Ceramic copper circuit board, semiconductor device, and method for manufacturing ceramic copper circuit board

Abstract

The present invention provides: a ceramic copper circuit board which is capable of improving electric conductivity, bonding strength, or TCT characteristics of a copper circuit part; a semiconductor device; and a method for manufacturing a ceramic copper circuit board. A ceramic copper circuit board according to an embodiment of the present invention comprises: a ceramic substrate; and a copper circuit part that is provided on the ceramic substrate by the intermediary of a bonding layer. The bonding layer contains copper, an active metal, and one or more elements that are selected from among tin and indium, and has a first bonding interface between the bonding layer and the ceramic substrate and a second bonding interface between the bonding layer and the copper circuit part. When ten or more measurement areas are set in the bonding layer in the thickness direction from the first bonding interface to the second bonding interface, and mass% of copper in each of the measurement areas is plotted, the plots of the mass% of copper have a downward peak, and the downward peak is located within a range of 40% to 90% inclusive of the thickness of the bonding layer from the first bonding interface.

Description

Ceramic copper circuit board, semiconductor device, and method for manufacturing ceramic copper circuit board

[0001] The embodiments generally relate to a ceramic copper circuit board, a semiconductor device, and a method for manufacturing a ceramic copper circuit board.

[0002] In a ceramic copper circuit board, a copper circuit portion is bonded to a ceramic substrate. Bonding between a ceramic substrate and a copper circuit portion can be divided into two main forms. One is a form in which the ceramic substrate and copper are directly bonded. The other is a form in which the ceramic substrate and copper are indirectly bonded via a bonding layer. In particular, ceramic copper circuit boards that use an active metal brazing filler metal containing an active metal such as titanium (Ti) as a bonding layer have high bonding strength and heat cycle characteristics. Semiconductor devices that incorporate semiconductor elements such as power elements on such highly reliable ceramic copper circuit boards are used in devices that handle high voltages or large currents, such as automobiles (including electric vehicles), electric railway vehicles, solar power generation facilities, and inverters for industrial machinery.

[0003] As power modules become smaller, lighter, and more densely packed, ceramic copper circuit boards are also required to have higher properties and reliability, and various manufacturing methods have been devised. For example, Japanese Patent No. 6789955 (Patent Document 1) discloses a ceramic copper circuit board in which the peel strength is improved and cracks are prevented by controlling the size and hardness of the bonding layer that protrudes from between the ceramic substrate and the metal plate. Furthermore, Patent Document 1 also discloses a ceramic copper circuit board that has improved TCT (thermal cycle test) characteristics and increased resistance to stress caused by heat generation from semiconductor elements.

[0004] Patent No. 6789955

[0005] Ceramics and copper (Cu) components using active metal brazing filler metals are typically joined by heating at temperatures between 800 and 900°C. In contrast, joining is performed at lower temperatures to reduce energy costs and mitigate the thermal expansion difference between ceramics and metals. One commonly used method for lowering the joining temperature is to add low-melting-point metals such as tin (Sn) or indium (In) to the active metal brazing filler metal to lower the melting temperature. However, tin and indium are prone to diffusion due to their low melting points. The diffusion of tin or indium into copper components used in circuits reduces the electrical conductivity of the circuit. Furthermore, uneven diffusion of tin or indium into copper components can cause variations in the joining, resulting in reduced joint strength and TCT characteristics.

[0006] The embodiments are intended to solve these problems, and provide a ceramic copper circuit board, a semiconductor device, and a method for manufacturing a ceramic copper circuit board that can improve the electrical conductivity, bonding strength, or TCT characteristics of the copper circuit portion.

[0007] A ceramic copper circuit board according to an embodiment includes a ceramic substrate and a copper circuit portion provided on the ceramic substrate via a bonding layer. The bonding layer includes copper, an active metal, and at least one selected from tin and indium, and has a first bonding interface with the ceramic substrate and a second bonding interface with the copper circuit portion. Ten or more measurement areas are set on the bonding layer in the thickness direction from the first bonding interface to the second bonding interface. When the mass percent of copper in each measurement area is plotted, the plot of the mass percent of copper has a downward peak, and the downward peak is located within a range of 40% to 90% of the thickness of the bonding layer from the first bonding interface.

[0008] 3(a) to 3(c). A side view showing an example of a ceramic copper circuit board according to an embodiment. An enlarged cross-sectional view showing part A of the bonding layer in the ceramic copper circuit board shown in FIG. 1. A graph showing an example of a plot of an analysis result by SEM-EDX. A graph showing the first-order differential results of the plots shown in FIGS. 3(a) to 3(c). A side view showing an example of a semiconductor device according to an embodiment. A flowchart showing an example of a manufacturing method according to an embodiment. A side view showing an example of a kneading process.

[0009] The present embodiment will be described below with reference to the drawings. Each drawing is an example of the description of the embodiment, and is not limited to the illustrated form. Furthermore, the drawings are schematic or conceptual, and the relationship between the thickness and width of each part, the size ratio between parts, etc. are not necessarily the same as in reality. In the present specification and each drawing, elements similar to those already described are assigned the same reference numerals, and detailed description will be omitted as appropriate.

[0010] Fig. 1 is a side view showing an example of a ceramic copper circuit board. In Fig. 1, reference numeral 1 denotes a ceramic copper circuit board, reference numeral 2 denotes a ceramic substrate, reference numeral 3 denotes a copper circuit portion, reference numeral 4 denotes a bonding layer containing a brazing material, and reference numeral 5 denotes a back copper plate. The ceramic substrate 2 has a front surface 2a (first surface) and a back surface 2b (second surface). The copper circuit portion 3 is bonded to the front surface 2a of the ceramic substrate 2 via a bonding layer 4.

[0011] In the example shown in FIG. 1, multiple copper circuit portions 3 are bonded to the front surface 2a via multiple bonding layers 4. One copper circuit portion 3 or three or more copper circuit portions 3 may be bonded to the front surface 2a. Also, in the example shown in FIG. 1, a back copper plate 5 is bonded to the back surface 2b. The back copper plate 5 functions as a heat sink rather than a circuit. The back copper plate 5 is provided as needed. Instead of the back copper plate 5, a patterned copper circuit portion may be provided on the back surface 2b.

[0012] FIG. 2 is an enlarged cross-sectional view showing portion A of the bonding layer in the ceramic copper circuit board shown in FIG. 1 . As shown in FIG. 2 , the bonding layer 4 includes a first bonding interface 4a between the ceramic substrate 2 and the bonding layer 4 and a second bonding interface 4b between the ceramic substrate 2 and the copper circuit portion 3. In the ceramic copper circuit board 1 according to the embodiment, 10 or more measurement areas M are set in the thickness direction from the first bonding interface 4a to the second bonding interface 4b. When the mass percentage of copper in each measurement area M is plotted, the plot of the mass percentage of copper has a downward peak. This downward peak is located within a range of 40% to 90% of the thickness of the bonding layer 4 from the first bonding interface 4a. The mass percentage of elements in the measurement area M is measured using a scanning electron microscope-energy dispersive X-ray fluorescence analyzer (SEM-EDX). The SEM used is a JEOL JSM-IT100 or an apparatus with equivalent or better performance. The EDX used is a JEOL EX-9440IT4L11 or an apparatus with equivalent or better performance. The SEM may be a Field Emission (FE)-SEM. EDX is also called EDS.

