Manufacturing method for aluminum-ceramic bonded substrate

Abstract

To easily form an aluminum member having a fine crystal grain diameter without adding a fining agent and imparting ultrasonic waves in a molten metal joining step, when an aluminum-ceramic joined substrate is manufactured by a molten metal joining method.SOLUTION: An aluminum member is joined to one surface or both surfaces of a ceramic plate arranged in a cast by preparing Al-based molten metal by melting an Al-based solid material composed of a coagulum regulated by the following (A), and solidifying the Al-based molten metal in the state of being brought into contact with the surface of the ceramic plate. (A) Coagulum obtained by forming molten metal at 730°C or higher having a composition containing 0.01-0.2 mass% Ti, 0.001-0.1 mass% B and 99.0 mass% or more Al, where Ti and B exist in the state of being dissolved in a liquid phase of Al, then imparting ultrasonic vibration to the molten metal in a molten metal temperature range of 720-680°C, and solidifying the molten metal.SELECTED DRAWING: Figure 8

Description

[Technical Field]

[0001] The present invention relates to a method for producing an "aluminum-ceramic bonded substrate" in which a ceramic plate and an Al-based plate-like member are bonded together, and which is useful as an insulated circuit board for mounting semiconductor elements. [Background technology]

[0002] In semiconductor devices that generate a large amount of heat, such as power modules, an insulated circuit board is generally used, in which a plate-shaped metal circuit member is bonded to the surface of a ceramic plate, and semiconductor elements are mounted on the metal circuit member by soldering or other methods. Cu-based or Al-based metal materials, which have good electrical conductivity, are used as the metal circuit member. Among these, insulated circuit boards that use Al-based metal circuit members (aluminum-ceramic bonded substrates) are expected to see increased demand in automotive applications and other areas, due to the excellent resistance of the ceramic plate to damage during heat cycles that involve repeated temperature increases and decreases.

[0003] When an aluminum-ceramic bonding substrate is subjected to a heat cycle, the Al-based component undergoes moderate plastic deformation, absorbing the difference in thermal expansion with the ceramic plate and reducing the stress applied to the ceramic plate. When the Al-based component repeatedly undergoes plastic deformation while restrained by the ceramic plate, steps may appear at the crystal grain boundaries exposed on the surface, resulting in unevenness on the semiconductor device mounting surface. If the surface steps are large, there is a risk of damaging the semiconductor device mounted on that surface. To reduce these steps, it is effective to increase the total length of the crystal grain boundaries exposed on the surface and disperse the steps caused by plastic deformation. In other words, it is effective to reduce the crystal grain size of the Al-based component.

[0004] One known manufacturing method for aluminum-ceramic bonded substrates is the "molten metal bonding" method, which directly bonds a ceramic plate to an Al-based metal circuit component by solidifying a molten Al-based metal on the surface of the ceramic plate. Using this method, the Al-based metal circuit component solidifies into a solidification structure, which, unlike processed products such as rolled materials, tends to result in coarsened grains. Therefore, to minimize the aforementioned surface irregularities that can form during heat cycles, it is important to employ a technology for refining the grains as the Al-based molten metal solidifies. Furthermore, for use as a metal circuit component, it is also important to maintain aluminum's inherent high conductivity and softness as much as possible.

[0005] Patent Document 1 discloses a technique for producing an aluminum-ceramic bonded substrate with a small crystal grain size of an Al-based component by melt bonding. This technique involves melting solid Al and an Al-Ti-B alloy to produce an Al-based molten metal, which is then poured into a mold and bonded to a ceramic plate. The Al-Ti-B alloy is recommended to contain, for example, 3 to 8 mass% Ti and 0.1 to 3 mass% B (paragraph 0021). The Al-Ti-B alloy contains solidification nuclei, such as TiAl3, AlB2, and TiB2, that refine the crystal grains of the Al-based component. To refine the crystal grains while maintaining the electrical conductivity of the Al-based component, the patent also teaches that it is preferable to generate the Al-based molten metal at a relatively low temperature to prevent the solidification nuclei provided by the Al-Ti-B alloy from dissolving in the molten Al, and to rapidly pour the molten metal into the mold to prevent Ti and B from dissolving in the Al (paragraph 0020).

[0006] Patent Document 2 describes that when casting aluminum, irradiating molten metal with ultrasonic waves can have effects such as controlling the solidification structure. The molten metal can be irradiated with ultrasonic waves by inserting an ultrasonic horn into the molten metal flowing through a moving trough or into the molten metal in a mold (paragraph 0002).

[0007] Patent Document 3 discloses a technique for forming an equiaxed crystal structure with finer crystal grains than columnar crystals by applying ultrasonic vibrations to a mold via chills when producing an aluminum-ceramic bonded substrate by a molten metal bonding method. The ultrasonic vibrations propagate through the aluminum much faster than the growth of columnar crystals, disrupting crystal growth at the time of solidification, thereby allowing the formation of an equiaxed crystal structure (paragraph 0057). [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Publication No. 2019-141879 [Patent Document 2] Japanese Patent Application Laid-Open No. 2011-177787 [Patent Document 3] Japanese Patent Application Publication No. 2018-163995 Summary of the Invention [Problem to be solved by the invention]

[0009] According to the technique described in Patent Document 1, the molten metal bonding method can refine the crystal grains of the Al-based component and produce an aluminum-ceramic bonded substrate that maintains high electrical conductivity. However, during the molten metal bonding process, an Al-Ti-B alloy (grain refiner) must be melted together with solid Al to introduce particles such as TiB2, which function as heterogeneous nuclei, into the molten Al. When the Al raw material and the Al-Ti-B alloy are placed in a molten metal container (a part that functions as a crucible) and melted, the resulting molten metal may have an uneven distribution of Ti and B concentrations. Injecting such a molten metal into the product-shaped space in the mold can result in segregation of Ti and B in the product's composition, potentially resulting in reduced product quality. Furthermore, because the Ti and B contents required in the molten Al are minute, adding accurately weighed small amounts of the Al-Ti-B alloy to the molten metal container of the mold for each individual mold is cumbersome and reduces productivity in the mass production of aluminum-ceramic bonded substrates. There is also a risk that the Al-Ti-B alloy may be forgotten to be added at the manufacturing site, resulting in the production of defective products. Therefore, when pouring raw materials into the molten metal container of the mold (the part that functions as the crucible) and melting them, it is desirable to use only a single type of Al-based raw material whose composition has been adjusted in advance.

[0010] The use of means for applying ultrasonic vibrations as disclosed in Patent Documents 2 and 3 can have the effect of refining the crystal grains of Al-based members formed by molten metal bonding. However, installing an ultrasonic vibration applying device in each mold used in the molten metal bonding method is extremely cumbersome in the mass production process of aluminum-ceramic bonded substrates, and is not easy to put into practice.

