JP7473066B2 - Pure copper materials, insulating substrates, electronic devices - Google Patents

Description

The present invention relates to a pure copper material suitable for electrical and electronic components such as heat sinks and thick copper circuits, and in particular to a pure copper material used for insulating substrates on which power semiconductors and the like are mounted, as well as insulating substrates and electronic devices that use this pure copper material.

Conventionally, pure copper materials with high electrical conductivity have been used for electric and electronic components such as heat sinks and thick copper circuits.
Recently, resistance heating has become a problem as the amount of current used in electrical and electronic equipment components increases.
In electronic devices such as semiconductor devices, for example, insulating substrates in which a pure copper material is bonded to a ceramic substrate to form the above-mentioned heat sink or thick copper circuit are used.

When joining a ceramic substrate and pure copper material, pressure treatment is performed in a high-temperature atmosphere, which can cause the crystal grain size of the pure copper material to become coarse or grow unevenly, resulting in poor joining, poor appearance, and problems during the inspection process.
In order to solve this problem, pure copper materials are required to have small changes in crystal grain size and to have uniform size even after heat treatment.

Therefore, for example, Patent Documents 1 and 2 propose techniques for suppressing the growth of crystal grains in pure copper materials.
This patent document describes that by including 0.0006 to 0.0015 wt % of S, it is possible to adjust the crystal grains to a constant size even when heat-treated at a temperature equal to or higher than the recrystallization temperature.

Japanese Patent Application Laid-Open No. 06-002058 International Publication No. 2020/203071

Incidentally, in Patent Documents 1 and 2, the composition is specified to suppress the coarsening of crystal grains. However, depending on the heat treatment conditions, etc., there is a risk that the coarsening of crystal grains and the variation in crystal grain size cannot be sufficiently suppressed.
In particular, when a ceramic substrate and a copper plate are firmly bonded to each other, a high-temperature heat treatment is performed while the ceramic substrate and the copper plate are pressed together with a constant pressure in the lamination direction. In this case, crystal grains in the pure copper plate tend to grow unevenly, and the coarsening and uneven growth of crystal grains can cause poor bonding, poor appearance, and problems during the inspection process.

This invention was made in consideration of the above-mentioned circumstances, and aims to provide a pure copper material that has little change in crystal structure even after heat treatment, and that can obtain a uniform crystal structure with suppressed variation in crystal grain size, as well as an insulating substrate and an electronic device that use this pure copper material.

In order to solve this problem, the inventors conducted extensive research and discovered that in order to suppress coarsening of crystal grains during heat treatment for joining, it is important to control the high-temperature hardness of the material within a certain range.
Normally, the material strength of copper material is significantly lower at high temperatures than at room temperature. If the material strength at high temperatures is too low, the difference in linear expansion coefficient between the ceramic and the copper material will promote the introduction of strain, which may lead to the introduction of greater strain that drives the growth of crystal grains. Furthermore, if the strength at high temperatures is too high, it will impart stress to the ceramic, reducing the thermal reliability of the insulating substrate. Therefore, it has become clear that it is important to control the strength (hardness) at high temperatures.

The present invention has been made based on the above findings, and a pure copper material according to an aspect 1 of the present invention has a Cu content of 99.96 mass% or more, and contains one or more A group elements selected from Ca, Ba, Sr, Zr, Hf, Y, Sc, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu, and one or more A group elements selected from O, S, Se, and Te. The steel sheet is characterized in that it contains both of the above B group elements in a total amount within the range of 10 ppm by mass or more and 300 ppm by mass or less, the ratio A/B of the total content A of the A group elements to the total content B of the B group elements, B ppm by mass, is greater than 1.0, the average crystal grain size on the rolled surface is 15 μm or more, and the high-temperature Vickers hardness at 850° C. is 4.0 HV or more and 10.0 HV or less.

According to the pure copper material of aspect 1 of the present invention, the Cu content is 99.96 mass% or more, and one or more A group elements selected from Ca, Ba, Sr, Zr, Hf, Y, Sc, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu, and one or more B group elements selected from O, S, Se, and Te are contained in a total amount within the range of 10 mass ppm to 300 mass ppm. Therefore, the material has particularly excellent electrical conductivity and heat dissipation properties, and can suppress the growth of crystal grains at high temperatures, making it particularly suitable as a material for electronic and electrical equipment parts for large current applications.
In addition, since the average crystal grain size on the rolled surface is set to 15 μm or more, the progress of recrystallization during heat treatment can be suppressed, making it possible to suppress coarsening of crystal grains and non-uniformity of the structure.
Furthermore, since the high-temperature Vickers hardness at 850°C is within the range of 4.0 HV or more and 10.0 HV or less, the introduction of strain due to the difference in linear expansion coefficient between the ceramic and the copper material can be suppressed, and the introduction of strain that serves as the driving force for the growth of crystal grains can be suppressed.
In addition, since the ratio A/B of the total content A ppm of the A group elements to the total content B ppm of the B group elements is set to be more than 1.0, it is possible to suppress the reaction between the A group elements and the B group elements, and it is possible to reliably form a compound consisting of either or both of the A group elements and the B group elements and Cu, and it is possible to further reliably suppress the growth of crystal grains during heat treatment due to the pinning effect of the compound.

