High-thermal-stability oxygen-free copper strip for power semiconductor device and preparation method of high-thermal-stability oxygen-free copper strip

Abstract

The invention discloses a high-thermal-stability oxygen-free copper strip for a power semiconductor device and a preparation method of the high-thermal-stability oxygen-free copper strip. The blank is sequentially subjected to high-temperature diffusion annealing, continuous hot rolling, room-temperature first rough rolling in the front and back alternating directions, single-face one-way room-temperature second rough rolling, recrystallization annealing and finish rolling to form the oxygen-free copper strip, and the crystal orientation, the grain size, the oxygen content, the hardness and the strength of the copper strip can be accurately controlled; meanwhile, the oxygen-free copper strip provided by the invention has high conductivity and heat conductivity coefficient, and shows excellent grain size high-temperature stability in the high-temperature treatment process. The oxygen-free copper strip can be applied to semiconductor power devices such as DBC and AMB ceramic copper-clad plates, the preparation process has the advantages of being good in stability, simple, efficient and high in yield, and the oxygen-free copper strip is suitable for industrial large-scale production.

Description

Technical Field

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

[0002] Power semiconductor devices are the cornerstone of modern power electronics technology, playing a key role in power conversion and power control, and directly affecting the progress of high-tech fields such as new energy, smart grid, electric vehicles, renewable energy power generation, and high-speed rail transit. With the development of semiconductor devices towards high 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 high-power semiconductor devices. Ceramic copper clad laminate is a composite metal-ceramic plate formed by bonding a highly conductive oxygen-free copper strip to the ceramic surface at high temperature. It has both the characteristics of high thermal conductivity, high insulation, high mechanical strength, and low expansion of ceramics, as well as the high electrical conductivity and excellent welding performance of copper, and has become the preferred packaging substrate material for power semiconductor devices.

[0003] However, during the high-temperature (generally 800 - 1070 °C) forming process of the copper clad laminate, the driving force for the migration of large-angle grain boundaries in the copper strip increases significantly with the increase in temperature. At high temperatures, the driving force for grain boundary migration may even exceed the driving force for recrystallization nucleation. At this time, under the driving force of the interfacial energy, it is extremely easy to induce abnormal growth of grains through the secondary recrystallization mechanism, forming coarse and uneven grain structures, resulting in a decline in the mechanical properties and processing performance of the copper strip, leading to deterioration of the service performance of the ceramic copper clad laminate and making it difficult to meet the quality requirements of high-performance ceramic copper clad laminates in the industrial field. Currently, there are mainly two methods to improve the high-temperature tissue stability of copper strips: ① Adding alloying elements to form second-phase particles with copper to pin the grain boundaries and inhibit grain growth; for example, a copper-based composite material with high-temperature creep resistance and high thermal stability and a preparation method thereof disclosed in Patent CN114934208B. ② Introducing huge strain through severe plastic deformation to make the grains tend to be equiaxed and refined; for example, a method for refining grains by severe plastic deformation disclosed in Patent CN102199741A. Although the above two methods can improve the high-temperature tissue stability of copper strips, the alloying method usually causes a decrease in electrical and thermal conductivity, while the deformation processing process is complex, costly, and difficult for industrial production. Summary of the Invention

