Package, semiconductor module, and method for producing package

Abstract

A package (51) has a cavity (CV) and includes a heat-dissipating plate (11) and a ceramic frame (21). The heat-dissipating plate (11) is made of a metal-containing first sintered material and has a main surface (P2) including a cavity surface that faces the cavity; a heat-dissipating surface (P1) opposite to the main surface (P2); and a side surface (P4b) that is between the heat-dissipating surface (P1) and the main surface (P2). The ceramic frame (21) has an inner surface (P3) that surrounds the cavity (CV), and an outer surface (P4a) opposite to the inner surface (P3). The main surface (P2) of the heat-dissipating plate (11) includes a bonding surface directly bonded to the ceramic frame (21).

Description

Package, semiconductor module, and method for manufacturing the package

[0001] The present invention relates to a package, a semiconductor module, and a method for manufacturing the package.

[0002] Japanese Patent Laid-Open Publication No. 2015-204426 (Patent Document 1) discloses a package. This package includes a heat sink plate and a ceramic frame. The heat sink plate is a rectangular metal plate that dissipates heat generated by electronic components mounted on its upper surface. The ceramic frame is joined to the heat sink plate so as to surround the area where the electronic components are mounted. This joining is performed by brazing. The brazing temperature is approximately 780°C. The ceramic frame is made of, for example, alumina or aluminum nitride.

[0003] The ceramic frame has a frame shape and is formed by joining an upper layer sheet and a lower layer sheet. A metallized film and a plated coating are provided on the lower surface of the lower layer sheet. The plated coating on the lower surface of the lower layer sheet is joined to the heat sink plate via a brazing material. The inner peripheral edge of the lower layer sheet is positioned more toward the outer periphery than the inner peripheral edge of the upper layer sheet. This allows the electronic component to be mounted close to the inner periphery of the upper layer sheet of the ceramic frame, avoiding the fillet of the brazing material.

[0004] The heat sink plate is a metal plate. A metal plate having high thermal conductivity and capable of mitigating package warpage due to differences in linear expansion coefficients during brazing with the ceramic frame is selected. For example, a composite metal plate or a clad metal plate is used. The composite metal plate is formed, for example, by an impregnation method. Specifically, it is formed by impregnating a porous high-melting-point metal plate with Cu. Since the linear expansion coefficient of high-melting-point metals such as tungsten (W) or molybdenum (Mo) is close to that of ceramic, the linear expansion coefficient of the heat sink plate can be made close to that of the ceramic frame. Furthermore, Cu has excellent thermal conductivity, which can improve the heat dissipation performance of the heat sink plate.

[0005] When the linear expansion coefficient of the heat sink plate needs to be close to that of the ceramic frame, composite metal plates or clad metal plates are widely used, as described above. When matching the linear expansion coefficients is not important, simple metal materials are also widely used, such as pure copper, which can significantly increase thermal conductivity. Furthermore, as heat sink plates (i.e., heat sinks or heat dissipation substrates) for semiconductor light-emitting elements, those containing metal oxides have also been proposed, as described below.

[0006] According to Japanese Patent Laid-Open No. 2009-88205 (Patent Document 2), a heat dissipation substrate has an element body whose main component is a metal oxide, and a plurality of metal chunks that are arranged throughout the entire interior of the element body and have flaky portions. The plurality of metal chunks are characterized in that their thickness direction is aligned in a predetermined direction. This characteristic results in anisotropy in the thermal conductivity. The metal oxides are, for example, ZnO, Al ２ O ３ , SiO ２ or ZrO ２ ZnO is white, so it can better reflect light from semiconductor light-emitting elements. Furthermore, when the metal mass is made of silver or a silver alloy, using ZnO as the metal oxide makes the heat dissipation substrate more flexible, thereby making it less likely to crack. This method for manufacturing a heat dissipation substrate includes the steps of preparing a slurry in which flaky metal powder and metal oxide are dispersed, applying the slurry to a film by a doctor blade method to form a green sheet, and firing the green sheet.

[0007] JP 2015-204426 A JP 2009-88205 A

[0008] There are usually limitations on the size of a package. Under such limitations, in order to shift the inner peripheral edge of the lower layer sheet toward the outer periphery relative to the inner peripheral edge of the upper layer sheet, as in the technology of JP 2015-204426 A, it is necessary to reduce the width dimension (dimension between the inner periphery and the outer periphery) of the frame shape of the lower layer sheet. As a result, the sealing reliability or ease of manufacture of the package is likely to be reduced. For these reasons, a technology is needed for mounting electronic components (typically semiconductor elements) close to a frame body while avoiding the width dimension (dimension between the inner periphery and the outer periphery) of the frame body being too small.

[0009] The present invention has been made to solve the above-mentioned problems, and its object is to provide a package, a semiconductor module, and a method for manufacturing a package that allows a semiconductor element to be mounted close to a frame body while avoiding the width dimension of the frame body being too small.

[0010] Aspect 1 is a package (51-55, 51a, 51b, 51q, 51r) having a cavity (CV), comprising a heat sink (11, 15) and a ceramic frame (21-25). The heat sink (11, 15) is made of a first sintered material containing a metal and has a main surface (P2) including a cavity surface (P2a) facing the cavity (CV), a heat sink surface (P1) opposite the main surface (P2), and a side surface (P4b) between the heat sink surface (P1) and the main surface (P2). The ceramic frame (21-25) has an inner surface (P3) surrounding the cavity (CV) and an outer surface (P4a) opposite the inner surface (P3). The main surface (P2) of the heat sink (11, 15) includes a joining surface that is directly joined to the ceramic frame (21 to 25).

[0011] Aspect 2 is the package (51 to 53, 51a, 51b, 51q, 51r) according to aspect 1, in which the side surface (P4b) of the heat sink (11) is not directly joined to the ceramic frame (21 to 23).

[0012] Aspect 3 is the package (51 to 55, 51a, 51b, 51q, 51r) according to aspect 1 or 2, wherein the first sintered material is a sintered metal material.

[0013] Aspect 4 is a package (51-55, 51a, 51b, 51q, 51r) according to aspect 1 or 2, wherein the first sintered material contains copper and at least one high-melting-point metal selected from the group consisting of tungsten and molybdenum.

[0014] Aspect 5 is a package (51-55, 51a, 51b, 51q, 51r) according to Aspect 4, wherein in a cross-sectional view of at least a portion of the bonding surface, the bonding surface extends macroscopically along a straight line, and microscopically forms an undulating boundary line between the heat sink (11, 15) and the ceramic frame (21-25), the boundary line having a copper section made of copper and a high-melting point metal section made of the at least one high-melting point metal, and the proportion of the high-melting point metal section in the projection of the boundary line onto the straight line is greater than the volume ratio of the at least one high-melting point metal in the heat sink (11, 15).

[0015] Aspect 6 is a package (51-55) according to aspect 4 or 5, further comprising a metallized layer (31) provided on the upper surface (P5) of the ceramic frame (21-25) and made of a second sintered material containing copper at a higher volume ratio than the first sintered material of the heat sink (11, 15).

[0016] Aspect 7 is a package (51 to 55, 51a, 51b, 51q, 51r) according to any one of Aspects 1 to 6, wherein the ceramic frame (21 to 25) contains Mn, and in an element distribution diagram of Mn, the ceramic frame (21 to 25) includes a layer portion having a depth of 3 μm, including a depth position within 3 μm from the joining surface into the ceramic frame (21 to 25), and a bulk portion having a depth of 3 μm, including a depth position from the joining surface into the ceramic frame (21 to 25) of 6 μm to 9 μm, and the concentration of the Mn element is higher in the layer portion than in the bulk portion.

[0017] Aspect 8 is the package (51-55, 51a, 51b, 51q, 51r) according to any one of Aspects 1 to 6, wherein the ceramic frame (21-25) contains Mn, and the ceramic frame (21-25) includes a layer portion located within a depth of 3 μm from the joining surface and a bulk portion separated from the joining surface by the layer portion, and a Mn concentration profile with respect to the depth from the joining surface into the ceramic frame (21-25) includes a maximum peak located within the layer portion.

[0018] A ninth aspect is the package according to the eighth aspect, wherein in the Mn concentration profile with respect to the depth, the maximum peak is 150% or more of a representative value of the bulk portion.

[0019] A tenth aspect is the package (51 to 55, 51a, 51b, 51q, 51r) according to any one of the first to ninth aspects, wherein the joint surface (P2b) of the heat sink (11) does not contain silver.

[0020] Aspect 11 is a package (51, 51q, 51r, 53) according to any one of aspects 1 to 10, wherein the side surface (P4b) of the heat sink (11) is connected to the outer surface (P4a) of the ceramic frame (21, 23).

