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 ceramic plate, and a joining portion that joins the copper plate and the ceramic plate. In the bonding portion, the mass ratio of Sn is higher than the mass ratio of Ag. When a cross section of the joined body orthogonal to the main surface of the ceramic plate is viewed, the joined body has a Sn-containing layer containing Sn along the main surface of the ceramic plate, and the Sn-containing layer has a thickness T of 105 μm or more with reference to the main surface of the ceramic plate.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 together with a bonding portion 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] Since the 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 ceramic plate, and a joining portion joining the copper plate and the ceramic plate, The joint has a higher mass ratio of Sn than a mass ratio of Ag, When viewed in a cross section perpendicular to a main surface of the ceramic plate, a Sn-containing layer containing Sn is provided along the main surface, The Sn-containing layer has a thickness T of 105 μm or more from the main surface. [2] The joined body according to [1], wherein the ratio of Ag to Sn in the Sn-containing layer is less than 5 mass %. [3] The joined body according to [1] or [2], wherein the Sn-containing layer is formed in the joint and in a region of the copper plate closer to the joint. [4] The bonded body according to any one of [1] to [3], wherein the bonded portion contains Cu. [5] The joined body according to any one of [1] to [4], wherein, when viewed in cross section, the Sn-containing layer includes a compositionally gradient layer in which the mass ratio of Sn decreases with increasing distance from the ceramic plate. [6] The bonded body according to any one of [1] to [5], wherein the void ratio in the bonded portion in the cross section is 20% or less. [7] The joined body according to any one of [1] to [6], wherein the ceramic plate is a silicon nitride plate, and the joining portion includes a TiN layer.

[0006] The bonded body of [1] above has a bonded portion in which the mass ratio of Sn is higher than that of Ag. Sn can sufficiently form a Cu-Sn intermetallic compound with Cu contained in the copper plate. This reduces thermal stress caused by heat cycles. In addition, the Sn-containing layer has a sufficient thickness T based on the main surface of the ceramic plate, which reduces local concentration of thermal stress caused by heat cycles. Therefore, the bonded body has excellent heat cycle characteristics.

[0007] In the bonded body of [2] above, the proportion of Ag, which is more likely to have a non-uniform diffusion length than Sn when bonding a ceramic plate and a copper plate, is sufficiently reduced. This further suppresses the local concentration of thermal stress caused by heat cycles, thereby further improving the heat cycle characteristics.

[0008] In the bonded body of the above [3], the Sn-containing layer is formed in the bonding portion and in the region of the copper plate close to the bonding portion, so that the bonding between the copper plate and the bonding portion can be sufficiently strengthened, and therefore the heat cycle characteristics can be further improved.

[0009] In the joined body of the above [4], the uniformity of the structure of the joined portion can be sufficiently improved by the inclusion of Cu in the joined portion. This can further suppress the local concentration of thermal stress caused by heat cycles. Therefore, the heat cycle characteristics can be further improved.

[0010] The joined body of [5] above has a composition gradient layer in which the mass ratio of Sn decreases with increasing distance from the ceramic plate, thereby further suppressing the local concentration of thermal stress caused by heat cycles, thereby further improving the heat cycle characteristics.

[0011] The bonded body of the above [6] can further improve the heat cycle characteristics by having a void ratio of 20% or less.

[0012] The bonded body of the above [7] can further strengthen the bond between the silicon nitride plate and the bonded portion by including a TiN layer.

[0013] 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 ceramic plate via a brazing material containing Sn and Cu to obtain a laminate; and heating the laminate to 800°C or higher to bond the copper plate and the ceramic plate, 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 the joined body has a Sn-containing layer that contains Sn along the main surface when viewed in a cross section perpendicular to the main surface of the ceramic plate, and the Sn-containing layer has a thickness T of 105 μm or more based on the main surface.

[0014] The method for manufacturing a joined body in [8] above includes a step of joining a copper plate and a ceramic plate by heating to 800°C or higher using a brazing filler metal of a predetermined composition. At this heating temperature, Sn sufficiently forms a Cu-Sn intermetallic compound with Cu contained in the copper plate. In addition, Ag, which tends to have non-uniform diffusion distances, is reduced. Due to these factors, the manufacturing method described above can form a highly uniform structure. Therefore, the joined body obtained by the manufacturing method described above has excellent heat cycle properties. The joined body obtained by the manufacturing method described above has even better heat cycle properties.