A second aspect of the present invention is characterized in that in the pure copper material of the first aspect, a compound consisting of either or both of the A group element and the B group element and Cu is present.
According to the pure copper material of aspect 2 of the present invention, since a compound consisting of Cu and either one or both of the A group elements and the B group elements is present, the growth of crystal grains at high temperatures can be suppressed, and even after heat treatment, the change in the crystal structure is further reduced, and a more uniform crystal structure can be obtained.

A third aspect of the present invention is characterized in that in the pure copper material of the second aspect, the number density of the compounds is 1.0×10 ⁻⁴ /μm ² or more.
According to the pure copper material of aspect 3 of the present invention, the number density of the compounds is 1.0× ¹⁰ /μm or ^more , and therefore, due to the pinning effect of the compounds, it is possible to more reliably suppress the growth of crystal grains during heat treatment.

A fourth aspect of the present invention is characterized in that in the pure copper material according to any one of the first to third aspects , the standard deviation of the high temperature Vickers hardness is 1.0 HV or less.
According to the pure copper material of aspect 4 of the present invention, the standard deviation of the high-temperature Vickers hardness is set to 1.0 HV or less, so that the variation in high-temperature hardness is small and local deformation can be suppressed.

A fifth aspect of the present invention is characterized in that, in the pure copper material according to any one of the first to fourth aspects , the P content is 3.00 mass ppm or less.
According to the pure copper material of the fifth aspect of the present invention, the P content is 3.00 mass ppm or less, so that oxygen contained as an impurity can be rendered harmless, and the grain growth suppression effect (the effect of suppressing the growth of grains) of the A group elements and the B group elements can be fully exerted. When the P content is 0 mass ppm or more and less than 0.01 mass ppm, the above-mentioned effect is poor.

A sixth aspect of the present invention is characterized in that the pure copper material according to any one of the first to fifth aspects contains one or more elements selected from Ag, Fe and Pb in a total amount of 50.0 mass ppm or less.
According to the pure copper material of the sixth aspect of the present invention, one or more selected from Ag, Fe, and Pb are contained in a total amount of 50.0 mass ppm or less, so that Ag, Fe, and Pb are dissolved in the copper matrix, and the growth of crystal grains during heat treatment can be further suppressed. When the total amount of one or more selected from Ag, Fe, and Pb is 0 mass ppm or more and less than 5.0 mass ppm, the above-mentioned effect is poor.

The insulating substrate of aspect 7 of the present invention comprises a ceramic substrate and a copper plate bonded to one surface of the ceramic substrate, and is characterized in that the copper plate is made of any one of the pure copper materials of aspects 1 to 6 .
According to the insulating substrate of aspect 7 of the present invention, the copper plate to be joined to the ceramic substrate is made of any one of the pure copper materials of aspects 1 to 6 , so that the growth of crystal grains during joining is suppressed, the substrate has a uniform crystal structure, and can be used stably.

An electronic device according to an eighth aspect of the present invention is characterized by comprising the insulating substrate according to the seventh aspect and an electronic component mounted on the insulating substrate.
According to the electronic device of aspect 8 of the present invention, since it is equipped with the insulating substrate of aspect 7 , the copper plate has a uniform crystal structure and can be used stably.

The present invention provides a pure copper material that exhibits minimal changes in crystal structure even after heat treatment, suppresses variation in crystal grain size, and provides a uniform crystal structure, as well as an insulating substrate and an electronic device that use this pure copper material.

1 is a schematic diagram illustrating an insulating substrate and an electronic device according to an embodiment of the present invention. FIG. 1 is a flow diagram of a method for producing a pure copper material according to the present embodiment. 1 shows the observation results of a compound in Example 2 of the present invention, that is, a TEM image (transmission electron image). 1 shows an electron beam diffraction image of the compound in Example 2 of the present invention.

Hereinafter, a pure copper material, an insulating substrate, and an electronic device according to an embodiment of the present invention will be described.
The pure copper material of this embodiment is used as a material for electric/electronic components such as heat sinks and thick copper circuits, and when forming the aforementioned electric/electronic components, the pure copper material is bonded to, for example, a ceramic substrate to form an insulating substrate.

FIG. 1 shows an insulating substrate 10 according to an embodiment of the present invention and an electronic device 1 using this insulating substrate 10.
The electronic device 1 of this embodiment comprises an insulating substrate 10 of this embodiment, an electronic component 3 joined to one side (the upper side in Figure 1) of the insulating substrate 10 via a first solder layer 2, and a heat sink 51 joined to the other side (the lower side in Figure 1) of the insulating substrate 10 via a second solder layer 8.
In this embodiment, the electronic component 3 is a power semiconductor element, and the electronic device 1 is a power module.

The insulating substrate 10 comprises a ceramic substrate 11, a circuit layer 12 disposed on one surface (the upper surface in FIG. 1) of the ceramic substrate 11, and a metal layer 13 disposed on the other surface (the lower surface in FIG. 1) of the ceramic substrate 11.
The ceramic substrate 11 prevents electrical connection between the circuit layer 12 and the metal layer 13 .

The circuit layer 12 is formed by bonding a copper plate to one surface of the ceramic substrate 11. A circuit pattern is formed on this circuit layer 12, and one surface (the upper surface in FIG. 1 ) serves as a mounting surface on which electronic components 3 are mounted.
The metal layer 13 is formed by joining a copper plate to the other surface of the ceramic substrate 11. This metal layer 13 has the function of efficiently transferring heat from the electronic component 3 to the heat sink 51.