[0021] Aspect 12 is the package (51, 51q, 51r, 53) according to aspect 11, wherein the side surface (P4b) of the heat sink (11) is flush with and connected to the outer surface (P4a) of the ceramic frame (21, 23).

[0022] Aspect 13 is a package (51q, 51r) according to any one of aspects 1 to 12, wherein the main surface (P2) of the heat sink and the outer surface of the ceramic frame (21-25) form an acute angle.

[0023] Aspect 14 is a package (51r) according to any one of aspects 1 to 13, wherein the ceramic frame (21) has an upper surface (P5) that is separated from the main surface (P2) of the heat sink (11) by the ceramic frame (21) and is connected to the outer surface (P4a), and a corner (AP) formed by the upper surface (P5) of the ceramic frame (21) and the outer surface (P4a) of the ceramic frame (21) has a radius of curvature of 0.1 mm or more and 0.5 mm or less.

[0024] Aspect 15 is a package (51-55, 51a, 51b, 51q, 51r) according to any one of aspects 1 to 14, further comprising a metal terminal (30) provided on an upper surface (P5) of the ceramic frame (21-25).

[0025] Aspect 16 is a semiconductor module (90) including the package (51-55, 51a, 51b, 51q, 51r) according to any one of aspects 1 to 15, and a semiconductor element (8) mounted on the cavity surface (P2a) of the main surface (P2) of the heat sink (11). The distance between the semiconductor element (8) and the inner surface (P3) of the ceramic frame (21) is 25 μm or less.

[0026] Aspect 17 is a manufacturing method for a package (51-55, 51a, 51b, 51q, 51r) having a cavity (CV), and includes a step of forming a green structure (SG) that combines a first green member (11G) that will become the heat sink (11, 15) when fired and a second green member (21G) that will become the ceramic frame (21-25) when fired, and a step of firing the green structure (SG).

[0027] Aspect 18 is a method for manufacturing a package (51-55, 51a, 51b, 51q, 51r) described in Aspect 17, wherein the step of forming the green structure (SG) includes a step of forming the second green member (21G), and the step of forming the second green member (21G) includes a step of removing a portion corresponding to the cavity (CV) from a green sheet that will become at least a part of the second green member (21G).

[0028] Aspect 19 is a manufacturing method for the package (51-55, 51a, 51b, 51q, 51r) according to Aspect 17 or 18, in which the first green member (11G) is formed using a first metal powder containing copper and at least one high-melting-point metal selected from the group consisting of tungsten and molybdenum. The green structure (SG) includes an additional layer (31G) that will become a metallized layer (31) on the upper surface (P5) of the ceramic frame (21-25) by firing, and the additional layer (31G) is formed using a second metal powder containing copper and at least one high-melting-point metal selected from the group consisting of tungsten and molybdenum. The second metal powder contains copper at a higher volumetric ratio than the first metal powder.

[0029] The symbols in parentheses in the above-mentioned embodiments are merely supplementary to help understand the contents of the above-mentioned embodiments, and do not limit the above-mentioned embodiments.

[0030] According to the above aspect, the ceramic frame and the heat sink are directly bonded to each other. This eliminates the need for brazing material to bond the ceramic frame and the heat sink. This prevents brazing material from flowing into the cavity and interfering with the mounting of the semiconductor element. This allows the semiconductor element to be mounted in close proximity to the ceramic frame.

[0031] The objects, features, aspects, and advantages of the present invention will become more apparent from the following detailed description and the accompanying drawings.

[0032] 1 is a schematic perspective view showing the configuration of a semiconductor module according to a first embodiment, with some parts omitted so that the interior of the cavity can be seen. It is a schematic cross-sectional view taken along line II-II of the semiconductor module of FIG. 1. It is a schematic cross-sectional view showing the configuration of a package as a component of the semiconductor module of FIG. 2. It is a flow diagram showing an outline of a method for manufacturing the package of FIG. 3. It is a schematic partial cross-sectional view illustrating one step of the ... the configuration of a package of a comparative example. It is a schematic cross-sectional view showing the configuration of a semiconductor module using the package of FIG. 9. It is a schematic partial cross-sectional view showing a first example in which the side surface of the heat sink and the outer surface of the ceramic frame are connected flatly. It is a schematic partial cross-sectional view showing a second example in which the side surface of the heat sink and the outer surface of the ceramic frame are connected flatly. It is a schematic partial cross-sectional view showing a third example in which the side surface of the heat sink and the outer surface of the ceramic frame are connected flatly. It is a schematic partial cross-sectional view showing a package of a first modified example of FIG. 17 is a schematic partial cross-sectional view showing a package of a second modified example of FIG. 11 . FIG. 18 is a schematic partial cross-sectional view showing a bonding strength test between a heat sink and a ceramic frame. FIG. 19 is a schematic cross-sectional view showing the configuration of a heat sink and a ceramic frame included in a package according to embodiment 1. FIG. 20 is a schematic cross-sectional view showing the configuration of a package according to embodiment 2, from the same field of view as FIG. 17 . FIG. 21 is a schematic cross-sectional view showing the configuration of a package according to embodiment 3, from the same field of view as FIG. 17 . FIG. 22 is a schematic cross-sectional view showing the configuration of a package according to embodiment 4, from the same field of view as FIG. 17 . FIG. 23 is a schematic cross-sectional view showing the configuration of a package according to embodiment 5, from the same field of view as FIG. 17 . FIG. 24 is a schematic cross-sectional view showing the configuration of a package according to embodiment 6, from the same field of view as FIG. 17 . FIG. 25 is an electron microscope photograph showing a cross-section of a portion of the bonding surface between the heat sink and the ceramic frame in embodiment 1. In a cross-sectional view of at least a portion of the bonding surface, the bonding surface extends along a straight line macroscopically, and forms an undulating boundary line between the heat sink and the ceramic frame microscopically, and the figure shows the projection of the boundary line onto the straight line.A figure showing the Cu element distribution (upper part) near the joint surface of the heat dissipation plate and the ceramic frame together with an electron micrograph (upper part) corresponding to the field of view of the distribution diagram. A figure showing the W element distribution (upper part) near the joint surface of the heat dissipation plate and the ceramic frame together with an electron micrograph (upper part) corresponding to the field of view of the distribution diagram. A figure showing the Mn element distribution (upper part) near the joint surface of the heat dissipation plate and the ceramic frame together with an electron micrograph (upper part) corresponding to the field of view of the distribution diagram. A figure showing the layer part and the bulk part regarding the Mn element distribution shown in the lower part of FIG. 27. A graph (upper part) showing the depth profile of the SEM-EDX count number in the Mn element analysis, a figure (lower part) in which a rectangular region corresponding to the profile is added to the electron micrograph shown in FIG. 27, and a figure (middle part) in which the region is arranged so as to coincide with the horizontal axis of the graph are shown together. A graph (upper part) showing the depth profile of the SEM-EDX count number in the Mn element analysis, a figure (lower part) in which a rectangular region corresponding to the profile is added to the electron micrograph shown in FIG. 27, and a figure (middle part) in which the region is arranged so as to coincide with the horizontal axis of the graph are shown together. A graph (upper part) showing the depth profile of the SEM-EDX count number in the Mn element analysis, a figure (lower part) in which a rectangular region corresponding to the profile is added to the electron micrograph shown in FIG. 27, and a figure (middle part) in which the region is arranged so as to coincide with the horizontal axis of the graph are shown together. A graph (upper part) showing the depth profile of the SEM-EDX count number in the Mn element analysis, a figure (lower part) in which a rectangular region corresponding to the profile is added to the electron micrograph shown in FIG. 27, and a figure (middle part) in which the region is arranged so as to coincide with the horizontal axis of the graph are shown together. A graph (upper part) showing the depth profile of the SEM-EDX count number in the Mn element analysis, a figure (lower part) in which a rectangular region corresponding to the profile is added to the electron micrograph shown in FIG. 27, and a figure (middle part) in which the region is arranged so as to coincide with the horizontal axis of the graph are shown together.

[0033] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In this specification, unless otherwise specified, the term "metal" can refer to either a pure metal or an alloy. The term "green" refers to a state before firing. Therefore, a component labeled "green" is intended to be fired, but has not yet been fired.

[0034] First Embodiment FIG. 1 is a schematic perspective view showing the configuration of a semiconductor module 90 according to the first embodiment. FIG. 2 is a schematic cross-sectional view of the semiconductor module 90 taken along line II-II in FIG. 1. The semiconductor module 90 has a package 51 and a semiconductor element 8. The semiconductor module 90 may also have wires 9 as wiring members for the semiconductor element 8. The semiconductor module 90 may also have a lid 80 for sealing a cavity CV. The lid 80 may be attached to the package 51 by an adhesive layer 70. Note that in FIG. 1, the lid 80 and the adhesive layer 70 are partially omitted so that the interior of the cavity CV of the package 51 can be partially seen.

