Aluminum nitride film circuit substrate and preparation method thereof

Abstract

The invention discloses an aluminum nitride film circuit substrate and a preparation method thereof, and relates to the technical field of aluminum nitride substrates. Titanium plating and copper plating are sequentially carried out on the surface of the aluminum nitride ceramic substrate through magnetron sputtering, and the aluminum nitride film circuit substrate is prepared in cooperation with a chemical nickel plating method. A gradient alloy layer is formed through a titanium-copper gradient dynamic transition technology to reduce interface stress, titanium and the surface of aluminum nitride are combined through chemical bonds to form a compact transition layer to relieve the difference of thermal expansion coefficients, copper on the surface of an aluminum nitride ceramic substrate enhances the conductivity of the aluminum nitride ceramic substrate, and titanium makes up the interface defect that copper and aluminum nitride ceramic lattices are not matched. Through chemical nickel plating, the hardness and the corrosion resistance of the aluminum nitride ceramic substrate are enhanced, and the weldability and the bonding property of the aluminum nitride film substrate are endowed.

Description

Technical Field

[0001] The present invention relates to the technical field of aluminum nitride substrates, in particular to an aluminum nitride thin film circuit substrate and a preparation method thereof. Background Art

[0002] In recent years, copper thin film circuit substrates (DPC) with semiconductor components mounted on a metal layer have been wildly sought after. 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 ceramics are currently the ceramics with the highest commercial thermal conductivity on the market, 5 to 8 times higher than aluminum oxide. Therefore, DPC liner based on aluminum nitride is an ideal liner in the field of high heat dissipation packaging.

[0003] The main preparation method of DPC is to magnetron sputter or evaporate a seed layer of copper / titanium copper / titanium tungsten on a ceramic substrate to achieve metallization of the ceramic substrate surface and then electroplating thickening. Due to the lattice mismatch between copper and aluminum nitride, the copper thin film circuit substrate coating has poor adhesion and poor heat resistance. In application scenarios above 200°C, the coating is prone to blistering and even peeling, which can no longer meet the use requirements of many high-temperature commercial scenarios. It is urgent to develop a new type of thin film circuit substrate to solve the above problems. Summary of the Invention

[0004] In response to the shortcomings of the existing technology, the present invention provides a method for preparing an aluminum nitride thin film circuit substrate, which has strong metal layer bonding, high thermal conductivity, and can be used for a long time above 200°C without failure, meeting the high-temperature application scenarios in the field of electronic information technology such as thin film circuits.

[0005] In order to solve the above 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 Ti-Cu seed layer

[0007] An aluminum nitride ceramic substrate is taken and magnetron sputtered to sequentially deposit 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.

[0008] S2: Electroless Nickel Plating

[0009] The aluminum nitride ceramic substrate A obtained in S1 is placed in a chemical nickel plating solution, and chemical nickel is plated on the surface of the titanium-copper seed layer to form a nickel layer, thereby obtaining a composite aluminum nitride ceramic substrate;

[0010] The above technical effects: The present invention uses chemical nickel plating to make the aluminum nitride ceramic substrate have higher bonding strength and high temperature resistance, and also gives the aluminum nitride ceramic substrate weldability and bonding properties; because the chemical bonding ability of nickel and titanium is significantly better than that of nickel and copper, in the process of magnetron sputtering, copper is sputtered first and then titanium is sputtered. Titanium compensates for the interface defects of copper and aluminum nitride lattice mismatch, 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 is vacuum sintered and cooled to room temperature in the furnace to form a thin film to obtain a composite aluminum nitride ceramic substrate B;

[0013] S4: Chemical etching

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

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

[0016] Furthermore, in step S1, the cleaning process is: cleaning with 3% to 15% NaOH solution at a temperature of 35°C to 65°C for 10 to 20 minutes; the drying process is: drying at a temperature of 80 to 100°C in a nitrogen atmosphere oven for 10 to 30 minutes.

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

[0018] Furthermore, the pH of the chemical nickel plating solution is 4 to 5.5.

[0019] The above 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 film substrate.

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

[0021] Furthermore, in step S2, the nickel layer has a thickness of 2 to 20 μm.

