Package

Abstract

To provide a package which can reduce thermal stress concentration in the package under temperature changes when manufacturing or using the package.SOLUTION: A package 51 has a cavity CV to be sealed with a lid body 80. The package 51 includes: a heat sink 10 made of a first metallic material which has, in a temperature range from 25 to 200°C, a first linear expansion coefficient; and a frame body 20 which is provided on the heat sink 10 and surrounds the cavity CV in plan view. The frame body 20 includes: a ceramic part 21 made of a ceramic material which has a second linear expansion coefficient lower than the first linear expansion coefficient in the temperature range; and a buffer part 22 which is disposed between the ceramic part 21 and the heat sink 10, and which is made of a buffer material having a third linear expansion coefficient lower than the first linear expansion coefficient but higher than the second linear expansion coefficient in the temperature range.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a package, and more particularly to a package having a cavity to be sealed by a lid. [Background technology]

[0002] Packages with cavities are often used to house electronic components such as power semiconductor devices. After the electronic components are mounted in the package cavity, a lid is attached to the package, hermetically sealing the cavity. This results in an electronic device with electronic components protected from the external environment. The bottom surface of the heat sink (the surface opposite the surface on which the electronic components are mounted) is typically 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. Heat from the electronic components is efficiently dissipated outside the package (typically to the support member) through the heat sink. This limits the temperature rise of the electronic components to, for example, around 150°C. However, depending on the external environment in which the electronic device is placed, the temperature of the package can drop to below freezing. Therefore, the electronic device must be able to withstand the heat cycle caused by these temperature differences.

[0003] According to the technology disclosed in Japanese Patent Laid-Open Publication No. 2003-282751 (Patent Document 1), a Cu or Cu-based metal plate is used as a heat sink. Cu is inexpensive yet has a high thermal conductivity exceeding 300 W / m·K. This allows the heat dissipation performance of the heat sink to be improved while reducing the material cost of the heat sink. According to this technology, a semiconductor element is first mounted on the heat sink by brazing. Next, a frame, to which external connection terminals have already been bonded, is bonded to the heat sink so as to surround the semiconductor element. By using a low-melting-point bonding material for this bonding, the frame is bonded at a temperature below the brazing temperature of the semiconductor element. Next, a lid is bonded to the top surface of the frame, sealing the cavity. This results in an electronic device.

[0004] Japanese Patent Laid-Open Publication No. 2005-243819 (Patent Document 2) discloses that CPC (registered trademark) is widely used for heat sinks. CPC is a composite metal plate (composite material) having a Cu-Mo alloy layer and Cu layers disposed above and below it. The linear expansion coefficient of CPC is lower than that of Cu. Therefore, by using CPC instead of Cu as a heat sink material, the linear expansion coefficient of the heat sink can be made closer to that of ceramic.

[0005] Japanese Patent Application Laid-Open Publication No. 2015-204426 (Patent Document 3) discloses a package for storing electronic components. The package includes a heat sink plate for dissipating heat generated by the electronic components and a frame-shaped ceramic frame brazed to the heat sink plate. The ceramic frame is a frame-shaped assembly of an upper sheet and a lower sheet. The ceramic frame has a step on the inner periphery side, where the lower sheet is recessed from the upper sheet. When viewed from above, the upper surface of the heat sink plate does not have any flow of brazing material inside the inner periphery of the upper sheet. The heat sink plate is made of a material with a thermal expansion coefficient similar to that of ceramic.

[0006] Korean Patent No. 10-1175613 (Patent Document 4) discloses a package in which a device that dissipates heat during operation is mounted. The package includes a first base, a frame-shaped second base bonded to the first base, an insulator bonded to the second base, and a lead frame bonded to the insulator. The first and second bases may be made of metal materials, and the second base may have a linear expansion coefficient smaller than that of the first base. The metal material of the first base may be copper (Cu) or a Cu alloy, and the metal material of the second base may be any one of Kovar®, iron (Fe)-nickel (Ni) alloy, molybdenum (Mo), Mo alloy, tungsten (W), and W alloy, or an alloy thereof. The first and second bases may be bonded by laser welding or seam welding. The insulator may be made of a ceramic material and may be bonded to the second base by brazing. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-282751 [Patent Document 2] Japanese Patent Application Laid-Open No. 2005-243819 [Patent Document 3] Japanese Patent Application Laid-Open No. 2015-204426 [Patent Document 4] Korean Patent No. 10-1175613 Summary of the Invention [Problem to be solved by the invention]