[0035] The semiconductor element 8 may be a power semiconductor element, in which case the semiconductor module 90 is a power module. The power semiconductor element may be for radio frequency (RF) use, in which case the semiconductor module 90 is an RF power module. Although one semiconductor element 8 is shown in FIGS. 1 and 2 , multiple semiconductor elements 8 may be mounted in the package 51. Elements other than the semiconductor element 8, such as passive elements, may also be mounted.

[0036] 3 is a schematic cross-sectional view showing the configuration of a package 51 as a component of the semiconductor module 90 (FIG. 2). When the package 51 is prepared for manufacturing the semiconductor module 90, the semiconductor element 8 does not have to be mounted thereon, as shown in FIG. 3. The package 51 has a cavity CV that will be sealed by a lid 80. The package 51 has a heat sink 11 and a ceramic frame 21.

[0037] The heat sink 11 is made of a first sintered material containing a metal. For example, the first sintered material contains copper (Cu) and a refractory metal. The refractory metal has a higher melting point than Cu. The refractory metal may be at least one of tungsten (W) and molybdenum (Mo). Therefore, the first sintered material may contain Cu and at least one refractory metal selected from the group consisting of W and Mo. The following description will mainly focus on the case where the refractory metal is W, but Mo may be used instead of or in addition to W. The first sintered material does not need to contain a non-metal. In other words, the first sintered material may be a sintered metal material. In other words, the first sintered material may be a sintered material consisting essentially of a metal. The sintered metal material may contain Cu and W, for example, an alloy of Cu and W, i.e., a copper-tungsten alloy. Alternatively, the first sintered material may also contain a non-metal. The nonmetal is, for example, Al. ２ O ３ , SiO ２ or ZrO ２ The ceramic may be, for example, a ceramic.

[0038] To improve the heat dissipation performance of the heat sink 11, the material of the heat sink 11 preferably has a high thermal conductivity. Such high thermal conductivity can be easily achieved by including a sufficient amount of Cu in the heat sink 11. On the other hand, including a sufficient amount of W in the heat sink 11 can bring the linear expansion coefficient of the heat sink 11 closer to that of ceramics such as alumina. This similarity in the linear expansion coefficient is useful for suppressing thermal stress between the heat sink 11 and the ceramic frame 21. If the total volume of the metal components of the heat sink 11 is defined as 100 vol%, the heat sink 11 may contain, for example, 10 vol% to 90 vol% Cu, with the remainder being essentially a high-melting-point metal. More preferably, the heat sink 11 may contain 25 vol% to 50 vol% Cu, with the remainder being essentially a high-melting-point metal.

[0039] The heat sink 11 has a heat dissipation surface P1 and a main surface P2 opposite to the heat dissipation surface P1. The heat dissipation surface P1 of the heat sink 11 is typically attached to a support member (not shown). The support member is, for example, a mounting board or a heat dissipation member. The heat sink 11 may have a through-hole (not shown) through which a fastener (e.g., a screw) for attaching the heat sink 11 to the support member passes.

[0040] The ceramic frame 21 is a frame made of ceramic. By using the ceramic frame 21 as the frame of the package 51, the heat resistance and insulating properties of the package 51 can be improved. The material of the ceramic frame 21 is alumina (Al ２ O ３ ), and may contain a small amount of silica (SiO ２ The raw material powder as the material for the ceramic frame 21 may contain, for example, 50 wt % or more of Al as the main component. ２ O ３ powder and SiO ２ The mixed powder may be a powder containing 5 to 17% by weight of Si element in terms of Si content and 3 to 14% by weight of Mn element in terms of MnO content. When the mixed powder is used, the firing temperature is, for example, 1150 to 1300°C.

[0041] The ceramic frame 21 is disposed on the main surface P2 of the heat sink 11. The ceramic frame 21 has an inner surface P3 surrounding the cavity CV and an outer surface P4a opposite the inner surface P3. The heat sink 11 has a side surface P4b between the heat sink surface P1 and the main surface P2. The side surface P4b may be flush with the outer surface P4a of the ceramic frame 21, as will be described in detail with reference to Figures 11 to 13. The outer edge of the ceramic frame 21 may have a rectangular shape in an in-plane direction perpendicular to the thickness direction, as shown in Figure 1. The size of each side of the rectangular shape is, for example, 4 mm or more and 40 mm or less. The thickness of the ceramic frame 21 is, for example, 0.1 mm or more and 1 mm or less.

[0042] The main surface P2 of the heat sink 11 includes a cavity surface P2a facing the cavity CV and a bonding surface P2b directly bonded to the ceramic frame 21. Therefore, the ceramic frame 21 and the heat sink 11 are directly bonded to each other. Therefore, no silver (Ag) brazing material is used for bonding them. Therefore, the bonding surface P2b of the heat sink 11 does not need to contain Ag.

[0043] The inventors confirmed that the ceramic frame 21 and the heat sink 11 are bonded to each other with sufficient strength. Furthermore, they confirmed that the ceramic frame 21 and the heat sink 11 are directly bonded to each other through optical microscope observation or scanning electron microscope observation. In this specification, the expression "directly bonded" means that no components other than those derived from the heat sink 11 and the ceramic frame 21 are detected at the bonded portion. For example, if the heat sink 11 contains Cu and the ceramic frame 21 contains silica and / or Mn, the inventors speculate that the extremely thin reaction layer described above may be formed by a reaction between molten Cu and silica and / or Mn during the firing process described below. The composition of the bonded portion can be verified, for example, by energy dispersive X-ray spectroscopy (EDX). EDX can be performed using a scanning electron microscope equipped with an EDX spectrometer.

[0044] The package 51 may have a lead frame 30 (metal terminals). The lead frame 30 is provided on the upper surface P5 of the ceramic frame 21 and is separated from the heat sink 11 by the ceramic frame 21. The upper surface P5 may be flat. The lead frame 30 forms an electrical path connecting the inside and outside of the cavity CV. A bonding material (not shown) may be provided between the lead frame 30 and the ceramic frame 21 to bond them together. This bonding material may be formed, for example, by Ag sinter bonding. In this case, the bonding material is a mixture of a thermosetting resin (e.g., epoxy resin or silicone resin) and Ag particles. Alternatively, silver solder may be used as the bonding material. In this case, a metallized layer 31 for silver solder is typically formed in advance on the upper surface P5 of the ceramic frame 21. In one example of a method for forming the metallized layer 31, a paste for the metallized layer 31 is printed on a green sheet that will become the ceramic frame 21 before the firing process (described in detail below) for forming the ceramic frame 21 and the heat sink 11. Specifically, a metal powder of at least one of W, Mo, and Cu is first blended with additives, resin, a solvent, and the like, and ceramic powder is further added as needed, followed by kneading to prepare a paste. This paste is then printed, for example, by screen printing, on a green sheet prepared in a previous process. After printing, the green sheet is dried, for example, at a temperature of 110°C for 5 minutes. Alternatively, the metallized layer 31 may be formed by laminating a green sheet containing a metal on the green sheet that will become the ceramic frame 21 before the firing process (described in detail below) for forming the ceramic frame 21 and the heat sink 11.

[0045] The metallization layer 31 may be made of a second sintered material containing Cu at a higher volume ratio than the first sintered material of the heat sink 11. In this case, the linear expansion coefficient of the metallization layer 31 is higher than that of the heat sink 11. Considering that the thickness of the metallization layer 31 is usually smaller than that of the heat sink 11, in a configuration in which the ceramic frame 21 is disposed between the metallization layer 31 and the heat sink 11, the above-mentioned linear expansion coefficient relationship facilitates balancing thermal stress in the package 51. This can suppress warping of the package 51 under temperature changes. The thickness of the metallization layer 31 is preferably 5 μm or more and 200 μm or less. A thickness of 5 μm or more facilitates balancing thermal stress, thereby more effectively suppressing warping of the package 51. Furthermore, the metallization layer 31 can fully function as a conductive layer. A thickness of 200 μm or less can reduce peeling of the metallization layer 31.

[0046] The lid 80 (FIGS. 1 and 2) may be made of a ceramic material, which may contain alumina as a main component, e.g., be substantially alumina. Alternatively, the lid 80 may contain a resin, e.g., a liquid crystal polymer. The resin may have an inorganic filler dispersed therein, e.g., silica particles. Dispersing the inorganic filler in the resin can increase the strength and durability of the lid 80.