[0013] The analysis method for the bonding layer 4 is as follows. First, an arbitrary cross section of the ceramic copper circuit substrate 1 is observed using an SEM. In the SEM electron image, the ceramic substrate 2, bonding layer 4, and copper circuit portion 3 are observed to have different colors, shapes, etc. The positions of the ceramic substrate 2, bonding layer 4, and copper circuit portion 3 are determined based on their appearance. To ensure that the entire thickness of the bonding layer 4 is included in the measurement range, multiple measurement areas M are set, as shown in Figure 2, from the interior of the ceramic substrate 2 to the interior of the copper circuit portion 3. The size of each measurement area is 120 μm or more in length × any desired thickness. "Length" refers to the dimension in the direction perpendicular to the direction connecting the ceramic substrate 2 and the copper circuit portion 3. If the length is shorter than 120 μm, the measurement results may fluctuate significantly due to partial composition bias, making it difficult to accurately measure the peak position. There is no upper limit to the length, but it is preferably 280 μm or less. "Thickness" refers to the dimension in the direction connecting the ceramic substrate 2 and the copper circuit portion 3. The components of each measurement area are analyzed by EDX.

[0014] From the analysis results, the mass % of copper was calculated, assuming that the total content of the active metal, one or more selected from tin and indium, and the main component of the ceramic substrate 2 was 100 mass %, and the calculated mass % was plotted on a graph from the ceramic substrate 2 side toward the copper circuit portion 3 side. In the graph, the mass % of copper decreases from the bonding layer 4 toward the ceramic substrate 2. With the direction from the bonding layer 4 toward the copper circuit portion 3 defined as "up" and the direction from the bonding layer 4 toward the ceramic substrate 2 defined as "down," the bottom line BL1 of the measurement area where the mass % of copper is 1% or more is the first bonding interface 4a identified from the analysis results. Furthermore, in the graph, the mass % of copper increases from the bonding layer 4 toward the copper circuit portion 3. The bottom line BL2 of the measurement area where the mass % of copper exceeds 90% is the second bonding interface 4b identified from the analysis results. In other words, this bottom line BL2 is also the top line of the measurement area where the mass % of copper is less than 90% but closest to 90%. At this time, if the number of measurement areas between the first bonding interface 4 a and the second bonding interface 4 b is nine or less, ten or more measurement areas M are set again between the determined first bonding interface 4 a and the second bonding interface 4 b, and the components of each measurement area M are analyzed again. In addition, in this explanation, the ceramic substrate 2 side of the ceramic copper circuit board 1 is defined as the bottom, and the copper circuit portion 3 side is defined as the top.

[0015] The SEM measurement conditions are set to an acceleration voltage of 15 kV and a magnification of 500 to 3000 times. The SEM-EDX measurement conditions are set to a scan count of 50 and a dwell time of 0.2 ms. The dwell time is the measurement speed per pixel. For area analysis, the capture pixel count is set to 512 pixels horizontally x 384 pixels vertically, the detection count is set to 8000 to 14000 cps (Counts Per Second), and the quantitative map is set to 5 x 5 bits / point.

[0016] The ceramic substrate is made of silicon nitride (Si ３ N ４When the ceramic substrate is an alumina (AlN) substrate, the main components of the ceramic substrate are silicon (Si) and nitrogen (N). When the ceramic substrate is an aluminum nitride (AlN) substrate, the main components of the ceramic substrate are aluminum (Al) and nitrogen (N). In the case of oxide ceramics, the main components other than oxygen are the measurement targets. For example, when the ceramic substrate is an alumina (Al ２ O ３ ), only aluminum is measured. Each element contained in the ceramic copper circuit board 1 can be oxidized. Therefore, if oxygen (O) is included in the measurement target, it becomes difficult to accurately obtain the original component distribution of the bonding surface due to the influence of oxidation, etc.

[0017] Copper has a relatively low melting point as a metal and melts easily at temperatures suitable for brazing. For this reason, copper is widely used as a brazing material component. Copper alloys can further lower the melting point. Using copper alloys as brazing materials allows copper components to be joined to ceramic substrates without melting them. Copper also has the excellent fluidity and permeability required for brazing. Copper easily spreads between components using capillary action, contributing to the strength and durability of the brazed joint. Furthermore, copper does not easily generate stress between ceramics or copper components. Therefore, using copper reduces cracking and deformation of the joint during the cooling process after brazing. Copper has excellent thermal and electrical conductivity, which does not adversely affect the functionality of the brazed joint.

[0018] Examples of active metals added to brazing filler metals include titanium, zirconium (Zr), and hafnium (Hf). Active metals react with ceramics that have poor wettability with metals, reducing interfacial energy and improving wettability. Improved wettability allows the brazing filler metal to penetrate more easily into gaps between components, improving joint strength. Active metals also form metallic bonds between the atoms of the base metal and brazing filler metal, creating a solid solution at the joint interface and contributing to improved strength and durability of the joint.

[0019] In addition to the active metal, the brazing filler metal contains one or more selected from tin and indium. The melting point of tin is 232°C, and the melting point of indium is 157°C. The melting point of copper is 1085°C, the melting point of titanium is 1666°C, the melting point of zirconium is 1852°C, and the melting point of hafnium is 2233°C. The melting points of tin and indium are lower than the melting points of the other metals contained in the bonding layer 4. By adding one or more low-melting point metals selected from tin and indium to the active metal brazing filler metal, the melting temperature of the brazing filler metal can be lowered.

[0020] However, when a low-melting-point metal is heat-treated for bonding, diffusion begins earlier than with other metals. For this reason, low-melting-point metals are more likely to diffuse toward the copper circuit portion 3 than other metals. If a large amount of tin or indium diffuses into the copper circuit portion 3, the mechanical strength of the copper circuit portion 3 or the bonding strength of the ceramic copper circuit board 1 may decrease. In addition, tin or indium hinders the free movement of electrons. This may decrease the conductivity of the copper circuit portion 3, resulting in a decrease in the electrical conductivity of the copper circuit portion 3.

[0021] 3(a) to 3(c) are graphs showing examples of plots of the analysis results by SEM-EDX. In Fig. 3(a) to 3(c), the horizontal axis represents the position (X) in the thickness direction, and the vertical axis represents mass % (wt%).