[0004] The present invention aims to overcome the above-mentioned problems existing in the copper strip preparation method of the prior art, and provides a high thermal stability oxygen-free copper strip for power semiconductor devices and a preparation method thereof. The blank is subjected to high temperature diffusion annealing, continuous hot rolling, first rough rolling at room temperature in alternating directions of the front and back sides, second rough rolling at room temperature on one side and in one direction, recrystallization annealing, and finish rolling to form an oxygen-free copper strip, which can achieve precise control of the crystal orientation, grain size, oxygen content, hardness and strength of the copper strip. At the same time, the oxygen-free copper strip provided by the present invention has high electrical conductivity and thermal conductivity, and exhibits excellent high temperature stability of grain size during high temperature treatment.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions: A method for preparing a high thermal stability oxygen-free copper strip for a power semiconductor device, comprising the following steps: (1) vacuum melting the copper raw material, and then continuously casting to obtain a copper plate; (2) placing the copper plate in a vacuum furnace for diffusion annealing and then cooling; (3) hot rolling the cooled copper plate to form a blank, and then milling the copper plate to remove the surface oxide scale after it cools to room temperature; (4) firstly rough rolling the hot-rolled copper sheet in alternating directions of the front and back sides at room temperature, and then rough rolling any one side in one direction at room temperature to obtain a copper strip; (5) placing the copper strip in a reducing atmosphere furnace for recrystallization annealing; (6) performing room temperature finish rolling on the annealed copper strip; (7) The copper strip after fine rolling is pickled, cleaned, ground, polished, cleaned, and hot-air dried in sequence.

[0006] The present invention first performs vacuum melting, deoxidation and impurity removal on the copper raw material, and then performs downward continuous casting to form an oxygen-free copper plate blank in one step, and then performs high-temperature diffusion annealing to uniformly organize the cast high-purity oxygen-free copper plate, continuous hot rolling, first rough rolling at room temperature in alternating directions on the front and back sides, second rough rolling at room temperature on one side and in one direction, recrystallization annealing to eliminate deformation lines, and fine rolling to form a high-purity oxygen-free copper strip. The method of the present invention can achieve precise control of the crystal orientation, grain size, oxygen content, hardness and strength of the copper strip. At the same time, the oxygen-free copper strip provided by the present invention has high electrical conductivity and thermal conductivity, and exhibits excellent high-temperature stability of grain size during high-temperature treatment. The oxygen-free copper strip provided by the present invention can be used in semiconductor power devices such as DBC, AMB ceramic copper-clad laminates, and its preparation process has the characteristics of good stability, simplicity, high efficiency, and high yield, and is suitable for industrial large-scale production.

[0007] Preferably, the copper raw material in step (1) is cathode copper with a purity ≥ 99.9%. Before vacuum melting, the copper raw material is cleaned and dried. The cleaning agent during cleaning is one of deionized water, alcohol or acetone. The drying conditions are: temperature 80 - 150 °C, heat preservation for 30 - 180 min, and vacuum degree ≤ 100 Pa.

[0008] Preferably, the melting temperature in step (1) is 1120 - 1180 °C, the vacuum degree ≤ 10 -2 Pa. After the raw materials are melted, heat preservation is carried out for 30 - 60 min. The conditions for downward continuous casting 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.

[0009] Preferably, the conditions for diffusion annealing in step (2) are: heating temperature 700 - 800 °C, heat preservation time 30 - 90 min, heating rate 1 - 10 °C / min, and vacuum degree ≤ 10 -1 Pa.

[0010] Preferably, 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.

[0011] Preferably, 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.

[0012] Preferably, the conditions for recrystallization annealing in step (5) are: heating temperature 500 - 680 °C, heat preservation time 30 - 120 min, heating rate 5 - 20 °C / min, furnace cooling, and the protective atmosphere is hydrogen or ammonia-decomposed hydrogen, with dew point ≤ - 30 °C.

[0013] Preferably, the thickness of the copper strip after finish rolling in step (6) is 0.1 - 0.35 mm.

[0014] Preferably, the solution used for pickling in step (7) is 8 - 12 wt% dilute sulfuric acid solution, the mesh number of the brush roll for grinding is 600 - 1500 mesh, the mesh number of the brush roll for polishing is 3000 - 5000 mesh, the hot air drying temperature is 60 - 80 °C, and the surface roughness of the obtained oxygen-free copper strip ≤ 0.2 μm.

[0015] The present invention also provides a high-thermal-stability oxygen-free copper strip for power semiconductor devices prepared by the above method.

[0016] Preferably, by mass percentage, the chemical composition of the high-thermal-stability oxygen-free copper strip is: Cu ≥ 99.995%, O ≤ 0.0005%, and the balance is inevitable impurities.