[0022] Furthermore, in step S3, the sintering process conditions are: vacuum degree <0.01 Pa, heating to 650-900° C. at a rate of 10° C. / min-25° C. / min, and keeping the 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 a denickelizing powder, 1% to 5% of a corrosion inhibitor, and the remainder being pure water.

[0024] Furthermore, the fluorine-containing compound is hydrofluoric acid.

[0025] Furthermore, the denickelized powder includes 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 pressure of chemical etching is 0.2-0.5 MPa.

[0028] The above technical effects are: adding de-nickeling powder to the chemical etching solution, dissolving the nickel oxide layer through chemical reaction, restoring the surface of the ceramic substrate to the active state of metallic nickel, providing a clean base for metal layer patterning, and ensuring precise etching. Sodium nitrate acts as a strong oxidant, and sodium chloride is ionized into sodium ions and chloride ions in the solution, enhancing conductivity, thereby improving nickel removal efficiency; sodium hydroxide can neutralize the acidic substances in the solution, maintain the chemical stability of the solution, and ensure that the nickel removal reaction can proceed in the expected direction.

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

[0030] First, an aluminum nitride ceramic substrate is placed in a NaOH solution for cleaning, placed in an oven with a nitrogen atmosphere for drying, and heat treatment; then, copper and titanium are sputtered in sequence by DC magnetron sputtering, with a target power of 100-150W, a substrate negative bias voltage of -90V--70V, an argon gas flow rate of 30-40sccm, a working gas pressure of 0.3-0.5Pa, and a deposition time of 20-30min. The copper target power is reduced by dynamic transition and the titanium target power is gradually increased, the copper sputtering power is reduced from 100-150W to 0W, and the titanium sputtering power is increased from 0W to 100-150W. After the copper target is turned off, sputtering is continued for 10-30min with a titanium target power of 100-150W, and heat treatment is performed to obtain an aluminum nitride ceramic substrate A.

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

[0032] Furthermore, the heat treatment process is: heating the temperature to 600-700°C, keeping the temperature for 1-2 hours, and cooling to room temperature at a speed of 10-20°C / min.

[0033] The above technical effects are: NaOH solution is used for surface cleaning, and organic pollutants such as grease and fingerprints on the surface of the ceramic substrate are decomposed through saponification reaction, providing a clean surface for the subsequent metal bonding process and preventing impurities from affecting the bonding strength of the coating; the aluminum nitride ceramic substrate is heat-treated to release residual stress and improve the surface flatness of the substrate; through gradient dynamic transition technology, a gradient alloy layer is formed to reduce interface stress, and the seed layer and the aluminum nitride surface are chemically bonded to form a dense transition layer to alleviate the difference in thermal expansion coefficient. Copper atoms are coated on the surface of the aluminum nitride ceramic substrate to enhance its electrical conductivity; heat treatment is performed after magnetron sputtering to promote titanium-copper interface diffusion, reduce grain boundary defects, and improve its electrical conductivity and mechanical strength.

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

[0035] The above technical effect: adding aluminum oxide to the chemical nickel plating solution, aluminum oxide is a filler to increase thermal conductivity, which can not only significantly improve the hardness and wear resistance, but also increase the nickel plating rate, while increasing the thermal conductivity of the aluminum nitride thin film circuit substrate.

[0036] The photosensitive film is evenly covered by the laminating machine. Pressure control and temperature adjustment 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 accurately removed, significantly improving resolution. The redox reaction of chemical solutions and metals is used to selectively remove metal in exposed areas, improving etching uniformity and reducing surface roughness.

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] 1. The aluminum nitride thin film circuit substrate of the present invention contains mixed elements of nickel, copper and phosphorus to lower the melting point of nickel, allowing for rapid diffusion and solidification. The titanium base layer improves bonding strength and does not produce molten liquid, thus avoiding the problem of uneven molding caused by cooling flow shrinkage.

