High-purity high-thermal-stability oxygen-free copper strip for ceramic copper-clad plate and production process thereof

Abstract

This invention belongs to the field of copper alloy technology, specifically relating to a high-purity, high-heat-stable oxygen-free copper strip for ceramic copper-clad laminates and its production process, including the following steps: S1, upward continuous casting: using cathode copper as raw material, it is melted in a pure graphite crucible induction furnace at 1150-1210℃, the surface of the copper liquid is covered with graphite flakes / calcined charcoal, and a copper rod with a diameter of 30-32mm is obtained by upward continuous casting; S2, continuous extrusion: the copper rod is fed into a continuous extrusion press to obtain a copper strip billet; S3 S1, Homogenization Hot Rolling: The copper strip billet is homogenized and heated to 700-750℃ before hot rolling. The initial rolling temperature is 700-750℃, the final rolling temperature is 450-550℃, and the hot rolling passes are 2-3 times. The total deformation during hot rolling is ≥25%. S4, Milling: The upper and lower surfaces of the hot-rolled copper strip billet are milled by 0.2-0.8mm each. S5, Cold Rolling and Annealing: The milled copper strip billet is subjected to multiple cold rolling passes, combined with intermediate annealing, to finally prepare a finished copper strip with a thickness of 0.1-0.8mm.

Description

Technical Field

[0001] This invention belongs to the field of copper alloy technology, specifically relating to a high-purity, high-thermal-stable oxygen-free copper strip for ceramic copper-clad laminates and its production process. Background Technology

[0002] Power semiconductor devices are widely used in new energy vehicles, smart grids, high-speed rail transportation, and other fields. DBC (Direct Copper Clad) and AMB (Active Metal Brazing) ceramic copper-clad laminates are key substrate materials for their packaging. IGBT modules (Insulated Gate Bipolar Transistors), as the core packaging material for power semiconductor devices, require both DBC and AMB ceramic copper-clad laminates to be bonded to the ceramic substrate at high temperatures using oxygen-free copper strips. The DBC process utilizes a Cu-O eutectic solution of copper at 1065–1083℃ to achieve direct bonding between the copper strip and the ceramic; the AMB process uses silver-copper-titanium active solder to achieve metallurgical connection between the copper strip and the ceramic in a vacuum environment at 800–950℃. Both processes require prolonged high-temperature holding, placing extremely high demands on the oxygen content and high-temperature performance of the copper strip.

[0003] For the DBC process, the Cu2O content in the copper strip must be precisely controlled. Excessive oxygen content will lead to excessive eutectic liquid generation at high temperatures, resulting in uneven thickness of the copper / ceramic bonding layer and reducing the interfacial bonding strength and reliability. At the same time, after high-temperature heat treatment, the copper strip grains grow rapidly, with grain sizes reaching the millimeter level, forming an "orange peel" structure on the bonding surface. This leads to increased interfacial gaps, decreased bonding strength, and adverse effects on subsequent etching and welding processes.

[0004] For the AMB process, the active element Ti in the silver-copper-titanium active solder is extremely sensitive to oxygen. The oxygen released by the residual Cu2O in the copper strip under vacuum and high temperature will preferentially react with Ti, causing the active element to oxidize and deactivate. The solder cannot effectively wet the ceramic surface, which in turn leads to large-area cold solder joints and missing solder joints, causing the copper / ceramic bonding to fail. In addition, the abnormal growth of the copper strip grains after high temperature will also lead to a rough brazing interface, affecting the uniform spread of the solder and the quality of the interface bonding.

[0005] Therefore, both DBC and AMB copper clad laminate processes require the use of oxygen-free copper strips with an oxygen content of no more than 0.0003% to ensure the interface cleanliness, welding reliability, and fine-grain thermal stability of the copper strips during high-temperature bonding.

