A method for preparing an oxygen-free copper back plate

Abstract

The application relates to a preparation method of an oxygen-free copper back plate, which comprises the following steps: sequentially performing forging stretching treatment, first heat treatment, hot rolling treatment, cold rolling treatment, second heat treatment and annealing treatment on an oxygen-free copper ingot. After the forging stretching treatment is performed on the oxygen-free copper ingot, the grains are uniformly hot-rolled, then the back plate is in a hardened state through the cold rolling and the second heat treatment, annealing is introduced, internal stress is removed under the premise of not reducing the hardness, and the oxygen-free copper back plate with stable hardness, small fluctuation and a flatness of less than 0.5 mm is obtained.

Description

Technical Field

[0001] This application relates to the field of semiconductor target technology, and in particular to a method for preparing an oxygen-free copper backplate. Background Technology

[0002] Oxygen-free copper is widely used for sputtering targets due to its excellent electrical and thermal conductivity, high plasticity, and ease of processing, serving as a support and heat conductor. The oxygen-free copper backplate is a core supporting component in sputtering target assemblies. Sputtering targets are the main raw materials for physical vapor deposition (PVD) of electronic thin film materials, widely used in integrated circuits, information storage, liquid crystal displays, laser memory, and electronic control devices, among other electronic and information industry applications. The backplate, with its excellent electrical and thermal conductivity, serves to fix the sputtering target and conduct heat during bombardment. Furthermore, the copper backplate is connected to the target via brazing and can be reused approximately 20 times. After sputtering, the copper backplate is desoldered from the target and rebonded to a new target, achieving cost reduction and efficiency improvement.

[0003] As a support backplate for sputtering targets, its flatness, hardness control, and dimensional stability directly affect the welding quality and service life of the target assembly. For brittle targets, such as oxide targets, ceramic dielectric targets, silicon nitride targets, or silicon targets, their common characteristics include low bending strength, a large difference in thermal expansion coefficient compared to copper, susceptibility to thermal shock cracking, and a high risk of edge chipping due to stress at the welding interface. Oxygen-free copper, if too soft, is prone to deformation and warping. Under clamping force or heat during installation, the backplate easily bends, leading to poor adhesion between the target and cooling water, uneven heat dissipation, and in mild cases, affecting sputtering uniformity; in severe cases, localized overheating can cause the brittle target to crack. Therefore, oxygen-free copper backplates are often hardened. However, hardening the backplate results in high internal residual stress, which may deform after long-term thermal cycling due to stress release.

[0004] CN117230393A discloses a method for preparing an oxygen-free copper backplate. The method includes the following steps: (1) preheating a copper ingot and then forging and heat-treating it sequentially to obtain a forged copper ingot; (2) subjecting the forged copper ingot obtained in step (1) to a first rolling and a first heat treatment sequentially to obtain a rolled copper plate; (3) subjecting the rolled copper plate obtained in step (2) to a second rolling and a second heat treatment sequentially to obtain an oxygen-free copper backplate. The flatness of the oxygen-free copper backplate prepared therefrom is <1mm.

[0005] In summary, a new method for preparing oxygen-free copper backplates is needed to reduce the flatness of oxygen-free copper backplates. Summary of the Invention

[0006] To solve the above-mentioned technical problems, this application provides a method for preparing an oxygen-free copper backplate. In this application, after forging and stretching the oxygen-free copper ingot, it is first hot-rolled to uniform grain size, then cold-rolled and subjected to a second heat treatment to make the backplate hardened. Annealing is then introduced to remove internal stress while maintaining the hardness, resulting in an oxygen-free copper backplate with stable hardness, small fluctuations, and a flatness of less than 0.5 mm.

[0007] To achieve this objective, the following technical solution is adopted in this application: In a first aspect, this application provides a method for preparing an oxygen-free copper backplate, the method comprising: sequentially subjecting an oxygen-free copper ingot to forging and stretching treatment, a first heat treatment, hot rolling treatment, cold rolling treatment, a second heat treatment, and annealing treatment.