The copper plate that forms the circuit layer 12 and the ceramic substrate 11, and the copper plate that forms the metal layer 13 and the ceramic substrate 11 are bonded by an existing bonding method such as the DBC method or the AMB method.
Here, the temperature during bonding is a high temperature condition of, for example, 750° C. or more, and there is a risk that crystal grains in the circuit layer 12 and the metal layer 13 will become coarse.

Therefore, in this embodiment, the copper plate that becomes the circuit layer 12 and the copper plate that becomes the metal layer 13 are made of the pure copper material of this embodiment.

The pure copper material of this embodiment has a Cu content of 99.96 mass% or more, and contains one or more A group elements selected from Ca, Ba, Sr, Zr, Hf, Y, Sc, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu, and one or more B group elements selected from O, S, Se, and Te in a total amount of 10 mass ppm or more and 300 mass ppm or less.
In addition, the pure copper material of this embodiment preferably contains both group A elements and group B elements, and the ratio A/B of the total content A mass ppm of the group A elements to the total content B mass ppm of the group B elements is preferably greater than 1.0.

In the pure copper material of this embodiment, the P content may be 3.00 mass ppm or less.
Furthermore, the pure copper material of this embodiment may contain one or more elements selected from Ag, Fe, and Pb in a total amount of 50.0 mass ppm or less.

In the pure copper material of this embodiment, the average crystal grain size on the rolled surface is 15 μm or more, and the high-temperature Vickers hardness at 850° C. is in the range of 4.0 HV to 10.0 HV.
In the pure copper material of this embodiment, it is preferable that the standard deviation of the above-mentioned high-temperature Vickers hardness is 1.0 HV or less.

In the pure copper material of this embodiment, it is preferable that a compound consisting of either one or both of the A group element and the B group element and Cu is present. Furthermore, it is preferable that the number density of this compound is 1×10 ⁻⁴ pieces/μm ² or more.

Here, the reasons for specifying the Cu content, average crystal grain size, high-temperature Vickers hardness, content of various elements, and compounds in the pure copper material of this embodiment as described above will be explained below.

(Cu content: 99.96 mass% or more)
Electrical and electronic components for large current applications are required to have excellent electrical conductivity and heat dissipation properties in order to suppress heat generation when electricity is passed through them, and it is preferable to use pure copper, which has particularly excellent electrical conductivity and heat dissipation properties.
Therefore, in the pure copper material of this embodiment, the purity of Cu is specified to be 99.96 mass% or more. The purity of Cu is preferably 99.965 mass% or more, and more preferably 99.97 mass% or more. There is no particular upper limit on the purity of Cu, but if it exceeds 99.999 mass%, a special refining process is required, and the manufacturing cost increases significantly, so it is preferably 99.999 mass% or less.

(Average grain size on rolled surface: 15 μm or more)
In the pure copper material of this embodiment, if the grain size of the crystal grains on the rolled surface is fine, when this pure copper material is heated to, for example, 800°C or higher, recrystallization is likely to proceed, and there is a risk that the growth of the crystal grains and the non-uniformity of the structure will be promoted.
For this reason, in the pure copper material of this embodiment, the average crystal grain size on the rolled surface is set to 15 μm or more in order to suppress the coarsening of crystal grains and the non-uniformity of the structure during heat treatment.
In order to further suppress the coarsening of crystal grains during heat treatment, the average crystal grain size on the rolled surface is preferably 30 μm or more, more preferably 35 μm or more, and even more preferably 40 μm or more. The average crystal grain size on the rolled surface is preferably 300 μm or less, more preferably 275 μm or less, and even more preferably 250 μm or less.

(High temperature Vickers hardness at 850°C: 4.0HV to 10.0HV)
In the pure copper material of this embodiment, the mechanical properties decrease significantly as the temperature increases. At high temperatures, deformation is easily concentrated locally due to external forces. Therefore, by increasing the hardness at high temperatures, the deformation can be dispersed. On the other hand, if the hardness at high temperatures is too high, a large stress may be applied to the bonded ceramic substrate 11, and the reliability of the insulating substrate 10 may decrease.
Therefore, in this embodiment, the high-temperature Vickers hardness at 850° C. is set to be within the range of 4.0 HV to 10.0 HV.
The high-temperature Vickers hardness at 850° C. is preferably 4.25 HV or more, and more preferably 4.5 HV or more. The high-temperature Vickers hardness at 850° C. is preferably 9.9 HV or less, and more preferably 9.8 HV or less.

(Standard deviation of high temperature Vickers hardness at 850°C: 1.0 HV or less)
In the pure copper material of this embodiment, if there is a large variation in high-temperature Vickers hardness, local deformation is likely to occur.
Therefore, in this embodiment, it is preferable that the standard deviation value of the high-temperature Vickers hardness at 850° C. is set to 1.0 HV or less.
The standard deviation value of the high-temperature Vickers hardness at 850° C. is more preferably 0.90 HV or less, even more preferably 0.80 HV or less, and even more preferably 0.70 HV. The standard deviation value of the high-temperature Vickers hardness at 850° C. is preferably 0.05 or more, even more preferably 0.075 or more, and even more preferably 0.10 or more.

