Pure copper plate
Patent Information
- Authority / Receiving Office
- TW · TW
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2021-03-08
- Publication Date
- 2021-10-16
Smart Images
Figure TWG2TA000830284_001 
Figure TWG2TA000830284_002
Abstract
Description
[Technical Field]
[0001] This invention relates to a pure copper plate suitable for electrical and electronic components such as heat sinks or thick copper circuits, and particularly to a pure copper plate for suppressing the coarsening of crystal grains during heating. This invention claims priority based on Japanese Patent Application No. 2020-038770, filed on March 6, 2020, the contents of which are incorporated herein by reference. [Previous Technology]
[0002] In the past, copper or copper alloys with high conductivity were used in electrical and electronic components such as heat sinks or thick copper circuits. Recently, with the increase in the current of electronic and electrical machines, due to the decrease in current density and the heat diffusion caused by Joule heating, there has been a trend of larger and thicker electrical and electronic components used in such electronic and electrical machines.
[0003] Here, in semiconductor devices, insulating circuit boards, such as those formed by bonding copper material to a ceramic substrate, are used to constitute the aforementioned heat sinks or thick copper circuits. When bonding the ceramic substrate and the copper plate, the bonding temperature is often 800°C or higher. During bonding, there is a concern that the crystal grains of the copper material forming the heat sink or thick copper circuit may become coarse. In particular, the crystal grains tend to coarsen easily in copper materials made of pure copper, which has excellent conductivity and heat dissipation.
[0004] In the heat sink or thick copper circuit after bonding, when the crystal grains become coarse, there are concerns about the appearance due to the coarsening of the crystal grains. For example, Patent Document 1 proposes a pure copper plate that inhibits the growth of crystal grains. Patent Document 1 describes a method where, by containing 0.0006 to 0.0015 wt% S, even after heat treatment at a recrystallization temperature or higher, the crystal grains can be adjusted to a certain size. [Prior Art Documents] [Patent Documents]
[0005] [Patent Document 1] Japanese Patent Application Publication No. 06-002058 [Summary of the Invention]
[0006] [The problem the invention aims to solve]
[0007] However, when bonding a ceramic substrate and a copper plate, the ceramic substrate and the copper plate are subjected to high-temperature heat treatment under relatively high pressure (e.g., 0.1 MPa or higher) in the lamination direction. At this time, in the pure copper plate, the crystal grains tend to grow unevenly. Due to the coarsening or uneven growth of the crystal grains, poor bonding or poor appearance occurs, leading to problems in the inspection process. To solve this problem, there is a need for the pure copper plate to have minimal change in crystal grain size and uniform size after the pressure heat treatment for bonding with dissimilar materials.
[0008] Here, in Patent Document 1, although the coarsening of crystal grains is suppressed by specifying the content of sulfur, simply specifying the content is insufficient to achieve a sufficient effect in suppressing crystal grain coarsening after pressurized heat treatment. Furthermore, after pressurized heat treatment, localized crystal grain coarsening occurs, resulting in an uneven crystal structure. Moreover, increasing the content of sulfur to suppress crystal grain coarsening significantly reduces hot workability, leading to a substantial decrease in the manufacturing yield of pure copper plates.
[0009] This invention is made in view of the above-mentioned circumstances, and aims to provide a pure copper plate with excellent hot workability, which, after pressure heat treatment, can suppress the coarsening and inhomogenization of crystal grains. [Means for solving the problem]
[0010] To solve this problem, the inventors, through professional review, made the following discovery. In pure copper plates, trace amounts of impurity elements exist at the grain boundaries, exhibiting a grain growth inhibition effect that suppresses grain coarsening. Here, it was found that by utilizing elements with this grain growth inhibition effect (hereinafter referred to as grain growth inhibition elements), grain coarsening or inhomogeneity can also be suppressed after pressure heat treatment. Furthermore, it was discovered that limiting the content of specific elements is effective in fully utilizing the effect of these grain growth inhibition elements. Moreover, it was found that suppressing the driving force of grain growth during pressure heat treatment is effective in inhibiting grain size increases and maintaining strain energy accumulated in the material at a low level.
[0011] The present invention is based on the above-mentioned discovery. The pure copper plate of the present invention has a Cu content of 99.96 mass% or more, a P content of 0.01 massppm or more and 3 massppm or less, a total Ag and Fe content of 3 massppm or more, and the residue is composed of unavoidable impurities. The average crystal grain size of the rolled surface is 10μm or more. In addition to the measurement of a measurement area of 1 mm2 or more by means of the EBSD method with measurement intervals of 5μm steps, the measurement points with a CI value of 0.1 or less as analyzed by the data analysis software OIM are characterized by a KAM (Kernel Average Misorientation) value of 1.5 or less when the boundary with an orientation difference of 5° or more between adjacent pixels is regarded as the crystal grain boundary.
