Method for manufacturing substrate with recessed part, ceramic wiring substrate, and power module

Abstract

To provide a substrate with a recessed part which can provide a sufficient joint strength between a peripheral part of a semiconductor element and the recessed part, and a ceramic wiring substrate and a power module having the substrate with the recessed part.SOLUTION: In the power module, a ceramic wiring substrate with a recessed part 81 has a first metal layer 8. The recessed part 81 is recessed from a surface 800 of the first metal layer 8 in the thickness direction of the substrate. The recessed part 81 has a wall surface 811 continuing in the surface, a flat bottom surface 812, and a recess 813 continuing to the wall surface and a bottom surface and recessed in the thickness direction of the bottom surface.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a substrate with concave portions, a ceramic wiring substrate, and a power module. [Background technology]

[0002] 2. Description of the Related Art Power modules such as IGBT modules are used in inverters that control high-output motors such as those used in electric railways, power generation, and electric / hybrid automobiles (see Patent Document 1). This power module includes a ceramic insulating substrate having metal layers provided on both sides of a ceramic base, and a semiconductor element bonded onto the metal layers of the ceramic insulating substrate. Furthermore, in order to improve the accuracy of positioning the semiconductor element relative to the metal layer, a recess for accommodating the semiconductor element is often formed in the surface of the metal layer.

[0003] The recesses are formed in the surface of the metal layer by, for example, wet etching. Fig. 5 is a diagram for explaining a conventional method for forming a recess. Fig. 6 is a cross-sectional view showing the configuration of a recess formed by the method shown in Fig. 5. In Fig. 5, the upper diagram is a plan view, and the lower diagram is a cross-sectional view. Specifically, first, a metal layer 80' is prepared (see FIG. 5(a)), and a mask M' is formed on the surface of the metal layer 80' except for the area where the recess 81' is to be formed (see FIG. 5(b)). Next, the metal layer 80' is wet-etched using this mask M'. As a result, the metal layer 80' exposed from the mask M' is dissolved in the etching solution and removed, forming the recess 81'.

[0004] Thereafter, the mask M' is removed to obtain a metal layer 80' having recesses 81' formed on its surface (see FIG. 5(c)). However, this method is prone to causing a skirt-like shape (so-called "sagging 89'") at the corners of the recess 81' as shown in Fig. 6. In this case, if a bonding agent is supplied into the recess 81', the bonding agent will gather in the center of the recess 81'. As a result, it becomes difficult to obtain sufficient bonding strength between the peripheral edge of the semiconductor element and the metal layer 80'. A semiconductor element tends to expand and contract more at its periphery than at its center due to thermal expansion, and if the bonding strength between the periphery and the metal layer 80' is insufficient, this portion will be prone to peeling. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2021-185639 A Summary of the Invention [Problem to be solved by the invention]

[0006] In view of the above circumstances, the present invention provides a substrate with a recess that can obtain sufficient bonding strength between the peripheral portion of a semiconductor element and the recess, as well as a ceramic wiring substrate and a power module that include such a substrate with a recess. [Means for solving the problem]

[0007] According to one aspect of the present invention, there is provided a substrate with a recess. The substrate in this substrate has a surface. The recess is formed by being recessed from the surface in the thickness direction of the substrate. The recess has a wall surface continuous with the surface, a flat bottom surface, and a recess continuous with the wall surface and the bottom surface and recessed from the bottom surface in the thickness direction.