[0008] To fully improve the thermal conductivity or reduce the cost of a heat sink, it is often difficult to adequately match the thermal expansion coefficient of the heat sink to that of the ceramic. If the thermal expansion coefficients differ significantly, thermal stress concentrations can become a problem in the package when the package is manufactured or subjected to temperature changes during use.

[0009] The present invention has been made to solve the above-mentioned problems, and its object is to provide a package that can reduce thermal stress concentration in the package when subjected to temperature changes during package manufacture or use. [Means for solving the problem]

[0010] In one embodiment, the package has a cavity to be sealed by a lid. The package includes: a heat sink made of a first metal material having a first linear expansion coefficient in a temperature range between 25°C and 200°C; and a frame provided on the heat sink and surrounding the cavity in a plan view. The frame includes: a ceramic part made of a ceramic material having a second linear expansion coefficient smaller than the first linear expansion coefficient in the temperature range; and a buffer part disposed between the ceramic part and the heat sink and made of a buffer material having a third linear expansion coefficient smaller than the first linear expansion coefficient and larger than the second linear expansion coefficient in the temperature range. [Effects of the Invention]

[0011] In one embodiment of the package, the third linear expansion coefficient of the buffer portion is smaller than the first linear expansion coefficient of the heat sink and larger than the second linear expansion coefficient of the ceramic portion. This allows the buffer portion to buffer the thermal expansion difference between the heat sink and the ceramic portion. This reduces thermal stress concentration in the package when subjected to temperature changes during package manufacturing or use.

[0012] The buffer material may include a second metallic material different from the first metallic material, which can prevent brittle fracture of the buffer portion under thermal stress compared to when the buffer material does not include any metallic material.

[0013] The buffer material may include stainless steel. In this case, brittle fracture of the buffer portion under thermal stress can be prevented compared to when the buffer material does not include any metal material. When stainless steel is used, its composition can be easily controlled to adjust the third linear expansion coefficient of the buffer material to a value smaller than the first linear expansion coefficient of the heat sink and larger than the second linear expansion coefficient of the ceramic portion. The stainless steel may contain chromium atoms in an amount of 11.5 mass percent or more and 18 mass percent or less. In this case, the third linear expansion coefficient of the buffer material can be approximately 11 ppm / °C. This allows the second linear expansion coefficient of the ceramic material constituting the ceramic portion to be large, close to 11 ppm / °C, while still satisfying the condition that the second linear expansion coefficient of the ceramic material constituting the ceramic portion is smaller than the third linear expansion coefficient of the buffer material. By selecting a ceramic material with a larger second linear expansion coefficient, the thermal expansion difference between the ceramic portion made of the ceramic material and the heat sink can be suppressed.

[0014] The second linear expansion coefficient of the ceramic material may be 9 ppm / K or more. In this case, it is possible to suppress the difference in thermal expansion between the ceramic part made of the ceramic material and the heat sink having a relatively high first linear expansion coefficient.

[0015] The ceramic material may contain zirconia. In this case, the second linear expansion coefficient of the ceramic material can be set to 9 ppm / K or more. This makes it possible to suppress the difference in thermal expansion between the ceramic part made of the ceramic material and the heat sink.

[0016] The first metal material may have a thermal conductivity of greater than 300 W / m·K. In this case, the heat dissipation performance of the heat sink made of the first metal material can be improved.

[0017] The first metal material may contain copper with a purity of 95.0 weight percent or more. In this case, a thermal conductivity of greater than approximately 300 W / m·K can be obtained. This improves the heat dissipation performance of the heat sink made of the first metal material.

[0018] The first metallic material may be a non-composite material. In this case, the first linear expansion coefficient of the first metallic material cannot be suppressed by the material design of the composite material. As a result, the thermal expansion difference between the heat sink and the ceramic part tends to be large. However, even in such a case, for the reasons described above, stress concentration in the package can be reduced when the package is subjected to temperature changes during manufacturing or use.