[0008] In this application, the oxygen-free copper ingot is first subjected to forging and stretching treatment to break the originally coarse grains into fine grains, thereby compacting and welding the porosity, pores and inclusions inside the oxygen-free copper ingot, resulting in a more compact microstructure and improved internal grain refinement. Then, hot rolling is performed to homogenize the grains, followed by cold rolling and a second heat treatment to harden the back plate. Finally, annealing is introduced to remove internal stress while maintaining the hardness, resulting in an oxygen-free copper back plate with stable hardness, small fluctuations, and a flatness of less than 0.5 mm.

[0009] In some embodiments, the forging process includes a preheating process and a forging process performed sequentially; wherein the forging process includes alternating drawing and upsetting.

[0010] In some embodiments, the forging and stretching process satisfies at least one of the following conditions: The preheating temperature is 800~900℃, for example, it can be 800℃, 820℃, 850℃, 880℃ or 900℃, but it is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0011] In some embodiments, the preheating time is 30 to 60 minutes, for example, 30 minutes, 35 minutes, 40 minutes, 50 minutes or 60 minutes, but is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0012] In some embodiments, the forging process is repeated 2 to 3 times, for example, 2 or 3 times, but is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0013] In some embodiments, the forging ratio of the forging process is 2 to 3, for example, it can be 2, 2.2, 2.5, 2.8 or 3, but it is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0014] In some embodiments, the temperature of the first heat treatment is 300~350°C, for example, it can be 300°C, 310°C, 320°C, 330°C, 340°C or 350°C, but is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0015] In some embodiments, the holding time of the first heat treatment is 90 to 120 minutes, for example, 90 minutes, 100 minutes, 110 minutes or 120 minutes, but it is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0016] In this application, the first heat treatment is performed by water cooling.

[0017] In some embodiments, the temperature of the hot rolling process is 600~700°C, for example, 600°C, 620°C, 650°C, 680°C or 700°C, but is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0018] In some embodiments of this application, the hot rolling temperature is limited to 600~700°C to ensure uniform grain size, so that the flatness of the final oxygen-free copper backplate is less than 0.5mm. If the hot rolling temperature is too low, it will be lower than the recrystallization temperature of the oxygen-free copper ingot, which will not provide a billet with uniform structure for cold rolling. If the hot rolling temperature is too high, it will result in coarse grains or even local melting and overheating, which will impair the performance of the final oxygen-free copper backplate.

[0019] In some embodiments, the hot rolling process includes at least three passes, such as three, four, five, six, or seven passes, but is not limited to the listed values; other unlisted values ​​within the above range are also applicable.

[0020] In some implementations, the deformation per hot rolling pass is ≤16%, for example, it can be 6%, 8%, 10%, 12%, 14% or 16%, but is not limited to the listed values, and other unlisted values ​​within the above range are also applicable.

[0021] In some embodiments of this application, the deformation of each hot rolling pass is limited to ≤16% to uniformly refine the grains and provide a billet with a uniform and good internal structure for subsequent cold rolling. If the deformation of each hot rolling pass is too large, it will result in excessive width expansion, which will damage the quality of the pattern, reduce the yield of the product, and increase the cost.

[0022] In some embodiments, the total deformation of the hot rolling process is 30-40%, for example, it can be 30%, 32%, 35%, 38% or 40%, but it is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0023] In this application, the hot rolling process is cooled by water cooling.

[0024] In some embodiments, the temperature of the cold rolling process is 20~25°C, for example, 20°C, 21°C, 22°C, 23°C, 24°C or 25°C, but is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0025] In some embodiments, the cold rolling process includes at least 5 passes, such as 5 passes, 6 passes, 7 passes, 8 passes or 9 passes, but is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0026] In some implementations, the deformation per cold rolling pass is ≤10%, for example, it can be 5%, 6%, 7%, 8%, 9% or 10%, but is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0027] In some embodiments of this application, the deformation of each cold rolling pass is limited to ≤10% to precisely control the shape and size of the plate and to achieve a hardening effect on the oxygen-free copper back plate. If the deformation of each cold rolling pass is too large, it will lead to an increase in mill pressure and a sharp increase in material work hardening, making it impossible for subsequent cold rolling passes to proceed smoothly.

