JP2025094030A - Ceramic Circuit Board - Google Patents

Abstract

To provide a ceramic circuit board in which a copper plate has high electrical conductivity.SOLUTION: A ceramic circuit board W includes a copper plate bonded to one surface of a ceramic substrate S via a brazing material layer, and the ceramic substrate S has pores on its surface with a diameter of 15 μm or less, the copper plate has an average crystal grain size of 100 μm or less as measured by a cutting method in the grain size test method for drawn copper products specified in JIS 0501:1986, and has electrical conductivity of 96% or more and less than 100% of the IACS standard.SELECTED DRAWING: Figure 1

Description

The present invention relates to a ceramic circuit board used in a power module.

Ceramic circuit boards (hereinafter sometimes simply referred to as circuit boards) are disclosed, for example, in JP 2003-110222 A. The circuit board described in JP 2003-110222 A comprises a copper plate bonded to at least one surface of a ceramic substrate via a brazing material. According to the disclosure in JP 2003-110222 A, a copper plate is bonded to at least one surface of a ceramic substrate via a brazing material, a resist is applied to a predetermined portion of the surface of the copper plate, and unnecessary portions of the copper plate are etched to form a circuit section, unnecessary brazing material and reaction products between the brazing material and the ceramic substrate are removed while maintaining the resist, and then the resist is peeled off to form a circuit pattern and produce a circuit substrate.

JP 2003-110222 A

For example, if the average crystal grain size of the copper plate constituting the circuit board is excessively large, there is concern that this will impair the bondability to the ceramic substrate via the brazing material. When a copper plate with a relatively small average crystal grain size was then bonded to one side of a ceramic substrate using brazing material, the electrical conductivity of the copper plate constituting the circuit substrate decreased. There is concern that the electrical performance of the circuit substrate will decrease due to this decrease in the electrical conductivity of the copper plate.

The object of the present invention is to provide a ceramic circuit board having a high electrical conductivity, in which a copper plate is bonded to one side of the ceramic substrate via a brazing material layer.

In view of the above objective, as a result of intensive research, it was discovered that the conductivity of the copper plate constituting the circuit board decreases due to the coarsening of the crystal grains of the copper plate when it is joined to the ceramic substrate via a brazing material. It was then discovered that the decrease in the conductivity of the copper plate constituting the circuit substrate can be suppressed by devising a temperature profile when brazing the copper plate to the ceramic substrate, and this led to the invention.

The ceramic circuit board of the present invention is a ceramic circuit board having a copper plate bonded to one surface of the ceramic substrate via a brazing material layer, the ceramic substrate has pores on the surface of which have a diameter of 15 μm or less, the copper plate has an average grain size of 100 μm or less as measured by the cutting method of the grain size test method for drawn copper products specified in JIS H0501:1986, and has an electrical conductivity of 96% or more but less than 100% of the IACS standard.

The present invention can provide a ceramic circuit board with a highly conductive copper plate and a manufacturing method thereof.

FIG. 2 is a front view showing a schematic diagram of a ceramic circuit board. FIG. 2 is a plan view of FIG. 1 as seen from above. FIG. 2 is a first plan view illustrating a method for manufacturing the ceramic circuit board of FIG. 1. FIG. 2 is a second plan view illustrating the method for manufacturing the ceramic circuit board of FIG. 1. FIG. 4 is a third plan view illustrating the method for manufacturing the ceramic circuit board of FIG. 1 . FIG. 4 is a fourth plan view illustrating the method for manufacturing the ceramic circuit board of FIG.

The ceramic circuit board of the present invention is, for example, the ceramic circuit board W shown in Figures 1 and 2. This ceramic circuit board W basically comprises a ceramic substrate S, two brazing layers C1, C2 (hereinafter sometimes referred to as the first brazing layer C1 and the second brazing layer C2) formed on the upper surface (one surface) of the ceramic substrate S with a gap G therebetween, and two copper plates M1, M2 (hereinafter sometimes referred to as the first copper plate M1 and the second copper plate substrate M2) that function as circuit boards on which semiconductor elements or the like are mounted, each bonded to the upper surface side of the ceramic substrate S via the two brazing layers C1, C2. A plating layer of Ni, Au, or the like may be formed on the surfaces of the two copper plates M1, M2 as necessary. The ceramic circuit board W shown in Figures 1 and 2 has a copper plate M3 that functions as a heat sink, bonded to the lower surface (other surface) of the ceramic substrate S via the brazing layer C3. The number of copper plates is not limited to two, M1 and M2, and there may be three or more copper plates on the top surface.

