Method for refining copper grains on surface of ceramic copper-clad substrate

Abstract

The invention provides a method for refining copper grains on the surface of a ceramic copper-clad substrate. The method comprises the following steps: (1) sequentially carrying out oxidation treatment and sintering treatment on a copper strip; and (2) the copper strip subjected to sintering treatment in the step (1) is attached to a ceramic substrate, brazing treatment is carried out, and the ceramic copper-clad substrate is obtained. According to the method, after the copper strip is subjected to oxidation treatment and sintering treatment, the ceramic substrate and the treated copper strip are brazed, so that the grain size of copper on the surface of the ceramic copper-clad substrate is effectively controlled, the average grain size of the copper on the surface of the ceramic copper-clad substrate is 60-150 microns, and the bonding strength of a surface lead is high.

Description

Technical Field

[0001] The invention belongs to the technical field of ceramic metallization and relates to a method for refining copper grains on the surface of a ceramic copper-clad substrate. Background Art

[0002] Most power hybrid integrated circuit packaging materials have been using Al2O3 and BeO ceramics, but due to performance, environmental protection, cost and other factors, these materials can no longer fully meet the needs of the development of power electronic devices. Therefore, a new type of AMB (Active Metal Brazing) ceramic with superior comprehensive performance, including alumina ceramics, aluminum nitride ceramics or silicon nitride ceramics, will undoubtedly become a substitute for traditional Al2O3 and BeO ceramics. Compared with Al2O3 and BeO ceramics, AMB ceramics not only have higher thermal conductivity, but also have a good thermal expansion coefficient that matches well with semiconductor materials such as Si and Ge, and have good electrical properties and mechanical strength, making them ideal power electronic packaging materials.

[0003] To achieve reliable connection between AMB materials and electronic chips, it is usually necessary to metallize the surface of AMB ceramics. Therefore, making AMB ceramic copper-clad substrates is a key step in the application of AMB ceramics. AMB ceramic substrates are usually composite materials that use active metal solders containing a small amount of active elements to achieve welding between copper foil and ceramic substrates.

[0004] At present, in the conventional AMB process, the oxygen-free copper strip is first cleaned by surface deoxidation, and then the oxygen-free copper strip is covered on both sides of the ceramic substrate and high-temperature welded at the same time to form the copper grain state on the surface of the AMB ceramic substrate. However, the larger copper grain size (300-500μm) will cause the AMB ceramic substrate to produce the orange peel phenomenon of roughened metal surface due to the separate off-plane displacement of the metal surface crystals during the temperature shock process. At the same time, there will also be problems such as low surface wire bonding strength and poor silver sintering bonding strength.

[0005] In summary, a method for refining copper grains on the surface of a ceramic copper-clad substrate is provided to adjust the average grain size of the surface copper to 60-150 μm, which is a key technical means to solve the low wire bonding strength on the surface of AMB ceramic substrates. Summary of the invention

[0006] The object of the present invention is to provide a method for refining copper grains on the surface of a ceramic copper-clad substrate, by performing an oxidation treatment and a sintering treatment on an oxygen-free copper strip, and then brazing the ceramic substrate and the treated copper strip, so that the average grain size of the copper on the surface of the obtained ceramic copper-clad substrate is 60-150 μm, and the surface lead bonding strength is high.

[0007] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0008] The present invention provides a method for refining copper grains on the surface of a ceramic copper-clad substrate, the method comprising the following steps:

[0009] (1) The copper strip is subjected to oxidation treatment and sintering treatment in sequence;

[0010] (2) The copper strip sintered in step (1) is bonded to a ceramic substrate and brazed to obtain a ceramic copper-clad substrate.

[0011] In the present invention, copper tapes are bonded to both surfaces of the ceramic substrate.

[0012] The present invention provides a method for refining copper grains on the surface of a ceramic copper-clad substrate. The method comprises the following steps: performing an oxidation treatment on an oxygen-free copper strip to form a Cu2O pre-oxidation layer on the Cu surface, and then performing a sintering treatment. By high-temperature sintering, the Cu2O layer on the surface is reduced to a Cu layer, and the grain size of the copper can be controlled. Finally, the ceramic substrate and the treated copper strip are brazed. The method can effectively control the grain size of the copper on the surface of the ceramic copper-clad substrate, and avoid the problem of low surface lead bonding strength of the ceramic copper-clad substrate.

[0013] As a preferred technical solution of the present invention, the copper strip in step (1) is an oxygen-free copper strip.

[0014] As a preferred technical solution of the present invention, the oxidation treatment in step (1) is carried out under the protection of an inert gas.

[0015] In the present invention, the inert gas includes nitrogen and / or argon.

