Bonded body, ceramic copper circuit board, method for producing bonded body, and method for producing ceramic

Abstract

A bonded body provided with a ceramic substrate and a copper plate bonded to the ceramic substrate with a bonding layer interposed therebetween, the bonded body being 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 three 5 mm * 5 mm regions included in the surface, the thickness of the copper plate is smaller than that of the ceramic substrate, and the thickness of the copper plate is smaller than that of the ceramic substrate. And the proportion of the number of copper crystal grains with long diameters exceeding 400 [mu] m is 0%-5%. It is preferable that the bonding temperature is 800 DEG C or less. It is preferable that the ratio of the number of copper crystal grains having a major diameter of more than 400 [mu] m is 1% or less.

Description

[0001] This application is a divisional application of Chinese Patent Application No. 202180007322.7, with an application date of March 8, 2021 and an invention title of "Bonded Body, Ceramic Copper Circuit Board, Method for Manufacturing Bonded Body, and Method for Manufacturing Ceramic Copper Circuit Board". Technical Field

[0002] The embodiments described below relate to a bonded body, a ceramic copper circuit board, a method for manufacturing a bonded body, and a method for manufacturing a ceramic copper circuit board. Background Art

[0003] A bonded body of a ceramic substrate and a copper plate is used for a circuit board on which semiconductor elements and the like are mounted. A ceramic copper circuit board obtained by bonding a ceramic substrate and a copper plate is disclosed in International Publication No. 2018 / 021472 (Patent Document 1). In Patent Document 1, a solder containing Ag, Cu, Ti, etc. is used as a bonding layer. Further, the TCT characteristics are improved by controlling the nanoindentation hardness of the bonding layer. In Patent Document 1, the nanoindentation hardness is controlled by allowing AgTi crystals, TiC, etc. to be present in the bonding layer. In Patent Document 1, the bonding strength and TCT characteristics are improved by controlling the nanoindentation hardness.

[0004] In Patent Document 1, bonding is performed at a high temperature of 780 to 850°C. If the bonding temperature is high, the burden on the bonding equipment increases. Further, bonding at a high temperature applies thermal stress to the ceramic substrate and the copper plate. The load of the thermal stress causes deformation of the ceramic copper circuit board. Therefore, bonding at a lower temperature is required.

[0005] For example, a ceramic copper circuit board bonded at a bonding temperature of 720 to 800°C is disclosed in International Publication No. 2018 / 199060 (Patent Document 2).

[0006] Prior Art Documents

[0007] Patent Documents

[0008] Patent Document 1: International Publication No. 2018 / 021472

[0009] Patent Document 2: International Publication No. 2018 / 199060 Summary of the Invention

[0010] Problems to be Solved by the Invention

[0011] Since the bonding temperature in Patent Document 2 is lower than that in Patent Document 1, thermal stress can be alleviated. On the other hand, however, no further performance improvement has been achieved. For example, when the ceramic substrate is enlarged, there arises a problem that the warpage amount of the bonded body becomes large. After investigating the cause, it has been found that this problem is caused by the grain growth of the copper plate. The present invention is an invention for solving such a problem. The present invention is an invention for providing a ceramic copper circuit board in which the grain growth of the copper plate is suppressed.

[0012] Means for Solving the Problem

[0013] A bonded body comprising 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 three 5 mm × 5 mm regions contained in the surface, the number ratio of copper grains having a major axis exceeding 400 μm is 0% to 5%. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a diagram showing an example of the bonded body according to the embodiment.

[0015] Figure 2 It is a diagram showing an example of the crystal structure of the copper plate.

[0016] Figure 3 It is a diagram showing an example for performing simultaneous processing of multiple pieces.

[0017] Figure 4 It is a diagram showing another example of the ceramic copper circuit board according to the embodiment.

[0018] Figure 5 It is a diagram showing an example of the ceramic copper circuit board according to the embodiment.

[0019] Figure 6 It is a diagram showing an example of the semiconductor device according to the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0020] The bonded body according to the embodiment includes a ceramic substrate and a copper plate bonded to the ceramic substrate via a bonding layer. Characteristically, the copper plate has a surface perpendicular to the direction in which the ceramic substrate and the copper plate are bonded, and in three 5 mm × 5 mm regions contained in the surface, the number ratio of copper grains having a major axis exceeding 400 μm is 0% to 5%.

[0021] Figure 1 Shows an example of the bonded body according to the embodiment. In Figure 1Among them, 1 is the joined body. 2 is the ceramic substrate. 3 is the copper plate (front copper plate). 4 is the copper plate (back copper plate). 5 is the joining layer (front joining layer). 6 is the joining layer (back joining layer). In Figure 1 In the example of, the longitudinal dimension and the transverse dimension of the ceramic substrate are the same as the longitudinal dimension and the transverse dimension of the copper plate respectively.