[0022] 3(a) is an example in which each measurement area M shown in FIG. 2 is analyzed by SEM-EDX and the mass % of copper is plotted based on the analysis results. In the example shown in FIG. 3(a), at least 14 measurement areas M are plotted from the ceramic substrate 2 toward the copper circuit portion 3. １ ~M １４ The mass % of the constituent elements in each measurement area is measured. １ The lower end line of the measurement area M １４ Since the copper composition ratio in the measurement area above reaches 90 mass%, the measurement area M １４ The upper end line of the second bonded interface 4b is identified as the second bonded interface 4b.

[0023] As shown in FIG. 3A, a downward peak Pc is present in the plot of copper mass %. The peak Pc is located within a range of 40% to 90% of the thickness of the bonding layer 4 from the first bonding interface 4a. In other words, the ratio Lc / L of the distance Lc from the first bonding interface 4a to the peak Pc to the distance L from the first bonding interface 4a to the second bonding interface 4b is 40% to 90%. Hereinafter, the ratio Lc / L will be simply referred to as "Lc / L".

[0024] 3(a), as the analysis proceeds from a point where copper is not substantially detected (where the copper mass is below the detection limit) toward the copper circuit portion 3, copper in the bonding layer 4 begins to be detected, and the copper mass percentage increases. Finally, when the analysis reaches the copper circuit portion 3, the detected copper mass percentage is 100 mass% or approximately 100 mass%. In other words, as the analysis proceeds from the ceramic substrate 2 side toward the copper circuit portion 3 side, a plot that generally slopes upward to the right is obtained.

[0025] In the ceramic copper circuit board 1 according to the embodiment, a downward peak Pc is present in the plot of copper mass %, and the distance Lc is within the range of 40% to 90% of the distance L. That is, the copper content is locally reduced at positions where Lc / L is 40% to 90%. At the locations where the copper content is locally reduced, the content of other constituent elements (active metal, tin, or indium) in the bonding layer 4 increases.

[0026] For example, in order to obtain the aforementioned effects such as a lowered melting point, it is effective to disperse tin or indium in the bonding layer 4. On the other hand, if tin or indium diffuses into the copper circuit portion 3, it may deteriorate the characteristics of the copper circuit portion 3. For this reason, it is preferable that the amount of tin and indium is small near the copper circuit portion 3.

[0027] The fact that Lc / L is in the range of 40% or more and 90% or less indicates that at least one selected from the active metal, tin, and indium remains locally in large amounts within a range of 40% or more and 90% or less of the distance L from the first bonding interface 4a.

[0028] When Lc / L is less than 40%, tin or indium is unevenly distributed near the ceramic substrate 2, and tin or indium is not sufficiently diffused throughout the bonding layer 4. This distribution can result from insufficient reduction in the bonding temperature. When the reduction in the bonding temperature is insufficient, the metal components of the bonding layer 4 are less likely to melt, resulting in poor bonding. Alternatively, to resolve this issue, the bonding temperature must be increased. On the other hand, when Lc / L exceeds 90%, tin or indium is locally abundant near the copper circuit portion 3. The tin or indium present near the copper circuit portion 3 can cause deformation of the copper circuit portion 3. This distribution can also result from uneven diffusion of tin and indium into the copper circuit portion 3 during the bonding process. When tin or indium is abundant near the copper circuit portion 3, it is highly likely that uneven diffusion into the copper circuit portion 3 occurs in the bonded body, which can result in variations in bonding strength.

[0029] For example, when tin or indium is present in a large amount within a range of 40% to 90% of the distance L from the first bonding interface 4a, the proportion of tin or indium within a range of 10% or less of the distance L from the second bonding interface 4b can be reduced, thereby suppressing the diffusion of tin or indium into the copper circuit portion 3. Furthermore, since the active metal bonds with tin or indium in the bonding layer to form a compound, the presence of a large amount of active metal within a range of 40% to 90% of the distance L from the first bonding interface 4a further suppresses the diffusion of tin or indium into the copper circuit portion 3.

[0030] If the downward peak Pc does not exist, it is possible that constituent elements other than copper have diffused uniformly. In such a case, although not as severe as when Lc / L exceeds 90%, it is similarly the result of tin or indium diffusing into the copper circuit portion 3. This may result in variations in bonding strength.

[0031] In the ceramic copper circuit board 1 according to the embodiment, peaks of elements other than copper may be present in the plot of mass % from the first bonding interface 4a to the second bonding interface 4b of the bonding layer 4. For example, one or more upward peaks selected from the mass % of the active metal, the mass % of tin, and the mass % of indium may be present at a position 40% to 90% of the thickness of the bonding layer 4 from the first bonding interface 4a. The mass % of the active metal, tin, and indium may be measured simultaneously with the mass % of copper.

[0032] FIG. 3(b) is an example of a plot of the mass percentage of titanium, an active metal component. The plot in FIG. 3(b) is obtained from the results of SEM-EDX analysis of each measurement area M shown in FIG. 2. If the bonding layer 4 contains an active metal other than titanium, a plot similar to that in FIG. 3(b) is obtained for the other active metal. In the example plot shown in FIG. 3(b), multiple upward peaks are present. Of the multiple peaks, the peak closest to the copper circuit portion 3 is designated as peak Pa. The ratio La / L of the distance La from the first bonding interface 4a to peak Pa to the distance L of the bonding layer 4 is 40% or more and 90% or less. Hereinafter, the ratio La / L will be simply referred to as "La / L."

[0033] In order to suppress variations in the bonding strength between ceramic and metal, it is effective for the active metal to remain within the bonding layer 4. With respect to the peak Pa closest to the copper circuit portion 3, an La / L ratio of 40% or more and 90% or less indicates that the active metal is present locally in the bonding layer 4. As described above, the active metal bonds with tin or indium to form a compound, so that an La / L ratio of 40% or more and 90% or less can suppress the diffusion of tin or indium into the copper circuit portion 3, thereby improving the bonding strength between the ceramic substrate 2 and the copper circuit portion 3.

[0034] FIG. 3(c) is an example of a plot of tin by mass %. The plot in FIG. 3(c) is also obtained from the results of SEM-EDX analysis of each measurement area M shown in FIG. 2. When the bonding layer 4 contains indium, a plot similar to that in FIG. 3(c) is obtained for indium. The plot for tin may include multiple peaks. The peak closest to the copper circuit portion 3 in the plot is designated as peak Ps. The ratio Ls / L of the distance Ls from the first bonding interface 4a to peak Ps relative to the distance L of the bonding layer 4 is 40% or more and 90% or less. Hereinafter, the ratio Ls / L will be simply referred to as "Ls / L".

