JP2023077604A - package - Google Patents

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

The present invention relates to packages, and more particularly to packages having a cavity to be sealed by a lid.

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

According to the technique disclosed in Japanese Patent Application Laid-Open No. 2003-282751 (Patent Document 1), a Cu or Cu-based metal plate is used as a heat sink. Cu is inexpensive and has a high thermal conductivity exceeding 300 W/m·K. Therefore, the heat dissipation performance of the heat sink can be improved while suppressing the material cost of the heat sink. According to this technique, first, a semiconductor element is mounted on a heat sink by brazing. Next, a frame to which external connection terminals are bonded in advance is bonded onto 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 lower than the brazing temperature of the semiconductor element. Next, the cavity is sealed by joining a cover to the upper surface of the frame. An electronic device is thus obtained.

Japanese Patent Laying-Open 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 provided above and below it. The coefficient of linear expansion of CPC is lower than that of Cu. Therefore, by using CPC instead of Cu as a heat sink material, the coefficient of linear expansion of the heat sink can be made close to that of ceramic.

Japanese Patent Laying-Open No. 2015-204426 (Patent Document 3) discloses an electronic component storage package. The package has a heat sink plate for dissipating heat generated from the electronic component, and a frame-shaped ceramic frame brazed to the heat sink plate. The ceramic frame is composed of a joined body of an upper layer sheet and a lower layer sheet, and has a frame shape. The ceramic frame has a step portion on the inner peripheral side due to the lower layer sheet retreating from the upper layer sheet. When viewed from above, the upper surface of the heat sink plate does not have solder flow in the brazing joint inward from the inner circumference of the upper layer sheet. The heat sink plate is made of a material with a coefficient of thermal expansion similar to that of ceramics.

Korean Patent No. 10-1175613 (Patent Document 4) discloses a package in which an element that emits heat during operation is mounted. The package includes a first base, a second base bonded to the first base and formed in a frame shape, an insulator bonded to the second base, and a lead frame bonded to the insulator. The first base and the second base may be made of metal material, and the coefficient of linear expansion of the second base may be smaller than the coefficient of linear expansion of the first base. The first base metal material can be copper (Cu) or a Cu alloy, and the second base metal material is Kovar, iron (Fe)-nickel (Ni) alloy, molybdenum (Mo), Any one of Mo alloy, tungsten (W) and W alloy, or an alloy thereof may be used. The first base and the second base may be joined by laser welding or seam welding. The insulator may be made of a ceramic material and may be joined to the second base by brazing.

Japanese Patent Application Laid-Open No. 2003-282751 JP 2005-243819 A JP 2015-204426 A Korean Patent No. 10-1175613

When trying to sufficiently improve the thermal conductivity of the heatsink or reduce the cost, it tends to be difficult to sufficiently match the thermal expansion coefficient of the heatsink to that of the ceramic. Large differences in coefficients of thermal expansion tend to cause problems of thermal stress concentration in the package under temperature changes during manufacture or use of the package.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and its object is to provide a package that can reduce the concentration of thermal stress in the package under temperature changes during manufacture or use of the package. It is to be.

The package of one embodiment 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 plan view. include. The frame body is disposed between the ceramic part made of a ceramic material having a second coefficient of linear expansion smaller than the first coefficient of linear expansion in the above temperature range and the ceramic part and the heat sink, and is arranged between the ceramic part and the heat sink. and a cushioning portion made of a cushioning material having a third coefficient of linear expansion smaller than the coefficient of linear expansion of and larger than the second coefficient of linear expansion.

According to the package of one embodiment, 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. Thereby, the thermal expansion difference between the heat sink and the ceramic portion is buffered by the buffer portion. Therefore, it is possible to reduce the concentration of thermal stress in the package under temperature changes during manufacture or use of the package.

The buffer material may comprise a second metallic material different from the first metallic material. In that case, brittle fracture of the buffer portion under thermal stress can be prevented compared to the case where the buffer material does not contain any metal material.

The cushioning material may include stainless steel. In that case, brittle fracture of the buffer portion under thermal stress can be prevented compared to the case where the buffer material does not contain any metal material. When stainless steel is used, the composition control makes the third coefficient of linear expansion of the buffer material smaller than the first coefficient of linear expansion of the heat sink and larger than the second coefficient of linear expansion of the ceramic part. It can be easily adjusted to larger values. The stainless steel may contain 11.5% or more and 18% or less by weight of chromium atoms. In that case, the buffer material may have a third coefficient of linear expansion of about 11 ppm/°C. As a result, while satisfying the condition that the second linear expansion coefficient of the ceramic material forming the ceramic portion is smaller than the third linear expansion coefficient of the buffer material, the second linear expansion coefficient of the ceramic material is 11 ppm/°C. Large values close to each other are allowed. By selecting a ceramic material having a larger second coefficient of linear expansion, it is possible to suppress the difference in thermal expansion between the ceramic portion made of the ceramic material and the heat sink.

The second coefficient of linear expansion of the ceramic material may be 9 ppm/K or greater. In that case, the difference in thermal expansion between the ceramic portion made of the ceramic material and the heat sink having a relatively high first linear expansion coefficient can be suppressed.