[0028] In some embodiments, the total deformation of the cold rolling process is 30-40%, for example, it can be 30%, 32%, 35%, 38% or 40%, but it is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0029] In some embodiments, the temperature of the second heat treatment is 200~250°C, for example, it can be 200°C, 210°C, 220°C, 230°C, 240°C or 250°C, but is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0030] In some embodiments of this application, the temperature of the second heat treatment is limited to 200~250°C to remove some stress and retain some hardening effect. If the temperature of the second heat treatment is too low, the stress of the billet after cold rolling will still be too high, making subsequent machining difficult. If the temperature of the second heat treatment is too high, the hardening will be completely eliminated, and the back plate hardening effect will not be achieved.

[0031] In some embodiments, the holding time of the second heat treatment is 90 to 120 minutes, for example, 90 minutes, 95 minutes, 100 minutes, 110 minutes or 120 minutes, but is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0032] In this application, the second heat treatment is performed by water cooling.

[0033] In some embodiments, the annealing temperature is 150~200°C, for example, it can be 150°C, 160°C, 170°C, 180°C, 190°C or 200°C, but is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0034] In some embodiments, the holding time for the annealing treatment is 120 to 180 minutes, for example, 120 minutes, 140 minutes, 150 minutes, 160 minutes or 180 minutes, but is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0035] In this application, the annealing process is performed by air cooling.

[0036] In some embodiments, the preparation method further includes performing a first leveling treatment, rough machining, and a second leveling treatment sequentially between the second heat treatment and the annealing treatment.

[0037] In some embodiments, the flatness of the blank obtained after the first leveling treatment is <1mm, for example, it can be 0.5mm, 0.6mm, 0.7mm, 0.8mm or 0.9mm, but it is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0038] In some embodiments, the roughing process includes rough milling.

[0039] In some embodiments, the flatness of the blank obtained after the second leveling treatment is <1mm, for example, it can be 0.5mm, 0.6mm, 0.7mm, 0.8mm or 0.9mm, but it is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0040] In some embodiments, the preparation method further includes finishing after annealing.

[0041] In some embodiments, the flatness of the oxygen-free copper backplate obtained after finishing is <0.5mm, for example, it can be 0.1mm, 0.15mm, 0.2mm, 0.3mm or 0.4mm, but it is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0042] In some embodiments, the Vickers hardness of the oxygen-free copper backplate obtained after finishing is 100~120Hv, for example, it can be 100Hv, 105Hv, 110Hv, 115Hv or 120Hv, but it is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0043] In some embodiments, the Leeb hardness of the oxygen-free copper backplate obtained after finishing is 350~400HL, for example, it can be 350HL, 360HL, 370HL, 380HL, 390HL or 400HL, but it is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0044] In some embodiments, the preparation method includes the following steps: (1) The oxygen-free copper ingot is subjected to forging and squaring treatment in sequence to obtain a square billet. The forging treatment includes a preheating treatment at a temperature of 800~900℃ and a time of 30~60min and a forging treatment with a forging ratio of 2~3 in sequence. The forging treatment includes alternating drawing and upsetting. The forging treatment is repeated 2~3 times in the forging treatment. (2) The square billet is subjected to a first heat treatment at a temperature of 300~350℃ and a holding time of 90~120min, a hot rolling treatment at a temperature of 600~700℃ and a total deformation of 30~40%, a cold rolling treatment at a temperature of 20~25℃ and a total deformation of 30~40%, and a second heat treatment at a temperature of 200~250℃ and a holding time of 90~120min to obtain an oxygen-free copper back plate semi-finished product; (3) The oxygen-free copper backplate semi-finished product is subjected to first leveling treatment, rough processing, second leveling treatment, annealing treatment at a temperature of 150~200℃ and a holding time of 120~180min and fine processing in sequence to obtain an oxygen-free copper backplate with a flatness of <0.5mm.

