Bonded body, method of manufacturing the same, and power module

Abstract

To provide a joined body excellent in heat cycle characteristics.SOLUTION: The joined body includes a copper plate, a nitride ceramic plate, and a joining portion that joins the copper plate and the nitride ceramic plate and has a higher Sn content than Ag. In the joined body, when a cross section orthogonal to the main surface of the nitride ceramic plate is viewed, the joining part, or the joining part and the copper plate include a network structure in which the Ti component is distributed in a network shape.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a bonded assembly, a manufacturing method thereof, and a power module. [Background technology]

[0002] A bonded body in which a ceramic plate and a metal plate are bonded via a bonding portion is used as a circuit board mounted on an electronic device. Patent Document 1 discloses a ceramic circuit board in which a ceramic substrate and a copper plate are bonded with a bonding layer containing at least one active metal element selected from Ti, Zr, Hf, Al, and Nb, and at least one element selected from Ag, Cu, Sn, In, and C. Patent Document 2 discloses that a protruding portion containing 70 mass % or more of titanium is provided around the bonding portion provided between the ceramic substrate and the copper circuit portion. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2013 / 094213 [Patent Document 2] International Publication No. 2023 / 074470 Summary of the Invention [Problem to be solved by the invention]

[0004] Because the nitride ceramic plate and the metal plate have different thermal expansion coefficients, stress occurs at the joint when the temperature changes. Patent Documents 1 and 2 attempt to improve heat cycle characteristics, but the improvement is still insufficient. One aspect of the present disclosure provides a joined body having excellent heat cycle characteristics and a method for manufacturing the same. Another aspect of the present disclosure provides a power module including such a joined body. [Means for solving the problem]

[0005] One aspect of the present disclosure provides the following conjugate: [1] A joined body comprising a copper plate, a nitride ceramic plate, and a joint portion joining the copper plate and the nitride ceramic plate, the joint portion having a higher Sn content than Ag, A joined body, wherein, when viewed in a cross section perpendicular to the main surface of the nitride ceramic plate, the joint, or the joint and the copper plate, include a network structure in which Ti components are distributed in a network pattern. [2] The joined body according to [1], wherein the Ti component is distributed in a Cu—Sn matrix phase. [3] The joined body according to [1] or [2], wherein the network structure of the Ti component is connected to a TiN layer along the main surface of the nitride ceramic plate. [4] The bonded body according to any one of [1] to [3], wherein when a virtual line parallel to the main surface is drawn in the cross section so as to intersect with the network structure, the maximum number of intersections between the network lines constituting one of the network structures and the virtual line is six or more. [5] The bonded body according to any one of [1] to [4], wherein the distance D from the main surface of the nitride ceramic plate to the most distant part of the network structure in the cross section is 5 μm or more. [6] The joined body according to any one of [1] to [5], wherein the ratio of Ag to Sn in the joint is less than 5 mass %. [7] The bonded body according to any one of [1] to [6], wherein the void ratio in the bonded portion in the cross section is 20% or less.

[0006] The bonded body of [1] above has a bonded part in which the mass ratio of Sn is higher than that of Ag. By including a network structure in which Ti components are distributed in a network pattern in such a bonded part or in the bonded part and copper plate, it is possible to suppress localized concentration of thermal stress caused by heat cycles. Therefore, the bonded body has excellent heat cycle characteristics.

[0007] The bonded body of the above [2] has improved uniformity of the structure at the bonded portion, and can further suppress the local concentration of thermal stress caused by heat cycles, thereby further improving the heat cycle characteristics.

[0008] The bonded body of the above [3] can further improve the heat cycle characteristics because the nitride ceramic plate and the bonded portion are bonded firmly enough.

[0009] The Ti component in the bonded body of [4] or [5] is sufficiently dispersed in a network structure. This further suppresses localized concentration of thermal stress caused by heat cycles, thereby further improving heat cycle characteristics.

[0010] The bonded body of [6] above has a sufficiently low ratio of Ag to Sn. This prevents the Ti component from agglomerating and further prevents the thermal stress generated by heat cycles from concentrating locally. This further improves the heat cycle characteristics.

[0011] The bonded body of the above [7] can further improve the heat cycle characteristics by having a void ratio of 20% or less.

[0012] One aspect of the present disclosure provides the following method for producing a bonded body. [8] A step of laminating a copper plate and a nitride ceramic plate via a brazing material containing Sn, Cu, and TiH2 to obtain a laminate; and heating the laminate to 800°C or higher to bond the copper plate and the nitride ceramic plate together, The brazing filler metal has a ratio of Sn to the total of Sn and Cu of 40 mass % or more, and a ratio of Ag to Sn of less than 5 mass %. [9] The method for manufacturing a joined body according to [8], wherein, when viewed in a cross section perpendicular to the main surface of the nitride ceramic plate, the joined portion joining the nitride ceramic plate and the copper plate, or the joined portion and the copper plate, include a mesh structure in which Ti components are distributed in a mesh pattern.

