JP2024019155A - Package and package manufacturing method - Google Patents

Abstract

To provide a package which includes a heat dissipation plate and a ceramic frame, and can be fully and easily suppressed in the occurrence of warpage due to difference between the linear expansion coefficient of the heat dissipation plate and that of the ceramic frame, and a manufacturing method of the package.SOLUTION: A heat dissipation plat 11 is made of a sintered material containing metal, and has : a heat radiation surface P1; and a main surface P2 opposite to the heat radiation surface P1 in a thickness direction. The ceramic frame body 21 is disposed on the main surface P2 of the heat dissipation plat 11, and has an inner surface P3 surrounding a cavity CV, and includes a ceramic frame body 21. The heat dissipation plat 11 includes: a first layer that contains a plurality of elements at a first composition ratio, and has a first liner expansion coefficient; and a second layer that is arranged between the first layer and the ceramic frame body 21, contains the plurality of elements at a second composition ratio different from the first composition ratio, and has a second linear expansion coefficient larger than the first linear expansion coefficient.SELECTED DRAWING: Figure 4

Description

The present invention relates to a package and a method for manufacturing the package.

Packages with cavities are often used to house electronic components such as power semiconductor devices. After the electronic component is mounted into the cavity of the package, the cavity is hermetically sealed by joining the lid to the package. This results in an electronic device having electronic components protected from the external environment. The bottom surface (the surface opposite to the surface on which electronic components are mounted) of the heat sink plate (in other words, the heat sink board or heat sink plate) is usually attached to a support member that supports it. The support member is, for example, a mounting board or a heat dissipation member. The support member is in thermal contact with the bottom surface of the heat sink. By passing through the heat sink, heat from the electronic components is efficiently dissipated to the outside of the package (typically to the support member). Thereby, the temperature rise of the electronic components can be suppressed to, for example, about 150°C. On the other hand, depending on the external environment in which the electronic device is placed, the temperature of the package can drop to below freezing. Therefore, electronic devices need to withstand heat cycles caused by these temperature differences.

According to the technique disclosed in Japanese Unexamined Patent Publication No. 2005-150133 (Patent Document 1), first, a heat sink plate, a ceramic frame, and an external connection terminal are connected to each other. This prepares a package with a cavity. The heat sink plate and the ceramic frame are joined by silver (Ag)-copper (Cu) brazing at about 780°C to 900°C. A semiconductor element is mounted on this package, and a lid is adhered to the upper surface of the ceramic frame. The heat sink is made of a material with a coefficient of thermal expansion similar to that of ceramic. Examples of the material include a composite metal plate (clad material) of Cu and other metals.

Japanese Unexamined Patent Publication No. 2018-041868 (Patent Document 2) discloses a heat dissipation board applied to electronic components. A ceramic substrate is bonded to one surface side of the heat dissipation substrate via a bonding portion containing silver solder. Silver brazing is performed while being heated. During cooling after this heating, the heat dissipation substrate and the ceramic substrate each contract. Here, this heat dissipation substrate is made of a cladding material configured by alternately laminating Cu layers and metal A layers made of metal A. According to the publication, this configuration suppresses the warping deformation caused by the contraction described above. Metal A is Mo or W. The method for manufacturing a heat dissipation board includes a step of joining a Cu plate and a metal A plate. In this step, hot pressing is performed in which Cu plates and metal A plates are alternately stacked and pressed uniaxially at high temperature.

Note that as a heat sink plate (in other words, a heat sink plate or a heat sink board) for a semiconductor light emitting device, one containing a metal oxide as described below has also been proposed.

According to Japanese Unexamined Patent Publication No. 2009-88205 (Patent Document 3), a heat dissipation substrate manufactured using a firing process is disclosed. The heat dissipation substrate includes an element body mainly composed of a metal oxide, and a plurality of metal lumps arranged throughout the interior of the element body and having flaky portions. The plurality of metal lumps are characterized in that their thickness directions are aligned in a predetermined direction. This feature results in anisotropy in thermal conductivity. The metal oxide is, for example, ZnO, Al ₂ O ₃ , SiO ₂ or ZrO ₂ . Since ZnO is white, it can better reflect light from the semiconductor light emitting device. Further, when the metal lump is made of silver or a silver alloy, by using ZnO as the metal oxide, the heat dissipation substrate becomes more flexible, and therefore the heat dissipation substrate can be made less likely to break. The manufacturing method of this heat dissipation board consists of a step of preparing a slurry in which flaky metal powder and metal oxide are dispersed, a step of forming a green sheet by applying the slurry onto a film using a doctor blade method, and a step of forming a green sheet by applying the slurry onto a film using a doctor blade method. and a step of firing.

Japanese Patent Application Publication No. 2005-150133 Japanese Patent Application Publication No. 2018-041868 Japanese Patent Application Publication No. 2009-88205

According to the technique disclosed in Japanese Patent Application Publication No. 2018-041868, the material of each layer in the laminated structure of the heat dissipation board is either a Cu plate or a metal A plate (specifically, a Mo plate or a W plate). Therefore, flexibility in designing the linear expansion coefficient of each layer is low. If it is possible to apply many types of metal A plates, flexibility in design may be ensured to some extent. However, preparing many types of metal plates tends to be a heavy burden on manufacturing. Therefore, with the technique disclosed in the publication, it is difficult to sufficiently and easily suppress warpage caused by the difference in linear expansion coefficient between the heat dissipation substrate (heat dissipation plate) and the ceramic substrate attached thereto.

The present invention has been made to solve the above-mentioned problems, and its purpose is to sufficiently and easily suppress warpage caused by the difference in linear expansion coefficient between the heat sink and the ceramic frame. An object of the present invention is to provide a package and a method for manufacturing the package.

