High-thermal-stable oxygen-free copper strip for power semiconductor device and preparation method thereof

Abstract

The application discloses a kind of high thermal stability oxygen-free copper strip for power semiconductor device and preparation method thereof, by vacuum smelting deoxidation and impurity removal, down-casting continuous casting one-time forming blank, and the blank is sequentially subjected to high-temperature diffusion annealing, continuous hot rolling, first rough rolling in alternating direction of front and back, single-sided one-way second rough rolling at room temperature, recrystallization annealing, and is refined into oxygen-free copper strip, which can realize accurate control of copper strip crystal orientation, grain size, oxygen content, hardness and strength, and the oxygen-free copper strip provided by the application has high electrical conductivity and thermal conductivity coefficient, and exhibits excellent high-temperature stability of grain size during high-temperature processing. The oxygen-free copper strip provided by the application can be applied in DBC, AMB ceramic copper-clad plate and other semiconductor power devices, and the preparation process has the characteristics of good stability, simplicity, high efficiency and high yield, and is suitable for industrial large-scale production.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of non-ferrous metal processing, in particular to a high-thermal-stability oxygen-free copper strip for power semiconductor devices and a preparation method thereof. BACKGROUND

[0002] Power semiconductor devices are the cornerstone of modern power electronics technology, playing a key role in electric energy conversion and power control, directly affecting the progress of high-tech fields such as new energy, smart grid, electric vehicles, renewable energy generation, and high-speed rail transportation. As semiconductor devices develop towards large power, integration, high performance, and low loss, scientific packaging of devices and effective management and dissipation of heat have become one of the key factors affecting the performance and lifespan of large power semiconductor devices. Ceramic copper-clad plates are a kind of composite metal ceramic plates formed by bonding high-conductivity oxygen-free copper strips to the surface of ceramics at high temperatures, which have both the characteristics of ceramics, such as high thermal conductivity, high insulation, high mechanical strength, and low expansion, and the characteristics of copper, such as high electrical conductivity and excellent welding performance, and have become the preferred packaging substrate material for power semiconductor devices.

[0003] However, during the high-temperature (generally 800-1070℃) forming process of the copper-clad plate, the driving force for migration of large-angle grain boundaries in the copper strip increases significantly with temperature, and the driving force for migration of grain boundaries at high temperatures may even exceed the driving force for recrystallization nucleation. At this time, under the driving of interface energy, it is easy to induce abnormal grain growth through secondary recrystallization mechanism, forming coarse and uneven grain structure, resulting in a decrease in mechanical properties and processing performance of the copper strip, leading to deterioration of the service performance of the ceramic copper-clad plate, and making it difficult to meet the quality requirements of high-performance ceramic copper-clad plates in the industrial field. Currently, there are two main methods to improve the high-temperature organizational stability of the copper strip: ① By adding alloying elements to form second-phase particles to pin the grain boundaries and inhibit grain growth; for example, a high-thermal-stability copper-based composite material resistant to high-temperature creep and a preparation method thereof disclosed in patent CN114934208B. ② By introducing a large strain through severe plastic deformation to make the grains tend to be equiaxed and refined; for example, a method for refining grains through large plastic deformation disclosed in patent CN102199741A. Although the above two methods can improve the high-temperature organizational stability of the copper strip, alloying usually causes a decrease in electrical and thermal conductivity, and the deformation processing process is complex, high in cost, and difficult to industrialize. SUMMARY

[0004] The present application is to overcome the above-mentioned problems existing in the prior art copper strip preparation method, and provides a high-thermal-stability oxygen-free copper strip for power semiconductor devices and a preparation method thereof, which sequentially performs high-temperature diffusion annealing, continuous hot rolling, first rough rolling in alternating directions of front and back surfaces at room temperature, second rough rolling in one direction of one surface at room temperature, recrystallization annealing, and finish rolling on the blank to form the oxygen-free copper strip, so that the crystal orientation, grain size, oxygen content, hardness and strength of the copper strip can be accurately controlled, and meanwhile, the oxygen-free copper strip provided by the present application has high electrical conductivity and thermal conductivity, and exhibits excellent high-temperature stability of grain size during high-temperature processing.

