Bonded body, ceramic copper circuit substrate, method for manufacturing bonded body, and method for manufacturing ceramic copper circuit substrate

Abstract

A bonded body, which is a bonded body provided with a ceramic substrate and a copper plate bonded to the ceramic substrate via a bonding layer, characterized in that the copper plate has a surface perpendicular to the direction in which the ceramic substrate and the copper plate are bonded, and in that the proportion of the number of copper grains having a long diameter of more than 400 μm is 0% to 5% in three regions of 5 mm x 5 mm contained in the surface. The bonding temperature is preferably 800°C or lower. Furthermore, the proportion of the number of copper grains having a long diameter of more than 400 μm is preferably 1% or lower.

Description

TECHNICAL FIELD

[0001] Embodiments described later relate to a joined body, a ceramic copper circuit substrate, a manufacturing method of a joined body, and a manufacturing method of a ceramic copper circuit substrate. BACKGROUND

[0002] A joined body of a ceramic substrate and a copper plate is used for a circuit substrate on which a semiconductor element or the like is mounted. A ceramic copper circuit substrate in which a ceramic substrate and a copper plate are joined is disclosed in International Publication No. 2018 / 021472 (Patent Document 1). In Patent Document 1, a solder containing Ag, Cu, Ti, or the like is used as a joining layer. Further, TCT characteristics are improved by controlling the nanoindentation hardness of the joining layer. In Patent Document 1, the nanoindentation hardness is controlled by causing AgTi crystals, TiC, or the like to exist in the joining layer. In Patent Document 1, the joining strength and the TCT characteristics are improved by controlling the nanoindentation hardness.

[0003] In Patent Document 1, joining is performed at a high temperature of 780 to 850°C. If the joining temperature is high, the burden on the joining equipment increases. Further, joining at a high temperature exerts thermal stress on the ceramic substrate and the copper plate. The load of the thermal stress becomes a cause of deformation of the ceramic copper circuit substrate. Therefore, joining at a lower temperature is required.

[0004] For example, a ceramic copper circuit substrate in which joining is performed at a joining temperature of 720 to 800°C is disclosed in International Publication No. 2018 / 199060 (Patent Document 2).

[0005] PRIOR ART DOCUMENTS

[0006] PATENT DOCUMENTS

[0007] Patent Document 1: International Publication No. 2018 / 021472

[0008] Patent Document 2: International Publication No. 2018 / 199060 SUMMARY

[0009] PROBLEMS TO BE SOLVED BY THE INVENTION

[0010] The joining temperature in Patent Document 2 is lower than the joining temperature in Patent Document 1, and thus thermal stress can be alleviated. However, on the other hand, too much performance improvement is not achieved. For example, if the ceramic substrate is increased in size, the amount of warping of the joined body becomes large. The cause of this problem was investigated, and as a result, it was found that the problem is caused by the grain growth of the copper plate. The present invention is an invention for coping with such a problem. The present invention is an invention for providing a ceramic copper circuit substrate in which the grain growth of a copper plate is suppressed.

[0011] MEANS FOR SOLVING THE PROBLEMS

[0012] A bonded body provided with a ceramic substrate and a copper plate bonded to the ceramic substrate via a bonding layer, characterized in that the copper plate has a surface perpendicular to the direction in which the ceramic substrate and the copper plate are bonded, and in that the proportion of the number of copper grains having a major axis of more than 400 μm is 0 to 5% in three regions of 5 mm x 5 mm contained in the surface. BRIEF DESCRIPTION OF DRAWINGS

[0013] Figure 1 is a view showing one example of a bonded body according to the embodiment.

[0014] Figure 2 is a view showing one example of a crystal structure of a copper plate.

[0015] Figure 3 is a view showing one example of a process for performing simultaneous processing of a plurality of pieces.

[0016] Figure 4 is a view showing another example of a ceramic copper circuit substrate according to the embodiment.

[0017] Figure 5 is a view showing one example of a ceramic copper circuit substrate according to the embodiment.

[0018] Figure 6 is a view showing one example of a semiconductor device according to the embodiment. DETAILED DESCRIPTION

[0019] A bonded body according to the embodiment is provided with a ceramic substrate and a copper plate bonded to the ceramic substrate via a bonding layer. It is characterized in that the copper plate has a surface perpendicular to the direction in which the ceramic substrate and the copper plate are bonded, and in that the proportion of the number of copper grains having a major axis of more than 400 μm is 0 to 5% in three regions of 5 mm x 5 mm contained in the surface.