[0045] Compared with the prior art, this application has at least the following beneficial effects: This application involves forging and stretching an oxygen-free copper ingot, followed by hot rolling to achieve uniform grain size, then cold rolling and a second low-temperature heat treatment to harden the backplate. Annealing is then introduced to remove internal stress while maintaining the hardness. Finally, the flatness of the backplate is measured using a CMM coordinate measuring machine. The results show that this application produces an oxygen-free copper backplate with a flatness of less than 0.3 mm. Detailed Implementation

[0046] To facilitate understanding of this application, the following embodiments are provided. Those skilled in the art should understand that these embodiments are merely illustrative and should not be construed as limiting the scope of this application.

[0047] Example 1 This embodiment provides a method for preparing an oxygen-free copper backplate, the method comprising the following steps: (1) The oxygen-free copper ingot is subjected to forging and squaring in sequence, and then water-cooled to obtain a square billet. The forging process includes a preheating process at a temperature of 850°C for 30 minutes and a forging process with a forging ratio of 2.5 in sequence. The forging process includes alternating drawing and upsetting. The forging process is repeated twice in the forging process. (2) The square billet is subjected to a first heat treatment at 320°C and a holding time of 100 min, a hot rolling treatment at 650°C and a total deformation of 35%, a cold rolling treatment at 22°C and a total deformation of 35%, and a second heat treatment at 220°C and a holding time of 100 min. After water cooling, an oxygen-free copper backplate semi-finished product is obtained. The hot rolling treatment consists of 5 passes, with a deformation of 7% per pass; the cold rolling treatment consists of 7 passes, with a deformation of 5% per pass. (3) The oxygen-free copper back plate semi-finished product is subjected to first leveling treatment, rough milling treatment, second leveling treatment, annealing treatment at 180℃ and holding time of 150min and fine machining in sequence to obtain an oxygen-free copper back plate with a flatness of 0.254mm. The flatness of the blank obtained after the first leveling treatment is 0.5 mm, and the flatness of the blank obtained after the second leveling treatment is 0.5 mm.

[0048] Example 2 This embodiment provides a method for preparing an oxygen-free copper backplate, the method comprising the following steps: (1) The oxygen-free copper ingot is subjected to forging and squaring in sequence, and then water-cooled to obtain a square billet. The forging process includes a preheating process at a temperature of 900℃ for 40 minutes and a forging process with a forging ratio of 3 in sequence. The forging process includes alternating drawing and upsetting. The forging process is repeated 3 times in the forging process. (2) The square billet is subjected to a first heat treatment at 300°C and a holding time of 120 min, a hot rolling treatment at 600°C and a total deformation of 30%, a cold rolling treatment at 25°C and a total deformation of 40%, and a second heat treatment at 200°C and a holding time of 120 min. After water cooling, an oxygen-free copper backplate semi-finished product is obtained. The hot rolling treatment consists of 4 passes, with a deformation of 7.5% per pass; the cold rolling treatment consists of 5 passes, with a deformation of 8% per pass. (3) The oxygen-free copper back plate semi-finished product is subjected to first leveling treatment, rough milling treatment, second leveling treatment, annealing treatment at 200℃ and holding time of 120min and finishing treatment in sequence to obtain an oxygen-free copper back plate with a flatness of 0.152mm. The flatness of the blank obtained after the first leveling treatment is 0.5 mm, and the flatness of the blank obtained after the second leveling treatment is 0.5 mm.