Aspect 1 is a package (51 to 55) having a cavity (CV), and includes a heat sink (11) and a ceramic frame (21 to 25). The heat dissipation plate (11) is made of a sintered material containing metal, and has a heat dissipation surface (P1) and a main surface (P2) opposite to the heat dissipation surface (P1) in the thickness direction. The ceramic frame (21 to 25) is disposed on the main surface (P2) of the heat sink (11) and has an inner surface (P3) surrounding the cavity (CV). The heat sink (11) includes a first layer containing a plurality of elements in a first composition ratio and having a first linear expansion coefficient, the first layer and the ceramic frame (21 to 25). and a second composition containing the plurality of elements at a second composition ratio different from the first composition ratio, and having a second coefficient of linear expansion larger than the first coefficient of linear expansion. and a layer.

Aspect 2 is the package (51 to 55) according to Aspect 1, in which the first layer of the heat sink (11) has the same thickness as the heat sink surface (P1) of the heat sink (11). The second layer of the heat sink (11) is located between the center position and the ceramic frame (21 to 25) in the direction of the heat sink (11), and the second layer of the heat sink (11) It is located in

Aspect 3 is the package (51-55) according to Aspect 1 or 2, wherein the plurality of elements include copper and at least one high melting point metal selected from the group consisting of tungsten and molybdenum.

Aspect 4 is the package (51 to 55) according to any one of Aspects 1 to 3, in which the main surface (P2) of the heat sink (11) faces the cavity (CV). a surface (P2a), and a joint surface (P2b) directly joined to the ceramic frame (21 to 25).

Aspect 5 is the package (51 to 55) according to any one of aspects 1 to 4, in which the sintered material is a sintered metal material.

Aspect 6 is the package (51 to 55) according to any one of aspects 1 to 5, wherein the ceramic frame (21 to 25) has an outer surface (P4a) opposite to the inner surface (P3). The heat sink (11) has a side surface (P4b) flatly connected to the outer surface (P4a) of the ceramic frame (21-25).

Aspect 7 is a package (51 to 55) having a cavity (CV), and includes a heat sink (11) and a ceramic frame (21 to 25). The heat dissipation plate (11) is made of a sintered material containing metal, and has a heat dissipation surface (P1) and a main surface (P2) opposite to the heat dissipation surface (P1) in the thickness direction. The ceramic frame (21 to 25) is disposed on the main surface (P2) of the heat sink (11) and has an inner surface (P3) surrounding the cavity (CV). The heat sink (11) includes a first layer and a second layer. The first layer is disposed between the heat dissipation surface (P1) of the heat dissipation plate (11) and a center position of the heat dissipation plate (11) in the thickness direction, and has a first coefficient of linear expansion. . The second layer is disposed between the center position and the ceramic frame (21-25), and has a second coefficient of linear expansion larger than the first coefficient of linear expansion.

Aspect 8 is a method of manufacturing a package (51 to 55) having a cavity (CV). The package (51 to 55) includes a heat dissipation plate (11) made of a sintered material containing metal and having a heat dissipation surface (P1) and a main surface (P2) opposite to the heat dissipation surface (P1); A ceramic frame (21 to 25) is provided on the main surface (P2) of the plate (11) and has an inner surface (P3) surrounding the cavity (CV). The heat dissipation plate (11) is arranged between a first layer having a first linear expansion coefficient and the first layer and the ceramic frame (21 to 25), and has a first linear expansion coefficient. a second layer having a second coefficient of linear expansion larger than the coefficient. The manufacturing method includes a step of forming a first green sheet that becomes the first layer of the heat sink (11) by being fired; a step of forming a second green sheet that will become the second layer; and a step of forming a ceramic green sheet (21G) that will become the ceramic frame (21 to 25) by firing. a step of forming a laminate in which the first green sheet, the second green sheet, and the ceramic green sheet (21G) are laminated; and a step of firing the laminate; Equipped with

A ninth aspect is a method for manufacturing the package (51 to 55) according to the eighth aspect, in which the cavity (CV) is formed from the ceramic green sheet (21G) before the step of forming the laminate (SG). The method further includes the step of removing a portion corresponding to .

According to the above aspect, it is possible to sufficiently and easily suppress warpage of the package due to the difference in linear expansion coefficient between the heat sink and the ceramic frame.

Objects, features, aspects, and advantages of the invention will become more apparent from the following detailed description and accompanying drawings.

1 is a schematic perspective view showing the configuration of a semiconductor module according to Embodiment 1, with part of the illustration omitted so that the inside of a cavity can be seen; FIG. FIG. 2 is a schematic cross-sectional view of the semiconductor module of FIG. 1 taken along line II-II. 3 is a schematic cross-sectional view showing the structure of a package as a component of the semiconductor module of FIG. 2. FIG. 4 is a partially enlarged view of FIG. 3. FIG. 1 is a flow diagram schematically showing a method for manufacturing a package according to the first embodiment; FIG. 1 is a schematic partial cross-sectional view illustrating one step of the method for manufacturing a package according to the first embodiment; FIG. 7 is a partially enlarged view of FIG. 6. FIG. 1 is a schematic partial cross-sectional view illustrating one step of the method for manufacturing a package according to the first embodiment; FIG. 1 is a schematic partial cross-sectional view illustrating one step of the method for manufacturing a package according to the first embodiment; FIG. FIG. 3 is a schematic cross-sectional view showing the configuration of a package of a comparative example. 11 is a schematic cross-sectional view showing the configuration of a semiconductor module using the package of FIG. 10. FIG. FIG. 3 is a schematic cross-sectional view showing the configuration of a heat sink and a ceramic frame included in the package according to the first embodiment. 13 is a schematic cross-sectional view showing the configuration of a package according to Embodiment 2 from the same view as FIG. 12. FIG. 13 is a schematic cross-sectional view showing the configuration of a package according to Embodiment 3 from the same view as FIG. 12. FIG. 13 is a schematic cross-sectional view showing the configuration of a package according to Embodiment 4 from the same view as FIG. 12. FIG. 13 is a schematic cross-sectional view showing the configuration of a package according to Embodiment 5 from the same field of view as FIG. 12. FIG.