[0039] 2. The aluminum nitride thin film circuit substrate of the present invention is simple to operate by chemical nickel plating, has a uniform coating, and is corrosion-resistant; meets the requirements of electric fusion connection, has a uniform surface and high thermal conductivity; can match the current carrying capacity requirements of the thin film substrate, and has high circuit precision;

[0040] 3. The aluminum nitride thin film circuit substrate of the present invention improves the hardness and wear resistance and the chemical nickel plating rate by adding a thermally conductive filler and alumina to the nickel plating solution, while also increasing the thermal conductivity of the aluminum nitride thin film substrate;

[0041] 4. The aluminum nitride thin film circuit substrate of the present invention has a simple manufacturing process, and the substrate has nickel properties, and has good direct bonding functional components or further gold / silver plating processes, which meets the packaging requirements of the substrate. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 is a flow chart of the present invention;

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

[0044] Figure 3 This is a cross-sectional SEM morphology image of the aluminum nitride thin film circuit substrate according to Example 1 of the present invention; DETAILED DESCRIPTION

[0045] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0046] In the following specific embodiments:

[0047] The nickel-removed powder includes the following mass components: 50% sodium nitrate (NaNO3), 25% sodium chloride (NaCl), and 25% sodium hydroxide (NaOH);

[0048] The fluorine-containing compound is hydrofluoric acid;

[0049] The corrosion inhibitor is thiourea;

[0050] Alumina, particle size 30 nm, model 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 titanium copper seed layer

[0053] A 0.638 mm aluminum nitride ceramic substrate was cleaned with a 12% NaOH solution at 50°C for 13 min, placed in a nitrogen atmosphere oven, and dried at 95°C for 15 min. The substrate was taken out and magnetron sputtered to sequentially deposit a copper layer and a titanium layer on the aluminum nitride ceramic surface to form a titanium-copper seed layer. The target power was 150 W, the substrate negative bias voltage 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 had a thickness of 360 nm and the titanium layer had a thickness of 50 nm, thereby obtaining an aluminum nitride ceramic substrate a.

[0054] Step 2: Chemical Nickel Plating

[0055] An aluminum nitride ceramic substrate a was placed in an electroless nickel plating solution, and electroless nickel was plated on the surface of the titanium copper seed layer to form a nickel layer. The nickel plating was performed at a temperature of 75° C. for 30 minutes, and the substrate was dried in an oven at a temperature of 70° C. in a nitrogen atmosphere for 7 minutes to obtain a composite aluminum nitride ceramic substrate. The electroless nickel plating solution consisted of the following components by weight: 10% NiSO4·7H2O, 3% NaH2PO2·H2O, 2% NaC2H3O2, 3% Na3C6H5O7·2H2O, and the remainder was pure water, with a pH of 4.2. The nickel layer had a thickness of 4.3 μm.

[0056] Step 3: Vacuum sintering

[0057] The composite aluminum nitride ceramic substrate obtained in step 2 was vacuum sintered at a vacuum degree of 0.001 Pa and a heating rate of 15°C / min to a temperature of 700°C, kept at that temperature for 3 hours, and then cooled to room temperature in the furnace to obtain a composite aluminum nitride ceramic substrate b;

[0058] Step 4: Chemical Etching

[0059] Laying a photosensitive film on the surface of the composite aluminum nitride ceramic substrate b, exposing, developing, and chemically etching to form a thin film circuit, etching at a pressure of 0.3 MPa, removing the remaining photosensitive film, and obtaining an aluminum nitride thin film circuit substrate; Figure 2 is the substrate surface view, Figure 3 This is a SEM morphology image of the cross section of the substrate; the mass components of the chemical etching solution include: 2% fluorine-containing compound, 13% nickel-removing powder, 5% corrosion inhibitor, and the balance 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 titanium copper seed layer

[0062] A 0.635 mm aluminum nitride ceramic substrate was taken and cleaned with 12% NaOH solution at 55 ° C for 15 minutes, placed in a nitrogen atmosphere oven, and dried at 90 ° C for 18 minutes; taken out for magnetron sputtering, and copper layer and titanium layer were deposited on the surface of aluminum nitride ceramic in sequence to form a titanium-copper seed metal layer. The copper target power was 120 W, the substrate negative bias voltage was -80 V, the argon flow rate was 35 sccm, the working pressure was 0.4 Pa, and the deposition time was 25 minutes. The copper layer was reduced by dynamic transition. The target power was gradually increased, 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, the titanium target was sputtered at 120W for 20 minutes. The dynamic transition rate was 10W / min and the time was 12 minutes. The heat treatment was carried out by heating the temperature to 650℃ and keeping the temperature for 1.5 hours. The heat treatment was carried out by cooling the temperature to room temperature at a rate of 15℃ / min. The thickness of the copper layer was 350nm and the thickness of the titanium layer was 60nm. An aluminum nitride ceramic substrate a was obtained.