[0006] Currently, the mainstream production processes for oxygen-free copper strips mainly fall into two categories, both of which have significant shortcomings: (1) Downward semi-continuous casting process: The copper liquid is melted in an open or semi-closed furnace and then continuously cast into large-size ingots, which are then hot-rolled and cold-rolled to produce strips. In this process, the furnace is usually lined with furnace bricks, whose main components are oxides such as SiO2 and Al2O3. At high temperatures above 1150℃, the oxides in the furnace bricks will continuously release trace amounts of oxygen into the copper liquid. Combined with the oxygen absorption of the copper liquid from contact with air during the smelting process, the initial oxygen content of the ingot is usually in the range of 10 to 30 ppm, and the oxygen content of the finished strip is difficult to be stably lower than 3 ppm, which is far from meeting the <1 ppm requirement of high-end DBC / AMB copper clad laminates. In order to further reduce the oxygen content, some companies use the method of adding deoxidizing elements such as phosphorus, calcium, and magnesium, but this inevitably leads to a decrease in the purity and conductivity of the copper strip, which also does not meet the application requirements of high-purity oxygen-free copper strips.

[0007] (2) Upward continuous casting + continuous extrusion process: The copper molten metal is continuously drawn upward into a copper rod in a closed smelting device. Theoretically, the oxygen content of the cast rod can be controlled at an extremely low level through a protective atmosphere. However, the existing upward continuous casting process generally uses a furnace lined with furnace bricks for smelting. It relies solely on the charcoal covering layer above the copper molten metal for oxygen protection. The problem of continuous oxygen release from furnace brick oxides still exists, and in actual production, the oxygen content of the copper rod is usually difficult to be lower than 1 ppm. Even if the oxygen content of the cast rod meets the standard, the copper rod is subjected to strong asymmetric shear deformation in the extrusion wheel groove during continuous extrusion. The outer layer of the copper rod flows violently, and the gas accumulates to the outer layer. Inevitably, segregated pores are formed in the shallow layer (0-3 mm from the surface) of the copper strip billet. The above-mentioned pores cannot achieve metallurgical bonding at room temperature during subsequent cold rolling. Under the action of rolling pressure, the pores expand, causing serious defects such as delamination, peeling, and even strip breakage, resulting in low yield and inability to achieve stable industrial production.

[0008] In summary, existing technologies present an irreconcilable contradiction: to control the oxygen content below 1 ppm, a pure graphite crucible combined with an upward continuous casting process must be used to eliminate oxygen release pollution from the furnace bricks, while maintaining high purity without adding any deoxidizing elements. However, the shallow porosity problem generated by upward continuous casting combined with continuous extrusion makes subsequent cold rolling unstable. How to simultaneously solve these two mutually restrictive problems of oxygen content control and porosity elimination is the technical challenge that this invention aims to address.

[0009] It should be noted that the information disclosed in this background section is only for understanding the background technology of the present application concept, and therefore, the above description is not considered to constitute prior art information. Summary of the Invention

[0010] This disclosure provides at least one high-purity, high-thermal-stable oxygen-free copper strip for ceramic copper-clad laminates and its manufacturing process.

[0011] In a first aspect, the present disclosure provides a production process for oxygen-free copper strip, comprising the following steps: S1, upward continuous casting: using Grade A cathode copper plate as raw material, it is placed in a pure graphite crucible induction furnace and melted at 1150-1210℃. The surface of the copper liquid is covered with graphite flakes / calcined charcoal. The casting speed is 150-2500 mm / min, and a copper rod with a diameter of 30-32 mm is obtained by upward continuous casting unit; S2, continuous extrusion: the copper rod is fed into a continuous extrusion press, the extrusion roller speed is 5-6 r / min, and the introduced pores are concentrated in the shallow area of ​​the copper strip billet to obtain a strip with a width of 300-420 mm and a thickness of 18 mm. S3, Homogenization Hot Rolling: The copper strip billet is homogenized and heated to 700-750℃ before hot rolling. The initial rolling temperature is 700-750℃, and the final rolling temperature is 450-550℃. There are 2-3 hot rolling passes, and the total deformation is ≥25%. The high temperature and pressure of hot rolling cause metallurgical bonding at the interface of shallow pores, eliminating pore defects. S4, Milling: The upper and lower surfaces of the hot-rolled copper strip billet are milled by 0.2-0.8mm to remove the surface oxide layer. S5, Cold Rolling and Annealing: The milled copper strip billet is subjected to multiple cold rolling passes, combined with intermediate annealing, to finally prepare a finished copper strip with a thickness of 0.1-0.8mm.

[0012] In one optional embodiment, the pure graphite crucible induction furnace is a high-purity isostatic graphite crucible with a graphite purity ≥99.9%.

