Pure copper plate, copper / ceramic joined body, and insulated circuit substrate

Abstract

The pure copper plate of the present invention has a Cu content of 99.96 mass% or more, a total Pb, Se and Te content of 10.0 massppm or less, a total Ag and Fe content of 3.0 massppm or more, and a residual portion consisting of unavoidable impurities. The average crystal grain size of the rolled surface is 10 μm or more, and the aspect ratio of the rolled surface crystal grains is 2.0 or less. After pressure heat treatment under the conditions of applying a pressure of 0.6 MPa, heating temperature of 850°C, and holding the heating temperature for 90 minutes, the average crystal grain size of the rolled surface crystal grains is 500 μm or less. This pure copper plate has a composition in which the Cu content is 99.96 mass% or greater, the total content of Pb, Se, and Te is 10.0 mass ppm or less, and the total content of Ag and Fe is 3.0 mass ppm or greater, the balance being unavoidable impurities. The average crystal grain size of crystal grains in a rolled surface of the pure copper plate is 10 [mu]m or greater, the aspect ratio of crystal grains in the rolled surface is 2.0 or less, and the average crystal grain size of crystal grains in the rolled surface after heat treatment under pressure in conditions of an applied pressure of 0.6 MPa, a heating temperature of 850 DEG C, and a holding time of 90 minutes at the heating temperature is 500 [mu]m or less.

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 pressurized heating, copper / ceramic bonding bodies using this pure copper plate, and insulating circuit boards. This invention claims priority based on Japanese Patent Application No. 2020-038763, 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, copper materials are bonded to ceramic substrates to form heat sinks or thick copper insulating circuit boards, as described above. When bonding ceramic substrates and copper plates, the bonding temperature is often 800°C or higher, which raises concerns about the coarsening of the crystal grains in the copper materials forming heat sinks or thick copper circuits. In particular, the crystal grains tend to coarsen 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 material that inhibits the growth of crystal grains. Patent Document 1 describes a method that, by containing 0.0006 to 0.0015 wt% S, can adjust the crystal grains to a certain size even after heat treatment at a recrystallization temperature or higher. [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, the crystal grains in the pure copper plate are more prone to uneven growth. 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 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, a copper / ceramic bonding body using this pure copper plate, and an insulating circuit board. [Means for solving the problem]

[0010] To solve this problem, the inventors, through careful examination, discovered that trace amounts of impurity elements present at the grain boundaries in pure copper plates have 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 found 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 controlling the aspect ratio of the crystals is effective in suppressing the driving force of crystal growth during pressure heat treatment, thereby preventing the grain size from becoming larger and keeping the strain energy accumulated in the material at a low level.

[0011] The present invention is made 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 total Pb, Se and Te content of 10.0 massppm or less, a total Ag and Fe content of 3.0 massppm or more, and a residual portion having an unavoidable composition of impurities. The average crystal grain size of the rolled surface is 10 μm or more, and the aspect ratio of the rolled surface crystal grains is 2.0 or less. The roll surface crystal grains after pressure heat treatment under the conditions of applying a pressure of 0.6 MPa, heating temperature of 850°C, and holding the heating temperature for 90 minutes have an average crystal grain size of 500 μm or less.

[0012] When producing a pure copper plate according to this composition, the Cu content is 99.96 mass% or more, the total content of Pb, Se, and Te is 10.0 massppm or less, and the total content of Ag and Fe 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, Pb, Se, and Te are elements that segregate at grain boundaries due to the low solubility of Cu. Therefore, although they may be present in trace amounts, they significantly reduce hot workability. Thus, by limiting the total content of Pb, Se, and Te to 10.0 massppm or less, hot workability can be ensured.

