A method for preparing an IGBT ceramic copper clad substrate by hot isostatic pressing sintering

Abstract

The application belongs to the field of active metal brazing, and discloses a method for preparing an IGBT ceramic copper-clad substrate by hot isostatic pressing sintering. The active metal filler is added under specific conditions to combine the ceramic and copper, so that the wetting performance of the ceramic and copper combination can be effectively improved. The vacuum bagging and hot isostatic pressing sintering process are performed by using a hot pressing sintering furnace to realize high-strength and tight connection between the ceramic and the metal copper, so that the problems of low bonding strength of the ceramic copper-clad substrate in a high-power semiconductor device can be effectively solved. The method solves the problems of complicated preparation steps and long time consumption of the ceramic copper-clad substrate.

Description

Technical Field

[0001] This invention belongs to the field of active metal brazing, and relates to a method for preparing IGBT ceramic copper-clad substrates by hot isostatic pressing sintering. Background Technology

[0002] With the continuous development of technology, the ceramic copper-clad substrate in electronic power devices such as IGBT chips plays a crucial role in connecting internal and external heat dissipation channels, while also serving functions such as electrical interconnection and mechanical support. Ceramics are ideal packaging and heat dissipation materials due to their excellent mechanical properties, low coefficient of thermal expansion, low dielectric constant, and high-temperature resistance. However, the significant difference in thermal expansion coefficients between ceramics and metals generates substantial residual thermal stress, greatly reducing bonding strength and lifespan, severely limiting their application in high-power semiconductor devices.

[0003] In recent years, to improve the poor bonding strength between ceramics and metals and the short service life of ceramic copper-clad laminates, the addition of active metals as brazing filler metals has gradually become a research hotspot. The principle is that a chemical reaction occurs at the interface to generate new compounds, thus enhancing the bonding strength. Furthermore, adding suitable active metal filler metals can significantly reduce brazing temperature, decrease residual stress, and extend service life. However, currently, the preparation of ceramic copper-clad laminates typically involves first bonding the active metal filler metal to the ceramic using methods such as vacuum magnetron sputtering or molten salt reaction, and then bonding the surface-treated ceramic to copper. Xin et al. proposed a new method for preparing nano-Cu / Ti-Si3N4 ceramic copper-clad laminates. They used vacuum magnetron sputtering to deposit nano-scale active metal Ti as a transition layer on the surface of Si3N4 ceramic, and then sintered the nano-copper powder with Si3N4 ceramic in an SPS vacuum furnace. Under these conditions, the maximum peel strength was only 4.29 N / mm. The low peel strength is due to the thinness of the Ti layer deposited by vacuum magnetron sputtering, resulting in insufficient reaction with the Si3N4 ceramic, and the cumbersome and time-consuming process. (Xin C, Huang L, Zeng Q, et al. A novel nano Cu / Ti–Si3N4 ceramic substrates fabricated by spark plasma sintering and its bonding mechanism[J]. Vacuum, 2021, 187:110093.DOI:10.1016 / j.vacuum.2021.110093.) Paik et al. formed an oxide layer with a thickness of 1-4 μm on the surface of AlN ceramics by holding at 1250℃ for 90 min. The maximum peel strength between Cu and AlN ceramics reached 5.67 N / mm. The low peel strength is because this oxidation process cannot completely eliminate the micropores between copper and AlN ceramics, and there is still a difference in the coefficient of thermal expansion between the oxide layer and Cu. This will seriously affect the reliability of the substrate and the application of the module in the packaging of high-power devices. (Entezarian M, Drew RA L. Direct bonding of copper to aluminum nitride [J]. Materials Science and Engineering: A, 1996, 212(2): 206-212. DOI: 10.1016 / 0921-5093(96)10190-8.).

[0004] These methods are cumbersome, time-consuming, and costly, but the bonding strength is not high. Therefore, a simple and effective method is needed to prepare ceramic copper-clad substrates to reduce experimental steps, shorten preparation time, and enhance bonding strength. Summary of the Invention

[0005] To overcome the shortcomings of existing technologies, this invention provides a method for preparing IGBT ceramic copper-clad substrates using hot isostatic pressing (HIP) sintering, thus solving the problems of cumbersome and time-consuming steps in preparing ceramic copper-clad substrates. Furthermore, a high-bonding-strength ceramic copper-clad substrate is prepared by applying pressure and gradient heating from all directions in a hot isostatic pressing furnace.

