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

Abstract

To provide a method for manufacturing a substrate with a recessed part, a substrate with a recessed part, a ceramic wiring substrate, and a power module.SOLUTION: A method for manufacturing a first metal layer 8 as a substrate with a recessed part includes the steps of: forming a first mask M1 in a surface of the substrate so that a frame-like region 81b with a predetermined width along the outline of a recessed part 81 of a region A81 in which the recessed part 81 is to be formed in the surface of the substrate is exposed; forming a frame-like trench 81g by performing a first etching on the substrate by using a first mask; removing the first mask from the substrate; forming a second mask M2 in a surface of the substrate by excluding the region in which the recessed part 81 is to be formed of the surface; and performing a second wet etching on the substrate by using the second mask to form the recessed part 81 and obtaining the substrate with the recessed part.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to a method for manufacturing a substrate with concave portions, 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 so-called side etching. That is, as shown in FIG. 6, a hollowed-out portion ("hollowed-out portion 88'") is likely to occur on the wall surface of the recess 81' below the mask M'. In this case, it is difficult to fill the hollowed-out portion 88' with bonding agent, and the recess 81' and the side surface of the semiconductor element cannot be sufficiently bonded, which causes the semiconductor element to wobble in the recess 81'. In addition, a skirt-like shape (so-called "sagging 89'") is likely to occur at the corners of the recess 81'. In this case, the size of the bottom surface of the recess 81' is reduced by the amount of the sagging 89', so that the bottom surface of the semiconductor element and the sagging 89' interfere with each other, and the semiconductor element cannot be inserted to the desired depth of the recess 81'. [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 method for manufacturing a substrate with a recess that can suppress the occurrence of gouges and sagging, a substrate with a recess that can firmly bond a semiconductor element, and 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 method for manufacturing a substrate with concave portions, comprising the steps of forming a first mask on a surface of the substrate so as to expose a frame-shaped region having a predetermined width along the contour of the concave portion in a region on the substrate surface where the concave portion is to be formed, performing a first wet etching on the substrate using the first mask to form a frame-shaped groove, removing the first mask from the substrate, forming a second mask on the surface of the substrate except for the region on the substrate surface where the concave portion is to be formed, and performing a second wet etching on the substrate using the second mask to form the concave portion and obtain a substrate with concave portions.

[0008] According to this aspect, it is possible to manufacture a substrate with concave portions in which the occurrence of recesses and sagging is suppressed. [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 a recess 81 of the first metal layer 8 via a 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 (substrate) 80.

[0016] Since the metal plate 80 has the recess 81, the semiconductor element 6 can be mounted (inserted) in the recess 81. This makes it easier to place the semiconductor element 6 at a desired position on the metal plate 80. In other words, the recess 81 allows the semiconductor element 6 to be positioned with respect to the metal plate 80. Furthermore, the size of the bonding surface is larger when the semiconductor element 6 is bonded to the recess 81 of the metal plate 80, which is a substrate with a recess, than when the semiconductor element 6 is bonded to a flat metal plate via the second solder 5. Therefore, the bond between the semiconductor element 6 and the metal plate 80 can be strengthened, and peeling (falling off) of the semiconductor element 6 can be suitably prevented.

[0017] The depth to which the semiconductor element 6 is placed within the recess 81 (the distance in the thickness direction of the metal plate 80 from the lower surface of the semiconductor element 6 to the surface 800) is preferably approximately 1 / 5 to 12 / 5 of the thickness of the semiconductor element 6, more preferably approximately 1 / 4 to 9 / 4, and even more preferably approximately 1 / 3 to 2. This is expected to improve the positioning accuracy of the semiconductor element 6 with respect to the metal plate 80. For example, if the semiconductor element 6 has a thickness of about 1 mm, the recess 81 should occupy a portion that is between 0.2 mm and 2.4 mm from the bottom surface of the semiconductor chip.

[0018] As shown in FIG. 3, the recess 81 has a wall surface 811 continuous with the surface 800, a flat bottom surface 812, 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 in the center of the semiconductor element 6 but also in the peripheral portion. As a result, even if the semiconductor element 6 thermally expands, peeling (falling off) from the recess 81 can be prevented.