[0013] In one optional embodiment, the covering thickness of the calcined charcoal in S1 is ≥200mm or the covering thickness of the graphite flakes is ≥50mm; the holding temperature of the pure graphite crucible induction furnace is 1140~1160℃; the crystallizer of the upward continuous casting unit is a copper-chromium-zirconium water-cooled crystallizer, and the cooling water outlet temperature is ≤28℃.

[0014] In one optional embodiment, the porosity of the hot-rolled copper strip cross-section in S3 is ≤0.01%.

[0015] In an optional embodiment, the homogenization heating in S3 is carried out in a protective atmosphere, which is nitrogen or a nitrogen-hydrogen mixture; the reduction in each pass of the hot rolling is ≤15%, and the final rolling temperature is not lower than 450°C to maintain sufficient metallurgical bonding activity.

[0016] In one optional embodiment, the milling cutter rotation speed in S4 is 600-800 r / min, and the milling speed is 6-8 m / min; after milling, the surface roughness of the copper strip blank is ≤10 μm, the longitudinal thickness tolerance is ≤0.05 mm, and 0.2-0.8 mm is milled on each side to completely remove the oxide layer on the hot-rolled surface.

[0017] In one optional embodiment, the pass rate of the multi-pass cold rolling in S5 is 20-35%; the annealing temperature of the intermediate annealing is 350-500°C, and the annealing protective atmosphere is a mixture of 15-20% H2 and 80-85% N2 by volume.

[0018] In one optional embodiment, after intermediate annealing in step S5, the process further includes cleaning and passivation, straightening, and slitting; the straightened copper strip has a plate shape ≤10I; the cleaning and passivation is performed using a benzotriazole aqueous solution; and the slitting copper strip has a side curvature ≤1mm / m and a twist ≤5° / m.

[0019] Secondly, this disclosure also provides an oxygen-free copper strip, which is produced by the production process described above. The oxygen-free copper strip has a copper content ≥99.997%, an oxygen content ≤1ppm, a conductivity ≥100%IACS, a tensile strength of 300~370MPa, an elongation ≥2%, and a thickness tolerance ≤±0.003mm.

[0020] Thirdly, this disclosure also provides a ceramic copper-clad laminate, which uses the oxygen-free copper strip as described above. After high-temperature bonding, the copper strip grain size is 50-70 μm, and the grain growth rate is ≤40%. The high-temperature bonding includes holding at 900-1080°C for no less than 30 minutes.

[0021] The beneficial effects of this invention are as follows: the high-purity, high-heat-stable oxygen-free copper strip used in this ceramic copper-clad laminate and its production process utilize pure graphite crucibles instead of brick furnace chambers for smelting. By leveraging the reducing properties of the graphite crucibles and the synergistic protective effect of charcoal / graphite flakes covering, the oxygen content of the copper strip is fundamentally eliminated from the furnace brick oxides. Without adding any deoxidizing elements, the oxygen content of the copper strip is stably controlled below 1 ppm. Simultaneously, a homogenization hot rolling process is added between the continuous extrusion and milling processes. Utilizing the distribution pattern of pores concentrated in the shallow layer of the copper strip blank after extrusion, atomic diffusion bonding occurs at the shallow pore interface through a total hot rolling deformation of ≥25% at the metallurgical bonding temperature, completely eliminating pore defects and fundamentally solving the problems of cold rolling peeling and strip breakage.

[0022] Other features and advantages of the invention will be set forth in the following description, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention are realized and obtained through the structures particularly pointed out in the description and the drawings.

[0023] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, preferred embodiments are described below in detail with reference to the accompanying drawings. Attached Figure Description