[0011] An object of the present invention is to easily form an aluminum member with a refined crystal grain size when manufacturing an aluminum-ceramic bonded substrate by a molten metal bonding method, without adding a refiner or applying ultrasonic waves during the molten metal bonding process. [Means for solving the problem]

[0012] As a result of research, the inventors discovered that the solidified product obtained by applying ultrasonic vibrations to an Al-based molten metal containing Ti and B and then solidifying it has an inherent property of forming a solidified structure with refined crystal grains when remelted and resolidified. The present invention was made based on this finding. That is, to achieve the above object, the present invention applies ultrasonic vibrations to an Al-based molten metal containing Ti and B, and then solidifies the molten metal to prepare an Al-based solid material in advance, and uses the Al-based solid material as a raw material for forming the molten metal in a molten metal joining method. Specifically, this specification discloses the following inventions.

[0013] [1] A method for producing an aluminum-ceramic bonding substrate, comprising melting an Al-based solid material consisting of a solidified product as defined in (A) below to produce an Al-based molten metal, and solidifying the Al-based molten metal while it is in contact with the surface of a ceramic plate placed in a mold, thereby bonding an aluminum member to one or both sides of the ceramic plate. (A) A solidified product obtained by forming a molten metal at 730°C or higher, which has a composition containing 0.01 to 0.2 mass% Ti, 0.001 to 0.1 mass% B, and 99.0 mass% or more Al, in which Ti and B are present in a dissolved state in the liquid phase of Al, and then lowering the temperature of the molten metal and subjecting the molten metal to a treatment of applying ultrasonic vibrations within a molten metal temperature range of 720 to 680°C, and then solidifying the molten metal that has been subjected to the treatment. [2] The method for producing an aluminum / ceramic bonding substrate according to the above [1], wherein the treatment of applying ultrasonic vibrations is a treatment of applying ultrasonic vibrations with a vibration amplitude of 10 to 80 μm (pp). [3] The method for producing an aluminum-ceramic bonding substrate according to [1] or [2] above, wherein the aluminum-ceramic bonding substrate has a structure in which aluminum members are bonded to both sides of a ceramic plate, one of the aluminum members being a metal member for a circuit on which a semiconductor element is mounted, and the other being a heat dissipation member. Here, the "(pp)" in reference to vibration amplitude means that the amplitude is measured in peak-to-peak mode. [Effects of the Invention]

[0014] According to the present invention, when manufacturing an aluminum-ceramic bonded substrate by a molten metal bonding method, it is possible to easily form an Al-based member with a refined crystal grain size without adding a refiner or applying ultrasonic waves during the molten metal bonding process. Simply melting a prepared Al-based solid material and subjecting it to molten metal bonding with a ceramic can effectively refine the crystal grains of the Al-based member, and therefore the present invention contributes to improving the quality and productivity of aluminum-ceramic bonded substrates. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a cross-sectional view schematically illustrating an example of the cross-sectional structure of an aluminum / ceramic bonding substrate to which the present invention is directed. [Figure 2] 1 is a cross-sectional view schematically illustrating an example of the cross-sectional structure of an aluminum / ceramic bonding substrate to which the present invention is directed. [Figure 3] FIG. 2 is a cross-sectional view showing a schematic example of the arrangement in a mold for producing an aluminum / ceramic bonding substrate having the cross-sectional structure shown in FIG. 1. [Figure 4] 3 is a cross-sectional view showing a schematic example of the arrangement in a mold for producing an aluminum / ceramic bonding substrate having the cross-sectional structure shown in FIG. 2. FIG. [Figure 5] FIG. 4 is a cross-sectional view showing the state in which molten metal has been introduced into the mold shown in FIG. 3. [Figure 6] FIG. 5 is a cross-sectional view showing the state in which molten metal has been introduced into the mold shown in FIG. 4. [Figure 7] FIG. 1 is a cross-sectional view showing a schematic example of the configuration of a melting apparatus for producing an Al-based solid material used in a molten metal joining method. [Figure 8] 3 is a macrostructure photograph of the vicinity of the center of the metal members for circuits obtained in Example 2 and Comparative Example 2. [Figure 9] 1 is a macrostructure photograph of the vicinity of the center of the metal members for circuits obtained in Example 3 and Comparative Example 3. DETAILED DESCRIPTION OF THE INVENTION

[0016] [Aluminum-ceramic bonded substrate] An aluminum-ceramic bonding substrate is an insulating substrate for mounting semiconductor elements, and has a laminated structure in which a plate-shaped aluminum member, which is a metal circuit member, is bonded to one side of a ceramic plate. An aluminum member responsible for heat transfer for heat dissipation may be bonded to the side of the ceramic plate opposite the metal circuit member. The aluminum member bonded to the side of the ceramic plate opposite the metal circuit member is sometimes referred to as a "backing member" in this specification. Examples of the backing member include (i) a plate-shaped body for bonding to a heat dissipation component such as a heat sink, (ii) a heat dissipation member that is strong enough to directly attach an insulating substrate to the inside of a semiconductor device or to a housing and functions as a "heat dissipation base," and (iii) a heat dissipation member with multiple pin-shaped protrusions or fins.

[0017] FIG. 1 shows a schematic cross-sectional view of an example of an aluminum-ceramic bonded substrate according to the present invention. A circuit metal member 20, made of a plate-shaped aluminum material, is bonded to one side of a ceramic plate 10. The circuit metal member 20 is formed by solidifying an Al-based molten metal on the surface of the ceramic plate 10 using a molten metal bonding method, as described below. A semiconductor element is mounted on the surface of the circuit metal member 20. Because the circuit metal member 20 is an Al-based metal, the upper surface (semiconductor element mounting surface 22) of the metal circuit member 20 is typically plated with Ni to improve solder wettability, and then the semiconductor element is bonded to the plated layer via a solder layer. The thickness of the ceramic plate 10 varies depending on the design of the insulated circuit board, but can be set, for example, in the range of 0.3 to 1.5 mm. The thickness of the circuit metal member 20 can be set, for example, in the range of 0.3 to 1.5 mm. Note that the thicknesses of the components are exaggerated in FIG. 1.

[0018] Typical ceramics that are the main component of the ceramic plate 10 include AlN (aluminum nitride), which has good thermal conductivity, Si3N4 (silicon nitride), which has high strength, and Al2O3 (alumina), which is inexpensive and highly versatile. In the case of a power module, it is preferable to use an AlN plate or Si3N4 plate from the viewpoint of ensuring reliability and heat dissipation. The thickness of the ceramic plate 10 varies depending on the design of the insulating circuit board, but can be set, for example, in the range of 0.3 to 1.5 mm.