[0015] 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.

[0016] The power module of

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

[0017] 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]

[0018] [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 joined 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] FIG. 5(A) is an SEM photograph (magnification: 300 times) of a cross section of the bonded body of Example 2, and FIG. 5(B) is a mapping photograph of Sn elements in the cross section shown in FIG. 5(A). [Figure 6] FIG. 6(A) is an SEM photograph (magnification: 300 times) of a cross section of the bonded body of Comparative Example 3, and FIG. 6(B) is a mapping photograph of Sn elements in the cross section shown in FIG. 6(A). [Figure 7] Fig. 7(A) is a mapping photograph of Ag elements in the cross section shown in Fig. 7(A), and Fig. 7(B) is an enlarged SEM photograph (magnification: 300 times) of region R in Fig. 7(A). [Figure 8] 1 is an SEM photograph (magnification: 3000 times) of a cross section of a bonded body of Comparative Example 4. DETAILED DESCRIPTION OF THE INVENTION

[0019] 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.

[0020] A bonded structure according to one embodiment includes a copper plate, a ceramic plate, and a bonding portion bonding the copper plate and the ceramic plate. Examples of ceramic plates include those containing, as a main component, nitride-based ceramics such as silicon nitride and aluminum nitride, oxide-based ceramics such as aluminum oxide and zirconium oxide, carbide-based ceramics such as silicon carbide, and boride-based ceramics such as lanthanum boride. The ceramic plate may be, for example, a nitride-based ceramic plate or a silicon nitride plate. The nitride-based ceramic plate may contain a nitride-based 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. In the present disclosure, the term "main component" refers to the component that is most abundant by mass, and may account for 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.

[0021] The shape of the ceramic plate is not particularly limited. The shape of the main surface of the 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 surfaces whose area is larger than the other surfaces and which are two surfaces that intersect perpendicularly in the thickness direction. The copper plate contains copper as its 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 ceramic plate. The shapes and thicknesses of the copper plates arranged on one main surface of the ceramic plate may be the same or different from each other. One or more copper plates may be provided on only one main surface of the ceramic plate, or one or more copper plates may be provided on each of the two main surfaces of the ceramic plate.

[0022] The joint between the ceramic plate and the copper plate has a higher mass ratio of Sn than the mass ratio of Ag. This can improve the uniformity of the joint structure. From the viewpoint of improving the uniformity of the joint 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 improving the uniformity of the joint structure, 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 of the joint may be the same as the ratio of the raw material composition of the brazing filler metal.

[0023] 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. Ag, Sn, and Cu in the joint may be contained as a compound or alloy with other components. For example, Sn and Cu may form a Cu-Sn intermetallic compound. This can reduce thermal stress caused by heat cycles. Note that the above mass ratios of Ag, Sn, and Cu are all values ​​converted into simple metals.

[0024] The joint may contain other metals or metal compounds. For example, the joint may contain a TiN layer. When the 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. The TiN layer may be formed along the main surface of the silicon nitride plate.

[0025] The joint contains Sn. In the present disclosure, when viewing a cross section of the joint obtained by cutting the ceramic plate in a direction perpendicular to the main surface, a layer containing Sn is referred to as an Sn-containing layer. The copper plate may also contain Sn. The copper plate may contain Sn only in a region closer to the joint. In this case, the Sn-containing layer is formed in a region closer to the joint between the joint and the copper plate. The Sn-containing layer may be formed in a strip shape along the main surface of the ceramic plate at the joint or in a region closer to the joint between the joint and the copper plate.

[0026] The Sn-containing layer has a thickness T of 105 μm or more from the main surface of the ceramic plate when viewed in a cross section perpendicular to the main surface of the ceramic plate. The thickness T of the Sn-containing layer does not need to be constant. The thickness T of the Sn-containing layer is determined from the results of element mapping using an energy dispersive X-ray spectrometer (EDS). That is, the area where Sn is detected is determined from the Sn matching results, and the width of the area (= the shortest distance between the main surface of the ceramic plate and the Sn detected at the position farthest from the main surface of the ceramic plate) is measured.