[0017] Preferably, the structure of the high thermal stability oxygen-free copper strip is α-Cu, the crystal preferred orientation is Cu(200), the room temperature grain size is 30-70 μm, and the grain growth change rate after high temperature heat treatment (holding at 900-1070 °C for 30 min) is ≤40%.

[0018] Preferably, the conductivity of the high thermal stability oxygen-free copper strip is ≥58 MS / m, the thermal conductivity is ≥390 W / (m·K), the hardness is 105-115 HV, the tensile strength is 330-350 MPa, and the elongation is 3%-6%.

[0019] Therefore, the present invention has the following beneficial effects: After vacuum melting and downward continuous casting, the as-cast high-purity oxygen-free copper plate is subjected to high-temperature diffusion annealing to homogenize the structure, continuous hot rolling, first rough rolling at room temperature with alternating front and back directions, second rough rolling at room temperature with a single-sided unidirectional direction, recrystallization annealing to eliminate deformation lines, and finish rolling to produce a high-purity oxygen-free copper strip. It can achieve precise control of the crystal orientation, grain size, oxygen content, hardness, and strength of the copper strip. At the same time, the oxygen-free copper strip provided by the present invention has a high conductivity and thermal conductivity, and exhibits excellent high-temperature stability of grain size during the high-temperature treatment process. Description of the Drawings

[0020] Figure 1 is the OM morphology of the original grains of the oxygen-free copper strip prepared in Example 1 of the present invention.

[0021] Figure 2 is the OM morphology of the grains of the oxygen-free copper strip prepared in Example 1 of the present invention after high-temperature treatment.

[0022] Figure 3 is the grain size distribution diagram of the oxygen-free copper strip prepared in Example 1 of the present invention before and after high-temperature treatment.

[0023] Figure 4 is the XRD spectrum of the oxygen-free copper strip prepared in Example 1 of the present invention. Detailed Embodiments

[0024] The present invention will be further described below in conjunction with the drawings and specific embodiments.

[0025] In the present invention, unless otherwise specified, all equipment and raw materials can be purchased from the market or are commonly used in this industry. The methods in the following embodiments, unless otherwise specified, are conventional methods in this field.

[0026] General Embodiment: A preparation method of a high thermal stability oxygen-free copper strip for power semiconductor devices, the steps include: (1) Vacuum melting the copper raw material, and then downward continuous casting to obtain a copper plate; (2) Placing the copper plate in a vacuum furnace for diffusion annealing treatment, and then cooling; (3) Hot-roll and bloom the cooled copper plate, and mill the surface to remove the surface oxide scale after the copper plate is cooled to room temperature; (4) First, perform the first rough rolling of the hot-rolled copper plate at room temperature in an alternating front and back direction, and then perform the second rough rolling of any side in a single direction at room temperature to obtain a copper strip; (5) Place the copper strip in a reducing atmosphere furnace for recrystallization annealing treatment; (6) Perform finish rolling of the annealed copper strip at room temperature; (7) The finish-rolled copper strip is successively pickled, cleaned, ground, polished, cleaned, and dried with hot air to obtain the product.

[0027] As a specific embodiment, the copper raw material described in step (1) is cathode copper with a purity ≥ 99.9%; before vacuum melting, the copper raw material is first cleaned and dried. The cleaning agent during cleaning is one of deionized water, alcohol, or acetone. The drying conditions are: temperature 80 - 150°C, heat preservation for 30 - 180 min, and vacuum degree ≤ 100 Pa.

[0028] As a specific embodiment, the melting temperature in step (1) is 1120 - 1180°C, the vacuum degree ≤ 10 -2 Pa, and after the raw materials are melted, heat preservation is carried out for 30 - 60 min; the conditions for downward continuous casting 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.

[0029] As a specific embodiment, the diffusion annealing conditions in step (2) are: heating temperature 700 - 800°C, heat preservation time 30 - 90 min, heating rate 1 - 10°C / min, and vacuum degree ≤ 10 -1 Pa.