[0049] Example 3 This embodiment provides a method for preparing an oxygen-free copper backplate, the method comprising the following steps: (1) The oxygen-free copper ingot is subjected to forging and squaring in sequence, and then water-cooled to obtain a square billet. The forging process includes a preheating process at a temperature of 800℃ for 50 minutes and a forging process with a forging ratio of 2 in sequence. The forging process includes alternating drawing and upsetting. The forging process is repeated twice in the forging process. (2) The square billet is subjected to a first heat treatment at 350°C and a holding time of 90 min, a hot rolling treatment at 700°C and a total deformation of 40%, a cold rolling treatment at 20°C and a total deformation of 30%, and a second heat treatment at 250°C and a holding time of 90 min. After water cooling, an oxygen-free copper backplate semi-finished product is obtained. The hot rolling treatment consists of 5 passes, with a deformation of 8% per pass; the cold rolling treatment consists of 6 passes, with a deformation of 5% per pass. (3) The oxygen-free copper back plate semi-finished product is subjected to first leveling treatment, rough milling treatment, second leveling treatment, annealing treatment at 150℃ and holding time of 180min and fine machining in sequence to obtain an oxygen-free copper back plate with a flatness of 0.201mm. The flatness of the blank obtained after the first leveling treatment is 0.6 mm, and the flatness of the blank obtained after the second leveling treatment is 0.5 mm.

[0050] Example 4 This embodiment provides a method for preparing an oxygen-free copper backplate. The only difference from Embodiment 1 is that the hot rolling temperature is adjusted from 650°C to 500°C. All other aspects are the same as in Embodiment 1.

[0051] Example 5 This embodiment provides a method for preparing an oxygen-free copper backplate. The only difference from Embodiment 1 is that the hot rolling temperature is adjusted from 650°C to 800°C. All other aspects are the same as in Embodiment 1.

[0052] Example 6 This embodiment provides a method for preparing an oxygen-free copper backplate. The only difference from Embodiment 1 is that the deformation of each hot rolling process is adjusted from 7% to 17.5%, while keeping the total deformation of the hot rolling process unchanged. All other aspects are the same as in Embodiment 1.

[0053] Example 7 This embodiment provides a method for preparing an oxygen-free copper backplate. The only difference from Embodiment 1 is that the deformation of each cold rolling process is adjusted from 5% to 17.5%, while keeping the total deformation of the cold rolling process unchanged. All other aspects are the same as in Embodiment 1.

[0054] Example 8 This embodiment provides a method for preparing an oxygen-free copper backplate. The only difference from Embodiment 1 is that the temperature of the second heat treatment is adjusted from 220°C to 150°C. All other aspects are the same as in Embodiment 1.

[0055] Example 9 This embodiment provides a method for preparing an oxygen-free copper backplate. The only difference from Embodiment 1 is that the temperature of the second heat treatment is adjusted from 220°C to 300°C. All other aspects are the same as in Embodiment 1.

[0056] Comparative Example 1 This comparative example provides a method for preparing an oxygen-free copper backplate. The only difference between this method and Example 1 is that, except that the preparation method does not include hot rolling, all other aspects are the same as in Example 1.

[0057] Comparative Example 2 This comparative example provides a method for preparing an oxygen-free copper backplate. The only difference between this method and Example 1 is that, except that the preparation method does not include cold rolling, everything else is the same as in Example 1.

[0058] Comparative Example 3 This comparative example provides a method for preparing an oxygen-free copper backplate. The only difference from Example 1 is that step (2) is adjusted to sequentially perform a first heat treatment, a cold rolling treatment, a hot rolling treatment, and a second heat treatment. All other steps are the same as in Example 1.

[0059] Comparative Example 4 This comparative example provides a method for preparing an oxygen-free copper backplate. The only difference from Example 1 is that step (2) is adjusted to perform a first heat treatment, a pressing treatment, and a second heat treatment in sequence, and the length, width, and thickness of the blank obtained after pressing treatment are consistent with those of the blank obtained after cold rolling treatment. All other aspects are the same as in Example 1.