The ceramic substrate constituting the ceramic circuit board of the present invention is not particularly limited in type, and alumina, silicon carbide, etc. can be used, but silicon nitride or aluminum nitride is preferred from the viewpoint of high thermal conductivity. It is preferable that the maximum diameter of the voids present on the surface of the ceramic substrate is 15 μm. If the maximum diameter of the voids exceeds 15 μm, the strength of the ceramic substrate decreases, for example, deteriorating the reliability of the ceramic circuit substrate under thermal cycles. It is more preferable to construct the ceramic substrate from a silicon nitride sintered body, which is particularly excellent in terms of mechanical strength such as strength and fracture toughness.

The silicon nitride sintered body can be produced, for example, by using a raw material powder containing 90 to 97% by mass of silicon nitride and 0.5 to 10% by mass of a sintering aid (containing a compound of Mg and at least one compound of Y and other rare earth elements). Specifically, the silicon nitride sintered body is produced by adding an appropriate amount of an organic binder, a plasticizer, a dispersant, and an organic solvent to the raw material powder, mixing them in a ball mill or the like to form a slurry, and forming the slurry into a thin plate shape by a doctor blade method or a calendar roll method to obtain a ceramic green sheet. The obtained ceramic green sheet can be obtained by punching or cutting into a desired shape and sintering at a temperature of 1700 to 1900 ° C. In this case, if the sintering aid exceeds 10% by mass, the characteristics of joining the ceramic substrate and the copper plate may become insufficient. Also, if the sintering aid is less than 0.5% by mass, the sintering of the silicon nitride particles may become insufficient. To obtain high thermal conductivity and high strength, it is preferable to include 2 to 4 mass% magnesium (Mg) in terms of magnesium oxide and 2 to 5 mass% yttrium (Y) in terms of yttrium oxide as sintering aids.

In the ceramic circuit board of the present invention, the number of copper plates bonded to one surface of the ceramic substrate via the brazing material is not particularly limited. The copper plates constituting the ceramic circuit board of the present invention are made of a copper alloy containing more than 0.03 mass% and not more than 0.15 mass% Zr, with the remainder being copper and unavoidable impurities. Copper plates are preferred in terms of electrical resistance and ductility, high thermal conductivity (low thermal resistance), low migration, etc.

The method for manufacturing a ceramic circuit board of the present invention is a method for manufacturing a ceramic circuit board that includes a joining step of joining a copper plate to one surface of a ceramic substrate via a brazing material, and the joining step includes a heating step of heating the copper plate, which is made of a copper alloy containing more than 0.03 mass% and not more than 0.15 mass% Zr, with the balance being copper and unavoidable impurities, at a temperature within a range of 770 to 880°C, and a cooling step of lowering the temperature to 350°C over a period of 50 minutes or more after the heating step.

Hereinafter, the method for manufacturing the ceramic circuit board of the present invention will be described with reference to the drawings as appropriate, taking the case of manufacturing the ceramic circuit board W shown in Figures 1 and 2 as an example. Here, the method for manufacturing the ceramic circuit board W can be divided into, for example, (a) a preparation step of preparing a ceramic substrate, a brazing material, and a copper plate, (b) a brazing material region forming step of applying a brazing material to the ceramic substrate, (c) a placement step of stacking the ceramic substrate, the brazing material, and the copper plate in that order, (d) a bonding step, (e) a circuit pattern forming step of etching the copper plate, (f) a step of removing unnecessary brazing material layers, and (g) a cleaning step. (d) The bonding step includes the "heating step" and "cooling down step" in the method for manufacturing the ceramic circuit board of the present invention.

(a) Preparation Step A ceramic substrate S, a brazing material (a paste containing brazing material powder and an organic binder), and a copper plate M are prepared.

3, a brazing material is applied to a ceramic substrate S by a method such as screen printing to form brazing material regions c1 and c2 containing a brazing material powder and an organic binder with a gap G. Examples of the brazing material powder include brazing material powder containing Ag, Cu, etc. in a predetermined composition, and various organic resins can be used as the organic binder.

(c) Placing Step A copper plate M is placed on the side of the ceramic substrate S on which the brazing material is applied, and is fixed in place using a jig.