[0022] The joined body 1 has a structure in which the copper plate 3 and the copper plate 4 are joined to both sides of the ceramic substrate 2 via the joining layer 5 and the joining layer 6 respectively. For convenience, the copper plate 3 is called the front copper plate, and the joining layer 5 is called the front joining layer. In addition, the copper plate 4 is called the back copper plate, and the joining layer 6 is called the back joining layer. In Figure 1 In the example of, copper plates are joined to both sides of the ceramic substrate. The joined body involved in the embodiment is not limited to such a shape. The size of the copper plate can be appropriately changed. In addition, copper plates can also be joined to only one side of the ceramic substrate.

[0023] Figure 2 An example of the crystal structure of the copper plate is shown. In Figure 2 Among them, 3 is the copper plate. 7 is the copper grain. The copper plate is a polycrystal. For example, each copper grain has a face-centered cubic lattice structure.

[0024] The copper grains are observed using an enlarged photograph. The enlarged photograph is taken by an optical microscope or a scanning electron microscope (SEM). When it is difficult to confirm the grain boundary, chemical polishing or etching treatment can also be performed. The magnification is set to 100 times or more. The observation object is the surface of the copper plate perpendicular to the joining direction of the ceramic substrate and the copper plate. The thickness of the copper plate removed by the chemical polishing or etching treatment is set to be less than the amount of one copper grain in the joining direction. Because if the thickness of two or more copper grains is removed, it will no longer be the so-called copper plate surface. That is, the so-called copper plate surface refers to the copper plate surface when used as a ceramic copper circuit substrate. As the thickness of less than the amount of one copper grain, for example, it is set to 10 μm or less.

[0025] Set 5 mm × 5 mm as the unit area, and set the area of 5 mm × 5 mm of the unit area as one observation area. In the magnified photograph, measure the major axis of the copper grains photographed in the unit area of 5 mm × 5 mm. The major axis of the copper grains corresponds to the longest distance between two points on the outer edge of the copper grains. In the unit area of 5 mm × 5 mm, only the copper grains with all contours photographed are set as the measurement objects. Observe three areas of 5 mm × 5 mm of the unit area and measure the total grain index. The so-called grain index is a value obtained by calculating the number ratio using the major axis of each copper grain in each area. Three areas that are sufficiently separated from each other are selected as the observation areas. The observation areas are randomly selected. In addition, the copper grains whose contours are interrupted by the ends of the magnified photograph are not included in the measurement objects. In addition, when the unit area of 5 mm × 5 mm cannot be observed in one field of view, multiple adjacent magnified photographs can also be connected to each other to obtain a photograph of 5 mm × 5 mm.

[0026] The bonded body according to the embodiment is characterized in that, in three observation areas on the surface of the copper plate, the number ratio of copper grains with a major axis exceeding 400 μm is 0% to 5%. This means that the number ratio of copper grains 7 with a major axis of 400 μm or less is 95% or more.

[0027] The copper grains with a major axis exceeding 400 μm are coarse grains formed by grain growth during heat treatment. When the ceramic substrate is bonded to the copper plate through the bonding layer, the copper plate is exposed to a high temperature of about 800 °C. The copper plate undergoes grain growth due to the high temperature. If grain growth occurs in the direction parallel to the surface to form coarse grains, it becomes easy to generate warping in the bonded body. The inventors of the present invention found that if the copper grains with a major axis exceeding 400 μm in the unit area of 5 mm × 5 mm on the surface reach 6% or more, the warping becomes larger. Especially when the bonded body becomes larger, warping is likely to occur. In the bonded body according to the embodiment, since the number of copper grains with a major axis exceeding 400 μm is suppressed, warping can be reduced.

[0028] It should be noted that grain growth in the cross-sectional direction perpendicular to the surface is not likely to affect the warping of the bonded body. Therefore, as long as the above-mentioned number ratio on the surface of the copper plate is 0% to 5%, the number ratio of copper grains with a major axis exceeding 400 μm in the cross-section can also exceed 5%.

[0029] The number ratio of copper grains with a major axis exceeding 400 μm is preferably 1% or less. The major axis of the copper grains 7 is preferably 300 μm or less. If the major axis of the copper grains 7 is as small as 300 μm or less, the warping suppression effect is further improved.

[0030] The lower limit value of the major axis of the copper grains is not particularly limited. Preferably, the major axis is 10 μm or more. A copper plate with small-sized copper grains 7 may lead to an increase in manufacturing cost.

[0031] The average major axis length of the copper grains 7 is preferably 30 μm to 300 μm.