[0013] Furthermore, since the average crystal grain size of the rolled surface is 10 μm or more, and the aspect ratio of the rolled surface crystal grains is 2.0 or less, the grain size becomes larger and the strain energy is lower in the state before pressure heat treatment. This reduces the driving force for recrystallization during pressure heat treatment and inhibits particle growth. When pressure heat treatment is performed at 0.6 MPa, heating temperature at 850°C, and holding time at the heating temperature at 90 minutes, the average crystal grain size of the rolled surface crystal grains is limited to 500 μm or less. This effectively controls crystal growth after pressure heat treatment, and when joined to other components, it can suppress poor bonding or poor appearance.

[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 inhomogenization of grains can be reliably suppressed after pressure 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 15.0 massppm. As unavoidable impurities, the elements Mg, Sr, Ba, Ti, Zr, Hf, and Y contain concerns that they may form compounds with grain growth inhibitors such as Pb, Se, Te, and S, thus 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 15.0 massppm, the grain growth inhibition effect of the grain growth inhibitors can be fully utilized, and after pressure heat treatment, the coarsening or inhomogenization of the grains can be effectively suppressed.

[0016] Furthermore, in the pure copper plate of the present invention, after the aforementioned pressure heat treatment, 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, dmax / dave, is preferably 20.0 or less. In this case, after pressure heat treatment, it is possible to effectively suppress the crystal grains from becoming uneven, and it is also possible to suppress the occurrence of appearance defects.

[0017] Furthermore, in the pure copper plate of the present invention, it is preferable that the Vickers hardness is below 150 HV. At this point, the Vickers hardness is below 150 HV, which is sufficiently soft, ensuring the characteristics of a pure copper plate, making it particularly suitable as a material for components of electrical and electronic parts used in high-current applications.

[0018] The copper / ceramic bonding system of the present invention is characterized by bonding the aforementioned pure copper plate and ceramic component. When the copper / ceramic bond body is constructed according to this, even during pressure heat treatment, the local coarsening of the crystal grains of the pure copper plate is suppressed, thereby preventing poor bonding or poor appearance and the occurrence of improper inspection processes.

[0019] The copper / ceramic bonding system of the present invention is characterized by bonding the aforementioned pure copper plate and ceramic component. When an insulating circuit board with this configuration is used to bond the pure copper plate and the ceramic substrate, even during pressure heat treatment, localized coarsening of the crystal grains in the pure copper plate is suppressed, thereby preventing poor bonding or appearance defects and ensuring proper inspection. [Effects of the Invention]

[0020] According to the present invention, a pure copper plate with excellent hot workability and which can suppress grain coarsening and non-uniformity after pressure heat treatment is provided, a copper / ceramic bond using the pure copper plate, and an insulating circuit board are provided.

Implementation Method

[0021] 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.

[0022] The pure copper plate of this embodiment has a Cu content of 99.96 mass% or more, a total Pb, Se and Te content of 10.0 massppm or less, a total Ag and Fe content of 3.0 massppm or more, and the residue consists of unavoidable impurities. Hereinafter, "mass%" and "massppm" will be referred to as "%" and "ppm" respectively.

[0023] 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 15.0 massppm or less.

[0024] 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, and the aspect ratio of the crystal grains on the rolled surface is 2.0 or less. Also, in the case of pressure heat treatment under conditions of a pressure of 0.6 MPa, a heating temperature of 850°C, and a holding time of 90 minutes, the average grain size of the crystal grains on the rolled surface is 500 μm or less. The average grain size of the crystal grains on the rolled surface can be, for example, the average value of the grain size measured at three equidistant points from the center of the rolled surface.

[0025] However, in the pure copper plate of this embodiment, the ratio of the maximum crystal grain size dmax to the average crystal grain size dave within a 50mm × 50mm area after the above-mentioned pressure heat treatment, dmax / dave, is preferably 20.0 or less. The maximum crystal grain size dmax is determined by selecting any area of ​​50mm × 50mm, and measuring the grain size of crystals at at least three locations within this area, preferably selecting the largest of the measured grain sizes. Furthermore, in the pure copper plate of this embodiment, the Vickers hardness is preferably 150HV or less.