[0030] As a specific embodiment, the hot-rolling temperature in step (3) is 400 - 500°C, and the thickness of the hot-rolled copper plate is 8 - 12 mm.

[0031] 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.

[0032] As a specific embodiment, the recrystallization annealing conditions in step (5) are: heating temperature 500 - 680°C, heat preservation time 30 - 120 min, heating rate 5 - 20°C / min, furnace cooling, and the protective atmosphere is hydrogen or ammonia-decomposed hydrogen, with a dew point ≤ -30°C.

[0033] As a specific embodiment, the thickness of the finish-rolled copper strip in step (6) is 0.1 - 0.35 mm.

[0034] As a specific embodiment, in step (7), the pickling solution is an 8-12 wt% dilute sulfuric acid solution, the mesh number of the brush roll for grinding is 600-1500 meshes, the mesh number of the brush roll for polishing is 3000-5000 meshes, the hot air drying temperature is 60-80 °C, and the surface roughness of the obtained oxygen-free copper strip is ≤0.2 μm.

[0035] As a specific embodiment, by mass percentage, the chemical composition of the obtained high thermal stability oxygen-free copper strip is: Cu≥99.995%, O≤0.0005%, and the balance is inevitable impurities.

[0036] As a specific embodiment, the structure 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 30-70 μm, and the grain growth change rate after high temperature heat treatment (holding at 900-1070 °C for 30 min) is ≤40%.

[0037] As a specific embodiment, the obtained high thermal stability oxygen-free copper strip has a conductivity ≥58 MS / m, a thermal conductivity ≥390 W / (m·K), a hardness of 105-115 HV, a tensile strength of 330-350 MPa, and an elongation of 3%-6%.

[0038] Example 1: A preparation method of a high thermal stability oxygen-free copper strip for power semiconductor devices, the steps are as follows: (1) Ultrasonically clean the cathode copper with a purity ≥99.9% with deionized water, and then keep it at 120 °C for 90 min in an oven with a vacuum degree ≤10 Pa, and dry it for standby; (2) Load the raw materials processed in step (1) into a vacuum melting furnace, the vacuum degree in the furnace is 3.5×10 -2 Pa, heat to 1160 °C, keep it warm for 30 min after all the raw materials are melted, and then start the downward continuous casting traction system to draw out the copper plate from the graphite mold at a speed of 75 mm / min. During the continuous casting process, the cooling water flow rate is 3.5±0.2 m 3 / h, the cooling water temperature is 28±1 °C, and the thickness of the continuously cast copper plate is 25 mm; (3) Place the copper plate prepared in step (2) in a vacuum furnace, evacuate the vacuum in the furnace to 0.5×10 -1 Pa, and then heat it to 725 °C at a rate of 10 °C / min and keep it warm for 60 min for diffusion annealing treatment to homogenize the non-uniform casting structure, and keep it for standby; (4) Cool the copper plate processed in step (3) to 450 °C for hot rolling and blooming, and then mill the surface to remove the surface oxide scale after the copper plate is cooled to room temperature. The thickness of the processed copper plate is 10±0.5 mm, and keep it for standby; (5) The copper plate after hot rolling in step (4) is first roughly rolled at room temperature in an alternating front and back direction to a thickness of 1.8 ± 0.1 mm, and then randomly select any one side and unidirectionally roughly roll it at room temperature to a thickness of 0.7 ± 0.1 mm for standby; (6) Place the copper strip after cold rolling in step (5) in a reducing atmosphere furnace. First, evacuate the air and then fill it with ammonia-decomposed hydrogen with a dew point of -40 °C. Then heat it to 600 °C at a rate of 10 °C / min and hold for 60 min for recrystallization annealing treatment, and cool it to room temperature with the furnace for standby; (7) Carry out finish rolling on the copper strip after the treatment in step (6) at room temperature. The thickness of the copper strip after finish rolling is 0.3 ± 0.05 mm for standby; (8) The copper strip after finish rolling in step (7) is successively pickled with a 10 wt% dilute sulfuric acid solution - cleaned - ground with an 800-mesh brush roll - polished with a 3000-mesh brush roll - cleaned - dried with hot air at 60 °C - trimmed - wound - packaged to obtain the high-thermal-stability oxygen-free copper strip for power semiconductor devices. The surface roughness of the copper strip is 0.15 μm, and its original grain OM morphology is as shown in Figure 1 shown in, and the XRD spectrum is as shown in Figure 4 shown in.