[0032] The average major axis length of the copper grains 7 is the average major axis length of the copper grains photographed in a unit area of 5 mm × 5 mm at 3 locations. In one unit area of 5 mm × 5 mm, only the copper grains with all their contours photographed are selected as the measurement objects. Observe 3 unit areas of 5 mm × 5 mm, and obtain the average value by calculating the average major axis length of the copper grains serving as the measurement objects. The average value is calculated by the number ratio. For example, when observing 5 copper grains with major axis lengths of 350 μm, 220 μm, 200 μm, 120 μm, and 40 μm respectively, the average major axis length is 186 μm (= (350 + 220 + 200 + 120 + 40) ÷ 5).

[0033] If the average major axis length is less than 30 μm, the copper grains are too small. In the case of an aggregate containing small crystals of the copper plate, the influence when there are large crystals becomes greater. In addition, if the average major axis length exceeds 300 μm, the possibility of an increase in the number of copper grains with a major axis length exceeding 400 μm becomes high. Therefore, the average major axis length is preferably 30 μm to 300 μm, and more preferably 50 μm to 150 μm.

[0034] In addition, the number ratio of the copper grains with a major axis length within the average range is preferably 80% or more. The average range is 0.5 times to 2 times the average major axis length of the copper grains. Small or large copper grains are likely to cause local stress generated by grain growth. Therefore, it is preferable that the number of copper grains with a size close to the average value is large. Therefore, the number ratio of the copper grains with a major axis length within the average range is preferably 80% or more, and more preferably 90% to 100%.

[0035] The number ratio relative to the average value can be determined by measuring the particle size distribution. Measure the major axis length of the copper grains photographed in a unit area of 5 mm × 5 mm. Measure 3 unit areas of 5 mm × 5 mm in quantity, and obtain a particle size distribution chart. Alternatively, a particle size distribution chart can also be obtained by image analysis of an enlarged photograph.

[0036] In addition, it is preferable that: the arithmetic mean waviness Wa of the waviness curve of the ceramic substrate is 2 μm or less, and the maximum section height Wt of the waviness curve is 10 μm or less.

[0037] The so-called waviness curve is a contour curve obtained by applying a phase compensation type filter with cut-off values λf and λc to the cross-section curve. The waviness curve is set to be measured in accordance with JIS-B-0601(2013)(ISO4287).

[0038] The so-called Wa being less than 2 μm and Wt being less than 10 μm indicate that the unevenness on the surface of the ceramic substrate is small. If the unevenness on the surface of the ceramic substrate is large, the heat conduction mode to the copper plate during bonding is partially different. If the heat conduction mode of a part is different, it will affect the bonding property of that part. If the ceramic substrate is enlarged, it is likely to cause warping.

[0039] Examples of the ceramic substrate include a silicon nitride substrate, an aluminum nitride substrate, an alumina substrate, an Alusil high-silicon heat-resistant aluminum alloy substrate, etc.

[0040] The thickness of the ceramic substrate is preferably 0.1 mm to 1 mm. When the substrate thickness is less than 0.1 mm, there may be a reduction in strength. In addition, if the thickness is greater than 1 mm, the ceramic substrate becomes a thermal resistor, which may reduce the heat dissipation of the bonded body.

[0041] The three-point bending strength of the silicon nitride substrate is preferably 600 MPa or more. In addition, 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, the substrate thickness can be reduced. Therefore, the three-point bending strength of the silicon nitride substrate is preferably 600 MPa or more, and more preferably 700 MPa or more. Thus, the substrate thickness of the silicon nitride substrate can be reduced to 0.40 mm or less, and further to 0.30 mm or less.

[0042] The three-point bending strength of the aluminum nitride substrate is about 300 - 450 MPa. On the other hand, the thermal conductivity of the aluminum nitride substrate is 160 W / m·K or more. Since the strength of the aluminum nitride substrate is lower than that of the silicon nitride substrate, the substrate thickness is preferably 0.60 mm or more.

[0043] In addition, the three-point bending strength of the alumina substrate is about 300 - 450 MPa, but the alumina substrate is inexpensive. In addition, the three-point bending strength of the Alusil high-silicon heat-resistant aluminum alloy substrate is as high as about 550 MPa, but the thermal conductivity of the Alusil high-silicon heat-resistant aluminum alloy substrate is about 30 - 50 W / m·K.

[0044] The ceramic substrate is preferably either a silicon nitride substrate or an aluminum nitride substrate. The silicon nitride substrate or the aluminum nitride substrate can improve the bonding strength with the copper plate by using the active metal bonding method described later. The silicon nitride substrate is particularly preferred. Since the silicon nitride substrate has high strength, even when a thick copper plate is bonded to the silicon nitride substrate, excellent reliability can be obtained.