[0005] In order to achieve the above-mentioned purposes, the present application adopts the following technical solutions:

[0006] A preparation method of a high-thermal-stability oxygen-free copper strip for power semiconductor devices, comprising the following steps:

[0007] (1) vacuum smelting of copper raw material, and then down-drawing continuous casting to obtain a copper plate;

[0008] (2) diffusion annealing treatment of the copper plate in a vacuum furnace, and then cooling;

[0009] (3) hot rolling of the cooled copper plate, and then milling of the surface to remove the surface oxide scale after the copper plate is cooled to room temperature;

[0010] (4) first rough rolling of the hot-rolled copper plate in alternating directions of front and back surfaces at room temperature, and then second rough rolling of the copper plate in one direction of one surface at room temperature to obtain a copper strip;

[0011] (5) recrystallization annealing treatment of the copper strip in a reducing atmosphere furnace;

[0012] (6) finish rolling of the annealed copper strip at room temperature;

[0013] (7) acid pickling, cleaning, grinding, polishing, cleaning and hot air drying of the finish-rolled copper strip in sequence.

[0014] The present application first performs vacuum smelting, deoxidization and impurity removal on copper raw material, and then down-drawing continuous casting to form a cast high-purity oxygen-free copper plate blank, and then sequentially performs high-temperature diffusion annealing, continuous hot rolling, first rough rolling in alternating directions of front and back surfaces at room temperature, second rough rolling in one direction of one surface at room temperature, recrystallization annealing to eliminate deformation lines, and finish rolling on the cast high-purity oxygen-free copper plate to form a high-purity oxygen-free copper strip. The method of the present application can accurately control the crystal orientation, grain size, oxygen content, hardness and strength of the copper strip, and meanwhile, the oxygen-free copper strip provided by the present application has high electrical conductivity and thermal conductivity, and exhibits excellent high-temperature stability of grain size during high-temperature processing. The oxygen-free copper strip provided by the present application can be applied in DBC, AMB ceramic copper-clad plates and other semiconductor power devices, and the preparation process thereof has the characteristics of good stability, simplicity, high efficiency and high material yield, and is suitable for industrialized mass production.

[0015] As preferred, the copper raw material in step (1) is cathode copper with purity ≥99.9%; the copper raw material is cleaned and dried before vacuum smelting, the cleaning agent is one of deionized water, alcohol or acetone, the drying conditions are: temperature 80-150℃, holding for 30-180min, vacuum degree ≤100Pa.

[0016] As preferred, the smelting temperature in step (1) is 1120-1180℃, vacuum degree ≤10 -2 Pa, holding for 30-60min after the raw material is melted; the down-drawing continuous casting conditions are: drawing speed 30-150mm / min, cooling water flow rate 3-5m 3 / h, cooling water temperature 20-40℃, copper plate thickness 20-35mm.

[0017] As preferred, the diffusion annealing conditions in step (2) are: heating temperature 700-800℃, holding time 30-90min, heating rate 1-10℃ / min, vacuum degree ≤10 -1 Pa.

[0018] As preferred, the hot rolling temperature in step (3) is 400-500℃, the copper plate thickness after hot rolling is 8-12mm.

[0019] As preferred, the copper plate thickness after the first rough rolling at room temperature in step (4) is 1.5-2mm, the copper strip thickness after the second rough rolling at room temperature is 0.5-1mm.

[0020] As preferred, the recrystallization annealing conditions in step (5) are: heating temperature 500-680℃, holding time 30-120min, heating rate 5-20℃ / min, cooling with furnace, protective atmosphere is hydrogen or ammonia decomposition hydrogen, dew point ≤-30℃.

[0021] As preferred, the copper strip thickness after the finish rolling in step (6) is 0.1-0.35mm.

[0022] As preferred, the solution for pickling in step (7) is 8-12wt% dilute sulfuric acid solution, the brush roll mesh number for grinding is 600-1500mesh, the brush roll mesh number for polishing is 3000-5000mesh, the hot air drying temperature is 60-80℃, the surface roughness of the obtained oxygen-free copper strip is ≤0.2μm.

[0023] The application also provides a high-thermal-stability oxygen-free copper strip for power semiconductor devices, which is prepared by the above method.