[0024] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0025] Figure 1 A comparative schematic diagram of a pure graphite crucible and a furnace brick furnace top-drawing continuous casting melting device provided in the embodiments of this disclosure, indicating the CO reducing atmosphere formation mechanism of the graphite crucible; Figure 2 This is a schematic diagram of the porosity distribution of the cross-section of the continuously extruded copper strip billet provided in the embodiments of this disclosure, with the shallow porosity clustered area (0-3mm) and the core low porosity area marked. Figure 3 This is a partial schematic diagram of the porosity distribution in the cross-section of a continuously extruded copper strip billet provided in an embodiment of this disclosure; Figure 4 A defect state diagram of a continuously extruded copper strip billet after subsequent rolling, provided in an embodiment of this disclosure; Figure 5 A defect state diagram of a continuously extruded copper strip billet after subsequent rolling, provided in an embodiment of this disclosure; Figure 6 The metallographic comparison diagram of the cross section of the copper strip before hot rolling provided in the embodiments of this disclosure shows the effect of eliminating the metallurgical bond of porosity; Figure 7 A metallographic comparison diagram of the cross section of the hot-rolled copper strip billet provided in the embodiments of this disclosure, demonstrating the effect of eliminating the metallurgical bond of porosity; Figure 8 The surface morphology of the defective product after sintering is provided in the embodiments of this disclosure; Figure 9 The surface morphology of the defective product after sintering is provided in the embodiments of this disclosure; Figure 10 This is a diagram showing the state of a non-conforming product after sintering, provided in an embodiment of this disclosure. Figure 11 Metallographic images of non-conforming products after sintering provided in this embodiment of the disclosure; Figure 12 The morphology of the finished copper strip after DBC sintering in Example 1 is provided for the present disclosure. Figure 13 Metallographic image of the finished copper strip after DBC sintering in Example 1, provided as an embodiment of this disclosure; Figure 14 The grain size diagram (grain size 50-70 μm) of the finished copper strip DBC after sintering in Example 1 provided for the present disclosure. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] As used herein, the phrases “in one embodiment,” “according to one embodiment,” “in some embodiments,” etc., generally refer to the fact that a particular feature, structure, or characteristic following the phrase can be included in at least one embodiment of this disclosure. Therefore, a particular feature, structure, or characteristic can be included in more than one embodiment of this disclosure, such that these phrases do not necessarily refer to the same embodiment. As used herein, the terms “example,” “exemplary,” etc., are used to “serve as an example, instance, or illustration.” Any implementation, aspect, or design described herein as “example” or “exemplary” is not necessarily to be construed as preferred or superior to other implementations, aspects, or designs. Rather, the use of the terms “example,” “exemplary,” etc., is intended to present concepts in a specific manner.

[0028] The following detailed description of some embodiments of the present invention is provided in conjunction with the accompanying drawings. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0029] This disclosure provides a production process for oxygen-free copper strip, comprising the following steps: S1, upward continuous casting: using Grade A cathode copper plate as raw material, it is melted in a pure graphite crucible induction furnace at 1150-1210℃. The surface of the copper liquid is covered with graphite flakes / calcined charcoal. The casting speed is 150-2500 mm / min, and a copper rod with a diameter of 30-32 mm is obtained by upward continuous casting unit; S2, continuous extrusion: the copper rod is fed into a continuous extrusion press, the extrusion roller speed is 5-6 r / min, and the introduced pores are concentrated in the shallow area of ​​the copper strip billet to obtain a width of 300-420 mm and a thickness of 18-20 mm. S3, Homogenization Hot Rolling: The copper strip billet is homogenized and heated to 700-750℃ before hot rolling. The initial rolling temperature is 700-750℃, and the final rolling temperature is 450-550℃. There are 2-3 hot rolling passes, and the total deformation is ≥25%. The high temperature and pressure of hot rolling cause metallurgical bonding at the interface of shallow pores, eliminating pore defects. S4, Milling: The upper and lower surfaces of the hot-rolled copper strip billet are milled by 0.2-0.8mm to remove the surface oxide layer. S5, Cold Rolling and Annealing: The milled copper strip billet is subjected to multiple cold rolling passes, combined with intermediate annealing, to finally prepare a finished copper strip with a thickness of 0.1-0.8mm.

[0030] In some embodiments, specifically, the pure graphite crucible induction furnace is a high-purity isostatic graphite crucible with a graphite purity ≥99.9%. The graphite crucible does not contain any oxide materials. The carbon on the inner wall of the crucible forms a CO reducing atmosphere at the interface with the copper liquid at high temperature, forming the first oxygen barrier at the copper liquid contact interface.

[0031] In some embodiments, specifically, the covering thickness of the calcined charcoal in S1 is ≥200mm or the covering thickness of the graphite flakes is ≥50mm; the holding furnace temperature of the pure graphite crucible induction furnace is 1140~1160℃, and the upper surface of the copper liquid is covered with calcined charcoal (thickness ≥200mm) or graphite flakes (thickness ≥50mm) to form a second oxygen barrier. Under the synergistic effect of dual protection, the oxygen content of the copper liquid can be stably controlled within 1ppm; the crystallizer of the upward continuous casting unit is a copper-chromium-zirconium water-cooled crystallizer, and the cooling water outlet temperature is ≤28℃.