[0016] Preferably, the oxygen content of the oxidation treatment in step (1) is 300-1000ppm, for example, it can be 350ppm, 400ppm, 450ppm, 500ppm, 550ppm, 600ppm, 650ppm, 700ppm, 750ppm, 800ppm, 850ppm, 900ppm or 950ppm, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0017] In the present invention, the oxygen content refers to the volume content of oxygen.

[0018] It is worth noting that the control of oxygen content during the oxidation treatment affects the surface copper grain size. If the oxygen content of the oxidation treatment is too low, the oxide layer formed on the surface is too thin, resulting in uneven growth of the average surface copper grain size of the obtained ceramic copper-clad substrate and affecting the surface wire bonding strength; if the oxygen content of the oxidation treatment is too high, the oxide layer formed on the surface is too thick, resulting in an increase in the average surface copper grain size of the obtained ceramic copper-clad substrate and affecting the surface wire bonding strength.

[0019] As a preferred technical solution of the present invention, the temperature of the oxidation treatment in step (1) is 500-900°C, for example, it can be 550°C, 600°C, 650°C, 700°C, 750°C, 800°C, 850°C or 880°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0020] It is worth noting that if the temperature of the oxidation treatment is too low, the oxide layer formed on the surface is too thin, resulting in uneven growth of the average grain size of the surface copper of the obtained ceramic copper-clad substrate, and affecting the surface wire bonding strength; when the temperature of the oxidation treatment is too high, the oxide layer formed on the surface is too thick, resulting in an increase in the average grain size of the surface copper of the ceramic copper-clad substrate, and affecting the surface wire bonding strength.

[0021] Preferably, the oxidation treatment time in step (1) is 10-60 min, for example, it can be 15 min, 20 min, 30 min, 35 min, 40 min, 45 min, 50 min or 55 min, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0022] As a preferred technical solution of the present invention, the sintering treatment in step (1) is carried out under the protection of an inert gas.

[0023] Preferably, the oxygen content of the sintering treatment in step (1) is 5-100 ppm, for example, it can be 10 ppm, 15 ppm, 20 ppm, 25 ppm, 30 ppm, 35 ppm, 40 ppm, 45 ppm, 50 ppm, 55 ppm, 60 ppm, 75 ppm, 80 ppm, 85 ppm, 90 ppm or 95 ppm, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0024] It is worth noting that if the sintering treatment is carried out under oxygen-free and inert gas protection conditions, the average grain size of the surface copper of the obtained ceramic copper-clad substrate grows unevenly due to the lack of atmosphere protection, and affects the surface wire bonding strength; when the oxygen content of the sintering treatment is too high, the oxide layer formed is too thick, resulting in an increase in the average grain size of the surface copper of the ceramic copper-clad substrate and affecting the surface wire bonding strength.

[0025] As a preferred technical solution of the present invention, the temperature of the sintering treatment in step (1) is 950-1080°C, for example, it can be 960°C, 970°C, 980°C, 990°C, 1000°C, 1010°C, 1020°C, 1030°C, 1040°C, 1050°C, 1060°C or 1070°C, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0026] It is worth noting that by regulating the oxygen content and temperature range during the sintering process of the oxidized copper strip, it is beneficial to refine the copper grains and avoid the problem of copper grain re-growth. If the sintering temperature is too low, the average copper grain size on the surface of the ceramic copper-clad substrate will grow unevenly due to the failure to reach the grain growth temperature, and the surface wire bonding strength will be affected; if the sintering temperature is too high, the grain growth will increase, resulting in a larger average copper grain size on the surface of the ceramic copper-clad substrate, and the surface wire bonding strength will be affected.

[0027] Preferably, the sintering time in step (1) is 10-60 min, for example, 15 min, 20 min, 30 min, 35 min, 40 min, 45 min, 50 min or 55 min, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0028] As a preferred technical solution of the present invention, the material of the ceramic substrate in step (2) includes any one of aluminum oxide, aluminum nitride or silicon nitride.

[0029] Preferably, the brazing process in step (2) is performed under vacuum or inert gas protection.

[0030] As a preferred technical solution of the present invention, the temperature of the brazing treatment in step (2) is 800-900°C, for example, it can be 810°C, 820°C, 830°C, 840°C, 850°C, 860°C, 870°C, 880°C or 890°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0031] Preferably, the brazing treatment time in step (2) is 10-60 min, for example, it can be 15 min, 20 min, 30 min, 35 min, 40 min, 45 min, 50 min or 55 min, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0032] As a preferred technical solution of the present invention, the average grain size of the surface copper of the ceramic copper-clad substrate in step (2) is 60-150 μm, for example, it can be 65 μm, 70 μm, 75 μm, 80 μm, 85 μm, 90 μm, 95 μm, 100 μm, 105 μm, 110 μm, 115 μm, 120 μm, 125 μm, 130 μm, 135 μm, 140 μm or 145 μm, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable, preferably 60-70 μm.