[0039] Example 2: A preparation method of a high-thermal-stability oxygen-free copper strip for power semiconductor devices, the steps are as follows: (1) Ultrasonically clean the cathode copper with a purity ≥ 99.9% with deionized water, and then keep it at 80 °C in an oven with a vacuum degree ≤ 10 Pa for 180 min, and dry it for standby; (2) Load the raw materials processed in step (1) into a vacuum melting furnace. The vacuum degree in the furnace is 3.5 × 10 -2 Pa, heat it to 1120 °C, and continue to hold for 60 min after all the raw materials are melted. Then start the down-drawing continuous casting traction system and draw out the copper plate from the graphite mold at a speed of 100 mm / min. During the continuous casting process, the cooling water flow rate is 4 ± 0.2 m 3 / h, and the cooling water temperature is 35 ± 1 °C. The thickness of the copper plate obtained by continuous casting is 20 mm; (3) Place the copper plate prepared in step (2) in a vacuum furnace. Evacuate the air in the furnace to 0.5 × 10 -1 Pa, and then heat it to 800 °C at a rate of 10 °C / min and hold for 30 min for diffusion annealing treatment to homogenize the non-uniform casting structure for standby; (4) Cool the copper plate processed in step (3) to 400 °C for hot rolling and blooming. After the copper plate is cooled to room temperature, mill the surface to remove the surface oxide scale. The thickness of the processed copper plate is 10 ± 0.5 mm for standby; (5) The hot-rolled copper plate obtained in step (4) is first rough-rolled at room temperature in an alternating front and back direction to a thickness of 1.5 ± 0.1 mm, and then randomly select any one side and perform a second rough-rolling at room temperature in a single direction to a thickness of 0.5 ± 0.1 mm for standby; (6) Place the cold-rolled copper strip obtained in step (5) in a reduction atmosphere furnace. First, evacuate the air and then fill it with ammonia-decomposed hydrogen with a dew point of -40 °C. Then, heat it to 500 °C at a rate of 5 °C / min and hold for 120 min for recrystallization annealing treatment, and cool it to room temperature with the furnace for standby; (7) Perform finish rolling on the copper strip treated in step (6) at room temperature. The thickness of the copper strip after finish rolling is 0.2 ± 0.05 mm for standby; (8) The copper strip after finish rolling in step (7) is successively pickled with a 10 wt% dilute sulfuric acid solution - cleaned - ground with a 600-mesh brush roll - polished with a 4000-mesh brush roll - cleaned - dried with hot air at 70 °C - trimmed - wound - packaged to obtain the high-thermal-stability oxygen-free copper strip for power semiconductor devices. The surface roughness of the copper strip is 0.08 μm.