[0045] The bonding layer preferably contains an active metal. The active metal is one selected from Ti (titanium), Zr (zirconium), and Hf (hafnium). The solder containing the active metal is called an active metal solder. In addition, the bonding method using the active metal solder is called the active metal bonding method. A bonded body is obtained by disposing the active metal solder between a ceramic substrate and a copper plate and performing heat treatment. After obtaining the bonded body, the active metal solder becomes the bonding layer. In addition, as the active metal, Ti is preferred. Ti is a more active metal than Zr and Hf. In addition, the cost of Ti is lower than that of Zr and Hf. The active metal is not limited to a metal element, and may also be added to the solder as a compound or an alloy. As the compound, hydrides, oxides, nitrides, etc. can be cited.

[0046] In addition, the active metal solder preferably contains one or more selected from Ag (silver), Cu (copper), Sn (tin), In (indium), and C (carbon) as components other than the active metal. Ag or Cu is a component that becomes the base material of the solder. Sn or In has the effect of lowering the melting point of the solder. C has the effect of controlling the fluidity of the solder or reacting with other components to control the structure of the bonding layer. Therefore, 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, Cu-Sn-Ti-C can be cited. In addition, In can be used instead of Sn. Both Sn and In can be used. Low melting point metals such as Bi (bismuth), Sb (antimony), and Ga (gallium) can also be used instead of Sn and In.

[0047] Regarding the composition of the active metal solder, preferably Ag (silver) is 0 mass% to 75 mass%, Cu (copper) is 15 mass% to 85 mass%, and Ti (titanium) or TiH2 (titanium hydride) is 1 mass% to 15 mass%. When both Ti and TiH2 are used, their total is preferably in the range of 1 to 15 mass%. When both Ag and Cu are used, preferably Ag is 20 to 60 mass% and Cu is 15 to 40 mass%.

[0048] The solder may also contain one or both of 1 mass% to 50 mass% of Sn (tin) or In (indium) as needed. The content of Ti or TiH2 is preferably 1 to 15 mass%. In addition, the solder may also contain 0.1 mass% to 2 wt% of C (carbon) as needed.

[0049] Regarding the ratio of the composition of the active metal solder, it is calculated by setting the total of the mixed raw materials to 100% by mass. For example, in the case where the solder is composed of three types of Ag, Cu, and Ti, Ag + Cu + Ti = 100% by mass. In the case where the solder is composed of four types of Ag, Cu, TiH₂, and In, Ag + Cu + TiH₂ + In = 100% by mass. In the case where the solder is composed of five types of Ag, Cu, Ti, Sn, and C, Ag + Cu + Ti + Sn + C = 100% by mass.

[0050] In addition, the bonding layer preferably contains Ag, Cu, and Ti. The bonding layer containing Ag, Cu, and Ti means that the active metal solder contains Ag, Cu, and Ti. The Ag-Cu-Ti-based solder can improve the bonding strength. In addition, the Ag-Cu-Ti-Sn-based solder can reduce the melting point of the solder, and thus can reduce the bonding temperature.

[0051] By setting the bonding temperature to 700°C or lower, the diffusion amount 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 bonding temperature to 700°C or lower, Ag mainly diffuses to the crystal grain boundaries of the copper plate. Thereby, the diffused Ag can be suppressed from hindering the etching of the copper plate.

[0052] Next, a method for manufacturing the joined body will be described. As long as the joined body according to the embodiment has the above configuration, its manufacturing method is not limited. Here, as a method for obtaining the joined body with good yield, the following examples can be cited.

[0053] The manufacturing method of the joined body according to the embodiment is characterized in that it includes: a step of disposing a solder for the bonding layer between the ceramic substrate and the copper plate; and a bonding step in which the bonding temperature is 800°C or lower.

[0054] First, a step of disposing a copper plate on the ceramic substrate via the solder for the bonding layer is performed. The solder is the above-mentioned active metal solder. The active metal solder is a solder containing active metals such as Ti. The active metal may also be added as an active metal compound such as a hydride. The active metal solder preferably contains one or more selected from Ag (silver), Cu (copper), Sn (tin), In (indium), and C (carbon) as components other than the active metal.

[0055] First, by performing a step of mixing the required components, an active metal solder paste is prepared. In order to obtain a paste, it is effective to mix with a binder and a solvent.

[0056] The active metal solder paste is applied onto at least one of a ceramic substrate and 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 is dried. When the thickness is less than 5 μm, the bonding strength may decrease. In addition, if it is thicker than 60 μm, the thermal stress in the bonding process may become large and the warpage of the bonded body may become large. Therefore, the thickness of the active metal solder paste is preferably 5 μm to 60 μm, and more preferably 10 μm to 50 μm.