[0033] As a preferred technical solution of the present invention, the method comprises the following steps:

[0034] (1) The oxygen-free copper strip is oxidized in an inert gas with an oxygen content of 300-1000 ppm and a temperature of 500-900° C. for 10-60 min, and then sintered in an inert gas with an oxygen content of 5-100 ppm and a temperature of 950-1080° C. for 10-60 min;

[0035] (2) laminating the copper strip sintered in step (1) onto a ceramic substrate, and performing a brazing treatment for 10-60 min under vacuum or inert gas to obtain a ceramic copper-clad substrate having an average surface copper grain size of 60-150 μm;

[0036] The material of the ceramic substrate includes any one of aluminum oxide, aluminum nitride or silicon nitride;

[0037] The temperature of the brazing process is 800-900°C.

[0038] Compared with the prior art, the present invention has the following beneficial effects:

[0039] (1) The method for refining copper grains on the surface of a ceramic copper-clad substrate provided by the present invention is a process method in which an oxygen-free copper strip is subjected to oxidation treatment and sintering treatment, and then the ceramic substrate and the treated copper strip are brazed. Combined with controlling the oxygen content, temperature and other relevant parameter ranges of the above process, the grain size of the copper on the surface of the ceramic copper-clad substrate is effectively controlled, so that the average grain size of the copper on the surface of the ceramic copper-clad substrate is 60-150 μm, and the surface wire bonding strength is high;

[0040] (2) The method for refining copper grains on the surface of a ceramic copper-clad substrate provided by the present invention has simple process operation, does not require complicated process conditions, has low preparation cost, and has wide applicability. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 The SEM image (X100) of the surface copper grains of the ceramic copper-clad substrate obtained in Example 1;

[0042] Figure 2 This is the SEM image (X100) of the surface copper grains of the ceramic copper-clad substrate obtained in Comparative Example 2. DETAILED DESCRIPTION

[0043] The technical solution of the present invention is further described below by specific implementation methods. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0044] Example 1

[0045] This embodiment provides a method for refining copper grains on the surface of a ceramic copper-clad substrate, the method comprising the following steps:

[0046] (1) The oxygen-free copper strip was oxidized in a N2 atmosphere with an oxygen content of 600 ppm and a temperature of 700°C for 30 min, and then sintered in a N2 atmosphere with an oxygen content of 50 ppm and a temperature of 1020°C for 30 min;

[0047] (2) The copper strip sintered in step (1) was bonded to an AlN ceramic substrate and placed under a vacuum of 1×10 -3 The brazing treatment was carried out at a temperature of 850° C. and 30 min to obtain an AlN ceramic copper-clad substrate.

[0048] In this embodiment, the average grain size of copper on the surface of the obtained AlN ceramic copper-clad substrate is 61.1 μm. Figure 1 shown.

[0049] Example 2

[0050] This embodiment provides a method for refining copper grains on the surface of a ceramic copper-clad substrate, the method comprising the following steps:

[0051] (1) The oxygen-free copper strip was oxidized in a N2 atmosphere with an oxygen content of 300 ppm and a temperature of 900°C for 15 min, and then sintered in a N2 atmosphere with an oxygen content of 5 ppm and a temperature of 1080°C for 15 min;

[0052] (2) The copper strip sintered in step (1) is bonded to a SiN ceramic substrate, and brazing is performed for 15 min in a N2 atmosphere at a temperature of 900°C to obtain a SiN ceramic copper-clad substrate.

[0053] Example 3

[0054] This embodiment provides a method for refining copper grains on the surface of a ceramic copper-clad substrate, the method comprising the following steps:

[0055] (1) The oxygen-free copper strip was oxidized in a N2 atmosphere with an oxygen content of 1000 ppm and a temperature of 500°C for 60 min, and then sintered in a N2 atmosphere with an oxygen content of 100 ppm and a temperature of 950°C for 60 min;

[0056] (2) The copper strip sintered in step (1) is bonded to an AlN ceramic substrate, and brazing is performed for 60 min in an Ar atmosphere at a temperature of 800° C. to obtain an AlN ceramic copper-clad substrate.

[0057] Comparative Example 1

[0058] This comparative example provides a method for refining copper grains on the surface of a ceramic copper-clad substrate. Except that the sintering treatment in step (1) is not performed, other conditions are the same as those in Example 1.

[0059] Comparative Example 2

[0060] The comparative example provides a method for refining copper grains on the surface of a ceramic copper-clad substrate, the method comprising: deoxidizing and cleaning an oxygen-free copper strip, and then laminating the oxygen-free copper strip on an AlN ceramic substrate, and -3 The brazing treatment was carried out at a temperature of 850° C. and 30 min to obtain an AlN ceramic copper-clad substrate.