[0047] The semiconductor element 8 (FIG. 2) is mounted on the cavity surface P2a (FIG. 3) of the main surface P2 of the heat sink 11 of the package 51. The distance L1 (FIG. 2) between the mounted semiconductor element 8 and the inner surface P3 of the ceramic frame 21 may be 25 μm or less. The distance L1 may also be zero. In other words, the semiconductor element 8 and the inner surface P3 of the ceramic frame 21 may be in contact with each other.

[0048] The semiconductor element 8 may be mounted using, for example, a solder material (not shown). After mounting the semiconductor element 8, wires 9 ( FIG. 2 ) may be formed to electrically connect the semiconductor element 8 to the lead frame 30. This formation may be performed by wire bonding. Subsequently, the lid 80 may be attached to the package 51. This attachment may be performed using an adhesive layer 70. The adhesive layer 70 may be a thermosetting resin. The adhesive layer 70 is provided on the ceramic frame 21 so as to surround the cavity CV. As shown in FIG. 2 , the adhesive layer 70 may have a portion that is provided on the ceramic frame 21 via the lead frame 30. The thickness of the adhesive layer 70 between the lid 80 and the package 51 is, for example, 100 μm or more and 360 μm or less.

[0049] Fig. 4 is a flow diagram that shows a schematic method for manufacturing the package 51 (Fig. 3). Figs. 5 to 8 are schematic partial cross-sectional views that illustrate steps of the manufacturing method.

[0050] In each of steps ST11 and ST12 (FIG. 4), at least one first green sheet (first green structure) 11G (FIG. 5) and at least one second green sheet (second green structure) 21G (FIG. 5) are formed. The first green sheet 11G (FIG. 5) is a green sheet that will be fired to form the heat sink 11 (FIG. 3). The second green sheet 21G (FIG. 5) is a green sheet that will be fired to form the ceramic frame 21 (FIG. 3).

[0051] To form the green sheet, a slurry is first prepared. The slurry is obtained by mixing powders that will become the components of the sintered body with resin, plasticizer, solvent, etc., using a ball mill. The powder for the slurry to form the ceramic frame 21 is, for example, Al as the main component. ２ O ３ SiO powder and sintering aid ２The powder for the slurry used to form the first green sheet 11G that becomes the heat sink 11 may be Cu powder, W powder, or the like. Specifically, the process of forming the first green sheet 11G may be performed using a first metal powder containing Cu and at least one high-melting-point metal selected from the group consisting of W and Mo. The first metal powder may be a mixed powder of a powder containing Cu and a powder containing a high-melting-point metal. The powder containing Cu may be Cu powder. The slurry is processed into a green sheet by a doctor blade method. The planar shape of the green sheet is determined according to the shape of the target component. The planar shape of the first green sheet 11G used to form the heat sink 11 is usually approximately rectangular. The planar shape of the second green sheet 21G used to form the ceramic frame 21 is a frame-like shape with the portion corresponding to the cavity CV (FIG. 3) removed. Specifically, the second green sheet 21G is formed as a simple sheet by a doctor blade method, and then the portion corresponding to the cavity CV is removed.

[0052] In step ST14, an additional layer 31G, which will be fired to form the metallized layer 31 on the upper surface P5 of the ceramic frame 21, is formed on the second green sheet 21G. This formation may be performed using a second metal powder containing Cu and at least one high-melting-point metal selected from the group consisting of W and Mo. The second metal powder may contain Cu at a higher volume ratio than the first metal powder described above.

[0053] Next, in step ST20 ( FIG. 4 ), a second green sheet 21G is laminated on the first green sheet 11G, as indicated by the arrow in FIG. 5 . This results in a laminate (green structure) SG ( FIG. 6 ) in which the first green sheet 11G and the second green sheet 21G are combined. At this time, pressure may be applied to the green structure in the thickness direction. Next, trenches (not shown) may be formed in the surfaces of the first green sheet 11G and the second green sheet 21G at positions where breaking will be performed, as described below, by mechanical processing using a cutting edge CT or laser processing using a laser processing device (not shown).

[0054] In step ST30 (FIG. 4), the stack SG (FIG. 6) is fired. This transforms the stack SG into a fired body SF (FIG. 7). The firing temperature is, for example, 1100°C or higher and 1400°C or higher. By setting the firing temperature to 1100°C or higher, the stack SG can be heated to a temperature higher than the melting point of Cu. This allows the formation of a high-quality heat sink 11 containing Cu. On the other hand, by setting the firing temperature to 1400°C or lower, process difficulties caused by an excessively high firing temperature can be avoided.

[0055] Next, a breaking step is performed starting from the trenches, as shown by the broken lines BR (FIG. 7). As a result, the sintered body SF is divided into a plurality of parts (FIG. 8). This results in a plurality of sintered bodies SF corresponding to a plurality of packages 51 (FIG. 3).

[0056] Next, a lead frame 30 (FIG. 3) is attached to the sintered body SF, thereby obtaining a package 51 (FIG. 3).

[0057] In the above manufacturing method, plating may be performed at an appropriate timing after the firing step. As mentioned above, the above manufacturing method is merely an example, and various modifications may be applied. For example, instead of performing the breaking step on the fired body SF, cutting may be performed on the pre-fired stack SG. Furthermore, although the mounting of the semiconductor element 8 ( FIG. 2 ) is performed after the breaking step according to the above manufacturing method, it may instead be performed after the firing step and before the breaking step.

[0058] FIG. 9 is a schematic cross-sectional view showing the configuration of a package 59 of a comparative example. FIG. 10 is a schematic cross-sectional view showing the configuration of a semiconductor module 99 of a comparative example using the package 59. The package 59 has a heat sink 19 and a frame 29 instead of the heat sink 11 and ceramic frame 21 (FIG. 3: Embodiment 1). The material of the heat sink 19 is typically a copper-tungsten alloy formed by an impregnation method, or a clad material having a laminated structure of copper and copper-molybdenum alloy. The frame 29 is made of a ceramic material, typically alumina.

[0059] The frame 29 is joined to the heat sink 19 with a brazing filler material 36. The brazing filler material 36 is fluid when formed and flows inward beyond the inner peripheral surface of the frame 29 (the surface facing the cavity CV), as shown in FIG. 9 . The portion of the brazing filler material 36 that flows into the cavity CV forms a fillet 36f at the edge of the cavity CV, as shown in FIG. 10 . The flow distance, or in other words, the width of the fillet 36f, tends to be greater than 25 μm. Therefore, to sufficiently reduce the possibility of interference between the fillet 36f and the semiconductor element 8, the distance L9 ( FIG. 10 ) between the semiconductor element 8 and the inner surface of the frame 29 must be greater than 25 μm. This large gap between the semiconductor element 8 and the frame 29 results in a smaller mounting area in the cavity CV (the area in which the semiconductor element 8 can be mounted). Furthermore, the length of the wire 9 increases, which typically leads to deterioration of electrical characteristics, such as an unintended increase in inductance.

[0060] Typically, an Ag brazing filler metal is used as the brazing filler metal 36. When the brazing filler metal 36 contains Ag, Ag migration is likely to occur as indicated by arrow MG ( FIG. 10 ) if a negative potential is applied to the lead frame 30 for a long period of time relative to the potential of the heat sink 19. This Ag migration may result in insufficient electrical insulation between the heat sink 19 and the lead frame 30.

[0061] Furthermore, when the brazing filler metal 36 is formed, it is necessary to ensure the wettability of the molten brazing filler metal 36. For this purpose, it is necessary to form a plating layer that has high wettability with the molten brazing filler metal 36 on the surface of the frame 29 made of a ceramic material that faces the brazing filler metal 36. Furthermore, in preparation for forming this plating layer, it is usually necessary to form a metallized layer (not shown) for the brazing filler metal 36 on the frame 29.

[0062] According to the first embodiment, the ceramic frame 21 and the heat sink 11 are directly bonded together. This eliminates the need for brazing filler metal 36 ( FIG. 10 : comparative example) to bond the ceramic frame 21 and the heat sink 11. This prevents the brazing filler metal 36 from flowing into the cavity CV and interfering with the mounting of the semiconductor element 8. This reduces the distance L1 ( FIG. 2 ) between the semiconductor element 8 and the inner surface P3 of the ceramic frame 21, for example, to 25 μm or less. In other words, the semiconductor element 8 can be mounted in close proximity to the ceramic frame 21. This increases the mounting area within the cavity CV. Furthermore, the length of the wire 9 is reduced, which typically leads to improved electrical characteristics. Furthermore, because the brazing filler metal 36 ( FIG. 10 : comparative example) is not required, migration of Ag contained in the brazing filler metal between the heat sink 11 and the lead frame 30 is prevented. Furthermore, a layer for ensuring the wettability of the brazing material 36 (typically, the above-mentioned plating layer and metallized layer (not shown) for the brazing material 36) is not required.

