A method for manufacturing a ceramic copper clad substrate

Abstract

This invention relates to the field of semiconductor materials and discloses a method for preparing a ceramic copper-clad substrate. First, silicon nitride ceramic and oxygen-free copper sheets are encapsulated to isolate them from oxygen. The encapsulated sample is then placed in a spark plasma sintering furnace and evacuated to a vacuum of 1.0 x 10⁻⁶. ‑3 The sample was heated to 700-750℃ to obtain a sealed enclosure with a high internal vacuum. Finally, it was placed in a hot isostatic pressing furnace under a uniform pressure of 150-200 MPa and a temperature of 700-750℃ to ensure a uniform and tightly bonded internal structure within the silicon nitride ceramic substrate. A transition layer of approximately 2 μm thick was formed between the ceramic and the copper sheet through interdiffusion, resulting in a tight bond between the silicon nitride ceramic and copper with low porosity.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor materials, and specifically relates to a method for preparing a ceramic copper-clad substrate. Background Technology

[0002] Ceramic copper-clad substrate is a composite metal-ceramic substrate formed by directly bonding highly conductive oxygen-free copper to the surface of ceramic at high temperature. It has the characteristics of ceramic such as high thermal conductivity, high electrical insulation, high mechanical strength and low expansion, as well as the high conductivity and excellent welding performance of oxygen-free copper. Furthermore, various patterns can be etched on its surface. It is one of the key materials for power module packaging, connecting chips and heat dissipation substrates in the field of power electronics.

[0003] Traditional direct copper cladding (DBC) technology involves heating the ceramic surface at approximately 1063°C in an oxygen-containing nitrogen atmosphere and directly soldering a copper foil layer onto the ceramic surface. However, due to the poor wettability between the silicon nitride substrate and the oxygen-free copper surface, and the reaction to produce N2 at high temperatures, small bubbles easily form at the interface between the silicon nitride ceramic and the oxygen-free copper, leading to copper layer bulging. The resulting silicon nitride ceramic copper clad substrate exhibits high surface porosity and poor bonding strength. (Harbin Institute of Technology) 1 In 2021, in a vacuum environment (5×10⁻⁶) -3 Under the condition of applying a uniaxial pressure of 2MPa-5MPa and heating to 805℃ for 30 minutes, the direct bonding of silicon nitride ceramic and copper was studied. The results showed that the silicon nitride ceramic debonded from the copper and obvious cracks appeared at the bonding interface, so it cannot be used directly.

[0004] References:

[0005] 1.Song Yanyu,et al."Fabrication of Si3N4 / Cu direct-bondedheterogeneous interface assisted by laser irradiation."Journal of MaterialsScience&Technology 99.(2022).doi:10.1016 / J.JMST.2021.05.032. Summary of the Invention

[0006] The purpose of this invention is to overcome the problems existing in the prior art and provide a ceramic copper-clad substrate and its preparation method. First, silicon nitride ceramic and copper sheet undergo a vacuum encapsulation pretreatment, followed by sintering in a hot isostatic pressing furnace. Compared to traditional direct copper-clad ceramic technology, this method, through encapsulation and limiting specific heating conditions and rates, ensures that the final silicon nitride copper-clad ceramic substrate has a uniform internal structure and tight bonding. Furthermore, the method of this invention has a lower temperature and better stability than existing technologies.

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

[0008] A method for preparing a ceramic copper-clad substrate includes the following steps:

[0009] (1) After ultrasonic cleaning, ceramic and metal sheets are placed into the encapsulation mold in the order of titanium sheet, metal, ceramic, metal and titanium sheet.

[0010] (2) Use dust-free paper dipped in anhydrous ethanol to wipe the entire furnace chamber of the discharge plasma sintering furnace. Place the cladding mold from step (1) into the discharge plasma sintering furnace, evacuate and heat to 700-750℃ and hold for 0.5h, then cool to room temperature at a rate of 10-30℃ / min.

[0011] (3) After the encapsulation in step (2) reaches a high vacuum state, it is taken out to obtain the workpiece to be welded in a high vacuum state. The workpiece to be welded in a high vacuum state is placed in a hot isostatic pressing furnace and heated to 700-750℃, and a pressure of 150-200Mpa is applied and kept at the temperature for 0.5h.