[0020] Figure 1 One example of a bonded body according to the embodiment is shown in Figure 1 In the example shown in Figure 1 In the example shown in

[0021] The bonded body 1 has a structure in which the copper plate 3 and the copper plate 4 are bonded to both faces of the ceramic substrate 2 via the bonding layer 5 and the bonding layer 6, respectively. For convenience, the copper plate 3 is referred to as the top copper plate, and the bonding layer 5 is referred to as the top bonding layer. In addition, the copper plate 4 is referred to as the back copper plate, and the bonding layer 6 is referred to as the back bonding layer. Figure 1In this example, copper plates are bonded to both sides of the ceramic substrate. The bonding body described in the embodiment is not limited to this shape. The size of the copper plates can be appropriately varied. Alternatively, a copper plate may be bonded to only one side of the ceramic substrate.

[0022] Figure 2 An example representing the crystal structure of a copper plate. In Figure 2 In the diagram, 3 represents the copper plate, and 7 represents the copper grain. The copper plate is polycrystalline. For example, each copper grain has a face-centered cubic lattice structure.

[0023] Copper grains are observed using magnified photographs. These photographs are taken using an optical microscope or a scanning electron microscope (SEM). Chemical polishing or etching can be performed when grain boundaries are difficult to identify. The magnification is set to 100x or higher. The object of observation is the surface of the copper plate perpendicular to the direction of bonding between the ceramic substrate and the copper plate. The thickness of the copper plate removed by chemical polishing or etching is set to less than one copper grain in that bonding direction. This is because if a thickness of more than two copper grains is removed, it ceases to be considered a copper plate surface. That is, the term "copper plate surface" refers to the surface of the copper plate when used as a ceramic copper circuit board. A thickness of less than one copper grain is, for example, set to less than 10 μm.

[0024] A unit area of ​​5mm × 5mm is defined, and each 5mm × 5mm unit area is designated as one observation area. In the magnified photograph, the major axis of the copper grains photographed within the 5mm × 5mm unit area is measured. The major axis of the copper grain corresponds to the longest distance between two points on the outer edge of the copper grain. Within the 5mm × 5mm unit area, only copper grains whose entire outline is captured are designated as the measurement objects. Three 5mm × 5mm unit areas are observed, and their combined grain index is measured. The grain index is a value obtained by calculating the proportion of each copper grain using the major axis of each region. Three sufficiently separated regions are selected as observation areas. Observation areas are randomly selected. Furthermore, copper grains whose outlines are interrupted at the ends of the magnified photograph are not included in the measurement objects. Additionally, when a 5mm × 5mm unit area cannot be observed in one field of view, multiple adjacent magnified photographs can be connected to obtain a 5mm × 5mm photograph.

[0025] The bonding body involved in the embodiment is characterized in that, in three observation areas on the surface of the copper plate, the proportion of copper grains with a major diameter greater than 400 μm is 0% to 5%. This means that the proportion of copper grains 7 with a major diameter of less than 400 μm is 95% or more.

[0026] The copper grains having a length of more than 400 μm are coarse grains that occur due to grain growth accompanying heat treatment. In the case where the ceramic substrate is joined to the copper plate via the joining layer, the copper plate is exposed to a high temperature of about 800°C. The copper plate is subjected to grain growth due to the high temperature. If coarse grains are formed due to grain growth in the direction parallel to the surface, warping is likely to occur in the joined body. The inventors of the present application have found that if the number of copper grains having a length of more than 400 μm per 5 mm x 5 mm is 6% or more, warping becomes large. In particular, if the joined body is large, warping is likely to occur. In the joined body according to the embodiment, since the number of copper grains having a length of more than 400 μm is suppressed, warping can be reduced.

[0027] Note that grain growth in the direction perpendicular to the surface is less likely to affect warping of the joined body. Therefore, as long as the number ratio in the surface of the copper plate is 0% to 5%, the number ratio of the copper grains having a length of more than 400 μm in the cross section can be more than 5%.

[0028] The number ratio of the copper grains having a length of more than 400 μm is preferably 1% or less. The length of the copper grain 7 is preferably 300 μm or less. If the length of the copper grain 7 is as small as 300 μm or less, the effect of suppressing warping is further improved.

[0029] The lower limit of the length of the copper grain is not particularly limited. The length is preferably 10 μm or more. A copper plate in which the size of the copper grain 7 is small can increase the manufacturing cost.

[0030] The average value of the length of the copper grain 7 is preferably 30 μm to 300 μm.

[0031] The average value of the length of the copper grain 7 is the average value of the lengths of the copper grains photographed in 5 mm x 5 mm of the unit area at three points. In 5 mm x 5 mm of the unit area, only the copper grains of which the entire profile is photographed are selected as measurement targets. The average value is obtained by calculating the average of the lengths of the copper grains selected as the measurement targets by observing 5 mm x 5 mm of the unit area at three points. The average value is calculated by the number ratio. For example, when five copper grains having lengths of 350 μm, 220 μm, 200 μm, 120 μm, and 40 μm are observed, the average value of the lengths is 186 μm (= (350 + 220 + 200 + 120 + 40) ÷ 5).