Embodiments of the present invention will be described below based on the drawings. Note that in this specification, unless otherwise specified, metal may mean either a pure metal or an alloy.

<Embodiment 1>
(Semiconductor module configuration)
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 of FIG. 1 taken along line II-II. The semiconductor module 90 includes a package 51 and a semiconductor element 8. Further, the semiconductor module 90 may include wires 9 as wiring members for the semiconductor element 8. Further, the semiconductor module 90 may include a lid 80 for sealing the cavity CV. The lid 80 may be attached to the package 51 by an adhesive layer 70. In FIG. 1, illustration of the lid 80 and the adhesive layer 70 is partially omitted so that the inside of the cavity CV included in the package 51 can be partially seen.

The semiconductor element 8 may be a power semiconductor element, in which case the semiconductor module 90 is a power module. The power semiconductor device may be for radio frequency (RF), and in this case, the semiconductor module 90 is an RF power module. Note that although one semiconductor element 8 is illustrated in FIGS. 1 and 2, a plurality of semiconductor elements 8 may be mounted on the package 51. Furthermore, elements other than the semiconductor element 8, such as passive elements, may also be mounted.

(Package composition)
FIG. 3 is a schematic cross-sectional view showing the structure of the package 51 as a component of the semiconductor module 90 (FIG. 2). At the time when the package 51 is prepared for manufacturing the semiconductor module 90, the semiconductor element 8 does not need to be mounted yet, as shown in FIG. The package 51 has a cavity CV that is sealed by a lid 80. The package 51 has a heat sink 11 and a ceramic frame 21.

The heat sink 11 is made of a sintered material containing metal. For example, the sintered material contains copper (Cu) and high melting point metals. The high melting point metal has a higher melting point than Cu. The high melting point metal may be at least one of tungsten (W) and molybdenum (Mo). The sintered material need not contain non-metals. In other words, the sintered material may be a sintered metallic material. In other words, the sintered material may be a sintered material consisting essentially of metal. The sintered metal material may contain Cu and W, for example an alloy of Cu and W, ie a copper-tungsten alloy. In order to improve the heat dissipation performance of the heat sink 11, it is preferable that the material of the heat sink 11 has high thermal conductivity. Such high thermal conductivity can be easily obtained by making the heat sink 11 contain Cu in a sufficient proportion. On the other hand, when the heat sink 11 contains W in a sufficient proportion, the linear expansion coefficient of the heat sink 11 can be made close to that of ceramic such as alumina. This approximation of the coefficient of linear expansion is useful for suppressing thermal stress between the heat sink 11 and the ceramic frame 21. The sintered material may contain non-metals to approximate the coefficient of linear expansion of ceramics such as alumina. The non-metal may be, for example, a ceramic such as alumina and/or silica.

The heat sink 11 has a heat sink P1 and a main surface P2 opposite to the heat sink P1. The heat radiation surface P1 of the heat radiation plate 11 will typically be attached to a support member (not shown). The support member is, for example, a mounting board or a heat dissipation member. The heat dissipation plate 11 may have penetrations (not shown) through which fasteners (eg, screws) for attachment to the support member pass.

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 insulation properties of the package 51 can be improved. The material of the ceramic frame 21 may contain alumina as a main component, and may also contain a trace amount of silica and/or a trace amount of an additive containing a manganese element to promote sintering of the ceramic frame 21. You may do so.

The ceramic frame 21 is arranged 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 to the inner surface P3. The heat sink 11 may have a side surface P4b flatly connected to the outer surface P4a of the ceramic frame 21. The outer edge of the ceramic frame 21 may have a rectangular shape as shown in FIG. 1 in the in-plane direction perpendicular to the thickness direction. 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.

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

The inventor has confirmed that the ceramic frame 21 and the heat sink 11 are bonded to each other with sufficient strength. Furthermore, it was confirmed by optical microscope observation that the ceramic frame 21 and the heat sink 11 were directly bonded to each other. In this specification, the expression "directly joined" means that no components other than those originating from the heat sink 11 and the ceramic frame 21 are detected at the joint. For example, if the heat sink 11 contains Cu and the ceramic frame 21 contains silica and/or manganese, the inventor estimates that molten Cu and silica and/or manganese will be mixed together in the firing process described below. may form the extremely thin reaction layer mentioned above. Note that the above components can be verified by a simple method using an electron microscope or by energy dispersive X-ray spectroscopy (EDX), as described below.

The package 51 may have a lead frame 30 (metal terminal). The lead frame 30 is provided on the ceramic frame 21 and separated from the heat sink 11 by the ceramic frame 21. The lead frame 30 constitutes 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 to each other. This bonding material may be formed, for example, by Ag sinter bonding, in which case the bonding material is a mixture of a thermosetting resin (eg, an epoxy resin or a silicone resin) and Ag particles. Moreover, silver solder may be used for this bonding material. In this case, a metallized layer for silver solder is usually formed on the ceramic frame 21 in advance. As an example of a method for forming a metallized layer, first, before a firing process (to be described in detail later) for forming the ceramic frame 21 and the heat sink 11, a metallized layer is formed on a green sheet that will become the ceramic frame 21. Layers of paste are printed. Specifically, first, a metal powder of at least one of W, Mo, and Cu is mixed with additives, a resin, a solvent, etc., and if necessary, ceramic powder is added and kneaded. A paste is made. This paste is printed, for example, by screen printing, on the green sheet prepared in the previous step. After this printing, the green sheet is dried, for example, at a temperature of 110° C. for 5 minutes. Alternatively, this metallized layer may be applied to a green sheet containing metal on a green sheet that will become the ceramic frame 21 before the firing process (to be described in detail later) for forming the ceramic frame 21 and the heat sink 11. It may be formed by laminating.