[0008] According to this aspect, sufficient bonding strength can be obtained between the peripheral portion of the semiconductor element and the metal layer. [Brief description of the drawings]

[0009] [Figure 1]1 is a cross-sectional view showing a configuration of an embodiment of a power module of the present invention. [Diagram 2] 2 is a plan view showing a configuration of a portion of a first metal layer shown in FIG. 1. [Diagram 3] 3 is a cross-sectional view taken along line AA in FIG. 2. [Figure 4] 4 is a diagram for explaining a method of forming the first metal layer shown in FIG. 3. FIG. [Diagram 5] 1A to 1C are diagrams for explaining a conventional method for forming a recessed portion. [Figure 6] 6 is a cross-sectional view showing the configuration of a recess formed by the method shown in FIG. 5. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Various features shown in the following embodiment can be combined with each other. First, an embodiment of a power module of the present invention will be described. FIG. 1 is a cross-sectional view showing the configuration of an embodiment of a power module of the present invention. In the following description, the upper side in FIG. 1 will be referred to as "top" or "upper", and the lower side will be referred to as "bottom" or "lower". The power module 1 shown in FIG. 1 comprises a base plate 2, a ceramic wiring board 4 joined to the base plate 2 via a first solder 3, and a semiconductor element 6 joined to the ceramic wiring board 4 via a second solder 5.

[0011] The ceramic wiring board 4 includes a ceramic plate 7, a first metal layer 8 provided on an upper surface (one surface) of the ceramic plate 7, and a second metal layer 9 provided on a lower surface (the other surface) of the ceramic plate 7. That is, the first metal layer 8 and the second metal layer 9 are provided on both surfaces of the ceramic plate 7, respectively. At least the first metal layer 8 forms an electric circuit (metal circuit). The second metal layer 9 may or may not form an electric circuit (metal circuit). The base plate 2 is joined to the second metal layer 9 via the first solder 3 . Moreover, the first metal layer 8 is constituted by a substrate with concave portions of the present invention, which will be described later, and has a plurality of concave portions 81. The semiconductor element 6 is mounted in the recess 81 of the first metal layer 8 via the second solder 5, and is electrically connected to a predetermined location of the first metal layer 8 via a metal wire 10 such as an aluminum wire (aluminum line).

[0012] The components provided on the base plate 2 are covered with and housed in a resin housing 11 having a hollow box shape with one side open, for example. The hollow space between the base plate 2 and the housing 11 is filled with a filler 12 such as silicone gel. An electrode 13 that penetrates the housing 11 is joined to a predetermined portion of the first metal layer 8 via solder 14 so as to enable electrical connection to the outside of the housing 11. Mounting holes 2a for screw fastening are formed in the edge of the base plate 2. The number of mounting holes 2a is, for example, four or more. Instead of the mounting holes 2a, mounting grooves may be formed in the edge of the base plate 2 so that the side wall of the base plate 2 has a U-shaped cross section.

[0013] Heat dissipation fins 22 are provided on the lower surface side of the base plate 2. The heat dissipation fins 22 are fixed to the base plate 2 by screws (bolts) 23 inserted into mounting holes 2a formed in the base plate 2. The surface of the heat dissipation fins 22 facing the base plate 2 is substantially flat. Furthermore, grease (heat dissipation grease) 24 is placed between the base plate 2 and the heat dissipation fins 22 to ensure adhesion between them. The grease 24 usually has a thermal conductivity of about 1 W / mK to 2 W / mK, and has the highest thermal resistance among the components of the power module 1. Therefore, in order to improve the heat dissipation of the power module 1, it is important to make the thermal resistance of this grease 24 as small as possible.

[0014] The ceramic plate 7 is made of, for example, sintered silicon nitride. The constituent materials of the first metal layer 8 and the second metal layer 9 may be the same or different. The first metal layer 8 and the second metal layer 9 are made of, for example, copper. The base plate 2 is preferably made of a material having high thermal conductivity (eg, aluminum). The power module 1 as described above has excellent heat dissipation characteristics, and is therefore suitable for use in power modules using SiC and GaN semiconductor elements capable of achieving high output, in addition to Si. That is, the semiconductor element 6 may be formed of any of Si, SiC, and GaN. The power module 1 is also suitable for use as a drive inverter for trains or automobiles that require high voltage resistance and high output.