[0032] If the average value of the length is less than 30 μm, the copper grains are too small. In the case of an aggregate including small crystals of the copper plate, the influence of the presence of large crystals becomes large. Further, if the average value of the length exceeds 300 μm, the number of copper grains having a length of more than 400 μm is likely to increase. Therefore, the average value of the length is preferably 30 μm to 300 μm, and further preferably 50 μm to 150 μm.

[0033] Further, the proportion of the number of copper grains having a length and a diameter within an average range is preferably 80% or more. The average range is 0.5 to 2 times the average value of the length and the diameter of the copper grains. Small copper grains or large copper grains easily become a cause of local stress generated by grain growth. Therefore, it is preferable that the number of copper grains having a size close to the average value be large. Therefore, the proportion of the number of copper grains having a length and a diameter within an average range is preferably 80% or more, and further preferably 90 to 100%.

[0034] The proportion with respect to the average value can be determined by measuring the particle size distribution. The length and the diameter of the copper grains photographed in a unit area of 5 mm x 5 mm are measured. A unit area of 5 mm x 5 mm is measured at three points, and a particle size distribution chart is obtained. Alternatively, a particle size distribution chart can be obtained by image analysis of an enlarged photograph.

[0035] Further, it is preferable that the arithmetic average waviness Wa of the waviness curve of the ceramic substrate be 2 μm or less, and the maximum cross-sectional height Wt of the waviness curve be 10 μm or less.

[0036] The waviness curve is a profile curve obtained by applying a phase compensation filter of cut-off values λf and λc to a cross-sectional curve. The waviness curve is measured in accordance with JIS-B-0601 (2013) (ISO 4287).

[0037] The fact that Wa is 2 μm or less and Wt is 10 μm or less means that the concave-convex of the surface of the ceramic substrate is small. If the concave-convex of the surface of the ceramic substrate is large, the conduction mode of heat at the time of joining differs partially to the copper plate. If the conduction mode of heat differs partially, the joining property of the portions is affected. If the ceramic substrate is large, it easily becomes a cause of warping.

[0038] As the ceramic substrate, a silicon nitride substrate, an aluminum nitride substrate, an alumina substrate, an A6061 aluminum alloy substrate, and the like can be given.

[0039] The thickness of the ceramic substrate is preferably 0.1 mm to 1 mm. If the thickness of the substrate is less than 0.1 mm, it can lead to a decrease in strength. Further, if the thickness is more than 1 mm, the ceramic substrate becomes a thermal resistor, and it can decrease the heat dissipation property of the joined body.

[0040] The three-point bending strength of the silicon nitride substrate is preferably 600 MPa or more. Further, the thermal conductivity of the silicon nitride substrate is preferably 80 W / m·K or more. By increasing the strength of the silicon nitride substrate, it is possible to thin the thickness of the substrate. Therefore, the three-point bending strength of the silicon nitride substrate is preferably 600 MPa or more, and further preferably 700 MPa or more. Thus, it is possible to thin the thickness of the silicon nitride substrate to 0.40 mm or less, and further to 0.30 mm or less.

[0041] The three-point bending strength of the aluminum nitride substrate is about 300 to 450 MPa. On the other hand, the thermal conductivity of the aluminum nitride substrate is 160 W / m-K or more. The strength of the aluminum nitride substrate is lower than that of the silicon nitride substrate, and thus the substrate thickness is preferably 0.60 mm or more.

[0042] Further, the three-point bending strength of the aluminum oxide substrate is about 300 to 450 MPa, but the aluminum oxide substrate is inexpensive. Further, the three-point bending strength of the Alusil high-silicon heat-resistant aluminum alloy substrate is as high as 550 MPa or more, but the thermal conductivity of the Alusil high-silicon heat-resistant aluminum alloy substrate is about 30 to 50 W / m-K.

[0043] The ceramic substrate is preferably either of a silicon nitride substrate or an aluminum nitride substrate. The silicon nitride substrate or the aluminum nitride substrate can increase the joining strength to a copper plate by using the active metal joining method described later. The silicon nitride substrate is particularly preferable. The silicon nitride substrate has high strength, and thus even if a thick copper plate is joined to the silicon nitride substrate, excellent reliability can be obtained.

[0044] The joining layer preferably contains an active metal. The active metal is one selected from the group consisting of Ti (titanium), Zr (zirconium), and Hf (hafnium). A solder containing an active metal is referred to as an active metal solder. Further, a joining method using an active metal solder is referred to as an active metal joining method. A joined body is obtained by disposing an active metal solder between a ceramic substrate and a copper plate and performing heat treatment. After the joined body is obtained, the active metal solder becomes a joining layer. Further, as the active metal, Ti is preferable. Ti is a more active metal than Zr and Hf. Further, the cost of Ti is less expensive than that of Zr and Hf. The active metal is not limited to a metal element, and can be added to a solder as a compound or an alloy. As the compound, hydrides, oxides, nitrides, and the like can be exemplified.