(Total content of either or both of group A elements and group B elements: 10 mass ppm or more and 300 mass ppm or less)
A group elements (Ca, Ba, Sr, Zr, Hf, Y, Sc, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) and B group elements (O, S, Se, Te) have a very small solid solubility limit in Cu and form a compound with Cu. Therefore, by adding either one or both of the A group elements and the B group elements, a compound stable even at high temperatures is formed. In addition, since this compound contains Cu, there is no risk of significantly lowering the thermal conductivity. Therefore, by adding either one or both of the A group elements and the B group elements, a compound stable at high temperatures is generated, and it is possible to suppress the movement of the crystal grain boundary at high temperatures and suppress the growth of the crystal grains. In addition, since the compound is present, the change in the crystal structure is even less even after heat treatment, and it is possible to obtain a more uniform crystal structure. On the other hand, if either one or both of the A group elements and the B group elements are contained in a large amount, there is a risk that it will have a negative effect on the manufacturability.
For this reason, in this embodiment, the total content of either or both of the A group elements and the B group elements is set to a range of 10 ppm by mass or more and 300 ppm by mass or less.
The total content of either or both of the A group elements and the B group elements is preferably 15 mass ppm or more, more preferably 20 mass ppm or more, and the total content of either or both of the A group elements and the B group elements is preferably 290 mass ppm or less, more preferably 280 mass ppm or less.

(The ratio A/B of the total content A of group A elements to the total content B of group B elements is greater than 1.0)
Group A elements (Ca, Ba, Sr, Zr, Hf, Y, Sc, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) and group B elements (O, S, Se, Te) are highly reactive with each other, so group A elements and group B elements are consumed by reaction with each other.
Therefore, in order to sufficiently form a compound consisting of Cu and either or both of the A group elements and the B group elements, it is preferable that the ratio A/B of the total content A of the A group elements to the total content B of the B group elements is more than 1.0.
The ratio A/B of the total content A of the A group elements to the total content B of the B group elements is more preferably more than 1.5, and even more preferably more than 2.0. The ratio A/B is preferably 100 or less, more preferably 75 or less, and even more preferably 50 or less.

(Number density of compounds consisting of either or both of the A group element and the B group element and Cu: 1.0 × ^10-4 pieces/ ^μm2 or more)
As described above, the compound consisting of Cu and either one or both of the A group element and the B group element has high stability at high temperatures, and therefore, during heat treatment, the pinning effect of this compound makes it possible to sufficiently suppress the growth of crystal grains.
Therefore, in this embodiment, the number density of the compound consisting of either or both of the A group element and the B group element and Cu is preferably 1.0×10 ⁻⁴ pieces/μm ² or more. The number density of the compound consisting of either or both of the A group element and the B group element and Cu is more preferably 2.5×10 ⁻⁴ pieces/μm ² or more, and even more preferably 5.0×10 ⁻⁴ pieces/μm ² or more. The number density of the compound consisting of either or both of the A group element and the B group element and Cu is preferably 1000×10 ⁻⁴ pieces/μm ² or less, more preferably 900×10 ⁻⁴ pieces/μm ² or less, and even more preferably 800×10 ⁻⁴ pieces/μm ² or less.

(P: 3.00 mass ppm or less)
P is widely used as an element that neutralizes oxygen in copper. However, when P is contained at a certain level or more, it inhibits not only oxygen but also the action of grain growth inhibitors (elements that inhibit grain growth) present at grain boundaries. Therefore, when heated to high temperatures, the elements that inhibit grain growth do not function sufficiently, and there is a risk that the grains will become coarse and uneven.
Therefore, in this embodiment, the P content is preferably set to 3.00 mass ppm or less.
The lower limit of the P content is preferably 0.01 ppm by mass or more, and the upper limit of the P content is preferably 2.50 ppm by mass or less, and more preferably 2.00 ppm by mass or less.

(Total content of one or more selected from Ag, Fe, and Pb: 50.0 mass ppm or less)
Ag, Fe, and Pb are elements that have the effect of suppressing the coarsening of crystal grains by dissolving in the copper matrix. However, if the alloy contains a large amount of Ag, Fe, or Pb, there are concerns that the manufacturing cost will increase and the electrical conductivity will decrease.
For this reason, in this embodiment, the total content of one or more elements selected from Ag, Fe, and Pb is preferably 50.0 mass ppm or less.
The lower limit of the total content of one or more selected from Ag, Fe, and Pb is preferably 5.0 mass ppm or more, more preferably 6.0 mass ppm or more, and even more preferably 7.0 mass ppm or more. On the other hand, the total content of one or more selected from Ag, Fe, and Pb is more preferably 40.0 mass ppm or less, and even more preferably 30.0 mass ppm or less.

(Other unavoidable impurities)
Examples of inevitable impurities contained in the remainder other than the elements whose contents are specified above include Al, As, B, Be, Bi, Cd, Cr, Sc, V, Nb, Ta, Mo, Mg, Ni, W, Mn, Re, Ru, Ti, Os, Co, Rh, Ir, Pd, Pt, Au, Zn, Hg, Ga, In, Ge, Tl, N, Sb, Si, Sn, Li, etc. These inevitable impurities may be contained to the extent that they do not affect the characteristics.
Here, since these unavoidable impurities may reduce electrical conductivity, the total amount is preferably 0.04 mass% or less, more preferably 0.03 mass% or less, even more preferably 0.02 mass% or less, and further preferably 0.01 mass% or less.
The upper limit of the content of each of these unavoidable impurities is preferably 30 ppm by mass or less, more preferably 20 ppm by mass or less, and even more preferably 15 ppm by mass or less.

Next, the method for producing the pure copper material according to this embodiment will be described with reference to the flow diagram shown in FIG.