[0040] Example 3: A preparation method of a high-thermal-stability oxygen-free copper strip for power semiconductor devices, the steps are as follows: (1) The cathode copper with a purity ≥ 99.9% is ultrasonically cleaned with deionized water, and then kept at 150 °C for 60 min in an oven with a vacuum degree ≤ 10 Pa, and dried for standby; (2) Load the raw materials treated in step (1) into a vacuum melting furnace. The vacuum degree in the furnace is 3.5×10 -2 Pa, heat it to 1180 °C, and continue to hold for 30 min after all the raw materials are melted. Then, start the downward continuous casting traction system and draw out the copper plate from the graphite mold at a speed of 150 mm / min. During the continuous casting process, the cooling water flow rate is 5 ± 0.2 m 3 / h, the cooling water temperature is 40 ± 1 °C, and the thickness of the continuously cast copper plate is 35 mm; (3) Place the copper plate prepared in step (2) in a vacuum furnace. Evacuate the air in the furnace to 0.5×10 -1 Pa, and then heat it to 700 °C at a rate of 5 °C / min and hold for 90 min for diffusion annealing treatment to homogenize the non-uniform casting structure for standby; (4) Cool the copper plate treated in step (3) to 500 °C for hot rolling and blooming. After the copper plate is cooled to room temperature, mill the surface to remove the surface oxide scale. The thickness of the treated copper plate is 10 ± 0.5 mm for standby; (5) The hot-rolled copper plate obtained in step (4) is first rough-rolled at room temperature in an alternating front and back direction to a thickness of 2 ± 0.1 mm, and then randomly select any one side and perform a second rough-rolling at room temperature in a single direction to a thickness of 1 ± 0.1 mm for standby; (6) Place the cold-rolled copper strip obtained in step (5) into a reduction atmosphere furnace. First, evacuate the air and then fill it with ammonia-decomposed hydrogen with a dew point of -40°C. Then, heat it to 650°C at a rate of 10°C / min and hold for 60 min for recrystallization annealing treatment. Cool it to room temperature in the furnace for standby; (7) Subject the copper strip treated in step (6) to finish rolling at room temperature. The thickness of the copper strip after finish rolling is 0.1 ± 0.05 mm for standby; (8) Subject the copper strip finish-rolled in step (7) to pickling with 10 wt% dilute sulfuric acid solution - cleaning - grinding with a 1500-mesh brush roll - polishing with a 3000-mesh brush roll - cleaning - hot air drying at 70°C - trimming - winding - packaging in sequence to obtain the high-thermal-stability oxygen-free copper strip for power semiconductor devices, and the surface roughness of the copper strip is 0.11 μm.

[0041] Comparative Example 1: The difference between Comparative Example 1 and Example 1 is that the diffusion annealing treatment in step (3) is not carried out, and the remaining steps are the same as those in Example 1.

[0042] Comparative Example 2: The difference between Comparative Example 2 and Example 1 is that in step (5), first randomly select any one side and perform unidirectional first rough rolling at room temperature to a thickness of 2 ± 0.1 mm, and then perform unidirectional second rough rolling on the other side at room temperature to a thickness of 1 ± 0.1 mm; the remaining steps are the same as those in Example 1.

[0043] Comparative Example 3: 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 an alternating front and back direction; the remaining steps are the same as those in Example 1.

[0044] Comparative Example 4: The difference between Comparative Example 4 and Example 1 is that in step (6), the temperature of the recrystallization annealing treatment is 400°C, and the rest are the same as those in Example 1.