[0045] Further, the active metal solder preferably contains one or two or more selected from the group consisting of Ag (silver), Cu (copper), Sn (tin), In (indium), and C (carbon) as a component other than the active metal. Ag or Cu is a component that becomes a base material of the solder. Sn or In has an effect of lowering the melting point of the solder. C has an effect of controlling the fluidity of the solder or controlling the structure of the joining layer by reacting with other components. Thus, as the components of the solder, Ag-Cu-Ti, Ag-Cu-Sn-Ti, Ag-Cu-Ti-C, Ag-Cu-Sn-Ti-C, Ag-Ti, Cu-Ti, Ag-Sn-Ti, Cu-Sn-Ti, Ag-Ti-C, Cu-Ti-C, Ag-Sn-Ti-C, and Cu-Sn-Ti-C can be exemplified. Further, In can be used instead of Sn. Both Sn and In can be used. A low-melting metal such as Bi (bismuth), Sb (antimony), Ga (gallium), or the like can be used instead of Sn and In.

[0046] As for the composition of the active metal brazing material, it is preferable that Ag (silver) is 0 to 75 mass%, Cu (copper) is 15 to 85 mass%, and Ti (titanium) or TiH2 (titanium hydride) is 1 to 15 mass%. In the case of using both Ti and TiH2, the total of them is preferably in the range of 1 to 15 mass%. In the case of using both Ag and Cu, it is preferable that Ag is 20 to 60 mass% and Cu is 15 to 40 mass%.

[0047] The brazing material can also contain one or both of Sn (tin) or In (indium) in the range of 1 to 50 mass% as needed. The content of Ti or TiH2 is preferably in the range of 1 to 15 mass%. In addition, the brazing material can also contain C (carbon) in the range of 0.1 to 2 mass% as needed.

[0048] As for the ratio of the composition of the active metal brazing material, it is calculated by setting the total of the mixed raw materials to 100 mass%. For example, in the case where the brazing material is composed of Ag, Cu, and Ti, Ag + Cu + Ti = 100 mass%. In the case where the brazing material is composed of Ag, Cu, TiH2, and In, Ag + Cu + TiH2 + In = 100 mass%. In the case where the brazing material is composed of Ag, Cu, Ti, Sn, and C, Ag + Cu + Ti + Sn + C = 100 mass%.

[0049] In addition, the joint layer preferably contains Ag, Cu, and Ti. The joint layer containing Ag, Cu, and Ti means that the active metal brazing material contains Ag, Cu, and Ti. The Ag-Cu-Ti-based brazing material increases the joint strength. In addition, the Ag-Cu-Ti-Sn-based brazing material can lower the melting point of the brazing material, and thus can lower the joining temperature.

[0050] By setting the joining temperature to 700°C or lower, the amount of diffusion of Ag into the copper plate can be suppressed. The diffusion of Ag to the surface of the copper plate can be suppressed. In addition, by setting the joining temperature to 700°C or lower, Ag mainly diffuses to the crystal grain boundaries of the copper plate. Thus, the diffused Ag can be suppressed from hindering the etching of the copper plate.

[0051] Next, the method of manufacturing the joint body will be described. The method of manufacturing the joint body according to the embodiment is not limited as long as it has the above-described configuration. Here, as a method for obtaining the joint body with a good yield, the following examples can be listed.

[0052] The method of manufacturing the joint body according to the embodiment is characterized in that it includes a step of disposing a brazing material for a joint layer between a ceramic substrate and a copper plate, and a joining step at a joining temperature of 800°C or lower.

[0053] First, a process is performed to deposit a copper plate on a ceramic substrate via a solder used for bonding layers. The solder is the aforementioned active metal solder. The active metal solder contains an active metal such as Ti. The active metal may also be added as an active metal compound such as a hydride. Preferably, the active metal solder contains one or more components selected from Ag (silver), Cu (copper), Sn (tin), In (indium), and C (carbon) as components other than the active metal.

[0054] First, an active metal solder paste is prepared by mixing the desired components. Mixing the paste with a binder and solvent is effective in obtaining this paste.

[0055] An active metal solder paste is applied to at least one of a ceramic substrate or a copper plate. The thickness of the active metal solder paste is preferably 5 μm to 60 μm. The thickness of the active metal solder paste refers to the thickness after the applied paste has dried. A thickness less than 5 μm may result in reduced bond strength. Furthermore, a thickness exceeding 60 μm may increase thermal stress during the bonding process and lead to greater warping of the bonded joint. Therefore, the thickness of the active metal solder paste is preferably 5 μm to 60 μm, and more preferably 10 μm to 50 μm.