[0015] Next, the first metal layer 8 will be described. Fig. 2 is a plan view showing a configuration of a portion of the first metal layer shown in Fig. 1. Fig. 3 is a cross-sectional view taken along line AA in Fig. 2. In Fig. 3, the size of the first metal layer 8 in the thickness direction (depth direction of the recess 81) is shown exaggerated. The first metal layer 8 is configured as one embodiment of the substrate with concave portions of the present invention. The first metal layer 8 shown in Fig. 2 comprises a metal plate (substrate) 80 having a surface 800, and a concave portion 81 is formed by being recessed from the surface 800 in the thickness direction of the metal plate 80. As shown in FIG. 3, the recess 81 has a wall surface 811 continuous with the surface 800, a flat bottom surface 812 (the bottom surface 812 is substantially parallel to the surface 800), and a recess 813 continuous with the wall surface 811 and the bottom surface 812 and recessed from the bottom surface 812 in the thickness direction. By providing the recess 813 on the peripheral portion of the bottom of the recess 81, the second solder (bonding agent) 5 is easily stored in the recess 813. Therefore, sufficient bonding strength can be obtained between the recess 81 (first metal layer 8) not only at the center of the semiconductor element 6 but also at the peripheral portion. As a result, even if the semiconductor element 6 thermally expands, peeling (falling off) from the recess 81 can be prevented. In this specification, the flat bottom surface 812 refers to a surface that is substantially parallel to the horizontal direction (a direction perpendicular to the thickness direction of the metal plate 80) and does not have a shape that prevents the bonding of the semiconductor element 6.

[0016] 3, the inclination angle θ of the wall surface 811 with respect to the thickness direction of the metal plate 80 is approximately constant along the thickness direction of the metal plate 80. That is, the wall surface 811 is inclined with respect to the thickness direction of the metal plate 80, but there is no point where the inclination changes extremely. Specifically, the wall surface 811 is located inside the recess 81 with respect to the imaginary line VL extending from the intersection point I between the surface 800 and the wall surface 811 along the thickness direction without intersecting with the imaginary line VL. With this configuration, when the semiconductor element 6 is inserted into the recess 81 , the wall surface 811 functions as a guide for the semiconductor element 6 , and the semiconductor element 6 can be accurately guided to the vicinity of the bottom surface 812 of the recess 81 .

[0017] In addition, since the wall surface 811 is slightly inclined, the width of the gap formed between the wall surface 811 and the side surface of the semiconductor element 6 gradually increases upward. Therefore, even if the second solder 5 in a molten state flows onto the side surface of the semiconductor element 6, the capillary phenomenon in which the second solder 5 creeps up to the upper surface (functional surface) of the semiconductor element 6 is unlikely to occur. In other words, by holding the second solder 5 between the side surface of the semiconductor element 6 and the wall surface 811, the bonding strength of the semiconductor element 6 to the recess 81 can be further increased. 6 (wherein the wall surface 811' intersects the imaginary line VL'), the wall surface 811 does not intersect the imaginary line VL, and this makes it possible to prevent the thickness of the wall portion 82 separating the adjacent recesses 81 from becoming thin. As a result, even if the metal plate 80 (particularly the wall portion 82) is exposed to high temperatures during use of the power module 1, deformation of the metal plate 80 (particularly the wall portion 82) can be suppressed.

[0018] The inclination angle θ of the wall surface 811 with respect to the thickness direction of the metal plate 80 is preferably about 10° to 40°, more preferably about 15° to 35°, and even more preferably about 20° to 30°. In this case, the above-mentioned effect can be further improved. When viewed in a cross section along the thickness direction of metal plate 80, if the intersection between the extension line of bottom surface 812 extended toward wall surface 811 and wall surface 811 is defined as "intersection II," the distance L (so-called "sagging amount") in the horizontal direction (direction perpendicular to the thickness direction) between intersection II and virtual line VL is preferably approximately 0.2 mm or more and 0.5 mm or less, more preferably approximately 0.23 mm or more and 0.4 mm or less, and even more preferably approximately 0.26 mm or more and 0.3 mm or less.