[0063] Step 2: Chemical Nickel Plating

[0064] An aluminum nitride ceramic substrate a was placed in an electroless nickel plating solution, and electroless nickel was plated on the surface of the titanium copper seed layer to form a nickel layer. The nickel plating was performed at a temperature of 70° C. for 30 minutes, and the substrate was dried in an oven at a temperature of 70° C. in a nitrogen atmosphere for 7 minutes to obtain a composite aluminum nitride ceramic substrate. The electroless nickel plating solution comprised the following components by weight: 12% NiSO4·7H2O, 3% NaH2PO2·H2O, 2% Al2O3, 2.5% NaC2H3O2, 4% Na3C6H5O7·2H2O, and the remainder was pure water; the pH was 4.5; and the nickel layer had a thickness of 4.3 μm.

[0065] Step 3: Vacuum sintering

[0066] The composite aluminum nitride ceramic substrate obtained in step 2 was vacuum sintered at a vacuum degree of 0.005 Pa and a heating rate of 20°C / min to a temperature of 700°C, kept at that temperature for 4 hours, and then cooled to room temperature in the furnace to obtain a composite aluminum nitride ceramic substrate b;

[0067] Step 4: Chemical Etching

[0068] A photosensitive film is laid on the surface of a composite aluminum nitride ceramic substrate b, and the substrate is exposed, developed, and chemically etched to form a thin film circuit. The etching pressure is 0.4 MPa, and the remaining photosensitive film is removed to obtain an aluminum nitride thin film circuit substrate. The chemical etching solution comprises, by mass, 5% of a fluorine-containing compound, 15% of a nickel-removing powder, 5% of a 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 titanium copper seed layer

[0071] A 0.645 mm aluminum nitride ceramic substrate was taken, cleaned with a 14% NaOH solution at a temperature of 60 ° C for 18 minutes, placed in a nitrogen atmosphere oven, and dried at a temperature of 95 ° C for 25 minutes; taken out for magnetron sputtering, and a copper layer and a titanium layer were sequentially deposited on the surface of the aluminum nitride ceramic to form a titanium-copper seed layer. The copper target power was 100 W, the substrate negative bias voltage was -70 V, the argon flow rate was 30 sccm, the working pressure was 0.5 Pa, and the deposition time was 28 minutes. The copper target power was reduced by dynamic transition and the titanium target power was gradually increased. The copper sputtering power was reduced from 100 W to 0 W, and the titanium sputtering power was increased from 0 W to 100 W. After the copper target was turned off, the titanium target was sputtered at a power of 100 W for 10 minutes. The dynamic transition rate was 15 W / min and the time was 15 minutes. Heat treatment was performed, the heating temperature was increased to 700 ° C, the temperature was kept for 2 hours, and the temperature was cooled 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. An aluminum nitride ceramic substrate a was obtained;

[0072] Step 2: Chemical Nickel Plating

[0073] An aluminum nitride ceramic substrate a was placed in an electroless nickel plating solution, and electroless nickel was plated on the surface of the titanium copper seed layer to form a nickel layer. The nickel plating was performed at a temperature of 75° C. for 30 minutes, and the substrate was dried in an oven at a temperature of 70° C. in a nitrogen atmosphere for 7 minutes to obtain a composite aluminum nitride ceramic substrate. The electroless nickel plating solution comprised the following components by weight: 14% NiSO4·7H2O, 7% NaH2PO2·H2O, 4% Al2O3, 4% NaC2H3O2, 6% Na3C6H5O7·2H2O, and the remainder was pure water; the pH was 5.0; and the nickel layer had a thickness of 4.3 μm.