[0060] The Vickers hardness of the oxygen-free copper backplate was tested using a T402MA Vickers hardness tester, and the Leeb hardness was tested using a TIME5300 Leeb hardness tester. The flatness of the oxygen-free copper backplate was inspected using a CMM coordinate measuring machine. The flatness of the backplate surface is measured as the deviation of each point on the entire plate surface from an ideal plane, and the flatness of the weld surface is measured as the difference between the highest and lowest points on the weld surface. The test results are shown in Table 1.

[0061] Table 1 The test results show that: (1) As can be seen from Examples 1 to 3, in this application, the oxygen-free copper ingot is first subjected to forging and stretching treatment to break the original coarse grains into fine grains, and the looseness, pores and inclusions inside the oxygen-free copper ingot are compacted and welded, thereby making the microstructure more compact and improving the degree of internal grain refinement. Then, hot rolling treatment is performed to uniform grains, followed by cold rolling treatment and a second heat treatment to make the back plate in a hardened state. Finally, annealing is introduced to remove internal stress while maintaining the hardness, resulting in an oxygen-free copper back plate with stable hardness, small fluctuations and a flatness of less than 0.3 mm.

[0062] (2) As can be seen from Examples 1 and 4-5, the application limits the hot rolling temperature to 600~700℃ to uniform grains, so that the flatness of the final oxygen-free copper back plate is less than 0.5mm. If the hot rolling temperature is not reasonable, that is, if the hot rolling temperature is too high or too low, it cannot provide a billet with uniform internal structure for subsequent rolling, resulting in the hardness or flatness of the final oxygen-free copper back plate not meeting the requirements.

[0063] (3) As can be seen from Examples 1 and 6, this application limits the deformation of each hot rolling process to ≤16% in order to uniformly refine the grains and provide a billet with a uniform internal structure for subsequent cold rolling. When the hot rolling deformation is too large, the grains are fully recrystallized, and the billet after hot rolling is completely soft. The subsequent cold rolling hardening is insufficient, which ultimately leads to the oxygen-free copper back plate not meeting the hardening requirements.

[0064] (4) As can be seen from Examples 1 and 7, this application limits the deformation of each cold rolling process to ≤10% in order to accurately control the shape and size of the plate and make the oxygen-free copper back plate achieve a hardening effect. When the cold rolling deformation is too large, the back plate hardens significantly, and the oxygen-free copper back plate obtained after subsequent stress relief annealing cannot meet the flatness requirements.

[0065] (5) As can be seen from Examples 1 and 8-9, the application limits the temperature of the second heat treatment to 200~250℃ in order to remove some stress and retain some hardening effect. When the temperature range of the second heat treatment is unreasonable, if the temperature is too low, the stress relief annealing cannot effectively eliminate the internal stress, and the final oxygen-free copper back plate is too flat. If the temperature is too high, the back plate is already in a soft state, and the hardness is directly reduced, which cannot meet the hardening requirements.

[0066] (6) As can be seen from Example 1 and Comparative Examples 1-4, compared with hot rolling and cold rolling in sequence, hot rolling or cold rolling alone cannot obtain oxygen-free copper backplates that meet the requirements of hardness and flatness. Furthermore, hot rolling after cold rolling will cause the hardened backplate to return to a soft state. Moreover, pressing is a one-time deformation, resulting in large deformation on the surface of the backplate and small deformation inside, ultimately leading to an excessive difference in hardness between the surface and the interior of the backplate.

[0067] In summary, this application involves forging and stretching an oxygen-free copper ingot, followed by hot rolling to achieve uniform grain size, then cold rolling and a second low-temperature heat treatment to harden the backplate. Annealing is then introduced to remove internal stress while maintaining the hardness. Finally, the flatness of the backplate is measured using a CMM coordinate measuring machine. The results show that this application produces an oxygen-free copper backplate with a flatness of less than 0.3 mm.