[0019] The buffer portion may be bonded to the heat sink and the ceramic portion using a bonding material. This bonding process usually requires heating and subsequent cooling, but the thermal stress concentration that occurs during this process can be reduced for the reasons described above. The bonding material may contain resin or nanometal particles. In this case, the maximum temperature required for the bonding process is lower than when the bonding material is a typical brazing material. This reduces the thermal stress that occurs during the bonding process.

[0020] The ceramic portion has a ceramic surface facing the heat sink, the ceramic surface having an inner edge surrounding the cavity, the inner edge including a bent portion. The bent portion may be separated from the buffer portion in a plan view. In this case, thermal stress concentration at the bent portion can be suppressed. The ceramic surface of the ceramic portion has an outer edge surrounding the inner edge. At least a portion of the outer edge may overlap the buffer portion in a plan view. In this case, it is easier to ensure sufficient rigidity of the buffer portion while designing the buffer portion so that the bent portion of the inner edge of the ceramic surface is separated from the buffer portion in a plan view.

[0021] The objects, features, aspects, and advantages of the present invention will become more apparent from the following detailed description and the accompanying drawings. [Brief explanation of the drawings]

[0022] [Figure 1] 1 is a schematic perspective view showing the configuration of an electronic device according to a first embodiment, with a portion thereof omitted so that the inside of a cavity can be seen. [Figure 2] 2 is a schematic cross-sectional view of the electronic device of FIG. 1 taken along line II-II. [Figure 3] 3 is a schematic cross-sectional view showing the configuration of a package as a component of the electronic device of FIG. 2. FIG. [Figure 4] FIG. 1 is a graph illustrating the temperature dependence of the coefficient of thermal expansion (CTE) of each of copper (Cu), alumina (Al 2 O 3 ), and a composite material (CPC). [Figure 5] FIG. 10 is a plan view showing dimensions of a configuration used in simulation conditions for thermal stress caused by a bonding process in package manufacturing. [Figure 6] FIG. 10 is a graph showing simulation results of maximum values ​​of thermal stress in the ceramic portion of the frame caused by a bonding process in the manufacture of a package. [Figure 7] FIG. 7 is a graph showing the tendency of the distribution of thermal stress in the ceramic part of the frame in the simulation results of FIG. 6. [Figure 8] FIG. 10 is a schematic cross-sectional view showing the configuration of a package according to a second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0023] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In this specification, unless otherwise specified, metal can mean either a pure metal or an alloy. Furthermore, plan view means projection onto a plane perpendicular to the thickness direction. Unless otherwise specified, the coefficient of thermal expansion (CTE) is expressed as a linear expansion coefficient. When the linear expansion coefficient has non-negligible anisotropy, the linear expansion coefficient in the in-plane direction is used. The in-plane direction is the direction perpendicular to the thickness direction.

[0024] <First Embodiment> FIG. 1 is a schematic perspective view showing the configuration of an electronic device 90 according to a first embodiment. FIG. 2 is a schematic cross-sectional view of the electronic device 90 taken along line II-II in FIG. 1. The electronic device 90 includes a package 51, a lid 80, and an electronic component 8. The electronic device 90 may also include an adhesive layer 70. The electronic device 90 may also include wires 9 (wiring members). Note that in FIG. 1, the lid 80 and the adhesive layer 70 are partially omitted so that the interior of a cavity CV of the package 51 can be partially seen. The electronic component 8 may be a power semiconductor element, in which case the electronic device 90 is a power module. The power semiconductor element may be for radio frequency (RF) use, in which case the electronic device 90 is an RF power module. Note that although one electronic component 8 is shown in FIGS. 1 and 2, multiple electronic components 8 may be mounted in the package 51.

[0025] Fig. 3 is a schematic cross-sectional view showing the configuration of a package 51 as a component of an electronic device 90 (Fig. 2). When the package 51 is prepared for manufacturing the electronic device 90, as shown in Fig. 3, an electronic component 8 has not yet been mounted. The package 51 has a cavity CV to be sealed by a lid 80. The package 51 includes a heat sink 10, a frame 20, and a lead frame 30 (metal terminals).