[0013] The method for manufacturing a bonded body described in [8] above includes a step of heating a copper plate and a nitride ceramic plate to 800°C or higher using a brazing filler metal of a predetermined composition. When the laminate is heated at this temperature, the Ti component is distributed in a network pattern. This prevents the thermal stress generated by heat cycles from concentrating locally. Therefore, the bonded body obtained by the above manufacturing method has excellent heat cycle characteristics. The bonded body obtained by the manufacturing method described in [9] above has even better heat cycle characteristics.

[0014] One aspect of the present disclosure provides the following power module.

[10] A power module comprising the bonded body according to any one of [1] to [7] above, or the bonded body manufactured by the manufacturing method according to [8] or [9] above, and a semiconductor element electrically connected to the copper plate.

[0015] The power module of

[10] above has a bonded body with excellent heat cycle characteristics, and therefore has excellent reliability. [Effects of the Invention]

[0016] One aspect of the present disclosure can provide a joined body having excellent heat cycle characteristics and a method for manufacturing the same. Another aspect of the present disclosure can provide a power module including such a joined body. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 is a perspective view showing an example of a bonded body. [Figure 2] FIG. 10 is a perspective view showing another example of a bonded body. [Figure 3] FIG. 2 is a cross-sectional view schematically showing an enlarged image of a part of a cross section of a bonded body. [Figure 4] FIG. 1 is a cross-sectional view showing an example of a power module. [Figure 5] 1 is an SEM photograph (magnification: 3000 times) of a cross section of a bonded body of Example 2. [Figure 6] 1 is an SEM photograph (magnification: 3000 times) of a cross section of a bonded body of Comparative Example 3. [Figure 7] 1 is an SEM photograph (magnification: 300 times) of a cross section of a bonded body of Comparative Example 4. DETAILED DESCRIPTION OF THE INVENTION

[0018] Hereinafter, embodiments of the present disclosure will be described, occasionally with reference to the drawings. However, the following embodiments are merely examples for explaining the present disclosure and are not intended to limit the present disclosure to the following content. In the description, the same reference numerals will be used for identical elements or elements having the same functions, and redundant descriptions will be omitted where appropriate. Positional relationships, such as up, down, left, and right, are based on the positional relationships relative to the orientation of the reference numerals shown in the drawings, unless otherwise specified. The dimensional ratios of each element are not limited to those shown. Numerical ranges indicated with the symbol "~" include the lower and upper limits. That is, a numerical range indicated as "A to B" means A or greater and B or less. Numerical ranges in which the upper or lower limit of each numerical range is replaced with the numerical value of any of the examples are also included in the present disclosure. When multiple numerical ranges are exemplified in stages, a numerical range in which the upper or lower limit of a first numerical range is replaced with the upper or lower limit of a second numerical range that is narrower than the first numerical range is also included in the present disclosure. Multiple exemplified substances and materials may be used singly or in combination of two or more arbitrarily selected types.

[0019] A bonded body according to one embodiment includes a copper plate, a nitride ceramic plate, and a bonding portion bonding the copper plate and the nitride ceramic plate. The nitride ceramic plate may be a silicon nitride plate or an aluminum nitride plate. The nitride ceramic plate may be a nitride ceramic plate containing aluminum nitride and silicon nitride. The nitride ceramic plate may contain nitride ceramic as a main component and a component derived from a sintering aid as a secondary component. The silicon nitride plate may contain silicon nitride as a main component and a component derived from a sintering aid as a secondary component. The aluminum nitride plate may contain aluminum nitride as a main component and a component derived from a sintering aid as a secondary component. In the present disclosure, the main component refers to the component that is contained in the largest amount by mass, and may be 80% by mass or more, 90% by mass or more, 95% by mass or more, 98% by mass or more, or 99% by mass or more of the total.

[0020] The shape of the nitride ceramic plate is not particularly limited. The shape of the main surface of the nitride ceramic plate may be a polygon, such as a triangle or a rectangle, or may be a circle or an ellipse. Alternatively, the corners of the polygon may be chamfered. The main surfaces are two surfaces that are larger in area than the other surfaces and intersect perpendicularly in the thickness direction. The copper plate contains copper as a main component. The copper plate may be a commercially available oxygen-free copper plate. The copper plate may form a heat sink or a circuit. Therefore, the shape of the copper plate is not particularly limited. One or more copper plates may be provided on one main surface of the nitride ceramic plate. The copper plates arranged on one main surface of the nitride ceramic plate may have the same shape and thickness or may be different from each other. One or more copper plates may be provided on only one main surface of the nitride ceramic plate, or one or more copper plates may be provided on each of the two main surfaces of the nitride ceramic plate.