[0045] Comparative Example 5: Adopt the 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 specific steps are as follows: (1) Load the raw material cathode copper into a vacuum melting furnace and cover it with a layer of charcoal. The vacuum degree in the furnace is 3.5×10 -2 Pa, heat it to 1200°C, and after all the raw materials are melted, continue to hold for 60 min. Then, start the downward continuous casting traction system and draw out the copper plate from the graphite mold at a speed of 75 mm / min. During the continuous casting process, the cooling water flow rate is 1.5 m 3 / h, the cooling water temperature is 28°C, and the thickness of the continuously cast copper plate is 25 mm; (2) Heat the copper plate obtained in step (1) to 800 °C and hold for 60 min, then perform hot rolling at 600 °C with 5 passes, and the deformation per pass is 15%. After the copper plate is cooled to room temperature, face milling is carried out to remove the surface oxide scale. The thickness of the treated copper plate is 10 ± 0.5 mm for standby. (3) Perform multi-pass cold rolling on the sheet obtained in step (2) with a deformation rate of 10% per pass, a rolling speed of 300 m / min, and the thickness after rolling is 6 ± 0.5 mm for standby. (4) Place the copper plate prepared in step (3) in a continuous annealing furnace with a nitrogen atmosphere and perform annealing treatment at 500 °C for 60 min to eliminate the rolling stress and restore plasticity for standby. (5) Perform multi-pass cold rolling on the copper plate treated in step (4) with a deformation rate of 10% per pass, a rolling speed of 300 m / min, and the thickness after rolling is 3 + 0.5 mm for standby. (6) Place the copper plate prepared in step (5) in a continuous annealing furnace with a nitrogen atmosphere and perform a return treatment at 500 °C for 60 min to eliminate the rolling stress and restore plasticity for standby. (7) Perform multi-pass cold rolling on the copper plate treated in step (6) with a deformation rate of 10% per pass, a rolling speed of 300 m / min, and the thickness after rolling is 0.3 ± 0.05 mm for standby. (8) Place the copper strip prepared in step (7) in a 5% sulfuric acid solution pool and clean it at 50 °C for 3 min for standby. (9) Clean and dry the copper strip treated in step (8) with deionized water or ethanol for standby. (10) Slit the copper strip treated in step (9) 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.

[0046] Test the properties of the oxygen-free copper strips obtained in the above examples and comparative examples, and the results are shown in Table 1 and Figures 1 to 4 as shown in.

[0047] Among them, the tests of the components (copper content, oxygen content), average grain size, hardness, electrical conductivity, thermal conductivity, strength, elongation, etc. involved in the oxygen-free copper strip all refer to the national standard GB / T 2059-2017 "Copper and Copper Alloy Strip". The high-temperature grain size is the grain size after holding at 900 °C for 30 min.

[0048] 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 × 100%.

[0049] 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, the scanning angle is 15 - 100 °C, and the scanning speed is 2 ° / min. The curve measured by XRD is calibrated using MDI Jade 6.0 software.

[0050] Table 1: Test results of oxygen-free copper strip properties.

[0051] From Table 1 and Figures 1 to 4 it can be seen that the oxygen-free copper strip prepared by the method of the present invention in the examples can achieve precise control of the crystal orientation (Cu(200)), grain size (30 - 70 μm), oxygen content (≤5 ppm), hardness (105 - 115 HV), and strength (330 - 350 MPa) of the copper strip. At the same time, the oxygen-free copper strip provided by the present invention has high electrical conductivity (≥58 MS / m) and thermal conductivity (≥390 W / (m·K)), and exhibits excellent high-temperature stability of grain size (grain growth change rate ≤40%) during the high-temperature treatment process.

[0052] In Comparative Example 1, diffusion annealing treatment is not carried out before hot rolling. Due to the rapid cooling of continuous casting, a large amount of dendritic structure exists in the copper plate. Without diffusion annealing treatment, internal composition segregation, dendritic structure, and microdefects cannot be eliminated, resulting in large differences in grain size and significantly reducing the high-temperature stability of the grain size of the copper strip.

[0053] In Comparative Example 2, single-sided unidirectional cold rolling is carried out for both the first rough rolling and the second rough rolling during cold rolling. The crystal orientation of the obtained copper strip is Cu(111), and the high-temperature stability of the grain size of the copper strip is significantly reduced compared with that in the examples.

[0054] In Comparative Example 3, only cold rolling in alternating directions on the front and back sides is carried out during cold rolling. The crystal orientation of the copper strip is Cu(111), and the high-temperature stability of the grain size of the copper strip is significantly reduced compared with that in the examples.

[0055] In Comparative Example 4, the temperature during recrystallization annealing treatment is lower than the range of the present invention. Due to the too low temperature, the rolling stress cannot be completely eliminated, resulting in a significant decrease in the high-temperature stability of the grain size and the elongation of the copper strip compared with that in the examples.