[0012] (4) After the hot isostatic pressing treatment in step (3), take out the cladding sample and cut it along the edge of the cladding sample to obtain a ceramic copper-clad substrate.

[0013] Furthermore, the sheathing material in step (1) is a titanium sheet.

[0014] Furthermore, the heating rate in step (2) is 20-25℃ / min, with a preferred heating rate of 20℃ / min.

[0015] The heating rate in step (3) is 20-30℃ / min, with a preferred heating rate of 20℃ / min.

[0016] Furthermore, in step (2), the vacuum level needs to reach 1.0 x 10⁻⁶. -3 ~1.0x10 -2 The preferred vacuum level is 1.0 x 10⁻⁶. -3 .

[0017] Furthermore, the ceramic is silicon nitride ceramic, and the metal is oxygen-free copper.

[0018] The beneficial effects of this invention compared to the prior art are:

[0019] In this invention, the silicon nitride ceramic and oxygen-free copper sheet are first encapsulated to isolate oxygen. The encapsulated sample is then placed in a spark plasma sintering furnace and evacuated to a vacuum of 1.0 x 10⁻⁶. -3 The sample is heated to 700-750℃ to obtain a sealed sample with a high vacuum inside. Finally, it is placed in a hot isostatic pressing furnace and subjected to a uniform pressure of 150-200 MPa and a temperature of 700-750℃ to ensure that the internal structure of the silicon nitride ceramic substrate is uniform and tightly bonded.

[0020] Traditional direct copper cladding (DBC) technology requires temperatures exceeding 1000 degrees Celsius to bond ceramics and copper. However, due to poor wettability between the metal and ceramic, voids easily form at the ceramic-copper interface, and the prepared ceramic substrate is unstable and prone to cracking after a period of time. In 2021, Harbin Institute of Technology achieved a breakthrough in a vacuum environment at 5 × 10⁻⁶ degrees Celsius. -3 Silicon nitride ceramic direct copper-clad substrates prepared by heating to 805℃ under a uniaxial pressure of 2MPa-5MPa under Pa showed that the silicon nitride ceramic debonded from the copper and obvious cracks appeared at the bonding interface.

[0021] Achieving a simple and tight bond between ceramic and copper using a modern method is currently very difficult and remains a challenging problem in this field. However, the ceramic-copper direct-coated substrate produced in this invention features a transition layer of approximately 2 μm thick formed by interdiffusion between the ceramic and copper sheets. This is demonstrated by SEM images of the ceramic-metal cross-section. Figure 2 It can be seen that silicon nitride ceramics are tightly bonded to copper and have a low porosity. Furthermore, after 100 thermal cycling tests, the silicon nitride ceramic direct copper-clad substrate prepared in this invention still did not crack. Attached Figure Description

[0022] Figure 1 This is a diagram illustrating the packaging sequence.

[0023] Figure 2 This is a SEM image of a ceramic-metal cross-section.

[0024] Figure 3 This is a line scan energy spectrum of the cross-section of a ceramic substrate. Detailed Implementation

[0025] 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.

[0026] Example 1

[0027] A method for preparing a ceramic copper-clad substrate, the specific steps of which are as follows:

[0028] (1) As Figure 1 The cleaned silicon nitride ceramic and oxygen-free copper sheet are placed into the encapsulation mold in the following order: titanium sheet, oxygen-free copper sheet, ceramic, oxygen-free copper sheet, and titanium sheet.

[0029] (2) After wiping the entire furnace chamber of the discharge plasma sintering furnace with lint-free paper soaked in anhydrous ethanol, place the cladding mold from step (1) into the discharge plasma sintering furnace and reduce the vacuum level to 1.0 x 10⁻⁶. -3 After the pressure drops below 6 MPa, heat to 750°C at a rate of 20°C / min. When the pressure reaches 6 MPa, maintain this temperature for 0.5 hours, ensuring the vacuum level inside the furnace does not exceed 1.0 x 10⁻⁶. -3 After the encapsulation is completed, the pressure is released and the temperature is lowered to room temperature at a rate of 10℃ / min to obtain an encapsulated sample in a high vacuum state.