[0019] When using the molten metal bonding method, the circuit metal member 20 generally tends to have a solidification structure consisting of coarse crystal grains. If the crystal grains of the circuit metal member 20 are coarse, as described above, steps may occur at the grain boundaries exposed on the surface due to heat cycles, potentially damaging the solder layer bonding the semiconductor element and the semiconductor element. In the present invention, the solidification structure of the circuit metal member 20 is prevented from becoming coarse by using a solidified material solidified by ultrasonic treatment, as described below, as the Al-based solid material used for molten metal bonding. In the aluminum-ceramic bonding substrate according to the present invention, the observation surface obtained by polishing the upper surface (semiconductor element mounting surface 22) of the circuit metal member 20 exhibits a fine solidification structure mainly composed of equiaxed crystals. The entire semiconductor element mounting surface 22 does not necessarily need to be equiaxed crystals; by having only the portion where the semiconductor element is bonded be equiaxed crystals, the adverse effects of steps are significantly reduced. Therefore, even if the area ratio of equiaxed crystals to the total area of the upper surface of the circuit metal member 20 is, for example, approximately 50%, sufficient effects can be obtained depending on the mounting layout of the semiconductor elements. However, from the perspective of providing a highly versatile insulated circuit board, the area ratio of equiaxed crystals to the total area of the upper surface of the circuit metal member 20 is preferably 80 area% or more, more preferably 90 area% or more. It is even more preferable that the entire upper surface of the circuit metal member 20 is made of equiaxed crystals. The average crystal grain size of the equiaxed crystals is preferably 3.0 mm or less, more preferably 1.0 mm or less, as measured by a cutting method conforming to, for example, JIS H0501-1986. Here, among the crystal grains revealed by buffing and then etching the surface of the circuit metal member 20, crystal grains with an aspect ratio of 3 or less are considered to be equiaxed crystals. The area ratio of equiaxed crystals to the surface of the circuit metal member 20 is referred to as the "area ratio of equiaxed crystals (%)." Here, the aspect ratio is the ratio expressed as the long axis / short axis of the crystal grain. The major axis refers to the length of the longest line segment connecting any two points on the contour line (grain boundary) of a crystal grain, and the minor axis refers to the longest distance between the contour lines (grain boundaries) of the crystal grains measured perpendicular to the major axis. The aspect ratio of a crystal grain cut by the peripheral contour line (edge) of the circuit metal member 20 is determined by assuming that the peripheral contour line is also part of the grain boundary.

[0020] It is desirable that the metal circuit member 20 have as high conductivity as possible. Specifically, it is preferably an aluminum member with an Al content of 99.0 mass % or more. Elements other than Al include Ti and B, which are added during the preparation of the Al-based solid material described below. A composition of 0.01 to 0.2 mass % Ti, 0.001 to 0.1 mass % B, with the remainder being Al and unavoidable impurities is more preferable, and a composition of 0.02 to 0.1 mass % Ti, 0.02 to 0.1 mass % B, with the remainder being Al and unavoidable impurities is even more preferable. The content ratio of Ti to B is more preferably in the range of 1:1 to 6:1 by mass.

[0021] In the example shown in Figure 1, a heat dissipation member 50 made of a plate-shaped aluminum member is bonded as a backing member to the surface of the ceramic plate 10 opposite the metal circuit member 20. This aluminum-ceramic bonding substrate corresponds to the above-mentioned form (ii). This type of aluminum-ceramic bonding substrate is sometimes called a "base-integrated insulated circuit board." As shown in the figure, this heat dissipation member 50 can optionally incorporate a plate-shaped reinforcing member 110. The plate-shaped reinforcing member 110 strengthens the heat dissipation member 50 and suppresses deformation of the base-integrated insulated circuit board due to thermal expansion of aluminum. The plate-shaped reinforcing member 110 can be made of, for example, a ceramic plate such as AlN or Si3N4, or a carbon plate. The heat dissipation member 50 can also be formed simultaneously with the metal circuit member 20 by molten metal bonding.

[0022] FIG. 2 shows a schematic cross-sectional view of an example of an aluminum-ceramic bonding substrate according to the present invention. The cross-section shows two adjacent circuit metal members 20. The two circuit metal members 20 are electrically insulated from each other by grooves 21 formed on the ceramic plate 10. The heat dissipation member 50 is an aluminum-based backing member having multiple pin-shaped protrusions 53. Depending on the arrangement of the pin-shaped protrusions 53, some of the rear pin-shaped protrusions may be visible between the pin-shaped protrusions 53 shown in FIG. 2; however, these pin-shaped protrusions are not shown here. The pin-shaped protrusions 53 function as a heat sink to enhance heat dissipation. This aluminum-ceramic bonding substrate corresponds to the above-described form (iii). In this example, the end of the heat dissipation member 50 perpendicular to the thickness direction is integrated with a peripheral wall 51 that surrounds the end face of the ceramic plate 10. 2 is formed on almost the entire surface of the ceramic plate 10 opposite the surface on which the metal circuit member 20 is formed, on the end face (side face) of the ceramic plate 10, and around the surface on which the metal circuit member 20 is formed. The peripheral wall portion 51 and the metal circuit member 20 are electrically insulated from each other by grooves 52 formed on the ceramic plate 10. The heat dissipation member 50 having the pin-shaped protrusions 53 and the peripheral wall portion 51 can also be formed by casting an Al-based molten metal using the molten metal joining process used to form the metal circuit member 20. Instead of the pin-shaped protrusions, heat dissipation fins made of plate-shaped members can also be formed by casting using the molten metal joining process as a member for improving heat dissipation.

[0023] [Molten metal joining method] In the present invention, a known molten metal joining method can be used, except that an Al-based solid material made of a solidified product previously melted by a method described below is used as the raw material for the Al-based molten metal used in molten metal joining. Molten metal joining is achieved mainly by a "member placement process" and a "joining process."

[0024] (Component placement process) The component placement step is a step of placing components such as ceramic plates to which the molten Al alloy will be bonded in the mold. Figure 3 shows a cross-sectional view of the mold interior for producing the aluminum-ceramic bonding substrate shown in Figure 1. Mold 1 is composed of upper and lower dies 1a and 1b. Upper and lower dies 1a and 1b are made of gas-permeable carbon or metal materials. Mold 1 includes a reservoir 5, formed by the internal space between upper and lower dies 1a and 1b. This reservoir 5 contains the molten metal to be supplied to the product-shaping space within the mold. Aluminum-based molten metal can also be obtained by melting an aluminum-based solid material in the reservoir 5. In this case, the reservoir 5 also functions as a crucible. A pressure port 2 is located above the reservoir 5, and pressure is applied to the molten metal from outside the mold 1 through the pressure port 2 to deliver the molten metal into the product-shaping space. The lower die 1b is equipped with a runner 3 for supplying the molten metal from the reservoir 5 to various locations within the mold. In the example of Fig. 3, a narrow cross-section flow path 103, which narrows the cross section of the flow path through which the molten metal passes, is provided in a part of the runner 3. When the Al-based molten metal passes through the narrow cross-section flow path 103, the oxide film on the surface of the molten metal is removed.