[0056] In Comparative Example 5, the traditional oxygen-free copper strip preparation process is adopted: vacuum melting - continuous casting - hot rolling - milling - cold rolling - annealing - cold rolling - annealing - cold rolling - pickling - cleaning - slitting. The crystal orientation of the obtained copper strip is Cu(220), and the high-temperature stability of the grain size of the copper strip is significantly reduced compared with that in the examples.

[0057] The above are only the preferred embodiments of the present invention, and do not impose any formal or substantial limitations on the present invention. It should be noted that for those of ordinary skill in the art of this technology, without departing from the method of the present invention, several improvements and supplements can still be made, and these improvements and supplements should also be regarded as the protection scope of the present invention. Any slight changes, modifications and equivalent changes in evolution made by those skilled in the art who are familiar with this specialty without departing from the spirit and scope of the present invention, using the technical content disclosed above, are all equivalent embodiments of the present invention; at the same time, any changes, modifications and evolutions of equivalent changes made to the above embodiments based on the substantial technology of the present invention still fall within the scope of the technical solutions of the present invention.

Claims

1. A preparation method of a high thermal stability oxygen-free copper strip for a power semiconductor device, characterized in that the steps Including: (1) Vacuum melting the copper raw material, and then downward continuous casting to obtain a copper plate; (2) Placing the copper plate in a vacuum furnace for diffusion annealing treatment, and then cooling; (3) Subjecting the cooled copper plate to hot rolling for blooming, and milling the surface to remove the surface scale after the copper plate is cooled to room temperature; (4) First performing the first rough rolling on the hot-rolled copper plate at room temperature in an alternating front and back direction, and then performing the second rough rolling on any one side unidirectionally at room temperature to obtain a copper strip; (5) Placing the copper strip in a reducing atmosphere furnace for recrystallization annealing treatment; (6) Performing finish rolling on the annealed copper strip at room temperature; (7) Sequentially pickling, cleaning, grinding, polishing, cleaning, and hot air drying the finish-rolled copper strip to obtain the product.

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

3. The preparation method of the high thermal stability 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 °C, the vacuum degree ≤ 10 -2 Pa. After the raw materials are melted, keep them warm for 30~60 min. The conditions for downward continuous casting are: the traction speed is 30~150 mm / min, the cooling water flow rate is 3~5 m 3 / h, the cooling water temperature is 20~40 °C, and the thickness of the copper plate is 20~35 mm.

4. The preparation method of the high thermal stability oxygen-free copper strip for a power semiconductor device according to claim 1, characterized in that, The diffusion annealing conditions in step (2) are as follows: heating temperature 700~800 °C, holding time 30~90 min, heating rate 1~10 °C / min, and vacuum degree ≤ 10 -1 Pa.

5. The preparation method of the 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°C, and the thickness of the hot-rolled copper plate is 8~12 mm.

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

7. The preparation method of the high thermal stability oxygen-free copper strip for power semiconductor devices according to claim 1, characterized in that, The recrystallization annealing conditions in step (5) are: heating temperature 500~680°C, heat preservation time 30~120 min, heating rate 5~20°C / min, furnace cooling, and the protective atmosphere is hydrogen or ammonia-decomposed hydrogen, with a dew point ≤ -30°C.

8. The preparation method of the high thermal stability oxygen-free copper strip for a power semiconductor device according to claim 1, characterized in that, The thickness of the finish-rolled copper strip in step (6) is 0.1~0.35 mm.

9. The preparation method of the high thermal stability oxygen-free copper strip for a power semiconductor device according to claim 1, characterized in that, The pickling solution in step (7) is an 8 - 12wt% dilute sulfuric acid solution, the mesh number of the brush roll for grinding is 600 - 1500 meshes, the mesh number of the brush roll for polishing is 3000 - 5000 meshes, the hot air drying temperature is 60~80°C, and the surface roughness of the obtained oxygen-free copper strip is ≤0.2μm.

10. A high thermal stability oxygen-free copper strip for power semiconductor devices, characterized in that, Prepared by using the preparation method described in any one of claims 1~9.

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