[0012] When producing a pure copper plate according to this configuration, the Cu content is 99.96 mass% or more, the P content is 0.01 massppm or more and 3.00 massppm or less, and the combined Ag and Fe content is 3.0 massppm or more. Since the residual portion inevitably contains impurities, the coarsening of crystal grains can be suppressed by the solid dissolution of Ag and Fe in the copper matrix. Furthermore, since the P content is 3.00 massppm or less, the decrease in hot workability can be suppressed.
[0013] Furthermore, since the average crystal grain size of the rolled surface is 10 μm or more, the grain size can be made larger in the state before pressure heat treatment, the driving force for recrystallization during pressure heating is reduced, and particle growth is suppressed. Then, since the KAM value is 1.50 or less, the translocation density is low, and the accumulated strain energy is less, which can reduce the driving force for recrystallization during pressure heat treatment and suppress particle growth.
[0014] Here, in the pure copper plate of the present invention, the content of sulfur (S) is preferably in the range of 2.0 massppm to 20.0 massppm. In this case, as a grain growth inhibitor, by containing 2.0 massppm or more of S, the coarsening or unevenness of the grains can be reliably suppressed after heat treatment. Furthermore, by limiting the content of S to 20.0 massppm or less, hot workability can be sufficiently ensured.
[0015] Furthermore, in the pure copper plate of the present invention, the total content of Mg, Sr, Ba, Ti, Zr, Hf, and Y is preferably below 10.0 massppm. As unavoidable impurities, the elements Mg, Sr, Ba, Ti, Zr, Hf, and Y are suspected of segregating at the grain boundaries and forming compounds with grain growth inhibitors (S, Se, Te, etc.) that suppress grain growth, thus potentially hindering the effect of these grain growth inhibitors. Therefore, by limiting the total content of Mg, Sr, Ba, Ti, Zr, Hf, and Y to below 10.0 massppm, the grain growth inhibition effect of the grain growth inhibitors can be fully utilized, and after heat treatment, grain coarsening or inhomogenization can be effectively suppressed.
[0016] Furthermore, in the pure copper plate of the present invention, after pressure heat treatment under the conditions of applying a pressure of 0.6 MPa, a heating temperature of 850°C, and a holding time of 90 minutes, the ratio of the maximum crystal grain size dmax to the average crystal grain size dave within a 50 mm × 50 mm area is preferably 20.0 or less. In this case, pressure heat treatment under the above conditions can effectively suppress the coarsening and unevenness of the crystal grains, and further suppress the occurrence of appearance defects.
[0017] Furthermore, in the pure copper plate of the present invention, a Vickers hardness of 150 HV or less is preferred. At this Vickers hardness of 150 HV or less, it is sufficiently soft, ensuring the properties of a pure copper plate, thus making it particularly suitable as a material for components in electrical and electronic parts used in high-current applications. [Effects of the Invention]
[0018] According to the present invention, a pure copper plate with excellent hot workability is provided, and after pressure heat treatment, the coarsening and inhomogenization of crystal grains can be suppressed.
Implementation Method
[0019] Hereinafter, a pure copper plate according to one embodiment of the present invention will be described. The pure copper plate of this embodiment is used as a material for electrical and electronic components such as heat sinks or thick copper circuits. When forming the aforementioned electrical and electronic components, it can be bonded to a ceramic substrate for example.
[0020] The pure copper plate of this embodiment has a Cu content of 99.96 mass% or more, a P content of 0.01 massppm or more and 3.00 massppm or less, a combined Ag and Fe content of 3.0 massppm or more, and the residue is composed of unavoidable impurities. Hereinafter, "mass%" and "massppm" will be referred to as "%" and "ppm" respectively.
[0021] However, in the pure copper plate of this embodiment, the content of S is preferably in the range of 2.0 massppm to 20.0 massppm. Furthermore, in the pure copper plate of this embodiment, the total content of one or more elements selected from Mg, Sr, Ba, Ti, Zr, Hf, and Y (group A elements) is preferably 10.0 massppm or less.