[0019] When viewed in a cross section along the thickness direction of metal plate 80, width X of opening 810 of recess 81 is preferably about 5 mm or more and 20 mm or less, more preferably about 7 mm or more and 18 mm or less, and even more preferably about 9 mm or more and 16 mm or less. In recess 81 of such a size, from the viewpoint of reliably inserting semiconductor element 6 into recess 81, it is useful to set the degree of inclination of wall surface 811 within the above range. In this embodiment, the recess 81 (opening 810) has a rectangular shape in a plan view, and the cross section along the thickness direction of the metal plate 80 is a cross section parallel to one side of the recess 81.

[0020] When the depth from the opening 810 of the recess 81 to the bottom surface 812 is D1 [mm] and the maximum depth from the opening 810 of the recess 81 to the recess 813 is D2 [mm], D2 / D1 is preferably about 1.05 to 1.25, more preferably about 1.1 to 1.24, and even more preferably about 1.15 to 1.23. In this case, since the recess 81 has a sufficient depth, it is easy to position the semiconductor element 6 and the recess 81. In addition, since the recess 813 can store a sufficient amount of the second solder 5, a higher bonding strength with the semiconductor element 6 can be obtained. Furthermore, when the depth from the opening 810 of the recess 81 to the bottom surface 812 is D1 [mm] and the thickness of the metal plate 80 is T [mm], D1 / T is preferably about 0.5 to 0.9, more preferably about 0.6 to 0.85, and even more preferably about 0.7 to 0.8. In this case, it is possible to prevent the time required for processing the recess 81 from becoming long. As a result, the shape of the recess 81 is unlikely to become unstable. Also, it is possible to prevent or suppress an extreme decrease in the mechanical strength of the metal plate 80.

[0021] The specific thickness T of the metal plate 80 is not particularly limited, but is preferably about 0.6 mm to 1 mm, more preferably about 0.65 mm to 0.95 mm, and even more preferably about 0.7 mm to 0.9 mm. In this case, the height of the ceramic wiring substrate 4 and therefore the height of the power module 1 can be reduced. When viewed in a cross section along the thickness direction of the metal plate 80, if the width of the bottom surface 812 is W1 [mm] and the maximum width of the recess 813 is W2 [mm], then W2 / W1 is preferably about 0.3 to 0.6, more preferably about 0.35 to 0.55, and even more preferably about 0.4 to 0.5. In this case, it is easy to balance the amount of the second solder 5 present in the recess 813 and the amount of the second solder 5 present on the bottom surface 812, and the bonding strength of the semiconductor element 6 to the recess 81 can be further increased. For example, when the width X of the opening 810 is about 10 mm, the width W1 of the bottom surface 812 is preferably about 4 mm or more and 5 mm or less, and the maximum width W2 of the recess 813 is preferably about 2.15 mm or more and 2.55 mm or less.

[0022] Such a first metal layer 8 (recess 81) can be formed, for example, as follows. FIG. 4 is a diagram for explaining a method of forming the first metal layer shown in FIG. In FIG. 4, the upper diagram is a plan view, and the lower diagram is a cross-sectional view. One embodiment of a method for forming a first metal layer 8 (a method for manufacturing a substrate with a recess) includes a first mask formation step, a first wet etching step, a first mask removal step, a second mask formation step, a second wet etching step, and a second mask removal step. Each step will be described below in order.

[0023] [1] First mask formation process First, a first mask M1 is formed on the surface 800 of the metal plate 80 as shown in FIG. 4(b) so as to expose a frame-shaped region A81b having a predetermined width that follows the contour of the recess 81 in an area A81 where the recess 81 is to be formed on the surface 800 of the metal plate 80 as shown in FIG. 4(a). The first mask M1 can be formed by, for example, photolithography, inkjet printing, screen printing, etc. In particular, it is preferable to form the first mask M1 by photolithography. By forming the first mask M1 by photolithography, the width and shape of the opening M1a that exposes the frame-shaped region A81b can be precisely adjusted.