[0026] Hereinafter, the reasons for specifying the composition and various properties of the pure copper plate as described above are explained.

[0027] (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 during thermal cycles. In this embodiment, the purity of Cu in the pure copper plate is specified to be 99.96 mass% or higher. However, a Cu 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 Cu purity, exceeding 99.999 mass% requires special refining processes, significantly increasing manufacturing costs; therefore, 99.999 mass% or lower is preferred.

[0028] (Total content of Pb, Se, and Te: 10.0 massppm or less) Pb, Se, and Te have low solid solubility limits in Cu and segregate at grain boundaries. While they suppress grain coarsening, they also significantly reduce hot workability. Therefore, in this embodiment, to ensure hot workability, the total content of Pb, Se, and Te is limited to 10.0 massppm or less. However, to further improve hot workability, it is preferable that the total content of Pb, Se, and Te is 9.0 massppm or less, more preferably 8.0 massppm or less. Furthermore, to effectively suppress grain coarsening, it is preferable that the total content of Pb, Se, and Te is 0.1 massppm or more, more preferably 0.2 massppm or more, and most preferably 0.3 massppm or more.

[0029] (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 most preferably 10.0 massppm or more. Furthermore, due to concerns that excessive addition may increase manufacturing costs or decrease conductivity, the upper limit of the total content of Ag and Fe is preferably less than 100.0 massppm, more preferably less than 50.0 massppm, and even more preferably less than 20.0 massppm.

[0030] (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.

[0031] (Total content of Mg, Sr, Ba, Ti, Zr, Hf, Y (Group A elements): 15.0 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 grain-coarsening inhibitors' effects. Therefore, to reliably suppress grain coarsening after pressure heat treatment, the total content of Mg, Sr, Ba, Ti, Zr, Hf, and Y (Group A elements) is preferably 15.0 massppm or less. However, the total content of Mg, Sr, Ba, Ti, Zr, Hf, and Y (Group A elements) is preferably 10.0 massppm or less, more preferably 7.5 massppm or less, and most preferably 5.0 massppm or less.

[0032] (Other elements) However, Al, Cr, Sn, P, Be, Cd, Mg, and Ni (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 effectively suppress the coarsening of crystal grains after pressure heat treatment, it is preferable that the total content of Al, Cr, Sn, P, Be, Cd, Mg, and Ni (group M elements) exceeds 2.0 massppm. However, when Al, Cr, Sn, P, Be, Cd, Mg, and Ni (group M elements) are intentionally included, it is preferable that the lower limit of the total content of Al, Cr, Sn, P, Be, Cd, Mg, and Ni (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, P, Be, Cd, Mg, and Ni (M element group) are present. Therefore, it is preferable that the total content of Al, Cr, Sn, P, Be, Cd, Mg, and Ni (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.

[0033] (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.

[0034] (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 likely to occur during pressurized heat treatment of the pure copper plate, which may promote grain growth and lead to uneven microstructure. Therefore, in order to further suppress the coarsening of the grains, 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.

[0035] (Aspect ratio of grains on the roll-pressed surface: 2.0 or less) The aspect ratio of grains is an indicator of the degree of material processing. The higher the aspect ratio, the higher the degree of processing, and the higher the strain energy accumulated in the material. Here, when the strain energy accumulated in the material is high, the driving force for recrystallization becomes high, and the grains tend to coarsen during pressure heat treatment. Therefore, to further suppress grain coarsening, it is preferable that the aspect ratio of grains on the roll-pressed surface be 2.0 or less. The aspect ratio value here is the value obtained by dividing the major axis by the minor axis, i.e., expressed as major axis / minor axis. However, it is preferable that the aspect ratio of grains on the roll-pressed surface be 1.9 or less, and more preferably 1.8 or less.