[0024] As preferred, the chemical composition of the high-thermal-stability oxygen-free copper strip is, in mass percentage: Cu ≥99.995%, O ≤0.0005%, the balance being inevitable impurities.

[0025] As preferred, the high thermal stability oxygen-free copper strip has a structure of α-Cu, a crystal preferred orientation of Cu(200), a room temperature grain size of 30-70 μm, and a grain size change rate of ≤40% after high temperature heat treatment (900-1070 °C for 30 min).

[0026] As preferred, the high thermal stability oxygen-free copper strip has an electrical conductivity of ≥58 MS / m, a thermal conductivity of ≥390 W / (m·K), a hardness of 105-115 HV, a tensile strength of 330-350 MPa, and an elongation of 3%-6%.

[0027] Therefore, the present application has the following beneficial effects: the present application can realize accurate control of the crystal orientation, grain size, oxygen content, hardness and strength of the copper strip, and the oxygen-free copper strip provided by the present application has high electrical conductivity and thermal conductivity and exhibits excellent high temperature stability of grain size during high temperature treatment. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 is the original grain OM morphology of the oxygen-free copper strip prepared in Example 1 of the present application.

[0029] Figure 2 is the grain OM morphology of the oxygen-free copper strip prepared in Example 1 of the present application after high temperature treatment.

[0030] Figure 3 is the grain size distribution graph of the oxygen-free copper strip prepared in Example 1 of the present application before and after high temperature treatment.

[0031] Figure 4 is the XRD spectrum of the oxygen-free copper strip prepared in Example 1 of the present application. DETAILED DESCRIPTION

[0032] The present application will be further described below in combination with the drawings and specific embodiments.

[0033] In the present application, all the equipment and raw materials can be purchased from the market or commonly used in the industry, and the methods in the following examples are conventional methods in the field unless otherwise specified.

[0034] General Example:

[0035] A preparation method of a high thermal stability oxygen-free copper strip for power semiconductor devices, comprising the following steps:

[0036] (1) vacuum smelting of copper raw material, and then down-drawing continuous casting to obtain a copper plate;

[0037] (2) Diffusion annealing treatment of the copper plate in a vacuum furnace, and then cooling;

[0038] (3) Hot rolling of the cooled copper plate, and then milling to remove the surface oxide after the copper plate is cooled to room temperature;

[0039] (4) First rough rolling of the hot-rolled copper plate at room temperature in the alternating direction of the front and back surfaces, and then second rough rolling of the copper plate at room temperature in the direction of any one surface to obtain a copper strip;

[0040] (5) Recrystallization annealing treatment of the copper strip in a reducing atmosphere furnace;

[0041] (6) Finish rolling of the annealed copper strip at room temperature;

[0042] (7) The finish-rolled copper strip is sequentially subjected to pickling, cleaning, grinding, polishing, cleaning, and hot air drying.

[0043] As a specific embodiment, the copper raw material in step (1) is cathode copper with a purity of ≥99.9%; the copper raw material is cleaned and dried before vacuum melting, the cleaning agent used in cleaning is one of deionized water, alcohol or acetone, and the drying conditions are: temperature 80-150°C, holding time 30-180 min, and vacuum degree ≤100 Pa.

[0044] As a specific embodiment, the melting temperature in step (1) is 1120-1180°C, the vacuum degree is ≤10 -2 Pa, and the raw material is held for 30-60 min after melting; the down-drawing continuous casting conditions are: drawing speed 30-150 mm / min, cooling water flow rate 3-5 m 3 / h, cooling water temperature 20-40°C, and copper plate thickness 20-35 mm.

[0045] As a specific embodiment, the diffusion annealing conditions in step (2) are: heating temperature 700-800°C, holding time 30-90 min, heating rate 1-10°C / min, and vacuum degree ≤10 -1 Pa.

[0046] As a specific embodiment, the hot rolling temperature in step (3) is 400-500°C, and the thickness of the copper plate after hot rolling is 8-12 mm.

[0047] As a specific embodiment, the thickness of the copper plate after the first rough rolling at room temperature in step (4) is 1.5-2 mm, and the thickness of the copper strip after the second rough rolling at room temperature is 0.5-1 mm.