[0025] The ceramic plate 10 is placed in a predetermined position (ceramic plate storage section) in the lower mold 1b. In the example of FIG. 3, the plate-shaped reinforcing member 110 is further placed in the predetermined position by being placed on a support section (not shown) provided inside the lower mold 1b. A space A is formed between the ceramic plate 10 and the inner wall surface of the lower mold 1b. The space A is connected to the molten metal storage section 5 by a runner (not shown) inside the lower mold 1b. The Al-based molten metal filled in the space A solidifies to form a plate-shaped metal component for circuits (reference numeral 20 in FIG. 1). A space B is formed on the upper surface side of the ceramic plate 10 so as to surround the plate-shaped reinforcing member 110. The space B is connected to the molten metal storage section 5 by a runner inside the lower mold 1b. The Al-based molten metal filled in the space B solidifies to form a heat dissipation component (reference numeral 50 in FIG. 1) incorporating the plate-shaped reinforcing member 110. The ceramic plate 10 and the plate-like reinforcing member 110 are both restrained in position by a support member or a clamping member inside the mold so that they do not shift from their predetermined positions when molten metal is poured in the joining process. In Figure 3, the thickness of the ceramic plate 10, the thickness of the plate-shaped reinforcing member 110, the distance between the ceramic plate 10 and the lower mold 1b in space A, the distance between the ceramic plate 10 and the plate-shaped reinforcing member 110 in space B, and the distance between the plate-shaped reinforcing member 110 and the upper mold 1a in space B are each exaggerated.

[0026] FIG. 4 is a cross-sectional view showing a schematic example of the arrangement inside a mold for producing an aluminum-ceramic bonding substrate having the cross-sectional structure shown in FIG. 2. In this case, space B has multiple pin-shaped recesses 4 formed by the wall surface of upper mold 1a. The molten aluminum filled into pin-shaped recesses 4 solidifies to form pin-shaped protrusions (reference numeral 53 in FIG. 2) that function as heat sinks. The mold structure in FIG. 4 is basically the same as that in FIG. 3, except that pin-shaped recesses 4 are formed, the arrangement of ceramic plate 10, space A, and space B is different, and there is no structure for installing a plate-shaped reinforcing member (reference numeral 110 in FIG. 3). The ceramic plate 10 is restrained in position by a support member or clamping member inside the mold so that it does not shift from its predetermined position when molten aluminum is poured into it during the bonding process.

[0027] (Joining process) The joining process is a process in which an Al-based molten metal is poured into a mold, and the Al-based molten metal is solidified while in contact with the surface of a ceramic plate or further plate-shaped reinforcing member placed inside the mold, thereby forming a structure in which an aluminum member derived from the Al-based molten metal and a ceramic plate or further plate-shaped reinforcing member are joined together.

[0028] 5 and 6 show cross-sectional views of the molds shown in FIGS. 3 and 4, respectively, with molten metal introduced therein. Casting for molten metal joining is performed, for example, as follows. Mold 1 is prepared, with ceramic plate 10 and, if necessary, plate-shaped reinforcing member 110 set as described above. When reservoir 5 is used as a crucible, the Al-based solid material, which is the raw material for the Al-based molten metal, is placed in reservoir 5 in the form of granules or small pieces, for example. Mold 1 is then placed in a heating furnace and heated in a non-oxidizing gas atmosphere, such as nitrogen gas. When using an Al-based molten metal obtained by melting the Al-based solid material in a melting furnace outside mold 1, the molten metal is introduced into reservoir 5 through pressure inlet 2. When reservoir 5 is used as a crucible, the raw Al-based solid material is melted in reservoir 5 to obtain the Al-based molten metal.

[0029] After the mold has reached a predetermined temperature (for example, 700 to 725°C), it is pressurized with an inert gas such as nitrogen gas at a pressure of, for example, 5 to 50 kPa through the pressure port 2, and the molten Al-based metal 100 contained in the molten metal storage section 5 (i.e., the molten Al-based solid material prepared by the method described below) is poured into the space within the mold via the runner 3. In the present invention, when obtaining the molten Al-based metal to be poured into the mold, there is no need to adjust the composition using a solid metal such as a refiner, and it is sufficient to melt only a single type of Al-based solid material that has been prepared in advance, so that once the Al-based solid material has completely melted and reached the predetermined pouring temperature, pouring of the molten metal (pouring) can begin immediately.

[0030] In the examples shown in Figures 5 and 6, the molten Al-based metal 100 passes through the narrow-section flow path 103, removing the oxide film formed on the surface of the molten metal. Solidification begins after the entire space within the mold, connected by the runner, is filled with the molten Al-based metal 100. Directional solidification is preferably achieved by contacting a water-cooled copper block as a cooling device with a portion of the outer wall of the mold 1 (e.g., the left end of Figures 5 and 6). To prevent casting defects such as shrinkage cavities, solidification is preferably performed while continuously applying pressure of, for example, 5 to 50 kPa using an inert gas such as nitrogen gas through the pressure port 2. The aluminum component obtained by solidifying the molten Al-based metal 100 in space A and space B is formed by remelting and resolidifying an Al-based solid material prepared by the method described below. Using this Al-based solid material as the aluminum raw material for the molten metal bonding method allows the aluminum component of the aluminum-ceramic bonding substrate to have a fine solidification structure primarily composed of equiaxed crystals.

[0031] [Method for producing Al-based solid materials] In the present invention, an Al-based solid material consisting of a solidified product as specified in (A) below is used as the raw material for the Al-based molten metal to be poured into a mold in the melt joining method. (A) A solidified product obtained by forming a molten metal at 730°C or higher, which has a composition containing 0.01 to 0.2 mass% Ti, 0.001 to 0.1 mass% B, and 99.0 mass% or more Al, in which Ti and B are present in a dissolved state in the liquid phase of Al, and then lowering the temperature of the molten metal and subjecting the molten metal to a treatment of applying ultrasonic vibrations within a molten metal temperature range of 720 to 680°C, and then solidifying the molten metal that has been subjected to the treatment.

[0032] FIG. 7 shows a schematic cross-sectional view of a melting apparatus for producing the Al-based solid material. A crucible 71 is installed inside a furnace 70. Metal raw materials are placed in the crucible 71 and heated and melted in the furnace 70 to form a molten metal 72. The furnace 70 can be, for example, an electric furnace equipped with a heater (not shown) or a high-frequency induction furnace equipped with a high-frequency coil (not shown). The crucible 71 can be, for example, an alumina crucible. A horn 74 attached to an ultrasonic vibrator 73 with a built-in vibrator can be immersed in the molten metal 72 and withdrawn from the molten metal 72 by operating the device from outside the furnace. A thermocouple sensor 75, for example, is installed inside the crucible 71 to monitor the temperature of the molten metal 72. Here, a method for producing an Al-based solid material will be described using a melting apparatus with this configuration.