[0022] Furthermore, in the pure copper plate of this embodiment, the average grain size of the crystal grains on the rolled surface is 10 μm or more. The average grain size of the crystal grains on the rolled surface is determined, for example, by cutting five longitudinal and transverse lines of a specific length on the rolled surface according to the cutting method of JIS H 0501, counting the number of completely cut crystal grains, and obtaining the average value of the cutting length. Then, in the pure copper plate of this embodiment, except for the measurement points with a measurement area of 1 mm2 or more measured at measurement intervals of 5 μm steps by the EBSD method, and the CI value analyzed by the data analysis software OIM being 0.1 or less, the KAM (Kernel Average Misorientation) value when the boundary between adjacent pixels with an orientation difference of 5° or more is considered as the grain boundary is 1.50 or less.
[0023] However, in the pure copper plate of this embodiment, it is preferable that the ratio of the maximum crystal grain size dmax to the average crystal grain size dave within a 50mm × 50mm area after pressure heat treatment under conditions of a pressure of 0.6MPa, a heating temperature of 850°C, and a holding time of 90 minutes is dmax / dave or less. The maximum crystal grain size dmax is obtained, for example, by selecting any area of 50mm × 50mm, within which the average value of the major axis of the crystal grain and the minor axis cut off through the grain boundary perpendicular to the drawing line can be obtained. Furthermore, in the pure copper plate of this embodiment, it is preferable that the Vickers hardness is 150HV or less.
[0024] Hereinafter, the reasons for specifying the composition, KAM value and various properties as described above in the pure copper plate of this embodiment are explained as follows.
[0025] (Cu purity: 99.96 mass% or higher) In electrical and electronic components used for high-current applications, excellent conductivity and heat dissipation are required to suppress heat generation during energization. Therefore, pure copper with particularly excellent conductivity and heat dissipation is preferred. Furthermore, when bonding to ceramic substrates, low deformation resistance is preferable to mitigate thermal strain generated under cyclic loading. In this embodiment, the purity of Cu in the pure copper plate is specified to be 99.96 mass% or higher. However, a purity of 99.965 mass% or higher is preferred, and more preferably 99.97 mass% or higher. While no specific upper limit is imposed on the purity of Cu, exceeding 99.999 mass% requires special refining processes, significantly increasing manufacturing costs; therefore, 99.999 mass% or lower is preferred.
[0026] (P: 0.01 massppm to 3.00 massppm) P is widely used to neutralize oxygen in copper. However, when P content exceeds a certain level, it not only inhibits oxygen but also hinders the function of grain growth inhibitors present at grain boundaries. Therefore, when heated to high temperatures, the grain growth inhibitors cannot function sufficiently, raising concerns about grain coarsening and inhomogeneity. Furthermore, it can reduce hot workability. Therefore, in this invention, the P content is limited to 0.01 massppm to 3.00 massppm. However, the upper limit of the P content is preferably 2.50 massppm or less, and more preferably 2.00 massppm or less. On the other hand, the lower limit of the P content is preferably 0.02 massppm or more, and more preferably 0.03 massppm or more.
[0027] (Total content of Ag and Fe: 3.0 massppm or more) Ag and Fe are elements that, through solid solution into the copper matrix, have the effect of suppressing grain coarsening. Therefore, in this embodiment, when the content of Ag and Fe is 3.0 massppm or more, the grain coarsening suppression effect of Ag and Fe can be fully utilized, and grain coarsening can be reliably suppressed even after pressure heat treatment. However, the lower limit of the total content of Ag and Fe is preferably 5.0 massppm or more, more preferably 7.0 massppm or more, and even more preferably 10.0 massppm or more. On the other hand, although the upper limit of the total content of Ag and Fe is not specifically limited, if the addition is necessary, it will lead to an increase in manufacturing costs or a decrease in conductivity. It is preferable to be less than 100.0 massppm, more preferably less than 50.0 massppm, and even more preferably less than 20.0 massppm.
[0028] (S content: 2.0 massppm to 20.0 massppm) S is an element that, by inhibiting grain boundary movement, has the effect of suppressing grain coarsening, which can reduce hot workability. Therefore, in this embodiment, when the S content is 2.0 massppm or more, the grain coarsening suppression effect of S can be fully utilized, and grain coarsening can be reliably suppressed even after pressure heat treatment. On the other hand, when the S content is limited to 20.0 massppm or less, hot workability can be ensured. However, the lower limit of the S content is preferably 2.5 massppm or more, and more preferably 3.0 massppm or more. Furthermore, the upper limit of the S content is preferably 17.5 massppm or less, and more preferably 15.0 massppm or less.