[0026] The heat sink 10 has a bottom surface BT and a mounting surface MT opposite the bottom surface BT in the thickness direction. The heat sink 10 is made of a first metal material (hereinafter also referred to as heat sink material). The heat sink material has a first coefficient of linear expansion (hereinafter also referred to as CTE1) in a temperature range between 25°C and 200°C. In other words, when the heat sink 10 is at 25°C, the dimension L 25 and has a dimension L at 200°C. 200 CTE1 has CTE1={(L 200 -L 25 ) / (200-25)} / L 25 The definitions of CTE2 and CTE3 described below in relation to other components are similar.

[0027] To improve the heat dissipation performance of the heat sink 10, the heat sink material preferably has a high thermal conductivity, specifically, a thermal conductivity of greater than 300 W / m·K. Such a high thermal conductivity can be easily achieved by the heat sink material containing a high proportion of Cu. To improve thermal conductivity, the heat sink material preferably contains Cu at a purity of 95.0 weight percent (wt%) or more, more preferably 99.8 wt% or more. The heat sink material may be a non-composite material. A non-composite material is a pure metal or alloy material and does not have a layered structure like a CPC.

[0028] The frame 20 is provided on the outer periphery of the mounting surface MT of the heat sink 10 and surrounds the cavity CV in a plan view. The outer edge of the frame 20 may have a rectangular shape, as shown in FIG. 1, with each side measuring, for example, 10 mm or more and 40 mm or less. The thickness of the frame 20 is, for example, 0.25 mm or more and 1.25 mm or less. If the thickness of the frame 20 is less than 0.25 mm, the height of the cavity CV is likely to be insufficient. If the thickness of the frame 20 is greater than 1.25 mm, the length of the wire 9 (FIG. 2) that needs to be connected to the lead frame 30 on the frame 20 increases, resulting in an increase in the inductance of the wire 9. An increase in the inductance of the wire 9 is generally undesirable from the viewpoint of electrical characteristics.

[0029] The frame 20 includes a ceramic portion 21 and a buffer portion 22. The buffer portion 22 is disposed between the ceramic portion 21 and the heat sink 10. In other words, the ceramic portion 21 is disposed on the heat sink 10 via the buffer portion 22. The buffer portion 22 may be bonded to the heat sink 10 and the ceramic portion 21 using a bonding material (not shown). The bonding material may contain a resin, specifically a mixture of a thermosetting resin (e.g., epoxy resin or silicone resin) and Ag particles. Alternatively, the bonding material may be a low-temperature sintering material, specifically a sintering material containing at least one of Ag particles and Cu particles. These particles may be nanometal particles. Nanometal particles are metal particles with a diameter of 100 nm or less. The thickness of the bonding material (the vertical dimension in FIG. 3 ) may be sufficiently smaller than the thicknesses of the ceramic portion 21, the buffer portion 22, and the heat sink 10. In this case, the influence of the bonding material can be substantially ignored when considering thermal stress in the package 51. The thickness of the bonding material is, for example, not less than 0.01 mm and not more than 0.2 mm.

[0030] The ceramic portion 21 is made of a ceramic material having a CTE2 (second coefficient of linear expansion) smaller than CTE1. CTE2 is preferably 9 ppm / K or greater. The ceramic material may contain zirconia (ZrO2) or may be substantially zirconia. The thickness of the ceramic portion 21 may be 0.2 mm or greater and 1.0 mm or less. A thickness of 0.2 mm or greater allows the ceramic portion 21 to be easily formed by firing a green sheet.

[0031] The buffer section 22 is made of a buffer material having a CTE3 (third coefficient of linear expansion) smaller than CTE1 and larger than CTE2. The buffer material preferably includes a second metallic material different from the first metallic material described above, and may be substantially the second metallic material. The second metallic material is preferably stainless steel, and more preferably an Fe-Cr (chromium) alloy. The Fe-Cr alloy contains Fe atoms as the main component and preferably contains 11.5 wt% to 18 wt% Cr atoms. The Fe-Cr alloy may further contain other trace elements, but the total amount is typically less than 3 wt%. Commonly used Fe-Cr alloys with such compositions include 18Cr stainless steel (e.g., a material known as SUS430) and 13Cr stainless steel (e.g., a material known as SUS410 or SUS403). The Cr content of SUS430 is 16 wt% to 18 wt%. The Cr atom content of SUS410 and SUS403 is 11.5 wt% or more and 13 wt% or less. Of these three examples, SUS430 is usually the least expensive material. The thickness of the buffer portion 22 may be 0.05 mm or more and 0.5 mm or less. By setting the thickness to 0.05 mm or more, the effect of the buffer portion 22 can be more fully obtained.