The ceramic material may include zirconia. In that case, the second linear expansion coefficient of the ceramic material can be 9 ppm/K or more. Thereby, the difference in thermal expansion between the ceramic portion made of the ceramic material and the heat sink can be suppressed.

The first metallic material may have a thermal conductivity greater than 300 W/m·K. In that case, the heat dissipation performance of the heat sink made of the first metal material can be enhanced.

The first metal material may contain copper with a purity of 95.0 weight percent or higher. In that case, thermal conductivities greater than about 300 W/m·K can be obtained. Thereby, the heat dissipation performance of the heat sink made of the first metal material can be enhanced.

The first metallic material may be a non-composite material. In that case, the first linear expansion coefficient of the first metal material cannot be suppressed by the material design of the composite material. As a result, the difference in thermal expansion between the heat sink and the ceramic portion tends to increase. Stress concentrations can be reduced.

The buffer section may be bonded to each of the heat sink and the ceramic section using a bonding material. This bonding process normally requires heating and subsequent cooling, and the thermal stress concentration at that time can be reduced for the reasons described above. The bonding material may contain resin or nano metal particles. In that case, the maximum temperature required for the joining process is lower than when the joining material is a typical brazing material. Thereby, the thermal stress generated in the bonding process can be reduced.

The ceramic part has a ceramic face facing toward the heat sink, the ceramic face having an inner edge surrounding the cavity, the inner edge including a bent portion. The bent portion may be separated from the cushioning portion in plan view. In that case, thermal stress concentration on the bent portion can be suppressed. The ceramic face of the ceramic portion has an outer edge that surrounds the inner edge. At least part of the outer edge may overlap the cushioning portion in plan view. In this case, it is easy to sufficiently secure the rigidity of the cushioning portion while designing the cushioning portion so that the bent portion of the inner edge of the ceramic surface is deviated from the cushioning portion in a plan view.

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

1 is a schematic perspective view showing the configuration of an electronic device according to Embodiment 1, partly omitted so that the inside of a cavity can be seen; FIG. 2 is a schematic cross-sectional view along line II-II of the electronic device of FIG. 1; FIG. 3 is a schematic cross-sectional view showing the configuration of a package as a component of the electronic device of FIG. 2; FIG. FIG. 2 is a graph illustrating temperature dependence of coefficient of thermal expansion (CTE) of copper (Cu), alumina (Al ₂ O ₃ ), and composite material (CPC). FIG. 4 is a plan view showing the dimensions of the structure used for the simulation conditions of thermal stress due to the bonding process in the manufacture of the package; FIG. 4 is a graph showing simulation results of the maximum value of thermal stress in the ceramic portion of the frame due to the bonding process in the manufacture of the package; 7 is a graph showing the tendency of thermal stress distribution in the ceramic portion of the frame in the simulation results of FIG. 6. FIG. 6 is a schematic cross-sectional view showing the configuration of a package according to Embodiment 2; FIG.

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described below based on the drawings. In this specification, metal can mean either a pure metal or an alloy unless otherwise specified. Planar view means projection onto a plane perpendicular to the thickness direction. The coefficient of thermal expansion (CTE) is represented by the coefficient of linear expansion unless otherwise specified. If the coefficient of linear expansion has non-negligible anisotropy, the coefficient of linear expansion in the in-plane direction is adopted. The in-plane direction is the direction perpendicular to the thickness direction.

<Embodiment 1>
FIG. 1 is a schematic perspective view showing the configuration of an electronic device 90 according to Embodiment 1. FIG. FIG. 2 is a schematic cross-sectional view of electronic device 90 of FIG. 1 along line II-II. The electronic device 90 has a package 51 , a lid 80 and electronic components 8 . The electronic device 90 may also have an adhesive layer 70 . Further, the electronic device 90 may have wires 9 (wiring members). In FIG. 1, the illustration of the lid 80 and the adhesive layer 70 is partially omitted so that the inside of the 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 device may be for radio frequency (RF) applications, in which case the electronic device 90 is an RF power module. Although one electronic component 8 is illustrated in FIGS. 1 and 2 , a plurality of electronic components 8 may be mounted on the package 51 .

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

The heat sink 10 has a bottom surface BT and a mounting surface MT opposite to 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 CTE ₁ ) in the temperature range between 25°C and 200°C. In other words, if heat sink 10 has dimension L ₂₅ at 25° C. and dimension L ₂₀₀ at 200° C., CTE ₁ is:
CTE ₁ = {(L ₂₀₀ −L ₂₅ )/(200−25)}/L ₂₅
defined by The definitions of CTE ₂ and CTE ₃ described below with respect to other members are similar.

The heat sink material preferably has a large thermal conductivity from the viewpoint of improving the heat dissipation performance of the heat sink 10, and specifically, preferably has a thermal conductivity of 300 W/m·K or more. . Such high thermal conductivity is easily obtained by including a high proportion of Cu in the heat sink material. From the viewpoint of increasing thermal conductivity, the heat sink material preferably contains Cu with a purity of 95.0 weight percent (wt%) or higher, more preferably with a purity of 99.8 wt% or higher. The heat sink material may be non-composite. A non-composite material is a pure metallic or alloy material that does not have a layered structure like that of CPC.