[0035] In order to obtain the aforementioned effects, such as lowering the melting point, it is effective to uniformly disperse tin within the bonding layer 4. On the other hand, when tin diffuses into the interior of the copper circuit portion 3, it degrades the characteristics of the copper circuit portion 3. With respect to the peak Ps closest to the copper circuit portion 3, an Ls / L ratio of 40% to 90% indicates that the mass percentage of tin is locally increased at a position 10% or more of the distance L from the copper circuit portion 3 (second bonding interface 4b). As a result of suppressing the diffusion of tin into the copper circuit portion 3, Ls / L is 40% to 90%, and the characteristics of the copper circuit portion 3 can be improved.

[0036] In the example shown in FIG. 3(a), in the plot of copper mass %, the peak top of peak Pc is located in the measurement area M ９ In the example shown in FIG. 3(b), in the plot of the mass % of the active metal, the peak top of the peak Pa is located in the measurement area M ９ In the example shown in FIG. 3(c), in the plot of tin mass %, the peak top of peak Ps is located in the measurement area M ９ That is, peak Pc, peak Pa, and peak Ps are all located in the same measurement area.

[0037] The position of the mass % peak for each component described above is determined from the differential value of the mass % for each component. Specifically, a first mass % graph is obtained by plotting the mass % measurement results for each component from the first bonding interface 4a to the second bonding interface 4b. A second mass % graph is obtained by first-order differentiation of this first mass % graph. In the second mass % graph, the points where the value changes from negative to positive are the minimum points in the first mass % graph. In the second mass % graph, the points where the value changes from positive to negative are the maximum points in the first mass % graph.

[0038] For example, the position where the value changes from negative to positive in the second weight percent graph for copper is the position of the downward peak in the first weight percent graph, and the position where the value changes from positive to negative in the second weight percent graph for the active metal and the low-melting point metal (tin, indium, or both) is the position of the upward peak in the first weight percent graph.

[0039] Figures 4(a) to 4(c) are graphs showing the first-order derivatives of the plots shown in Figures 3(a) to 3(c). In Figures 4(a) to 4(c), the horizontal axis represents the position in the thickness direction (X), and the vertical axis represents the value obtained by differentiating mass % with respect to position (dwt% / dX).

[0040] Figure 4(a) shows the first derivative of the plot shown in Figure 3(a). In the second copper mass percentage graph shown in Figure 4(a), the value changes from negative to positive at a change point P1c. The position of change point P1c corresponds to the position of the downward peak Pc in the first copper mass percentage graph shown in Figure 3(a).

[0041] Figure 4(b) shows the first derivative of the plot shown in Figure 3(b). In the second titanium mass percentage graph shown in Figure 4(b), the value changes from positive to negative at a change point P1a. The position of change point P1a corresponds to the position of the upward peak Pa in the first titanium mass percentage graph shown in Figure 3(b).

[0042] Figure 4(c) shows the first derivative of the plot shown in Figure 3(c). In the second tin mass % graph shown in Figure 4(c), the value changes from positive to negative at a change point P1s. The position of change point P1s corresponds to the position of the upward peak Ps in the first tin mass % graph shown in Figure 3(c).

[0043] With respect to the position of peak Pc, Lc / L may be 85% or less, or may be 80% or less. A smaller Lc / L indicates that the position where the mass fraction of copper is locally high is farther from the copper circuit portion 3. Therefore, Lc / L is preferably 75% or less, and more preferably 70% or less. Furthermore, with respect to the lower limit, Lc / L may be 42% or more, 46% or more, or 50% or more.

[0044] With respect to the position of peak Pa, La / L may be 85% or less, or may be 80% or less. The smaller La / L, the closer the active metal is to the ceramic substrate 2. Therefore, La / L is preferably 75% or less, and more preferably 70% or less. Furthermore, with respect to the lower limit, La / L may be 42% or more, 46% or more, or 50% or more.

[0045] With respect to the position of the peak Ps, Ls / L may be 85% or less, or may be 80% or less. A smaller Ls / L indicates that the position where the mass fraction of tin is locally high is farther from the copper circuit portion 3. Therefore, Ls / L is preferably 75% or less, and more preferably 70% or less. Furthermore, with respect to the lower limit, Ls / L may be 42% or more, 46% or more, or 50% or more.

[0046] The copper composition ratio at Peak Pc is not particularly limited, but may be, for example, in the range of 40% by mass to 80% by mass. The upper limit of this composition ratio may be 75% by mass or less, preferably 70% by mass or less, and most preferably 65% ​​by mass or less. The lower limit of this composition ratio may be 45% by mass or more, preferably 50% by mass or more, and most preferably 55% by mass or more.

[0047] The titanium composition ratio at peak Pa is not particularly limited, but may be, for example, in the range of 4 mass% to 30 mass%. The upper limit of this composition ratio may be 27 mass% or less, preferably 24 mass% or less, and most preferably 20 mass% or less. The lower limit of this composition ratio may be 6 mass% or more, preferably 8 mass% or more, and most preferably 10 mass% or more.

[0048] The tin composition ratio at peak Ps is not particularly limited, but may be, for example, in the range of 10% by mass to 50% by mass. The upper limit of this composition ratio may be 45% by mass or less, preferably 40% by mass or less, and most preferably 35% by mass or less. The lower limit of this composition ratio may be 13% by mass or more, preferably 16% by mass or more, and most preferably 20% by mass or more.

[0049] In the ceramic copper circuit board 1 according to the embodiment, the ceramic substrate 2 is a silicon nitride substrate, an aluminum nitride substrate, or an aluminum oxide substrate. Among these substrates, a silicon nitride substrate is preferred. The three-point bending strength of an aluminum nitride substrate or an aluminum oxide substrate is approximately 300 to 450 MPa. In contrast, the three-point bending strength of a silicon nitride substrate is 600 MPa or higher, and can be increased to 700 MPa or higher. Furthermore, the thermal conductivity of a silicon nitride substrate is 50 W / (m·K) or higher, and can be increased to 80 W / (m·K) or higher. In particular, silicon nitride substrates that combine both high strength and high thermal conductivity have become available in recent years. Furthermore, due to their high strength, silicon nitride substrates can be made thin. For example, the thickness of a silicon nitride substrate is 0.635 mm or less, and can even be 0.3 mm or less. Thinning the substrate can further improve heat dissipation. While there is no particular lower limit for the thickness of the ceramic substrate, a thickness of 0.1 mm or more is preferred. If the ceramic substrate 2 is too thin, the electrical insulation of the ceramic substrate 2 may be reduced.

[0050] 1, bonding layers 4 are formed on both surfaces of ceramic substrate 2. As described above, bonding layer 4 contains copper, an active metal, and one or more elements selected from tin and indium. As other elements, one or more elements selected from silver (Ag), aluminum (Al), silicon (Si), carbon (C), and magnesium (Mg) may be added to bonding layer 4 in a range of 1 to 15 mass % as needed.