[0019] 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. 3, the wall surface 811 and the bottom surface 812 are indirectly connected to each other via the depression 813, but they may be directly connected to each other without the depression 813 (without providing the depression 813). In this case, the bonding agent such as solder can be applied thinly and uniformly to the bottom surface 812 without accumulating in the depression 813, which has the advantage of saving the bonding agent.

[0020] 3, the inclination angle θ of the wall surface 811 with respect to the thickness direction of the metal plate (substrate) 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, when viewed in a cross section along the thickness direction of the metal plate (substrate) 80, the wall surface 811 is located inside the recess 81 with respect to the imaginary line VL, which is extended along the thickness direction from the intersection point I between the surface 800 and the wall surface 811, without intersecting with the imaginary line VL. As a result, 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 .

[0021] Furthermore, 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. Furthermore, since the metal plate 80 is permitted to move slightly in the in-plane direction near the surface 800 compared to when the wall surface 811 is parallel to the thickness direction of the metal plate 80, the semiconductor element 6 can be easily inserted into the recess 81. Furthermore, since a gap is generated between the side surface of the semiconductor element 6 and the wall surface 811 after insertion, if necessary, it is easy to add bonding agent to the gap between the side surface of the semiconductor element 6 and the wall surface 811, and the side surface of the semiconductor element 6 and the recess 81 can be bonded more firmly.

[0022] 6 (having a recessed portion (wall recess) 88' and a wall surface 811' intersecting the imaginary line VL'), the wall surface 811 does not intersect the imaginary line VL, so that it is possible to prevent the thickness of the wall portion 82 separating 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.

[0023] 6, it is difficult to fill recess 88' with adhesive. In particular, because the area around intersection I' protrudes (overhangs) toward the inside of recess 81', it is not possible to add adhesive to recess 88' when semiconductor element 6 is inserted in recess 81'. This results in insufficient bonding between the side surface of semiconductor element 6 and wall surface 811', causing semiconductor element 6 to peel off (detach) from recess 81'. On the other hand, according to this embodiment, the recess 81 does not have the hollowed-out portion 88', so that the side surface of the semiconductor element 6 can be well bonded to the wall surface 811. If there is not enough bonding agent between the side surface of the semiconductor element 6 and the wall surface 811, it is sufficient to add more bonding agent between the side surface of the semiconductor element 6 and the wall surface 811.

[0024] 6, the vicinity of intersection I' protrudes toward the inside of recess 81', which reduces the thickness of metal layer 80' near intersection I', making metal layer 80' near intersection I' prone to chipping. Also, the vicinity of intersection I' has a sharp shape, which makes it prone to scratching semiconductor element 6 when it comes into contact with it when inserting semiconductor element 6 into recess 81'. On the other hand, in this embodiment, recess 88' is not formed, and wall surface 811 is slightly inclined, so that the thickness of metal plate 80 near intersection I does not become thin, and therefore metal plate 80 near intersection I is less likely to chip. In addition, since the area near intersection I has a smooth shape, semiconductor element 6 is less likely to be damaged when semiconductor element 6 is inserted into recess 81.

[0025] The inclination angle θ of the wall surface 811 with respect to the thickness direction of the metal plate (substrate) 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.

[0026] 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.

[0027] 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.

[0028] The specific thickness T of the metal plate 80 is not particularly limited, but is preferably about 0.2 mm to 1.8 mm, more preferably about 0.5 mm to 1.5 mm, and even more preferably about 0.8 mm to 1.2 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.

[0029] Next, a method for manufacturing the first metal layer 8 (substrate with concave portions) will be described with reference to FIG. 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 step of forming a first mask), a first wet etching step (a step of forming a frame-shaped groove), a first mask removal step (a step of removing the first mask from the substrate), a second mask formation step (a step of forming a second mask), a second wet etching step (a step of obtaining a substrate with a recess), and a second mask removal step. Each step will be described below in order.

[0030] [1] First mask formation process First, a first mask M1 is formed on the surface 800 of the metal plate (substrate) 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 (substrate) 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.

[0031] 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.

[0032] 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.

[0033] [2] First wet etching process Next, a first wet etching is performed on the metal plate (substrate) 80 using the first mask M1, thereby forming 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 to 90 minutes, and more preferably about 40 minutes to 70 minutes, which makes it easier to minimize the amount of recesses and sagging. 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.