[0024] Therefore, in the following, a case where a resist layer formed by photolithography is used as the first mask M1 will be representatively described. First, a resist material is applied to the surface 800 of the metal plate 80 . The liquid type resist material can be applied by using, for example, a spin coating method, a dipping method, a spray coating method, etc. Also, the dry film type resist material can be applied by using a method of directly pressing the resist material onto the metal plate 80, etc.

[0025] The resist material is composed of a resin composition containing a photosensitive resin. Either a negative type or a positive type can be used for this photosensitive resin. In this embodiment, a case where a resin composition containing a negative type photosensitive resin is used as the resist material will be described as an example. Next, the resist material is exposed to light using a photomask that corresponds to the shape of the first mask M1 to be formed, and then the uncured portions of the resist material are removed (developed), thereby forming the first mask M1 having the openings M1a as shown in FIG. The thickness of the first mask M1 is not particularly limited, but is set to about 20 μm or more and 30 μm or less (preferably, about 25 μm or more and 30 μm or less). Thereafter, as necessary, the vicinity of the surface of the first mask M1 is hardened by, for example, irradiation with ultraviolet light, electron beams, radiation, or the like, heating, etc. By hardening the vicinity of the surface of the first mask M1, it is possible to improve the resistance of the first mask M1 to treatments in subsequent steps.

[0026] [2] First wet etching process Next, a first wet etching is performed on the metal plate 80 using the first mask M1 to form a frame-shaped groove 81g. The etching solution may be an aqueous solution of a metal chloride, an aqueous solution of an alkali, an aqueous solution of an acid, etc. When the metal plate 80 is a copper plate, an aqueous solution of cupric chloride is preferably used as the etching solution. The etching time for the first wet etching is not particularly limited, but is preferably about 20 minutes or more and 90 minutes or less, and more preferably about 40 minutes or more and 70 minutes or less. In other embodiments, the frame-shaped groove 81g can be formed by dry etching using, for example, CF4, CHF3, oxygen, or a mixed gas containing these as a plasma gas, laser processing, or the like.

[0027] Here, when viewed in a cross section along the thickness direction of the metal plate 80, if the width of the region A81 where the recess 81 is to be formed is X [mm] and the width of the frame-shaped region A81b is Y [mm], then Y / X is preferably about 0.001 to 0.15, more preferably about 0.005 to 0.1, and even more preferably about 0.01 to 0.05. This allows etching of the metal plate 80 along the thickness direction to take precedence over the horizontal direction, making it easy to form the recess 81 with a small sagging amount (distance L) as shown in FIG. When viewed in a cross section along the thickness direction of the metal plate 80, if the depth of the recess 81 to be formed is D (the same as or slightly larger than D1) [mm] and the width A81b of the frame-like region is Y [mm], then Y / D is preferably about 0.1 to 1.25, more preferably about 0.15 to 1, and even more preferably about 0.2 to 0.75. In this case, it is easy to prevent unnecessary side etching from occurring in the metal plate 80.

[0028] [3] First mask removal process Next, as shown in FIG. 4(c), the first mask M1 is removed from the metal plate 80. The first mask M1 can be removed by using, for example, an alkaline remover, an organic remover, or the like. [4] Second mask formation process 4(d), a second mask M2 is formed on the surface 800 of the metal plate 80 except for an area A81 where the recesses 81 are to be formed on the surface 800 of the metal plate 80. This second mask M2 can be formed in the same manner as the first mask M1.

[0029] [5] Second wet etching process Next, a second wet etching is performed on the metal plate 80 using the second mask M2, and the region A81a of the metal plate 80 remaining inside the frame-shaped groove 81g is etched to form the recesses 81, thereby obtaining the first metal layer (substrate with recesses) 8. This second wet etching can be performed in the same manner as the first wet etching. The etching time for the second wet etching is not particularly limited either, but is preferably about 20 minutes or more and 90 minutes or less, and more preferably about 40 minutes or more and 70 minutes or less. In addition, in other embodiments, a dry etching method using, for example, CF4, CHF3, oxygen or a mixed gas containing these as a plasma gas can also be used to etch the region A81a of the metal plate 80 remaining inside the frame-shaped groove 81g. [6] Second mask removal process Finally, as shown in FIG. 4(e), the second mask M2 is removed from the metal plate 80.