[0057] After the step of applying the active metal solder paste onto one of them, a step of placing the other one without the applied paste onto the one is performed. For example, when the active metal solder paste is applied onto the ceramic substrate, a step of placing the copper plate onto the ceramic substrate through the active metal solder paste is performed. The active metal solder paste may be applied onto both surfaces of the ceramic substrate, and the copper plates may be arranged on both surfaces. The active metal solder paste may also be applied onto the copper plate, and the ceramic substrate may be arranged on the copper plate through the active metal solder paste.

[0058] Next, a bonding step with a bonding temperature of 800 °C or lower is performed. The bonding temperature refers to the highest temperature among the temperatures maintained for a certain period of time in the bonding step. If the bonding temperature is high, the grain growth of the copper grains constituting the copper plate can be promoted. In the conventional active metal bonding method, the bonding temperature is about 850 °C. If the bonding temperature exceeds 800 °C, the grain growth of the copper plate becomes large. If the grain growth of the copper plate is large, it becomes easy to generate large copper grains with a major axis exceeding 400 μm.

[0059] The bonding temperature is preferably 800 °C or lower, and more preferably 700 °C or lower. It should be noted that the lower limit of the bonding temperature is not particularly limited, but it is preferably 500 °C or higher. If the bonding temperature is low, the bonding reliability may decrease. Therefore, the bonding temperature is preferably 500 °C to 800 °C, and more preferably 550 °C to 700 °C. In addition, the holding time of 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. When it is less than 1 minute, the Ag diffusion may be insufficient and the bondability may be unstable.

[0060] In addition, when the average particle size of the copper plate before bonding is set as A (μm) and the average particle size of the copper plate after bonding is set as B (μm), it is preferably satisfied that B / A ≤ 10. In addition, it is more preferably satisfied that 1.1 ≤ B / A ≤ 5.

[0061] The so-called B / A ≤ 10 means that the ratio of grain growth before and after bonding is 10 times or less. Grain growth refers to the phenomenon in which the copper grains of the copper plate become larger due to heat. Since the grain growth causes each copper grain to gradually become larger, stress is generated. If B / A exceeds 10 times and is large, the stress becomes too large and warping of the bonded body is likely to occur. Therefore, B / A preferably satisfies B / A ≤ 10, and more preferably satisfies 1.1 ≤ B / A ≤ 5.

[0062] The average grain size A can be calculated by the following method. Observe three regions of 5 mm × 5 mm per unit area contained in the surface of the copper plate before bonding. In each region, select the copper grains to be measured. Measure the major axis of each selected copper crystal. By calculating the average of each major axis, the average grain size can be obtained.

[0063] The average grain size B is, as described above, the average value of the major axes obtained from the results of observing three regions of 5 mm × 5 mm per unit area.

[0064] Regarding the brazing filler metal for bonding, the maximum endothermic peak in the DSC curve is preferably 700 °C or lower. In order to suppress grain growth, it is effective to set the bonding temperature to 800 °C or lower. Therefore, it is effective for the melting point of the brazing filler metal to be 700 °C or lower. Preferably, the melting point of the brazing filler metal is 550 °C to 700 °C.

[0065] The so-called DSC curve is a curve obtained by measuring the peaks of endothermic reactions and exothermic reactions using a differential scanning calorimeter (DSC). A peak in the negative direction indicates that an endothermic reaction has occurred. A peak in the positive direction indicates that an exothermic reaction has occurred.

[0066] The DSC curve is measured via a temperature curve including a heating process, a holding process at a certain temperature, and a cooling process. In this temperature curve, in the heating process, the temperature is raised from room temperature at a heating rate of 5 °C / min to 500 °C. Then, in the heating process, 500 °C is held for 60 minutes. Then, in the heating process, the temperature is raised from 500 °C at a heating rate of 5 °C / min to 845 °C. After that, in the holding process, the temperature of 845 °C is held for 30 minutes. In the cooling process, the temperature is lowered from 845 °C at a cooling rate of 5 °C / min to room temperature.

[0067] As the DSC, a TGA-DSC simultaneous thermal analysis device STA449-F3-Jupiter manufactured by NETZSCH or a device having equivalent performance can be used. In addition, the measurement is carried out by dropping an appropriate amount of brazing filler metal into an alumina container and in an Ar (argon) gas flow. It is necessary to prevent the reaction between the brazing filler metal and the atmosphere by performing the measurement in an Ar atmosphere. In addition, the flow rate of the Ar gas flow is set to: 20 ml / min on the sample side and 200 ml / min on the cooling side.

[0068] In the heating process of the DSC curve, the detection temperature of the largest endothermic peak in the temperature range of 550 °C to 800 °C is regarded as the melting point. When the melting point of the filler metal is 700 °C or lower, it indicates that the largest endothermic peak exists in the range of 550 to 700 °C. It should be noted that even if there is a peak in the negative direction below 550 °C, it is advisable not to count it as an endothermic peak. This endothermic reaction is caused by the melting, decomposition, etc. of the active metal filler metal. For example, when titanium hydride (TiH2) is used as the active metal, a peak in the negative direction is detected around 500 °C. This peak represents the endothermic reaction that occurs when TiH2 decomposes into Ti and H. Therefore, the detection temperature of the largest endothermic peak in the temperature range of 550 °C to 800 °C is regarded as the melting point.