[0074] Step 3: Vacuum sintering

[0075] The composite aluminum nitride ceramic substrate obtained in step 2 was vacuum sintered at a vacuum degree of 0.001 Pa and a heating rate of 15°C / min to a temperature of 700°C, kept at that temperature for 3 hours, and then cooled to room temperature in the furnace to obtain a composite aluminum nitride ceramic substrate b;

[0076] Step 4: Chemical Etching

[0077] A photosensitive film is laid on the surface of a composite aluminum nitride ceramic substrate b, and the substrate is exposed, developed, and chemically etched to form a thin film circuit. The etching pressure is 0.3 MPa, and the remaining photosensitive film is removed to obtain an aluminum nitride thin film circuit substrate. The mass composition of the etching solution used for chemical etching includes: 4% fluorine-containing compound, 24% nickel-removing 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 is as follows:

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

[0080] A 0.644 mm aluminum nitride ceramic substrate was cleaned with a 13% NaOH solution at 60°C for 18 min, and then dried in a nitrogen atmosphere oven at 95°C for 25 min. The substrate was taken out and chromium, nickel, and copper seed metal layers were sequentially deposited on its surface by magnetron sputtering. The chromium target power was 110 W, the substrate negative bias voltage 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 reduced by dynamic transition and the nickel target power was gradually increased. The chromium sputtering power was reduced from 110 W to 0 W, and the nickel sputtering power was increased from 0 W to 110 W. After the chromium target is turned off, the nickel target is sputtered at a power of 110W for 10 minutes. The nickel target power is reduced by dynamic transition and the copper target power is gradually increased. The nickel sputtering power is reduced from 110W to 0W, and the copper sputtering power is increased from 0W to 110W. After the nickel target is turned off, the copper target is sputtered at a power of 110W for 10 minutes. The dynamic transition rate is 15W / min and the time is 15 minutes. Heat treatment is performed at a heating temperature of 700°C and kept warm for 2 hours. It is cooled to room temperature at a rate of 20°C / min. The copper layer thickness is 450nm and the titanium layer thickness is 120nm to obtain an aluminum nitride ceramic substrate a.

[0081] Step 2: Chemical Nickel Plating

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

[0083] Step 3: Vacuum sintering

[0084] The composite aluminum nitride ceramic substrate obtained in step 2 was vacuum sintered at a vacuum degree of 0.001 Pa and a heating rate of 15°C / min to a temperature of 700°C, kept at that temperature for 3 hours, and then cooled to room temperature in the furnace to obtain a composite aluminum nitride ceramic substrate b;

[0085] Step 4: Chemical Etching

[0086] A photosensitive film is laid on the surface of a composite aluminum nitride ceramic substrate b, and the substrate is exposed, developed, and chemically etched to form a thin film circuit. The etching pressure is 0.3 MPa, and the remaining photosensitive film is removed to obtain an aluminum nitride thin film circuit substrate. The chemical etching solution comprises, by mass, 4% of a fluorine-containing compound, 24% of a nickel-removing powder, 5% of a 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 is as follows:

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

[0089] A 0.638 mm aluminum nitride ceramic substrate was taken, cleaned with a 12% NaOH solution at a temperature of 50°C for 13 minutes, and dried in a nitrogen atmosphere oven at a temperature of 95°C for 15 minutes; taken out, and copper and titanium seed metal layers were sequentially deposited on its surface by magnetron sputtering. The copper target power was 150 W, the substrate negative bias voltage was -90 V, the argon flow rate was 32 sccm, the working pressure was 0.3 Pa, and the deposition time was 20 minutes. The copper target power was reduced by dynamic transition and the titanium target power was gradually increased. The copper sputtering power was reduced from 150 W to 0 W, and the titanium sputtering power was increased from 0 W to 150 W. After the copper target was turned off, the titanium target was sputtered at a power of 150 W for 10 minutes, wherein the dynamic transition rate was 7.6 W / min, and the time was 12 minutes. Heat treatment was performed, the heating temperature was heated to 600°C, the temperature was kept for 1 hour, and the temperature was 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, thereby obtaining an aluminum nitride ceramic substrate a;