[0063] The heat sink 11 (FIG. 2) may have a side surface P4b that is flush with the outer surface P4a of the ceramic frame 21. Three examples in which the side surface P4b of the heat sink 11 is flush with the outer surface P4a of the ceramic frame 21 will now be described with reference to FIGS.

[0064] In the package 51 illustrated in Fig. 11, the end of the outer surface P4a (lower end in the figure) and the end of the side surface P4b (upper end in the figure) are at the same position, which is also the same position as the end of the main surface P2 (right end in the figure). In the package 51a illustrated in Fig. 12, the end of the outer surface P4a (lower end in the figure) and the end of the side surface P4b (upper end in the figure) are at substantially the same position, but strictly speaking, the side surface P4b protrudes from the outer surface P4a by a dimension E1, which is 0.1 mm or less. In the package 51b illustrated in Fig. 13, the end of the outer surface P4a (lower end in the figure) and the end of the side surface P4b (upper end in the figure) are at substantially the same position, but strictly speaking, the outer surface P4a protrudes from the side surface P4b by a dimension E2, which is 0.1 mm or less.

[0065] These packages 51, 51a, and 51b (FIGS. 11 to 13) can suppress stress concentration near the edge of the main surface P2 due to misalignment between the heat sink 11 and the ceramic frame 21. This prevents peeling between the heat sink 11 and the ceramic frame 21 from occurring near the edge of the main surface P2.

[0066] The orientation of the outer surface P4a at its end (the lower end in each of FIGS. 11 to 13) (in other words, the orientation of the normal vector) and the orientation of the side surface P4b at its end (the upper end in each of FIGS. 11 to 13) (in other words, the orientation of the normal vector) may be the same. In the examples shown in FIGS. 11 to 13, the normal vector is perpendicular to the thickness direction, but is not limited to this and may be any vector that intersects with the thickness direction.

[0067] A portion of the side surface P4b may be a fracture surface from the breaking process ( FIG. 8 ). In this case, it is easy to ensure the mounting area (the area of ​​the region where a semiconductor element 8 or the like can be mounted) while preventing the area between the outer surface P4a and the side surface P4b from becoming the starting point of fracture of the package 51. Typical examples of the side surface P4b not being flush with the outer surface P4a include a case where the outer surface P4a substantially protrudes outward from the side surface P4b (specifically, a case where the dimension E2 is greater than 0.1 mm in FIG. 13 ) or a case where the outer surface P4a is located substantially inside the side surface P4b (specifically, a case where the dimension E1 is greater than 0.1 mm in FIG. 12 ). In the former case, the protruding portion may become the starting point of fracture. In the latter case, since the outer edge of the ceramic frame 21 is moved inward, the inner edge of the ceramic frame 21 also moves inward as long as the width of the ceramic frame 21 needs to be maintained at a predetermined dimension, resulting in a smaller mounting area.

[0068] FIG. 14 is a schematic partial cross-sectional view showing a package 51q according to a first modification of the package 51 (FIG. 11). In the package 51q, the angle DG1 between the main surface P2 of the heat sink 11 and the outer surface P4a of the ceramic frame 21 is an acute angle, preferably 80° to 89°, and more preferably 80° to 85°. The ceramic frame 21 may have a top surface P5 that is separated from the main surface P2 of the heat sink 11 by the ceramic frame 21 and connects to the outer surface P4a. The top surface P5 is a surface approximately parallel to the main surface P2. The angle DG2 between the top surface P5 and the outer surface P4a may be an obtuse angle, corresponding to the acute angle of the angle DG1, and is preferably 91° to 100°, and more preferably 95° to 100°. The orientation of the outer surface P4a at its end (the lower end in FIG. 14 ) (in other words, the orientation of the normal vector) and the orientation of the side surface P4b at its end (the upper end in FIG. 14 ) (in other words, the orientation of the normal vector) may be approximately the same. In this case, since the angle DG1 is an acute angle, the angle DG0 between the main surface P2 of the heat sink 11 and the side surface P4b of the heat sink 11 is an obtuse angle, preferably 91° or more and 100° or less, and more preferably 95° or more and 100° or less.

[0069] In addition, when the corner AP (see FIG. 15) formed by the outer surface P4a and the upper surface P5 is rounded, the angle DG2 may be the angle formed by the tangent plane of the outer surface P4a at the lower end of the outer surface P4a of the ceramic frame 21 in FIG. 14 (in other words, the end that substantially coincides with the end of the main surface P2) and the upper surface P5.

[0070] Because the angle DG1 is an acute angle, the edge of the upper surface P5 is pulled inward (to the left in FIG. 14 ). This makes it difficult for an external impact to be applied to the edge of the upper surface P5 of the ceramic frame 21. This prevents the ceramic frame 21 from being chipped by an impact. On the other hand, because the angle DG1 is not excessively small, the heat sink 11 and the ceramic frame 21 are prevented from peeling off from each other when they are formed by co-firing.

[0071] FIG. 15 is a schematic partial cross-sectional view showing a package 51r, a second modification of the package 51 (FIG. 11). In this modification, the corner AP formed by the top surface P5 and the outer surface P4a is rounded. This prevents the corner AP of the ceramic frame 21 from chipping due to impact. Specifically, the corner AP has a radius of curvature of 0.1 mm or more and 0.5 mm or less. A radius of curvature of 0.1 mm or more sufficiently prevents chipping of the corner AP. A radius of curvature of 0.5 mm or less prevents excessive reduction in the area of ​​the top surface P5 due to the rounded corner AP. This ensures a sufficient bonding area for the lead frame 30 (FIG. 3), thereby enabling the lead frame 30 to be bonded with high strength. Note that the angle DG1 is preferably within the angle range described above with reference to FIG. 14, but is not limited thereto.

[0072] 11 (package 51), FIG. 14 (package 51q of a first modified example), and FIG. 15 (package 51r of a second modified example) each illustrate an example in which the outer surface P4a of the ceramic frame 21 and the side surface P4b of the heat sink 11 are parallel near the end of the main surface P2 of the heat sink 11 (the right end in each figure). However, as long as the outer surface P4a and the side surface P4b are connected to each other, they do not necessarily have to be parallel to each other. For example, FIG. 15 illustrates a case in which DG1 = 180° - DG0, but DG1 < 180° - DG0 may also be satisfied. Furthermore, at least one of the outer surface P4a and the side surface P4b, which are connected to each other, may be a curved surface. In other words, the outer surface P4a and the side surface P4b may be connected to each other, and the outer surface P4a and / or the side surface P4b may be a curved surface. The same applies to the other packages described above.

[0073] Fig. 16 is a schematic partial cross-sectional view showing a bonding strength test between the heat sink 11 and the ceramic frame 21. For ease of operation, a simple laminate, as shown in Fig. 16, in which the heat sink 11 and the ceramic frame 21 each have the same shape in the in-plane direction was used as the sample in the test. The laminate was fixed by placing it at the corner of an L-shaped lower jig 100. The bonding strength test device used was an Autograph (registered trademark) "AG-X plus" manufactured by Shimadzu Corporation.

[0074] The powder raw material for the heat sink 11 was a mixture of Cu powder with an average particle size of 5 μm and W powder with an average particle size of 3 μm. The ratio of the Cu powder to the W powder was adjusted so that the volume ratio of Cu to W after firing would be 50 / 50 (in other words, equal). The powder raw material for the ceramic frame 21 was Al ２ O ３ , SiO ２ , and MnO ２ The pressing pressure between the first green sheet 11G (heat sink) and the second green sheet 21G (ceramic frame) during lamination was 50 kgf / cm ２The simultaneous firing process of the heat sink 11 and the ceramic frame 21 was carried out by maintaining the maximum temperature of 1250° C. for 2 hours.

[0075] The bonding strength test was carried out by applying a lateral load LD (FIG. 16) of 1000 N. Even with the application of this lateral load LD, the heat sink 11 and the ceramic frame 21 did not peel off from each other. This lateral load LD was 12 N / mm ２ (1.2kgf / mm ２ ) or more, which is sufficiently high for practical use as a package.

[0076] 17 was also subjected to a temperature cycle test to evaluate the resistance to peeling between the ceramic frame 21 and the heat sink 11 due to repeated thermal expansion. Specifically, a temperature cycle test was performed in accordance with MIL Standard 883K, Method Number 1010, Condition C, in which a process of holding at a predetermined temperature for 15 minutes was repeated 100 times. During this test, it was visually confirmed that there was no peeling between the ceramic frame 21 and the heat sink 11.