[0069] The melting point of the active metal filler metal is preferably in the range of 550 °C to 700 °C, and more preferably in the range of 550 °C to 650 °C. By lowering the melting point, the grain growth of copper grains can be suppressed. Thereby, B / A ≤ 10, and further 1.1 ≤ B / A ≤ 5 can be achieved.

[0070] To control the melting point of the active metal filler metal, it is effective to control the composition, the particle size of the raw material powder, etc. As described above, Sn or In has the effect of lowering the melting point of the filler metal. Among the components constituting the filler metal, it is effective to make the particle size of Sn or In powder the largest. For example, when using Ag-Cu-Sn-Ti filler metal, among Ag powder, Cu powder, Sn powder, and Ti powder, the particle size of Sn powder is made the largest. Sn is an element that easily reacts with other filler metal components. By increasing the particle size of Sn powder, Sn powder becomes more likely to come into contact with other components. Thereby, the melting point of the filler metal can be lowered. The same applies when using In instead of Sn. It is effective to make the particle size of the component having the effect of lowering the melting point larger than that of other components. In addition, lowering the bonding temperature can reduce the load on the bonding equipment.

[0071] As the copper plate, a pure copper plate or a copper alloy plate can be used. The copper plate is preferably oxygen-free copper. The copper purity of oxygen-free copper is 99.96 wt% or more as shown in JIS-H-3100. In addition, in the copper plate before bonding, the average value of the major axis of the copper grains is preferably 10 μm to 200 μm. When the average value of the major axis is less than 10 μm, there may be an increase in fine copper grains that are likely to grow in grains. In addition, if the average value exceeds 200 μm, after bonding, the number of copper grains with a major axis exceeding 400 μm may increase. Therefore, the average value of the major axis before bonding is preferably 10 μm to 200 μm, and more preferably 20 μm to 150 μm. The average value of the major axis before bonding can be prepared 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 of the material after processing by the cross-sectional area of the material before processing.

[0072] Through the above processes, a bonded body formed by bonding a ceramic substrate and a copper plate can be manufactured. By performing the bonding at a bonding temperature of 800 °C or lower, the grain growth of copper grains can be suppressed. Thus, even if the bonded body is enlarged, the warpage amount can be reduced. If the bonded body is enlarged, multi-piece simultaneous processing can be performed. Multi-piece simultaneous processing is a method of obtaining small bonded bodies by cutting a large bonded body. There are also methods of dividing the bonded body or dividing the ceramic copper circuit board. In order to facilitate division, scribing processing can also be performed. According to the embodiment, even if 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 amount of the bonded body can be reduced to 0.1 mm or less. In addition, by setting the bonding temperature to 700 °C or lower, the diffusion amount of Ag in the copper plate can be suppressed.

[0073] Figure 3 It shows an example of a bonded body for performing multi-piece simultaneous processing. In Figure 3 1 is the bonded body and 8 is the scribing line. The scribing line 8 is a dividing groove. The dividing groove can be various shapes such as dot-shaped and linear. In addition, the dividing groove can be provided on only one surface or on both surfaces. The scribing line 8 is formed by laser processing or the like. Figure 3 It shows an example in which scribing lines 8 for dividing the bonded body 1 into four are provided. The conditions for setting the scribing lines 8 are not limited to this example and can be appropriately changed. It is also possible to divide a large ceramic copper circuit board to obtain a small ceramic copper circuit board. That is, multi-piece simultaneous processing can be performed on the bonded body, or multi-piece simultaneous processing can be performed on the ceramic copper circuit. Multi-piece simultaneous processing is a method with good mass productivity.

[0074] In addition, by imparting a circuit structure to the copper plate of the bonded body 1, a ceramic copper circuit board can be manufactured. For imparting the circuit structure, an etching process is effective. Figure 4 It shows an example of the ceramic copper circuit board 1a to which a circuit structure is imparted. Figure 4 In 3 is the surface copper plate processed into a circuit structure. The embodiment is not limited to such a manner, and a necessary circuit structure can be applied. Alternatively, in the manufacture of the above-mentioned bonded body, it may also be a copper plate processed into a circuit structure bonded to a ceramic substrate. In this case, as the bonded body, a ceramic copper circuit board can be obtained. In addition, an inclined structure can be imparted to the side surface of the copper plate. In addition, a structure in which the bonding layer is exposed from the side surface of the copper plate can also be imparted.

[0075] Figure 5 It is a diagram showing an example of the ceramic copper circuit board according to the embodiment.