[0029] (Total content of Mg, Sr, Ba, Ti, Zr, Hf, Y (Group A elements): 10.0 massppm or less) As unavoidable impurities, elements selected from Mg, Sr, Ba, Ti, Zr, Hf, and Y (Group A elements) segregate at the grain boundaries and form compounds with grain-coarsening inhibitors (S, Se, Te, etc.), which inhibit grain coarsening. This raises concerns that these inhibitors may hinder the effectiveness of the grain-coarsening inhibitors. Therefore, to reliably suppress grain coarsening after heat treatment, the total content of Mg, Sr, Ba, Ti, Zr, Hf, and Y (Group A elements) is preferably 10.0 massppm or less. However, the total content of Mg, Sr, Ba, Ti, Zr, Hf, and Y (Group A elements) is preferably 7.5 massppm or less, and more preferably 5.0 massppm or less.
[0030] (Other Elements) However, Al, Cr, Sn, Be, Cd, Mg, Ni, and Pb (Group M elements) have the effect of solid solution or grain boundary segregation in the copper matrix, and further inhibit grain growth through the formation of oxides. Therefore, in order to reliably suppress the coarsening of crystal grains after heat treatment, it is preferable that the total content of Al, Cr, Sn, Be, Cd, Mg, Ni, and Pb (Group M elements) exceeds 2.0 massppm. However, when Al, Cr, Sn, Be, Cd, Mg, Ni, and Pb (Group M elements) are intentionally included, it is preferable that the lower limit of the total content of Al, Cr, Sn, Be, Cd, Mg, Ni, and Pb (Group M elements) is 2.1 massppm or more, more preferably 2.3 massppm or more, even more preferably 2.5 massppm or more, and most preferably 3.0 massppm or more. On the other hand, there are concerns that the conductivity may decrease when Al, Cr, Sn, Be, Cd, Mg, Ni, and Pb (M element group) are present. Therefore, it is preferable that the total content of Al, Cr, Sn, Be, Cd, Mg, Ni, and Pb (M element group) is less than 100.0 massppm, more preferably less than 50.0 massppm, even more preferably less than 20.0 massppm, and even more preferably less than 10.0 massppm.
[0031] (Other unavoidable impurities) Other unavoidable impurities besides the elements mentioned above include B, Bi, Ca, Sc, rare earth elements, V, Nb, Ta, Mo, W, Mn, Re, Ru, Os, Co, Rh, Ir, Pd, Pt, Au, Zn, Hg, Ga, In, Ge, As, Sb, Tl, N, C, Si, Li, H, and O. These unavoidable impurities may cause a decrease in conductivity, so the fewer they are, the better.
[0032] (Average grain size of the rolled surface: 10 μm or more) In the pure copper plate of this embodiment, when the average grain size of the rolled surface is fine, recrystallization is easily carried out when the pure copper plate is heated, which may promote grain growth and cause unevenness in the microstructure. Therefore, in order to further suppress the coarsening of the grains during pressure heat treatment, it is preferable that the average grain size of the rolled surface is 10 μm or more. However, it is preferable that the average grain size of the rolled surface is 15 μm or more, and more preferably 20 μm or more.
[0033] (KAM value: 1.50 or less) The KAM (Kernel Average Misorientation) value measured by EBSD is calculated by averaging the orientation difference between a pixel and the surrounding pixels. Since the shape of a pixel is a regular hexagon, the average of the orientation differences of the six adjacent pixels when the number of proximity is 1 (1st) is used as the KAM value for calculation. By using this KAM value, the local orientation difference can be visualized, revealing the distribution of strain. Areas with a high KAM value are areas with high translocation density introduced during processing, which facilitates recrystallization and may promote grain growth and lead to concerns about unevenness in the microstructure. Therefore, by controlling the KAM value to 1.50 or less, grain coarsening or unevenness can be suppressed. However, a KAM value of 1.40 or less is preferred, and more preferably 1.30 or less. However, in this embodiment, the KAM value is obtained with a proximity of 1. Furthermore, in this embodiment, the average KAM value is obtained from the areas of clearly defined crystalline patterns with well-developed processing structures, where the CI value is 0.1 or less and the clarity of crystallinity, which cannot be obtained to represent the resolution point, are excluded. It is preferable to calculate the average KAM value, for example, using KAM values measured at three points equidistant from the center of the roll surface.