[0021] The joint between the nitride ceramic plate and the copper plate has a higher mass ratio of Sn than the mass ratio of Ag. When Ag is contained in the joint, Ti components tend to aggregate near the Ag-rich phase. From the viewpoint of suppressing aggregation of Ti components and sufficiently dispersing the Ti components in a network-like structure, the mass ratio of Ag in the joint may be less than 35 mass%, less than 30 mass%, less than 20 mass%, less than 10 mass%, less than 5 mass%, less than 1 mass%, or 0. From the viewpoint of increasing the uniformity of the structure of the joint, the mass ratio of Sn in the joint may be 35 mass% or more, 40 mass% or more, 50 mass% or more, 60 mass% or more, or 70 mass% or more. The ratio of each component in the joint may be the same as the ratio of the raw material composition of the brazing filler metal.

[0022] The joint may contain copper. This improves wettability with the copper plate and further improves the uniformity of the joint structure. From the viewpoint of further improving the wettability of the copper plate and the joint, the mass ratio of Cu in the joint may be 5 mass% or more, 10 mass% or more, 15 mass% or more, or 20 mass% or more. In the joint, copper may form a Cu-Sn intermetallic compound. This suppresses aggregation of the Ti component and allows it to be sufficiently dispersed in a network-like pattern. As a result, thermal stress caused by heat cycles can be reduced. Sn, Cu, and Ag may be contained as compounds or alloys with other components. Note that the mass ratios of Sn, Cu, and Ag are all values ​​converted into simple metals.

[0023] When viewed in a cross section obtained by cutting the nitride ceramic plate in a direction perpendicular to the main surface, the bonded body includes a network structure in which the Ti component is distributed in a network pattern at the bonded portion or at the bonded portion and the copper plate. The network structure may be contained only at the bonded portion, or may be contained in the bonded portion and the copper plate (e.g., in a region closer to the bonded portion). The Ti component in this disclosure is a concept that encompasses all of metallic titanium, alloys containing titanium, and compounds containing titanium. The Ti component may be distributed in a Cu—Sn matrix phase at the bonded portion or at the bonded portion and the copper plate. The Cu—Sn matrix phase is composed of an alloy mainly composed of Cu and Sn. The Cu—Sn matrix phase may be contained only at the bonded portion, or may be contained in the bonded portion and the copper plate.

[0024] The joint may contain other metals or metal compounds. For example, the joint may contain a TiN layer along the major surface of the nitride ceramic plate. When the nitride ceramic plate is a silicon nitride plate and the joint contains a TiN layer, the bond between the silicon nitride plate and the joint can be sufficiently strong.

[0025] The network structure, in which Ti components are distributed in a mesh-like pattern, can be detected in a 3000x magnification image of a cross section of the bonded body obtained by cutting the nitride ceramic plate in a direction perpendicular to its main surface, using a scanning electron microscope (SEM).The fact that the components that make up the network structure contain Ti can be confirmed by elemental mapping using an energy dispersive X-ray spectrometer (EDS).

[0026] The void fraction at the joint may be 20% or less, 10% or less, 5% or less, or 3% or less. By reducing the void fraction, the heat cycle characteristics can be further improved. The void fraction can be determined by the method described in the Examples.

[0027] FIG. 1 is a perspective view showing an example of a bonded body. The bonded body 100 in FIG. 1 includes a nitride ceramic plate 10 and a copper plate 20 and a copper plate 30 bonded to two main surfaces of the nitride ceramic plate 10, respectively. The copper plate 20 and the copper plate 30 are bonded to the main surfaces of the nitride ceramic plate 10 by joints (not shown). Portions of the copper plate 20 and / or the copper plate 30 may be removed by etching after resist printing, and processed into a desired pattern. A circuit board obtained in this manner also corresponds to the bonded body of the present disclosure.

[0028] Fig. 2 is a perspective view showing another example of a bonded body. The bonded body 102 in Fig. 2 is a circuit board and includes a nitride ceramic plate 10, a plurality of conductors 22 bonded to one main surface of the nitride ceramic plate 10, and a heat sink 32 bonded to the other main surface of the nitride ceramic plate 10. The conductors 22 may be terminals that constitute a circuit in a power module, for example. The conductors 22 and the heat sink 32 are made of copper plates and are bonded to the main surface of the nitride ceramic plate 10 by bonding parts (not shown).

[0029] FIG. 3 is a cross-sectional view schematically illustrating an enlarged image of a portion of a cross section of a bonded body. The cross section of the bonded body can be obtained by cutting the bonded body in a direction perpendicular to the main surfaces of the nitride ceramic plates. Such an image can be observed, for example, with an ultra-high resolution field emission scanning electron microscope (JSM-7900F) manufactured by JEOL Ltd. The nitride ceramic plate 10 and the copper plate 20 are bonded at a joint 50. The joint 50 has a TiN layer 52 along the main surface 10A of the nitride ceramic plate 10. A network structure 40 in which Ti components are distributed in a network pattern is formed in the region of the joint 50 and the copper plate 20 near the joint 50. In the present disclosure, "Ti components are distributed in a network pattern" refers to a state in which the network lines 42 intersect with each other. In the network structure 40, the network lines 42 may be entangled with each other. The network lines 42 may have a thickness of 2 μm or less, or 1 μm or less.