(d) Bonding Process The bonding process includes a "heating process" and a "temperature lowering process". A holding process may be added to the bonding process. As shown in FIG. 4, (i) a ceramic substrate S, (ii) brazing material regions c1 and c2 formed on the ceramic substrate, which contain brazing material powder and an organic binder, and (iii) a copper plate M placed through the brazing material region are heated to bond the ceramic substrate S and the copper plate M through the brazing material layer, forming a bonded body. The heating for bonding is preferably performed in a vacuum or a reducing atmosphere. In order to remove organic components in the brazing material paste during the heating process, it is preferable to hold the temperature near the volatilization temperature of the organic binder (for example, near 400° C.) once (holding process). After that, the material is heated at a brazing temperature of 770 to 880° C. (heating process (brazing process)). The heating process is preferably continued for 10 minutes or more. The brazing temperature is a temperature at which a brazing material layer can be appropriately formed, that is, a temperature equal to or higher than the melting point of the brazing material. The brazing temperature is usually the maximum temperature in the temperature rise process. After the heating process, the temperature is lowered to 350° C. over a period of 50 minutes or more (temperature lowering process). Then, the temperature is lowered from 350° C. to room temperature.

In the holding step during the joining process, if the holding temperature for removing the organic binder is low, the organic binder components cannot volatilize, and there is a risk that organic binder residue will remain. Therefore, the holding temperature for removing the organic binder is preferably 300°C or higher. For example, in the case of an organic binder containing an acrylic resin, this holding temperature is preferably 360°C or higher. In order to prevent the active metal in the brazing material from being oxidized by the oxygen contained in the resin in the organic binder, the holding temperature for removing the organic binder is set lower than the brazing temperature in the heating step (brazing step).

The brazing material used in the joining step is preferably, for example, an Ag-Cu-based active brazing material, which is a eutectic composition of Ag and Cu as the main components and which has been added with active metals such as Ti, Zr, and Hf, and which can provide high strength and high sealing properties. Furthermore, from the viewpoint of the joining strength between the ceramic substrate S and the copper plates M1 to M3, a ternary Ag-Cu-In-based active brazing material, in which In is added to the Ag-Cu-based active brazing material, is more preferable. The joining between the ceramic substrate S and the copper plates is performed using a brazing material paste containing the brazing material powder and an organic binder, as described above. For example, an Ag-Cu-based active brazing material having a melting point of 770 to 880°C is used as the brazing material, and the brazing temperature is preferably 770 to 880°C. If the brazing material is 770°C or higher, the brazing material is sufficiently melted and the formation of voids is suppressed. More preferably, the brazing temperature is 790°C or higher. If the brazing material is 880°C or lower, the brazing material does not wet and spread too much. More preferably, the brazing temperature is 830 to 870°C. The time to hold at the brazing temperature depends on the amount of material put into the bonding furnace, but considering normal productivity, it is preferably within 5 hours, and more preferably within 2 hours. The time to hold at the brazing temperature is set by adjusting appropriately according to the number of samples put in, and, for example, in the case of a vacuum atmosphere, according to the volume of the bonding furnace and the displacement of the vacuum pump. In order to bond the copper plate and ceramic without voids, it is preferable to apply a load to fix them during the placement process and then heat them in the bonding process.

When ordinary oxygen-free copper is used for the copper plate, there is a concern that the crystal grain size will grow to a size exceeding 300 μm when heated to the brazing temperature. In contrast, the copper plate using the copper alloy of the present invention containing more than 0.03 mass% and not more than 0.15 mass% Zr can suppress the average crystal grain size to 100 μm or less even when heated at the brazing temperature. Here, when the Zr content is 0.03 mass% or less, the average crystal grain size cannot be suppressed to 100 μm or less when heated to the brazing temperature. In addition, when the Zr content exceeds 0.15 mass%, the decrease in electrical conductivity is large, raising concerns that it will not be possible to ensure 96% or more of the IACS standard.