[0006] This invention improves the wetting properties of the ceramic-copper bond by adding active metal solder under specific conditions. Furthermore, it achieves a high-strength and tight bond between the ceramic and copper by using a vacuum encapsulation and hot isostatic pressing sintering process in a hot pressing furnace. This invention effectively solves the problem of low bonding strength of ceramic copper-clad substrates in high-power semiconductor devices.

[0007] The above-mentioned objective of this invention is achieved through the following technical solution:

[0008] A method for preparing IGBT ceramic copper-clad substrates by hot isostatic pressing (HIP) includes the following steps:

[0009] S1. After grinding and cleaning, ceramic, brazing filler metal, Cu foil, and titanium foil are placed into the cladding mold in sequence, and vacuum is drawn in a hot pressing sintering furnace to obtain a high vacuum part to be welded;

[0010] S2. Place the workpiece to be welded after vacuum encapsulation in step 1 into a hot isostatic pressing furnace for brazing, i.e., ceramic copper-clad substrate.

[0011] Furthermore, the ceramic mentioned in step S1 is any one of Si3N4, AlN, or other ceramic materials, with a thickness of 0.30–5.00 mm; the brazing filler metal is any one of silver-copper-titanium alloy, silver-titanium alloy, or other titanium-containing alloys, with a thickness of 0.03–0.10 mm; the Cu foil has a thickness of 0.02–5.00 mm; and the titanium foil is an industrially pure titanium alloy with a thickness of 0.10–0.50 mm.

[0012] Furthermore, the titanium foil obtained in step S1 is sanded with sandpaper to remove the oxide layer, and finally wiped clean with lint-free paper soaked in anhydrous ethanol.

[0013] Furthermore, the ceramic, brazing filler metal, and Cu foil mentioned in step S1 are respectively placed in acetone and anhydrous ethanol for ultrasonic cleaning to remove oil and dust from the sample surface, and then dried.

[0014] Furthermore, the vacuuming process described in step S1 involves: opening the mechanical pump and the pre-evacuation valve, then opening the diffusion pump, closing the pre-evacuation valve, and opening the high vacuum valve, reducing the vacuum level to 10. -2 ~10 -3 Pa, perform vacuum encapsulation.

[0015] Furthermore, the encapsulation procedure in step S1 is as follows: ① The temperature is uniformly increased from 25°C to 700-800°C at a rate of 15-20°C / min, and the pressure is increased to 6-6.5 MPa; ② The temperature and pressure are maintained for 30-45 minutes; ③ After the encapsulation is completed, the pressure is released, and the product is taken out after cooling to room temperature.

[0016] Furthermore, the step S2, which involves placing the workpiece to be welded into the hot isostatic pressing furnace, is as follows: place the workpiece to be welded in a crucible, open the furnace lid of the hot isostatic pressing sintering furnace, place the crucible in, and tighten the furnace lid.

[0017] Furthermore, the sintering process in the hot isostatic pressing furnace described in step S2 is as follows: the temperature is increased from 25°C to 550-650°C at a rate of 10-20°C / min, the pressure is increased to 80-100 MPa, and held for 30-60 min; then the temperature is increased to 700-900°C at a rate of 5-10°C / min, and the pressure is increased to 150-200 MPa; the temperature is held at the highest temperature and pressure for 30-60 min; then the temperature is decreased to 200-300°C at a rate of 10-20°C / min; finally, the temperature is reduced to room temperature with the furnace.

[0018] Furthermore, after sintering, the sample is cooled to room temperature in the hot isostatic pressing furnace, the furnace lid is opened, the sample is taken out, and the cladding is cut off to obtain the ceramic copper-clad substrate.

[0019] The advantages of this invention compared to the prior art are:

[0020] (1) The prepared ceramic copper-clad substrate has a tight bond between ceramic and Cu, and the steps are simple and the time is short. It is prepared by one-step method.

[0021] (2) The prepared ceramic copper-clad substrate undergoes a chemical reaction between the ceramic and Cu due to the presence of Ag-Cu-Ti solder, producing a new compound TiN, which increases the bonding strength. Attached Figure Description

[0022] The present invention will be further described below with reference to the accompanying drawings and examples:

[0023] Figure 1 This is a schematic diagram of a vacuum enclosure.

[0024] Figure 2 Photo of the workpiece to be welded after successful encapsulation.

[0025] Figure 3 Photographs of samples taken from a hot isostatic pressing furnace.

[0026] Figure 4 This is a schematic diagram of the structure of the ceramic copper-clad substrate prepared according to the present invention.