[0034] (The ratio of the maximum crystal grain size dmax to the average crystal grain size dave within a 50mm × 50mm area after pressure heat treatment, dmax / dave: 20.0 or less) In the pure copper plate of this embodiment, when the ratio of the maximum crystal grain size dmax to the average crystal grain size dave within a 50mm × 50mm area of the rolled surface after pressure heat treatment, under the conditions of a pressure of 0.6MPa, a heating temperature of 850°C, and a holding time of 90 minutes, is dmax / dave, the non-uniformity of the crystal grains can be effectively suppressed even after pressure heat treatment, making it particularly suitable as a material for bonding thick copper circuits or heat sinks to ceramic substrates. However, it is more preferable that the ratio of the maximum crystal grain size dmax to the average crystal grain size dave within a 50mm × 50mm area after pressure heat treatment is dmax / dave or less.
[0035] (Vickers hardness: 150 HV or less) In the pure copper sheet of this embodiment, by setting the Vickers hardness to 150 HV or less, the properties of pure copper sheet are ensured, making it particularly suitable as a material for components of electrical and electronic parts used in high-current applications. Furthermore, it is sufficiently flexible to be bonded to other components such as ceramic substrates under thermal cycles, thus relieving thermal strain caused by deformation of the pure copper sheet. However, a Vickers hardness of 140 HV or less is preferred for the pure copper sheet, more preferably 130 HV or less, and most preferably 110 HV or less. Although the lower limit of the Vickers hardness of the pure copper sheet is not specifically limited, if the hardness is too low, it is easy to deform during manufacturing, making processing more difficult; therefore, 30 HV or more is preferred, more preferably 45 HV or more, and most preferably 60 HV or more.
[0036] Next, the manufacturing method of the pure copper plate of this embodiment will be described with reference to the flowchart shown in FIG1.
[0037] (Melting and Casting Process S01) First, copper raw materials are melted to produce a copper molten metal. However, it is preferable to use 4NCu with a purity of 99.99 mass% or higher, or 5NCu with a purity of 99.999 mass% or higher, as the copper raw material. However, when adding sulfur, sulfur monomer or Cu-S master alloy can be used. However, when manufacturing the Cu-S master alloy, it is also preferable to use 4NCu with a purity of 99.99 mass% or higher, or 5NCu with a purity of 99.999 mass% or higher. Furthermore, in the melting process, to reduce the hydrogen concentration, melting is performed in an inactive gas environment with low H2O vapor pressure (e.g., Ar gas), and the holding time during dissolution is kept to a minimum. Then, the copper molten metal with adjusted composition is poured into a mold to produce a cast block. However, considering mass production, continuous casting or semi-continuous casting is preferable.
[0038] (Heat Treatment Process S02) The obtained casting block is cut off, and the surface is ground to remove the dimensional marks. Then, heat treatment is performed for homogenization and melting. While the heat treatment conditions are not specifically limited, to suppress the formation of precipitates, the heat treatment temperature is preferably between 500°C and 900°C, and the holding time at the heat treatment temperature is preferably between 0.1 hours and 100 hours, preferably in a non-oxidizing or reducing environment. Furthermore, while the cooling method is not specifically limited, a cooling rate of 200°C / min or higher, such as water quenching, is preferred. Also, to achieve a homogenized microstructure, hot working may be performed after heat treatment. While the processing method is not specifically limited, when the final shape is a plate or strip, roll forming is used. Other methods include forging, pressure rolling, or grooved roll forming. While the temperature during hot working is not specifically limited, it is preferably between 500°C and 900°C. Furthermore, a total processing rate of 50% or more is preferred for hot processing, 60% or more is even better, and 70% or more is even better.
[0039] (Intermediate Roll Forming Process S03) Next, the copper material after heat treatment process S02 is subjected to intermediate rolling to process it into a specific shape. While the temperature conditions for this intermediate rolling process S03 are not particularly limited, it is preferable to perform it within a range of -200°C to 200°C. Furthermore, the processing rate of this intermediate rolling process S03 is appropriately selected to approximate the final shape, but to improve productivity, a rate of 30% or higher is preferred.
[0040] (Recrystallization Heat Treatment Process S04) Next, the copper material after the intermediate rolling process S03 is subjected to a heat treatment for recrystallization. Here, it is preferable that the average grain size of the recrystallized grains on the rolling surface is 10 μm or more. If the recrystallized grains are fine, there is a concern that the grains may grow during subsequent pressure heat treatment, leading to uneven microstructure. Although the heat treatment conditions for the recrystallization heat treatment process S04 are not specifically limited, it is preferable to maintain the heat treatment temperature in the range of 200°C to 900°C for 1 second to 10 hours. For example, in short-time heat treatment, conditions such as holding at 850°C for 5 seconds or more, or in long-time heat treatment such as holding at 400°C for 8 hours can be cited. Furthermore, in order to homogenize the recrystallized microstructure, the intermediate rolling process S03 and the recrystallization heat treatment process S04 may be repeated more than twice.