[0027] In the present disclosure, "having a thickness T of 105 μm or more based on the main surface of the ceramic plate" means that the minimum thickness based on the main surface of the ceramic plate is 105 μm or more. From the viewpoint of further improving heat cycle characteristics (durability against heat cycles), the thickness T of the Sn-containing layer based on the main surface of the ceramic plate may be 110 μm or more, 120 μm or more, 140 μm or more, 150 μm or more, or 160 μm or more. From the viewpoint of improving the efficiency of the manufacturing process, the thickness T of the Sn-containing layer based on the main surface of the ceramic plate may be 300 μm or less, 250 μm or less, or 200 μm or less.

[0028] The Sn-containing layer may have a composition gradient layer in which the mass ratio of Sn decreases with increasing distance from the ceramic substrate. This further suppresses localized concentration of thermal stress caused by heat cycles, thereby further improving heat cycle characteristics.

[0029] The void ratio at the joint may be 20% or less, 10% or less, 5% or less, or 3% or less. By reducing the void ratio, the heat cycle characteristics can be further improved. The void ratio can be determined by the method described in the Examples.

[0030] FIG. 1 is a perspective view showing an example of a bonded body. The bonded body 100 in FIG. 1 includes a ceramic plate 10 and a copper plate 20 and a copper plate 30 bonded to the two main surfaces of the ceramic plate 10, respectively. The copper plate 20 and the copper plate 30 are each bonded to the main surface of the 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.

[0031] 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 ceramic plate 10, a plurality of conductors 22 bonded to one main surface of the ceramic plate 10, and a heat sink 32 bonded to the other main surface of the 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 ceramic plate 10 by bonding parts (not shown).

[0032] 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 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 ceramic plate 10 and the copper plate 20 are bonded at a joint 50. The Sn-containing layer 40 is a region where Sn is detected using the ultra-high resolution field emission scanning electron microscope, and is formed over the entire joint 50 and a portion of the copper plate 20 on the joint 50 side. The boundary S between the joint 50 and the copper plate 20 does not need to be discernible. The outer edge 40A of the Sn-containing layer 40 in the copper plate 20 is drawn by connecting the Sn detected by element mapping at the furthest positions when viewed in a direction perpendicular to the main surface 10A of the ceramic plate 10. The shortest distance between the outer edge 40A thus drawn and the main surface 10A of the ceramic plate 10 is the thickness T of the Sn-containing layer 40. The lower detection limit of Sn with an ultra-high resolution field emission scanning electron microscope may be 1500 to 2000 ppm.

[0033] In the example of Fig. 3, the Sn-containing layer 40 includes a portion of the copper plate 20, but this is not limiting. In a modified example, the entire Sn-containing layer 40 may be included in the joint 50. In either example, the joined body 100 (102) includes the Sn-containing layer 40 having a sufficient thickness T based on the main surface 10A of the ceramic plate 10, thereby reducing local concentration of thermal stress caused by heat cycles. Such joined body 100 (102) has excellent heat cycle characteristics.

[0034] When the cross section of the bonded body is observed at multiple locations using an ultra-high resolution field emission scanning electron microscope, it is not necessary for the thickness T of the Sn-containing layer to be within the above-mentioned numerical range in all images. It is sufficient that the thickness T of the Sn-containing layer be within the above-mentioned numerical range in at least one of multiple images showing enlarged images of different locations. Furthermore, when multiple cross sections are obtained by cutting the ceramic plate 10 in a direction perpendicular to the main surface 10A, it is sufficient that the thickness T of the Sn-containing layer be within the above-mentioned numerical range in at least one of the multiple cross sections. In the portion where the thickness T of the Sn-containing layer is within the above-mentioned numerical range, local concentration of thermal stress caused by heat cycles is suppressed, thereby improving heat cycle characteristics.

[0035] A method for producing a bonded body according to one embodiment includes a lamination step of laminating a copper plate and a ceramic plate via a brazing filler metal containing Sn and Cu to obtain a laminate, and a firing step of heating the laminate to 800°C or higher to bond the copper plate and the ceramic plate. The copper plate and the ceramic plate are as described in the embodiment of the bonded body. The copper plate and the ceramic plate may be commercially available or may be produced by a known method.