[0030] 2, the first metal layer 8 has a plurality of recesses 81. According to the above-described manufacturing method, side etching as shown in Fig. 6 is unlikely to occur, so that the distance between two adjacent recesses 81 (the thickness of the wall portion 82 partitioning the two adjacent recesses 81) can be designed to be sufficiently small. Specifically, the minimum distance between two adjacent recesses 81 is preferably about 0.9 mm to 5 mm, more preferably about 1.2 mm to 4 mm, and even more preferably about 1.5 mm to 3 mm. Even if the thickness of the wall 82 separating two adjacent recesses 81 is reduced in this way, it is possible to prevent the wall 82 from being penetrated and ensure sufficient mechanical strength.

[0031] Similarly, the distance between the periphery of the first metal layer 8 and the periphery of the recess 81 can also be designed to be sufficiently small. Specifically, the minimum distance between the periphery of first metal layer 8 and the periphery of recess 81 is preferably about 1 mm to 5 mm, more preferably about 1.5 mm to 4 mm, and even more preferably about 2 mm to 3 mm. Even if the thickness of peripheral wall 83 defining recess 81 is reduced in this manner, it is possible to prevent peripheral wall 83 from being penetrated and ensure sufficient mechanical strength. According to the substrate with concave portions, ceramic wiring board, and power module as described above, sufficient bonding strength can be obtained between the peripheral edge of the semiconductor element 6 and the concave portions 81. Furthermore, it may be provided in the following aspects:

[0032] (1) A substrate with a recess, the substrate having a surface, the recess being formed by being recessed from the surface in a thickness direction of the substrate, the recess having a wall surface continuous with the surface, a flat bottom surface, and a recess continuous with the wall surface and the bottom surface and recessed from the bottom surface in the thickness direction.

[0033] (2) The substrate with concave portions according to (1) above, wherein an inclination angle of the wall surface with respect to the thickness direction of the substrate is approximately constant along the thickness direction.

[0034] (3) The substrate with concave portions according to (2) above, wherein the inclination angle of the wall surface with respect to the thickness direction of the substrate is 10° or more and 40° or less.

[0035] (4) The substrate with concave portions according to any one of (1) to (3) above, wherein, when viewed in a cross section along the thickness direction of the substrate, the width of an opening of the concave portion is 5 mm or more and 20 mm or less.

[0036] (5) The substrate with concave portions according to any one of (1) to (4) above, wherein when the depth from the opening of the concave portion to the bottom surface is D1 [mm] and the maximum depth from the opening of the concave portion to the depression is D2 [mm], D2 / D1 is 1.05 or more and 1.25 or less.

[0037] (6) The substrate with concave portions according to any one of (1) to (5) above, wherein when the depth from the opening of the concave portion to the bottom surface is D1 [mm] and the thickness of the substrate is T [mm], D1 / T is 0.5 or more and 0.9 or less.

[0038] (7) The substrate with concave portions according to (6) above, wherein the thickness T of the substrate is 0.6 mm or more and 1 mm or less.

[0039] (8) The substrate with concave portions according to any one of (1) to (7) above, wherein, when viewed in a cross section along the thickness direction of the substrate, the width of the bottom surface is W1 [mm] and the maximum width of the concave portion is W2 [mm], and W2 / W1 is 0.3 or more and 0.6 or less.

[0040] (9) The substrate with concave portions according to any one of the above (1) to (8), wherein the substrate is a metal plate.

[0041] (10) A ceramic wiring board comprising: a ceramic plate; a first metal layer provided on one surface of the ceramic plate and made of the substrate with a recess as described in (9) above; and a second metal layer provided on the other surface of the ceramic plate.