[0051] The bonding layer 4 is formed from an active metal brazing paste. The active metal brazing paste is made by mixing the constituent elements into a paste. The active metal brazing paste is printed on a ceramic substrate and heated to form the bonding layer 4. By making the raw materials into a paste, the constituent elements can be distributed more uniformly. The active metal paste is made by adding an organic binder and an organic solvent to metal powder.

[0052] In this embodiment, an alloy powder is used as the metal powder when preparing the active metal paste. The molten state of the active metal brazing paste changes depending on the size of each raw material mixed in. When various metal powders with different particle size conditions are mixed to form a paste, the distribution in the paste is likely to be uneven due to the difference in size of the raw material powder. When the paste is printed, the state of the bonding layer is likely to change. For this reason, even if the composition is designed to achieve the characteristics of the bonding layer 4, the expected effect may not be obtained. In contrast, when an alloy powder is used, although the cost of the raw materials is higher, the particle size of the raw materials is constant and the particle size variation between the raw materials can be suppressed, making it easier to achieve the expected effect of the composition design.

[0053] The alloy powder may be an alloy powder containing all the components of the active metal brazing material. Alternatively, an alloy powder containing two or more of the components of the active metal brazing material may be mixed with a powder of another single metal. The components of the alloy powder are not particularly limited, but it is preferable that the alloy powder contains copper, which is the main component of the active metal brazing material, and a low-melting-point metal (tin or indium).

[0054] The particle size of the metal powder used in the active metal brazing material is preferably 12 μm or less, and more preferably 10 μm or less. By using metal powder with such a small particle size, the components can be easily dispersed in the active metal brazing material paste.

[0055] The type of organic binder used in the active metal brazing paste is not particularly limited as long as it is burned off in the subsequent drying or joining process. A preferred example is ethyl cellulose. Similarly, the organic solvent is not particularly limited as long as it is burned off in the subsequent drying or firing process. A preferred example is terpineol or butyl carbitol.

[0056] In this embodiment, the active metal brazing paste is kneaded in a three-roll mill. The three-roll mill includes three rolls called a charge roll, an intermediate roll, and a finishing roll. The charge roll, intermediate roll, and finishing roll rotate at low, medium, and high speeds, respectively. The paste is compressed and sheared as it passes between the rolls. For this reason, kneading using a three-roll mill is excellent in terms of pulverization and degassing effects. As a result, a paste is obtained that has a different shape and dispersion state of the metal powder than pastes kneaded using other kneading devices, such as a revolving agitator.

[0057] The conditions for the three-roll mill may be appropriately set depending on the viscosity of the paste, the particle size of the metal powder used, the equipment used, and the like. As an example, it is preferable to set the spacing between the rolls so that the pressure between each roll is 0.1 MPa to 2 MPa. More preferably, the pressure between the rolls is 0.1 MPa to 1.5 MPa. If the pressure between the rolls is too high, excessive pressure may be applied to the paste, potentially causing the binder and metal powder to separate. Furthermore, the metal powder may be crushed between the rolls, changing its shape and preventing the intended effect from being achieved. On the other hand, if the spacing is too wide, the pressure between the rolls may be weak, potentially resulting in insufficient crushing or dispersion effects. It is also preferable to pass the paste through the three-roll mill three or more times. Passing the paste through the rolls multiple times allows for more uniform mixing. When passing the paste through the three-roll mill multiple times, the same roll width and pressure conditions may be used each time, or different conditions may be used each time. It is also effective to pass the paste through the three-roll mill once at low pressure as a premix (pre-mixing), and then knead it at a higher pressure.

[0058] A paste kneaded using an alloy powder with a three-roll mill is more susceptible to separation of the metal powder and binder components than a paste containing individual metal powders. In a separated state, the metal components are more likely to aggregate. For this reason, it is preferable to continuously rotate the kneaded paste until use. Alternatively, if continuous rotation is difficult, it is preferable to rotate the paste stored without rotation for at least 3 hours, more preferably at least 6 hours, using a pot mill or the like before use. The rotation does not need to be performed at high speed; it is sufficient if the paste container rotates at approximately 1 to 5 rpm.

[0059] The inventors of the present application conducted experiments and found that the above-mentioned peaks Pc, Pa, and Ps were observed when a paste kneaded using a three-roll mill was used. On the other hand, when the paste was kneaded using a mixer, peak Pc was not observed, or peak Pc was observed at a position close to the ceramic substrate 2 or the copper circuit portion 3. The detailed mechanism behind this is unknown, but it is thought to be related to the fact that the paste can be kneaded more uniformly when a three-roll mill is used compared to when a mixer is used. It is presumed that when the paste is kneaded more uniformly, the metal components in the paste are dispersed more uniformly, resulting in the observation of the above-mentioned peaks.

[0060] When printing the active metal brazing paste, the thickness is preferably 10 to 30 μm. If the printing thickness is less than 10 μm, the thickness of the active metal brazing paste layer is likely to vary, which may result in a decrease in bonding strength. On the other hand, the printing thickness may exceed 30 μm, but printing the paste thicker than 30 μm does not result in an improvement in properties such as bonding strength in proportion to the increased amount. Therefore, from the perspective of reducing raw material consumption, the printing thickness is preferably 30 μm or less.

[0061] The active metal brazing paste is printed using a method that allows the paste to be printed with a uniform thickness, such as screen printing. If the printing thickness is uneven, the active metal brazing paste will be excessive in thicker areas, causing brazing material accumulation and cracks due to thermal stress. In thinner areas, the brazing material will run out, causing leak defects. For this reason, it is preferable that the difference in thickness between the thick and thin parts of the printed paste be 5 μm or less.

[0062] A copper plate is placed on the active metal brazing paste printed on the ceramic substrate and then heat-treated. This results in a ceramic copper-clad substrate in which the ceramic substrate and the copper plate are bonded via a bonding layer. A ceramic copper circuit board having a copper circuit portion is obtained by etching the copper plate of this ceramic copper-clad substrate. Alternatively, a ceramic copper circuit board can be obtained by bonding a copper circuit portion on which a circuit pattern has been formed to the ceramic substrate.

[0063] The ceramic copper circuit board 1 manufactured by the above-described method is suitable for a semiconductor device in which a semiconductor element is mounted via a bonding layer on the copper circuit portion 3. Fig. 5 is a side view showing an example of a semiconductor device. In Fig. 5, reference numeral 1 denotes a ceramic copper circuit board, reference numeral 6 denotes a semiconductor device, reference numeral 7 denotes a semiconductor element, reference numeral 8 denotes a bonding layer, reference numeral 9 denotes a wire bonding, and reference numeral 10 denotes a metal terminal.

[0064] 5 , two copper circuit portions 3 are bonded to the front surface 2 a of the ceramic substrate 2. A semiconductor element 7 is bonded to one of the copper circuit portions 3 via a bonding layer 8. A metal terminal 10 is bonded to another of the copper circuit portions 3 via another bonding layer 8. The semiconductor element 7 and the other of the copper circuit portions 3 are electrically connected by wire bonding 9.