[0076] Through holes can also be provided in the ceramic substrate. The ceramic copper circuit board preferably has a structure in which the surface copper plate and the back copper plate are electrically connected through the through holes. Figure 5Shows an example of a ceramic copper circuit board having a through hole. Figure 5 Is a cross-sectional view of the portion where the through hole is provided. In Figure 5 , 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. In Figure 5 , through the through hole 9, the front copper plate 3 and the back copper plate 4 are electrically connected. In Figure 5 , a plurality of through holes 9 respectively connect a plurality of front copper plates 3 and a plurality of back copper plates 4. The embodiment is not limited to such a structure. In the ceramic copper circuit board 1a, through holes 9 may be provided only in a part of the plurality of front copper plates 3. Through holes 9 may be provided only in a part of the plurality of back copper plates 4. Inside the through hole 9, it is preferable to fill the same material as the bonding layer 5 or 6. The structure inside the through hole 9 is not particularly limited as long as it can electrically connect the front copper plate and the back copper plate. Therefore, a metal thin film may be provided only on the inner wall of the through hole 9. On the other hand, by filling the same material as the bonding layer 5 or 6, the bonding strength can be improved.

[0077] Figure 6 Is a diagram showing an example of a semiconductor device according to an embodiment.

[0078] The ceramic copper circuit board according to the embodiment is suitable for a semiconductor device. In the semiconductor device, a semiconductor element is mounted on the copper plate of the ceramic copper circuit board via a bonding layer. Figure 6 Shows an example of a semiconductor device. In Figure 6 , 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 bonding. 14 is a metal terminal. In Figure 6 , on the copper plate of the ceramic copper circuit board 1a, a semiconductor element 11 is bonded via a bonding layer 12. Similarly, a metal terminal 14 is bonded via a bonding layer 12. Adjacent copper plates are electrically connected to each other by a wire bonding 13. In Figure 6 , in addition to the semiconductor element 11, a wire bonding 13 and a metal terminal 14 are also bonded. The semiconductor device according to the embodiment is not limited to such a structure. For example, either the wire bonding 13 or the metal terminal 14 may be provided. A plurality of semiconductor elements 11, wire bondings 13 and metal terminals 14 may be respectively provided on the front copper plate 3. On the back copper plate 4, semiconductor elements 11, wire bondings 13 and metal terminals 14 may be bonded as needed. For the metal terminal 14, various shapes such as a lead frame shape and a convex shape can be applied.

[0079] By using the bonded body according to the embodiment for the above-mentioned ceramic copper circuit board or semiconductor device, their warpage can be reduced.

[0080] (Example)

[0081] (Examples 1 - 7, Comparative Examples 1 - 3)

[0082] As the ceramic substrate, a silicon nitride substrate or an aluminum nitride substrate shown in Table 1 was prepared.

[0083] Table 1

[0084]

[0085] Next, copper plates shown in Table 2 were prepared. All the copper plates were oxygen - free copper.

[0086] Table 2

[0087]

[0088] Next, active metal solders shown in Table 3 were prepared. Among active metal solders 1 - 3, the particle size of Sn powder was the largest. Among active metal solder 4, the particle size of Ag powder was the largest. In addition, the melting point of the solder was the value obtained by measuring the DSC curve as described above.

[0089] Table 3

[0090]

[0091] Next, a bonding process was carried out using the ceramic substrate, the copper plate, and the active metal solder. The longitudinal and transverse dimensions of the copper plate corresponded to those of the ceramic substrate. In addition, in the bonding process, the bonding temperature was maintained for 10 - 30 minutes in a vacuum of 10 -3 Pa or less. The combination of each raw material was as shown in Table 4.

[0092] Table 4

[0093]

[0094] For the obtained bonded body, the major axis of the copper grains of the copper plate, the warpage amount of the bonded body, and the bonding strength were measured.

[0095] Regarding the major axis, after etching the surface of the copper plate, SEM observation was carried out. In the SEM observation, three places were arbitrarily observed in a region of 5 mm × 5 mm per unit area. The major axis of the observed copper grains was measured. In addition, the deviation from the average value of the major axis of the copper grains was calculated from the results obtained by arbitrarily observing three places in a region of 5 mm × 5 mm per unit area.

[0096] As the warpage amount of the bonded body, the warpage amount on the long side is measured. The warpage amount of the ceramic substrate is measured from the side of the bonded body. The ends of the long side of the ceramic substrate are connected by a straight line. The position farthest from the surface of the ceramic substrate on this straight line is set as the warpage amount. An embodiment with a warpage amount on the long side of 0.1 mm or less is indicated as a good product (〇), and an embodiment exceeding 0.1 mm is indicated as a defective product (×).