The lid 80 (FIGS. 1 and 2) may be made of a ceramic material, which may contain alumina as a main component, for example substantially alumina. Alternatively, the lid body 80 may contain resin. The resin is, for example, a liquid crystal polymer. Note that an inorganic filler may be dispersed in the resin, and the inorganic filler is, for example, silica particles. By dispersing the inorganic filler in the resin, the strength and durability of the lid 80 can be increased.

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 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.

The semiconductor element 8 may be mounted using, for example, a solder material (not shown). After mounting the semiconductor device 8, wires 9 (FIG. 2) may be formed to electrically connect the semiconductor device 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. The adhesive layer 70 may have a portion provided on the ceramic frame 21 via the lead frame 30, as shown in FIG. 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.

(Configuration of heat sink)
FIG. 4 is a partially enlarged view of FIG. 3 showing the package 51. As shown in FIG. Heat sink 11 includes a plurality of layers LF1 to LF9. Here, a case in which the number of layers included in the heat sink 11 is nine will be described in detail, but this number may be selected depending on the design of the heat sink 11. The layers LF1 to LF9 are laminated in order from the heat dissipation surface P1 to the main surface P2 in the thickness direction. Each of the plurality of layers LF1 to LF9 corresponds to a plurality of green sheets LG1 to LG9 (FIG. 7), which will be described later. The interfaces of the green sheets LG1 to LG9 (FIG. 7) are the lamination interfaces of the green sheet laminate SG. After the firing process, this laminated interface can hardly be recognized as a clear boundary.

The composition ratio of each layer can be measured as follows. When a cross section like the one shown in FIG. 4 is observed in the backscattered electron mode of a scanning electron microscope, an image with a contrast corresponding to the difference in atomic number is obtained. When the composition includes Cu and W, W has a higher atomic number than Cu, and the signal intensity of reflected electrons is higher. Therefore, a layer with a low proportion of Cu, that is, a layer with a high proportion of W, produces a bright image. On the other hand, a layer with a high proportion of Cu, that is, a layer with a low proportion of W, produces a dark image. The composition ratio can be evaluated based on this contrast. As a more rigorous evaluation method, for example, component analysis using EDX may be performed for each layer at several points in the thickness direction. Then, the average value of the composition ratios at the plurality of points of the layer may be used as the composition ratio of each layer.

Although there may be various configurations of the plurality of layers LF1 to LF9, first to third examples will be given below. Note that in these first to third examples, each of the layers LF1 to LF9 contains a plurality of elements in common. These multiple elements include copper (Cu) and at least one high melting point metal selected from the group consisting of tungsten (W) and molybdenum (Mo). In the following explanation, the case where these plural elements include Cu and W, and specifically, two of them, Cu and W, will be explained as an example. In other words, the following explanation will mainly be based on an example in which the layers LF1 to LF9 are made of a copper-tungsten (CuW) alloy. As a variant, Mo may be used instead of or in conjunction with W. The value of the composition ratio of the CuW alloy shall be expressed in weight percent of Cu in the CuW alloy. Here, since the heat sink 11 is made of a sintered material, if you have a standard manufacturing device for manufacturing a ceramic frame, you can use it to increase the composition ratio of the sintered material of the heat sink 11. can be easily adjusted.

(First example of multiple layer configuration)
In the first example, the heat sink 11 is configured such that the coefficient of linear expansion gradually increases from the layer LF1 to the layer LF9. Here, the composition ratios of the layers LF1 to LF9 are referred to as composition ratios C1 to C9. In this example, the composition ratio (Cu content) is gradually increased from composition ratio C1 to composition ratio C9. As a result, the coefficient of linear expansion gradually increases from the layer LF1 to the layer LF9.

Here, if m and n are integers satisfying the condition 1≦m<n≦9, and the layer LFm is regarded as the first layer and the layer LFn is regarded as the second layer, the following characteristics can be read from this example. .
- The first layer LFm contains the elements Cu and W at a first composition ratio Cm. The second layer LFn is disposed between the first layer LFm and the ceramic frame 21, and contains elements Cu and W at a second composition ratio Cn different from the first composition ratio Cm.
- the first layer LFm has a first coefficient of linear expansion; The second layer LFn has a second linear expansion coefficient larger than the first linear expansion coefficient.

Furthermore, if we focus on m and n that satisfy the conditions 1≦m<5 and 5<n≦9, the following characteristics can also be read from this example.
- The first layer LFm is arranged between the heat dissipation surface P1 and the center position of the heat dissipation plate 11 in the thickness direction (the position of the layer LF5 in FIG. 4). The second layer LFn is arranged between the center position (the position of the layer LF5 in FIG. 4) and the ceramic frame 21.

(Second example of multiple layer configuration)
In the second example, the heat dissipation is performed such that the layers LF1 to LF6 and LF9 have a first coefficient of linear expansion, and the layers LF7 to LF8 have a second coefficient of linear expansion that is larger than the first coefficient of linear expansion. A plate 11 is constructed. In this example, the layers LF1 to LF6 and LF9 have a composition ratio Cm, and the layers LF7 to LF8 have a composition ratio Cn larger than the composition ratio Cm. As a result, the linear expansion coefficients of the layers LF7 to LF8 become larger than those of the layers LF1 to LF6 and LF9. Here, if the difference in linear expansion coefficient between the ceramic frame 21 and the heat sink 11 is too large, peeling may occur between the ceramic frame 21 and the heat sink 11. Further, it may be necessary to make subtle adjustments to the amount of warpage of the package 51. In order to solve these problems, LF9 having a coefficient of linear expansion smaller than that of layers LF7 to LF8 is laminated.