[0056] After the step of applying active metal solder paste to one side, a step of placing the uncoated side onto the other side is performed. For example, when applying active metal solder paste to a ceramic substrate, a step of placing a copper plate onto the ceramic substrate using the active metal solder paste is performed. Alternatively, active metal solder paste can be applied to both sides of the ceramic substrate, and copper plates can be disposed on both sides. Conversely, active metal solder paste can be applied to the copper plate, and the ceramic substrate can be disposed on the copper plate using the active metal solder paste.

[0057] Next, a bonding process is performed at a bonding temperature below 800°C. The bonding temperature refers to the highest temperature maintained for a certain period during the bonding process. A higher bonding temperature promotes the growth of copper grains that make up the copper plate. In conventional active metal bonding methods, the bonding temperature is around 850°C. If the bonding temperature exceeds 800°C, the copper grains grow larger. Larger grains make it easier to form large copper grains with a length diameter exceeding 400 μm.

[0058] The bonding temperature is preferably below 800°C, and more preferably below 700°C. It should be noted that the lower limit of the bonding temperature is not particularly limited, but it is preferably above 500°C. If the bonding temperature is low, the reliability of the bonding may decrease. Therefore, the bonding temperature is preferably 500°C to 800°C, and more preferably 550°C to 700°C. Furthermore, the holding time at the bonding temperature is preferably 60 minutes or less, and more preferably 30 minutes or less. The lower limit of the holding time is not particularly limited, but it is preferably 1 minute or more. Below 1 minute, Ag diffusion may become insufficient, resulting in unstable bonding.

[0059] Furthermore, when the average grain size of the copper plate before bonding is set to A (μm) and the average grain size of the copper plate after bonding is set to B (μm), it is preferable that B / A ≤ 10. More preferably, it is preferable that 1.1 ≤ B / A ≤ 5.

[0060] The statement that B / A ≤ 10 indicates that the ratio of grain growth before and after bonding is less than 10 times. Grain growth is the phenomenon of copper grains in a copper plate increasing in size due to heat. As each copper grain gradually increases in size, stress is generated. If B / A exceeds 10 times, the stress becomes excessive, making the bond more prone to warping. Therefore, B / A preferably satisfies B / A ≤ 10, and more preferably 1.1 ≤ B / A ≤ 5.

[0061] The average grain size A can be calculated using the following method: Observe three regions with a unit area of ​​5mm × 5mm on the surface of the copper plate before bonding. In each region, select copper grains as the measurement targets. Measure the major diameter of each selected isomorphous grain. The average grain size can be obtained by calculating the average of each major diameter.

[0062] The average particle size B, as described above, is the average of the major diameter obtained from observations of three regions with a unit area of ​​5 mm × 5 mm.

[0063] Regarding the solder used for bonding, the largest endothermic peak in the DSC curve is preferably below 700°C. Setting the bonding temperature to below 800°C is effective in suppressing grain growth. Therefore, a solder melting point of below 700°C is effective. Preferably, the solder melting point is between 550°C and 700°C.

[0064] A DSC curve is a curve obtained by using a differential scanning calorimeter (DSC) to measure the peaks of endothermic and exothermic reactions. A negative peak indicates an endothermic reaction, and a positive peak indicates an exothermic reaction.

[0065] The DSC curve is determined using a temperature profile that includes a heating process, a holding process at a specific temperature, and a cooling process. In this temperature profile, the heating process raises the temperature from room temperature to 500°C at a rate of 5°C / min. Then, the temperature is held at 500°C for 60 minutes. Next, the temperature is raised to 845°C at a rate of 5°C / min. Afterward, the temperature is held at 845°C for 30 minutes. Finally, the temperature is lowered from 845°C to room temperature at a rate of 5°C / min.

[0066] For DSC, a NETZSCH TGA-DSC simultaneous thermal analysis apparatus STA449-F3-Jupiter or an apparatus with equivalent performance can be used. Furthermore, the determination is performed by adding a suitable amount of solder dropwise into an alumina container and in an Ar (argon) gas flow. It is necessary to conduct the determination in an Ar atmosphere to prevent the solder from reacting with the atmosphere. The Ar gas flow rate is set as follows: 20 ml / min on the sample side and 200 ml / min on the cooling side.

[0067] In the heating process of DSC curves, the temperature at which the largest endothermic peak is detected within the temperature range of 550℃ to 800℃ is considered the melting point. A melting point below 700℃ indicates that the largest endothermic peak exists within the 550℃ to 700℃ range. It should be noted that even peaks with a negative orientation below 550℃ should not be counted as endothermic peaks. This endothermic reaction is caused by the melting and decomposition of the active metal solder. For example, when using titanium hydride (TiH2) as the active metal, a negative peak is detected around 500℃. This peak indicates an endothermic reaction occurring when TiH2 decomposes into Ti and H. Therefore, the temperature at which the largest endothermic peak is detected within the temperature range of 550℃ to 800℃ is considered the melting point.