[0065] The semiconductor device 6 according to the embodiment is not limited to such a structure. For example, only one of the wire bonding 9 and the metal terminal 10 may be provided. A plurality of semiconductor elements 7, a plurality of wire bonding 9, or a plurality of metal terminals 10 may be provided on one copper circuit portion 3. The semiconductor elements, wire bonding, or metal terminals 10 may be bonded to the back copper plate 5 as needed. The metal terminals 10 may have various shapes, such as a lead frame shape or a convex shape.

[0066] The bonding layer 8 that bonds the semiconductor element 7 or the metal terminal 10 uses solder or brazing filler metal. Note that "solder" refers to a bonding material with a melting point of 450°C or less, and "brazing filler metal" refers to a bonding material with a melting point of more than 450°C. It is preferable to use lead-free solder for the solder. Also, a bonding material with a melting point of 500°C or more is called a high-temperature brazing filler metal. A high-temperature brazing filler metal is, for example, a bonding material whose main component is Ag.

[0067] In the ceramic copper circuit board 1 according to the embodiment, the addition of tin or indium to the bonding layer 4 lowers the bonding temperature and reduces the difference in thermal expansion between the metal and the ceramic. Furthermore, by suppressing the diffusion of tin or indium into the copper circuit portion 3, deterioration of the copper circuit portion 3 is suppressed. As a result, it is possible to reduce the occurrence of cracks and the like due to the difference in stress between the ceramic substrate 2 and the copper circuit portion 3. Therefore, according to the present embodiment, a ceramic copper circuit board 1 with improved reliability can be obtained.

[0068] In semiconductor devices, while semiconductor elements continue to become smaller, the amount of heat generated from the chips is increasing. Therefore, improved heat dissipation is required for ceramic copper circuit substrates that mount semiconductor elements. In semiconductor devices (semiconductor modules), multiple semiconductor elements can be mounted on a ceramic copper circuit substrate to achieve higher performance. In this case, if one of the semiconductor elements exceeds its intrinsic temperature, the temperature coefficient of resistance becomes negative. This can lead to thermal runaway when power flows intensively, resulting in instantaneous destruction of the semiconductor device. To suppress temperature increases in semiconductor devices, it is effective to suppress deterioration of the copper circuit and cracks between the ceramic substrate and the copper circuit, and to promote heat dissipation from the copper circuit to the ceramic substrate. Therefore, improving the reliability of the bond between the semiconductor element and the copper circuit is extremely effective.

[0069] The semiconductor device 6 according to the embodiment can be used in a PCU, an IGBT, or an IPM module. The PCU, the IGBT, or the IPM module is used in, for example, an inverter. The inverter is used in products such as automobiles (including electric vehicles), electric railcars, and industrial machinery. With regard to automobiles, electric vehicles are becoming increasingly popular. The more reliable the semiconductor device, the more safety the automobile can be improved. The same is true for electric railcars, industrial machinery, and the like.

[0070] Next, a method for manufacturing the ceramic copper circuit board 1 according to the embodiment will be described. The method for manufacturing the ceramic copper circuit board 1 is not particularly limited as long as it has the above-described configuration. Here, an example of a method for obtaining the ceramic copper circuit board 1 with a high yield will be described.

[0071] First, a ceramic substrate and a copper plate are prepared. The ceramic substrate is preferably one selected from a silicon nitride substrate, an aluminum nitride substrate, and an aluminum oxide substrate. Considering the heat dissipation properties of the entire circuit board, the ceramic substrate is more preferably a silicon nitride substrate having a thermal conductivity of 50 W / (m·K) or more and a three-point bending strength of 600 MPa or more. When manufacturing a ceramic copper circuit board in which a copper circuit portion provided on the front surface of the ceramic substrate is electrically connected to a back copper plate provided on the back surface through through holes, a ceramic substrate having through holes is prepared. The through holes may be provided in the ceramic substrate in advance at the stage of a molded body before the ceramic sintering process, or they may be provided in the sintered ceramic substrate (ceramic sintered body) by laser processing, cutting using a drill, or the like.

[0072] The copper plate used in the ceramic copper circuit board is preferably made of copper or a copper alloy. Pure copper such as oxygen-free copper, tough pitch copper, and deoxidized copper can be used as the copper. Beryllium copper and other alloys can be used as the copper alloy. In the ceramic copper circuit board, copper circuit portions may be formed on both sides of the ceramic substrate. In this case, the material of the copper plate on one side may be different from the material of the copper plate on the opposite side. For example, the copper plate on one side may be made of copper, and the copper plate on the opposite side may be made of a copper alloy.

[0073] The ceramic substrate and the copper plate are joined by an active metal joining method. In the active metal joining method, an active metal brazing material is used. The active metal brazing material is prepared by mixing an active metal such as titanium, a brazing material metal such as copper, and a low-melting-point metal such as tin or indium. The active metal brazing material preferably contains 1 to 15 mass% of the active metal, 20 to 40 mass% of the low-melting-point metal such as tin or indium, and the remainder is copper. If necessary, one or more elements selected from the group consisting of silver (Ag), aluminum (Al), silicon (Si), carbon (C), and magnesium (Mg) may be added in a range of 1 to 15 mass%.

[0074] The active metal brazing paste is prepared by kneading the brazing material components with an organic material. It is preferable that the brazing material components are uniformly dispersed in the paste. If the brazing material components are not uniformly distributed, brazing will be unstable, which can lead to poor joining.

[0075] The active metal brazing paste thus produced is printed on a ceramic substrate. A copper plate is placed on the paste. Next, the ceramic substrate with the copper plate placed thereon is heated at 700 to 900°C to bond the ceramic substrate and the copper plate. The heating step is carried out in a vacuum or a non-oxidizing atmosphere as required. When the heating step is carried out in a vacuum, the pressure is 1×10 －２ The pressure is preferably not more than Pa. The non-oxidizing atmosphere is, for example, a nitrogen atmosphere or an argon atmosphere. By setting the atmosphere in a vacuum or a non-oxidizing atmosphere, oxidation of the bonding layer can be suppressed. The heating step is preferably performed in a continuous furnace, which is suitable for mass production.

[0076] The copper plate to be bonded to the ceramic substrate may be pre-processed into a circuit pattern, or may be a flat plate without a circuit pattern. When a flat plate is used, the plate is etched after bonding to process it into a pattern. This process produces a ceramic copper circuit board.

[0077] Next, a semiconductor element or the like is bonded to the ceramic copper circuit board. In this process, a bonding layer is provided at the location where the semiconductor element is to be bonded, and the semiconductor element is then provided on top of that. The bonding layer preferably contains solder or brazing material. If necessary, a metal terminal is bonded via the bonding layer. Wire bonding may also be provided if necessary.

