Method for pre-determining heat resistance of high-purity oxygen-free copper strip for DBC ceramic copper cladding

Abstract

A method for pre-determining the heat resistance of a high-purity oxygen-free copper strip for DBC ceramic copper cladding, comprising: firstly, sampling and cleaning a high-purity oxygen-free copper strip with Vickers hardness greater than or equal to 105, drying and then heating in an air atmosphere at 900-950°C for 30-60 minutes, and naturally cooling to room temperature after leaving a furnace; then performing determination according to one of the following methods: (1) performing electrolytic polishing treatment on a cooled sample, taking the sample out to observe the falling-off situation of an oxide film, and if the oxide film on the surface of the sample is dense and difficult to remove, and remains intact, indicating that the high-purity oxygen-free copper strip has good heat resistance; and (2) soaking the cooled sample in a nitric acid solution, then taking the sample out to observe the falling-off situation of an oxide scale, and if the oxide film on the surface of the soaked sample is dense and difficult to remove, and remains intact, indicating that the copper strip has good heat resistance. The method can achieve rapid testing and evaluation of the heat resistance of the high-purity oxygen-free copper strip for DBC ceramic copper cladding, and determine whether the high-purity oxygen-free copper strip can meet the requirements of ceramic cladding.

Description

A method for predicting the heat resistance of high-purity oxygen-free copper strip for DBC ceramic copper cladding Technical Field

[0001] The invention belongs to the field of nonferrous metal smelting and processing, and particularly relates to a method for predicting the heat resistance of a high-purity oxygen-free copper strip for DBC ceramic copper cladding. Background Art

[0002] As core components for energy conversion and transmission, IGBT modules are widely used in new energy vehicles, rail transit, power engineering, and smart grids. Their high integration, high power, and miniaturization trends require that the high-purity oxygen-free copper strips used in electronic packaging ceramic cladding exhibit high heat resistance, high thermal conductivity, low stress, and low thermal expansion.

[0003] Low-thermal-resistance DBC ceramic copper tape for IGBT modules is a composite material formed by directly bonding high-purity oxygen-free copper tape to a ceramic substrate on one or both sides at temperatures of 1060-1075°C. To facilitate etching in the next step, the copper tape must maintain a fine-grained state, with a grain size of ≤100μm, placing high demands on the heat resistance of the copper tape grains.

[0004] How to quickly and easily evaluate the heat resistance of high-purity oxygen-free copper strip and determine whether it meets the grain size requirements for ceramic lamination is currently a significant challenge for copper processing companies. Effective testing requires a thorough understanding of the ceramic lamination process and the use of the same equipment. Finding a method to rapidly test the heat resistance of high-purity oxygen-free copper strip, quickly determine whether it meets the requirements for ceramic lamination, and apply it to industrial production, is a major technical challenge facing copper processing companies. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for predicting the heat resistance of high-purity oxygen-free copper strip for DBC ceramic copper cladding, so as to realize rapid detection and evaluation of the heat resistance of high-purity oxygen-free copper strip for DBC ceramic copper cladding, and to judge whether the high-purity oxygen-free copper strip can meet the requirements of ceramic cladding.

[0006] To achieve the above objectives, the present invention adopts a technical solution: a method for predicting the heat resistance of high-purity oxygen-free copper strip for DBC ceramic copper cladding, first, sampling and cleaning the high-purity oxygen-free copper strip with a Vickers hardness of ≥105, drying it, heating it in an air atmosphere at 900°C-950°C for 30-60 minutes, and then naturally cooling it to room temperature after being removed from the furnace; then, judging it according to one of the following methods:

[0007] (1) The cooled sample is electrolytically polished, and then taken out to observe the oxide film shedding. If the oxide film on the surface of the sample is dense and difficult to remove and remains intact, it means that the heat resistance of the high-purity oxygen-free copper strip is good and can meet the requirements of DBC lamination between the high-purity oxygen-free copper strip and the ceramic substrate; otherwise, the heat resistance of the high-purity oxygen-free copper strip cannot meet the requirements of DBC lamination between the high-purity oxygen-free copper strip and the ceramic substrate;

[0008] (2) The cooled sample is immersed in nitric acid solution, and then taken out to observe the oxide scale shedding. If the oxide film on the surface of the sample after immersion is dense and difficult to remove and remains intact, it means that the copper strip has good heat resistance and can meet the requirements of DBC lamination of high-purity oxygen-free copper strip and ceramic substrate; otherwise, the heat resistance of the high-purity oxygen-free copper strip cannot meet the requirements of DBC lamination of high-purity oxygen-free copper strip and ceramic substrate.

[0009] The electrolyte used in the electrolytic polishing treatment is prepared by mixing water and 85% phosphoric acid in a volume ratio of 3:4.