[0030] Aggregates of Ti components forming lumps do not qualify as a network structure. From the viewpoint of reducing stress concentration, it is preferable that the length of the Ti component lumps along the main surface 10A of the nitride ceramic plate 10 in the cross section be small. It is preferable that the bonded body does not contain Ti component lumps with a length of 3 μm or more, or 2 μm or more. This can suppress localized concentration of thermal stress caused by heat cycles.

[0031] In a cross section such as that shown in FIG. 3 , when imaginary lines parallel to the main surface 10A of the nitride ceramic plate 10 are drawn so as to intersect with the network structure 40, the maximum number of intersections between the imaginary lines and the network lines 42 constituting one network structure 40 may be 6 or more, 7 or more, 8 or more, 9 or more, or 10 or more. The greater the maximum number of intersections in the network structure 40, the higher the dispersion of the Ti component. Therefore, the concentration of thermal stress caused by heat cycles can be sufficiently suppressed. The maximum number of intersections is determined by drawing multiple imaginary lines VL parallel to the main surface 10A, selecting the imaginary line VL1 with the maximum number of intersections, and counting the number of intersections between the imaginary line VL1 and the network lines 42 constituting the network structure 40, as shown in FIG. 3 . In the example of FIG. 3 , the maximum number of intersections between the imaginary lines VL and the network lines 42 constituting one network structure 40 is 7.

[0032] The distance D from the main surface 10A of the nitride ceramic plate 10 to the furthest part of the network structure 40 may be 5 μm or more, 8 μm or more, or 10 μm or more. A larger distance D can suppress localized concentration of thermal stress caused by heat cycles. The distance D is measured along a direction perpendicular to the main surface 10A in a cross section such as that shown in FIG. 3. The distance D may be greater than the thickness of the joint 50. The boundary between the joint 50 and the copper plate 20 does not need to be detectable.

[0033] In the example shown in FIG. 3 , the TiN layer 52 is formed to cover the entire main surface 10A of the nitride ceramic plate 10. However, in a modified example, the TiN layer 52 may be formed to cover only a portion of the main surface 10A. In another modified example, the network structure 40 may be formed only in the joint 50 and not on the copper plate 20. When observing the cross section of the bonded body at multiple locations using a scanning electron microscope (SEM), the network structure 40 does not need to be detected in all images. It is sufficient that the network structure 40 is detected in at least one of multiple images showing enlarged views of different locations. Furthermore, when the nitride ceramic plate 10 is cut in a direction perpendicular to the main surface 10A to obtain multiple cross sections, it is sufficient that the network structure 40 is detected in at least one of the multiple cross sections. In the area where the network structure 40 is detected, local concentration of thermal stress caused by heat cycles is suppressed, thereby improving heat cycle characteristics.

[0034] A method for producing a bonded body according to one embodiment includes a lamination step of laminating a copper plate and a nitride ceramic plate via a brazing filler metal containing Sn, Cu, and TiH to obtain a laminate, and a firing step of heating the laminate to 800°C or higher to bond the copper plate and the nitride ceramic plate. The copper plate and the nitride ceramic plate are as described in the embodiment of the bonded body. The copper plate and the nitride ceramic plate may be commercially available products or may be produced by a known method.

[0035] The brazing filler metal can be prepared by blending, for example, tin powder, copper powder, titanium hydride powder, an organic solvent, a binder, etc. The brazing filler metal may or may not contain silver powder. Furthermore, components other than those mentioned above may also be blended.

[0036] The ratio of Sn to the total of Sn and Cu in the brazing filler metal is 40% by mass or more, and may be 50% by mass or more, 60% by mass or more, or 70% by mass or more. When a laminate using such a brazing filler metal is heated to 800°C or more, Sn sufficiently forms a Cu-Sn intermetallic compound not only with the Cu contained in the brazing filler metal but also with the Cu contained in the copper plate. This results in the formation of a highly uniform structure, facilitating the distribution of the Ti component in a mesh-like pattern. The ratio of Sn to the total of Sn and Cu in the brazing filler metal may be 95% by mass or less, 90% by mass or less, or 85% by mass. Such a brazing filler metal has excellent wettability with copper plates, resulting in a stronger bond to the copper plates.

