composite aluminum nitride ceramic substrate was sintered under vacuum conditions with a vacuum degree of 0.001 Pa, a heating rate of 15 °C / min, and heated to 700 °C. The temperature was held for 3 hours and then cooled to room temperature in the furnace to obtain aluminum nitride ceramic substrate a.

[0110] Step 3: Chemical Etching

[0111] Take an aluminum nitride ceramic substrate a, lay a photosensitive film on its surface, expose and develop it, chemically etch it at an etching pressure of 0.3 MPa, remove the remaining photosensitive film, and obtain an aluminum nitride thin film circuit substrate; the chemical etching solution consists of: 3% fluorine-containing compound, 14% nickel stripping powder, 5% corrosion inhibitor, and the balance is water.

[0112] Experiment: The substrates obtained in Examples 1-3 and Comparative Examples 1-4 were placed in a muffle furnace and kept at 350℃ for 3 hours. No blistering or peeling of the coating was detected. Figure 3 The image shows the cross-sectional SEM morphology of the substrate after muffle furnace testing. No delamination was observed, indicating that the substrate meets commercial requirements.

[0113] The aluminum nitride thin film circuit boards obtained in Examples 1-3 and Comparative Examples 1-4 were used to prepare samples, and their performance was tested and the test results were recorded:

[0114] Thermal conductivity test: Referring to GB 5598-85 standard, the back of the sample is irradiated with laser pulses, and the temperature change curve of the front side over time is recorded by infrared thermometer. The thermal diffusivity is calculated. The thermal conductivity is calculated by combining the specific heat capacity and density of the sample.

[0115] Thermal expansion coefficient test: Referring to ASTM E831 standard, the aluminum nitride thin film circuit board was placed at 25°C for 10 minutes and then gradually heated to 300°C. The length change was measured and the thermal expansion coefficient was calculated.

[0116] Peel strength test: Refer to IPC-TM-650 standard, and measure its 90° peel strength using a universal testing machine under normal temperature and pressure conditions;

[0117] Performance Comparison Table

[0118]

[0119] Based on the data in the table above, the following conclusions can be clearly drawn:

[0120] The aluminum nitride thin film circuit substrates obtained in Examples 1-3 are compared with those obtained in Comparative Examples 1-4. The test results show that:

[0121] Compared with the comparative examples, the aluminum nitride thin film circuit boards obtained in Examples 1-3 have higher thermal conductivity, lower coefficient of thermal expansion, and greater peel strength.

[0122] Compared with Example 1, the aluminum nitride thin film circuit substrate obtained in Comparative Example 1 uses chromium, nickel, and copper as surface metal seed layer treatment, resulting in low thermal conductivity, low thermal performance, and a large coefficient of thermal expansion. It is prone to cracking after being affected by temperature. The peel strength is comparable. It can be seen that the aluminum nitride thin film circuit substrate prepared by the preparation process of the present invention does not have the same performance as the surface deposition treatment using chromium, nickel, and copper.

[0123] Compared with Example 1, the aluminum nitride thin film circuit substrate in Comparative Example 2 uses electroplated nickel instead of chemical nickel plating. The resulting aluminum nitride thin film circuit substrate has low thermal conductivity, high coefficient of thermal expansion, and low peel strength. It can be seen that if electroplated nickel is used instead of chemical nickel plating, the nickel layer is not as uniform as that plated by chemical nickel plating, the thermal conductivity is poor, the thermal stress of the material is high, it is easy to tear, the stability of the aluminum nitride ceramic substrate is poor, and the internal structure of the nickel layer and the metal seed layer is not uniformly dispersed. Using chemical nickel plating can uniformly plate nickel, and the bonding performance and peel strength are greater.

[0124] Compared to Example 1, the aluminum nitride thin film circuit substrate in Comparative Example 3 does not employ the titanium / copper gradient dynamic transition technology. The resulting substrate has lower thermal conductivity, higher coefficient of thermal expansion, and lower peel strength. This indicates that without the titanium / copper gradient dynamic transition technology, the aluminum nitride thin film circuit substrate has lower thermal conductivity, higher thermal stress on the material, less stable performance of the aluminum nitride ceramic substrate, and uneven internal structure dispersion of the metal seed layer. Using the titanium / copper gradient dynamic transition technology avoids thickness fluctuations caused by differences in substrate conductivity or geometry, and also provides better thermal conductivity and lower thermal stress between the material and the metal seed layer.