[0036] (Average grain size of the rolled surface after pressure heat treatment: 500 μm or less) When heat treatment is performed under pressure, the increased pressure causes coarsening of the crystals. Under pressure, the copper grains become locally coarser. In this embodiment, the average grain size of the rolled surface after pressure heat treatment at 0.6 MPa, 850°C, and 90 minutes is limited to 500 μm or less. Even under these conditions, grain coarsening can be effectively suppressed, making it particularly suitable as a material for bonding thick copper circuits or heat sinks to ceramic substrates. However, the upper limit of the average grain size of the rolled surface after pressure heat treatment is preferably 450 μm or less, and more preferably 400 μm or less. On the other hand, although the lower limit of the average crystal grain size of the rolled surface after the above-mentioned pressure heat treatment is not specifically limited, it is actually above 50 μm.

[0037] (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 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.

[0038] (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, by being sufficiently flexible, it can be bonded to other components such as ceramic substrates under thermal cycles, mitigating the thermal deformation caused by the pure copper sheet and suppressing cracking of the ceramic substrates. 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.

[0039] Next, the manufacturing method of the pure copper plate of this embodiment will be described with reference to the flowchart shown in FIG1.

[0040] (Melting and Casting Process S01) First, the aforementioned elements are added to the copper molten liquid obtained by melting oxygen-free copper raw materials to adjust the composition and produce a copper alloy molten liquid. However, for the addition of various elements, elemental monomers or master alloys can be used. Alternatively, the raw materials containing the above elements can be melted along with the copper raw materials. Here, it is preferable that the copper molten liquid is 4NCu with a purity of 99.99 mass% or higher, or 5NCu with a purity of 99.999 mass% or higher. In the melting process, in order to reduce the hydrogen concentration, melting is carried out in an environment with low vapor pressure of H2O (e.g., Ar gas), and the holding time during dissolution is preferably kept to a minimum. Then, the copper alloy molten liquid with adjusted composition is poured into a mold to produce a casting block. However, considering mass production, it is preferable to use a continuous casting method or a semi-continuous casting method.

[0041] (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 kept between 500°C and 900°C, and the holding time at the heat treatment temperature is kept between 0.1 hours and 100 hours. It is preferable to perform the heat treatment in an 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 preferable to keep it 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.

[0042] (Intermediate Rolling Process S03) Next, the copper material after the heat treatment process S02 is cold rolled to form a specific shape. While the temperature conditions for this intermediate rolling process S03 are not particularly limited, it is preferable to perform the process within a range of -200°C to 200°C. Furthermore, the processing rate for 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.

[0043] (Recrystallization Heat Treatment Process S04) Next, the copper material after the intermediate rolling process S03 is subjected to a heat treatment for recrystallization. Here, the average grain size of the recrystallized grains on the rolling surface is 10 μm or more. When the recrystallized grains are fine, there is a concern that the grains may grow rapidly 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 a heat treatment temperature in the range of 200°C to 900°C for 1 second to 10 hours. For example, in short-term heat treatment, conditions such as holding at 850°C for 5 seconds or more, or in long-term 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.

[0044] (Temperature Processing 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 processing rate of tempering is not specifically limited, it is preferable to perform the processing rate in the range of more than 0% and less than 50% in order to make the aspect ratio of the grains on the rolled surface less than 2.0 or less, or to make the Vickers hardness less than 150 HV. More preferably, it is limited to more than 0% and less than 40%. Furthermore, if necessary, heat treatment may be performed after tempering to remove residual strain. Although the final thickness is not specifically limited, it is appropriate to be in the range of 0.5 mm to 5 mm.

[0045] Through the above processes, a pure copper plate of this embodiment is manufactured.