[0068] The melting point of the active metal solder is preferably in the range of 550℃ to 700℃, and more preferably in the range of 550℃ to 650℃. By lowering the melting point, the growth of copper grains can be suppressed. Thus, it is possible to achieve B / A ≤ 10, and more preferably 1.1 ≤ B / A ≤ 5.

[0069] To control the melting point of active metal solders, controlling the composition and particle size of the raw material powders is effective. As mentioned above, Sn or In has the effect of lowering the melting point of the solder. It is effective to maximize the particle size of Sn or In powder among the components constituting the solder. For example, when using Ag-Cu-Sn-Ti solder, the particle size of Sn powder is maximized among Ag powder, Cu powder, Sn powder, and Ti powder. Sn is an element that readily reacts with other solder components. By increasing the particle size of Sn powder, Sn powder becomes easier to contact with other components. This lowers the melting point of the solder. The same applies when using In instead of Sn. It is effective to make the particle size of the component that lowers the melting point larger than the particle size of other components. Furthermore, lowering the bonding temperature reduces the load on the bonding equipment.

[0070] Pure copper plates and copper alloy plates can be used as copper plates. Oxygen-free copper is preferred. Oxygen-free copper, as shown in JIS-H-3100, has a copper purity of 99.96 wt% or higher. Furthermore, in the copper plate before bonding, the average length of the copper grains is preferably 10 μm to 200 μm. When the average length is less than 10 μm, the number of fine copper grains that are prone to growth may increase. Furthermore, if the average length exceeds 200 μm, the number of copper grains with a length exceeding 400 μm may increase after bonding. Therefore, the average length before bonding is preferably 10 μm to 200 μm, and more preferably 20 μm to 150 μm. The average length before bonding can be achieved by changing the processing rate, etc. It should be noted that the processing rate is expressed as a percentage (%) obtained by dividing the difference between the cross-sectional area of ​​the material before processing and the cross-sectional area after processing by the cross-sectional area of ​​the material before processing.

[0071] Through the above processes, a bonded body formed by bonding a ceramic substrate and a copper plate can be manufactured. By bonding at a temperature of 800°C or below, the growth of copper grains can be suppressed. Therefore, even when the bonded body is enlarged, the warpage can be reduced. If the bonded body is enlarged, multiple parts can be processed simultaneously. Simultaneous processing of multiple parts refers to a method of cutting a large bonded body to obtain a smaller bonded body. There are also methods for dividing the bonded body or dividing the ceramic copper circuit board. For easy division, dicing can also be performed. According to the embodiment, even when the size of the ceramic substrate 2 is enlarged to 200 mm or more in length and 200 mm or more in width, the warpage of the bonded body can be reduced to less than 0.1 mm. Furthermore, by setting the bonding temperature to 700°C or below, the diffusion of Ag in the copper plate can be suppressed.

[0072] Figure 3 This is an example of a joint used for simultaneous processing of multiple parts. Figure 3In the diagram, 1 represents the joining body, and 8 represents the scribe line. The scribe line 8 is a dividing groove. The dividing groove can be dot-shaped, line-shaped, or various other shapes. Furthermore, the dividing groove can be provided on only one surface or on two surfaces. The scribe line 8 is formed through laser processing or other methods. Figure 3 This example illustrates a scribe line 8 used to divide the bond 1 into four parts. The conditions for setting the scribe line 8 are not limited to this example and can be varied appropriately. Large ceramic copper circuit boards can also be divided to obtain smaller ceramic copper circuit boards. That is, multiple parts of the bond can be processed simultaneously, as can multiple parts of the ceramic copper circuit. Simultaneous processing of multiple parts is a method with good mass production capabilities.

[0073] Furthermore, a ceramic copper circuit board can be manufactured by imparting a circuit structure to the copper plate of the bonding body 1. An etching process is effective for imparting the circuit structure. Figure 4 This represents an example of a ceramic copper circuit board 1a with a circuit structure. Figure 4 The example shown is a copper plate 3 fabricated into a circuit structure. The implementation is not limited to this method; any necessary circuit structure can be applied. Alternatively, in the manufacture of the aforementioned bonding body, a copper plate fabricated into a circuit structure can be bonded to a ceramic substrate. In this case, a ceramic-copper circuit board can be obtained as the bonding body. Furthermore, an inclined structure can be given to the side surface of the copper plate. Additionally, a structure in which the bonding layer is exposed from the side surface of the copper plate can also be provided.

[0074] Figure 5 This is a diagram illustrating an example of a ceramic copper circuit board according to an embodiment.