(Melting and casting process S01)
First, the molten copper obtained by melting an oxygen-free copper raw material is added with either one or both of the above-mentioned group A elements and group B elements and other additive elements to adjust the composition, thereby producing a molten copper alloy. In addition, elemental substances, master alloys, etc. can be used to add various elements. In addition, raw materials containing the above-mentioned elements may be melted together with the copper raw material. Here, the molten copper is preferably so-called 4NCu having a purity of 99.99 mass% or more, or so-called 5NCu having a purity of 99.999 mass% or more.
In the melting step, in order to reduce the hydrogen concentration, it is preferable to melt the copper alloy in an inert gas atmosphere (e.g., Ar gas) in which the vapor pressure of _H2O is low, and to minimize the holding time during melting. The molten copper alloy with the adjusted composition is then poured into a mold to produce an ingot. In addition, when mass production is taken into consideration, it is preferable to use a continuous casting method or a semi-continuous casting method.
Here, by setting the cooling rate during casting to 0.1° C./sec or more, it is possible to uniformly disperse trace impurities and additive elements present in the copper during solidification.

(First cold working step S02)
The obtained ingot is subjected to cold working to change its shape to a predetermined size. The working ratio is not particularly specified, but is preferably 50% or more, more preferably 60% or more, and even more preferably 70% or more.
The processing method is not particularly limited, but if the final shape is a plate or strip, it is preferable to use rolling. If the final shape is a wire or rod, it is preferable to use extrusion or groove rolling. If the final shape is a bulk shape, it is preferable to use forging or pressing.

(First heat treatment step S03)
Next, the copper material after the first cold working step S02 is subjected to a heat treatment for the purpose of homogenizing the structure by recrystallization.
Here, the heat treatment method is not particularly limited, but it is preferable to perform the heat treatment in a non-oxidizing or reducing atmosphere. By performing the heat treatment at a high temperature of 500° C. or higher for a short period of time, such as 800° C. for 1 minute, it is possible to promote homogenization of the structure.
The cooling method is not particularly limited, but a method in which the cooling rate is 200° C./min or more, such as water quenching, is preferable.

(Second cold working step S04)
Next, the copper material after the first heat treatment step S03 is subjected to cold working while maintaining the surface temperature of the material in a temperature range of 10° C. or less.
During cold working, the temperature of the material rises due to processing heat. If recrystallization occurs in a part of the material due to the temperature rise caused by processing heat, it may adversely affect the structure control in the subsequent multi-stage heat treatment, and the elements may not be uniformly dispersed. The processing rate here is not particularly specified, but is preferably 50% or more, more preferably 60% or more, and even more preferably 70% or more.
The processing method is not particularly limited, but if the final shape is a plate or strip, it is preferable to use rolling. If the final shape is a wire or rod, it is preferable to use extrusion or groove rolling. If the final shape is a bulk shape, it is preferable to use forging or pressing.

(Multi-stage heat treatment step S05)
Next, the copper material that has been subjected to the second cold working step S04 is subjected to a multi-stage heat treatment to intentionally segregate trace amounts of additive elements at grain boundaries.
In the multi-stage heat treatment process S05, first, the copper material is held at a high temperature of 750°C or more to coarsen the crystal grain size to a certain level. Then, without cooling to room temperature, the temperature of the copper material is changed to a medium temperature range from 400°C to 750°C within 60 seconds, and held at this temperature for 1 minute or more, thereby making it possible to intentionally segregate a small amount of additive elements to the grain boundaries without introducing lattice defects (atomic vacancies) due to cooling. By segregating a small amount of additive elements to the grain boundaries, the high-temperature Vickers hardness at 850°C can be controlled to 4.0 to 10.0 HV. When changing the heat treatment temperature, this can be achieved by moving the copper material into a furnace held at each temperature range without significantly lowering the temperature.
Here, the heat treatment method is not particularly limited, but it is preferable to perform the heat treatment in a non-oxidizing or reducing atmosphere. Also, the heat treatment can be performed by moving the material between liquids held at high temperatures, such as a salt bath, during the heat treatment.
The cooling method after the multi-stage heat treatment is not particularly limited, but a method in which the cooling rate is 200° C./min or more, such as water quenching, is preferable.

(Temper rolling process S06)
The copper material after the multi-stage heat treatment step S05 may be subjected to temper rolling in order to adjust the material strength. Note that, when a low material strength is required, temper rolling does not have to be performed.
In this temper rolling step S06, the strain energy becomes high and the structure becomes unstable at high temperatures, so the processing rate is preferably 30% or less, more preferably 25% or less, and even more preferably 20% or less.
The final thickness is not particularly limited, but is preferably within the range of 0.5 mm to 5 mm, for example.

The above-mentioned processes result in the production of the pure copper material of this embodiment.