[0010] The working voltage of the electrolytic polishing process is 30-50V, and the processing time is 1-10 seconds.

[0011] The volume fraction of the nitric acid solution is 30-50%, and the soaking time is 5-20 minutes.

[0012] When cleaning the sample, a mixed solution of dilute sulfuric acid and dilute nitric acid is used as the cleaning solution.

[0013] The volume fractions of the dilute sulfuric acid and the dilute nitric acid are both 10%, and the volume ratio of the dilute sulfuric acid to the dilute nitric acid is 1:1.

[0014] The sample is heated using a high temperature resistance furnace.

[0015] The high temperature resistance furnace is a muffle furnace or a tubular resistance furnace.

[0016] The principle of the present invention is that ceramic-clad high-purity oxygen-free copper strips produced using the DBC process typically require an HV ≥ 105. The inventors have discovered that when samples of high-purity oxygen-free copper strips with an HV ≥ 105 are heated at 900-950°C for 30-60 minutes in an air atmosphere, the density of the oxide film on the surface of the samples is closely correlated with the heat resistance of the high-purity oxygen-free copper strips at high temperatures.

[0017] For oxygen-free copper strip with HV≥105, after heating at 950℃ for 30 minutes, the oxide scale and the matrix are easily separated, and the grain size of the strip after baking is usually above 500μm, and the heat resistance is poor; if the oxide scale and the matrix are tightly combined, the grain size of the strip after baking is ≤80μm, and after DBC ceramic coating at a temperature of 1060-1075℃, the grain size of the copper strip is tested to be ≤100μm, and the heat resistance can meet the use requirements.

[0018] Therefore, by detecting and observing the density of the oxide film after baking, it is possible to predict whether the high-purity oxygen-free copper strip meets the heat resistance requirements of DBC ceramic cladding, and the accuracy of the heat resistance prediction can be verified by the average grain size of the copper strip after the high-purity oxygen-free copper strip is clad with the ceramic substrate DBC.

[0019] The beneficial effects of the present invention are as follows: the present invention solves the difficult problem of predicting the heat resistance of high-purity oxygen-free copper strip for DBC ceramic copper cladding before the copper strip leaves the factory. The operation process is mainly realized by Vickers hardness detection and oxide scale peeling resistance. By creatively conducting oxide scale peeling tests and combining conventional inspection methods, the difficult problem of the detection method of the heat resistance of high-purity oxygen-free copper strip for DBC ceramic cladding is solved. The present invention is suitable for the production of high-purity oxygen-free copper strip and can quickly predict whether the heat resistance of the high-purity oxygen-free copper strip meets the requirements of DBC ceramic cladding. DETAILED DESCRIPTION

[0020] The present invention will be further described in detail below with reference to the examples, but they are not intended to limit the invention in any way.

[0021] A method for predicting the heat resistance of high-purity oxygen-free copper strip for DBC ceramic copper cladding, wherein the high-purity oxygen-free copper refers to pure copper with a copper content of 99.99% and an oxygen content of less than 10 ppm. The method comprises the following steps:

[0022] 1. Sampling: Cut two square samples of approximately 50×50mm in thickness from the coiled strip.

[0023] 2. Vickers hardness test: Use a Vickers hardness tester to test the sample in accordance with the method of "Vickers hardness test for metallic materials" in GB / T4340.1-2009;

[0024] 3. For samples with a Vickers hardness of 105 or above, perform oxide film peeling test;

[0025] 3.1. Cleaning: Use a mixed solution of dilute sulfuric acid (10% volume fraction) and dilute nitric acid (10% volume fraction) in a volume ratio of 1:1, then rinse with running water and dry;

[0026] 3.2. Baking: Place the cleaned and dried sample on a stand in a high-temperature resistance furnace and heat it at 900℃-950℃ in air atmosphere for 30-60 minutes;

[0027] 3.3 Cooling: After being taken out of the furnace, cool naturally to room temperature and visually observe the peeling of the oxide film on the surface of the copper substrate;

[0028] 3.4. Electrolytic polishing: After cooling in step 3.3, clamp the sample with a clamp and place it in an electrolyte. Connect the power supply to a working voltage of 30-50 V for 1-10 seconds. After polishing, remove the sample and observe the oxide film shedding. The electrolyte is a mixture of water and 85% phosphoric acid in a volume ratio of 3:4.

[0029] 3.5. Nitric acid immersion: Soak the sample after cooling in step 3.3 in a 30-50% nitric acid solution for 5-20 minutes. After soaking, take it out and observe the fall of oxide scale.