[0075] Through-holes can also be provided in ceramic substrates. Ceramic copper circuit boards preferably have a structure in which the copper plate on the front and the copper plate on the back are connected by through-holes. Figure 5 This represents an example of a ceramic copper circuit board with through-holes. Figure 5 This is a cross-sectional view of the section with the through hole. Figure 5 In the diagram, 1a is a ceramic copper circuit board. 2 is a silicon nitride substrate. 3 is a front copper plate. 4 is a back copper plate. 5 and 6 are bonding layers. 9 is a through-hole. Figure 5 In the middle, the copper plate 3 and the back copper plate 4 are connected by a through hole 9. Figure 5In this embodiment, multiple through holes 9 connect multiple front copper plates 3 to multiple back copper plates 4. The implementation is not limited to this structure. In the ceramic copper circuit board 1a, through holes 9 may be provided only for a portion of the multiple front copper plates 3. Through holes 9 may also be provided only for a portion of the multiple back copper plates 4. The interior of the through holes 9 is preferably filled with the same material as the bonding layer 5 or 6. The internal structure of the through holes 9 is not particularly limited as long as it allows for communication between the front and back copper plates. Therefore, a metal thin film may be provided only on the inner wall of the through holes 9. On the other hand, filling with the same material as the bonding layer 5 or 6 can improve the bonding strength.

[0076] Figure 6 This is a diagram illustrating an example of a semiconductor device involved in an implementation.

[0077] The ceramic copper circuit board described in the embodiments is suitable for semiconductor devices. In semiconductor devices, semiconductor elements are mounted on the copper plate of the ceramic copper circuit board via a bonding layer. Figure 6 This represents an example of a semiconductor device. Figure 6 In the diagram, 1a is a ceramic copper circuit board. 10 is a semiconductor device. 11 is a semiconductor element. 12 is a bonding layer. 13 is a wire bond. 14 is a metal terminal. Figure 6 In this process, a semiconductor element 11 is bonded to the copper plate of the ceramic copper circuit substrate 1a via a bonding layer 12. Similarly, a metal terminal 14 is bonded via the bonding layer 12. Adjacent copper plates are electrically connected to each other via lead bonding 13. Figure 6 In addition to the semiconductor element 11, wire bonds 13 and metal terminals 14 are also connected. The semiconductor device described in this embodiment is not limited to this structure. For example, either the wire bond 13 or the metal terminal 14 may be provided. Multiple semiconductor elements 11, wire bonds 13, and metal terminals 14 may also be provided on the front copper plate 3. On the back copper plate 4, semiconductor elements 11, wire bonds 13, and metal terminals 14 may be connected as needed. Various shapes, such as lead frame shapes and convex shapes, can be used for the metal terminals 14.

[0078] By using the bonding agent involved in the embodiments in the above-described ceramic copper circuit board or semiconductor device, their warpage can be reduced.

[0079] (Example)

[0080] (Examples 1-7, Comparative Examples 1-3)

[0081] As ceramic substrates, silicon nitride substrates or aluminum nitride substrates as shown in Table 1 were prepared.

[0082] Table 1

[0083]

[0084] Next, the copper plates shown in Table 2 were prepared. All copper plates were made of oxygen-free copper.

[0085] Table 2

[0086]

[0087] Next, the active metal solders shown in Table 3 were prepared. Among active metal solders 1 to 3, Sn powder had the largest particle size. Among active metal solder 4, Ag powder had the largest particle size. Furthermore, the melting points of the solders were obtained by measuring the DSC curves as described above.

[0088] Table 3

[0089]

[0090] Next, a bonding process was performed using a ceramic substrate, a copper plate, and an active metal solder. The dimensions of the copper plate correspond to those of the ceramic substrate. Furthermore, during the bonding process, at 10- 3 The bonding temperature is maintained for 10–30 minutes in a vacuum below Pa. The combination of raw materials is as shown in Table 4.

[0091] Table 4

[0092]

[0093] For the obtained joint, the major diameter of the copper grains in the copper plate, the warpage of the joint, and the joint strength were measured.

[0094] Regarding the major and minor axes, SEM observation was performed after etching the surface of the copper plate. In the SEM observation, three observations were randomly taken at three points within a 5mm × 5mm area. The major and minor axes of the observed copper grains were measured. Furthermore, the deviation from the average major and minor axes of the copper grains was calculated from the results obtained from the three random observations at a 5mm × 5mm area.

[0095] As the warpage of the joint, the warpage on the long side is measured. The warpage of the ceramic substrate is measured from the side of the joint. The ends of the long sides of the ceramic substrate are connected by a straight line. The warpage is defined as the position furthest from the surface of the ceramic substrate to this straight line. Examples with a warpage of 0.1 mm or less on the long side are considered good (〇), and examples with a warpage of more than 0.1 mm are considered defective (×).

[0096] The bond strength was determined by a peel test. Specifically, a peel test specimen was prepared using the bonding conditions of each embodiment and comparative example. The specimen consisted of a strip of copper plate bonded to a ceramic substrate. The bonding was performed with one end of the copper plate exposed from the ceramic substrate. The peel strength was measured by vertically stretching the exposed copper plate.