According to the pure copper material of the present embodiment having the above-mentioned configuration, the Cu content is 99.96 mass% or more, and one or more A group elements selected from Ca, Ba, Sr, Zr, Hf, Y, Sc, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and one or more B group elements selected from O, S, Se, and Te are contained in a total amount of 10 mass ppm or more and 300 mass ppm or less. Therefore, the material has particularly excellent electrical conductivity and heat dissipation properties, and can suppress the growth of crystal grains at high temperatures, making it particularly suitable as a material for electronic and electrical equipment parts for large current applications.
In addition, since the average crystal grain size on the rolled surface is set to 15 μm or more, the progress of recrystallization during heat treatment can be suppressed, making it possible to suppress coarsening of crystal grains and non-uniformity of the structure.
Furthermore, since the high-temperature Vickers hardness at 850°C is within the range of 4.0 HV or more and 10.0 HV or less, the introduction of strain due to the difference in linear expansion coefficient between the ceramic and the copper material can be suppressed, and the introduction of strain that serves as the driving force for the growth of crystal grains can be suppressed.
The means for obtaining a high-temperature Vickers hardness at 850°C within the above range is not limited to a specific method, but for example, it is possible to obtain the high-temperature Vickers hardness by controlling the temperatures in the first heat treatment step and the multi-stage heat treatment step, the material surface temperature in the second cold working step, and the rolling ratio in the temper rolling step as described above.

Here, in the pure copper material of this embodiment, when a compound consisting of Cu and either one or both of the A group elements and the B group elements is present, the pinning effect of the compound, which is stable at high temperatures, can suppress the growth of crystal grains at high temperatures, and even after heat treatment, the change in the crystal structure is even less, and a more uniform crystal structure can be obtained.

Furthermore, in the pure copper material of this embodiment, when the number density of the compound consisting of either one or both of the A group element and the B group element and Cu is 1.0 × ^10-4 pieces/ ^μm2 or more, the pinning effect of the compound stable at high temperatures can be sufficiently achieved, and it becomes possible to more reliably suppress the growth of crystal grains during heat treatment.

Furthermore, in the pure copper material of this embodiment, when the ratio A/B of the total content A mass ppm of group A elements to the total content B mass ppm of group B elements is greater than 1.0, the reaction and consumption of group A elements and group B elements can be suppressed, and a compound consisting of either or both of group A elements and group B elements and Cu can be reliably formed, and the pinning effect of this compound can further reliably suppress the growth of crystal grains during heat treatment.

In addition, in the pure copper material of this embodiment, when the standard deviation of the high-temperature Vickers hardness is 1.0 HV or less, the variation in high-temperature hardness is kept small, and localized deformation can be suppressed.

Furthermore, in the pure copper material of this embodiment, when the P content is 3.00 mass ppm or less, the oxygen contained as an impurity can be rendered harmless, and the grain growth inhibitory effect of the A group elements and B group elements can be fully exerted.

In addition, in the pure copper material of this embodiment, when one or more elements selected from Ag, Fe, and Pb are contained in a total amount of 50.0 mass ppm or less, Ag, Fe, and Pb are dissolved in the copper matrix, which further suppresses the growth of crystal grains during heat treatment.

The insulating substrate 10 of this embodiment has a ceramic substrate 11, a circuit layer 12 bonded to one side of the ceramic substrate 11, and a metal layer 13 bonded to the other side of the ceramic substrate 11. The copper plate that forms the circuit layer 12 and the metal layer 13 is made of the pure copper material of this embodiment, so that the growth of crystal grains during bonding with the ceramic substrate 11 is suppressed, and the variation in crystal grain size is suppressed, resulting in a uniform crystal structure and stable use.

The electronic device 1 of this embodiment has the insulating substrate 10 described above and electronic components 3 mounted on the circuit layer 12 of the insulating substrate 10, so that the copper plate that forms the circuit layer 12 and the metal layer 13 has a uniform crystal structure and can be used stably.

Although the pure copper material according to the embodiment of the present invention has been described above, the present invention is not limited thereto, and can be modified as appropriate without departing from the technical requirements of the invention.
For example, in the above embodiment, an example of a method for manufacturing a pure copper material is described, but the method for manufacturing a pure copper material is not limited to that described in the embodiment, and the pure copper material may be manufactured by appropriately selecting an existing manufacturing method.
Furthermore, when the manufacturing method includes a rolling step, the pure copper material of this embodiment can also be called a rolled pure copper material.

Below, we explain the results of the experiments conducted to confirm the effectiveness of the present invention.

The P concentration was refined to 0.001 mass ppm or less by a zone melting refining method to obtain pure copper with a purity of 99.999 mass% or more. This raw material made of pure copper was placed in a high-purity graphite crucible and melted by high-frequency induction heating in an atmospheric furnace with an Ar gas atmosphere.
A master alloy containing 1 mass% of various elements was prepared using 6N (purity of 99.9999 mass% or more) high purity copper and 2N (purity of 99 mass% or more) elements. The master alloy was added to the obtained molten copper to adjust the composition of the components shown in Tables 1 to 4, thereby obtaining a molten copper alloy. The obtained molten copper alloy was poured into a graphite mold to produce an ingot.
The size of the ingot was about 100 mm thick × about 100 mm wide × about 150 to 200 mm long. The cooling rate here was 0.1° C./sec or more in all samples.

The obtained ingots were subjected to cold rolling at the rolling ratios shown in Tables 5 and 6 as the first cold working.
Next, the copper material after the first cold working was subjected to a first heat treatment in an Ar gas atmosphere under the conditions shown in Tables 5 and 6. In addition, the surface was ground to remove an oxide film formed by the heat treatment, and the copper material was cut to a predetermined size.

Next, the copper material after the first heat treatment was subjected to the second cold working at the rolling ratios shown in Tables 5 and 6. Here, in the second cold working, the copper material was kept in a freezer at 0°C or less before each rolling pass, and rolling was performed immediately after the copper material was removed. The surface temperature of the copper material immediately after rolling was measured with a contact thermometer, and rolling was performed while confirming that the surface temperature was maintained at 10°C or less. In Comparative Example 5, the surface temperature of the copper material in the second cold working was 50°C.