[0037] The ratio of Ag to Sn in the brazing filler metal is less than 5% by mass, and may be less than 3% by mass, less than 1% by mass, or 0. Ag tends to cause non-uniform diffusion distances when the laminate is heated. By reducing the Ag ratio, a highly uniform structure is easily formed, and the precipitation of Ti components in clumps can be suppressed. The above-mentioned mass ratios of Ag, Sn, and Cu are all values ​​converted into simple metals. The mass ratio of titanium hydride (TiH2) in the brazing filler metal may be 1 to 8% by mass, 2 to 6% by mass, or 3 to 5% by mass, from the viewpoint of sufficiently dispersing the Ti component in a network while sufficiently forming a TiN layer along the main surface 10A of the nitride ceramic plate 10.

[0038] The ratio of tin powder to the total metal-containing powder used in preparing the brazing filler metal may be 30% by mass or more, 40% by mass or more, 50% by mass or more, 60% by mass or more, or 70% by mass or more. This facilitates the formation of a highly uniform structure, thereby reducing thermal stress caused by heat cycles. The metal-containing powder includes metal powder and metal compound powder (such as titanium hydride powder). The ratio of copper powder to the total metal-containing powder used in preparing the brazing filler metal may be 5% by mass or more, 10% by mass or more, or 15% by mass or more. Such a brazing filler metal has excellent wettability with copper plates, allowing for stronger bonding to copper plates.

[0039] The ratio of the silver powder to the entire metal-containing powder used in preparing the brazing filler metal may be less than 5 mass%, less than 3 mass%, less than 1 mass%, or 0. The ratio of the titanium hydride powder to the entire metal-containing powder used in preparing the brazing filler metal may be 1 to 8 mass%, 2 to 6 mass%, or 3 to 5 mass%.

[0040] A brazing filler metal is applied to the main surface of a nitride ceramic plate, and a copper plate is placed on the main surface to obtain a laminate. The brazing filler metal may be applied to the main surface of the nitride ceramic plate by a method such as a roll coater method, a screen printing method, or a transfer method. The viscosity of the brazing filler metal may be, for example, 5 to 20 Pa·s. The organic solvent content in the brazing filler metal may be, for example, 5 to 25 mass %, and the binder content may be, for example, 2 to 15 mass %.

[0041] The laminate thus produced is fired in a heating furnace. The heating temperature of the laminate is 800°C or higher, and may be 830°C or higher, 850°C or higher, or 900°C or higher. This allows the formation of a network structure in which the Ti component is sufficiently dispersed. The heating temperature of the laminate may be 950°C or lower. An example of the heating temperature of the laminate is 800 to 950°C. The time (retention time) for holding the above heating temperature may be 0.5 to 4 hours. The rate of temperature rise to the above heating temperature may be 0.5 to 10°C / min, or 1 to 8°C / min, from the viewpoint of efficiently producing a bonded body having excellent heat cycle characteristics.

[0042] The atmosphere in the heating furnace during firing may be an inert gas such as nitrogen gas, and may be a reduced pressure (1.0 × 10 -3The firing may be performed at a pressure of 1000 Pa or less, or in a vacuum. By firing the laminate under such conditions, the nitride ceramic and the copper plate can be sufficiently bonded together. The heating furnace may be a continuous type that continuously produces a plurality of bonded bodies, or may be a batch type that produces one or a plurality of bonded bodies. The firing may be performed while pressing the laminate in the lamination direction. The rate of cooling from the above heating temperature to room temperature may be 0.5 to 10°C / min, or 1 to 8°C / min, from the viewpoint of efficiently producing a bonded body having excellent heat cycle characteristics.

[0043] The bonded body manufactured in this manner may have the same appearance as the bonded body 100 of the above embodiment and the same microstructure as that shown in Fig. 3. The description of the bonded body 100 also applies to the manufacturing method of the bonded body of this embodiment. The manufacturing method of the bonded body 100 is not limited to the above manufacturing method.

[0044] When manufacturing a circuit board having a plurality of conductors, such as the bonded body 102, a step is performed in which a portion of the copper plate 20 in the bonded body 100 is removed to form the conductors 22 that constitute the circuit. This step may be performed by, for example, photolithography. Specifically, first, a photosensitive resist is printed on the main surface of the bonded body 100 (the main surface of the copper plate 20). Then, an exposure device is used to form a resist pattern having a predetermined shape. The resist may be either negative or positive. Uncured resist is removed, for example, by washing.

[0045] After forming the resist pattern, the portions of the copper plate 20 that are not covered by the resist pattern are removed by etching. This exposes a part of the main surface of the nitride ceramic plate 10 in the removed portions. Thereafter, the resist pattern is removed to obtain a circuit board having a plurality of conductors 22, such as the bonded body 102. The shape of the conductors 22 may be adjusted by changing the etching conditions or the number of times etching is performed.