[0030] Judgment method: (1) For the sample treated with electrolytic polishing, if the oxide film on the surface of the sample is dense and difficult to remove after polishing, and remains intact, it means that the heat resistance of the copper strip is good and can meet the requirement that the average grain size of the copper strip is ≤100μm after being laminated with the ceramic substrate at 1060-1075℃;

[0031] (2) For the samples treated with nitric acid immersion, the oxide film on the surface of the sample after immersion is dense, difficult to remove, and remains intact, which means that the copper strip has good heat resistance and can meet the requirement that the average grain size of the copper strip is ≤100μm after being laminated with the ceramic substrate at 1060-1075℃.

[0032] Both steps 3.4 and 3.5 can be used to treat the oxide film of the copper strip. You only need to choose one of the two steps and use the judgment method corresponding to the selected step to predict the heat resistance.

[0033] In the above method, the high-temperature resistance furnace can be a muffle furnace or a tubular resistance furnace.

[0034] The following examples and comparative examples illustrate the detection method of the above invention in more detail, but the present invention is not limited thereto.

[0035] First, oxygen-free copper with the same composition content is processed to the same finished strip thickness to obtain strips with the same or different hardness.

[0036] Samples of the same grade of strip were taken, cleaned, and baked in an air atmosphere high-temperature resistance furnace at 900-950°C for 30-60 minutes. After baking, the strips were removed and naturally cooled to room temperature. The above methods (1) and (2) were used for testing. The bonding between the oxide film on the copper substrate and the copper strip surface and the removal of the black oxide film were visually observed.

[0037] When using method (1) and method (2) for testing, electrolytic polishing or nitric acid soaking treatment is required accordingly.

[0038] The copper strip used in Examples 1 and 2 was C10100, and the heating conditions were 950°C / 30 minutes. The copper strip used in Examples 3 and 4 was TU1, and the heating conditions were 900°C / 60 minutes. The copper strip used in Examples 5 and 6 was C10200, and the heating conditions were 920°C / 45 minutes. The copper strip used in Comparative Examples 1 and 2 and the heating conditions were the same as in Example 1; the copper strip used in Comparative Examples 3 and 4 and the heating conditions were the same as in Example 3; and the copper strip used in Comparative Examples 5 and 6 and the heating conditions were the same as in Example 5.

[0039] Hardness HV: The hardness of the test material was measured. If the HV reached 105 or above, it was evaluated as "qualified", and if the HV was less than 105, it was evaluated as "unqualified". The specific test values ​​of HV of each embodiment and comparative example are listed in Table 1.

[0040] Oxide film peeling: After heating, baking, and natural cooling, the oxide film of the sample was subjected to the aforementioned electrolytic polishing and acid leaching treatments, and the oxide film peeling was observed. If the oxide film did not peel easily, it was evaluated as "dense", and otherwise it was evaluated as "not dense". The oxide film peeling conditions of various examples and comparative examples are listed in Table 1.

[0041] Heat resistance verification: Heat resistance verification requires measuring the average grain size of the copper strip after sintering. When the average grain size is ≤100μm, it means that the heat resistance of the copper strip meets the requirements for lamination with the ceramic substrate.

[0042] The copper strip baked in the air according to the present invention has an oxide film on its surface. If the average grain size of the copper strip is to be measured, the oxide film needs to be removed, but the removal of the oxide film is relatively difficult. Therefore, in order to facilitate the heat resistance verification, each sample of the embodiment is DBC-laminated with a ceramic substrate under a vacuum environment, and the sintering temperature is 1070°C. After lamination, the average grain size of the copper strip after lamination is measured according to the standard "grain size of copper and copper alloys" method. If the average grain size is ≤100μm, it is evaluated as "qualified", indicating that the corresponding copper strip has good heat resistance and meets the requirements for lamination with the ceramic substrate; otherwise, it is evaluated as "unqualified", indicating that the thermal stability of the corresponding copper strip does not meet the requirements for lamination with the ceramic substrate.

[0043] For the comparative examples, copper strips of the same grade and thickness as those used in the various examples were selected. The hardness of the comparative example copper strips was similar to that of the corresponding copper strips used in the examples. However, the comparative example copper strips and the corresponding example copper strips were produced by different manufacturers and were not identically processed. The comparative example copper strips were treated using the method of the present invention and tested according to the aforementioned heat resistance testing method. The average grain size of the copper strips was then measured. The average grain size values ​​for the various examples and comparative examples are listed in Table 1.

[0044]

[0045] Table 1 Test results of examples and comparative examples

[0046] In Examples 1-6, shown in Table 1, high-purity oxygen-free copper strips of varying grades and thicknesses for DBC ceramic lamination were treated using the method described herein. Visual inspection revealed that the scale on the samples adhered tightly to the substrate and was difficult to remove by electrolysis or acid leaching. This suggests that the copper strips possess excellent heat resistance and meet the requirements for lamination with ceramic substrates. Heat resistance testing confirmed that the copper strips of Examples 1-6, after lamination with ceramic substrates under vacuum conditions, all exhibited average grain sizes of less than 100 μm.