Furthermore, in the copper plate of the present invention, when heated to the brazing temperature, most of the Zr is dissolved in the copper matrix, and high electrical conductivity cannot be ensured in this state. Therefore, in order to ensure high electrical conductivity, the plate is slowly cooled from the brazing temperature to 350°C over a period of 50 minutes or more. This allows Zr to change from a state in which it is dissolved in the copper matrix in the temperature range from 550°C to 350°C to a state in which it forms a separate phase from the matrix and precipitates. By cooling slowly, sufficient time is ensured to pass through the above temperature range, and the precipitation of Zr progresses, the copper matrix becomes highly purified, and high electrical conductivity can be obtained. Note that if the cooling time from the brazing temperature to 350°C is shorter than 50 minutes, the precipitation of Zr becomes insufficient, and there is a concern that a conductivity of 96% or more cannot be ensured according to the IACS standard.

The content of unavoidable impurities in the copper plate is preferably suppressed to the same level as the content of impurities in oxygen-free copper, and more preferably to less than 0.04% by mass. The average crystal grain size of the copper plate is preferably 60 μm or less, more preferably 30 μm or less. It is more preferable that the thermal conductivity of the copper plate is 380 W/m·K or more. It is preferable that the average crystal grain size of the copper plate is G≦100 μm and the copper plate thickness T≧0.2 mm (T/G≧2.0). For example, when G=60 μm and T=0.3 mm, T/G=5.0, when G=60 μm and T=0.5 mm, T/G=8.3, and when G=60 μm and T=0.8 mm, T/G=13.3.

When acrylic resin is used as the organic binder contained in the brazing paste, deposits resulting from the gasified acrylic resin during the heating process are particularly likely to adhere to the ceramic substrate surface. Therefore, when acrylic resin is used as the organic binder, examples include polyacrylic acid ester and polymethacrylic acid ester. Methacrylic acid ester is preferably used.

(e) Circuit Pattern Forming Step With respect to the bonded body obtained in the bonding step, as shown in FIG. 5, resist films R1, R2 are formed on the surface of the copper plate M in a pattern that follows the outer edge of the brazing material layer formed in the bonding step, and the copper plate M is divided by etching to form circuit patterns M1, M2 as shown in FIG.

(f) Unnecessary brazing material layer removal step After the circuit pattern formation step (e), an unnecessary brazing material layer removal step can be provided for removing an unnecessary brazing material layer. The resist film is preferably formed in a pattern that follows the outer edge of the brazing material layer formed in the bonding step. The resist film formed in the circuit pattern formation step can be thinned to a thickness of 10 to 80 μm, preferably 30 to 70 μm. The resist film is desirably formed from an ultraviolet-curable resist agent.

For example, when using a chemical solution containing hydrogen peroxide and acidic ammonium fluoride as the brazing material remover, an aqueous solution containing 10 to 40 mass% (2.9 to 8.8 mol/L) hydrogen peroxide and 1 to 8 mass% (0.7 to 2.1 mol/L) acidic ammonium fluoride can be used. If the hydrogen peroxide is less than 10 mass%, the ability to remove the brazing material is insufficient, and if it exceeds 40 mass%, the copper plate is excessively corroded and the dimensional accuracy of the copper plate is deteriorated. If the acidic ammonium fluoride is less than 1 mass%, the ability to remove the reaction layer containing active metals generated at the bonding interface between the brazing material layer and the ceramic substrate is reduced, while if it exceeds 8 mass%, the crystal particles constituting the ceramic substrate are dissolved, reducing the electrical insulation and strength required of the ceramic substrate.

(g) Cleaning step In the cleaning step, the bonded body is immersed in a chemical to clean it. For example, if the oxygen in the atmosphere is not sufficiently reduced and the surface of the copper plate is oxidized in the heating step, this is not preferable because it may lead to a decrease in electrical conductivity and a decrease in solderability. Therefore, the bonded body is immersed in a chemical containing at least one selected from hydrogen peroxide, sulfuric acid, hydrochloric acid, and ammonium chloride to clean it, thereby removing the oxides on the surface of the copper plate. It is preferable to use sulfuric acid as the chemical.

After steps (e) to (g) above, any deposits that reduce the insulation resistance between the copper plates are removed or reduced.

Other processes may include (g) a cleaning process followed by (h) a plating process in which a plating layer of Ni, Au, Ag, etc. is formed on the surface of the copper plate. For example, when applying Ni plating, a Ni plating layer with a thickness of about 5 μm can be formed on the surface of the copper plate by immersing the plate for 20 to 30 minutes in an electroless plating solution (85°C) whose main component is nickel (Ni) and whose phosphorus (P) concentration is adjusted to 8 mass%.