[0042] (11) A power module comprising: the ceramic wiring substrate according to (10) above; and a semiconductor element mounted in the recess of the first metal layer and electrically connected to the first metal layer. Of course, this is not the case.

[0043] Finally, although various embodiments according to the present disclosure have been described, these are presented as examples and are not intended to limit the scope of the invention. The novel embodiment can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. The embodiments and their modifications are included within the scope and spirit of the invention, and are included in the scope of the invention and its equivalents described in the claims. In the above embodiment, the case where the recess is formed in the metal plate has been described, but in other embodiments, the recess may be formed in the ceramic plate. In this case, the metal plate (metal layer) is inserted into the recess in the ceramic plate and bonded via a bonding agent. In this case, the same effect can be obtained by using the same configuration as above. EXAMPLES

[0044] The present invention will be described in more detail below using the following examples and comparative examples, but the present invention is not limited to the following examples.

[0045] 1. Manufacturing copper plates with recesses Example 1 First, a resin composition (resist material) containing a commercially available negative-type photosensitive resin was applied by spin coating onto the surface of a copper plate (oxygen-free copper plate, manufactured by Mitsubishi Shindoh Co., Ltd.) having a thickness of 0.9 mm. Next, the resist material was exposed to light using a photomask that corresponded to the shape of the first mask to be formed, and the uncured resist material was then removed with a commercially available developer, resulting in a first mask (thickness: 5 μm) with an opening (width: 0.5 mm) that exposed the frame-shaped region on the surface of the copper plate.

[0046] Next, the copper plate was subjected to a first etching process using a commercially available aqueous solution of cupric chloride for 50 minutes, thereby forming a frame-shaped groove in the copper plate. Thereafter, the first mask was removed from the copper plate using a commercially available alkaline stripping solution. Again, a second mask (thickness: 5 μm) was formed on the surface of the copper plate, except for the area where the recesses were to be formed on the surface of the copper plate. The second mask was formed in the same manner as the first mask.

[0047] Next, a second etching was performed on the copper plate using a second mask. This removed the area remaining inside the frame-shaped groove to form a recess, thereby obtaining a copper plate with a recess. The second etching was performed in the same manner as the first etching. The second etching was performed for 60 minutes. The shape of the opening of each recess to be formed was a square with a side of 10 mm, the target depth was set to about 0.7 mm, and five recesses were formed. Thereafter, the second mask was removed from the copper plate in the same manner as the first mask.

[0048] Example 2 Five recesses were formed in the same manner as in Example 1, except that the width of the opening exposing the frame-shaped region on the surface of the copper plate was changed to 0.4 mm. Example 3 Five recesses were formed in the same manner as in Example 1, except that the width of the opening exposing the frame-shaped region on the surface of the copper plate was changed to 0.3 mm.

[0049] Example 4 Five recesses were formed in the same manner as in Example 1, except that the width of the opening exposing the frame-shaped region on the surface of the copper plate was changed to 0.2 mm. Example 5 Five recesses were formed in the same manner as in Example 1, except that the width of the opening exposing the frame-shaped region on the surface of the copper plate was changed to 0.1 mm.

[0050] Comparative Example 1 Five recesses were formed by machining, each having a size similar to that of the recesses formed in Example 1. The bottom surface was not formed flat, but was formed to have a convex curved surface that was convex upward. Comparative Example 2 Except for omitting the formation of the first mask, the first wet etching, and the removal of the first mask, five recesses were formed in the same manner as in Example 1. The second etching time was set to 60 minutes.

[0051] 2. Measuring the shape of the recess The shape of the recesses formed in each of the examples and comparative examples was measured using a three-dimensional measuring machine (VR-3000, manufactured by Keyence Corporation). The results are shown in Tables 1 and 2 below.

[0052] 3. Evaluation A semiconductor element was mounted in the recess formed in each of the examples and comparative examples using solder (lead-containing flux cored solder manufactured by Senju Metal Industry Co., Ltd.). At this time, the bonding property of the semiconductor element to the copper plate and the presence or absence of tilt were evaluated. The results are shown in Table 2 below.