[0077] <Embodiments 2 to 6> Figure 17 is a schematic cross-sectional view showing the configuration of the heat sink 11 and ceramic frame 21 of the package 51 (Figure 3) according to the first embodiment described above. For ease of explanation, the illustration in Figure 17 is simpler than that in Figure 3. The configurations of packages 52 to 56 according to each of embodiments 2 to 6 will be described below in comparison with Figure 17.

[0078] FIG. 18 is a schematic cross-sectional view showing the configuration of a package 52 according to the second embodiment. The package 52 has a ceramic frame 22 instead of the ceramic frame 21 ( FIG. 17 ). The ceramic frame 22 (specifically, its inner portion) is disposed on the main surface P2 of the heat sink 11. With respect to its position in the thickness direction, the ceramic frame 22 extends from a position above the main surface P2 of the heat sink 11 into the range between the main surface P2 and the heat sink surface P1 of the heat sink 11. The ceramic frame 22 may extend further; in the example shown in FIG. 18 , it extends to the position of the heat sink surface P1 of the heat sink 11. The ceramic frame 22 is spaced apart from the side surface P4b of the heat sink 11.

[0079] FIG. 19 is a schematic cross-sectional view showing the configuration of a package 53 according to the third embodiment. The package 53 includes a ceramic frame 23 instead of the ceramic frame 21 ( FIG. 17 ). The ceramic frame 23 includes a plate-shaped base 23a disposed on the main surface P2 of the heat sink 11 and a frame portion 23b fixed to the heat sink 11 via the base 23a. The boundary between the base 23a and the frame portion 23b (shown by the dashed line in the figure) may be imaginary. The frame portion 23b has an inner surface P3. In the third embodiment, the main surface P2 of the heat sink 11 includes a bonding surface P2b directly bonded to the base 23a of the ceramic frame 23. In the example shown in FIG. 19 , the entire main surface P2 is the bonding surface P2b. In the third embodiment, the cavity surface P2a of the heat sink 11 faces the cavity CV via the base 23a of the ceramic frame 23. Therefore, in the third embodiment as well, the cavity surface P2a can be said to face the cavity CV.

[0080] FIG. 20 is a schematic cross-sectional view showing the configuration of a package 54 according to the fourth embodiment. The package 54 has a ceramic frame 24 instead of the ceramic frame 21 ( FIG. 17 ). The ceramic frame 24 (specifically, its inner portion) is disposed on the main surface P2 of the heat sink 11. With respect to its position in the thickness direction, the ceramic frame 24 extends from a position above the main surface P2 of the heat sink 11 into the range between the main surface P2 and the heat sink surface P1 of the heat sink 11. The ceramic frame 24 may extend further; in the example shown in FIG. 20 , it extends to the position of the heat sink surface P1 of the heat sink 11. The side surface P4b of the heat sink 11 has a bonding surface directly bonded to the ceramic frame 24. In the example shown in FIG. 20 , the entire side surface P4b is a bonding surface, but only a portion of the side surface P4b may be a bonding surface.

[0081] The package 54 can be manufactured by firing a laminate of a lower layer LY1 and an upper layer LY2. The lower layer LY1 is formed, for example, as follows: First, a first unfired layer made of a material that will become the ceramic frame 24 after firing is formed. Next, a through hole corresponding to the area where the heat sink 11 will be located is formed in the first unfired layer using a mold. Next, a second unfired layer including a portion that will become the heat sink 11 after firing is laminated on the first unfired layer so as to cover the through hole. Next, the mold is used again to press the portion of the second unfired layer into the through hole. Next, the portion of the second unfired layer that was not pressed by the mold, in other words, the portion remaining on the top surface of the first unfired layer, is removed. This results in the lower layer LY1. The upper layer LY2 is obtained by removing a portion corresponding to the cavity CV from the unfired layer made of a material that will become the ceramic frame 24 after firing. The laminate of the lower layer LY1 and the upper layer LY2 is fired to obtain the package 54. Note that a package 55 (FIG. 21) and a package 56 (FIG. 22), which will be described later, can also be manufactured by a similar process.

[0082] FIG. 21 is a schematic cross-sectional view showing the configuration of a package 55 according to the fifth embodiment. The package 55 includes a heat sink 15 and a ceramic frame 25 instead of the heat sink 11 and ceramic frame 21 ( FIG. 17 ). The ceramic frame 25 (specifically, its inner portion) is disposed on the main surface P2 of the heat sink 15. The heat sink 15 includes a support portion 15b and a cavity portion 15a provided on a portion of the support portion 15b. The boundary between the cavity portion 15a and the support portion 15b (indicated by the dashed line in FIG. 21 ) may be imaginary. The main surface P2 of the heat sink 15 includes a cavity surface P2a formed by the cavity portion 15a and a bonding surface P2b formed by the support portion 15b. In the thickness direction of the main surface P2 of the heat sink 15, the position of the cavity surface P2a and the position of the bonding surface P2b are different, with the latter being closer to the heat sink surface P1. The cavity surface P2a and the bonding surface P2b may be surfaces that are approximately parallel to each other. The main surface P2 may further have a side wall surface P2c that is made of the cavity portion 15a and connects the cavity surface P2a and the bonding surface P2b to each other. The side wall surface P2c of the heat sink 15 may be approximately along the thickness direction. The side wall surface P2c may be a bonding surface that is directly bonded to the ceramic frame 25. The side surface P4b of the support portion 15b may have a bonding surface that is directly bonded to the ceramic frame 25.

[0083] 22 is a schematic cross-sectional view showing the configuration of a package 56 according to the sixth embodiment. The package 56 has a ceramic frame 26 instead of the ceramic frame 21 (FIG. 17). The ceramic frame 26 is disposed on the side surface P4b of the heat sink 11. The side surface P4b includes a bonding surface that is directly bonded to the ceramic frame 26. In the example shown in FIG. 22, the entire side surface P4b is a bonding surface, but only a portion of the side surface P4b may be a bonding surface.

[0084] The lead frame 30 (FIG. 3) may be applied to the packages 52 to 56, as in the package 51. The metallization layer 31 (FIG. 3) may be applied to the packages 52 to 56, as in the package 51. In any of the packages 51 to 56, another metallization layer not for the lead frame 30 may be formed on the upper surface P5 of the ceramic frame instead of or together with the metallization layer 31 for the lead frame 30. The material of this other metallization layer may be the same as the material of the metallization layer 31 described above.

[0085] Next, a comparison between the packages 51 to 56 will be described below.

[0086] First, the bonding strength will be described below.

[0087] In the lamination process of the green sheets for manufacturing the packages 51 to 56 (for example, in the case of package 51, see FIG. 5), pressure is applied in the lamination direction, in other words, in the thickness direction. If necessary, it is easy to apply a larger pressure in the thickness direction to the green structure obtained by the lamination process by performing a press process with a large load along the thickness direction. Applying this pressure before the co-firing process of the heat sink and the ceramic frame contributes to increasing the bonding strength between them. Since this pressure is applied perpendicular to the main surface P2, the bonding strength can be most effectively improved when the bonding surface is on the main surface P2. The pressure on the bonding surface at this time is 10 to 150 kgf / cm ２ By keeping the pressure within this range, it is possible to obtain sufficient bonding strength after firing while suppressing deformation and displacement of the green sheet. On the other hand, it is difficult to apply such pressure to the side surface P4b of the heat sink. It is also difficult to apply pressure by additional pressing. Therefore, the bonding surface of the side surface P4b of the heat sink is likely to have a smaller bonding strength than the bonding surface of the main surface P2.

[0088] As described above, package 56, which only has a bonding surface on side surface P4b, is likely to have a relatively low bonding strength across the entire bonding surface. As a result, the bonding surface can become a leak path, resulting in a decrease in the airtightness of the package. In contrast, packages 51 to 55 have at least a portion of their bonding surface formed on main surface P2, making it easy to ensure a high bonding strength at least partially. This makes it possible to suppress package leaks. In particular, packages 51 to 53 have their entire bonding surface formed on main surface P2, making it easy to ensure a high bonding strength across the entire bonding surface. This makes it possible to more reliably suppress package leaks.

[0089] If the package size were allowed to increase without any restrictions, the area of ​​the bonding surface would also be allowed to increase without any restrictions, and as a result, problems due to bonding strength would be less likely to occur. However, there is usually a limit to the package size. Comparing packages 51 to 53, packages 51 and 52 are preferable in terms of small size in the thickness direction, and packages 51 and 53 are preferable in terms of small size in the in-plane direction, with package 51 being preferable in both respects.