The present invention will be described in the following examples, but is not limited to these.

(Example)
The common parts of the examples will be explained as [(a) preparation step] to [(g) cleaning step], and then the copper plate and the joining step will be explained in Examples 1 to 4 and Reference Examples 1 to 5.

[(a) Preparation process]
A copper plate, a brazing material, and a ceramic substrate are prepared. As the ceramic substrate S, a silicon nitride substrate (30 mm and 40 mm in length and width, and 0.32 mm in thickness) containing 93 mass% Si3N4, 4 mass% Mg in oxide equivalent, and 3 mass% Y in oxide equivalent in 100 mass parts of the total raw material powder is used. As the brazing material, a brazing material paste is used, which is a mixture of 5.3 mass parts of polyacrylic acid ester as an organic binder, 19.1 mass parts of α-terpineol as an organic solvent, and 0.5 mass parts of polyoxyalkylene alkyl ether and alkylbenzene sulfonate as dispersants, with 100 mass parts of brazing material powder adjusted to have a composition of 70.6 mass% Ag, 2.9 mass% In, 1.9 mass% Ti, and the remainder Cu and a trace amount of impurities.

The manufacturing method of the ceramic circuit board S will be described with reference to Figures 3 to 6, which are plan views showing each process. Note that in the manufacturing process of the ceramic circuit board S described below, the content of each process for forming the copper plates M1 and M2, which are the circuit boards, and the copper plate M3, which is the heat sink, is basically the same, so only the copper plates M1 and M2 will be described in detail, and copper plate M3 will be omitted.

[(b) Brazing material region forming step]
As shown in Fig. 3, two brazing filler metal regions c1, c2, each having a thickness of 40 µm, are formed on the upper surface (one surface) of the ceramic substrate S by applying brazing filler metal paste by screen printing in a planar direction with a gap G therebetween. In the paper surface shown in Fig. 3, the size of the first brazing filler metal region c1 is 27.6 mm and 11.6 mm in length and width, respectively, the size of the second brazing filler metal region c2 is 27.6 mm and 23.6 mm in length and width, respectively, and the distance between the brazing filler metal regions c1 and c2 in the gap G is 1.0 mm.

[(c) Placing step]
After the brazing material region forming process, as shown in FIG. 4, a copper plate M having a thickness of 0.5 mm and a size sufficient to cover the brazing material regions c1, c2 is placed on the brazing material regions c1, c2, and the ceramic substrate S, the brazing material regions c1, c2 and the copper plate M are laminated and fixed using a jig.

[(d) Bonding process]
The copper plate M is inserted into a heating furnace and heated in a vacuum atmosphere to bond the ceramic substrate S and the copper plate M via the brazing layers C1 and C2 to form a bonded body. Taking into consideration the thermal expansion of the copper plate M during the bonding process, the copper plate M has a length and width of 29.5 mm and 39.5 mm, respectively, in the plane of the paper shown in FIG. 4, which is smaller than the size of the ceramic substrate S.

The joining process is carried out using a temperature pattern that includes a holding step in which the material is held at 400°C, the removal temperature of the acrylic resin, which is an organic binder, for 10 hours, a heating step in which the material is heated at a constant rate from the holding step, a heating step (brazing step) in which the material is held at 770°C to 880°C, the melting temperature of the brazing material, for 1 hour, a cooling step in which the temperature is lowered to 350°C over a period of 50 minutes or more after the heating step, and a step in which the temperature is lowered from 350°C to room temperature.

[(e) Circuit Pattern Forming Process]
After the joining process, as shown in Fig. 5, two resist films R1 and R2 are formed in a desired pattern on the surface of the copper plate M constituting the joint body, and then etching is performed to remove unnecessary parts of the copper plate M, and two copper plates M1 and M2 are formed as circuit patterns with a gap G in the planar direction as shown in Fig. 6. Specifically, a joint body in which an ultraviolet-curable etching resist is applied to the surface of the copper plate M by a screen printing method in a pattern corresponding to the dimensions of the first copper plate M1 and the second copper plate M2 described below is immersed in an etching solution [ferric chloride (FeCl3) solution (46.5Be)] at a liquid temperature of 50°C to form the copper plates M1 and M2. In addition, in the paper surface shown in Fig. 6, the length and width of the first copper plate M1 are 28 mm and 12 mm, respectively, and the length and width of the second copper plate M2 are 28 mm and 24 mm, respectively.