[0053] [Table 1]

[0054] [Table 2]

[0055] As shown in Tables 1 and 2, in each example, the semiconductor element had good bonding to the copper plate, but the degree of bonding seemed to be improved by adjusting the size of each part of the recess (especially in Examples 2 to 4). On the other hand, in Comparative Example 1, the recess did not have a flat bottom, so the semiconductor element was not stable in the recess and could not be bonded sufficiently. Also, the semiconductor element was tilted, making it difficult to connect the semiconductor element with a metal wire (wire bonding). In Comparative Example 2, no depression was formed in the recess, and bonding at the outer edge of the semiconductor element was insufficient, resulting in poor bonding. [Explanation of symbols]

[0056] 1: Power module 10: Metal wire 11: Housing 12: Filling material 13: Electrode 14: Solder 2: Base plate 2a: Mounting hole 22: Heat dissipation fin 23: Screw 24: Grease 3: First solder 4: Ceramic wiring board 5: Second solder 6: Semiconductor elements 7: Ceramic plate 8: First metal layer 80: Metal plate 81: Recess 81g: Groove 82: Wall part 83: Peripheral wall part 800: Surface 810 :Aperture 811: Wall 812: Bottom 813: Depression A81 :Area A81a :Area A81b :Area 9: Second metal layer I: Intersection II: Intersection L: distance M1: First mask M1a: opening M2: Second mask T: Thickness VL: Virtual line θ: Inclination angle D: Depth D1: Depth D2: Maximum depth L: Length W1:Width W2: Maximum width X: Width Y :Width 80': Metal layer 81': Recess 811': Wall 89': Who M' : Mask VL': Virtual line

Claims

1. A substrate with a recess, the substrate has a surface; The recess is formed by being recessed from the surface in a thickness direction of the substrate, The recessed portion has a wall surface continuous with the front surface, a flat bottom surface, and a recess continuous with the wall surface and the bottom surface and recessed from the bottom surface in the thickness direction.

2. The substrate with concave portions according to claim 1 , A substrate with a recess, wherein an inclination angle of the wall surface with respect to the thickness direction of the substrate is approximately constant along the thickness direction.

3. The substrate with concave portions according to claim 2 , A substrate with a recess, wherein an inclination angle of the wall surface with respect to the thickness direction of the substrate is 10° or more and 40° or less.

4. The substrate with concave portions according to claim 1 , A substrate with a recess, wherein the width of an opening of the recess is 5 mm or more and 20 mm or less when viewed in a cross section along the thickness direction of the substrate.

5. The substrate with concave portions according to claim 1 , A substrate with a recess, wherein D2 / D1 is 1.05 or more and 1.25 or less, where D1 [mm] is a depth from the opening of the recess to the bottom surface and D2 [mm] is a maximum depth from the opening of the recess to the depression.

6. The substrate with concave portions according to claim 1 , A substrate with a recess, wherein D1 / T is 0.5 or more and 0.9 or less, where D1 [mm] is a depth from the opening of the recess to the bottom surface and T [mm] is a thickness of the substrate.

7. The substrate with concave portions according to claim 6, The substrate has a thickness T of 0.6 mm or more and 1 mm or less.

8. The substrate with concave portions according to claim 1 , A substrate with a recess, in which, when viewed in a cross section along the thickness direction of the substrate, the width of the bottom surface is W1 [mm] and the maximum width of the recess is W2 [mm], and W2 / W1 is 0.3 or more and 0.6 or less.

9. The substrate with concave portions according to claim 1 , The substrate is a metal plate.

10. A ceramic wiring substrate, A ceramic plate; a first metal layer provided on one surface of the ceramic plate and made of the substrate with concave portions according to claim 9; a second metal layer provided on the other surface of the ceramic plate.

11. A power module, The ceramic wiring substrate according to claim 10; a semiconductor element mounted in the recess of the first metal layer and electrically connected to the first metal layer.

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