Next, the copper material after the second cold working was subjected to a multi-stage heat treatment. The multi-stage heat treatment was performed by moving the copper material between salt baths maintained at the temperatures shown in Tables 5 and 6. The copper material was surface ground to remove the oxide film formed during the heat treatment, and cut to a predetermined size to adjust the final thickness.
Finally, temper rolling was carried out under the conditions shown in Tables 5 and 6 to produce strips having a thickness of 0.8 mm and a width of 60 mm (strips for property evaluation).

Then, an evaluation was carried out on the following items:

(Composition Analysis)
Measurement samples were taken from the resulting ingot, and the contents of S and O were measured by infrared absorption, while the contents of other elements were measured using a glow discharge mass spectrometer (GD-MS). Measurements were performed at two locations, the center and the end in the width direction of the sample, and the larger content was recorded as the content of the sample.

(Average crystal grain size)
A sample of 20 mm x 20 mm was cut out from the obtained strip material for property evaluation, and the average crystal grain size was measured using a SEM-EBSD (Electron Backscatter Diffraction Patterns) measuring device. The conditions of the electron microscope and the EBSD detector are shown below.
(Electron microscope conditions)
Observation magnification or area of measurement field: 400 μm × 800 μm
Acceleration voltage: 20 kV
Working distance: 20mm
Sample tilt angle: 70°
(EBSD detector conditions)
Analysis software name: EDAX/TSL (now AMETEK) OIM Data Analysis ver. 8.6
CI value (confidence coefficient): Measurement points greater than 0.1 were used in the analysis.
Grain boundary angle difference: An angle of 5° or more was regarded as a grain boundary.
Minimum grain size: 2 steps or more were considered to be crystal grains.
Step size: 1 μm
Treatment of twins: Twins are considered as grain boundaries.
The rolled surface was mechanically polished using waterproof abrasive paper and diamond abrasive grains. Then, a colloidal silica solution was used to finish polish the sample. Then, a scanning electron microscope was used to irradiate individual measurement points (pixels) within the measurement range of the sample surface with an electron beam, and the boundaries between adjacent measurement points where the orientation difference between the measurement points was 5° or more were determined as grain boundaries by orientation analysis using the electron backscatter diffraction method. The boundaries between adjacent measurement points where the orientation difference between the measurement points was 5° or more and less than 15° were determined as small-angle grain boundaries. The boundaries between adjacent measurement points where the orientation difference between the measurement points was 15° or more were determined as high-angle grain boundaries. At this time, the twin boundaries were also determined as high-angle grain boundaries. In addition, the measurement range was adjusted so that each sample contained 100 or more crystal grains. A grain boundary map was created using the high-angle grain boundaries from the obtained orientation analysis results, and five lines of a predetermined length were drawn at predetermined intervals in the vertical and horizontal directions on the grain boundary map in accordance with the cutting method of JIS H 0501. The number of crystal grains that were completely cut was counted, and the average cut length was calculated as the crystal grain size.

(High temperature Vickers hardness)
A sample of 10 mm x 10 mm was cut out from the obtained strip material for property evaluation, and the rolled surface was mechanically polished using waterproof abrasive paper and diamond abrasive grains. The high-temperature Vickers hardness was measured using a high-temperature micro Vickers hardness tester (HTM-1200-III) manufactured by INTESCO.
After reducing the pressure to 1×10 ⁻³ Pa, the sample was heated to 850° C. at a heating rate of 20° C./min and held at 850° C. for 5 minutes. Next, a diamond indenter was used to drive the indenter in with a test force of 0.98 N, and the size of the indentation mark was measured to measure the Vickers hardness.
For each sample, the Vickers hardness was measured at 10 points, and the average value was calculated using the measured values at the 10 points, which was used as the high-temperature Vickers hardness of the sample. The standard deviation of the high-temperature Vickers hardness was also calculated using the measured values at the 10 points.

(Density of Compounds)
Measurement samples were taken from the strip material for property evaluation, and the rolled surface was subjected to CP polishing. Using a FE-SEM (field emission scanning electron microscope), 50 regions were observed at a 2000x field of view (approximately 2500 μm ² /field of view). The number density of compounds (compounds consisting of either or both of the A group element and the B group element and Cu) was calculated from the observation results in the 50 regions.

(Identification of Compounds)
A sample for observing the compound was prepared from the strip material for property evaluation using a FIB (Focused Ion Beam) method. The sample was subjected to particle observation using a transmission electron microscope (TEM: JEM-2010F, manufactured by JEOL Ltd.), and EDX analysis (energy dispersive X-ray spectroscopy) was performed to confirm whether the compound was a particle consisting of either or both of the A group element and the B group element and Cu.
3A and 3B show the observation results of the compound in Inventive Example 2. It was confirmed that the observed compound contained Cu ₅ Ca.