[0090] Step 2: Nickel plating on aluminum nitride ceramic substrate

[0091] Take aluminum nitride ceramic substrate a and plate nickel by electroplating with a current density of 0.5A / dm 2 , temperature 50 ℃, nickel plating 30 minutes, after electroplating with deionized water washing, temperature 70 ℃, nitrogen atmosphere drying 7 minutes, to obtain a composite aluminum nitride ceramic substrate; the mass composition of the nickel electroplating solution includes: 14% NiSO4·7H2O, 7% Ni(NH2SO3)2, 4% H3BO3, 6% NiCl2·6H2O, 8% Na2SO4, the rest is pure water; pH is 5.0; nickel layer thickness is 4.3μm;

[0092] Step 3: Vacuum sintering

[0093] The composite aluminum nitride ceramic substrate obtained in step 2 was vacuum sintered at a vacuum degree of 0.001 Pa and a heating rate of 15°C / min to a temperature of 700°C, kept at that temperature for 3 hours, and then cooled to room temperature in the furnace to obtain a composite aluminum nitride ceramic substrate b;

[0094] Step 4: Aluminum nitride film substrate pattern etching

[0095] A photosensitive film is laid on the surface of a composite aluminum nitride ceramic substrate b, and the substrate is exposed, developed, and chemically etched to form a thin film circuit. The etching pressure is 0.3 MPa, and the remaining photosensitive film is removed to obtain an aluminum nitride thin film circuit substrate. The chemical etching solution comprises, by mass, 2% of a fluorine-containing compound, 13% of nickel-removing powder, 5% of a 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 is as follows:

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

[0098] A 0.635 mm aluminum nitride ceramic substrate was taken, cleaned with a 13% NaOH solution at 60°C for 14 min, and then dried in a nitrogen atmosphere oven at 96°C for 16 min. The substrate was taken out and a copper and titanium seed metal layer was deposited on the surface by magnetron sputtering. The copper target power was 140 W, the substrate negative bias voltage 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 turned off and sputtering was continued for 10 min with a titanium target power of 150 W. The substrate was heat treated by heating to 600°C, holding for 1 h, and cooling 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, thereby obtaining an aluminum nitride ceramic substrate a.

[0099] Step 2: Chemical Nickel Plating

[0100] An aluminum nitride ceramic substrate a was placed in an electroless nickel plating solution, and electroless nickel was plated on the surface of the titanium copper seed layer to form a nickel layer. The nickel plating was performed at a temperature of 75° C. for 30 minutes, and the substrate was dried at a temperature of 70° C. in a nitrogen atmosphere for 7 minutes to obtain a composite aluminum nitride ceramic substrate. The electroless nickel plating solution comprised the following components by weight: 11% NiSO4·7H2O, 4% NaH2PO2·H2O, 3% Al2O3, 2% NaC2H3O2, 3% Na3C6H5O7·2H2O, and the remainder was pure water; the pH was 4.2; and the nickel layer had a thickness of 4.5 μm.

[0101] Step 3: Vacuum sintering

[0102] The composite aluminum nitride ceramic substrate obtained in step 2 was vacuum sintered at a vacuum degree of 0.001 Pa and a heating rate of 15°C / min to a temperature of 700°C, kept at that temperature for 3 hours, and then cooled to room temperature in the furnace to obtain a composite aluminum nitride ceramic substrate b;

[0103] Step 4: Chemical Etching

[0104] A photosensitive film is laid on the surface of a composite aluminum nitride ceramic substrate b, and the substrate is exposed, developed, and chemically etched to form a thin film circuit. The etching pressure is 0.3 MPa, and the remaining photosensitive film is removed to obtain an aluminum nitride thin film circuit substrate. The chemical etching solution comprises, by mass, 2% of a fluorine-containing compound, 13% of nickel-removing powder, 5% of a 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 is as follows:

[0106] Step 1: Chemical Nickel Plating

[0107] A 0.633 mm aluminum nitride ceramic substrate was cleaned with a 13% NaOH solution at 60° C. for 14 minutes, dried in a nitrogen atmosphere oven at 96° C. for 16 minutes, removed, and placed in an electroless nickel plating solution for electroless nickel plating to form a nickel layer. The substrate was then nickel plated at 75° C. for 30 minutes and dried in a nitrogen atmosphere oven at 70° C. for 7 minutes to obtain a composite aluminum nitride ceramic substrate. The electroless nickel plating solution consisted of 10% NiSO4·7H2O, 3% NaH2PO2·H2O, 2% NaC2H3O2, 3% Na3C6H5O7·2H2O, and the remainder was pure water, with a pH of 4.2. The nickel layer had a thickness of 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 and a heating rate of 15°C / min to a temperature of 700°C, kept at that temperature for 3 hours, and then cooled to room temperature in the furnace to obtain an aluminum nitride ceramic substrate a;

[0110] Step 3: Chemical Etching

[0111] An aluminum nitride ceramic substrate a was prepared, a photosensitive film was laid on the surface, and the substrate was exposed, developed, and chemically etched at an etching pressure of 0.3 MPa. The remaining photosensitive film was removed to obtain an aluminum nitride thin film circuit substrate. The chemical etching solution had a mass composition of: 3% fluorine-containing compound, 14% nickel-removing powder, 5% corrosion inhibitor, and the balance was water.

[0112] Experiment: The substrates obtained in Examples 1-3 and Comparative Examples 1-4 were placed in a muffle furnace at 350°C for 3 hours to check if the coating had any bulges or peeling. Figure 3 This is the cross-sectional SEM morphology of the substrate after muffle furnace testing. No delamination occurs, and the substrate meets commercial requirements.

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

[0114] Thermal conductivity test: Referring to GB 5598-85 standard, laser pulses are used to illuminate the back of the sample, and the front temperature is recorded with an infrared thermometer over time to calculate the thermal diffusivity. The thermal conductivity is calculated based on the specific heat capacity and density of the sample.

[0115] Thermal Expansion Coefficient Test: Refer to ASTM E831 standard, place the aluminum nitride thin film circuit substrate at 25°C for 10 minutes, gradually increase the temperature to 300°C, measure the length change, and calculate the thermal expansion coefficient;

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

[0117] Performance comparison table

[0118]

[0119] According to the data in the above table, we can clearly draw the following conclusions:

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

[0121] Compared with the comparative example, the aluminum nitride thin film circuit substrates obtained in Examples 1-3 have high thermal conductivity, small thermal expansion coefficient, and high 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 the surface metal seed layer treatment, has low thermal conductivity, low thermal conductivity, large thermal expansion coefficient, is easy to crack after being affected by temperature, and has comparable peel strength. It can be seen that the performance of the aluminum nitride thin film circuit substrate prepared using chromium, nickel, and copper for surface deposition treatment is not as good as that prepared using the preparation process of the present invention.

[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 prepared aluminum nitride thin film circuit substrate has low thermal conductivity, high thermal expansion coefficient, and low peel strength. It can be seen that if electroplated nickel is used instead of chemical nickel plating, the nickel layer is not more uniformly plated using the chemical nickel plating method, the thermal conductivity is poor, the thermal stress with the material is large, and 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 unevenly dispersed. Using the chemical nickel plating method, nickel can be evenly plated, and the bonding performance and peel strength are greater.

[0124] Compared with Example 1, the aluminum nitride thin film circuit substrate in Comparative Example 3 does not adopt the titanium / copper gradient dynamic transition technology, and the prepared substrate has low thermal conductivity, high thermal expansion coefficient, and low peel strength. It can be seen that if the titanium / copper gradient dynamic transition technology is not adopted, the prepared aluminum nitride thin film circuit substrate has low thermal conductivity, large thermal stress of the material, relatively unstable performance of the aluminum nitride ceramic substrate, and uneven internal structure of the metal seed layer. The use of titanium / copper gradient dynamic transition technology avoids thickness fluctuations caused by differences in substrate conductivity or geometric shape, and has better thermal conductivity and less thermal stress generated 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, larger thermal expansion coefficient, and smaller peel strength. Compared with other Comparative Examples 1-3, the thermal conductivity is the lowest, the thermal expansion coefficient is the largest, and the peel strength is the smallest. It can be seen that the aluminum nitride thin film circuit substrate that has not been surface treated by magnetron sputtering has poor thermal conductivity, small thermal stress of the material, 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 embodied 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 illustrative and non-restrictive, and the scope of the invention is defined by the appended claims rather than the foregoing description, and it is intended that all variations that come within the meaning and range of equivalents of the claims be embraced therein.