[0032] The lead frame 30 forms an electrical path connecting the inside and outside of the cavity CV. The material of the lead frame 30 is, for example, an Fe-Ni alloy, Cu, or a Cu alloy. The Fe-Ni alloy is, for example, a 42 alloy. The 42 alloy contains Fe atoms as the main component and approximately 42 wt% Ni atoms. The lead frame 30 is provided on the ceramic portion 21 of the frame 20. A bonding material (not shown) may be provided between the lead frame 30 and the ceramic portion 21 to bond them to each other. This bonding material may be made of the same material as the bonding material described above.

[0033] The ceramic portion 21 has a ceramic surface SC (FIG. 3) facing the heat sink 10. The ceramic surface SC has an inner edge PI that surrounds the cavity CV and an outer edge PE that surrounds the inner edge. The inner edge PI includes a bent portion BD. The bent portion BD may be one of the four corners of a rectangular shape. In this embodiment, the ceramic portion 21 and the buffer portion 22 may substantially overlap each other in a plan view. In other words, the inner edge PI and the outer edge PE of the ceramic surface SC may substantially coincide with the inner edge and the outer edge of the upper surface of the buffer portion 22 (the surface facing the ceramic surface SC), respectively.

[0034] Next, an example of a method for manufacturing the electronic device 90 will be described below.

[0035] A package 51 (FIG. 3) is prepared. An electronic component 8 is mounted on a mounting surface MT of a heat sink 10 of the package 51. This mounting may be performed by soldering. In other words, a solder material may be used as a mounting material for mounting the electronic component 8. Next, the electronic component 8 is electrically connected to the lead frame 30 by a wire 9. The wire 9 may be formed by wire bonding.

[0036] A lid 80 (FIGS. 1 and 2) is prepared. The lid 80 may be made of a ceramic material, which may contain alumina as a main component, for example, substantially alumina. Alternatively, the lid 80 may contain a resin. The resin may be, for example, a liquid crystal polymer. An inorganic filler may be dispersed in the resin, and the inorganic filler may be, for example, silica particles. Dispersing the inorganic filler in the resin can increase the strength and durability of the lid 80.

[0037] Next, the lid 80 is placed on the frame 20 with the lead frame 30 provided thereon, via the adhesive layer 70. In this example, the adhesive layer 70 contains a thermosetting resin and is in a semi-cured state at the time of placement. The adhesive layer 70 is provided on the frame 20 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 frame 20 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. The lid 80 may have an inner surface 81i facing the cavity CV (FIG. 1) and an opposite outer surface 81o. Typically, the inner surface 81i is provided with a frame portion 81p, which is a protrusion having a frame shape roughly corresponding to the frame shape of the ceramic frame 61. In this case, the adhesive layer 70 contacts the frame portion 81p.

[0038] Next, the lid 80 is pressed against the frame 20 with a predetermined load. The appropriate load depends on the dimensional design of the package 51, but is, for example, about 500 g or more and 1 kg or less. While the load is being applied, the adhesive layer 70 is heated. The heated adhesive layer 70 first changes to a softened state. This reduces the viscosity of the adhesive layer 70. As a result, the adhesive layer 70 wets and spreads. Thereafter, as the curing reaction due to heating progresses, the adhesive layer 70 changes to a hardened state, and as a result, the adhesive layer 70 bonds the lid 80 and the frame 20 together.