[0078] 6 is a flowchart showing an example of a manufacturing method according to an embodiment. First, a ceramic substrate and a copper plate are prepared (step S1). An organic binder and an organic solvent are added to metal powder containing alloy powder to prepare a brazing paste (step S2). The brazing paste is pre-mixed using a three-roll mill (step S3), and then kneaded (step S4). In the pre-mixing step S3, the brazing paste is kneaded at a lower pressure than in the kneading step S4.

[0079] Fig. 7 is a side view showing an example of a kneading process. A three-roll mill 100 shown in Fig. 7 can be used for kneading. The three-roll mill 100 includes three rolls (a feed roll 101, an intermediate roll 102, and a finishing roll 103) and a blade 110. The feed roll 101, the intermediate roll 102, and the finishing roll 103 are spaced apart from one another in one direction. The rotation direction of the intermediate roll 102 is opposite to the rotation direction of the feed roll 101 and the rotation direction of the finishing roll 103.

[0080] As shown in Fig. 7, the brazing paste 120 is supplied to the gap between the feed roll 101 and the intermediate roll 102. As the feed roll 101 and the intermediate roll 102 rotate, the brazing paste 120 is drawn into the gap between the feed roll 101 and the intermediate roll 102. When the brazing paste 120 passes through the gap between the feed roll 101 and the intermediate roll 102, pressure is applied to the brazing paste 120. As a result, the raw material powder contained in the brazing paste 120 is pulverized and the brazing paste 120 is degassed.

[0081] A portion of the brazing paste 120 that has passed through the gap between the feed roll 101 and the intermediate roll 102 adheres to the surface of the intermediate roll 102 and is drawn into the gap between the intermediate roll 102 and the finishing roll 103. When the brazing paste 120 passes through the gap between the intermediate roll 102 and the finishing roll 103, pressure is again applied to the brazing paste 120, causing the brazing paste 120 to be pulverized and degassed. A portion of the brazing paste 120 that has passed through the gap between the intermediate roll 102 and the finishing roll 103 adheres to the surface of the finishing roll 103 and flows over the upper surface of the blade 110 to be collected.

[0082] When a sufficient amount of the brazing paste 120 has been collected by the blade 110, the kneading is terminated. Alternatively, the brazing paste collected by the blade 110 may be supplied again to the gap between the feed roll 101 and the intermediate roll 102. Preferably, the kneading is repeated three or more times. Note that the period from the supply of the brazing paste 120 to the gap between the feed roll 101 and the intermediate roll 102 to the collection of a sufficient amount of the brazing paste 120 by the blade 110 is counted as one kneading cycle.

[0083] For example, the gap between the feed roll 101 and the intermediate roll 102 and the gap between the intermediate roll 102 and the finishing roll 103 are adjusted so that the pressure between the feed roll 101 and the intermediate roll 102 and the pressure between the intermediate roll 102 and the finishing roll 103 are 0.1 MPa to 2 MPa. The pressure between the feed roll 101 and the intermediate roll 102 and the pressure between the intermediate roll 102 and the finishing roll 103 may be different. The rotation speed of each roll may be set within a range of 10 to 500 rpm. The rotation speed of each roll may be different.

[0084] The kneaded brazing paste is printed on a ceramic substrate (Step S5). A copper plate is placed on the brazing paste (Step S6). The laminate including the ceramic substrate and the copper plate is heat-treated (Step S7) to obtain a ceramic copper-clad substrate in which the ceramic substrate and the copper plate are bonded. A circuit shape is imparted to the copper plate by etching (Step S8) to obtain a ceramic copper circuit substrate. A semiconductor element may then be mounted on the copper circuit portion (Step S9). By mounting the semiconductor element, a semiconductor device is obtained.

[0085] (Examples 1 to 7, Comparative Examples 1 to 6) Silicon nitride substrates, aluminum nitride substrates, and aluminum oxide (alumina) substrates were prepared as ceramic substrates. The silicon nitride substrates had a thermal conductivity of 90 W / (m·K) and a three-point bending strength of 650 MPa. The aluminum nitride substrates had a thermal conductivity of 170 W / (m·K) and a three-point bending strength of 300 MPa. The aluminum oxide substrates had a thermal conductivity of 20 W / (m·K) and a three-point bending strength of 350 MPa. Each ceramic substrate measured 50 mm long and 40 mm wide. The silicon nitride substrates were 0.32 mm thick. The aluminum nitride substrates and alumina substrates were 0.635 mm thick. The types of ceramic substrates used in each Example and Comparative Example are shown in Table 1. In Table 1, silicon nitride substrates are labeled "SiN" and aluminum nitride substrates are labeled "AlN."

[0086] Next, in Examples 1 to 7, raw material powders were prepared with the "paste component" ratios shown in Table 1. In Table 1, paste components connected by a hyphen indicate alloy powders. Paste components separated by a comma indicate single powders. For example, "60Cu-30Sn-10Ti" in Example 1 indicates an alloy powder composed of 60% by weight of copper, 30% by weight of tin, and 10% by weight of titanium. "60Cu-30Sn,10Ti" in Example 5 indicates a raw material powder in which a copper-tin alloy powder and a single titanium powder were mixed to have a composition of 60% by weight of copper, 30% by weight of tin, and 10% by weight of titanium. "60Cu,30Sn,10Ti" in Comparative Example 1 indicates a raw material powder in which single copper, tin, and titanium powders were mixed to have the indicated composition.

[0087] In Examples 1 to 7, ethyl cellulose and terpineol were added to a raw material powder using an alloy powder consisting of at least two elements and premixed. The premixed raw material was passed through a three-roll mill set at a pressure of 1 MPa three times to prepare an active metal brazing paste.

[0088] The prepared active metal brazing paste was printed on both sides of a ceramic substrate and dried. A pair of copper plates measuring 50 mm long x 40 mm wide x 0.5 mm thick was placed to sandwich the ceramic substrate with the active metal brazing paste printed on both sides. The laminate including the ceramic substrate and the pair of copper plates was heated to bond the ceramic substrate and each copper plate. Bonding was performed using a continuous furnace at 790-850°C for 5-20 minutes in a nitrogen atmosphere. The copper plate on the front surface (front copper plate) was then etched into a circuit shape. The copper plate on the back surface (back copper plate) was etched into a heat sink shape.

[0089] In Comparative Examples 1 to 6, single powders of the various elements of the "paste components" shown in Table 1 were prepared and mixed in the ratios shown to prepare raw material powders. Ethyl cellulose and terpineol were added to the raw material powders and premixed. The premixed raw materials were kneaded at 1,400 rpm in a kneading mixer (rotating and revolving mixer) for 3 minutes to prepare active metal brazing pastes. The obtained active metal brazing paste was printed on a ceramic substrate in the same manner as in the Examples, and a copper plate was bonded to it. The copper plate was then etched to obtain a ceramic copper circuit board.