[0033] First, aluminum raw material is placed in crucible 71. Al with few impurities is used as the aluminum raw material so that the final Al content is 99.0 mass% or more. From the viewpoint of ensuring high conductivity when the metal circuit component (reference numeral 20 in FIGS. 1 and 2) is formed, it is preferable to use pure Al with a purity of, for example, 99.9% or more. The atmosphere inside the furnace can be air, or it can be a vacuum or an inert gas atmosphere such as nitrogen. When the interior of the furnace is adjusted to a predetermined atmosphere other than air, a sealed furnace is used as furnace 70, and the predetermined gas atmosphere is maintained inside the furnace 70. Next, the aluminum raw material in crucible 71 is heated and melted using a heater or high-frequency coil to form molten metal 72 made of Al.

[0034] After the temperature of the molten metal 72 made of Al is raised to at least 730°C, an Al-Ti alloy as a Ti source and an Al-B alloy as a B source are respectively introduced into the molten metal 72, and Ti and B are dissolved in the liquid phase of Al. It is preferable to use an Al-Ti alloy and an Al-B alloy containing Ti and B alone, respectively, rather than an Al-Ti-B alloy containing both Ti and B. This is because the Al-Ti-B alloy already contains TiB2 particles, and it is not always easy to completely dissolve these in the liquid phase of Al. The following procedure can be used as a specific method for introducing the Ti and B sources. Specifically, the temperature of the molten metal 72 made of Al is first maintained as high as possible. Because TiB2 is easily generated at a temperature lower than 730°C, a high temperature range of at least 730°C or higher is necessary. However, it is preferable to raise the temperature even higher, for example, to a temperature in the range of 750 to 850°C. An Al-Ti alloy containing, for example, approximately 10% by mass of Ti is poured into the molten metal 72 made of Al maintained at this high temperature and completely melted. Next, an Al-B alloy containing, for example, approximately 4% by mass of B is poured and completely melted. Alternatively, the Al-B alloy may be poured first, followed by the Al-Ti alloy. The amounts of the Al-Ti alloy and Al-B alloy poured are adjusted so that the molten metal 72 has a target composition of 0.01-0.2% by mass of Ti and 0.001-0.1% by mass of B. It is more preferable to set the Ti:B content ratio to be 1:1-6:1 by mass. In this way, a molten metal 72 is formed at a temperature of 730°C or higher, more preferably 750°C or higher, in which Ti and B are dissolved in the liquid phase of Al.

[0035] Next, the temperature of the molten metal 72, in which Ti and B are dissolved in the liquid Al, is lowered, and the horn 74 of the ultrasonic vibrator 73 is immersed in the molten metal 72. When the temperature of the molten metal is between 720 and 680°C, ultrasonic vibrations are applied to the molten metal 72 from the horn 74. It is believed that as the temperature of the molten metal 72, in which Ti and B are dissolved in the liquid Al, is lowered, most of the Ti and B are consumed in the formation of TiB2. Some of the remaining Ti is consumed in the formation of Al3Ti, and the remainder exists in the molten Al as "dissolved Ti." Furthermore, most of the B not consumed in the formation of TiB2 exists in the molten Al as "dissolved B." It is believed that TiB2 formation is likely to occur actively during temperature reduction in the temperature range of 720 to 680°C. Therefore, ultrasonic vibrations are applied when the temperature of the molten metal 72 is within the range of 720 to 680°C. It is more preferable to apply ultrasonic vibration when the temperature of the molten metal 72 is at least in a range of 715 to 685°C.

[0036] The vibration amplitude of the ultrasonic vibrations applied to the molten metal 72 is preferably 10 to 80 μm (pp), and more preferably 40 to 70 μm (pp). The vibration amplitude described herein is a value measured in peak-to-peak (pp) mode. Because the formation of a cavitation field in the molten metal is expected to have a particle dispersion effect, the lower limit of the vibration amplitude is preferably 10 μm (pp), which is close to the threshold amplitude at which fully developed cavitation begins in the case of molten Al. Furthermore, considering the need to avoid, as much as possible, the phenomenon of acoustic (or cavitation) shielding, in which many cavitation bubbles are generated directly below the horn end face, significantly reducing the energy transmitted from the horn to the molten Al. Furthermore, considering that excessive vibration amplitude increases internal stress within the horn and increases the risk of horn breakage, the vibration amplitude is preferably 80 μm (pp) or less. The immersion position of the horn 74 is preferably set so that the ultrasonic vibrations are effective throughout the entire molten metal 72 being processed. Applying the above vibration amplitude to the entire molten metal 72 to be processed can be achieved by adjusting the ultrasonic vibration output of the ultrasonic vibrator 73 within a range of, for example, 0.05 to 0.5 kW per kg of molten metal. The duration of the ultrasonic vibration application can be set within a range of, for example, 30 to 300 seconds. While the term "ultrasonic" is often used to refer to sound waves of 20 kHz or higher, in this specification, the term "ultrasonic vibration" refers to vibrations of frequencies of 15 kHz or higher generated by a vibrator. Previous experiments have shown that ultrasonic vibrations of, for example, 15 kHz or higher can produce a cavitation effect in Al-based molten metal. While there is no specific upper limit, it is preferable to set the frequency to 30 kHz or lower, considering the occurrence of cavitation in molten Al.

[0037] The effects of ultrasonic vibration on molten aluminum are not fully understood at present, but the following is thought to be true. When the molten aluminum temperature is lowered while ultrasonic vibration is applied, the ultrasonic vibration prevents the aggregation of TiB2 particles, resulting in small TiB2 particles being dispersed throughout the molten aluminum. Furthermore, the surfaces of the TiB2 particles are cleaned and made more active by the ultrasonic vibration. It is thought that the dissolved Ti in the molten aluminum reacts with the dissolved B on the surfaces of the dispersed and activated TiB2 particles by ultrasonic vibration to form new TiB2 surfaces, or reacts with Al to form new Al3Ti surfaces. If a solidified product containing dispersed TiB2 particles with such new surfaces is used as the aluminum source (Al-based solid material) for the molten metal joining process, heterogeneous nucleation is promoted, resulting in significant refinement of the aluminum crystal grains.

[0038] After the ultrasonic vibration application process is completed, the horn 74 is lifted from the molten metal 72. Thereafter, the molten metal 72 is poured into a mold or the like installed in the furnace 70 by tilting the crucible 71 or the like and solidified, or the temperature of the molten metal 72 is lowered to solidify the molten metal 72 in the crucible 72, thereby obtaining a solidified product. It is desirable to maintain an inert gas atmosphere, such as a nitrogen gas atmosphere, until solidification is complete.

[0039] The solidified material is then cut into small pieces of a predetermined size suitable for remelting in the molten metal joining process, thereby obtaining an Al-based solid material to be used as the aluminum raw material in the molten metal joining method.