[0125] Compared with Example 1, the aluminum nitride thin film circuit substrate prepared by nickel plating surface treatment in Comparative Example 4 has lower thermal conductivity, higher coefficient of thermal expansion, and lower peel strength. Compared with other Comparative Examples 1-3, it has the lowest thermal conductivity, the highest coefficient of thermal expansion, and the lowest peel strength. It can be seen that the aluminum nitride thin film circuit substrate without magnetron sputtering surface treatment has poor thermal conductivity, low thermal stress, and low peel strength, and cannot meet the requirements of both high frequency and high thermal conductivity.

[0126] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

Claims

1. A method for producing an aluminum nitride thin film circuit substrate, characterized by comprising the steps of: The method comprises the following steps: S1: titanium copper seed layer preparation: taking an aluminum nitride ceramic substrate, performing magnetron sputtering, and sequentially depositing a copper layer and a titanium layer on the surface of the aluminum nitride ceramic substrate to form a titanium copper seed layer, thereby obtaining an aluminum nitride ceramic substrate A; ​ S2: electroless nickel plating: taking the aluminum nitride ceramic substrate A obtained in S1, placing it in an electroless nickel plating solution, and performing electroless nickel plating on the surface of the titanium copper seed layer to form a nickel layer, thereby obtaining a composite aluminum nitride ceramic substrate; S3: vacuum sintering: performing vacuum sintering on the composite aluminum nitride ceramic substrate obtained in S2, and cooling to room temperature in the furnace to form a thin film, thereby obtaining a composite aluminum nitride ceramic substrate B; S4: chemical etching: laying a photosensitive film on the surface of the composite aluminum nitride ceramic substrate B obtained in S3, exposing and developing, and performing chemical etching to form a thin film circuit, thereby obtaining an aluminum nitride thin film circuit substrate; In step S2, the electroless nickel plating solution comprises the following mass components: 5-15% nickel sulfate heptahydrate, 2-8% sodium hypophosphite, 1-5.5% sodium acetate trihydrate, 3-7% sodium citrate, and the rest is pure water; the thickness of the nickel layer is 2-20 μm; the electroless nickel plating solution further comprises 1-4% aluminum oxide; In step S4, the etching solution used for chemical etching comprises the following mass components: 1-7% fluorine-containing compound, 10-25% denickelizing powder, 1-5% corrosion inhibitor, and the rest is pure water; The process of step S1 is as follows: First, the aluminum nitride ceramic substrate is placed in a NaOH solution for cleaning, dried in a nitrogen atmosphere oven, and heat treated; then, copper and titanium are sputtered in sequence by using direct current magnetron sputtering, the target power is 100-150 W, the substrate negative bias is -90 V to -70 V, the argon flow rate is 30-40 sccm, the working gas pressure is 0.3-0.5 Pa, the deposition time is 20-30 min, the copper target power is gradually reduced and the titanium target power is gradually increased by using gradient dynamic transition technology, the copper sputtering power is reduced from 100-150 W to 0 W, the titanium sputtering power is increased from 0 W to 100-150 W, the copper target is turned off, and the titanium target is continuously sputtered at a power of 100-150 W for 10-30 min, heat treated, and the aluminum nitride ceramic substrate A is obtained; The process conditions of the gradient dynamic transition technology are as follows: the rate of dynamic transition is 7.5-15 W / min, and the time is 10-15 min.

2. The method of claim 1, wherein the aluminum nitride film circuit substrate is prepared by the steps of: In step S1, the cleaning process is as follows: the temperature is 35-65°C, the substrate is cleaned with a 3-15% NaOH solution for 10-20 min, and the drying process is as follows: the substrate is dried in a nitrogen atmosphere oven at a temperature of 80-100°C for 10-30 min. ​ 3. The method of claim 1, wherein the aluminum nitride film circuit substrate is prepared by the steps of: In step S1, the thickness of the copper layer is 50-800 nm, and the thickness of the titanium layer is 20-300 nm. ​ 4. The method of claim 1, wherein the aluminum nitride film circuit substrate is prepared by the steps of: In step S3, the process conditions of sintering are as follows: the vacuum degree is less than 0.01 Pa, the temperature is increased to 650-900°C at a rate of 10-25°C / min, and the temperature is maintained for 2-5 h; in step S4, the pressure of pattern etching is 0.2-0.5 MPa. ​ 5. The method of claim 1, wherein the aluminum nitride film circuit substrate is prepared by the steps of: The process conditions of the heat treatment are as follows: the heating temperature is 600-700°C, the temperature is maintained for 1-2 h, the temperature is cooled to room temperature at a rate of 10-20°C / min. ​ 6. An aluminum nitride thin film circuit substrate, characterized by: Prepared according to the process of any one of claims 1-5.

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