Here, if the layers LF1 to LF6 are regarded as the first layers and the layers LF7 to LF8 are regarded as the second layers, the following characteristics can be read from this example.
- The first layers LF1 to LF6 contain elements Cu and W at a first composition ratio Cm. The second layers LF7 to LF8 are arranged between the first layers LF1 to LF6 and the ceramic frame 21, and contain elements Cu and W at a second composition ratio Cn different from the first composition ratio Cm. contains.
- the first layers LF1 to LF6 have a first coefficient of linear expansion; The second layers LF7 to LF8 have a second coefficient of linear expansion larger than the first coefficient of linear expansion.
- Focusing on the layers LF1 to LF4 among the first layers LF1 to LF6, the first layers LF1 to LF4 among the first layers LF1 to LF6 have the heat dissipation surface P1 and the center of the heat dissipation plate 11 in the thickness direction. (the position of layer LF5 in FIG. 4). The second layers LF7 to LF8 are arranged between the center position (the position of the layer LF5 in FIG. 4) and the ceramic frame 21.

(Third example of multiple layer configuration)
In the third example, the heat sink 11 is arranged such that the layers LF1 to LF3 have a first coefficient of linear expansion, and the layers LF4 to LF9 have a second coefficient of linear expansion larger than the first coefficient of linear expansion. is configured. In this example, the layers LF1 to LF3 have a composition ratio Cm, and the layers LF4 to LF9 have a composition ratio Cn larger than the composition ratio Cm. As a result, the linear expansion coefficients of the layers LF4 to LF9 become larger than those of the layers LF1 to LF3.

Here, if the layers LF1 to LF3 are regarded as the first layers and the layers LF4 to LF9 are regarded as the second layers, the following characteristics can be read from this example.
- The first layers LF1 to LF3 contain elements Cu and W at a first composition ratio Cm. The second layers LF4 to LF9 are arranged between the first layers LF1 to LF3 and the ceramic frame 21, and contain elements Cu and W at a second composition ratio Cn different from the first composition ratio Cm. contains.
- the first layers LF1 to LF3 have a first coefficient of linear expansion; The second layers LF4 to LF9 have a second coefficient of linear expansion larger than the first coefficient of linear expansion.
- The first layers LF1 to LF3 are arranged between the heat dissipation surface P1 and the center position of the heat dissipation plate 11 in the thickness direction (the position of the layer LF5 in FIG. 4). Focusing on the layers LF6 to LF9 among the second layers LF4 to LF9, the second layers LF6 to LF9 among the second layers LF4 to LF9 have a center position (the position of the layer LF5 in FIG. 4) and a ceramic frame. It is arranged between the body 21 and the body 21.

(Package manufacturing method)
FIG. 5 is a flow diagram schematically showing a method for manufacturing the package 51 (FIG. 3) of the first to third examples. 6 to 9 are schematic partial cross-sectional views illustrating one step of the manufacturing method.

In step ST10 (FIG. 5), green sheets LG1 to LG9 (see FIG. 7, which will be described later), which become the layers LF1 to LF9 (FIG. 4), respectively, are formed by firing. Here, the first layer and the second layer (see the first to third examples above) are included in the layers LF1 to LF9. Therefore, step ST10 (FIG. 5) naturally includes step ST11 (FIG. 5) in which the first green sheet is formed by firing to become the first layer, and step ST11 (FIG. 5) in which the first green sheet is formed by firing to become the first layer. Step ST12 (FIG. 5) of forming a second green sheet to be used as a layer is included. Further, in step ST13 (FIG. 5), a ceramic green sheet 21G (see FIG. 7 described later) which will be fired to form the ceramic frame 21 is formed.

To form a green sheet, first a slurry is prepared. The slurry is obtained by mixing powder, which is a component of the sintered body, with a resin, a plasticizer, a solvent, and the like using a ball mill. The powders for the slurry for forming the ceramic frame 21 include, for example, Al ₂ O ₃ powder as the main component, SiO ₂ powder and/or MnCO ₃ powder as a sintering aid, and the like. The powders for the slurry for forming the layers LF1 to LF9 of the heat sink 11 include Cu powder and W powder. The slurry is processed into green sheets using the doctor blade method. The planar shape of the green sheet is determined depending on the shape of the intended part. The planar shape of the green sheet for forming the heat sink 11 is usually approximately rectangular. The planar shape of the ceramic green sheet 21G for forming the ceramic frame 21 is a frame shape with a portion corresponding to the cavity CV (FIG. 3) removed. Specifically, the ceramic 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.

In step ST20 (FIG. 5), the green sheets LG1 to LG9 (FIG. 7) and the ceramic green sheet 21G are laminated to form a laminate SG (FIGS. 6 and 7). Note that the laminate SG includes a laminate 11G of green sheets LG1 to LG9. The laminate 11G will become the heat sink 11 (FIG. 4) by being fired. In the laminate SG, a first green sheet that is fired to become a first layer (see the above-mentioned first to third examples) and a second green sheet that is fired to become a second layer (see the above-mentioned first to third examples). The second green sheet, which will be used as the first to third examples (see the above-mentioned first to third examples), and the ceramic green sheet 21G, which will be fired to form the ceramic frame 21, are laminated. There is.

Next, the laminated body 11G and the ceramic green sheet 21G are formed at a position where a break will be performed, which will be described later, using machining using a cutting edge CT (FIG. 6) or laser processing using a laser processing device (not shown). A trench (not shown) may be formed in each surface.

In step ST30 (FIG. 5), the stacked body SG (FIG. 6) is fired. Thereby, the stacked body SG changes into the fired body SF (FIG. 8). The firing temperature is, for example, 1100°C or higher and 1400°C. By setting the firing temperature to 1100° C. or higher, the laminate SG can be heated to a temperature higher than the melting point of Cu. Thereby, the heat sink 11 containing Cu can be formed with high quality. On the other hand, by setting the firing temperature to 1400° C. or lower, it is possible to avoid process difficulties caused by excessively high firing temperatures.

Next, a breaking process starting from the trench described above is performed as shown by the broken line BR (FIG. 8). As a result, the fired body SF is divided into multiple parts. Thereby, a plurality of fired bodies SF corresponding to the plurality of packages 51 (FIG. 3) are obtained (FIG. 9).

Next, the lead frame 30 (FIG. 3) is attached to the fired body SF. Thereby, a package 51 (FIG. 3) is obtained.