[0039] The adhesive layer 70 may contain at least one of epoxy resin, phenol resin, and silicone resin as its main component. Epoxy resin is particularly preferable because it has a good balance of heat resistance, mechanical strength, and chemical resistance. To optimally maintain these properties, the content of the epoxy resin as the main component is preferably 20 to 40 wt%, with the remainder being composed of auxiliary components such as a curing agent. Specifically, the auxiliary components may be, for example, 1 to 10 wt% curing agent, 50 to 70 wt% inorganic filler, 0.5 to 2 wt% coupling agent, 0.5 to 2 wt% catalyst, and 0.1 to 5 wt% low-stress agent. A phenoxy resin compound may be used as the curing agent. Silica may be used as the inorganic filler. Organic phosphorus or boron salt may be used as the catalyst. Silicone may be used as the low-stress agent. The adhesive layer 70 may have a flexural modulus smaller than that of the lid 80.

[0040] As a result of the above, a configuration is obtained in which the lid 80 seals the cavity CV, as shown in Figures 1 and 2. In other words, an electronic device 90 (Figures 1 and 2) is obtained. The bottom surface BT (Figure 2) of the heat sink 10 of the electronic device 90 is to be attached to a support member (not shown). The support member is, for example, a mounting board or a heat dissipation member. The heat sink 10 may have a through-hole (not shown) through which a fastener (e.g., a screw) for attachment to the support member passes.

[0041] Figure 4 is a graph illustrating the temperature dependence of the CTE of Cu, Al2O3, and CPC. Cu has a significantly larger CTE than Al2O3, while CPC has a similar CTE. Therefore, if a frame for forming a cavity in a package is made of Al2O3, using a heat sink made of CPC rather than Cu can significantly reduce the difference in thermal expansion between the frame and the heat sink. However, to improve the heat dissipation performance of the heat sink, it may be necessary to use a heat sink material with a higher thermal conductivity than that of CPC, typically substantially pure Cu. Furthermore, because CPC is a relatively expensive composite material, it may be necessary to use a cheaper non-composite material, typically substantially pure Cu. However, when a Cu heat sink is simply bonded to an Al2O3 frame with a bonding material, the large difference in CTE between the two materials can easily cause thermal stress concentration problems in the package during temperature changes during package manufacturing or use.

[0042] According to this embodiment, the CTE3 of the buffer portion 22 is smaller than the CTE1 of the heat sink 10 and larger than the CTE2 of the ceramic portion 21. This allows the difference in thermal expansion between the heat sink 10 and the ceramic portion 21 to be buffered by the buffer portion 22. This makes it possible to reduce the concentration of thermal stress in the package 51 when the package 51 is subjected to temperature changes during its manufacture or use.

[0043] By including a metal material (e.g., stainless steel) in the buffer material, brittle fracture of the buffer portion 22 under thermal stress can be prevented compared to a buffer material that does not include any metal material (typically a ceramic material). When stainless steel is used, its composition can be easily controlled to adjust the CTE3 of the buffer material to a value smaller than the CTE1 of the heat sink 10 and larger than the CTE2 of the ceramic portion 21. By including stainless steel in the buffer material with a Cr content of 11.5 wt% or more and 18 wt% or less, the CTE3 of the buffer material can be approximately 11 ppm / °C. This allows the CTE2 of the ceramic material constituting the ceramic portion 21 to be large, close to 11 ppm / °C, while still satisfying the condition that the CTE2 of the ceramic material constituting the ceramic portion 21 must be smaller than the CTE3 of the buffer material. By selecting a ceramic material with a larger CTE2, the thermal expansion difference between the ceramic portion 21 made of that ceramic material and the heat sink 10 can be reduced.

[0044] By making the CTE2 of the ceramic material 9 ppm / K or more, it is possible to suppress the difference in thermal expansion between the ceramic part 21 made of the ceramic material and the heat sink 10 having a relatively high CTE1. By making the ceramic material contain zirconia, it is possible to make the CTE2 of the ceramic material 9 ppm / K or more.

[0045] The heat sink material has a thermal conductivity greater than 300 W / m·K, which improves the heat dissipation performance of the heat sink 10. By including Cu with a purity of 95.0 wt% or greater in the heat sink material, a thermal conductivity greater than approximately 300 W / m·K can be easily achieved. If the heat sink material is a non-composite material, the CTE1 of the heat sink material cannot be controlled by the material design of the composite material. As a result, the thermal expansion difference between the heat sink 10 and the ceramic portion 21 tends to be large. However, even in such a case, for the reasons described above, stress concentration in the package 51 can be reduced when subjected to temperature changes during the manufacture or use of the package 51.