[0036] The brazing filler metal can be prepared by blending, for example, tin powder, copper powder, powder of an active metal or its compound (hydride), an organic solvent, a binder, etc. Silver powder may or may not be blended in the preparation of the brazing filler metal.

[0037] 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 facilitates the formation of a highly uniform structure and reduces thermal stress caused by heat cycles. 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, thereby forming a stronger bond to the copper plates.

[0038] 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 uneven diffusion distances when the laminate is heated. By reducing the Ag ratio, it becomes easier to form a highly uniform structure, and thermal stress caused by heat cycles can be reduced. The above-mentioned mass ratios of Ag, Sn, and Cu are all values ​​converted into simple metals.

[0039] 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 powder of a metal and powder of a metal compound (such as an active metal hydride). 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.

[0040] The ratio of silver powder to the total 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 active metal hydride used in preparing the brazing filler metal may be 1 to 8 mass%, 2 to 6 mass%, or 3 to 5 mass%. Examples of active metal hydrides include TiH2.

[0041] A brazing filler metal is applied to the main surface of a 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 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 %.

[0042] 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 a Sn-containing layer having a sufficient thickness T to be smoothly formed. 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 for which the laminate is held at the heating temperature (holding time) may be 0.5 to 4 hours. The rate of temperature rise to the 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.

[0043] 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 -3 The firing may be performed at a pressure of 1000 kJ / cm2 (or less than 1000 kJ / cm2) or in a vacuum. By firing the laminate under such conditions, the ceramic and the copper plate can be sufficiently bonded. 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.

[0044] 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.

[0045] 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.

[0046] 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 ceramic plate 10 in the removed portions. Thereafter, the resist pattern is removed to obtain a circuit board having a plurality of conductor portions, such as the bonded body 102. The shape of the conductor portion 22 may be adjusted by changing the etching conditions or the number of times etching is performed.

[0047] 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 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.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] 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]

[0054] 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.

[0055] [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 diameter D50: 3μm, specific surface area 0.1m 2 / g Titanium hydride powder (TiH2 powder): TCH-100 (product name), manufactured by Toho Tech Co., Ltd.

[0056] 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 binder were added to prepare a brazing filler metal. Table 1 also shows the mass ratio of tin powder to the total 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.

[0057] A laminate was obtained by placing an oxygen-free copper plate (thickness: 0.5 mm, purity: 99.60% by mass) on each of the main surfaces of a silicon nitride plate. 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 comprising 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.

[0058] (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: 3.0 μm, specific surface area: 0.4 m 2 / g

[0059] (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

[0060] [Table 1]

[0061] [Cross-section analysis] After embedding each bonded body in resin, a coater machine was used to cut each bonded body 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) and elemental mapping was performed using an energy dispersive X-ray spectrometer (EDS) (magnification: 300x). The measurement device used was an ultra-high resolution field emission scanning electron microscope (device name: JSM-7900F) manufactured by JEOL Ltd.

[0062] The elemental mapping results confirmed that, in all bonded bodies, an Sn-containing layer containing Sn was formed along the main surface of the silicon nitride plate. The thickness of the Sn-containing layer was measured based on the main surface of each silicon nitride plate. The minimum thickness of the measured Sn-containing layer (thickness T) was as shown in Table 2. That is, the Sn-containing layer in each example and comparative example had a thickness equal to or greater than the thickness T shown in Table 2. Furthermore, from the results of elemental mapping using the above-mentioned measuring device, when a layered region in which the Sn concentration decreases with increasing distance from the silicon nitride plate was confirmed, it was evaluated as "compositionally graded layer: present," and when not confirmed, it was evaluated as "compositionally graded layer: absent." The results are as shown in Table 2.

[0063] [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.

[0064] [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.

[0065] 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.

[0066] [Table 2]

[0067] As shown in Table 2, the bonded bodies of Examples 1 to 5 all had low void and crack rates. Fig. 5(A) is an SEM photograph (magnification: 300x) of a cross section of the bonded body of Example 2, and Fig. 5(B) is a mapping photograph of Sn elements in the cross section shown in Fig. 5(A). Fig. 5(B) shows that the Sn-containing layer 40 has a compositionally gradient layer in which the mass ratio of Sn decreases with increasing distance from the silicon nitride plate 12. In the bonded bodies of Examples 1 to 5, a TiN layer was formed along the main surface of the silicon nitride plate at the bonded portion.