[0032] In some embodiments, specifically during the continuous extrusion process in S2, the outer metal layer of the copper rod undergoes intense asymmetric shear deformation, with the deformation amount being much greater than that of the core. Gas within the copper rod and between the copper rod and the wheel groove flows with the outer metal layer and accumulates in the shallow layer of the copper strip, forming microscopic pores that are concentrated within a range of 0–3 mm from the surface, with a pore diameter of approximately 0.05–0.3 mm. The core region exhibits extremely low porosity due to its small deformation and long gas migration distance.

[0033] In some embodiments, specifically, the porosity of the hot-rolled copper strip cross-section in S3 is ≤0.01%.

[0034] In some embodiments, specifically, the homogenization heating in S3 is carried out in a protective atmosphere, which is nitrogen or a nitrogen-hydrogen mixture; the reduction in each pass of the hot rolling is ≤15%, and the final rolling temperature is not lower than 450°C to maintain sufficient metallurgical bonding activity.

[0035] Specifically, the normal compressive stress generated by hot rolling brings the shallow pore interfaces into close contact. Activated by the high temperature of 550–700℃, copper atoms at the pore interfaces gain sufficient diffusion kinetic energy, resulting in inter-atomic diffusion and metallurgical bonding. Since the pores are concentrated in the shallow layer (0–3 mm), the total hot rolling deformation of ≥25% sufficiently covers the pore distribution area, eliminating the need for excessive deformation of the core and ensuring both hot rolling efficiency and strip microstructure quality. The porosity of the hot-rolled copper strip cross-section is ≤0.01%, with no visible interlayer defects.

[0036] In some embodiments, specifically, the milling cutter rotation speed in S4 is 600-800 r / min, and the milling speed is 6-8 m / min; the surface roughness of the copper strip blank after milling is ≤10 μm, the longitudinal thickness tolerance is ≤0.05 mm, and 0.2-0.8 mm is milled on each side to completely remove the oxide layer on the hot-rolled surface.

[0037] In some embodiments, specifically, the pass rate of the multi-pass cold rolling in S5 is 20-35%; the annealing temperature of the intermediate annealing is 350-500°C, and the annealing protective atmosphere is a mixture of 15-20% H2 and 80-85% N2 by volume.

[0038] In some embodiments, specifically, after intermediate annealing in step S5, the process further includes cleaning and passivation, straightening, and slitting; the straightened copper strip has a plate shape ≤10I; the cleaning and passivation is performed using a benzotriazole aqueous solution; and the slitting copper strip has a side curvature ≤1mm / m and a twist ≤5° / m.

[0039] This disclosure also provides an oxygen-free copper strip, which is produced by the production process described above. The oxygen-free copper strip has a copper content ≥99.997%, an oxygen content ≤1ppm, a conductivity ≥100%IACS, a tensile strength of 300~370MPa, an elongation ≥2%, and a thickness tolerance ≤±0.003mm.

[0040] This disclosure also provides a ceramic copper-clad laminate, which uses the oxygen-free copper strip as described above. After high-temperature bonding, the copper strip grain size is 50-70 μm, and the grain growth rate is ≤40%. The high-temperature bonding includes holding at 900-1080°C for no less than 30 minutes.

[0041] Example 1, for DBC, finished product 0.3mm (1) Upward continuous casting: Using cathode copper with a purity ≥99.9% as raw material, it is melted in an induction furnace with a high-purity isostatic graphite crucible (C≥99.9%). The furnace temperature is 1180℃, and the surface of the copper liquid is covered with 200mm of calcined charcoal. The holding furnace temperature is 1150℃. The casting speed is 200mm / min, and the diameter of the casting rod is Φ32mm.

[0042] Test results: Oxygen content of copper rod <1ppm, copper content 99.998%, conductivity 102.1%IACS.