[0048] As a specific embodiment, the recrystallization annealing conditions in step (5) are: heating temperature 500-680℃, holding time 30-120min, heating rate 5-20℃ / min, furnace cooling, protective atmosphere hydrogen or ammonia decomposition hydrogen, dew point ≤-30℃.

[0049] As a specific embodiment, the thickness of the copper strip after finish rolling in step (6) is 0.1-0.35mm.

[0050] As a specific embodiment, the pickling solution in step (7) is 8-12wt% dilute sulfuric acid solution, the polishing brush roll mesh is 3000-5000 mesh, and the hot air drying temperature is 60-80℃. The surface roughness of the obtained oxygen-free copper strip is ≤0.2μm.

[0051] As a specific embodiment, the chemical composition of the obtained high-thermal-stability oxygen-free copper strip is: Cu≥99.995%, O≤0.0005%, and the balance is unavoidable impurities.

[0052] As a specific embodiment, the microstructure of the obtained high-thermal-stability oxygen-free copper strip is α-Cu, the crystal preferred orientation is Cu(200), the room temperature grain size is 30-70μm, and the grain growth change rate after high-temperature heat treatment (900-1070℃ holding for 30min) is ≤40%.

[0053] As a specific embodiment, the electrical conductivity of the obtained high-thermal-stability oxygen-free copper strip is ≥58MS / m, the thermal conductivity is ≥390W / (m·K), the hardness is 105-115HV, the tensile strength is 330-350MPa, and the elongation is 3%-6%.

[0054] Example 1:

[0055] A method for preparing a high-thermal-stability oxygen-free copper strip for power semiconductor devices, comprising the following steps:

[0056] (1) ultrasonic cleaning of cathode copper with purity ≥99.9% with deionized water, followed by drying in an oven with vacuum degree ≤10Pa at 120℃ for 90min, and standby;

[0057] (2) loading the raw material treated in step (1) into a vacuum melting furnace, with furnace vacuum degree 3.5×10 -2 Pa, heating to 1160℃, continuing to hold for 30min after the raw material is completely melted, then starting the down-drawing continuous casting traction system, drawing the copper plate from the graphite crystallizer at a speed of 75mm / min, with cooling water flow rate 3.5±0.2m 3 / h and cooling water temperature 28±1℃ during the continuous casting process, and the thickness of the copper plate obtained by continuous casting is 25mm;

[0058] (3) Put the copper plate prepared in step (2) into a vacuum furnace, and vacuumize the furnace to 0.5 x 10 -1 Pa, and then heat to 725℃ at a rate of 10℃ / min and keep for 60 min for diffusion annealing treatment to homogenize the uneven casting structure, ready for use;

[0059] (4) Hot rolling breakdown of the copper plate after step (3) treatment, and then mill the surface to remove the surface oxide skin after the copper plate is cooled to room temperature. The thickness of the treated copper plate is 10±0.5 mm, ready for use;

[0060] (5) First rough rolling of the copper plate after step (4) hot rolling to a thickness of 1.8±0.1 mm at room temperature in the alternating direction of the front and back surfaces, and then one-way second rough rolling to a thickness of 0.7±0.1 mm at room temperature, ready for use;

[0061] (6) Put the copper strip after step (5) cold rolling into a reducing atmosphere furnace, first vacuumize and then fill in ammonia decomposition hydrogen with a dew point of -40℃, and then heat to 600℃ at a rate of 10℃ / min and keep for 60 min for recrystallization annealing treatment, and cool to room temperature in the furnace, ready for use;

[0062] (7) Room temperature finish rolling of the copper strip after step (6) treatment, and the thickness of the copper strip after finish rolling is 0.3±0.05 mm, ready for use;

[0063] (8) The copper strip after step (7) finish rolling is sequentially subjected to 10wt% dilute sulfuric acid pickling-cleaning-800 mesh brush roller grinding-3000 mesh brush roller polishing-cleaning-60℃ hot air drying-trimming-rewinding-packaging to obtain the high thermal stability oxygen-free copper strip for power semiconductor devices, and the surface roughness of the copper strip is 0.15μm, and the original grain OM morphology is shown in Figure 1 , and the XRD spectrum is shown in Figure 4 .