[0027] Figure 5 This is a SEM image of the ceramic copper-clad substrate prepared according to the present invention.

[0028] Figure 6 This is a point scan energy spectrum of the cross-section of the ceramic copper-clad substrate prepared in Example 1 of the present invention. Detailed Implementation

[0029] The present invention is described in detail below through specific embodiments, but this does not limit the scope of protection of the present invention. Unless otherwise specified, the experimental methods used in the present invention are all conventional methods, and the experimental equipment, materials, reagents, etc. used can all be obtained commercially.

[0030] Example 1

[0031] (1) Si3N4 ceramic was selected, with dimensions of 10×10×0.35mm. 3 The commercially available Ag69.7-Cu27-Ti3.3 solder has dimensions of 10×10×0.05mm. 3 The dimensions of the Cu foil are 10×10×0.02mm. 3 and 10×10×0.20mm 3 Titanium foil is an industrially pure titanium alloy, and it is a circle with a diameter of 125 mm and a thickness of 0.15 mm.

[0032] (2) The titanium foil obtained after cutting was polished with 1200 grit sandpaper and then wiped clean with lint-free paper soaked in anhydrous ethanol. The Si3N4 ceramic, Ag69.7-Cu27-Ti3.3 solder and Cu foil were respectively placed in acetone and anhydrous ethanol for ultrasonic cleaning for 5 minutes each to remove oil and dust from the sample surface and then dried.

[0033] (3) Assembly. First, place a layer of titanium foil at the bottom, then place Cu, Ag69.7-Cu27-Ti3.3 solder, Si3N4, Ag69.7-Cu27-Ti3.3 solder, and Cu in the middle of the titanium foil in that order. Finally, place another layer of titanium foil on top, assemble, and put into the cladding mold.

[0034] (4) Vacuum Encasing. Place the assembled casing sample into a hot press sintering furnace, and evacuate the furnace cavity to 10°C. -2 The temperature was kept below 25°C and maintained thereafter. Then, the temperature was uniformly increased from 25°C to 800°C at a rate of 15°C / min, and the pressure was increased to 6 MPa. The temperature and pressure were maintained for 30 minutes, and the temperature was lowered to room temperature before the encapsulated sample was removed.

[0035] (5) Hot isostatic pressing (HIP) sintering. The sintered cladding sample from step (4) is placed in a HIP sintering furnace. The furnace lid is closed, and the furnace cavity is first evacuated to below 10 Pa. Then, the furnace cavity is repeatedly cleaned three times with high-purity argon. The temperature is increased from 25 °C to 600 °C at 10 °C / min, and the pressure is increased to 100 MPa and held for 30 min. Then, the temperature is increased to 700 °C at 5 °C / min, and the pressure is increased to 150 MPa and held for 30 min to promote the diffusion of Ti into Si3N4 ceramic and form a TiN transition layer. Then, the temperature is decreased to 300 °C at 10 °C / min. Finally, the temperature is lowered to room temperature with the furnace.

[0036] (6) Take out the sample. After the sintering in step (5) is completed, the sample is cooled to room temperature in the hot isostatic pressing furnace. Open the furnace cover, take out the sample, and cut off the cladding to obtain the ceramic copper-clad substrate.

[0037] After peel testing, the peel strength was 21.16 N / mm.

[0038] Table 1. Elemental composition of the cross-section of the ceramic copper-clad substrate prepared in Example 1 (point scan energy dispersive spectroscopy).

[0039] element Wt% At% N 29.90 63.71 Si 5.36 5.70 Ti 31.93 19.89 Cu 8.40 3.95 Ag 24.40 6.75 Total: 100.00 100.00

[0040] Comparative Example 1

[0041] (1) Si3N4 ceramic was selected. TiH2 powder (69.7wt%), polyvinyl alcohol (0.3wt%) and water (30wt%) were mixed evenly to prepare a mixed slurry. A 10μm thick TiH2 layer was coated on the upper and lower surfaces of the Si3N4 ceramic substrate and dried at 300℃ for 2h in a drying oven.

[0042] (2) The Si3N4 ceramic substrate coated with TiH2 layer was heat-treated under an argon protective atmosphere to decompose the coated TiH2 and form a Ti metal layer with a thickness of 6μm.

[0043] (3) Place the copper foil on the surface of the ceramic substrate coated with the Ti metal layer, and place it in a hot press mold. Under vacuum conditions, the vacuum degree reaches 2×10⁻⁶. -4 Pa, apply a pressure of 5 MPa, raise the temperature from room temperature to 1000℃, and keep it at that temperature for 1 hour.