[0043] (2) Continuous extrusion: The extrusion roller speed is 5.5 r / min, yielding a copper strip blank with a width of 300 mm and a thickness of 20 mm. Metallographic inspection of the strip blank cross-section: Pores are distributed in the range of 0 to 2.5 mm from the surface, with a pore diameter of 0.05 to 0.2 mm. Please refer to [reference needed]. Figure 2 and Figure 3 No pores were observed in the core (area >3mm).

[0044] (3) Homogenization hot rolling: Heat to 730℃ in a N2 protective atmosphere and hold for 15 min. Perform two passes of hot rolling: first pass reduction of 13% (20mm→17.4mm), second pass reduction of 14% (17.4mm→15mm), final rolling temperature of 510℃, total deformation of 25%. Please refer to [link / reference]. Figure 6 and Figure 7 Metallographic examination of the section after hot rolling: porosity was completely eliminated and no interlayer defects were found.

[0045] (4) Milling: Mill 0.5 mm on each side, with a thickness of 14 mm after milling, a surface roughness of 0.8 μm, and a longitudinal thickness tolerance of 0.03 mm.

[0046] (5) Multi-pass cold rolling: the pass processing rate is 25-30%, combined with intermediate annealing at 450℃ (20%H2+80%N2, 3h), and finally cold rolling to the finished product thickness of 0.3mm.

[0047] (6) Passivation, straightening, and cutting.

[0048] Please see Figures 12-14 Finished product testing: oxygen content <1ppm, copper content 99.997%, conductivity 101.8% IACS, tensile strength 330MPa, elongation 2%, plate type 8I, thickness tolerance ±0.01mm. After DBC sintering (1060℃, 30min), the grain size is 51μm, the grains are uniform, and there is no abnormal growth. There are no broken strips or peeling during the entire production process, and the yield is 92%.

[0049] Example 2, for AMB, finished product 0.2mm (1) Upward continuous casting: furnace temperature 1160℃, casting speed 250mm / min, rod diameter Φ30mm. Oxygen content of copper rod <1ppm, copper content 99.998%.

[0050] (2) Continuous extrusion: The extrusion roller rotates at 5 r / min to obtain a copper strip blank with a width of 300 mm and a thickness of 20 mm. The shallow pores are concentrated in the range of 0 to 2.8 mm.

[0051] (3) Homogenization hot rolling: Heat to 710℃, hold for 20 min, hot roll in 3 passes, with a reduction of 10% / 10% / 10% in each pass, a final rolling temperature of 480℃, and a total deformation of 27%. Porosity is completely eliminated after hot rolling.

[0052] (4) Milling: Mill 0.5mm on each side, resulting in a thickness of 14.5mm after milling.

[0053] (5) Multi-pass cold rolling: combined with 420℃ intermediate annealing, finished product thickness 0.2mm.

[0054] Finished product testing: Oxygen content <1ppm, copper content 99.998%, tensile strength 310MPa, elongation 4%. Grain size after AMB brazing: 58μm. Yield: 91%.

[0055] Example 3, for DBC, finished product 0.1mm (1) Upward continuous casting: furnace temperature 1200℃, casting speed 680mm / min, rod diameter Φ32mm. Oxygen content of copper rod 0.9ppm.

[0056] (2) Continuous extrusion: Extrusion roller speed 6r / min, copper strip blank 300mm wide × 20mm thick.

[0057] (3) Homogenization hot rolling: Heat to 740℃, hold for 10 min, hot roll in 2 passes, with a reduction of 13% / 13% in each pass, a final rolling temperature of 530℃, and a total deformation of 25%. Porosity is eliminated.

[0058] (4) Milling: Mill 0.5mm on each side, resulting in a thickness of 14mm after milling.

[0059] (5) Multi-pass cold rolling: combined with multiple intermediate annealing, the finished product thickness is 0.1mm.

[0060] Finished product testing: Oxygen content <1ppm, conductivity 101.5% IACS, DBC sintered grain size 55μm. Yield 88%.

[0061] Example 4, for DBC, finished product 0.4mm (1) Upward continuous casting: furnace temperature 1190℃, casting speed 500mm / min, rod diameter Φ30mm. Oxygen content of copper rod 0.6ppm.

[0062] (2) Continuous extrusion: Extrusion roller speed 5r / min, copper strip blank 300mm wide × 20mm thick.

[0063] (3) Homogenization hot rolling: Heat to 750℃, hold for 15min, hot roll in 2 passes, with a reduction of 15% / 14% in each pass, a final rolling temperature of 550℃, and a total deformation of 27%.