[0064] Example 2:

[0065] A preparation method of a high thermal stability oxygen-free copper strip for power semiconductor devices, comprising the following steps:

[0066] (1) Ultrasonic cleaning of the cathode copper with a purity of ≥99.9% with deionized water, and then drying in an oven with a vacuum degree of ≤10 Pa at 80℃ for 180 min, ready for use;

[0067] (2) Put the raw material treated in step (1) into a vacuum melting furnace, and the vacuum degree in the furnace is 3.5 x 10 -2Pa, and after the raw materials are completely melted, continue to keep the temperature for 60 min, then open the down-drawing continuous casting traction system, and draw the copper plate from the graphite crystallizer at a speed of 100 mm / min, the flow rate of the cooling water is 4±0.2 m 3 / h, the cooling water temperature is 35±1℃, and the thickness of the copper plate obtained by the continuous casting is 20 mm.

[0068] (3) placing the copper plate prepared in step (2) in a vacuum furnace, vacuumizing the furnace to 0.5×10 -1 Pa, then heating to 800℃ at a speed of 10℃ / min and keeping the temperature for 30 min to perform diffusion annealing treatment, so as to homogenize the uneven casting structure, and standby;

[0069] (4) cooling the copper plate treated in step (3) to 400℃ to perform hot rolling breakdown, and after the copper plate is cooled to room temperature, milling is performed to remove the surface oxide skin, the thickness of the treated copper plate is 10±0.5 mm, and standby;

[0070] (5) first rough rolling the copper plate after the hot rolling in step (4) to a thickness of 1.5±0.1 mm in the forward and reverse directions alternately at room temperature, and then randomly selecting any one side to perform second rough rolling to a thickness of 0.5±0.1 mm at room temperature in one direction, and standby;

[0071] (6) placing the copper strip after the cold rolling in step (5) in a reducing atmosphere furnace, first vacuumizing and then filling in ammonia decomposition hydrogen with a dew point of-40℃, then heating to 500℃ at a speed of 5℃ / min and keeping the temperature for 120 min to perform recrystallization annealing treatment, and cooling to room temperature with the furnace, and standby;

[0072] (7) performing finish rolling of the copper strip after the treatment in step (6) at room temperature, and the thickness of the copper strip after the finish rolling is 0.2±0.05 mm, and standby;

[0073] (8) sequentially performing the following processes on the copper strip after the finish rolling in step (7): 10wt% dilute sulfuric acid solution pickling-cleaning-600 mesh brush roller grinding-4000 mesh brush roller polishing-cleaning-70℃ hot air drying-trimming-rewinding-packaging, to obtain the high-thermal-stability oxygen-free copper strip for power semiconductor devices, and the surface roughness of the copper strip is 0.08μm.

[0074] Example 3:

[0075] A preparation method of a high-thermal-stability oxygen-free copper strip for power semiconductor devices, comprising the following steps:

[0076] (1) performing ultrasonic cleaning of cathode copper with a purity of≥99.9% in deionized water, and then drying in an oven with a vacuum degree of≤10 Pa at 150℃ for 60 min, and standby;

[0077] (2) The raw material treated in step (1) is loaded into a vacuum melting furnace, and the vacuum degree in the furnace is 3.5 x 10 -2 Pa, heated to 1180℃, and after the raw material is completely melted, the vacuum degree is kept for 30 min, then the drawing system of the lower continuous casting is opened, and the copper plate is drawn out of the graphite crystallizer at a speed of 150 mm / min, the flow rate of the cooling water is 5±0.2 m 3 / h during the continuous casting process, the cooling water temperature is 40±1℃, and the thickness of the copper plate obtained by continuous casting is 35 mm.