[0090]

[0091] Next, in each example and comparative example, the ceramic copper circuit board was cut through the center of the copper circuit portion on the front surface. The cut surface was polished and observed using an SEM. The approximate positions of the ceramic substrate, bonding layer, and copper circuit portion were determined based on differences in color and appearance. Multiple measurement areas, each 120 μm long and 2.5 μm thick, were set from the ceramic substrate side toward the copper circuit portion side, and each measurement area was sequentially analyzed. From the analysis results, the mass percent of copper was calculated when the total content of the active metal, one or more selected from tin and indium, and the main component of the ceramic substrate 2 in each measurement area was taken as 100 mass percent. The first and second bonding interfaces were determined from the calculated mass percent of copper. In the examples and comparative examples, the number of measurement areas from the first bonding interface to the second bonding interface was 10 to 13.

[0092] From the measurement results, the elements copper, tin (or indium), and titanium (or zirconium) were plotted on graphs such as those shown in Figures 3(a) to (c) to obtain a first mass % graph. The mass % of each element was calculated assuming that the sum of the mass % of tin (or indium), copper, active metal (titanium or zirconium), and the main constituent elements of the various ceramics excluding oxygen was 100%. Regarding the main constituent elements of ceramics, the main constituent elements of silicon nitride are nitrogen and silicon. The main constituent elements of aluminum nitride are nitrogen and aluminum. The main constituent element of alumina is aluminum.

[0093] Next, the obtained first mass% graph was subjected to first-order differentiation to obtain second mass% graphs such as those shown in Figures 4(a) to 4(c). In the second mass% graph of copper, the point where the value changes from negative to positive was identified as the peak (Pc) of the first mass% graph. In the second mass% graph of titanium, the point where the value changes from positive to negative was identified as the peak (Pa) of the first mass% graph. In the second mass% graph of tin or indium, the point where the value changes from positive to negative was identified as the peak (Ps) of the first mass% graph. When there were two or more change points in the second mass% graph, the position of the change point closest to the copper circuit portion was designated as the peak position. The peak positions of each component are shown in Table 2. In Comparative Example 1, the first mass% graph was flat, and no change points appeared when first-order differentiation was performed.

[0094]

[0095] Furthermore, peel strength was measured as the bonding strength between the copper circuit portion and the ceramic substrate. In measuring peel strength, a copper plate pre-formed to a width of 3 mm was bonded to the ceramic substrate, and the copper plate was pulled at 50 mm / min in a direction perpendicular to the ceramic substrate. The peel strength was measured from the tensile strength when the copper plate peeled off.

[0096] The reliability of the ceramic copper circuit boards of each example and comparative example was evaluated for the bondability of the semiconductor element. In this evaluation, samples prepared under the same conditions as the examples and comparative examples were used for evaluation, rather than samples for which the bond strength had been measured. Specifically, a semiconductor element and a metal terminal were bonded to the ceramic copper circuit board using lead-free solder, and wire bonding was then provided to fabricate a semiconductor device in which the semiconductor element and the metal terminal were electrically connected.

[0097] The semiconductor devices were subjected to a temperature cycle test (TCT) to examine the incidence of electrical continuity defects. The TCT consisted of a cycle of -40°C for 30 minutes, room temperature for 10 minutes, 150°C for 30 minutes, and room temperature for 10 minutes. The peeled area of ​​the copper circuit due to cracks after 300 cycles was calculated using scanning acoustic tomography (SAT). The peeled area rate was then evaluated as the TCT failure rate. A TCT failure rate of 0% indicates that no peeling of the copper circuit due to cracks was found. Electrical conductivity was also evaluated as an electrical characteristic value. The conductivity of the copper plates before and after bonding was measured using a conductivity meter (NDT Advance M4900C). A measured value of 95% or more of the conductivity of the copper plate before bonding was considered a pass, and a value less than 95% was considered a fail. The measurement results are shown in Table 3. In the conductivity evaluation results in Table 3, examples that passed are marked with a circle, and examples that failed are marked with a cross.

[0098]

[0099] According to Table 3, Examples 1 to 7 achieved good results, with a bonding strength of 60 MPa or more. In contrast, Comparative Examples 1 to 6 achieved bonding strengths of 55 MPa or less. Furthermore, Examples 1 to 7 achieved low or zero TCT defect rates. The electrical conductivity was high, at 95% or more, compared to the copper plates before bonding. In contrast, Comparative Examples 1 to 6 achieved higher TCT defect rates than Examples 1 to 7, and the electrical conductivity also deteriorated to less than 95%.

[0100] As is clear from the results shown above, improvements in bonding strength, TCT characteristics, and electrical characteristics were observed according to the examples compared to the comparative examples.

[0101] Although several embodiments of the present invention have been described above, these embodiments are presented by way of example only and are not intended to limit the scope of the invention. These novel embodiments can be embodied in various other forms, and various omissions, substitutions, modifications, etc. can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, as well as within the scope of the invention and its equivalents as set forth in the claims. Furthermore, the above-described embodiments can be implemented in combination with each other.

Claims

a ceramic substrate; a copper circuit portion provided on the ceramic substrate via a bonding layer, the bonding layer includes copper, an active metal, and at least one selected from tin and indium, and has a first bonding interface with the ceramic substrate and a second bonding interface with the copper circuit portion; a ceramic copper circuit board, wherein, when 10 or more measurement areas are set in the bonding layer in a thickness direction from the first bonding interface to the second bonding interface and the mass % of copper in each of the measurement areas is plotted, the plot of the mass % of copper has a downward peak, and the downward peak is located within a range of 40% to 90% of the thickness of the bonding layer from the first bonding interface.

2. The ceramic copper circuit board according to claim 1, wherein when the mass percentages of the active metal, tin, and indium in each of the measurement areas are plotted, the plot of the mass percentage of one or more selected from the active metal, tin, and indium has an upward peak, and the upward peak is located within a range of 40% to 90% of the thickness from the first bonding interface. 　 The ceramic copper circuit board according to claim 2 , wherein the peak top of the upward peak is located in the measurement area where the peak top of the downward peak is located, among the 10 or more measurement areas.

4. The ceramic copper circuit board according to claim 1, wherein the ceramic substrate is a silicon nitride substrate, an aluminum nitride substrate, or an aluminum oxide substrate. 　 A ceramic copper circuit board according to any one of claims 1 to 4, a semiconductor element mounted on the copper circuit portion via another bonding layer; A semiconductor device comprising: 　 The method for producing a ceramic copper circuit board according to any one of claims 1 to 4, the bonding layer is formed using an active metal brazing material, The active metal brazing material is produced by kneading alloy powder in a triple roll mill.

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