[0097] Examples with a bonding strength of 20 kN / m or more are designated as best (◎). Examples with a bonding strength of 15 kN / m or more but less than 20 kN / m are designated as good (〇). Examples with a bonding strength of 14 kN / m or less are designated as defective (×).

[0098] The results are shown in Table 5.

[0099] Table 5

[0100]

[0101] As can be seen from the table, the bonding assembly involved in the embodiments controls the copper grains of the copper plate. Furthermore, good results were obtained regarding warpage and bonding strength. This indicates that even when the bonding temperature is set below 800°C, and further below 700°C, a bonding assembly with sufficient strength can be obtained. However, regarding Embodiment 3, the bonding strength is reduced because Wa and Wt of the silicon nitride substrate deviate from their preferred ranges.

[0102] In contrast, as in Comparative Example 3, even when a high-melting-point solder was used to lower the bonding temperature, no bond was obtained. Furthermore, in Comparative Examples 1 and 2, because the bonding temperature exceeded 800°C, the degree of copper grain growth was significant. Therefore, the warpage of the bond was greater.

[0103] As described above, according to the embodiments, even with an increase in the size of the ceramic substrate, the warpage of the joint can be reduced. Furthermore, a joint with high bonding strength can be obtained. Since the size of the ceramic substrate can be increased, a joint suitable for simultaneous processing of multiple parts can be obtained.

[0104] The above embodiments of the present invention have been illustrated, but these embodiments are provided as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other ways, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These variations of the embodiments are included in the scope and spirit of the invention, and are also included in the scope of the invention as described in the claims and its equivalents. Furthermore, the above embodiments can be combined with each other.

Claims

1. A joint, characterized in that, It is a composite body comprising a ceramic substrate and copper plates bonded to both sides of the ceramic substrate via a bonding layer containing an active metal, wherein... The ceramic substrate is either a silicon nitride substrate with a thermal conductivity of 80 W / m·K or higher, or an aluminum nitride substrate with a thermal conductivity of 160 W / m·K or higher. The bonding layer contains one or more of the following: Ag, Cu, Sn, In, and C, and titanium. The copper plate has a surface perpendicular to the direction in which the ceramic substrate and the copper plate are joined. In the three 5mm × 5mm regions contained in the surface, the proportion of copper grains with a major axis exceeding 400μm is 0% to 5%, where the major axis is the longest distance between two points on the outer edge of the copper grain. The arithmetic mean height Wa of the waviness curve of the ceramic substrate is below 3.7 μm. The maximum cross-sectional height Wt of the waviness curve is below 24 μm. The bonding strength between the ceramic substrate and the copper plate is above 15 kN / m. In the three regions, the average major diameter of the copper grains ranges from 30 μm to 300 μm. In the three regions, the proportion of copper grains with a major diameter within the average range is over 80%. The average range is 0.5 to 2 times the average of the major diameter of the copper grains in the three regions.

2. The joint according to claim 1, characterized in that, The proportion of copper grains with a major diameter exceeding 400 μm is less than 1%.

3. The joint according to claim 1, characterized in that, In the three regions, the average length of the copper grains is 50 μm to 150 μm.

4. The joint according to claim 1, characterized in that, The arithmetic mean height Wa of the waviness curve of the ceramic substrate is less than 2 μm, and the maximum cross-sectional height Wt of the waviness curve is less than 10 μm.

5. The joint according to claim 1, characterized in that, The bonding layer contains Ag, Cu and Ti.

6. The joint according to claim 4, characterized in that, The bonding layer contains Ag, Cu and Ti.

7. A ceramic copper circuit board, characterized in that, The joint body according to any one of claims 1 to 6 is used.

8. A method for manufacturing a joint, characterized in that, It is a method for manufacturing the joint as described in any one of claims 1 to 6. It has the following processes: The process of depositing a solder containing the active metal for bonding the bonding layer between the ceramic substrate and the copper plate; and For bonding processes with a bonding temperature below 800℃, Wherein, when the average particle size of the copper plate before bonding is set to A (μm) and the average particle size of the copper plate after bonding is set to B (μm), B / A ≤ 10 is satisfied.

9. The method for manufacturing the joint according to claim 8, characterized in that, The bonding temperature is below 700°C.

10. The method for manufacturing the joint according to claim 8, characterized in that, It satisfies 1.1≤B / A≤5.

11. The method for manufacturing the joint according to claim 8, characterized in that, In the DSC curve of the brazing filler metal, the largest endothermic peak is below 700°C.

12. A method for manufacturing a ceramic copper circuit board, comprising: The process of manufacturing the joint according to any one of claims 1 to 6; and The process of imparting a circuit structure to the joined copper plate.

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