[0068] The crack rates of the bonded bodies of Comparative Examples 1 and 3 were higher than those of Examples 1 to 5. In Comparative Example 1, the thickness T of the Sn-containing layer was small and the void rate was also high. In the bonded body of Comparative Example 2, the copper plate peeled off from the main surface of the silicon nitride plate in the evaluation of the heat cycle properties. These results confirmed that Comparative Examples 1 to 3 were inferior to Examples 1 to 5 in durability against heat cycles.

[0069] FIG. 6(A) is an SEM photograph (magnification: 300x) of the cross section of the bonded body of Comparative Example 3, and FIG. 6(B) is a mapping photograph of Sn elements in the cross section shown in FIG. 6(A). As shown in FIG. 6(B), the thickness T of the Sn-containing layer 42 of Comparative Example 3 was significantly smaller than the thickness T of the Sn-containing layer of each Example. FIG. 7(A) is a mapping photograph of Ag elements in the cross section shown in FIG. 6(A). The diffusion distance of Ag varied greatly. FIG. 7(B) is an SEM photograph (magnification: 3000x) enlarging region R in FIG. 6(A). As shown in this SEM photograph, it was confirmed that Ag and Cu formed a eutectic structure. As such, it is believed that the bonded body of Comparative Example 3 had a non-uniform structure at the bonded portion, which made it more susceptible to thermal stress in the evaluation of heat cycle characteristics, resulting in a higher crack rate than Examples 1 to 5.

[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 bonded body of Example 6, in which the holding time was longer than that of Example 2, and the bonded body of Example 7, in which the heating rate and the temperature decrease rate were slower than those of Example 2, had a larger Sn-containing layer thickness T than the bonded body of Example 2. The bonded bodies of Example 8 and Comparative Example 4, in which the heating temperature was lower than that of Example 2, had a smaller Sn-containing layer thickness T than the bonded body of Example 2. FIG. 8 is an SEM photograph (magnification: 300x) of a cross section of the bonded body of Comparative Example 4. As shown in FIG. 8, 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. Therefore, when the bonded body of Comparative Example 4 was subjected to 15 cycles in an evaluation of heat cycle characteristics, the copper plate peeled off from the main surface of the silicon nitride plate. [Explanation of symbols]

[0076] 10...ceramic plate, 10A...main surface, 12...silicon nitride plate, 20, 30...copper plate, 22...conductor portion, 22a...conductor portion, 32...heat sink plate, 40...Sn-containing layer, 40A...outer edge, 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...casing, 90...semiconductor element, 100, 102...joint, 200...power module.

Claims

1. A joined body including a copper plate, a ceramic plate, and a joining portion joining the copper plate and the ceramic plate, The joint has a higher mass ratio of Sn than a mass ratio of Ag, When viewed in a cross section perpendicular to a main surface of the ceramic plate, a Sn-containing layer containing Sn is provided along the main surface, The Sn-containing layer has a thickness T of 105 μm or more from the main surface.

2. The joined body according to claim 1 , wherein the ratio of Ag to Sn in the Sn-containing layer is less than 5 mass %.

3. 3. The joined body according to claim 1, wherein the Sn-containing layer is formed in the joint and in a region of the copper plate close to the joint.

4. The bonded body according to claim 1 or 2, wherein the bonded portion contains Cu.

5. 3. The joined body according to claim 1, wherein, when viewed in cross section, the Sn-containing layer includes a compositionally gradient layer in which the mass ratio of Sn decreases with increasing distance from the ceramic plate.

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

7. 3. The joined body according to claim 1, wherein the ceramic plate is a silicon nitride plate, and the joining portion includes a TiN layer.

8. a step of laminating a copper plate and a ceramic plate via a brazing material containing Sn and Cu to obtain a laminate; and heating the laminate to 800°C or higher to bond the copper plate and the ceramic plate, 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 the main surfaces of the ceramic plates, the joined body has a Sn-containing layer that contains Sn along the main surfaces, and the Sn-containing layer has a thickness T of 105 μm or more based on the main surfaces.

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

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