Note that in the above manufacturing method, plating treatment may be performed at an appropriate timing after the firing step. Further, the above manufacturing method is an example as described above, and various modifications may be applied. For example, instead of performing a breaking process on the fired body SF, a cutting process may be performed on the laminate SG before firing. Further, according to the above manufacturing method, the semiconductor element 8 (FIG. 2) is mounted at a timing after the breaking process, but instead of this timing, it is carried out at a timing after the baking process and before the breaking process. It's okay to be hurt.

FIG. 10 is a schematic cross-sectional view showing the configuration of a package 59 of a comparative example. FIG. 11 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 ceramic frame 29 instead of the heat sink 11 and the ceramic frame 21 (FIG. 3: Embodiment 1). Ceramic frame 29 is made of a ceramic material, typically alumina.

The material for the heat sink 19 is preferably pure copper from the viewpoint of thermal conductivity. However, the linear expansion coefficient of copper is larger than that of alumina. In the process of joining the ceramic frame 29 and the heat sink 19 with a brazing material, in the cooling process after heating to melt the brazing material, after the brazing material has hardened, the main surface P2 side of the heat sink 19 is attached to the ceramic frame. While the shrinkage is suppressed by being restrained by the body 29, the shrinkage is not suppressed on the heat radiation surface P1 side. As a result, the package 59 is warped in an upwardly convex manner in FIG. Therefore, it is conceivable to make the linear expansion coefficient of the heat sink 19 smaller so that it approaches the linear expansion coefficient of alumina. For example, since tungsten and molybdenum have a smaller coefficient of linear expansion than alumina, it is possible to use these metal elements as the material for the heat sink 19. In that case, the material of the heat sink 19 is typically a copper-tungsten alloy material formed by an impregnation method, or a cladding material having a laminated structure of copper and a copper-molybdenum alloy. In the case of the former material, the heat sink 19 has a substantially uniform coefficient of linear expansion over its entirety, so it is difficult to change the coefficient of linear expansion in the thickness direction to suppress warping of the package 59 due to thermal stress. Can not. In the case of the latter material, there is little flexibility in designing the coefficient of linear expansion of each layer in the laminated structure. If it were possible to apply many types of metal plates to the cladding material, some degree of design flexibility might be ensured. However, preparing many types of metal plates tends to be a heavy burden on manufacturing. Therefore, it is difficult to sufficiently and easily suppress warping of the package 59 due to thermal stress.

The ceramic frame 29 is joined to the heat sink 19 by a brazing material 26. The brazing material 26 has fluidity when it is formed, and as shown in FIG. 10, flows inward from the inner peripheral surface (the surface facing the cavity CV) of the ceramic frame 29. The portion of the brazing material 26 that has flowed into the cavity CV forms a fillet 26f at the edge of the cavity CV. The distance into which the fillet flows, in other words, the width dimension of the fillet 26f tends to be larger than 25 μm. Therefore, in order to sufficiently reduce the possibility that the fillet 26f and the semiconductor element 8 interfere with each other, the distance L9 (FIG. 11) between the semiconductor element 8 and the inner surface of the ceramic frame 29 is set to be larger than 25 μm. There is a need. As a result of having to leave a large space between the semiconductor element 8 and the ceramic frame 29 in this way, the mounting area in the cavity CV (the area of the area where the semiconductor element 8 can be mounted) becomes small. Also, the length of the wire 9 increases, which usually leads to deterioration of the electrical properties, such as an unintended increase in inductance.

As the brazing filler metal 26, an Ag brazing filler metal is typically used. When the brazing filler metal 26 contains Ag, if a negative potential is applied to the lead frame 30 for a long period with reference to the potential of the heat sink 19, Ag migration tends to occur as shown by arrow MG (FIG. 11). Due to this Ag migration, the electrical insulation between the heat sink 19 and the lead frame 30 may become insufficient.

Furthermore, when the brazing filler metal 26 is formed, wettability of the molten brazing filler metal 26 needs to be ensured. For this purpose, it is necessary to form a plating layer having high wettability to the molten brazing material 26 on the surface of the ceramic frame 29 made of a ceramic material that faces the brazing material 26. Further, in preparation for forming this plating layer, it is usually necessary to form a metallized layer on the ceramic frame 29.

According to the first embodiment, as explained in the first to third examples above, the first layer included in the heat sink 11 contains a plurality of elements in the first composition ratio, and It has a linear expansion coefficient of Further, the second layer included in the heat sink 11 is disposed between the first layer and the ceramic frame 21, contains a plurality of elements at a second composition ratio different from the first composition ratio, and contains a plurality of elements at a second composition ratio different from the first composition ratio. It has a second linear expansion coefficient that is larger than the first linear expansion coefficient. According to these characteristics, the first layer is disposed closer to the heat radiation surface P1 and has a smaller coefficient of linear expansion than the second layer. Therefore, the shrinkage of the heat dissipation surface P1 side of the heat dissipation plate 11 when the temperature falls is reduced, so that the warpage of the package 51 (specifically, the upward convex warpage in FIG. 3) is suppressed. Therefore, warping of the package 51 due to the difference in linear expansion coefficient between the heat sink 11 and the ceramic frame 21 is suppressed. This warpage can be easily and sufficiently suppressed by optimizing the composition ratio and distribution of the sintered material forming the heat sink 11. As described above, warping of the package 51 due to the difference in linear expansion coefficient between the heat sink 11 and the ceramic frame 21 can be sufficiently and easily suppressed.