[0046] In the pure copper plate of this embodiment with the above-described structure, the Cu content is 99.96 mass% or more, the total content of Pb, Se, and Te is 10.0 massppm or less, and the total content of Ag and Fe is 3.0 massppm or more. Since the residue inevitably contains impurities, the coarsening of the crystal grains can be suppressed by Ag and Fe dissolving in the copper matrix. Furthermore, Pb, Se, and Te segregate at the grain boundaries and are grain growth inhibitors that suppress grain coarsening. Although they may be present in trace amounts, these elements greatly reduce hot workability. Therefore, by limiting the total content of Pb, Se, and Te to 10.0 massppm or less, hot workability can be ensured.

[0047] Furthermore, in the pure copper plate of this embodiment, since the average grain size of the crystal grains on the roll-pressed surface is 10 μm or more, and the aspect ratio of the crystal grains on the roll-pressed surface is 2.0 or less, the grain size becomes larger and the residual strain is less in the state before the pressure heat treatment. Therefore, the driving force for recrystallization during the pressure heat treatment is reduced, and particle growth is suppressed. Then, in the pure copper plate of this embodiment, the average grain size of the crystal grains on the roll-pressed surface after pressure heat treatment under the conditions of a pressure of 0.6 MPa, a heating temperature of 850°C, and a holding time of 90 minutes is limited to 500 μm or less. Therefore, crystal growth after pressure heat treatment is effectively suppressed, and when joined to other components, the occurrence of poor bonding or poor appearance can be suppressed.

[0048] 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 grains during pressurized heat treatment. In addition, hot workability can be ensured.

[0049] Furthermore, in this embodiment, when the total content of Mg, Sr, Ba, Ti, Zr, Hf, and Y (group A elements) is 15.0 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 during pressurized heat treatment can be effectively suppressed.

[0050] 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 non-uniformity of the crystal grains can be effectively suppressed after the pressure heat treatment.

[0051] Furthermore, in this embodiment, when the Vickers hardness is below 150 HV, it is sufficiently soft, ensuring the properties of a pure copper plate, making it particularly suitable as a material for components of electrical and electronic parts used in high-current applications.

[0052] However, in this embodiment, when Al, Cr, Sn, P, Be, Cd, Mg, Ni (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.

[0053] 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]

[0054] The following describes the results of the confirming experiments conducted to verify the effects of the present invention. Raw materials made of pure copper with a purity of 99.999 mass% or higher and a master alloy in which various elements are added by 1 mass% to Cu were prepared. These were placed in a high-purity graphite crucible and subjected to high-frequency melting in an ambient furnace under Ar gas. In the resulting molten copper, various 1-mass% master alloys made of high-purity copper with a purity of 6N (99.9999 mass% or higher) and pure metals with a purity of 2N (99 mass% or higher) were mixed to form a specific composition, and then poured into a mold to produce a casting block. However, the size of the casting block was approximately 80 mm thick × 100 mm wide × 150-200 mm long.

[0055] 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 40 mm. Simultaneously with cutting the hot-rolled copper material, surface grinding was performed to remove the oxide film on the surface. At this time, considering the rolling ratio of subsequent cold rolling and tempering rolling, the final thickness was adjusted to the thickness of the copper material supplied for cold rolling, as shown in Tables 1 and 2.

[0056] The copper material with the adjusted thickness as described above is cold-rolled and water-cooled under the conditions described in Tables 1 and 2. Next, the cold-rolled copper material is subjected to recrystallization heat treatment under the conditions described in Tables 1 and 2. Then, the recrystallization heat-treated copper material is subjected to tempering roll forming under the conditions described in Tables 1 and 2 to manufacture strips with a width of 60 mm for characteristic evaluation, showing the thicknesses in Tables 1 and 2.

[0057] Then, an evaluation is conducted for the following items.

[0058] (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.

[0059] (Processability Assessment) As a processability assessment, the presence or absence of edge cracks during the aforementioned hot rolling and cold rolling processes was observed. "A" represents cases where no or almost no edge cracks were visually detected; "B" represents cases with edge cracks less than 1 mm in length; and "C" represents cases with edge cracks longer than 1 mm. The assessment results are shown in Tables 3 and 4. 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.