(Crystal grain size after pressure heat treatment d _ave )
A sample of 40 _mm x 40 mm was cut out from the strip material for characteristic evaluation described above. A paste-like active silver brazing material (TB-608T manufactured by Tokyo Blaze) was applied to both sides of a ceramic plate (material: Si 3 N ₄ , 50 mm x 50 mm x thickness 0.32 mm). The ceramic plate was sandwiched between two of the above-mentioned samples (pure copper plates) and heat-treated under a load of 0.59 MPa. The heat treatment was performed under the following conditions. The laminated pure copper plate and ceramic plate were put into a furnace at 850°C, and after confirming with a thermocouple that the material temperature had reached 850°C, the plate was held for 60 minutes, and after heating was completed, the plate was cooled in the furnace until it reached room temperature. After the temperature had dropped to room temperature, the average crystal grain size d _ave was measured for the rolled surface of the pure copper plate by the following method.

First, the rolled surface (the surface not in contact with the ceramic plate) was mechanically polished using waterproof abrasive paper and diamond abrasive grains. Then, a colloidal silica solution was used for finish polishing. After that, etching was performed, and the rolled surface (observation surface) was observed under an optical microscope. In accordance with the cutting method of JIS H 0501, five lines of a specified length were drawn at specified intervals in the vertical and horizontal directions. The number of crystal grains that were completely cut was counted, and the average of the cut lengths was taken as the average crystal grain size. When the average crystal grain size was 200 μm or less, it was rated as "A" (excellent). When the average crystal grain size was more than 200 μm and less than 300 μm, it was rated as "B" (good). When the average crystal grain size was more than 300 μm and less than 500 μm, it was rated as "C" (fair). When the average crystal grain size was more than 500 μm, it was rated as "D" (poor).

(Variation in particle size after pressure heat treatment)
As described above, the maximum grain size d _max was the average value of the long and short diameters of the coarsest grains in the 40 mm × 40 mm test piece subjected to the pressurized heat treatment, excluding twin crystals. Here, the maximum value of the length of the line segment cut by the grain boundary among the line segments drawn on the coarsest grains was taken as the long diameter. And, the maximum value of the length of the line segment cut by the grain boundary among the line segments perpendicular to the long diameter was taken as the short diameter. When the ratio d _max / d _ave between the maximum grain size d _max and the above-mentioned average grain size d _ave was 15 or less, it was evaluated as "B" (good), when d _max / d _ave was more than 15 and less than 20, it was evaluated as "C" (fair), and when d _max / d _ave was more than 20, it was evaluated as "D" (poor).

In Comparative Example 1, the total content of group A elements and group B elements was 5.3 ppm by mass, the high-temperature Vickers hardness was low at 4.6 HV, and the crystal grains became coarse after the pressurized heat treatment, with the grain size also varying widely.
In Comparative Example 2, the total content of group A elements and group B elements was 537.1 ppm by mass, the high-temperature Vickers hardness was high at 11.6 HV, and the variation in grain size was also large.

In Comparative Example 3, the high temperature Vickers hardness was low at 3.9 HV, and the crystal grains became coarse after the pressurized heat treatment, and the grain size also varied widely.
In Comparative Example 4, the average crystal grain size on the rolled surface was 14 μm, and the crystal grains became coarse after the pressurized heat treatment, and the grain size also varied widely.
In Comparative Example 5, the high-temperature Vickers hardness was low at 3.8 HV, and the crystal grains became coarse after the pressurized heat treatment, and the grain size also varied widely.

In contrast, in Examples 1 to 26 of the present invention, the total content of group A elements and group B elements is within the range of 10 ppm by mass to 300 ppm by mass, the high-temperature Vickers hardness is within the range of 4.0 Hv to 10.0 Hv, and the average crystal grain size is 15 μm or more, and the average crystal grain size after the pressurized heat treatment is small and the grain size variation is small.

From the above, it has been confirmed that the present invention can provide a pure copper material that exhibits minimal changes in the crystal structure even after heat treatment, suppresses variation in crystal grain size, and provides a uniform crystal structure.

The pure copper material of this embodiment is suitable for use in electrical and electronic components such as heat sinks and thick copper circuits.

REFERENCE SIGNS LIST 1 Electronic device 3 Electronic component 10 Insulating substrate 11 Ceramic substrate 12 Circuit layer 13 Metal layer

Claims (8)

The Cu content is 99.96 mass% or more,
The composition contains one or more group A elements selected from Ca, Ba, Sr, Zr, Hf, Y, Sc, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu, and one or more group B elements selected from O, S, Se, and Te in a total amount of 10 ppm by mass or more and 300 ppm by mass or less, and the ratio A/B of the total content A ppm of the group A elements to the total content B ppm of the group B elements is greater than 1.0,
The average grain size on the rolled surface is 15 μm or more,
A pure copper material having a high-temperature Vickers hardness of 4.0 HV or more and 10.0 HV or less at 850°C. The pure copper material according to claim 1, characterized in that a compound consisting of either or both of the A group element and the B group element and Cu is present. The pure copper material according to claim 2, characterized in that the number density of the compounds is 1.0 x 10 ^-4 particles/μm ² or more. The pure copper material according to claim 1, characterized in that the standard deviation of the high-temperature Vickers hardness is 1.0 HV or less. The pure copper material according to claim 1, characterized in that the P content is 3.00 mass ppm or less. The pure copper material according to claim 1, characterized in that it contains one or more elements selected from Ag, Fe, and Pb in a total amount of 50.0 mass ppm or less. An insulating substrate comprising a ceramic substrate and a copper plate bonded to one surface of the ceramic substrate, the copper plate being made of the pure copper material according to any one of claims 1 to 6 . An electronic device comprising the insulating substrate according to claim 7 and an electronic component mounted on the insulating substrate.

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