[0068] The applicant declares that the above description is only a specific implementation of this application, but the protection scope of this application is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application fall within the protection and disclosure scope of this application.

Claims

1. A method for preparing an oxygen-free copper backplate, characterized in that, The preparation method includes: sequentially subjecting oxygen-free copper ingots to forging and stretching treatment, first heat treatment, hot rolling treatment, cold rolling treatment, second heat treatment, and annealing treatment.

2. The preparation method according to claim 1, characterized in that, The forging process includes a preheating process and a forging process performed sequentially; wherein, the forging process includes alternating drawing and upsetting. The forging and stretching process shall satisfy at least one of the following conditions: The temperature of the preheating treatment is 800~900℃; And / or, the preheating treatment time is 30~60 min; And / or, the forging process in the forging and stretching process is repeated 2 to 3 times; And / or, the forging ratio of the forging process is 2 to 3.

3. The preparation method according to claim 1 or 2, characterized in that, The temperature of the first heat treatment is 300~350℃; And / or, the holding time for the first heat treatment is 90~120 min.

4. The preparation method according to any one of claims 1-3, characterized in that, The hot rolling temperature is 600~700℃; And / or, the hot rolling process includes at least 3 passes; And / or, the deformation per hot rolling pass is ≤16%; And / or, the total deformation of the hot rolling process is 30-40%.

5. The preparation method according to any one of claims 1-4, characterized in that, The temperature of the cold rolling process is 20~25℃; And / or, the cold rolling process includes at least 5 passes; And / or, the deformation per cold rolling pass is ≤10%; And / or, the total deformation of the cold rolling process is 30-40%.

6. The preparation method according to any one of claims 1-5, characterized in that, The temperature of the second heat treatment is 200~250℃; And / or, the holding time for the second heat treatment is 90~120 min.

7. The preparation method according to any one of claims 1-6, characterized in that, The annealing temperature is 150~200℃; And / or, the holding time for the annealing treatment is 120~180 min.

8. The preparation method according to any one of claims 1-7, characterized in that, The preparation method further includes performing a first leveling treatment, rough machining, and a second leveling treatment sequentially between the second heat treatment and the annealing treatment. Wherein, the flatness of the blank obtained after the first leveling treatment is <1mm; and / or, the roughing includes rough milling; and / or, the flatness of the blank obtained after the second leveling treatment is <1mm.

9. The preparation method according to any one of claims 1-8, characterized in that, The preparation method further includes finishing after annealing; Wherein, the flatness of the oxygen-free copper back plate obtained after finishing is <0.5mm; and / or, the Vickers hardness of the oxygen-free copper back plate obtained after finishing is 100~120Hv; and / or, the Leeb hardness of the oxygen-free copper back plate obtained after finishing is 350~400HL.

10. The preparation method according to any one of claims 1-9, characterized in that, The preparation method includes the following steps: (1) The oxygen-free copper ingot is subjected to forging and squaring treatment in sequence to obtain a square billet. The forging treatment includes a preheating treatment at a temperature of 800~900℃ and a time of 30~60min and a forging treatment with a forging ratio of 2~3 in sequence. The forging treatment includes alternating drawing and upsetting. The forging treatment is repeated 2~3 times in the forging treatment. (2) The square billet is subjected to a first heat treatment at a temperature of 300~350℃ and a holding time of 90~120min, a hot rolling treatment at a temperature of 600~700℃ and a total deformation of 30~40%, a cold rolling treatment at a temperature of 20~25℃ and a total deformation of 30~40%, and a second heat treatment at a temperature of 200~250℃ and a holding time of 90~120min to obtain an oxygen-free copper back plate semi-finished product; (3) The oxygen-free copper backplate semi-finished product is subjected to first leveling treatment, rough processing, second leveling treatment, annealing treatment at a temperature of 150~200℃ and a holding time of 120~180min and fine processing in sequence to obtain an oxygen-free copper backplate with a flatness of <0.5mm.

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