[0060] (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.

[0061] (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.

[0062] (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. 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 pressure heat treatment. The evaluation results are shown in Tables 3 and 4.

[0063] (Aspect Ratio of Crystalline Grains) The aspect ratio of the crystalline grains on the rolled surface is determined by using the same SEM-EBSD (Electron Backscatter Diffraction Patterns) measurement device to create a grain boundary map on the rolled surface of the strip material used for the aforementioned characteristic evaluation. For this map, five lines are drawn in the width direction and five lines are drawn in the rolling direction, and the number of completely cut crystalline grains is calculated. Let the grain diameter obtained from the rolling direction be the major diameter and the grain diameter obtained from the width direction be the minor diameter. The average aspect ratio of the ratio of the major diameter to the minor diameter is calculated as the aspect ratio of the crystalline grains. However, the aspect ratio value here is the value obtained by dividing the major diameter by the minor diameter, i.e., expressed as major diameter / minor diameter. The evaluation results are shown in Tables 3 and 4.

[0064] (Average crystal grain size after pressure heat treatment) A 50mm × 50mm 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 0.6MPa. The heat treatment was carried out in a furnace at 850°C. For each ceramic substrate, the material temperature was reached at 850°C, confirmed by a thermocouple, and maintained for 90 minutes. After heating was terminated, the material was cooled in the furnace until it reached room temperature. After cooling to room temperature, the average crystal grain size was measured on the rolled surface of the pure copper plate. 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.

[0065] (Particle size variation after pressure heat treatment) As described above, for samples taken from test pieces subjected to pressure heat treatment, within a 50mm × 50mm 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 line 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 "○" 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.

[0066]

[0067]

[0068]

[0069]

[0070] Comparative Example 1 had a higher total content of Pb, Te, and Se than the scope of this invention, resulting in poor hot workability. Large cracks occurred during hot working, leading to the discontinuation of subsequent evaluation. Comparative Example 2 had a larger longitudinal and transverse grain size on the rolled surface compared to the scope of this invention, and a smaller average grain size. After pressure heat treatment, the grains became coarser, and the grain size unevenness increased. Comparative Example 3 had a lower total content of Ag and Fe than the scope of this invention. After pressure heat treatment, the grains became coarser, and the grain size unevenness increased.

[0071] In this regard, in Examples 1-30 of the present invention, the average crystal grain size after pressure 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 after pressure heat treatment, the coarsening and inhomogenization of crystal grains can be suppressed. [Simplified Explanation of the Diagram]

[0072] [Figure 1] Flowchart of the manufacturing method of pure copper plate in this embodiment.

Claims

1. A pure copper plate, characterized in that the Cu content is 99.96 mass% or more, the total content of Pb, Se and Te is 10.0 massppm or less, the total content of Ag and Fe is 3.0 massppm or more, the residue is composed of unavoidable impurities, the average grain size of the crystal grains on the rolled surface is 10.0 μm or more, and the aspect ratio of the crystal grains on the rolled surface is 2.0 or less, and the average grain size of the crystal grains on the rolled surface after pressure heat treatment under the conditions of applying a pressure of 0.6 MPa, heating temperature of 850°C, and holding the heating temperature for 90 minutes is 500 μm 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 15.0 mass ppm.

4. The pure copper plate described in any of claims 1 to 3, wherein, After the aforementioned pressure heat treatment, the ratio of the maximum crystal grain size dmax to the average crystal grain size dave within a 50mm×50mm area of ​​the aforementioned roller-pressed surface 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.

6. A copper / ceramic joint, characterized in that it is formed by joining a pure copper plate as described in any one of claims 1 to 5 and a ceramic component.

7. An insulating circuit board, characterized in that a pure copper plate as described in any one of claims 1 to 5 is bonded to the surface of a ceramic substrate.

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