[0046] The buffer portion 22 is bonded to the heat sink 10 and the ceramic portion 21 using a bonding material. This bonding process usually requires heating and subsequent cooling, but the thermal stress concentration that occurs during this process can be reduced for the reasons described above. The bonding material may contain resin or nanometal particles. In this case, the maximum temperature required for the bonding process is lower than when the bonding material is a typical brazing material. This reduces the thermal stress that occurs during the bonding process.

[0047] The linear expansion coefficient is obtained by measuring the displacement when the temperature is increased from 25°C using an optical interferometric method or a push-rod dilatometer. The thermal conductivity is measured using a flash method. The material composition is measured using ICP (Inductively Coupled Plasma) analysis. Samples for measuring the various physical properties described above may be obtained by disassembling the electronic device 90 or package 51 into individual components.

[0048] Next, a simulation of thermal stress caused by the bonding process in package manufacturing will be described below. Figure 5 is a plan view showing the dimensions of the configuration used in the simulation. The physical properties of the materials assumed in the simulation are listed in Table 1 below. Alumina and zirconia are ceramic materials that form the ceramic portion 21 of the frame 20. 42 alloy is the material that forms the lead frame 30. Cu is the material that forms the heat sink 10. SUS430 is the material that forms the buffer portion 22. In Table 1, two CTEs are shown: one for 200°C and one for 800°C, with 25°C as the reference temperature. In other words, the CTEs are shown for the range between 25°C and 200°C and the range between 25°C and 800°C.

[0049] [Table 1]

[0050] Simulations were performed for each of No. 1 to No. 5 shown in Table 2 below. The bonding temperature is the temperature at which a bonding material is applied to bond the components together. Regarding the bonding temperature, 200°C is the temperature assuming a bonding material containing resin or nanometal particles, and 800°C is the bonding temperature assuming a typical brazing material as the bonding material.

[0051] [Table 2]

[0052] FIG. 6 is a graph showing the simulation results of the maximum thermal stress in the ceramic part of the frame. The values ​​in the graph are normalized by the result of No. 1. This result shows that the application of the buffer part 22 reduces the maximum thermal stress. It also shows that the maximum thermal stress reduces by reducing the bonding temperature.

[0053] 7 is a graph showing the distribution of thermal stress in the ceramic part 21 of the frame body 20 based on the simulation results. In the figure, darker black indicates greater thermal stress. This result shows that thermal stress tends to concentrate at the bent part BD in the ceramic part 21.

[0054] <Embodiment 2> 8 is a schematic cross-sectional view showing the configuration of a package 52 according to embodiment 2. In this embodiment, at least a part of the inner edge PI of the ceramic surface SC is outside the buffer section 22 in plan view. In particular, the bent portion BD (see FIG. 1) of the inner edge PI is outside the buffer section 22 in plan view.

[0055] At least a portion of the outer edge PE of the ceramic surface may overlap the buffer section 22 in plan view. In the configuration of Fig. 8, the outer edge PE of the ceramic surface SC substantially coincides with the outer edge of the upper surface (the surface facing the ceramic surface SC) of the buffer section 22, and this configuration is also considered to be one type of configuration in which the outer edge PE overlaps the buffer section 22 in plan view.

[0056] Since the configuration other than the above is substantially the same as that of the first embodiment, the same or corresponding elements are denoted by the same reference numerals, and the description thereof will not be repeated. For electronic device 90 (FIGS. 1 and 2), package 52 (FIG. 8: second embodiment) may be used instead of package 51 (FIG. 3: first embodiment).

[0057] According to this embodiment, the bent portion BD of the inner edge PI of the ceramic surface SC of the ceramic portion 21 is, in plan view, outside the buffer portion 22. This makes it possible to suppress the concentration of thermal stress at the bent portion BD (see FIG. 7).