(f) Unnecessary brazing material layer removal process
As shown in FIG. 6, the resist film formed on the surfaces of the copper plates M1 and M2 is removed, and the unnecessary brazing material layer protruding from the outer edges of the copper plates M1 and M2 is removed with a brazing material remover containing 7.6 mol/L of hydrogen peroxide and acidic ammonium fluoride at a liquid temperature of 40° C. for a treatment time of 40 minutes.

[(g) Washing step]
The ceramic circuit board is washed by immersing it in sulfuric acid having a concentration of 1 mol/L and a temperature of 50° C. for 10 minutes, and then the washing liquid is removed and the board is dried to obtain the circuit board.

For copper plate, the average crystal grain size can be measured using the cutting method of the copper grain size test method specified in JIS H0501. After polishing the surface of the copper plate to a mirror finish with polishing paper and alumina abrasive grains, the surface is etched with ammonia water to which hydrogen peroxide has been added to reveal the crystal grain boundaries. After photographing the revealed crystal structure using a microscope, a line of known length is drawn on the photograph, and the number of crystal grains that are completely cut by the line is counted and the average cut length is taken as the average crystal grain size.

The conductivity of copper plates can be measured, for example, using a Sigma Test eddy current conductivity meter manufactured by Forster. An AC magnetic field is generated by a probe in contact with the surface of the copper plate, and the conductivity is measured by using the probe to detect the strength of eddy currents generated in the copper plate by changes in the magnetic field. With the Sigma Test, the measured conductivity value can be expressed in both % units according to the IACS standard and MS/m units according to the SI system of units.

It is difficult to measure the thermal conductivity of only the copper plate when it is joined to the ceramic substrate. However, it is known that there is a proportional relationship between thermal conductivity and electrical conductivity, known as the Wiedemann-Franz law. Therefore, the thermal conductivity of the copper plate can be calculated from the measured electrical conductivity using the following formula based on the Wiedemann-Franz law.

K = L T σ
K: Thermal conductivity (W/m K)
σ: Electrical conductivity (S/m)
L: Corrected Lorentz number for copper at 20°C, 2.3 x 10-8 W/S K2
T: Temperature (K)

The reasons for the Zr content of the copper plate specified in this invention are explained with examples and reference examples. In Examples 1 to 4, in which the Zr content satisfies the range specified in this invention, the copper plate has a small average crystal grain size of 100 μm or less, and has excellent bonding properties with ceramic substrates. In addition, the electrical conductivity of the copper plate is 96% or more of the IACS standard, and the thermal conductivity is 375 W/m·K or more. In Examples 1 to 4, an arbitrary 120 μm wide area was observed, but it was smooth, with no recesses of 20 μm or more in width.

Example 1
For the configuration described in [(a) Preparation Process] to [(g) Cleaning Process], a copper plate with a Zr content of 0.04 mass% was used in [(d) Joining Process]. In the brazing process, the atmosphere temperature was adjusted to 800°C using a brazing device, and the holding time was 1 h (heating process). After that, the atmosphere temperature was lowered from the brazing temperature to 350°C over 50 minutes (temperature lowering process). The average crystal grain size of the copper plate was measured for the fabricated circuit board, and was 60 μm. In addition, an arbitrary 120 μm wide area was observed at the interface between the copper plate and the brazing material layer, and it was smooth. In addition, the electrical conductivity of the copper plate was measured, and was 98% of the IACS standard. The thermal conductivity calculated from the measured electrical conductivity was 383 W/m·K.

Example 2
Regarding the configuration described in [(a) Preparation process] to [(g) Cleaning process], a copper plate having a Zr content of 0.07 mass% was used in [(d) Joining process]. In the brazing process, the brazing temperature was 800°C as in Example 1, and the holding time was 1 h (heating process). Thereafter, the atmospheric temperature was lowered from the brazing temperature to 350°C over 50 minutes as in Example 1 (temperature lowering process). The average crystal grain size of the copper plate was measured for the fabricated circuit board and found to be 30 μm. In addition, an arbitrary 120 μm wide region was observed at the interface between the copper plate and the brazing material layer, and found to be smooth. In addition, the electrical conductivity of the copper plate was measured and found to be 97% of the IACS standard. The thermal conductivity calculated from the measured electrical conductivity was 379 W/m·K.