[0090] Second, heat dissipation characteristics will be described. As mentioned above, the size of a package is usually limited. Given such limitations, in order to efficiently remove heat from the semiconductor element 8 ( FIG. 2 ) mounted on the main surface P2 to the lower side in FIG. 2 , it is desirable to arrange the heat sink 11 as widely as possible in the in-plane direction in an area lower than the main surface P2 in FIG. 2 . From this perspective, packages 51 to 53 are preferable. Comparing these, packages 51 and 52 are more preferable because they can avoid an increase in thermal resistance due to the presence of a ceramic frame between the semiconductor element 8 ( FIG. 2 ) and the heat sink 11.

[0091] From the above, when both the bonding strength and the heat dissipation characteristics are taken into consideration comprehensively, package 51 is often preferable among packages 51 to 56, although this depends on the application of the package.

[0092] <Analysis of the Bonding Surface Between the Heat Sink and the Ceramic Frame> Next, the analysis results of the bonding surface between the heat sink and the ceramic frame formed by co-firing will be described below.

[0093] FIG. 23 is an electron microscope photograph showing a cross section of a portion of the bonding surface (bonding surface P2b in FIG. 3 ) between the heat sink 11 and the ceramic frame 21 of a test specimen fabricated under the same conditions as the test specimens used in the bonding strength test and temperature cycle test described above. The electron microscope photograph in the figure was taken at an accelerating voltage of 15 kV, as was the case for the electron microscope photographs in the other figures. The Z direction in the figure is the direction in which the heat sink and the ceramic frame face each other across the bonding surface. Therefore, the Z direction corresponds to the thickness direction (vertical direction in FIG. 17 ) in FIG. 17 and the in-plane direction (horizontal direction in FIG. 22 ) in FIG. 22 . The X direction is a direction perpendicular to the Z direction. Therefore, the X direction corresponds to the in-plane direction (horizontal direction in FIG. 17 ) in FIG. 17 and the thickness direction (vertical direction in FIG. 22 ) in FIG. 22 . The powder raw materials for the heat sink 11 and the ceramic frame 21 were the same as those described with reference to FIG. 16 .

[0094] The area ratio of the refractory metal (at least one refractory metal selected from the group consisting of W and Mo, and W in the sample observed in FIG. 23 ) to the bonding surface of the heat sink 11 is greater than the volume ratio of the refractory metal to the heat sink 11. This volume ratio may be calculated based on the area ratio of the refractory metal in a micrograph of the cross section of the heat sink 11. For example, the area of ​​the heat sink 11 shown in FIG. 23 (approximately 160 μm × approximately 20 μm) may be used for the calculation. In this example, W = 50% and Cu = 50%. In the heat sink 11 shown in the photograph, the white parts are W and the gray parts are Cu, and there is a sufficient contrast between them, so the area ratio can be calculated by binarizing the image. This binarization may be performed using image processing software. For example, "ImageJ" may be used as the image processing software.

[0095] In the cross-sectional view, the bonding surface extends macroscopically along a straight line, while microscopically forming an undulating boundary line between the heat sink and the ceramic frame. Here, the macroscopic straight line may be obtained by linear approximation of the microscopic boundary line within a dimension range on the order of 100 μm. For example, in FIG. 23 , it may be obtained by linear approximation of the undulating boundary line within a range of 160 μm in the X direction. Note that, for example, in the structure of FIG. 17 , the straight line may be considered to extend substantially along the in-plane direction (the horizontal direction in FIG. 17 ), and in the structure of FIG. 22 , it may be considered to extend substantially along the thickness direction (the vertical direction in FIG. 22 ). Furthermore, the undulations can be easily observed by cross-sectional observation using a scanning electron microscope with normal resolution. For example, a cross-sectional view in which the undulations are clearly distinguishable, such as that shown in FIG. 23 , can be sufficiently observed if a resolution of about 0.1 μm (or less) is ensured. The undulating boundary line includes a copper section made of copper and a refractory metal section made of at least one refractory metal. In the micrograph of Figure 23, the refractory metal section (specifically, W) is white, while the copper section is gray. Because there is a large difference in contrast between the two, it is easy to distinguish between the copper section and the refractory metal section. As shown in Figure 24, by projecting the refractory metal section and the copper section on the boundary line onto the macroscopic straight line, i.e., onto the X-axis, the proportions of the refractory metal and copper on the boundary line can be easily calculated. In this example, in the projection of the boundary line onto the straight line, the proportion of the refractory metal section was 65.3%, and the proportion of the copper section was 34.7%.

[0096] From the above, the proportion of the high-melting-point metal section in the projection of the boundary line onto the straight line is estimated to be 65.3%, and the volume ratio of the high-melting-point metal in the heat sink 11 is estimated to be 50%, with the former being larger than the latter. In this example, this proportion was 1.3 times the volume ratio. This ratio is not limited to 1.3 and may be, for example, 1.3 or more, as in this example. To obtain the benefits of this high ratio, this ratio is preferably 1.1 or more. The inventors' studies have shown that the proportion of the high-melting-point metal section can be increased by increasing the firing temperature and firing time when fabricating the package. It is also believed that the application of pressure to the green structure in the stacking direction (thickness direction) may contribute to improving this proportion. By increasing this proportion, the thermal expansion coefficient of the portion of the heat sink 11 facing the ceramic frame 21 in the straight line direction can be made closer to the thermal expansion coefficient of the ceramic frame 21. This prevents the heat sink 11 and the ceramic frame 21 from peeling off from each other.

[0097] It is also conceivable that a structure in which the heat sink 11 and the ceramic frame 21 are bonded to each other can be obtained by stacking an unfired ceramic frame 21, which is a green material, on an already fired heat sink 11 and firing the green material. However, according to the inventors' studies, the bond strength between them is expected to be extremely weak compared to when the heat sink 11 and the ceramic frame 21 are formed by co-firing. One of the reasons for this is presumed to be the decrease in the above-mentioned ratio. The reason why the ratio is small when co-firing is not performed will be explained below using the heat sink made of an alloy of Cu and W, in other words, a CuW plate, as an example.

[0098] CuW plates are typically formed through a process in which W particles and molten Cu coexist at high temperatures exceeding the melting point of Cu. It is well known that molten Cu has high wettability with respect to solid W. From the perspective of wettability, the surface of the heat sink 11Z is likely to become a Cu-rich surface due to the spread of Cu. If an unfired ceramic frame, which is a green member, is stacked on a CuW plate having such a Cu-rich surface and then fired, the proportion of Cu at the bonding surface is likely to increase. In other words, the proportion of W is likely to decrease. Therefore, the aforementioned proportion is likely to decrease.

[0099] In contrast, when the co-firing method is used, in the laminate SG (FIG. 6) before firing, the unsintered W particles (more generally, high-melting-point metal particles) in the first green sheet 11G (corresponding to the unsintered heat sink 11) and the unsintered ceramic particles in the second green sheet 21G (corresponding to the unsintered ceramic frame 21) are likely to be in contact with or adjacent to each other. As a result, it is thought that the proportion of W occupying the bonding surface after the firing process is likely to be large. Therefore, it is thought that the above-mentioned proportion is likely to be large.

[0100] Each of Figures 25 to 27 shows the elemental distributions (lower row) of Cu, W, and Mn near the bonding surface between the heat sink 11 and the ceramic frame 21 of a test specimen fabricated under the same conditions as the test specimens used in the aforementioned bonding strength test and temperature cycle test, along with an electron microscope photograph (upper row) corresponding to the field of view of the distribution map. Figure 28 shows the Mn elemental distribution shown in the lower row of Figure 27 in detail, including the layer portion and bulk portion described below. In the elemental distribution map in the lower row, areas with high concentrations of each element are displayed in white. As can be seen from the elemental distribution map for Mn shown in Figure 27, Mn element is unevenly distributed in the layer portion of the ceramic frame 21 facing the bonding surface of the heat sink 11 (Figure 28). The elemental distribution was measured using scanning electron microscope energy dispersive X-ray spectroscopy (SEM-EDX). The measurement device used was a Miniscope (registered trademark) "TM3030" manufactured by Hitachi High-Tech Corporation.

[0101] Each of Figures 29 to 33 shows a graph (top row) showing a depth profile of SEM-EDX counts in a direction perpendicular to the joining surface (i.e., the Z direction in Figure 23) in Mn elemental analysis, along with an electron microscope photograph (bottom row) of Figure 27 with a rectangle corresponding to the profile added, and a graph (middle row) showing the region aligned to the horizontal axis of the graph. The counts correspond to the Mn element concentration (e.g., concentration expressed in wt%) in the ceramic frame 21. The upper graph also shows a depth profile of W. Note that the depth profiles shown in Figures 29 to 33 are measurement results for five regions located at different positions in the direction perpendicular to the thickness direction. A Mn concentration profile was obtained with respect to the depth from the joining surface into the ceramic frame, passing through the area where Mn was distributed in the layer portion in the Mn element distribution diagram.