[0064] (4) Milling: Mill 0.5mm on each side.

[0065] (5) Cold roll to a finished thickness of 0.4 mm, followed by annealing.

[0066] Finished product testing: Oxygen content <1ppm, conductivity 102.5% IACS, DBC sintered grain size 65μm. Yield 93%.

[0067] Please see Figure 4 and Figure 5This is a diagram showing the defect state of a continuously extruded copper strip after subsequent rolling.

[0068] Comparative Example 1: The hot rolling process is omitted, i.e., after continuous extrusion, the surface is directly milled and cold rolled. Process route: First, continuous casting is performed in a pure graphite crucible, followed by continuous extrusion, then milling, and finally, hot rolling is omitted and cold rolling is performed. The remaining parameters are the same as in Example 1.

[0069] Results: After milling, the copper strip billet entered cold rolling. When rolled to a thickness of 1.5 mm, surface peeling defects appeared. Further cold rolling to 1.0 mm resulted in strip breakage, making further rolling impossible. Dissection of the broken strip sample revealed multiple interlayer defects caused by the expansion of interlayer pores. The original copper rod had an oxygen content of <1 ppm, but due to pore defects, it was impossible to produce qualified finished products, resulting in a yield of <30%.

[0070] Conclusion: Omitting the hot rolling process and the inability of shallow pores to be metallurgically bonded during cold rolling is the direct cause of strip breakage and peeling, thus verifying the necessity of the hot rolling process in this invention.

[0071] Comparative Example 2: The furnace brick and lining continuous casting process combined with Conform continuous extrusion and hot rolling; please refer to [reference needed]. Figure 1 That is, the process is the same, only the material of the crucible is changed. Replace the pure graphite crucible in step (1) with furnace bricks (SiO2-Al2O2 refractory bricks) to build the furnace chamber, and keep the other process parameters exactly the same as in Example 1.

[0072] Results: The oxygen content of the copper rods ranged from 5 to 10 ppm, indicating significant batch-to-batch fluctuations and an inability to consistently achieve the target of ≤1 ppm. The finished strip had an oxygen content of 7 ppm, exceeding the target value. Bubbles appeared in localized areas after DBC sintering, resulting in a bonding failure rate of approximately 15%.

[0073] Conclusion: The continuous release of oxygen from oxides such as SiO2 in the furnace bricks into the molten copper is the root cause of excessive oxygen content. A pure graphite crucible is a necessary condition to achieve an oxygen content of ≤1ppm in the copper rod, which verifies the innovation of the crucible material selection in this invention.

[0074] Comparative Example 3: Downward semi-continuous casting process; this is the industry standard solution. Ingots are prepared by continuous casting with furnace bricks in the furnace chamber, and 0.3mm thick copper strips are prepared by hot rolling and multiple cold rolling processes without adding any deoxidizing elements.

[0075] Please see Figures 8-11 Results: The oxygen content of the finished product was 5-30 ppm, which did not meet the requirement of ≤1 ppm; the conductivity was 100.5% IACS; after DBC sintering, the grain size was above 150 μm, with some areas showing abnormally large grains >500 μm, indicating unstable bonding quality.

[0076] Table 1 Summary of key performance indicators for each embodiment and comparative example

[0077] In summary, the high-purity, high-heat-stable oxygen-free copper strip used in this ceramic copper-clad laminate and its production process utilize pure graphite crucibles instead of brick furnace chambers for smelting. By leveraging the reducing properties of the graphite crucibles and the synergistic protective effect of charcoal / graphite flakes covering, oxygen pollution from furnace brick oxides is fundamentally eliminated. Without adding any deoxidizing elements, the oxygen content of the copper strip is stably controlled below 1 ppm. Simultaneously, a homogenizing hot rolling process is added between the continuous extrusion and milling processes. Taking advantage of the distribution pattern of pores concentrated in the shallow layer of the copper strip blank after extrusion, atomic diffusion bonding occurs at the interface of the shallow pores through a total hot rolling deformation of ≥25% at the metallurgical bonding temperature, completely eliminating pore defects and fundamentally solving the problems of cold rolling peeling and strip breakage.