[0097] The bonding strength is measured by a peel test. Specifically, using the bonding conditions of each example and comparative example, specimens for the peel test were prepared. The specimen is a long strip of copper plate bonded to a ceramic substrate. At this time, bonding was performed in such a way that one end of the copper plate was exposed from the ceramic substrate. By vertically stretching the exposed copper plate, the peel strength was measured.

[0098] An embodiment with a bonding strength of 20 kN / m or more is indicated as an excellent product (◎). An embodiment with a bonding strength of 15 kN / m or more and less than 20 kN / m is indicated as a good product (〇). An embodiment with a bonding strength of 14 kN / m or less is indicated as a defective product (×).

[0099] The results are shown in Table 5.

[0100] Table 5

[0101]

[0102] As can be seen from the table, the bonded body according to the example controlled the copper grains of the copper plate. In addition, good results were also obtained for the warpage amount and the bonding strength. This indicates that even when the bonding temperature is set to 800 °C or lower, and further 700 °C or lower, a bonded body with sufficient strength can be obtained. In addition, for Example 3, since Wa and Wt of the silicon nitride substrate deviated from the preferred range, the bonding strength decreased.

[0103] On the contrary, as in Comparative Example 3, even when a solder with a high melting point was used to lower the bonding temperature, a bonded body was not obtained. In addition, for Comparative Examples 1 and 2, since the bonding temperature exceeded 800 °C, the degree of grain growth of the copper grains was large. Therefore, the warpage amount of the bonded body became large.

[0104] As described above, according to the example, even when the size of the ceramic substrate is increased, the warpage amount of the bonded body can be reduced. In addition, a bonded body with a high bonding strength can be obtained. Since the size of the ceramic substrate can be increased, a bonded body suitable for simultaneous processing of multiple pieces can be obtained.

[0105] As described above, several embodiments of the present invention have been illustrated. However, these embodiments are presented 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, changes, etc. can be made without departing from the gist of the invention. These embodiments and their modified forms are included in the scope and gist of the invention, and also included in the invention described in the claims and the scope equivalent thereto. In addition, the above-described embodiments can be implemented in combination with each other.

Claims

1. A bonded body, characterized in that, It is a bonded body having a ceramic substrate and copper plates with a thickness of 0.3 mm or more bonded to both sides of the ceramic substrate via a bonding layer containing an active metal. Among them, the copper plate has a surface perpendicular to the direction in which the copper plate is bonded to the ceramic substrate, in three 5 mm × 5 mm regions contained in the surface, the number ratio of copper grains with a major axis exceeding 400 μm is 0% to 5%, and the major axis is the longest distance between two points on the outer edge of the copper grain, the ceramic substrate is a silicon nitride substrate or an aluminum nitride substrate, and the copper plate is oxygen-free copper, the bonding strength between the ceramic substrate and the copper plate is 15 kN / m or more.

2. The bonded body according to claim 1, characterized in that, The number ratio is 1% or less.

3. The bonded body according to claim 1 or 2, characterized in that, In the three regions, the average value of the major axis of the copper grains is 30 μm to 300 μm.

4. The bonded body according to claim 1 or 2, characterized in that, In the three regions, the average value of the major axis of the copper grains is 50 μm to 150 μm.

5. The bonded body according to claim 1 or 2, wherein, In the three regions, the number ratio of copper grains with a major axis within the average range is 80% or more, and the average range is 0.5 times to 2 times the average value of the major axis of the copper grains in the three regions.

6. The bonded body according to claim 1 or 2, characterized in that, The arithmetic mean height Wa of the waviness curve of the ceramic substrate is 3.7 μm or less, and the maximum section height Wt of the waviness curve is 24 μm or less.

7. The bonded body according to claim 1 or 2, characterized in that, The arithmetic mean height Wa of the waviness curve of the ceramic substrate is 2 μm or less, and the maximum section height Wt of the waviness curve is 10 μm or less.

8. The bonded body according to claim 1 or 2, characterized in that, The bonding layer contains Ti and one or more selected from Ag, Cu, Sn, In, and C.

9. The bonded body according to claim 1 or 2, characterized in that, In the three regions, the average value of the major axis of the copper grains is 30 μm to 300 μm, in the three regions, the number ratio of copper grains with a major axis within the average range is 80% or more, and the average range is 0.5 times to 2 times the average value of the major axis of the copper grains in the three regions.

10. The bonded body according to claim 9, characterized in that, The arithmetic mean height Wa of the waviness curve of the ceramic substrate is 2 μm or less, and the maximum section height Wt of the waviness curve is 10 μm or less.

11. The bonded body according to claim 10, characterized in that, The bonding layer contains Ti and one or more selected from Ag, Cu, Sn, In, and C.

12. A ceramic copper circuit board, characterized in that, The bonded body according to any one of claims 1 to 11 is used.

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