[0030] (3) After the encapsulation in step (2) reaches a high vacuum state, it is taken out and placed in a hot isostatic pressing sintering furnace. The temperature is raised to 750°C at a rate of 20°C / min and held at a pressure of 180MPa for 0.5h to obtain a ceramic copper-clad substrate.

[0031] (4) After the hot isostatic pressing treatment in step (3), the cladding sample is taken out and cut along the edge of the cladding sample to obtain a ceramic copper-clad substrate.

[0032] The titanium sheet is a circle with a radius of 7cm, the silicon nitride ceramic is 15×15×0.3mm in size, and the copper sheet is 15×15×0.05mm in size.

[0033] After peel testing, the peel strength was 2.556 N / mm, which is the preferred embodiment.

[0034] Example 2

[0035] (1) As Figure 1 The cleaned silicon nitride ceramic and oxygen-free copper sheet are placed into the encapsulation mold in the following order: titanium sheet, oxygen-free copper sheet, ceramic, oxygen-free copper sheet, and titanium sheet.

[0036] (2) After wiping the entire furnace chamber of the discharge plasma sintering furnace with lint-free paper soaked in anhydrous ethanol, place the cladding mold from step (1) into the discharge plasma sintering furnace and reduce the vacuum level to 1.0 x 10⁻⁶. -3 After the pressure drops below 6 MPa, heat to 750°C at a rate of 25°C / min. When the pressure reaches 6 MPa, maintain this temperature for 0.5 hours, ensuring the vacuum level inside the furnace does not exceed 1.0 x 10⁻⁶. -3After the encapsulation is completed, the pressure is released and the temperature is lowered to room temperature at a rate of 10℃ / min to obtain an encapsulated sample in a high vacuum state.

[0037] (3) After the encapsulation in step (2) reaches a high vacuum state, it is taken out and placed in a hot isostatic pressing sintering furnace. The temperature is raised to 750°C at a rate of 20°C / min and held at a pressure of 180MPa for 0.5h to obtain a ceramic copper-clad substrate.

[0038] (4) After the hot isostatic pressing treatment in step (3), the cladding sample is taken out and cut along the edge of the cladding sample to obtain a ceramic copper-clad substrate.

[0039] The titanium sheet is a circle with a radius of 7cm, the silicon nitride ceramic is 15×15×0.3mm in size, and the copper sheet is 15×15×0.05mm in size.

[0040] After peel testing, the peel strength was 2.323 N / mm.

[0041] Example 3

[0042] (1) As Figure 1 The cleaned silicon nitride ceramic and oxygen-free copper sheet are placed into the encapsulation mold in the following order: titanium sheet, oxygen-free copper sheet, ceramic, oxygen-free copper sheet, and titanium sheet.

[0043] (2) After wiping the entire furnace chamber of the discharge plasma sintering furnace with lint-free paper soaked in anhydrous ethanol, place the cladding mold from step (1) into the discharge plasma sintering furnace and reduce the vacuum level to 1.0 x 10⁻⁶. -3 After the pressure drops below 6 MPa, heat to 750°C at a rate of 25°C / min. When the pressure reaches 6 MPa, maintain this temperature for 0.5 hours, ensuring the vacuum level inside the furnace does not exceed 1.0 x 10⁻⁶. -3 After the encapsulation is completed, the pressure is released and the temperature is lowered to room temperature at a rate of 10℃ / min to obtain an encapsulated sample in a high vacuum state.

[0044] (3) After the cladding in step (2) reaches a high vacuum state, it is taken out and placed in a hot isostatic pressing furnace. The temperature is raised to 750°C at a rate of 25°C / min and held at a pressure of 180MPa for 0.5h to obtain a ceramic copper-clad substrate.

[0045] (4) After the hot isostatic pressing treatment in step (3), the cladding sample is taken out and cut along the edge of the cladding sample to obtain a ceramic copper-clad substrate.