[0040] The Al-based solid material obtained as described above has an inherent tendency to form a fine solidification structure primarily composed of equiaxed crystals when remelted and resolidified. One possible reason for this is that the Al-based solid material contains a large number of TiB2 particles as described above. These TiB2 particles are thought to have clean surfaces when formed as primary particles, making them less likely to form coarse agglomerates as secondary particles. Furthermore, transmission electron microscopy (TEM) observations of the solidified material samples revealed that no intermediate products (heterogeneous phases) were present on the surfaces of the TiB2 particles formed with ultrasonic vibrations; instead, the TiB2 particles were in direct contact with the α-Al phase. This suggests that the TiB2 particles formed during ultrasonic treatment themselves function as heterogeneous nucleation sites for α-Al. When an aluminum-ceramic bonded substrate is produced by melt bonding using the molten metal obtained by remelting the above-mentioned Al-based solid material, a solidified structure of the aluminum member consisting of fine crystal grains can be easily obtained even when solidified at a conventional cooling rate. This is presumably because the numerous TiB2 particles floating in the remelted molten metal act quickly as heterogeneous nucleation sites during the solidification process. Note that although this Al-based solid material is thought to contain particles other than TiB2, such as TiAl3, which can function as heterogeneous nuclei, the inventors believe that TiB2 is dominant in terms of manifesting the effect of facilitating the formation of fine equiaxed crystals. [Example]

[0041] [Example 1] (Preparation of Al-based solid materials) An Al-based solid material to be used for molten metal joining was prepared using a melting apparatus having the configuration shown in Fig. 7. An electric furnace was used as the furnace 70, and the Al-based solid material was melted in the air atmosphere as follows.

[0042] A pure Al ingot with a purity of 99.9% or higher was placed in a crucible, and the electric furnace was heated to melt the pure Al ingot, yielding a molten metal. The temperature of the molten metal was monitored using a thermocouple sensor installed in the crucible. The temperature of the molten metal was further increased and maintained at 800°C. An Al-10% by mass Ti alloy was added as a Ti source to the molten metal composed of pure Al at 800°C, and the mixture was maintained at 800°C for 60 minutes, thereby completely dissolving the Al-10% by mass Ti alloy. An Al-4% by mass B alloy was added as a B source to the molten metal composed of Al and Ti, and the mixture was maintained at 800°C for 60 minutes, thereby completely dissolving the Al-4% by mass B alloy. Approximately 3 kg of molten metal was obtained, in which Ti and B existed in a dissolved state in the liquid phase of Al. The molten metal composition was 0.02% by mass Ti, 0.02% by mass B, and the remainder was Al.

[0043] The temperature of the molten metal was then lowered, and the ultrasonic vibrator horn was immersed in the molten metal. When the temperature was between 710 and 690°C, ultrasonic vibrations were applied to the molten metal. Here, ultrasonic vibrations with a frequency of 20 kHz and a vibration amplitude of 40 μm were applied to the molten metal for approximately 100 seconds. The ultrasonic vibration output was approximately 0.13 to 0.2 kW per kg of molten metal. After applying the ultrasonic vibrations, the horn was removed from the molten metal, and the molten metal in the crucible was poured into a mold at a temperature of 690°C or below, where it solidified. The solidified material was removed from the mold, cut into small pieces, and used as an Al-based solid material for molten metal joining.

[0044] (Fabrication of aluminum-ceramic bonded substrates) Using only the above-mentioned Al-based solid material (having a composition of 0.02 mass% Ti, 0.02 mass% B, and the remainder being Al) produced by the method of applying ultrasonic vibrations as the raw material for the Al-based molten metal, an aluminum-ceramic bonding substrate (base-integrated insulating circuit board) having the cross-sectional structure shown in Figure 1 was produced by the molten metal bonding method as follows.

[0045] A 120 mm × 92 mm × 1 mm plate made of AlN was prepared as the ceramic substrate (reference numeral 10 in Figure 1). A 126 mm × 94 mm × 1 mm plate made of AlN was prepared as the plate-shaped reinforcing member (reference numeral 110 in Figure 1). These were placed inside a mold made of a gas-permeable carbon material with the cross-sectional structure shown in Figure 3. In the mold space (space A in Figure 3) that would become the circuit metal member (reference numeral 20 in Figure 3), the distance between the mold wall and the ceramic substrate was 0.4 mm. In the mold space (space B in Figure 3) that would become the heat dissipation member (reference numeral 50 in Figure 1), the distance between the ceramic plate (reference numeral 10 in Figure 3) and the plate-shaped reinforcing member (reference numeral 110 in Figure 3) was 2.6 mm, and the distance between the plate-shaped reinforcing member (reference numeral 110 in Figure 3) and the mold wall was 0.4 mm. Both the ceramic plate and the plate-like reinforcing member are restrained in position by a support member or a clamping member inside the mold so that they do not shift from their predetermined positions when molten metal is poured into them.

[0046] The Al-based solid material prepared by the above method was placed in the reservoir of this mold (reference numeral 5 in Figure 3 ), and the mold was then placed in a furnace and heated in a nitrogen atmosphere. The heating temperature was monitored using a thermocouple attached to the mold. After the Al raw material was melted at 720°C, a pressure of 16 kPa was applied using nitrogen gas through the mold's pressure port (reference numeral 2 in Figure 5 ). The molten Al was then poured into the mold interior via a narrow-section channel (reference numeral 103 in Figure 5 ) installed in the runner. Approximately 4 minutes after the start of pouring, directional solidification was initiated by contacting the outer wall of the mold end (corresponding to the left end of Figure 5 ) with a water-cooled copper block as a cooling device. Solidification proceeded while nitrogen gas pressure and the supply of molten metal from the reservoir were continued. After the mold temperature dropped below approximately 50°C, the furnace was opened to the atmosphere, and the cast product (laminate structure) was removed from the mold. In this way, an aluminum-ceramic bonding substrate (integrated base-insulated circuit board) was obtained, the cross section of which has the structure shown in Figure 1. The dimensions of each component of this aluminum-ceramic bonding substrate (the dimensions of the product after removing it from the mold and removing unnecessary parts such as the runners) were as follows: metal circuit component (20 in Figure 1) 80 mm x 50 mm x 0.4 mm, ceramic plate (10 in Figure 1) 120 mm x 92 mm x 1.0 mm, heat dissipation component (50 in Figure 1) 140 mm x 100 mm x 4.0 mm, and plate-like reinforcing component (110 in Figure 1) built into the heat dissipation component 126 mm x 94 mm x 1.0 mm. The resulting aluminum / ceramic bonding substrate was examined for the following points.

[0047] (Macrostructure observation of metal circuit components) The surface of a metal circuit component (reference numeral 20 in Figure 1) was buffed, cleaned with a 3% by weight aqueous solution of sodium hydroxide, and then etched with a 13.5% by weight aqueous solution of ferric chloride at 25°C to obtain an observation surface revealing the grain boundaries. Based on a photograph of this observation surface, the area of equiaxed crystals relative to the total area (80 mm × 50 mm) of the upper surface of the metal circuit component was determined. The area ratio of equiaxed crystals was found to be 85%. Furthermore, the average grain size of the equiaxed crystals was determined by drawing lines on the photographic image in accordance with JIS H0501-1986 and counting the number of crystal grains completely cut by the lines. Multiple line segments, each 50 mm long, were drawn in the equiaxed crystal region at 15 mm intervals, parallel to the short sides of the 80 mm × 50 mm rectangle, approximately perpendicular to the solidification direction. The average grain size was determined by averaging the average cut lengths measured for each line segment. As a result, the average grain size of the equiaxed crystals was 1.48 mm.