[0034] Here, when viewed in a cross section along the thickness direction of the metal plate (substrate) 80, 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]. 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 makes it possible to prioritize etching of the metal plate 80 along the thickness direction while preventing side etching in the horizontal direction. As a result, not only is it easy to prevent the occurrence of the hollowed-out portion 88' and the sagging 89' as shown in FIG. 6, but it is also easy to form the recess 81 with a small sagging amount (distance L) as shown in FIG. 3.

[0035] When viewed in a cross section along the thickness direction of the metal plate (substrate) 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 of the frame-shaped region A81b 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, even if etching of the metal plate 80 along the thickness direction is prioritized, it is easy to prevent unnecessary side etching of the metal plate 80.

[0036] [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 (substrate) 80 except for an area A81 where the recesses 81 are to be formed on the surface 800 of the metal plate (substrate) 80. This second mask M2 can be formed in the same manner as the first mask M1.

[0037] [5] Second wet etching process Next, a second wet etching is performed on the metal plate (substrate) 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, but is preferably about 20 minutes to 90 minutes, and more preferably about 40 minutes to 70 minutes, which can minimize the occurrence of hollows and sagging. 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.

[0038] As shown in Fig. 2, the first metal layer (substrate with recesses) 8 has a plurality of recesses 81. According to the manufacturing method as described above, hollow portions 88' as shown in Fig. 6 are unlikely to occur, so the distance between two adjacent recesses 81 (the thickness of the wall portion 82 separating the two adjacent recesses 81) can be designed to be sufficiently small. Specifically, the minimum distance C1 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, the wall 82 can be prevented from being penetrated and sufficient mechanical strength can be ensured.

[0039] 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 C2 between the periphery of the first metal layer (substrate with recesses) 8 and the periphery of the recesses 81 is preferably about 1 mm or more and 5 mm or less, more preferably about 1.5 mm or more and 4 mm or less, and even more preferably about 2 mm or more and 3 mm or less. Even if the thickness of the peripheral wall portion 83 that defines the recesses 81 is reduced in this way, it is possible to prevent the peripheral wall portion 83 from being penetrated and to ensure sufficient mechanical strength.

[0040] In this way, since the minimum distances C1 and C2 can be designed to be small, a plurality of recesses 81 can be formed in a limited space. That is, a plurality of semiconductor elements 6 can be positioned while preventing the first metal layer 8 and the entire power module 1 from becoming large. The first metal layer 8 does not necessarily have to have a plurality of recesses 81, and may have only one recess 81. The number of recesses 81 can be appropriately set according to the number of semiconductor elements 6 to be positioned.

[0041] Moreover, when forming the recess 81 in the first metal layer 8, it is preferable to form both the frame-shaped groove 81g and the region A81a by wet etching. In this case, a relatively inexpensive device can be used for manufacturing the first metal layer 8. Furthermore, the first metal layer 8 can be easily mass-produced at low cost.

[0042] In this embodiment, the first metal layer 8 has been described as an example, but instead of the first metal layer 8, or in addition to the first metal layer 8, recesses may be formed in, for example, the ceramic plate 7. In this case, as an etching solution, for example, aqua regia, a strong acidic or alkaline solution such as an aqueous solution of hydrogen fluoride (hydrofluoric acid), or the like can be used. When the ceramic plate 7 has a recess, the first metal layer 8 is inserted into the recess of the ceramic plate 7 and bonded via a bonding agent. Therefore, even when multiple semiconductor elements 6 are positioned on the ceramic plate 7 as shown in FIG. 1, this positioning operation can be performed accurately. In addition, the bonding agent can firmly bond the first metal layer 8 to the recess. In addition, the same effects as those of the metal plate 80 having the recess 81 described above can be obtained.

[0043] According to the method for manufacturing a substrate with concave portions as described above, a substrate with concave portions in which the occurrence of hollows and sagging is suppressed can be manufactured. Furthermore, according to the substrate with concave portions in which the occurrence of hollows and sagging is suppressed and the power module having the same, sufficient bonding strength can be obtained between the peripheral portion of the semiconductor element 6 and the concave portions 81. It may be provided in any of the following ways:

[0044] (1) A method for manufacturing a substrate with concave portions, comprising the steps of: forming a first mask on a surface of the substrate so as to expose a frame-shaped region having a predetermined width following a contour of the concave portion in an area on the surface of the substrate where the concave portion is to be formed; performing a first wet etching on the substrate using the first mask to form a frame-shaped groove; removing the first mask from the substrate; forming a second mask on the surface of the substrate except for the area on the surface of the substrate where the concave portion is to be formed; and performing a second wet etching on the substrate using the second mask to form the concave portion and obtain the substrate with concave portions.