[0078] (3) The copper plate prepared in step (2) is placed in a vacuum furnace, and the vacuum in the furnace is extracted to 0.5 x 10 -1 Pa, then heated to 700℃ at a rate of 5℃ / min and kept for 90 min for diffusion annealing treatment to homogenize the uneven casting structure, and standby;

[0079] (4) The copper plate treated in step (3) is cooled to 500℃ for hot rolling breakdown, and then the surface oxide is removed by milling after the copper plate is cooled to room temperature, and the thickness of the treated copper plate is 10±0.5 mm, standby;

[0080] (5) The copper plate after hot rolling in step (4) is first first rough rolled at room temperature to a thickness of 2±0.1 mm in the alternating direction of the front and back surfaces, and then second rough rolled at room temperature to a thickness of 1±0.1 mm in the single direction of any one surface, standby;

[0081] (6) The copper strip after cold rolling in step (5) is placed in a reducing atmosphere furnace, first vacuum extraction, then filled with ammonia decomposition hydrogen with a dew point of-40℃, then heated to 650℃ at a rate of 10℃ / min and kept for 60 min for recrystallization annealing treatment, and cooled to room temperature with the furnace, standby;

[0082] (7) The copper strip after treatment in step (6) is precision rolled at room temperature, and the thickness of the copper strip after precision rolling is 0.1±0.05 mm, standby;

[0083] (8) The copper strip after precision rolling in step (7) is sequentially subjected to 10wt% dilute sulfuric acid solution pickling-cleaning-1500 mesh brush roller grinding-3000 mesh brush roller polishing-cleaning-70℃ hot air drying-trimming-rewinding-packaging to obtain the high-thermal-stability oxygen-free copper strip for power semiconductor devices, and the surface roughness of the copper strip is 0.11μm.

[0084] Comparative Example 1:

[0085] The difference between Comparative Example 1 and Example 1 is that the diffusion annealing treatment in step (3) is not performed, and the remaining steps are the same as in Example 1.

[0086] Comparative Example 2:

[0087] The difference between Comparative Example 2 and Example 1 is that in step (5), one side of the copper plate is first rough-rolled at room temperature to a thickness of 2±0.1 mm, and the other side of the copper plate is then rough-rolled at room temperature to a thickness of 1±0.1 mm; the other steps are the same as in Example 1.

[0088] Comparative Example 3:

[0089] The difference between Comparative Example 3 and Example 1 is that in step (5), the hot-rolled copper plate is rough-rolled at room temperature to a thickness of 1±0.1 mm in the alternating direction of the front and back sides; the other steps are the same as in Example 1.

[0090] Comparative Example 4:

[0091] The difference between Comparative Example 4 and Example 1 is that in step (6), the temperature of the recrystallization annealing treatment is 400℃; the other steps are the same as in Example 1.

[0092] Comparative Example 5:

[0093] A traditional oxygen-free copper strip preparation process is used: vacuum melting-continuous casting-hot rolling-milling-cold rolling-annealing-cold rolling-annealing-cold rolling-acid washing-cleaning-cutting. The specific steps are as follows:

[0094] (1) The raw material cathode copper is loaded into a vacuum melting furnace and covered with a charcoal layer, the vacuum degree in the furnace is 3.5×10 -2 Pa, heated to 1200℃, and after the raw material is completely melted, continue to keep warm for 60 min, then start the continuous casting traction system, and the copper plate is drawn out from the graphite crystallizer at a speed of 75 mm / min, the cooling water flow rate is 1.5 m 3 / h during the continuous casting process, and the cooling water temperature is 28℃, and the thickness of the copper plate obtained by continuous casting is 25 mm;

[0095] (2) The copper plate obtained in step (1) is heated to 800℃ and kept warm for 60 min, then hot-rolled at 600℃, 5 passes, and the single-pass deformation amount is 15%, and then the surface oxide is removed by milling after the copper plate is cooled to room temperature, the thickness of the treated copper plate is 10±0.5 mm, and it is ready for use;

[0096] (3) The plate obtained in step (2) is cold-rolled in multiple passes, the single-pass deformation rate is 10%, and the rolling speed is 300 m / min, and the thickness after rolling is 6±0.5 mm, and it is ready for use;

[0097] (4) The copper plate prepared in step (3) is placed in a continuous annealing furnace containing a nitrogen atmosphere for annealing treatment at 500℃ for 60 min to eliminate rolling stress and restore plasticity, and it is ready for use;