[0047] In Comparative Examples 1-6 shown in Table 1, the grade and thickness of the oxygen-free copper strips are the same as those in the examples, and the hardness values ​​of the strips are also similar to those in Examples 1-6. After treatment with the method described herein, visual inspection of the oxygen-free copper strips revealed that the oxide film on the samples was not tightly bonded to the substrate, and some fell off upon cooling. The remaining portions can be removed by electrolysis or acid leaching, resulting in a bright copper surface. In this case, the heat resistance of the copper strips is expected to be poor and not meet the requirements for lamination with ceramic substrates. Further heat resistance verification showed that the copper strips of Comparative Examples 1-6, after lamination with ceramic substrates under vacuum conditions, all had average grain sizes greater than 100 μm.

[0048] By comparing the above embodiments and comparative examples and the corresponding heat resistance verification, it is found that the oxide film peeling test results correspond to the heat resistance verification results. Therefore, the method for predicting the heat resistance of high-purity oxygen-free copper strip for DBC ceramic copper cladding described in the present invention is feasible.

[0049] The above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the same. Those skilled in the art should understand that the specific implementation methods of the present invention can be modified or replaced with equivalents with reference to the above embodiments. Any modifications or equivalent replacements that do not depart from the spirit and scope of the present invention are within the scope of protection of the pending claims.

Claims

1. A method for predicting the heat resistance of a high-purity oxygen-free copper strip for DBC ceramic copper cladding, characterized in that: First, sample and clean the high-purity oxygen-free copper strip with Vickers hardness ≥ 105, dry it, heat it at 900℃-950℃ in air atmosphere for 30-60 minutes, and cool it naturally to room temperature after it comes out of the furnace; then, judge it according to one of the following methods: (1) The cooled sample is electropolished, and then taken out to observe the oxide film shedding. If the oxide film on the surface of the sample is dense and difficult to remove and remains intact, it means that the heat resistance of the high-purity oxygen-free copper strip is good and can meet the requirements of DBC lamination of the high-purity oxygen-free copper strip and the ceramic substrate; otherwise, the heat resistance of the high-purity oxygen-free copper strip cannot meet the requirements of DBC lamination of the high-purity oxygen-free copper strip and the ceramic substrate; (2) The cooled sample is immersed in a nitric acid solution, and then taken out to observe the oxide scale shedding. If the oxide film on the surface of the sample after immersion is dense and difficult to remove and remains intact, it means that the copper strip has good heat resistance and can meet the requirements of DBC lamination of high-purity oxygen-free copper strip and ceramic substrate; otherwise, the heat resistance of the high-purity oxygen-free copper strip cannot meet the requirements of DBC lamination of high-purity oxygen-free copper strip and ceramic substrate.

2. The method for predicting the heat resistance of the high-purity oxygen-free copper strip for DBC ceramic copper cladding according to claim 1, characterized in that: The electrolyte used in the electrolytic polishing treatment is prepared by mixing water and 85% phosphoric acid in a volume ratio of 3:

4.

3. The method for predicting the heat resistance of the high-purity oxygen-free copper strip for DBC ceramic copper cladding according to claim 1, characterized in that: The working voltage in the electrolytic polishing process is 30-50V, and the processing time is 1-10 seconds.

4. The method for predicting the heat resistance of the high-purity oxygen-free copper strip for DBC ceramic copper cladding according to claim 1, characterized in that: The volume fraction of the nitric acid solution is 30-50%, and the soaking time is 5-20 minutes.

5. The method for predicting the heat resistance of the high-purity oxygen-free copper strip for DBC ceramic copper cladding according to claim 1, characterized in that: When cleaning the sample, a mixed solution of dilute sulfuric acid and dilute nitric acid is used as the cleaning solution.

6. The method for predicting the heat resistance of the high-purity oxygen-free copper strip for DBC ceramic copper cladding according to claim 5, characterized in that: The volume fractions of the dilute sulfuric acid and the dilute nitric acid are both 10%, and the volume ratio of the dilute sulfuric acid to the dilute nitric acid is 1:

1.

7. The method for predicting the heat resistance of the high-purity oxygen-free copper strip for DBC ceramic copper cladding according to claim 1, characterized in that: The sample is heated using a high temperature resistance furnace.

8. The method for predicting the heat resistance of the high-purity oxygen-free copper strip for DBC ceramic copper cladding according to claim 7, characterized in that: The high temperature resistance furnace is a muffle furnace or a tubular resistance furnace.

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