Further, the first layer included in the heat sink 11 is disposed between the heat sink surface P1 of the heat sink 11 and the center position of the heat sink 11 in the thickness direction, and has a first linear expansion coefficient. Furthermore, the second layer included in the heat sink 11 is disposed between the center position and the ceramic frame 21, and has a second coefficient of linear expansion larger than the first coefficient of linear expansion. According to these characteristics, the first layer is disposed closer to the heat radiation surface P1 and has a smaller coefficient of linear expansion than the second layer. Therefore, the shrinkage of the heat dissipation surface P1 side of the heat dissipation plate 11 when the temperature falls is reduced, so that the warpage of the package 51 (specifically, the upward convex warpage in FIG. 3) is suppressed. Therefore, warping of the package 51 due to the difference in linear expansion coefficient between the heat sink 11 and the ceramic frame 21 is suppressed. This warpage can be easily and sufficiently suppressed by optimizing the composition ratio and distribution of the sintered material forming the heat sink 11. As described above, warping of the package 51 due to the difference in linear expansion coefficient between the heat sink 11 and the ceramic frame 21 can be sufficiently and easily suppressed.

Moreover, the ceramic frame 21 and the heat sink 11 are directly joined. Thereby, the brazing material 26 (FIG. 11: comparative example) is not required for joining the ceramic frame 21 and the heat sink 11. Therefore, the brazing material 26 flowing into the cavity CV can be prevented from interfering with the mounting of the semiconductor element 8. Therefore, the distance L1 (FIG. 2) between the semiconductor element 8 and the inner surface P3 of the ceramic frame 21 can be made small, for example, 25 μm or less. In other words, the semiconductor element 8 can be mounted close to the ceramic frame 21. Therefore, the mounting area in the cavity CV can be made larger. Also, the length of the wire 9 is reduced, which usually leads to improved electrical properties. Furthermore, since there is no need to use the brazing filler metal 26 (FIG. 11: comparative example), it is possible to avoid the migration phenomenon of Ag contained in the brazing filler metal from occurring between the heat sink 11 and the lead frame 30. . Further, a layer for ensuring wettability of the brazing material 26 (typically, the above-mentioned plating layer and metallized layer) is not required.

The heat sink 11 (FIG. 2) may have a side surface P4b flatly connected to the outer surface P4a of the ceramic frame 21. In this case, the mounting area (the area of the area where the semiconductor element 8 and the like can be mounted) can be easily secured while avoiding the location between the outer surface P4a and the side surface P4b from becoming a starting point for destruction of the package 51. A part of such side surface P4b may be a fractured surface in the breaking process (FIG. 8). Typical forms in which the side surface P4b is not flatly connected to the outer surface P4a include a form in which the outer surface P4a protrudes outward from the side surface P4b, or a form in which the outer surface P4a is located inside the side surface P4b. In the former form, there is a risk that the protruding portion may become a starting point for destruction. In the latter configuration, since the outer edge of the ceramic frame 21 is inward, the inner edge of the ceramic frame 21 is also inward, as long as the width of the ceramic frame 21 needs to be maintained at a predetermined dimension. , the mounting area becomes smaller.

Note that as a modification, the heat sink 11 (FIG. 3) to which the ceramic frame 21 is not attached may be produced. For example, in the method for manufacturing the fired body SF, by omitting the formation of the ceramic green sheet 21G (FIG. 6), the heat sink 11 to which no other members are attached can be obtained. Other members may be attached to the heat sink 11 thus obtained. For example, if a frame is attached, a package is obtained.

<Modifications related to cavities>
Although the package 51 of the first embodiment has the cavity CV (FIG. 2), as a modification, a configuration with or without the cavity CV may be used. Specifically, a ceramic base may be used instead of the ceramic frame 21 constituting the cavity CV, and in that case, the ceramic base is attached to the heat sink 11 instead of the ceramic frame 21. Specifically, a joined body of the heat sink 11 and a ceramic base disposed on the main surface P2 of the heat sink 11 may be used. This joint may not have a cavity CV. The ceramic substrate is, for example, a ceramic flat plate. The ceramic flat plate has a first surface attached to the main surface P2 of the heat sink 11 and a second surface opposite to the first surface. A lead frame 30 may be attached to the second surface of the ceramic flat plate. To produce a semiconductor module, a semiconductor element 8 may be mounted on the second side of the ceramic flat plate. Even if the above-mentioned bonded body does not have a cavity CV, the semiconductor element 8 can be sealed within the cavity.

<Embodiments 2 to 5>
FIG. 12 is a schematic cross-sectional view showing the configuration of the heat sink 11 and the ceramic frame 21 included in the package 51 (FIG. 3) according to the first embodiment described above. Note that for convenience of explanation, the illustration in FIG. 12 is simpler than the illustration in FIG. 3. The configurations of packages 52 to 56 according to embodiments 2 to 6, respectively, will be described below in comparison with FIG. 12.

FIG. 13 is a schematic cross-sectional view showing the structure of the package 52 according to the second embodiment. The package 52 has a ceramic frame 22 instead of the ceramic frame 21 (FIG. 12). The ceramic frame 22 (specifically, the inner part thereof) is arranged on the main surface P2 of the heat sink 11. Regarding the position in the thickness direction, the ceramic frame 22 extends from a position above the main surface P2 of the heat sink 11 to a range between the main surface P2 of the heat sink 11 and the heat radiation surface P1. Note that the ceramic frame 22 may extend further, and in the example shown in FIG. 13, it extends to the position of the heat dissipation surface P1 of the heat dissipation plate 11. The ceramic frame 22 is separated from the side surface P4b of the heat sink 11.

FIG. 14 is a schematic cross-sectional view showing the structure of the package 53 according to the third embodiment. The package 53 has a ceramic frame 23 instead of the ceramic frame 21 (FIG. 12). The ceramic frame 23 has 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. Note that the boundary between the base portion 23a and the frame portion 23b (broken line in the figure) may be virtual. The frame portion 23b has an inner surface P3. In the third embodiment, the main surface P2 of the heat sink 11 has a joint surface P2b directly joined to the base 23a of the ceramic frame 23. In the example shown in FIG. 14, the entire main surface P2 is the joint surface P2b. Further, 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, it can be said that the cavity surface P2a faces the cavity CV.