[0048] (Electrical resistivity of metal circuit components) The conductivity (%IACS) of the buffed surface of the metal circuit component (reference numeral 20 in Figure 1) was measured by the eddy current method using a conductivity meter (FOERSTER, SIGMATEST2.069). The electrical resistivity (μΩ·cm) was calculated from the conductivity (%IACS) using the following conversion formula (1). Electrical resistivity (μΩ·cm) = 10000 / (58.001 × conductivity (%IACS)) …(1) As a result, the electrical resistivity was found to be 2.73 μΩ·cm.

[0049] (Hardness of metal circuit components) The surface of the metal circuit component (reference numeral 20 in Figure 1) was buffed and the Vickers hardness was measured in accordance with JIS Z2244-1:2020 at a test force F = 9.8 N. As a result, the hardness of the metal circuit component was 16.7 HV.

[0050] (Inspection of joint defects) The bonding interface between the metal circuit member (reference numeral 20 in Fig. 1) and the ceramic plate (reference numeral 10 in Fig. 1) of the obtained aluminum-ceramic bonded substrate was observed using an ultrasonic flaw detector (SAT) (FS100II, manufactured by Hitachi Construction Machinery Finetechs Co., Ltd.) As a result, no defects (unbonded portions) were found at the bonding interface.

[0051] [Comparative Example 1] In the process of producing the Al-based solid material of Example 1, the composition of the molten metal in which Ti and B existed in a dissolved state in the liquid phase of Al was set to Ti: 0.03 mass %, B: 0.03 mass %, and the balance Al, except that no treatment of applying ultrasonic vibration was performed, an Al-based solid material was produced under the same conditions as in Example 1. Only the above-mentioned Al-based solid material produced without applying ultrasonic vibration (having a composition of Ti: 0.03 mass %, B: 0.03 mass %, and the balance Al) was used as the raw material of the Al-based molten metal, and an aluminum-ceramic bonding substrate was produced under the same conditions as in Example 1.

[0052] Macrostructure observation of the metal circuit component under the same conditions as in Example 1 revealed that the entire upper surface (80 mm × 50 mm) of the metal circuit component exhibited a solidification structure consisting of columnar crystals. Using a cutting method conforming to JIS H0501-1986, similar to Example 1, multiple line segments equivalent to a length of 50 mm were drawn at 15 mm intervals in a direction parallel to the short sides of an 80 mm × 50 mm rectangle, approximately perpendicular to the solidification direction, and the average crystal grain size was measured. As a result, the average crystal grain size in the direction approximately perpendicular to the solidification direction of the columnar crystals was 17.0 mm.

[0053] The electrical resistivity of the metal circuit member was measured in the same manner as in Example 1, and was found to be 2.75 μΩ·cm. When the hardness of the metal circuit member was measured in the same manner as in Example 1, the hardness was 16.2 HV. When the bonding interface between the metal circuit member and the ceramic plate was inspected in the same manner as in Example 1, no defects (unbonded portions) were found at the bonding interface.

[0054] [Example 2] In the process of producing the Al-based solid material of Example 1, the composition of the molten metal in which Ti and B exist in a dissolved state in the liquid phase of Al was changed to Ti: 0.04 mass %, B: 0.04 mass %, and the remainder Al, except that the Al-based solid material was produced under the same conditions as in Example 1. Only the above-mentioned Al-based solid material (having a composition of Ti: 0.04 mass %, B: 0.04 mass %, and the remainder Al) produced by the method of applying ultrasonic vibration was used as the raw material of the Al-based molten metal, and an aluminum-ceramic bonding substrate was produced under the same conditions as in Example 1.

[0055] Macrostructure observation of the metal circuit component under the same conditions as in Example 1 revealed a solidification structure in which the area ratio of equiaxed crystals on the upper surface (80 mm × 50 mm) of the metal circuit component was 95 area %. Using a cutting method conforming to JIS H0501-1986, similar to Example 1, multiple line segments equivalent to a length of 50 mm were drawn at 15 mm intervals in a direction parallel to the short sides of an 80 mm × 50 mm rectangle, roughly perpendicular to the solidification direction, and the average crystal grain size was measured. The resulting average crystal grain size of the equiaxed crystals was 1.25 mm. A macroscopic photograph of the central portion of the metal circuit component obtained in this example is shown in Figure 8. The solidification direction is generally from the left to the right of the photograph.

[0056] The electrical resistivity of the metal circuit member was measured in the same manner as in Example 1, and was found to be 2.72 μΩ / cm. The hardness of the metal circuit member was measured in the same manner as in Example 1, and was found to be 16.8 HV. When the bonding interface between the metal circuit member and the ceramic plate was inspected in the same manner as in Example 1, no defects (unbonded portions) were found at the bonding interface.

[0057] Comparative Example 2 In Example 2, an experiment was carried out under the same conditions as in Example 2, except that the process of applying ultrasonic vibrations was omitted in the process of producing the Al-based solid material. That is, an aluminum-ceramic bonding substrate was produced under the same conditions as in Example 1, using only an Al-based solid material (having a composition of Ti: 0.04 mass %, B: 0.04 mass %, and the remainder Al) produced without applying ultrasonic vibrations as the raw material of the Al-based molten metal.

[0058] Macrostructure observation of the metal circuit component under the same conditions as in Example 1 revealed that the entire upper surface (80 mm × 50 mm) of the metal circuit component exhibited a solidification structure consisting of columnar crystals. Using a cutting method conforming to JIS H0501-1986, similar to Example 1, multiple line segments equivalent to a length of 50 mm were drawn at 15 mm intervals in a direction parallel to the short sides of an 80 mm × 50 mm rectangle, approximately perpendicular to the solidification direction, and the average crystal grain size was measured. As a result, the average crystal grain size in the direction approximately perpendicular to the solidification direction of the columnar crystals was 15.5 mm. Figure 8 shows a macroscopic photograph of the central portion of the metal circuit component obtained in this example. The solidification direction is generally from the left to the right of the photograph. Comparing this example with Example 2, it is clear that the effect of remelting and then resolidifying the Al-based solid component produced by the method of applying ultrasonic vibrations is significant in reducing the crystal grain size.

[0059] The electrical resistivity of the metal circuit member was measured in the same manner as in Example 1, and was found to be 2.72 μΩ·cm. The hardness of the metal circuit member was measured in the same manner as in Example 1, and was found to be 16.0 HV. When the bonding interface between the metal circuit member and the ceramic plate was inspected in the same manner as in Example 1, no defects (unbonded portions) were found at the bonding interface.