[0098] (5) The copper plate treated in step (4) is subjected to multi-pass cold rolling with a single-pass deformation rate of 10% and a rolling speed of 300 m / min, and the thickness after rolling is 3+0.5 mm, for standby;

[0099] (6) The copper plate prepared in step (5) is placed in a continuous annealing furnace containing a nitrogen atmosphere for annealing at 500°C for 60 min to eliminate rolling stress and restore plasticity, for standby;

[0100] (7) The copper plate treated in step (6) is subjected to multi-pass cold rolling with a single-pass deformation rate of 10% and a rolling speed of 300 m / min, and the thickness after rolling is 0.3+0.05 mm, for standby;

[0101] (8) The copper strip prepared in step (7) is cleaned in a 5% sulfuric acid solution pool at 50°C for 3 min, for standby:

[0102] (9) The copper strip treated in step (8) is cleaned with deionized water or ethanol and dried, for standby;

[0103] (10) The copper strip treated in step (9) is slitted to obtain the high-thermal-stability oxygen-free copper strip for power semiconductor devices, and the surface roughness of the copper strip is 0.15 μm.

[0104] The properties of the oxygen-free copper strips obtained in the above examples and comparative examples were tested, and the results are shown in Table 1 and Figures 1-4 .

[0105] Among them, the components (copper content, oxygen content) involved in the oxygen-free copper strip, the average grain size, the hardness, the electrical conductivity, the thermal conductivity, the strength, the elongation rate and the like are tested according to the national standard GB / T 2059-2017 “Copper and Copper Alloy Strip”. The high-temperature grain size is the grain size after being kept at 900°C for 30 min.

[0106] The grain growth rate of the oxygen-free copper strip after high-temperature treatment = (high-temperature grain size - room-temperature grain size) / room-temperature grain size x 100%.

[0107] The XRD test parameters are as follows: the working voltage is 40 kV, the working current is 30 mA, the selected target material is Cu target material, the scanning angle is 15-100°C, and the scanning speed is 2° / min. The curve measured by XRD is calibrated by MDI Jade 6.0 software.

[0108] Table 1: Test results of properties of oxygen-free copper strips.

[0109]

[0110]

[0111] From Table 1 andFigures 1-4 As can be seen from the examples, the oxygen-free copper strip prepared by the method of the present invention can achieve precise control of copper strip crystal orientation (Cu(200)), grain size (30~70μm), oxygen content (≤5ppm), hardness (105-115HV) and strength (330~350MPa). At the same time, the oxygen-free copper strip provided by the present invention has high electrical conductivity (≥58MS / m) and thermal conductivity (≥390W / (m·K)), and exhibits excellent high-temperature stability of grain size (grain growth change rate ≤40%) during high-temperature processing.

[0112] In contrast, Comparative Example 1 did not undergo diffusion annealing before hot rolling. Due to the rapid cooling caused by continuous casting, a large number of dendritic structures were present in the copper plate. Without diffusion annealing, the internal compositional segregation, dendritic structures, and micro-defects could not be eliminated, resulting in large differences in grain size and a significant decrease in the high-temperature stability of the copper strip grain size.

[0113] In Comparative Example 2, both the first and second roughing mills were subjected to single-sided unidirectional cold rolling during cold rolling. The resulting copper strip had a Cu(111) crystal orientation, and the high-temperature stability of the copper strip's grain size was significantly reduced compared to the examples.

[0114] In Comparative Example 3, cold rolling was performed only in alternating directions of the front and back sides. The crystal orientation of the copper strip was Cu(111). The high-temperature stability of the copper strip grain size was significantly reduced compared with the example.

[0115] In Comparative Example 4, the recrystallization annealing temperature was lower than that of the present invention. Due to the low temperature, the rolling stress could not be completely eliminated, resulting in a significant decrease in the high-temperature stability of the copper strip grain size and the elongation compared with the examples.

[0116] Comparative Example 5 used a traditional oxygen-free copper strip preparation process: vacuum melting - continuous casting - hot rolling - milling - cold rolling - annealing - cold rolling - annealing - cold rolling - pickling - cleaning - slitting. The resulting copper strip had a Cu(220) crystal orientation, and the high-temperature stability of the copper strip's grain size was significantly reduced compared to the examples.