[0041] (Temperature Processing Process S05) Next, to adjust the material strength, the copper material after the recrystallization heat treatment process S04 may be subjected to tempering. However, if it is not necessary to improve the material strength, tempering may not be performed. Although the tempering rate is not specifically limited, it is preferable to perform it within the range of more than 0% to less than 50% in order to adjust the material strength. Furthermore, it is preferable to make the material strength even lower and the KAM value less than 1.50, and more than 0% to less than 45%. Also, if necessary, heat treatment may be performed after tempering to remove residual strain. Although the final thickness is not specifically limited, a thickness within the range of 0.5 mm to 5 mm is appropriate.
[0042] Through the above processes, a pure copper plate of this embodiment is manufactured.
[0043] In the pure copper plate according to the above-described embodiment, the Cu content is 99.96 mass% or more, the P content is 0.01 massppm or more and 3.00 massppm or less, and the total Ag and Fe content is 3.0 massppm or more. Since the residue inevitably contains impurities, the coarsening of crystal grains can be suppressed by Ag and Fe dissolving in the copper matrix. Furthermore, by limiting the P content to 3.00 massppm or less, hot workability can be ensured.
[0044] Furthermore, since the average crystal grain size of the rolled surface is 10 μm or more, the grain size can be made larger in the state before pressure heat treatment, and the driving force for recrystallization during pressure heat treatment is reduced, thus inhibiting particle growth. Then, since the KAM value is 1.50 or less, the translocation density is low, and the accumulated strain energy is small, which can reduce the driving force for recrystallization during pressure heat treatment and inhibit particle growth.
[0045] Furthermore, in this embodiment, when the content of S is in the range of 2.0 massppm to 20.0 massppm, S, one of the grain growth inhibitory elements, will segregate at the grain boundaries, which can effectively suppress the coarsening or inhomogenization of the grains after pressure heat treatment. In addition, hot workability can be ensured.
[0046] Furthermore, in this embodiment, when the total content of Mg, Sr, Ba, Ti, Zr, Hf, and Y (group A elements) is 10.0 massppm or less, the reaction between these group A elements and grain growth inhibiting elements such as S, Se, and Te can be suppressed to form compounds, thus fully leveraging the role of grain growth inhibiting elements. Therefore, the coarsening and inhomogenization of crystal grains after pressure heat treatment can be effectively suppressed.
[0047] Furthermore, in this embodiment, when the ratio of the maximum crystal grain size dmax to the average crystal grain size dave after the aforementioned pressure heat treatment is dmax / dave less than 20.0, the unevenness of the crystal grains can be effectively suppressed after the pressure heat treatment, and the occurrence of poor appearance can be suppressed.
[0048] Furthermore, in this embodiment, when the Vickers hardness is below 150 HV, it is sufficiently soft, ensuring the characteristics of a pure copper plate, and is therefore particularly suitable as a material for components of electrical and electronic parts used in high-current applications.
[0049] However, in this embodiment, when Al, Cr, Sn, Be, Cd, Mg, Ni, Pb (M element group) contain more than 2.0 massppm, the solid solution or grain boundary segregation in the element parent phase of the M element copper group, and the formation of oxides, can more effectively suppress grain growth after pressure heat treatment.
[0050] Although the pure copper plate of the present invention has been described above, the present invention is not limited thereto, and appropriate modifications can be made without departing from the technical concept of the invention. For example, in the above embodiment, one example of a method for manufacturing a pure copper plate has been described, but the method for manufacturing a pure copper plate is not limited to that described in the embodiment, and an existing manufacturing method can be appropriately selected for manufacturing. [Example]
[0051] Hereinafter, the results of the confirming experiments conducted to verify the effects of the present invention will be described. A copper raw material with a purity of 99.999 mass% or higher was prepared, along with a Cu-1 mass% master alloy of various elements made using the aforementioned copper raw material and various elements with a purity of 99 mass% or higher. The aforementioned copper raw material was placed in a high-purity graphite crucible and subjected to high-frequency melting in an ambient furnace under an Ar gas atmosphere. The Cu-1 mass% master alloy of the aforementioned various elements was added to the resulting molten copper to prepare a specific composition. The resulting molten copper was poured into a mold to produce a mold block. However, the size of the mold block was approximately 50 mm thick × 60 mm wide × 150-200 mm long.