[0046] Examples of the etching solution that can be used include a ferric chloride solution, a cupric chloride solution, sulfuric acid, and hydrogen peroxide solution. If a brazing material layer or the like remains on the main surface of the nitride ceramic plate 10 after etching, it may be removed using a solution containing at least one selected from the group consisting of an ammonium halide aqueous solution, an inorganic acid such as sulfuric acid or nitric acid, and hydrogen peroxide solution. The method for removing the resist pattern is not particularly limited, and may be, for example, immersion in an alkaline aqueous solution. The bonded body 102 has excellent heat cycle characteristics and may be used, for example, as a circuit board for a power module.

[0047] A power module according to one embodiment includes the above-described assembly as a circuit board and a semiconductor element electrically connected to the copper plate of the assembly. The power module may include an assembly 102. A power module is an electronic component for converting and controlling electric power, and its performance and reliability are affected by the assembly used. Since the assembly has excellent heat cycle characteristics, a power module including the assembly operates stably and has high reliability even when used in a high-temperature environment. Note that the use of the assembly is not limited to power modules.

[0048] 4 is a cross-sectional view showing an example of a power module. The power module 200 includes a base plate 70 and a bonding body 102 bonded to one surface of the base plate 70 via solder 82. A heat sink 32 on one surface of the bonding body 102 is bonded to the base plate 70 via the solder 82.

[0049] A semiconductor element 90 is attached to at least one of the conductor portions 22 on the other surface side of the bonded body 102 via solder 81. The semiconductor element 90 is connected to a predetermined location of the conductor portion 22 by a metal wire 84 such as an aluminum wire. In this manner, the semiconductor element 90 and the conductor portion 22 are electrically connected. To electrically connect the outside of the housing 86 to the conductor portion 22, conductor portion 22a, which is one of the conductor portions 22, is connected to an electrode 83 provided to penetrate the housing 86 via solder 85.

[0050] A housing 86 is disposed on one main surface of the base plate 70, and is integrated with the main surface to house the bonded body 102. A housing space formed by the one main surface of the base plate 70 and the housing 86 is filled with a resin 80. The resin 80 seals the bonded body 102 and the semiconductor element 90. The resin may be, for example, a thermosetting resin or a photocurable resin.

[0051] Cooling fins 72, which form a heat dissipation section, are joined to the other main surface of the base plate 70 via grease 74. Screws 73 are attached to the ends of the base plate 70 to secure the cooling fins 72 to the base plate 70. The base plate 70 and the cooling fins 72 may be made of aluminum. The base plate 70 and the cooling fins 72 have high thermal conductivity and therefore function well as heat dissipation sections. Since the power module 200 includes the joined body 102, it operates stably even when used in a high-temperature environment and has high reliability.

[0052] Although several embodiments of the present disclosure have been described above, the present disclosure is not limited to the above-described embodiments. For example, the joined body and power module of the present disclosure are not limited to the shapes and structures described above. [Example]

[0053] The present disclosure will be described in more detail below with reference to examples, although the present disclosure is not limited to the following examples.

[0054] [Preparation of junction] Example 1 To prepare the brazing filler metal, the following raw material powders were prepared. Tin powder: Manufactured by Fukuda Metal Foil and Powder Co., Ltd.: Sn-HPN (trade name), average particle size D50: 3μm, specific surface area 0.1m 2 / g Titanium hydride powder (TiH2 powder): TCH-100 (product name), manufactured by Toho Tech Co., Ltd.

[0055] Tin powder and titanium hydride powder were mixed so that the mass ratio of Sn to TiH2 was as shown in Table 1, and an organic solvent and a binder were added to prepare a brazing filler metal. Table 1 also shows the mass ratio of tin powder to the total mass of tin powder and copper powder. The brazing filler metal was applied to both main surfaces of a commercially available silicon nitride plate (thickness: 0.32 mm) at a coating amount of 8 mg / cm. 2 The coating was carried out by screen printing so as to obtain the following.

[0056] A copper plate (thickness: 0.5 mm, purity: 99.60% by mass) was placed on each of the main surfaces of a silicon nitride plate to obtain a laminate. The laminate was heated in a vacuum using an electric furnace at a furnace temperature of 900°C for 1 hour to bond the silicon nitride plate and the copper plate. The heating rate from room temperature to the heating temperature and the cooling rate from the heating temperature to room temperature were both 5°C / min. In this way, a bonded body was produced that included a silicon nitride plate, a pair of copper plates, and bonding portions that bonded the pair of copper plates to the main surfaces of the silicon nitride plate.