[0102] Here, in the Mn element distribution diagram (lower part of Figure 28), the portion of the ceramic frame 21 located within 3 μm of the bonding surface of the heat sink 11, i.e., the 3 μm depth range including the depth position within 3 μm from the bonding surface into the ceramic frame 21, is defined as the layer portion. Because the layer portion of the ceramic frame 21 is located near the bonding surface of the heat sink 11, its composition is strongly affected by being bonded to the heat sink 11. On the other hand, the portion of the ceramic frame 21 separated from the bonding surface by the layer portion and located sufficiently deep from the bonding surface is a bulk region that is substantially unaffected by the above-mentioned influence. According to the inventors' studies, portions with a depth of 6 μm or more are included in the bulk region because they are located sufficiently deep. Therefore, in this specification, the 3 μm depth range including the depth position from the bonding surface into the ceramic frame 21 of 6 μm to 9 μm is referred to as the bulk portion as a representative portion of the bulk region.

[0103] As can be seen from the results in Figures 29 to 33, the Mn concentration profile relative to the depth from the bonding surface of the heat sink 11 into the ceramic frame 21 includes a maximum peak located within the layer portion (i.e., within a depth of 3 μm from the bonding surface). Therefore, if only a single maximum peak is observed, that maximum peak is located within the layer portion. If multiple maximum peaks with the same maximum count are observed, these multiple maximum peaks include a maximum peak located within the layer portion. As can be seen from Figures 29 to 33, the Mn concentration profile is considered to have bulk properties at positions approximately 6 μm or deeper from the bonding surface. Therefore, the representative value of the bulk portion in the Mn concentration profile can be estimated, for example, by the peak in a 3 μm depth range, including positions 6 μm to 9 μm deep from the bonding surface into the ceramic frame 21. The maximum peak located in the layer portion, as described above, may be 150% or more of the representative value of the bulk portion, as shown in Figures 29 to 33. In the study conducted by the present inventors, this percentage could be increased by increasing the baking time when producing the package.

[0104] Furthermore, as can be seen from the results of Figures 29 to 33, the concentration of Mn element is higher in the layer portion than in the bulk portion. Correspondingly, in the SEM-EDX (element distribution map) of Mn, the count number per unit area is higher in the layer portion than in the bulk portion. Furthermore, in a common range in the in-plane direction, the count number in the layer portion is higher than the count number in the bulk portion. It is usually sufficient if the dimension of the above-mentioned range in which the count numbers are totaled is approximately several tens of micrometers (e.g., approximately the horizontal dimension of the field of view in Figure 28). The concentration of Mn element in the layer portion may be 150% or more of the Mn element concentration in the bulk portion. Note that this percentage can be obtained, for example, by calculating the percentage of the total count number in the layer portion to the total count number in the bulk portion in the above-mentioned common range in the in-plane direction.

[0105] The inventors' investigations suggest that the bonding strength between the ceramic frame 21 and the heat sink 11 can be increased by locally increasing the Mn concentration in the layer portion of the ceramic frame 21. Although the mechanism behind this has not yet been verified, it is thought that this may be due to bonding between Mn atoms in the ceramic frame 21 and metal atoms in the heat sink 11. The effect of increasing bonding strength is more fully achieved when the maximum peak located in the layer portion is 150% or more of the representative value of the bulk portion. From the perspective of this effect, there is no particular upper limit to this percentage, and even taking other perspectives into account, it is thought that the bonding strength can be increased to, for example, approximately 1000%.

[0106] DESCRIPTION OF SYMBOLS 8: Semiconductor element 9: Wire (wiring member) 11, 15: Heat sink 11G: First green sheet 21 to 26: Ceramic frame 21G: Second green sheet 30: Lead frame (metal terminal) 31: Metallized layer 51 to 56, 51a, 51b, 51q, 51r: Package 70: Adhesive layer 80: Lid 90: Semiconductor module CV: Cavity P1: Heat dissipation surface P2: Main surface P2a: Cavity surface P2b: Bonding surface P3: Inner surface P4a: Outer surface P4b: Side surface SF: Fired body SG: Laminate

Claims

1. A package having a cavity, comprising: a heat sink made of a first sintered material containing a metal, the heat sink having a main surface including a cavity surface facing the cavity, a heat sink surface opposite the main surface, and a side surface between the heat sink surface and the main surface; and a ceramic frame having an inner surface surrounding the cavity and an outer surface opposite the inner surface, wherein the main surface of the heat sink includes a bonding surface directly bonded to the ceramic frame.

2. The package according to claim 1, wherein the side surface of the heat sink is not directly bonded to the ceramic frame.

3. A package according to claim 1 or 2, wherein the first sintered material is a sintered metal material.

4. A package according to claim 1 or 2, wherein the first sintered material contains copper and at least one high melting point metal selected from the group consisting of tungsten and molybdenum.

5. A package as claimed in claim 4, wherein in a cross-sectional view of at least a portion of said bonding surface, said bonding surface extends macroscopically along a straight line and microscopically forms an undulating boundary line between said heat sink and said ceramic frame, said boundary line having a copper section made of said copper and a high-melting point metal section made of said at least one high-melting point metal, and the proportion of said high-melting point metal section in the projection of said boundary line onto said straight line is greater than the volume ratio of said at least one high-melting point metal in said heat sink.

6. The package according to claim 4, further comprising a metallization layer provided on the upper surface of the ceramic frame and made of a second sintered material containing copper at a volume ratio higher than that of the first sintered material of the heat sink.

7. A package according to claim 1 or 2, wherein the ceramic frame contains Mn, and in an element distribution diagram of Mn, the ceramic frame includes a layer portion having a depth range of 3 μm including a depth position within 3 μm from the joining surface into the ceramic frame, and a bulk portion having a depth range of 3 μm including a depth position of 6 μm to 9 μm into the ceramic frame from the joining surface, and the concentration of Mn element is higher in the layer portion than in the bulk portion.

8. A package according to claim 1 or 2, wherein the ceramic frame contains Mn, the ceramic frame includes a layer portion located within a depth of 3 μm from the joining surface, and a bulk portion separated from the joining surface by the layer portion, and a Mn concentration profile with respect to the depth from the joining surface into the ceramic frame includes a maximum peak located within the layer portion.

9. The package according to claim 8, wherein in the Mn concentration profile with respect to the depth, the maximum peak is 150% or more of a representative value in the bulk portion.

10. The package according to claim 1 or 2, wherein the joining surface of the heat sink does not contain silver.

11. A package according to claim 1 or 2, wherein the side surface of the heat sink is connected to the outer surface of the ceramic frame.

12. The package of claim 11, wherein the side of the heat sink is flush with the outer surface of the ceramic frame.

13. The package according to claim 1 or 2, wherein the main surface of the heat sink and the outer surface of the ceramic frame form an acute angle.

14. A package as claimed in claim 1 or 2, wherein the ceramic frame has an upper surface that is separated from the main surface of the heat sink by the ceramic frame and is connected to the outer surface, and a corner formed by the upper surface of the ceramic frame and the outer surface of the ceramic frame has a radius of curvature of 0.1 mm or more and 0.5 mm or less.

15. The package according to claim 1 or 2, further comprising a metal terminal provided on an upper surface of the ceramic frame.

16. A semiconductor module comprising: the package according to claim 1 or 2; and a semiconductor element mounted on the cavity surface of the main surface of the heat sink, wherein the distance between the semiconductor element and the inner surface of the ceramic frame is 25 μm or less.

17. A method for manufacturing a package for producing the package according to claim 1 or 2, comprising the steps of: forming a green structure in which a first green member which will be fired to become the heat sink and a second green member which will be fired to become the ceramic frame; and firing the green structure.

18. A method for manufacturing a package as described in claim 17, wherein the step of forming the green structure includes a step of forming the second green member, and the step of forming the second green member includes a step of removing a portion corresponding to the cavity from a green sheet that will become at least a part of the second green member.

19. A method for manufacturing a package as recited in claim 17, wherein the first green member is formed using a first metal powder containing copper and at least one high melting point metal selected from the group consisting of tungsten and molybdenum, and the green structure includes an additional layer which will be fired to form a metallized layer on an upper surface of the ceramic frame, the additional layer being formed using a second metal powder containing copper and at least one high melting point metal selected from the group consisting of tungsten and molybdenum, the second metal powder containing a higher volumetric proportion of copper than the first metal powder.

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