[0052] The resulting mold block was heated for 1 hour in an Ar gas environment at the temperature conditions described in Tables 1 and 2, and then hot-rolled to a thickness of 25 mm. Simultaneously, the copper material after hot rolling was cut, and surface grinding was performed to remove the oxide film on the surface. At this time, considering the rolling ratios of subsequent hot rolling, intermediate rolling, and tempering rolling, the thickness of the copper material supplied for intermediate rolling was adjusted to achieve the final thickness shown in Tables 1 and 2.
[0053] For the copper material with the thickness adjusted as described above, intermediate rolling is performed under the conditions described in Tables 1 and 2, followed by water cooling. Next, the copper material after intermediate rolling is subjected to recrystallization heat treatment under the conditions described in Tables 1 and 2. Then, the copper material after recrystallization heat treatment is subjected to temper rolling under the conditions described in Tables 1 and 2, and a strip with a width of 60 mm is manufactured for characteristic evaluation with the thickness shown in Tables 1 and 2.
[0054] Then, an evaluation is carried out for the following items.
[0055] (Composition Analysis) Samples were taken from the obtained casting block for analysis. S was determined using infrared absorption spectrometry, and other elements were determined using glow discharge mass spectrometry (GD-MS). However, the measurements were performed at two locations: the center of the sample and the end in the width direction. The sample containing the higher concentration was taken as the total content of the sample. The results are shown in Tables 1 and 2.
[0056] (Processability Assessment) As a processability assessment, the presence or absence of edge cracks in the aforementioned hot rolling and intermediate rolling processes is observed. Let "A" represent edge cracks that are visually absent or barely detectable; "B" represent edge cracks with a length less than 1 mm; and "C" represent edge cracks with a length of 1 mm or more. However, the length of the edge crack is the length of the edge crack extending from the end of the rolled material in the width direction towards the center of the width direction.
[0057] (Vickers Hardness) The Vickers hardness was determined according to the micro Vickers hardness test method specified in JIS Z 2244, with a test load of 0.98 N. However, the test location was the roll-pressed surface of the test piece used for characteristic evaluation. The evaluation results are shown in Tables 3 and 4.
[0058] (Conductivity) A test piece with a width of 10 mm and a length of 60 mm was taken from the strip used for characteristic evaluation, and the resistance was obtained using the 4-terminal method. Furthermore, the dimensions of the test piece were measured using a micrometer, and the volume of the test piece was calculated. Then, the conductivity was calculated from the measured resistance value and volume. The evaluation results are shown in Tables 3 and 4. However, the test piece was taken with its length direction parallel to the rolling direction of the strip used for characteristic evaluation.
[0059] (Average crystal grain size before pressure heat treatment) A 20mm × 20mm sample was cut from the obtained characteristic evaluation strip and the average crystal grain size was measured using a SEM-EBSD (Electron Backscatter Diffraction Patterns) measuring device (FEI Quanta FEG 450, EDAX / TSL (now AMETEK) OIM Data Collection). The roller-pressed surface was mechanically ground using water-resistant abrasive paper and diamond abrasive grains, followed by final grinding using a colloidal silica solution. Subsequently, using a scanning electron microscope, electron beams were irradiated at each measurement point (pixel) within the measurement range on the sample surface. The orientation resolution formed by the backscattered electron beams determined that the orientation difference between adjacent measurement points was greater than 15°, and the measurement points were designated as large grain boundaries, while those less than 15° were designated as small grain boundaries. Using large-angle grain boundaries, a grain boundary map was created. According to the cutting method of JIS H 0501, five lines of specific length were drawn for each grain boundary map, both longitudinal and transverse. The number of grains completely cut out was counted, and the average value of the cut length was recorded as the average grain size before heat treatment. The evaluation results are shown in Tables 3 and 4.
[0060] (KAM Value) In addition to using the above-mentioned sample via EBSD measurement device (FEI Quanta FEG 450, EDAX / TSL (now AMETEK) OIM Data Collection) and analysis software (EDAX / TSL (now AMETEK) OIM Data Analysis ver. 7.3.1), with an electron beam accelerating voltage of 15kV, a measurement interval of 5μm steps, and a measurement area of more than 40000μm2, and a CI value of less than 0.1, the orientation difference of each crystal grain was analyzed. The boundary where the orientation difference between adjacent pixels is more than 5° is regarded as the crystal grain boundary, and the KAM value of the entire pixel is obtained to obtain the average value. The evaluation results are shown in Tables 3 and 4.