FIG. 15 is a schematic cross-sectional view showing the structure of the package 54 according to the fourth embodiment. The package 54 has a ceramic frame 24 instead of the ceramic frame 21 (FIG. 12). The ceramic frame 24 (specifically, the inner part thereof) is arranged on the main surface P2 of the heat sink 11. Regarding the position in the thickness direction, the ceramic frame 24 extends from a position above the main surface P2 of the heat sink 11 to a range between the main surface P2 and the heat sink P1 of the heat sink 11. Note that the ceramic frame 24 may extend further, and in the example shown in FIG. 15, it extends to the position of the heat dissipation surface P1 of the heat dissipation plate 11. The side surface P4b of the heat sink 11 has a joint surface directly joined to the ceramic frame 24. In the example shown in FIG. 15, the entire side surface P4b is a joint surface, but only a part of the side surface P4b may be a joint surface.

The package 54 can be manufactured by firing a stack of the lower layer LY1 and the upper layer LY2. For example, the lower layer LY1 is formed as follows. First, a first unfired layer made of a material that becomes the ceramic frame 24 by firing is formed. Next, a through hole corresponding to the area where the heat sink 11 is arranged 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 by being fired is laminated on the first unfired layer so as to cover the through hole. Next, the mold is used again to push the portion of the second unfired layer into the through hole. Next, the portion of the second green layer that was not pressed in by the mold, in other words, the portion remaining on the top surface of the first green layer is removed. Thereby, the lower layer LY1 is obtained. The upper layer LY2 is obtained by removing a portion corresponding to the cavity CV from an unfired layer made of a material that becomes the ceramic frame 24 by firing. The package 54 is obtained by firing the laminate of the lower layer LY1 and the upper layer LY2. Note that a package 55 (FIG. 16), which will be described later, can also be manufactured by a method similar to this.

FIG. 16 is a schematic cross-sectional view showing the structure of a package 55 according to the fifth embodiment. The package 55 has a heat sink 15 and a ceramic frame 25 instead of the heat sink 11 and the ceramic frame 21 (FIG. 12). The ceramic frame 25 (specifically, the inner part thereof) is arranged 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 (broken line in FIG. 16) may be virtual. The main surface P2 of the heat sink 15 has a cavity surface P2a consisting of the cavity portion 15a and a joint surface P2b consisting of the support portion 15b. In the main surface P2 of the heat dissipation plate 15, the position of the cavity surface P2a and the position of the joint surface P2b are different in the thickness direction, and the latter position is closer to the heat dissipation 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 include a side wall surface P2c that is made up of the cavity portion 15a and connects the cavity surface P2a and the joint surface P2b. 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 joint surface directly joined to the ceramic frame 25. The side surface P4b of the support portion 15b may have a joint surface directly joined to the ceramic frame 25.

8: Semiconductor element 9: Wire (wiring member)
11, 15: Heat sink 21-25: Ceramic frame 31G: Ceramic green sheet 30: Lead frame (metal terminal)
51 to 55: Package 70: Adhesive layer 80: Lid body 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: Sintered body SG : Laminate

Claims (9)

A package having a cavity,
a heat dissipation plate made of a sintered material containing metal and having a heat dissipation surface and a main surface opposite to the heat dissipation surface in the thickness direction;
a ceramic frame disposed on the main surface of the heat sink and having an inner surface surrounding the cavity;
Equipped with
The heat sink is
a first layer containing a plurality of elements in a first composition ratio and having a first coefficient of linear expansion;
A first layer disposed between the first layer and the ceramic frame, containing the plurality of elements at a second composition ratio different from the first composition ratio, and having a coefficient of linear expansion greater than the first coefficient of linear expansion. a second layer having a linear expansion coefficient of 2;
Including the package. The package according to claim 1,
The first layer of the heat sink is disposed between the heat sink surface of the heat sink and a center position of the heat sink in the thickness direction,
The package, wherein the second layer of the heat sink is disposed between the center position and the ceramic frame. The package according to claim 1 or 2,
The package, wherein the plurality of elements include copper and at least one high melting point metal selected from the group consisting of tungsten and molybdenum. The package according to claim 1 or 2,
In the package, the main surface of the heat sink includes a cavity surface facing the cavity and a bonding surface directly bonded to the ceramic frame. The package according to claim 1 or 2,
The package, wherein the sintered material is a sintered metal material. The package according to claim 1 or 2,
The ceramic frame has an outer surface opposite to the inner surface, and the heat sink has a side surface that is flatly connected to the outer surface of the ceramic frame. A package having a cavity,
a heat dissipation plate made of a sintered material containing metal and having a heat dissipation surface and a main surface opposite to the heat dissipation surface in the thickness direction;
a ceramic frame disposed on the main surface of the heat sink and having an inner surface surrounding the cavity;
Equipped with
The heat sink is
a first layer disposed between the heat dissipation surface of the heat dissipation plate and a center position of the heat dissipation plate in the thickness direction, and having a first coefficient of linear expansion;
a second layer disposed between the center position and the ceramic frame and having a second linear expansion coefficient larger than the first linear expansion coefficient;
Including package. A method for manufacturing a package having a cavity, the package comprising a heat sink made of a sintered material containing metal and having a heat sink and a main surface opposite to the heat sink, and a heat sink on the main surface of the heat sink. a ceramic frame having an inner surface surrounding the cavity; the heat sink includes a first layer having a first coefficient of linear expansion; and a combination of the first layer and the ceramic frame. a second layer having a second linear expansion coefficient larger than the first linear expansion coefficient, the manufacturing method comprising:
forming a first green sheet that is fired to become the first layer of the heat sink;
forming a second green sheet that will become the second layer of the heat sink by being fired;
forming a ceramic green sheet that will become the ceramic frame by firing;
forming a laminate in which the first green sheet, the second green sheet, and the ceramic green sheet are laminated;
a step of firing the laminate;
A method for manufacturing a package, comprising: A method for manufacturing a package according to claim 8, comprising:
The method for manufacturing a package further comprises the step of removing a portion corresponding to the cavity from the ceramic green sheet before the step of forming the laminate.

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