[0044] (4) Remove the sample and cool it to room temperature. A ceramic copper-clad substrate is obtained.

[0045] After peel testing, the peel strength was 11.00 N / mm.

[0046] Comparative Example 2

[0047] (1) Si3N4 ceramic was selected. Ti was sputtered on both sides of the Si3N4 ceramic substrate by magnetron sputtering at a rate of 25 nm / min for 20 min; then Cr was sputtered by magnetron sputtering at a rate of 25 nm / min for 15 min and placed in a muffle furnace with an air flow rate of 2.5 L / min.

[0048] (2) The obtained Si3N4 ceramic substrate with coating is placed in a muffle furnace and heated from room temperature to 1300°C at a rate of 5°C / min under an air flow rate of 2.5L / min. Then it is held at the temperature for 60min and cooled to 500°C at a rate of 3°C / min. The substrate is then cooled with the furnace.

[0049] (3) Place the flat Cu layer on a ceramic pad for pre-oxidation, keep it at 800°C for 20 min in an atmosphere with an O2 content of 160 ppm, and then cool it to room temperature in the furnace; then the oxidized surface of the Cu layer is bonded to the side of the hot-oxidized Si3N4 ceramic substrate covered with an oxide layer, and keep it at 1075°C for 15 min in an atmosphere with an O2 content of 35 ppm to obtain a ceramic copper-clad substrate.

[0050] After peel testing, the peel strength was 4.00 N / mm.

[0051] Comparative Example 3

[0052] The difference from Example 1 is that no active metal solder was added.

[0053] (1) Si3N4 ceramic was selected, with dimensions of 10×10×0.35mm. 3 The dimensions of the Cu foil are 10×10×0.02mm. 3 and 10×10×0.20mm 3 Titanium foil is an industrially pure titanium alloy, and it is a circle with a diameter of 125 mm and a thickness of 0.15 mm.

[0054] (2) The titanium foil obtained after cutting was polished with 1200 grit sandpaper and then wiped clean with lint-free paper soaked in anhydrous ethanol. The Si3N4 ceramic and Cu foil were placed in acetone and anhydrous ethanol respectively for ultrasonic cleaning for 5 minutes each to remove oil and dust from the sample surface and then dried.

[0055] (3) Assembly. First, place a layer of titanium foil at the bottom, then place Cu, Si3N4, Cu in the middle of the titanium foil in that order, and finally place another layer of titanium foil on top. Assemble the assembly and place it into the encapsulation mold.

[0056] (4) Vacuum Encasing. Place the assembled casing sample into a hot press sintering furnace, and evacuate the furnace cavity to 10°C. -2The temperature was kept below 25°C and maintained thereafter. Then, the temperature was uniformly increased from 25°C to 800°C at a rate of 15°C / min, and the pressure was increased to 6 MPa. The temperature and pressure were maintained for 30 minutes, and the temperature was lowered to room temperature before the encapsulated sample was removed.

[0057] (5) Hot isostatic pressing (HIP) sintering. Place the sintered cladding sample from step (4) into a HIP sintering furnace, close the furnace lid, first evacuate the furnace cavity to below 10 Pa, then repeatedly purge the furnace cavity three times with high-purity argon. First evacuate the furnace cavity to below 10 Pa, then repeatedly purge the furnace cavity three times with high-purity argon. Increase the temperature from 25°C to 600°C at 10°C / min, increase the pressure to 100 MPa, hold for 30 min, then increase the temperature to 700°C at 5°C / min, increase the pressure to 150 MPa, hold for 30 min, then decrease the temperature to 300°C at 10°C / min; finally, allow the furnace to cool to room temperature.

[0058] (6) Take out the sample. After the sintering in step (5) is completed, the sample is cooled to room temperature in the hot isostatic pressing furnace. Open the furnace cover, take out the sample, and cut off the cladding to obtain the ceramic copper-clad substrate.

[0059] After peel testing, the peel strength was 2.06 N / mm.

[0060] Comparative Example 4

[0061] (1) Si3N4 ceramic with a purity greater than 99.99wt% was selected as the substrate material. A Ti / TiN / Ti / TiN / Ti nanomultilayer film was used as the transition layer and deposited on the surface of Si3N4 ceramic by physical vapor deposition (PVD).