[0117] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any form or substance. It should be noted that those skilled in the art can make various improvements and additions without departing from the method of the present invention, and these improvements and additions should also be considered within the scope of protection of the present invention. Any modifications, alterations, and equivalent changes made by those skilled in the art based on the above-disclosed technical content without departing from the spirit and scope of the present invention are equivalent embodiments of the present invention. Furthermore, any modifications, alterations, and evolutions made to the above embodiments based on the essential technology of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A method for preparing a high thermally stable oxygen-free copper strip for power semiconductor devices, characterized in that the steps include... include: (1) The copper raw material is vacuum melted and then continuously cast to obtain copper plates; (2) Place the copper plate in a vacuum furnace for diffusion annealing, and then cool it; (3) The cooled copper plate is hot rolled into a blank, and the surface oxide scale is removed by milling after the copper plate has cooled to room temperature. (4) The hot-rolled copper plate is first rough rolled at room temperature in alternating directions on both sides, and then rough rolled at room temperature in one direction on any one side to obtain copper strip; (5) Place the copper strip in a reducing atmosphere furnace for recrystallization annealing treatment; the recrystallization annealing conditions are: heating temperature 500~680℃, holding time 30~120 min, heating rate 5~20℃ / min, cooling with the furnace, the protective atmosphere is hydrogen or ammonia decomposition hydrogen, and the dew point ≤-30℃. (6) The annealed copper strip is precision rolled at room temperature; (7) The finely rolled copper strip is pickled, cleaned, ground, polished, cleaned again, and dried with hot air in sequence to obtain the final product.

2. The method for preparing high thermally stable oxygen-free copper strip for power semiconductor devices according to claim 1, characterized in that, The copper raw material mentioned in step (1) is cathode copper with a purity of ≥99.9%; the copper raw material is cleaned and dried before vacuum melting. The cleaning agent is one of deionized water, alcohol or acetone. The drying conditions are: temperature 80~150℃, heat preservation for 30~180 min, vacuum degree ≤100 Pa.

3. The method for preparing high thermally stable oxygen-free copper strip for power semiconductor devices according to claim 1 or 2, characterized in that, The melting temperature in step (1) is 1120~1180℃, and the vacuum degree is ≤10. -2 Pa, after the raw material melts, it is held at a temperature of 30~60 min; the conditions for downward continuous casting are: traction speed 30~150 mm / min, cooling water flow rate 3~5 m / min. 3 / h, cooling water temperature 20~40℃, copper plate thickness 20~35 mm.

4. The method for preparing high thermally stable oxygen-free copper strip for power semiconductor devices according to claim 1, characterized in that, The diffusion annealing conditions in step (2) are: heating temperature 700~800℃, holding time 30~90 min, heating rate 1~10℃ / min, and vacuum degree ≤10. -1 Pa.

5. The method for preparing high thermal stability oxygen-free copper strip for power semiconductor devices according to claim 1, characterized in that, The hot rolling temperature in step (3) is 400-500℃, and the thickness of the copper plate after hot rolling is 8~12 mm.

6. The method for preparing high thermally stable oxygen-free copper strip for power semiconductor devices according to claim 1, characterized in that, In step (4), the thickness of the copper plate after the first rough rolling at room temperature is 1.5~2 mm, and the thickness of the copper strip after the second rough rolling at room temperature is 0.5~1 mm.

7. The method for preparing high thermally stable oxygen-free copper strip for power semiconductor devices according to claim 1, characterized in that, The thickness of the copper strip after precision rolling in step (6) is 0.1~0.35 mm.

8. The method for preparing high thermally stable oxygen-free copper strip for power semiconductor devices according to claim 1, characterized in that, In step (7), the pickling solution is 8-12wt% dilute sulfuric acid solution, the grinding brush roller has a mesh size of 600-1500 mesh, the polishing brush roller has a mesh size of 3000-5000 mesh, the hot air drying temperature is 60~80℃, and the surface roughness of the obtained oxygen-free copper strip is ≤0.2μm.

9. A high thermal stability oxygen-free copper strip for power semiconductor devices, characterized in that, It is prepared by any one of the preparation methods described in claims 1 to 8.

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