[0060] [Example 3] In the process of producing the Al-based solid material of Example 1, the composition of the molten metal in which Ti and B exist in a dissolved state in the liquid phase of Al was changed to Ti: 0.05 mass %, B: 0.05 mass %, and the remainder Al, except that the Al-based solid material was produced under the same conditions as in Example 1. Only the above-mentioned Al-based solid material (having a composition of Ti: 0.05 mass %, B: 0.05 mass %, and the remainder Al) produced by the method of applying ultrasonic vibration was used as the raw material of the Al-based molten metal, and an aluminum-ceramic bonding substrate was produced under the same conditions as in Example 1.

[0061] Macroscopic observation of the metal circuit component under the same conditions as in Example 1 revealed that the entire upper surface (80 mm × 50 mm) of the metal circuit component exhibited a solidification structure consisting of equiaxed crystals. Using a cutting method conforming to JIS H0501-1986, similar to Example 1, multiple line segments equivalent to a length of 50 mm were drawn at 15 mm intervals in a direction parallel to the short sides of an 80 mm × 50 mm rectangle, approximately perpendicular to the solidification direction, and the average crystal grain size was measured. The average crystal grain size of the equiaxed crystals was found to be 1.69 mm. A macroscopic photograph of the central portion of the metal circuit component obtained in this example is shown in Figure 9. The solidification direction is generally from the left to the right of the photograph.

[0062] The electrical resistivity of the metal circuit member was measured in the same manner as in Example 1, and was found to be 2.71 μΩ·cm. When the hardness of the metal circuit member was measured in the same manner as in Example 1, the hardness was 16.3 HV. When the bonding interface between the metal circuit member and the ceramic plate was inspected in the same manner as in Example 1, no defects (unbonded portions) were found at the bonding interface.

[0063] Comparative Example 3 In Example 3, an experiment was carried out under the same conditions as in Example 3, except that the process of applying ultrasonic vibrations was omitted in the process of producing the Al-based solid material. That is, an aluminum-ceramic bonding substrate was produced under the same conditions as in Example 1, using only an Al-based solid material (having a composition of Ti: 0.05 mass %, B: 0.05 mass %, and the remainder Al) produced without applying ultrasonic vibrations as the raw material of the Al-based molten metal.

[0064] Macrostructure observation of the metal circuit component under the same conditions as in Example 1 revealed that the entire upper surface (80 mm × 50 mm) of the metal circuit component exhibited a solidification structure consisting of columnar crystals. Using a cutting method conforming to JIS H0501-1986, similar to Example 1, multiple line segments equivalent to a length of 50 mm were drawn at 15 mm intervals in a direction parallel to the short sides of an 80 mm × 50 mm rectangle, approximately perpendicular to the solidification direction, and the average crystal grain size was measured. As a result, the average crystal grain size in the direction approximately perpendicular to the solidification direction of the columnar crystals was 16.8 mm. Figure 9 shows a macroscopic photograph of the central portion of the metal circuit component obtained in this example. The solidification direction is generally from the left to the right of the photograph. Comparing this example with Example 3, it is clear that the effect of remelting and then resolidifying the Al-based solid component produced by the method of applying ultrasonic vibrations is significant in reducing the crystal grain size.

[0065] The electrical resistivity of the metal circuit member was measured in the same manner as in Example 1, and was found to be 2.71 μΩ·cm. When the hardness of the metal circuit member was measured in the same manner as in Example 1, the hardness was 16.3 HV. When the bonding interface between the metal circuit member and the ceramic plate was inspected in the same manner as in Example 1, no defects (unbonded portions) were found at the bonding interface.

[0066] Comparative Example 4 An aluminum-ceramic bonding substrate was produced under the same conditions as in Example 1, using only a pure Al ingot with an Al content of 99.9 mass % or more as the Al-based solid material to be subjected to the molten metal bonding method.

[0067] Macrostructure observation of the metal circuit component under the same conditions as in Example 1 revealed that the entire upper surface (80 mm × 50 mm) of the metal circuit component exhibited a solidification structure consisting of columnar crystals. Using a cutting method conforming to JIS H0501-1986, similar to Example 1, multiple line segments equivalent to a length of 50 mm were drawn at 15 mm intervals in a direction parallel to the short sides of an 80 mm × 50 mm rectangle, approximately perpendicular to the solidification direction, and the average crystal grain size was measured. As a result, the average crystal grain size in the direction approximately perpendicular to the solidification direction of the columnar crystals was 15.9 mm.

[0068] The electrical resistivity of the metal circuit member was measured in the same manner as in Example 1, and was found to be 2.70 μΩ / cm. The hardness of the metal circuit member was measured in the same manner as in Example 1, and was found to be 16.0 HV. When the bonding interface between the metal circuit member and the ceramic plate was inspected in the same manner as in Example 1, no defects (unbonded portions) were found at the bonding interface. [Explanation of symbols]

[0069] 1. Mold 1a Upper mold 1b Lower mold 2 Pressure port 3 Yudo 4 Pin-shaped recess 5 Hot water storage section 10 Ceramic plate 20 Metallic circuit components 21 Groove 22 Semiconductor element mounting surface 50 Heat dissipation material 51 Peripheral wall section 52 Groove 53 Pin-like protrusion 70 Furnace 71 Crucible 72 Molten Metal 73 Ultrasonic vibrator 74 Horn 75 Thermocouple Sensor 100 molten metal 103 Narrow cross-section flow channel 110 Plate-shaped reinforcing member

Claims

1. A method for producing an aluminum-ceramic bonding substrate, comprising melting an Al-based solid material comprising a solidified product as defined in (A) below to produce an Al-based molten metal, and solidifying the Al-based molten metal in contact with the surface of a ceramic plate placed in a mold, thereby bonding an aluminum member to one or both surfaces of the ceramic plate. (A) Instead of using an Al-Ti-B alloy as the Ti source and the B source, an Al-Ti alloy and an Al-B alloy containing Ti and B alone are used, thereby forming a molten metal at 750 to 850°C having a composition of Ti: 0.01 to 0.2 mass%, B: 0.001 to 0.1 mass%, and the remainder being Al and unavoidable impurities, in which Ti and B are present in a dissolved state in a liquid phase of Al, and then the temperature of the molten metal is lowered and ultrasonic vibrations are applied to the molten metal within a molten metal temperature range of 720 to 680°C, and the treated molten metal is then solidified to obtain a solidified product.

2. 2. The method for producing an aluminum / ceramic bonding substrate according to claim 1, wherein the treatment of applying ultrasonic vibrations is a treatment of applying ultrasonic vibrations having a vibration amplitude of 10 to 80 μm (pp).

3. 3. The method for producing an aluminum-ceramic bonding substrate according to claim 1 or 2, wherein the aluminum-ceramic bonding substrate has a structure in which aluminum members are bonded to both surfaces of a ceramic plate, one of the aluminum members being a metal member for a circuit on which a semiconductor element is mounted, and the other being a heat dissipation member.

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