Claims

1. A method for preparing an aluminum nitride thin film circuit substrate, characterized in that: The following steps are involved: S1: Preparation of titanium-copper seed layer: An aluminum nitride ceramic substrate is prepared and magnetron sputtered to sequentially deposit 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: Chemical nickel plating: The aluminum nitride ceramic substrate A obtained in S1 is placed in a chemical nickel plating solution, and chemical nickel is plated 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: vacuum sintering the composite aluminum nitride ceramic substrate obtained in S2, cooling it to room temperature in the furnace to form a thin film, and obtaining a composite aluminum nitride ceramic substrate B; S4: Chemical etching: A photosensitive film is laid on the surface of the composite aluminum nitride ceramic substrate B obtained in S3, and the substrate is exposed, developed, and chemically etched to form a thin film circuit to obtain an aluminum nitride thin film circuit substrate.

2. The method for preparing an aluminum nitride thin film circuit substrate according to claim 1, wherein: In step S1, the cleaning process is: cleaning with 3% to 15% NaOH solution at a temperature of 35° C. to 65° C. for 10 to 20 minutes; the drying process is: drying at a temperature of 80 to 100° C. in a nitrogen atmosphere oven for 10 to 30 minutes.

3. The method for preparing an aluminum nitride thin film circuit substrate according to claim 1, wherein: In step S1 , the copper layer has a thickness of 50 nm to 800 nm, and the titanium layer has a thickness of 20 nm to 300 nm.

4. The method for preparing an aluminum nitride thin film circuit substrate according to claim 1, wherein: In step S2, the chemical nickel plating solution includes the following components by mass: 5% to 15% nickel sulfate heptahydrate, 2% to 8% sodium hypophosphite, 1% to 5.5% sodium acetate trihydrate, 3% to 7% sodium citrate, and the remainder is pure water; the nickel layer thickness is 2 to 20 μm.

5. The method for preparing an aluminum nitride thin film circuit substrate according to claim 1, wherein: In step S3, the sintering process conditions are: vacuum degree <0.01 Pa, heating to 650-900°C at a rate of 10°C / min-25°C / min, and keeping warm for 2-5 hours; in step S4, the pattern etching pressure is 0.2-0.5 MPa.

6. The method for preparing an aluminum nitride thin film circuit substrate according to claim 1, wherein: 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 a denickelizing powder, 1% to 5% of a corrosion inhibitor, and the remainder being pure water.

7. The method for preparing an aluminum nitride thin film circuit substrate according to claim 1, wherein: The process of step S1 is as follows: First, an aluminum nitride ceramic substrate is placed in a NaOH solution for cleaning, placed in an oven with a nitrogen atmosphere for drying, and heat treatment; then, copper and titanium are sputtered in sequence by DC magnetron sputtering, with a target power of 100-150W, a substrate negative bias voltage of -90V--70V, an argon gas flow rate of 30-40sccm, a working gas pressure of 0.3-0.5Pa, and a deposition time of 20-30min. The copper target power is reduced by dynamic transition and the titanium target power is gradually increased, the copper sputtering power is reduced from 100-150W to 0W, and the titanium sputtering power is increased from 0W to 100-150W. After the copper target is turned off, sputtering is continued for 10-30min with a titanium target power of 100-150W, and heat treatment is performed to obtain an aluminum nitride ceramic substrate A.

8. The method for preparing an aluminum nitride thin film circuit substrate according to claim 7, wherein: The rate of dynamic transition is 7.5-15W / min, and the time is 10-15min; the process conditions of heat treatment are: heating temperature to 600-700℃, keeping warm for 1-2h, and cooling to room temperature at a cooling rate of 10℃ / min-20℃ / min.

9. The method for preparing an aluminum nitride thin film circuit substrate according to claim 4, wherein: The chemical nickel plating solution also includes 1% to 4% of aluminum oxide.

10. An aluminum nitride thin film circuit substrate, characterized in that: Prepared according to the preparation method according to any one of claims 1 to 9.

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