[0046] The titanium sheet is a circle with a radius of 7cm, the silicon nitride ceramic is 15×15×0.3mm in size, and the copper sheet is 15×15×0.05mm in size.

[0047] After peel testing, the peel strength was 2.421 N / mm.

[0048] Example 4

[0049] (1) As Figure 1 The cleaned silicon nitride ceramic and oxygen-free copper sheet are placed into the encapsulation mold in the following order: titanium sheet, oxygen-free copper sheet, ceramic, oxygen-free copper sheet, and titanium sheet.

[0050] (2) After wiping the entire furnace chamber of the discharge plasma sintering furnace with lint-free paper soaked in anhydrous ethanol, place the cladding mold from step (1) into the discharge plasma sintering furnace and reduce the vacuum level to 1.0 x 10⁻⁶. -3 After the pressure drops below 6 MPa, heat to 750°C at a rate of 25°C / min. When the pressure reaches 6 MPa, maintain this temperature for 0.5 hours, ensuring the vacuum level inside the furnace does not exceed 1.0 x 10⁻⁶. -3 After the encapsulation is completed, the pressure is released and the temperature is lowered to room temperature at a rate of 15℃ / min to obtain an encapsulated sample in a high vacuum state.

[0051] (3) After the encapsulation in step (2) reaches a high vacuum state, it is taken out and placed in a hot isostatic pressing sintering furnace. The temperature is raised to 750°C at a rate of 30°C / min and held at a pressure of 180MPa for 0.5h to obtain a ceramic copper-clad substrate.

[0052] (4) After the hot isostatic pressing treatment in step (3), the cladding sample is taken out and cut along the edge of the cladding sample to obtain a ceramic copper-clad substrate.

[0053] The titanium sheet is a circle with a radius of 7cm, the silicon nitride ceramic is 15×15×0.3mm in size, and the copper sheet is 15×15×0.05mm in size.

[0054] After peel testing, the peel strength was 2.131 N / mm.

[0055] Example 5

[0056] (1) As Figure 1 The cleaned silicon nitride ceramic and oxygen-free copper sheet are placed into the encapsulation mold in the following order: titanium sheet, oxygen-free copper sheet, ceramic, oxygen-free copper sheet, and titanium sheet.

[0057] (2) After wiping the entire furnace chamber of the discharge plasma sintering furnace with lint-free paper soaked in anhydrous ethanol, place the cladding mold from step (1) into the discharge plasma sintering furnace and reduce the vacuum level to 1.0 x 10⁻⁶. -2 After the pressure drops below 6 MPa, heat it to 750°C at a rate of 25°C / min. When the pressure reaches 6 MPa, maintain the pressure for 0.5 h. After the encapsulation is completed, release the pressure and cool it to room temperature at a rate of 20°C / min to obtain an encapsulated sample with an internal high vacuum state.

[0058] (3) After the encapsulation in step (2) reaches a high vacuum state, it is taken out and placed in a hot isostatic pressing sintering furnace. The temperature is raised to 750°C at a rate of 30°C / min and held at a pressure of 180MPa for 0.5h to obtain a ceramic copper-clad substrate.

[0059] (4) After the hot isostatic pressing treatment in step (3), the cladding sample is taken out and cut along the edge of the cladding sample to obtain a ceramic copper-clad substrate.

[0060] The titanium sheet is a circle with a radius of 7cm, the silicon nitride ceramic is 15×15×0.3mm in size, and the copper sheet is 15×15×0.05mm in size.

[0061] After peel testing, the peel strength was 2.013 N / mm.

[0062] Example 6

[0063] (1) As Figure 1 The cleaned silicon nitride ceramic and oxygen-free copper sheet are placed into the encapsulation mold in the following order: titanium sheet, oxygen-free copper sheet, ceramic, oxygen-free copper sheet, and titanium sheet.

[0064] (2) After wiping the entire furnace chamber of the discharge plasma sintering furnace with lint-free paper soaked in anhydrous ethanol, place the cladding mold from step (1) into the discharge plasma sintering furnace and reduce the vacuum level to 1.0 x 10⁻⁶. -2 After the pressure drops below 6 MPa, heat it to 750°C at a rate of 25°C / min. When the pressure reaches 6 MPa, maintain the pressure for 0.5 h. After the encapsulation is completed, release the pressure and cool it to room temperature at a rate of 30°C / min to obtain an encapsulated sample with an internal high vacuum state.