[0057] (Examples 2 to 5, Comparative Examples 1 and 2) The following copper powders were prepared in addition to the powders used in Example 1. Copper powder, tin powder, and titanium hydride powder were blended so that the mass ratios of Cu, Sn, and TiH2 were as shown in Table 1, and an organic solvent and a binder were added to prepare each brazing filler metal. Joined bodies were produced in the same manner as in Example 1, except that the brazing filler metals prepared in this manner were used. Copper powder: manufactured by Fukuda Metal Foil & Powder Co., Ltd., Cu-HWQ (trade name), average particle size D50: 3.0μm, specific surface area: 0.4m 2 / g

[0058] (Comparative Example 3) The following silver powders were prepared in addition to the powders used in Example 2. Silver powder, copper powder, tin powder, and titanium hydride powder were blended so that Ag, Cu, Sn, and TiH2 had the mass ratios shown in Table 1, and an organic solvent and a binder were added to prepare brazing filler metals. A joined body was produced in the same manner as in Example 1, except that the brazing filler metal prepared in this manner was used. Silver powder: manufactured by Fukuda Metal Foil & Powder Co., Ltd., Ag-HWQ (trade name), average particle diameter D50: 2.5 μm, specific surface area 0.4 m 2 / g

[0059] [Table 1]

[0060] [Cross-section analysis] After embedding each bonded body in resin, it was cut using a coater machine in a direction perpendicular to the main surface so as to pass through the center of the main surface of the silicon nitride plate. Of the cross sections obtained by cutting, the area near the bond between one main surface of the silicon nitride plate and the copper plate was observed using a scanning electron microscope (SEM) (magnification: 3000x). The measurement device used was an ultra-high resolution field emission scanning electron microscope (device name: JSM-7900F) manufactured by JEOL Ltd.

[0061] Fig. 5 is an SEM photograph (magnification: 3000x) of a cross section of Example 2. As shown in Fig. 5, it was confirmed that in the bonded bodies of Examples 1 to 5, a network structure 40 composed of mesh lines was included in the bonded portion between the silicon nitride plate and the copper plate. Analysis of the composition of the bonded portion using an energy dispersive X-ray spectrometer (EDS) confirmed that Ti components were distributed in a network pattern in a Cu-Sn matrix phase 54 to form the network structure 40. Furthermore, it was confirmed that in the bonded bodies of Examples 1 to 5, a TiN layer 52 was formed along the main surface of the silicon nitride plate 12, and that the network structure 40 was connected to the TiN layer 52.

[0062] In an SEM photograph such as that shown in Figure 5, imaginary lines parallel to the main surface of the silicon nitride plate 12 were drawn so as to intersect with the network structure 40. The number of intersections between the network lines constituting the network structure 40 and the imaginary lines was counted, and the maximum number of intersections was determined. Evaluation was performed according to the maximum number of intersections using the following criteria. The results are shown in Table 2. When the SEM photograph contained multiple network structures, the maximum number of intersections in each network structure was counted, and evaluation was based on the largest of the maximum values. The evaluation results are shown in the "Evaluation of Number of Intersections" column in Table 2. A: 10 or more B: 8~9 pieces C: 6~7 pieces

[0063] In the SEM photograph shown in Fig. 5, the distance D from the main surface of the silicon nitride plate 12 to the farthest part of the network structure 40 was measured. The distance D was measured in a direction perpendicular to the main surface of the silicon nitride plate (nitride ceramic plate 10), as shown in Fig. 3. The results are shown in Table 2.

[0064] Fig. 6 is an SEM photograph (magnification: 3000 times) of a cross section of Comparative Example 3. In the cross sections of the joined bodies of Comparative Examples 1 to 3, as shown in Fig. 6, the Ti component was precipitated as lumps 60 near the main surface of the silicon nitride plate 12. The lumps 60 were precipitated so as to be surrounded by an Ag-rich phase 62.

[0065] [Void fraction measurement] Using an ultrasonic flaw detector (ES5000 manufactured by Hitachi Power Solutions Co., Ltd.), the area of ​​voids in the bonded portion between one main surface of the silicon nitride plate and the copper plate of each bonded body was measured. The void area was divided by the area of ​​the copper plate to calculate the void ratio. The void ratios were as shown in Table 2.

[0066] [Evaluation of heat cycle characteristics] Each bonded body was subjected to a heat cycle test. Specifically, a series of steps consisting of holding at -40°C for 15 minutes, 25°C for 5 minutes, 150°C for 15 minutes, and 25°C for 5 minutes was defined as one cycle, and this cycle was repeated 1,000 times. After that, the bonded body was etched using a ferric chloride solution and a mixed solution of ammonium fluoride and hydrogen peroxide to remove the copper plate and bonded parts from the bonded body.

[0067] Using a scanner, an image of the main surface of the silicon nitride plate from which the copper plate and joints had been removed was obtained at a resolution of 600 dpi x 600 dpi. The image was binarized using image analysis software GIMP2 (threshold 140) to calculate the area of ​​the cracks. The calculated crack area was divided by the area of ​​the main surface of the silicon nitride plate to determine the crack ratio. The results are shown in Table 2.

[0068] [Table 2]

[0069] The cross sections of Examples 1 to 5 contained a network structure of the Ti component. In contrast, the cross sections of Comparative Examples 1 to 3 contained clumps of the Ti component. As shown in Table 2, the crack rates of the bonded bodies of Comparative Examples 1 and 3 were higher than those of Examples 1 to 5. In the evaluation of the heat cycle properties of the bonded body of Comparative Example 2, the copper plate peeled off from the main surface of the silicon nitride plate. These results confirmed that Examples 1 to 5 were superior in durability against heat cycles to Comparative Examples 1 to 3.