[0061] (Average crystal grain size after pressure heat treatment) A 40mm × 40mm sample was cut from the strip used for the above-mentioned characteristic evaluation. The sample (pure copper plate) was sandwiched between two ceramic substrates (material: Si3N4, 50mm × 50mm × 1mm thickness) and subjected to heat treatment under a pressure of 0.60MPa. The heat treatment was carried out in a furnace at 850°C. For each ceramic substrate, the material temperature was reached at 850°C, and after confirmation by a thermocouple, it was maintained for 90 minutes. After the heating was terminated, the material was cooled in the furnace until it reached room temperature. After the temperature was lowered to room temperature, the average crystal grain size of the rolled surface of the pure copper plate was measured. First, the rolled surface was mechanically polished using water-resistant polishing paper and diamond abrasive grains, and then finished polished using a colloidal silica solution. Next, etching was performed, and five longitudinal and transverse lines of specific lengths were drawn out according to the cutting method of JIS H 0501. The number of crystal grains that were completely cut out was counted, and the average value of the cut lengths was recorded as the average crystal grain size. The evaluation results are shown in Tables 3 and 4.
[0062] (Particle size variation after pressure heat treatment) As described above, for samples taken from test pieces subjected to pressure heat treatment, within a 30mm × 30mm area, twinning was removed. The average of the major axis of the largest crystal grain and the minor axis cut off at the grain boundary when a line perpendicular to this axis is drawn is taken as the maximum crystal grain size dmax. The ratio of this maximum crystal grain size to the aforementioned average crystal grain size dave, dmax / dave, is evaluated as "0" when it is 15.0 or less, "△" when it is more than 15.0 but less than 20.0, and "×" when it is more than 20.0. The evaluation results are shown in Tables 3 and 4.
[0063]
[0064]
[0065]
[0066]
[0067] In Comparative Example 1, the P content was 160 massppm, which is higher than the range of the present invention, resulting in deteriorated processability. Furthermore, after pressure heat treatment, the average crystal grain size increased to over 500 μm, and the particle size inhomogeneity also increased. In Comparative Example 2, the combined Ag and Fe content was 0.2 massppm, which is lower than the range of the present invention. After pressure heat treatment, the crystal grains became coarser, and the particle size inhomogeneity also increased. In Comparative Example 3, the processing rate of the tempering roll pressing was 62%, which is higher than the preferred range of the present invention. The KAM value was 2.12, which is higher than the range of the present invention. After pressure heat treatment, the crystal grains became coarser, and the particle size inhomogeneity also increased.
[0068] In this regard, in Examples 1-28 of the present invention, the average crystal grain size after heat treatment is small, and the grain size inhomogeneity is also reduced. From the above description, according to the present invention, it can be confirmed that a pure copper plate with excellent hot workability is provided, and that grain coarsening and inhomogeneity can be suppressed after pressure heat treatment. [Simplified Explanation of the Diagram]
[0069] [Figure 1] Flowchart of the manufacturing method of pure copper plate in this embodiment.
Claims
1. A pure copper plate, characterized in that it has a Cu content of 99.96 mass% or more, a P content of 0.01 massppm or more and 3.00 massppm or less, a combined Ag and Fe content of 3.0 massppm or more, and the residue consists of unavoidable impurities. The average grain size of the rolled surface is 10 μm or more. Except for measurement points where the measurement area of 1 mm2 or more is measured by the EBSD method at measurement intervals of 5 μm steps and the CI value analyzed by the data analysis software OIM is 0.1 or less, the KAM (Kernel Average Misorientation) value when the boundary with an orientation difference of 5° or more between adjacent pixels is regarded as the grain boundary is 1.50 or less.
2. The pure copper plate as described in claim 1, wherein, The content of sulfur is in the range of 2.0 massppm to 20.0 massppm.
3. The pure copper plate as described in claim 1 or 2, wherein, The content of Mg, Sr, Ba, Ti, Zr, Hf, and Y is below 10.0 massppm.
4. The pure copper plate described in any of claims 1 to 3, wherein, Furthermore, after pressure heat treatment with a pressure of 0.6 MPa, a heating temperature of 850°C, and a holding time of 90 minutes, the ratio of the maximum crystal grain size dmax to the average crystal grain size dave within a 50 mm × 50 mm area is dmax / dave or less.
5. The pure copper plate described in any of claims 1 to 4, wherein, Its Vickers hardness is below 150 HV.