[0061] In this comparative example, the average grain size of copper on the surface of the obtained AlN ceramic copper-clad substrate is 393.2 μm. Figure 2 shown.

[0062] The ceramic copper-clad substrates obtained in the above examples and comparative examples were tested, wherein the average grain size of the surface copper of the ceramic copper-clad substrate was tested according to the cross-section method disclosed in the national standard GB / T 6394-2017 "Method for Determining Average Grain Size of Metals". The results are shown in Table 1.

[0063] Table 1

[0064] Average grain size of surface copper (μm) Thrust value (g) Example 1 61.1 1220.4 Example 2 62.5 1230.3 Example 3 61.3 1377.0 Comparative Example 1 403.3 1142.5 Comparative Example 2 393.2 1165.5

[0065] From Table 1, we can see that:

[0066] (1) The method for refining copper grains on the surface of a ceramic copper-clad substrate provided in Examples 1-3 of the present invention comprises a process of performing oxidation treatment and sintering treatment on an oxygen-free copper strip and then brazing the ceramic substrate and the treated copper strip, and controlling the relevant parameter ranges of the above process. The average grain size of copper on the surface of the obtained ceramic copper-clad substrate is 60-70 μm, and the surface wire bonding strength is high;

[0067] (2) By comparing Example 1 with Comparative Examples 1-2, it can be seen that when the sintering treatment is not performed, the average grain size of the surface copper of the ceramic copper clad substrate is too large because the grains do not change, and the surface wire bonding strength is low; when the conventional process is used for treatment, that is, when the oxidation + sintering treatment is not performed, there is no introduction of oxygen, and the grain production does not change. The average grain size of the surface copper of the obtained ceramic copper clad substrate is too large, and the surface wire bonding strength is low.

[0068] The applicant declares that the present invention illustrates the detailed structural features of the present invention through the above-mentioned embodiments, but the present invention is not limited to the above-mentioned detailed structural features, that is, it does not mean that the present invention must rely on the above-mentioned detailed structural features to be implemented. Those skilled in the art should understand that any improvement of the present invention, equivalent replacement of the components selected by the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for refining copper grains on the surface of a ceramic copper-clad substrate, characterized in that: The method comprises the following steps: (1) The copper strip is subjected to oxidation treatment and sintering treatment in sequence; (2) The copper strip sintered in step (1) is bonded to a ceramic substrate and brazed to obtain a ceramic copper-clad substrate.

2. The method according to claim 1, characterized in that The copper strip in step (1) is an oxygen-free copper strip.

3. The method according to claim 1 or 2, characterized in that: The oxidation treatment in step (1) is carried out under the protection of an inert gas; Preferably, the oxygen content in the oxidation treatment in step (1) is 300-1000 ppm.

4. The method according to any one of claims 1 to 3, characterized in that: The temperature of the oxidation treatment in step (1) is 500-900° C. Preferably, the oxidation treatment time in step (1) is 10-60 min.

5. The method according to any one of claims 1 to 4, characterized in that: The sintering process in step (1) is carried out under the protection of an inert gas; Preferably, the oxygen content of the sintering treatment in step (1) is 5-100 ppm.

6. The method according to any one of claims 1 to 5, characterized in that: The sintering temperature in step (1) is 950-1080°C; Preferably, the sintering time in step (1) is 10-60 minutes.

7. The method according to any one of claims 1 to 6, characterized in that: The material of the ceramic substrate in step (2) includes any one of aluminum oxide, aluminum nitride or silicon nitride; Preferably, the brazing process in step (2) is performed under vacuum or inert gas protection.

8. The method according to any one of claims 1 to 7, characterized in that: The temperature of the brazing treatment in step (2) is 800-900°C; Preferably, the brazing treatment time in step (2) is 10-60 minutes.

9. The method according to any one of claims 1 to 8, characterized in that: The average grain size of the surface copper of the ceramic copper-clad substrate in step (2) is 60-150 μm, preferably 60-70 μm.

10. The method according to any one of claims 1 to 9, characterized in that: The method comprises the following steps: (1) The oxygen-free copper strip is oxidized in an inert gas with an oxygen content of 300-1000 ppm and a temperature of 500-900° C. for 10-60 min, and then sintered in an inert gas with an oxygen content of 5-100 ppm and a temperature of 950-1080° C. for 10-60 min; (2) laminating the copper strip sintered in step (1) onto a ceramic substrate, and performing a brazing treatment for 10-60 min under vacuum or inert gas to obtain a ceramic copper-clad substrate having an average surface copper grain size of 60-150 μm; The material of the ceramic substrate includes any one of aluminum oxide, aluminum nitride or silicon nitride; The temperature of the brazing process is 800-900°C.

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