[0070] Example 6 A bonded body was produced in the same manner as in Example 2, except that the holding time at 900°C was changed to 2 hours. Cross-sectional analysis, measurement of void ratio, and evaluation of heat cycle characteristics were carried out in the same manner as in Example 2. The results are shown in Table 3.

[0071] Example 7 A bonded body was produced in the same manner as in Example 2, except that the temperature increase rate from room temperature to the heating temperature and the temperature decrease rate from the heating temperature to room temperature were both 2°C / min. Cross-sectional analysis, void ratio measurement, and heat cycle property evaluation were carried out in the same manner as in Example 2. The results are shown in Table 3.

[0072] Example 8 A bonded body was produced in the same manner as in Example 2, except that the heating temperature was set to 850°C. Cross-sectional analysis, measurement of void ratio, and evaluation of heat cycle characteristics were carried out in the same manner as in Example 2. The results are shown in Table 3.

[0073] Comparative Example 4 A bonded body was produced in the same manner as in Example 2, except that the heating temperature was set to 780°C. Cross-sectional analysis, measurement of void ratio, and evaluation of heat cycle characteristics were carried out in the same manner as in Example 2. The results are shown in Table 3.

[0074] [Table 3]

[0075] The cross sections of Examples 6 to 8 contained a network structure of the Ti component. In contrast, the cross section of Comparative Example 4 contained clumps of the Ti component. FIG. 7 is an SEM photograph (magnification: 300x) of the cross section of the bonded body of Comparative Example 4. As shown in FIG. 7, many voids V were formed in the bonded portion of the bonded body of Comparative Example 4. This is thought to be because the heating temperature was too low, which prevented sufficient diffusion of Sn from the bonded portion to the copper plate and Cu from the copper plate to the bonded portion. For this reason, when the bonded body of Comparative Example 4 was subjected to 15 cycles in an evaluation of its heat cycle properties, the copper plate peeled off from the main surface of the silicon nitride plate. [Explanation of symbols]

[0076] 10...nitride ceramic plate, 10A...main surface, 12...silicon nitride plate, 20, 30...copper plate, 22...conductor portion, 22a...conductor portion, 32...heat sink plate, 40...mesh structure, 42...mesh line, 50...joint portion, 70...base plate, 72...cooling fin, 73...screw, 74...grease, 80...resin, 81, 82, 85...solder, 83...electrode, 84...metal wire, 86...housing, 90...semiconductor element, 100, 102...joint, 200...power module.

Claims

1. A joined body comprising: a copper plate; a nitride ceramic plate; and a joint portion joining the copper plate and the nitride ceramic plate, the joint portion having a higher Sn content than Ag, A joined body, wherein, when viewed in a cross section perpendicular to the main surface of the nitride ceramic plate, the joint, or the joint and the copper plate, include a network structure in which Ti components are distributed in a network pattern.

2. 2. The joint body according to claim 1, wherein the Ti component is distributed in a Cu—Sn matrix phase.

3. 3. The joined body according to claim 1, wherein the network structure of the Ti component is connected to a TiN layer along the main surface of the nitride ceramic plate.

4. 3. The bonded structure according to claim 1, wherein, when a virtual line parallel to the main surface is drawn in the cross section so as to intersect with the network structure, the maximum number of intersections between the virtual line and a mesh line constituting one of the network structures is six or more.

5. 3. The joined body according to claim 1, wherein a distance D from a main surface of the nitride ceramic plate to the most distant part of the network structure in the cross section is 5 [mu]m or more.

6. 3. The joined body according to claim 1, wherein the ratio of Ag to Sn in the joint is less than 5 mass %.

7. 3. The bonded body according to claim 1, wherein the void ratio in the bonded portion in the cross section is 20% or less.

8. The copper plate and the nitride ceramic plate were bonded to each other with Sn, Cu and TiH ２ a step of laminating the layers via a brazing filler metal containing the compound to obtain a laminate; and heating the laminate to 800°C or higher to bond the copper plate and the nitride ceramic plate together, In the brazing filler metal, the ratio of Sn to the total of Sn and Cu is 40 mass % or more, and the ratio of Ag to Sn is less than 5 mass %.

9. 9. The method for manufacturing a joined body according to claim 8, wherein, when viewed in a cross section perpendicular to a main surface of the nitride ceramic plate, a joining portion joining the nitride ceramic plate and the copper plate, or the joining portion and the copper plate, include a mesh structure in which a Ti component is distributed in a mesh pattern.

10. A power module comprising the bonded body according to claim 1 or 2 and a semiconductor element electrically connected to the copper plate.

Images