[0078] Based on the above-described preferred embodiments of the present invention, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A production process for oxygen-free copper strip, characterized in that, Includes the following steps: S1, Upward continuous casting: Using Grade A cathode copper plates as raw materials, the copper is melted in a pure graphite crucible induction furnace at 1150-1210℃. The surface of the copper liquid is covered with graphite flakes / calcined charcoal. The casting speed is 150-2500 mm / min. Copper rods with a diameter of 30-32 mm are obtained by upward continuous casting unit. S2, Continuous extrusion: The copper rod is fed into the continuous extrusion press, and the extrusion roller rotates at 5-6 r / min. The introduced air holes are concentrated in the shallow area of ​​the copper strip blank to obtain a copper strip blank with a width of 300-420 mm and a thickness of 18-20 mm. S3, Homogenization hot rolling: The copper strip billet is homogenized and heated to 700-750℃ before hot rolling. The initial rolling temperature is 700-750℃, the final rolling temperature is 450-550℃, the hot rolling passes are 2-3, and the total hot rolling deformation is ≥25%. The high temperature and high pressure of hot rolling cause metallurgical bonding at the shallow pore interface, eliminating pore defects. S4, Milling: Mill 0.2-0.8 mm on both the top and bottom surfaces of the hot-rolled copper strip blank to remove the surface oxide layer; S5, Cold rolling and annealing: The milled copper strip blank is subjected to multiple cold rolling passes, combined with intermediate annealing, to finally produce a finished copper strip with a thickness of 0.1 to 0.8 mm.

2. The production process of oxygen-free copper strip as described in claim 1, characterized in that, The pure graphite crucible induction furnace is a high-purity isostatic graphite crucible with a graphite purity ≥ 99.9%.

3. The production process of oxygen-free copper strip as described in claim 1, characterized in that, The covering thickness of the calcined charcoal in S1 is ≥200mm or the covering thickness of the graphite flakes is ≥50mm. The holding temperature of the pure graphite crucible induction furnace is 1140-1160℃; The crystallizer of the upward continuous casting unit is a copper-chromium-zirconium water-cooled crystallizer with a cooling water outlet temperature of ≤28℃.

4. The production process of oxygen-free copper strip as described in claim 1, characterized in that, The porosity of the hot-rolled copper strip in S3 is ≤0.01%.

5. The production process of oxygen-free copper strip as described in claim 1, characterized in that, The homogenization heating in S3 is carried out in a protective atmosphere, which is nitrogen or a nitrogen-hydrogen mixture. The reduction in each pass of the hot rolling is ≤15%, and the final rolling temperature is not lower than 450℃ to maintain sufficient metallurgical bonding activity.

6. The production process of oxygen-free copper strip as described in claim 1, characterized in that, In S4, the milling cutter rotation speed is 600-800 r / min, and the milling speed is 6-8 m / min; After milling, the surface roughness of the copper strip blank is ≤10μm, the longitudinal thickness tolerance is ≤0.05mm, and 0.2~0.8mm is milled on both sides to completely remove the oxide layer on the hot-rolled surface.

7. The production process of oxygen-free copper strip as described in claim 1, characterized in that, The pass rate of the multi-pass cold rolling in S5 is 20-35%. The intermediate annealing temperature is 350–500°C, and the annealing protective atmosphere is a mixture of 15–20% H2 and 80–85% N2 by volume.

8. The production process of oxygen-free copper strip as described in claim 1, characterized in that, The intermediate annealing of S5 also includes cleaning and passivation, straightening and slitting processes. The straightened copper strip plate shape is ≤10I; The cleaning and passivation process was performed using an aqueous solution of benzotriazole. The side curvature of the cut copper strip is ≤1mm / m, and the twist is ≤5° / m.

9. An oxygen-free copper strip, characterized in that, The oxygen-free copper strip is produced by the production process described in any one of claims 1-8, wherein the copper content is ≥99.997%, the oxygen content is ≤1ppm, the conductivity is ≥100%IACS, the tensile strength is 300~370MPa, the elongation is ≥2%, and the thickness tolerance is ≤±0.003mm.

10. A ceramic copper-clad laminate, characterized in that, Using the oxygen-free copper strip as described in claim 9, the copper strip grain size after high-temperature bonding is 50-70 μm, and the grain growth rate is ≤40%; The high-temperature bonding includes holding at 900–1080°C for at least 30 minutes.

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