[0062] (2) Nano-Cu powder was vacuum sintered onto a ceramic substrate with a Ti / TiN / Ti / TiN / Ti nano-multilayer film deposited on its surface using a spark plasma sintering furnace. During the sintering process, a pressure of 30 MPa was applied, the temperature was raised to 600 °C, and the temperature and pressure were held for 200 s.

[0063] (3) Remove the sample. After sintering, cool to room temperature to prepare a ceramic copper-clad substrate.

[0064] After peel testing, the peel strength was 5.39 N / mm.

[0065] Comparative Example 5

[0066] (1) Si3N4 ceramic with a purity greater than 99.99wt% was selected as the substrate material. Ti was deposited on the ceramic surface by vacuum magnetron sputtering.

[0067] (2) Nano-Cu powder was vacuum sintered onto a Ti-deposited ceramic surface using a spark plasma sintering furnace. During the sintering process, a pressure of 30 MPa was applied, the temperature was raised to 600 °C, and the temperature and pressure were held for 200 s.

[0068] (3) Remove the sample. After sintering, cool to room temperature to prepare a ceramic copper-clad substrate.

[0069] After peel testing, the peel strength was 4.29 N / mm.

[0070] Performance testing: The peel strength of the ceramic copper-clad substrates prepared by the above different processes was compared. The comparison results are shown in Table 2.

[0071] Table 2 Peel strength of ceramic copper-clad substrates prepared by different processes

[0072]

[0073] The embodiments described above are merely preferred embodiments of the present invention, and not all feasible embodiments of the present invention. Any obvious modifications made by those skilled in the art without departing from the principles and spirit of the present invention should be considered to be included within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing IGBT ceramic copper-clad substrates by hot isostatic pressing (HIP), characterized in that, Includes the following steps: S1. Place a layer of titanium foil at the bottom, then place Cu foil, brazing filler metal, ceramic, brazing filler metal, and Cu in the middle of the titanium foil in that order, and finally place another layer of titanium foil on top. Assemble the assembly and place it in the cladding mold; perform vacuuming in a hot press sintering furnace to obtain a high-vacuum workpiece. S2. Place the workpiece to be welded after vacuum encapsulation in step 1 into a hot isostatic pressing furnace for brazing, i.e., ceramic copper-clad substrate. The ceramic mentioned in step S1 is any one of Si3N4 and AlN, with a thickness of 0.30~5.00mm; the brazing filler metal is any one of silver-copper-titanium alloy, silver-titanium alloy or other titanium-containing alloy, with a thickness of 0.03~0.10mm; the Cu foil has a thickness of 0.02~5.00mm; the titanium foil is an industrial pure titanium alloy with a thickness of 0.10~0.50mm. The encapsulation procedure in step S1 is as follows: ① The temperature is uniformly increased from 25°C to 700-800°C at a rate of 15-20°C / min, and the pressure is increased to 6-6.5MPa; ② Maintain heat and pressure for 30~45 minutes; ③ After wrapping, release the pressure and remove the garment after it has cooled to room temperature; The sintering process in the hot isostatic pressing furnace described in step S2 is as follows: the temperature is increased from 25°C to 550-650°C at a rate of 10-20°C / min, the pressure is increased to 80-100MPa, and held for 30-60min. Then the temperature is increased to 700-900°C at a rate of 5-10°C / min, and the pressure is increased to 150-200MPa. Maintain the temperature and pressure at the highest level for 30-60 minutes; then reduce the temperature to 200-300℃ at a rate of 10-20℃ / min; finally, allow the furnace to cool to room temperature.

2. The method for preparing IGBT ceramic copper-clad substrates by hot isostatic pressing as described in claim 1, characterized in that, In step S1, the ceramic, brazing filler metal, and Cu foil are respectively placed in acetone and anhydrous ethanol for ultrasonic cleaning to remove oil and dust from the sample surface, and then dried.

3. The method for preparing IGBT ceramic copper-clad substrates by hot isostatic pressing as described in claim 2, characterized in that, The vacuuming process described in step S1 involves: turning on the mechanical pump and pre-evacuation valve, then turning on the diffusion pump, closing the pre-evacuation valve, and turning on the high vacuum valve until the vacuum level drops to 10. -2 ~10 -3 Pa, perform vacuum encapsulation.

4. The method for preparing IGBT ceramic copper-clad substrates by hot isostatic pressing as described in claim 3, characterized in that, The step S2, which involves placing the workpiece to be welded into the hot isostatic pressing furnace, is as follows: place the workpiece to be welded in the crucible, open the furnace lid of the hot isostatic pressing furnace, place the crucible in, and tighten the furnace lid.

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