[0045] (2) The method for manufacturing a substrate with concave portions according to (1) above, wherein, when viewed in a cross section along the thickness direction of the substrate, the width of the region in which the concave portions are to be formed is X [mm] and the width of the frame-shaped region is Y [mm], then Y / X is 0.001 or more and 0.15 or less.

[0046] (3) The method for manufacturing a substrate with concave portions according to (1) or (2) above, wherein, when viewed in a cross section along the thickness direction of the substrate, the depth of the concave portion to be formed is D [mm] and the width of the frame-shaped region is Y [mm], then Y / D is 0.1 or more and 1.25 or less.

[0047] (4) The method for manufacturing a substrate with concave portions according to any one of (1) to (3) above, wherein the substrate with concave portions has a plurality of the concave portions, and the minimum distance between two adjacent concave portions is 0.9 mm or more and 5 mm or less.

[0048] (5) The method for manufacturing a substrate with concave portions according to any one of (1) to (4) above, wherein the minimum distance between the periphery of the substrate with concave portions and the periphery of the concave portions is 1 mm or more and 5 mm or less.

[0049] (6) 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 continuing with the surface and a bottom surface directly or indirectly continuing with the wall surface, the wall surface being located inside the recess with respect to a virtual line extending from an intersection of the surface and the wall surface along the thickness direction of the substrate when viewed in a cross section along the thickness direction of the substrate.

[0050] (7) The substrate with concave portions according to (6) 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.

[0051] (8) The substrate with concave portions according to (7) 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.

[0052] (9) The substrate with concave portions according to any one of the above (1) to (8), wherein the substrate is a metal plate.

[0053] (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.

[0054] (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.

[0055] 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. EXAMPLES

[0056] 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.

[0057] 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.

[0058] 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.

[0059] 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 D 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.

[0060] 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 The recess was 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. Five were formed.

[0061] 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.

[0062] Comparative Example 1 Except for omitting the formation of the first mask, the first 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. Comparative Example 2 Except for omitting the formation of the second mask, the second etching, and the removal of the second mask, five recesses were formed in the same manner as in Example 1. The first etching time was set to ? minutes.

[0063] 2. Measuring the shape of the recess The shape of the recesses formed in each Example and Comparative Example was measured using a three-dimensional measuring machine (Keyence Corporation, VR-3000). For each Example and Comparative Example, the average value was calculated from the measured values ​​of the five recesses formed. The results are shown in Table 1 below.

[0064] 3. Evaluation A semiconductor element having a thickness of about 1 mm was mounted in the recessed portion 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 target depth when the semiconductor element was inserted into the recess (the distance in the thickness direction of the copper plate from the underside of the semiconductor element to the surface of the copper plate) was set to 0.2 mm or more and 2.4 mm or less, and the possibility of insertion to the target depth was evaluated. The results are shown in Table 1 below.

[0065] [Table 1]

[0066] In Examples 1 to 5, recesses with little sagging could be formed, which prevented the bottom surface of the semiconductor element from interfering with the sagging, and as a result, as shown in Table 1, the semiconductor element could be inserted to the desired depth in all recesses. The wall surface of the recess is located inside the recess with respect to an imaginary line extending from the intersection point between the surface of the copper plate and the wall surface along the thickness direction of the copper plate, and is inclined at a substantially constant angle with respect to the thickness direction of the copper plate, so that the wall surface functions as a guide to accurately guide the semiconductor element to the vicinity of the bottom surface of the recess. In addition, the wall of the recess does not have a hollow, and the width of the gap between the wall and the side of the semiconductor element gradually increases upward. This makes it possible to prevent the solder from creeping up to the top surface of the semiconductor element. Furthermore, if necessary, solder can be added to this gap to fill the gap between the side of the semiconductor element and the wall, thereby achieving a stronger bond.