[0065] (3) After the encapsulation in step (2) reaches a high vacuum state, it is taken out and placed in a hot isostatic pressing sintering furnace. The temperature is raised to 750°C at a rate of 30°C / min and held at a pressure of 180MPa for 0.5h to obtain a ceramic copper-clad substrate.

[0066] (4) After the hot isostatic pressing treatment in step (3), the cladding sample is taken out and cut along the edge of the cladding sample to obtain a ceramic copper-clad substrate.

[0067] The titanium sheet is a circle with a radius of 7cm, the silicon nitride ceramic is 10×10×0.3mm in size, and the copper sheet is 15×15×0.05mm in size.

[0068] After peel testing, the peel strength was 2.105 N / mm.

[0069] Comparative Example 1

[0070] (1) Magnetron sputtering of Al was performed on both sides of a 0.32 mm thick silicon nitride ceramic substrate.

[0071] (2) Place the silicon nitride ceramic substrate with coating obtained in step (1) into a muffle furnace and heat it to 1300°C.

[0072] (3) Place the flat copper layer on the ceramic pad for pre-oxidation, and then bond the oxidized surface of the copper layer to the oxide-coated side of the thermally oxidized aluminum nitride ceramic substrate. Place it in an atmosphere with an O2 content of 35ppm at 1075℃ for 15min to obtain a silicon nitride ceramic copper-clad substrate.

[0073] Peel strength test: The peel strength in this study was 2.1 N / mm.

[0074] The difference between this invention and the previous one is that...

[0075] The pretreatment methods are different: this study magnetron sputtered Al on both sides of the silicon nitride ceramic and pre-oxidized the copper layer; this invention does not perform any surface treatment on the silicon nitride ceramic and copper, but directly vacuum-encapsulates the silicon nitride ceramic and copper sheet.

[0076] The preparation methods are different: In this study, an Al-plated silicon nitride ceramic substrate is first placed in a muffle furnace, and after an alumina is formed on the surface, a pre-oxidized copper sheet is bonded to it and then placed in a muffle furnace in an oxygen atmosphere to obtain a silicon nitride ceramic copper-clad substrate; while in this invention, the sample after vacuum encapsulation is directly placed in a hot isostatic pressing furnace for sintering.

[0077] As can be seen from the comparative examples, the silicon nitride ceramic copper-clad substrate preparation process provided by the present invention is simple, has low cost, and results in a tighter bond between the ceramic and the metallic copper.

[0078] 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 a ceramic copper-clad substrate, characterized in that, Includes the following steps: (1) After ultrasonic cleaning, ceramic and oxygen-free copper sheets are placed into the encapsulation mold in the order of titanium sheet, oxygen-free copper sheet, ceramic, oxygen-free copper sheet and titanium sheet. (2) Use a dust-free paper dipped in anhydrous ethanol to wipe the entire furnace chamber of the discharge plasma sintering furnace. Place the cladding mold from step (1) into the discharge plasma sintering furnace, evacuate it, raise the temperature to 700-750℃ and hold it for 0.5h, then lower it to room temperature at a rate of 10-30℃ / min. (3) After the encapsulation in step (2) reaches a high vacuum state, it is taken out to obtain the workpiece to be welded in a high vacuum state. The workpiece to be welded in a high vacuum state is placed in a hot isostatic pressing sintering furnace and heated to 700-750℃, and a pressure of 180MPa is applied and kept at the temperature for 0.5h. (4) After the hot isostatic pressing treatment in step (3), take out the cladding sample and cut it along the edge of the cladding sample to obtain a ceramic copper-clad substrate. The sheathing material in step (1) is titanium sheet; The heating rate in step (2) is 20℃ / min; The heating rate in step (3) is 20-30℃ / min; The ceramic is silicon nitride ceramic; In step (2), the vacuum level needs to reach 1.0 x 10⁻⁶. -3 ~1.0x10 -2 Pa.

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