[0058] At least a part of the outer edge PE of the ceramic surface SC of the ceramic portion 21 may overlap the buffering portion 22 in plan view. This makes it easier to ensure sufficient rigidity of the buffering portion 22 by designing the buffering portion 22 so that the bent portion BD of the inner edge PI of the ceramic surface SC is outside the buffering portion 22 in plan view while avoiding the width dimension of the buffering portion 22 from being too small.

[0059] It is preferable that the outer surface of the frame body 20 does not protrude outward beyond the side surface of the heat sink 10. In other words, it is preferable that the frame body 20 is disposed only within the range in which the heat sink 10 is disposed in a plan view. This reduces the risk of the frame body 20 coming into contact with some configuration (e.g., a printed circuit board) provided on a support member (not shown) when the electronic device 90 (see FIG. 2) is attached to the support member. This applies not only to the present second embodiment but also to the above-described first embodiment.

[0060] As described above, since the inner edge PI is out of the buffer portion 22 in plan view, the following equations are satisfied for the dimensions LA and LB. 0.1≦LB / LA≦0.6 It is preferable that the following formula is satisfied. Here, the dimension LA is the width dimension (the dimension perpendicular to the thickness direction) of the ceramic surface SC of the ceramic portion 21. Furthermore, the dimension LB is the dimension by which the inner edge PI of the ceramic surface SC protrudes from the buffer portion 22. The dimensions LA and LB are dimensions in a cross section perpendicular to the in-plane direction. In particular, when the cross section passes through the bent portion BD (see FIG. 1), it is preferable that the above formula is satisfied. When 0.1≦LB / LA is satisfied, the effect of mitigating thermal stress concentration becomes more sufficient. When LB / LA≦0.6 is satisfied, it becomes easier to ensure sufficient rigidity of the buffer portion 22. [Explanation of symbols]

[0061] 8: Electronic components 9: Wire (wiring material) 10: Heat sink 20:Frame body 21: Ceramic section 22:Buffer section 30: Lead frame (metal terminal) 51,52:Package 70: Adhesive layer 80: Lid 90:Electronic equipment BD: Bent part CV: Cavity PE: Outer edge PI: Inner edge SC: Ceramic surface

Claims

1. A package having a cavity to be sealed by a lid, a heat sink made of a first metallic material having a first coefficient of linear expansion in a temperature range between 25°C and 200°C; a frame provided on the heat sink and surrounding the cavity in a plan view; Equipped with The frame body is a ceramic portion made of a ceramic material having a second linear expansion coefficient smaller than the first linear expansion coefficient in the temperature range; a buffer portion disposed between the ceramic portion and the heat sink, the buffer portion being made of a buffer material having a third linear expansion coefficient that is smaller than the first linear expansion coefficient and larger than the second linear expansion coefficient in the temperature range; package.

2. the buffer material includes a second metallic material different from the first metallic material; The package of claim 1.

3. the buffer material comprises stainless steel; 3. The package of claim 1 or 2.

4. The stainless steel contains chromium atoms in an amount of 11.5 mass percent or more and 18 mass percent or less. The package of claim 3.

5. The second linear expansion coefficient of the ceramic material is 9 ppm / K or more. A package according to any one of claims 1 to 4.

6. the ceramic material comprises zirconia; A package according to any one of claims 1 to 5.

7. the first metallic material has a thermal conductivity greater than 300 W / m·K; A package according to any one of claims 1 to 6.

8. The first metal material contains copper with a purity of 95.0 weight percent or more. A package according to any one of claims 1 to 7.

9. the first metallic material is a non-composite material; A package according to any one of claims 1 to 8.

10. the buffer portion is bonded to each of the heat sink and the ceramic portion using a bonding material; A package according to any one of claims 1 to 9.

11. The bonding material contains resin or nanometal particles. The package of claim 10.

12. the ceramic portion has a ceramic surface facing the heat sink, the ceramic surface has an inner edge surrounding the cavity, the inner edge includes a bent portion, and the bent portion is out of alignment with the buffer portion in a plan view; A package according to any one of claims 1 to 11.

13. the ceramic surface of the ceramic portion has an outer edge surrounding the inner edge, and at least a portion of the outer edge overlaps the buffer portion in a plan view; 13. The package of claim 12.

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