[0067] On the other hand, in Comparative Example 1, a recess with a large sagging was formed as shown in FIG. 6. Therefore, the bottom surface of the semiconductor element interfered with the sagging. As a result, the semiconductor element could not be inserted to the intended depth in all the recesses. In Comparative Example 1, the semiconductor element could not be positioned by the recesses, so it was difficult to fix the semiconductor element in the correct position. Furthermore, a hollow was formed on the wall of the recess. Also, due to the presence of the hollow, the copper plate protruded inwardly into the recess near the intersection between the wall of the recess and the surface of the copper plate, resulting in a reduction in the thickness of the copper plate in this area. In Comparative Example 2, no recess was formed, and only a frame-shaped groove was formed, so that a semiconductor element could not be inserted.

[0068] Although not shown in the table, if the wet etching time in Comparative Example 1 is extended to prevent the bottom surface of the semiconductor element from interfering with the sagging, the recess becomes too deep. This causes holes to appear in the copper plate, or the recess becomes too large relative to the semiconductor element, making it difficult to accurately position the semiconductor element. In addition, if the semiconductor element is inserted into the recess beyond the desired depth, the solder tends to creep up to the upper surface side of the semiconductor element. Furthermore, since the size of the recessed portion becomes large, the wall portion is penetrated or the mechanical strength of the wall portion becomes insufficient, making it impossible to design an arrangement in which two adjacent recesses are close to each other or in which the periphery of the copper plate and the periphery of the recess are close to each other. In addition, the presence of the recessed portion increases the amount of protrusion of the copper plate toward the inside of the recess near the intersection between the wall surface of the recess and the surface of the copper plate. This makes it difficult to add solder between the wall surface and the side surface of the semiconductor element. In addition, there is a risk that the protruding copper plate will come into contact with the semiconductor element and damage the semiconductor element. [Explanation of symbols]

[0069] 1: Power module 10: Metal wire 11: Housing 12: Filler 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 800: Surface 81: Recess 81g: Groove 810 :Aperture 811: Wall 812: Bottom 813: Depression A81 :Area A81a :Area A81b :Area 82: Wall part 83: Peripheral wall part 9: Second metal layer C1: Minimum distance C2: Minimum distance D: Depth D1: Depth D2: Maximum depth I: Intersection II: Intersection L: distance M1: First mask M1a: opening M2: Second mask T: Thickness VL: Virtual line W1:Width W2: Maximum width X: Width Y :Width θ: Inclination angle 80': Metal layer 81': Recess 811': Wall 88': Hollow section 89': Who I': Intersection M' : Mask VL': Virtual line

Claims

1. A method for manufacturing a substrate with concave portions, comprising the steps of: forming a first mask on the surface of the substrate so as to expose a frame-shaped region having a predetermined width along a contour of the recess in a region on the surface of the substrate where the recess is to be formed; performing a first wet etching process on the substrate using the first mask to form a frame-shaped groove; removing the first mask from the substrate; forming a second mask on the surface of the substrate except in an area of ​​the surface of the substrate where the recess is to be formed; and performing a second wet etching on the substrate using the second mask to form the recesses, thereby obtaining the substrate with recesses.

2. The method for producing a substrate with concave portions according to claim 1 , a width of the region in which the recess is to be formed being X [mm] and a width of the frame-shaped region being Y [mm] when viewed in a cross section along a thickness direction of the substrate, the ratio Y / X being 0.001 or more and 0.15 or less.

3. The method for producing a substrate with concave portions according to claim 1 , A method for manufacturing a substrate with a recess, wherein, when viewed in a cross section along the thickness direction of the substrate, the depth of the recess to be formed is D [mm] and the width of the frame-shaped region is Y [mm], and Y / D is 0.1 or more and 1.25 or less.

4. The method for producing a substrate with concave portions according to claim 1 , the substrate with recesses has a plurality of the recesses, A method for manufacturing a substrate with concave portions, wherein the minimum distance between two adjacent concave portions is 0.9 mm or more and 5 mm or less.

5. The method for producing a substrate with concave portions according to claim 1 , The method for manufacturing a substrate with concave portions, wherein the minimum distance between a periphery of the substrate with concave portions and a periphery of the concave portions is 1 mm or more and 5 mm or less.

6. 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 recess has a wall surface continuous with the front surface and a bottom surface directly or indirectly continuous with the wall surface, A substrate with a recess, wherein when viewed in a cross section along the thickness direction of the substrate, the wall surface is located inside the recess with respect to a virtual line extending along the thickness direction from an intersection of the surface and the wall surface.

7. The substrate with concave portions according to claim 6, 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.

8. The substrate with concave portions according to claim 7, 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.

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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