Example 3
Regarding the configuration described in [(a) Preparation process] to [(g) Cleaning process], a copper plate with a Zr content of 0.15 mass% was used in [(d) Joining process]. In the brazing process, the brazing temperature was 800°C as in Example 1, and the holding time was 1 h (heating process). Thereafter, the atmospheric temperature was lowered from the brazing temperature to 350°C over 50 minutes as in Example 1 (temperature lowering process). The average crystal grain size of the copper plate was measured for the fabricated circuit board and found to be 15 μm. In addition, an arbitrary 120 μm wide area was observed at the interface between the copper plate and the brazing material layer, and found to be smooth. In addition, the electrical conductivity of the copper plate was measured and found to be 96% of the IACS standard. The thermal conductivity calculated from the measured electrical conductivity was 375 W/m·K.

Example 4
Regarding the configuration described in [(a) Preparation process] to [(g) Cleaning process], a copper plate with a Zr content of 0.04 mass% was used in [(d) Joining process]. In the brazing process, the brazing temperature was set to 880°C, and the holding time was set to 1 h (heating process). Thereafter, the atmospheric temperature was lowered from the brazing temperature to 350°C over 50 minutes (temperature lowering process) as in Example 1. The average crystal grain size of the copper plate was measured for the fabricated circuit board, and was 100 μm. In addition, an arbitrary 120 μm wide region was observed at the interface between the copper plate and the brazing material layer, and it was smooth. In addition, the electrical conductivity of the copper plate was measured, and was 98% of the IACS standard. The thermal conductivity calculated from the measured electrical conductivity was 383 W/m·K.

Compared to the above examples, in Reference Example 1, in which the Zr content is less than the range specified by the present invention, the average crystal grain size of the copper plate exceeds 100 μm, and the bondability of the ceramic substrate is reduced. In addition, in Reference Example 2, in which the Zr content is greater than the range specified by the present invention, the electrical conductivity of the copper plate is less than 96% of the IACS standard, and the thermal conductivity is also less than 375 W/m·K.

・Reference example 1
Regarding the configuration described in [(a) Preparation process] to [(g) Cleaning process], a copper plate with a Zr content of 0.03 mass% was used in [(d) Joining process]. In the brazing process, the brazing temperature was set to 800°C as in Example 1, and the holding time was set to 1 h (heating process). Thereafter, the atmospheric temperature was lowered from the brazing temperature to 350°C over 50 minutes as in Example 1 (temperature lowering process). The average crystal grain size of the copper plate was measured for the fabricated circuit board, and was found to be 110 μm. In addition, an arbitrary 120 μm wide area was observed at the interface between the copper plate and the brazing material layer, and one recess with a width of about 20 μm was found. In addition, the electrical conductivity of the copper plate was measured, and was 98% of the IACS standard. The thermal conductivity calculated from the measured electrical conductivity was 383 W/m·K.
・Reference example 2

For the configuration described in [(a) Preparation process] to [(g) Cleaning process], a copper plate with a Zr content of 0.18 mass% was used in [(d) Joining process]. The brazing process was performed at a brazing temperature of 800°C, as in Example 1, and the holding time was 1 h (heating process). Then, as in Example 1, the ambient temperature was lowered from the brazing temperature to 350°C over 50 minutes (temperature lowering process). The average crystal grain size of the copper plate was measured for the manufactured circuit board and found to be 15 μm. In addition, an arbitrary 120 μm wide area was observed at the interface between the copper plate and the brazing material layer, and found to be smooth. The electrical conductivity of the copper plate was measured and found to be 95% of the IACS standard. The thermal conductivity calculated from the measured electrical conductivity was 371 W/m·K.

The reasons for the temperature range of the heating step and the cooling time of the cooling step in the bonding process specified in this invention will be explained with examples and reference examples. In the above-mentioned Examples 1 to 4, the temperature of the heating step and the cooling time of the cooling step satisfy the ranges specified in this invention, and in all cases the average crystal grain size of the copper plate is small at 100 μm or less, providing excellent bonding properties for ceramic substrates. In addition, the electrical conductivity of the copper plate is 96% or more of the IACS standard, and the thermal conductivity is 375 W/m·K or more.

Reference Examples 3 and 4 are examples in which the temperature of the heating process falls outside the range specified by the present invention. In Reference Example 3, where the temperature is less than 770°C, the solder material is not melted sufficiently, resulting in a decrease in the bondability of the ceramic substrate. In Reference Example 4, where the temperature exceeds 880°C, the solder material spreads too much, resulting in a decrease in the bondability of the ceramic substrate. In addition, if the temperature is too high, there is a risk that the average crystal grain size of the copper plate will exceed 100 μm.

Reference Example 5 is an example in which the cooling time in the temperature-lowering step is shorter than the time specified in the present invention. In this case, the electrical conductivity of the copper plate is below 96% of the IACS standard, and the thermal conductivity is also below 375 W/m·K.

・Reference example 3
For the configuration described in [(a) Preparation process] to [(g) Cleaning process], a copper plate with a Zr content of 0.04 mass% was used in [(d) Joining process]. In the brazing process, the brazing temperature was set to 750°C and the holding time was set to 1 h (heating process). After that, the atmospheric temperature was lowered from the brazing temperature to 350°C over 50 minutes (temperature lowering process). The average crystal grain size of the copper plate was measured for the fabricated circuit board and found to be 30 μm. In addition, when an arbitrary 120 μm wide area was observed at the interface between the copper plate and the brazing material layer, two recesses with a width of about 20 μm were found. In addition, the electrical conductivity of the copper plate was measured and found to be 98% of the IACS standard. The thermal conductivity calculated from the measured electrical conductivity was 383 W/m·K.

・Reference example 4
Regarding the configuration described in [(a) Preparation process] to [(g) Cleaning process], a copper plate with a Zr content of 0.04 mass% was used in [(d) Joining process]. In the brazing process, the brazing temperature was set to 900°C and the holding time was set to 1 h (heating process). After that, the atmospheric temperature was lowered from the brazing temperature to 350°C over 50 minutes (temperature lowering process). The average crystal grain size of the copper plate was measured for the fabricated circuit board and found to be 110 μm. In addition, an arbitrary 120 μm wide area was observed at the interface between the copper plate and the brazing material layer, and one recess with a width of about 20 μm was found. In addition, the electrical conductivity of the copper plate was measured and found to be 98% of the IACS standard. The thermal conductivity calculated from the measured electrical conductivity was 383 W/m·K.

・Reference example 5
Regarding the configuration described in [(a) Preparation process] to [(g) Cleaning process], a copper plate with a Zr content of 0.04 mass% was used in [(d) Joining process]. In the brazing process, the brazing temperature was 800°C, and the holding time was 1 h, as in Example 1 (heating process). After that, the atmospheric temperature was lowered from the brazing temperature to 350°C over 30 minutes (temperature lowering process). The average crystal grain size of the copper plate was measured for the fabricated circuit board, and was 60 μm. In addition, an arbitrary 120 μm wide region was observed at the interface between the copper plate and the brazing material layer, and it was smooth. In addition, the electrical conductivity of the copper plate was measured, and was 95% of the IACS standard. The thermal conductivity calculated from the measured electrical conductivity was 371 W/m·K.

A, B: spherical electrode,
C1, C2, C3: brazing material layer,
c1, c2: brazing material region,
G: Gap;
M1, M2, M3: metal substrate,
M: metal substrate,
R1, R2: resist film,
S: ceramic substrate,
W: Ceramic circuit board

Claims (6)

A ceramic circuit board comprising a copper plate bonded to one surface of a ceramic substrate via a brazing material layer,
The ceramic substrate has pores on its surface each having a diameter of 15 μm or less,
The copper plate has an average crystal grain size of 100 μm or less according to the cutting method of the crystal grain size test method for drawn copper products specified in JIS H0501:1986, and an electrical conductivity of 96% or more but less than 100% of the IACS standard.
Ceramic circuit board. The copper plate has a thermal conductivity of 375 W/m·K or more.
2. The ceramic circuit board according to claim 1. The ceramic substrate is a silicon nitride sintered substrate.
3. The ceramic circuit board according to claim 1 or 2. The copper plate has an average crystal grain size of 60 μm or less.
The ceramic circuit board according to any one of claims 1 to 3. The copper plate has a thickness of 0.2 mm or more.
The ceramic circuit board according to any one of claims 1 to 4. The interface between the copper plate and the brazing material layer does not have a recess with a width of 20 μm or more.
The ceramic circuit board according to any one of claims 1 to 5.

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