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 plan view. The outer edge of the frame 20 may have a rectangular shape as shown in FIG. 1, and the size of each side is, 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 will also increase, resulting in an increase in the inductance of the wire 9 as well. An increase in the inductance of the wire 9 is usually undesirable due to its electrical properties.

Frame 20 includes ceramic portion 21 and buffer portion 22 . The buffer portion 22 is arranged between the ceramic portion 21 and the heat sink 10 . In other words, the ceramic portion 21 is arranged on the heat sink 10 with the buffer portion 22 interposed therebetween. The buffer portion 22 may be bonded to each of the heat sink 10 and the ceramic portion 21 using a bonding material (not shown). The bonding material may contain resin, and specifically may be a mixture of thermosetting resin (for example, epoxy resin or silicon 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 nano metal particles. Nano metal 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 thickness of each of the ceramic portion 21, the buffer portion 22 and the heat sink 10. can be practically ignored. The thickness of the bonding material is, for example, 0.01 mm or more and 0.2 mm or less.

The ceramic portion 21 is made of a ceramic material having a CTE ₂ (second coefficient of linear expansion) smaller than CTE ₁ . CTE ₂ is preferably greater than or equal to 9 ppm/K. The ceramic material may comprise zirconia ( _ZrO2 ) and may be substantially zirconia. The thickness of the ceramic portion 21 may be 0.2 mm or more and 1.0 mm or less. When the thickness is 0.2 mm or more, the ceramic portion 21 can be easily formed by firing the green sheet.

The buffer portion 22 is made of a buffer material having a CTE ₃ (third coefficient of linear expansion) smaller than CTE ₁ and larger than CTE ₂ . The buffer material preferably comprises a second metallic material different from the first metallic material described above, and may be substantially the second metallic material. The second metal material is preferably stainless steel, more preferably an Fe--Cr (chromium) alloy. The Fe—Cr alloy preferably contains Fe atoms as a main component and contains Cr atoms in an amount of 11.5 wt % or more and 18 wt % or less. The Fe--Cr alloy may also contain other trace elements, but the total amount is usually less than 3 wt%. Generally, 18Cr stainless steel (for example, a material called SUS430) and 13Cr stainless steel (for example, a material called SUS410 or SUS403) are widely used as Fe—Cr alloys having such a composition. The content of Cr atoms in SUS430 is 16 wt % or more and 18 wt % or less. The content of Cr atoms in SUS410 and SUS403 is 11.5 wt % or more and 13 wt % or less. Of these three examples, SUS430 is usually the cheapest material. The thickness of the buffer portion 22 may be 0.05 mm or more and 0.5 mm or less. When the thickness is 0.05 mm or more, the effect of the buffer portion 22 can be obtained more sufficiently.

The lead frame 30 constitutes an electrical path connecting the inside and outside of the cavity CV. The material of the lead frame 30 is, for example, Fe—Ni alloy, Cu, or Cu alloy. An Fe—Ni alloy is, for example, 42 alloy. 42 alloy contains Fe atoms as the main component and about 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 together. This bonding material may be made of the same material as the bonding material described above.

The ceramic part 21 has a ceramic surface SC (FIG. 3) facing towards the heat sink 10 . The ceramic surface SC has an inner edge PI surrounding the cavity CV and an outer edge PE surrounding the inner edge. The inner edge PI includes a bent portion BD. The bent portion BD may be the four corners of the rectangular shape. In the present embodiment, the ceramic portion 21 and the buffer portion 22 may substantially overlap each other in plan view. In other words, each of inner edge PI and outer edge PE of ceramic surface SC may substantially match the inner edge and outer edge of the upper surface of buffer portion 22 (the surface facing ceramic surface SC).

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

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

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, eg substantially alumina. Alternatively, the lid body 80 may contain resin. The resin is, for example, liquid crystal polymer. 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 enhanced.

Next, the lid 80 is placed via the adhesive layer 70 on the frame 20 provided with the lead frame 30 . The adhesive layer 70 contains a thermosetting resin in this example, 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. The adhesive layer 70 may have a portion provided on the frame 20 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. The lid 80 may have an inner surface 81i facing the cavity CV (FIG. 1) and an opposite outer surface 81o, and typically the inner surface 81i has the frame shape of the ceramic frame 61. A frame portion 81p, which is a projection having a frame shape roughly corresponding to the . In this case, the adhesive layer 70 is in contact with the frame portion 81p.

Next, the lid body 80 is pressed against the frame body 20 with a predetermined load. A suitable load depends on the dimensional design of the package 51, but is, for example, about 500 g or more and 1 kg or less. The adhesive layer 70 is heated while being pressed with a load. 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 is wetted and spread. After that, the adhesive layer 70 changes into a hardened state as the curing reaction by heating progresses, and as a result, the adhesive layer 70 bonds the lid body 80 and the frame body 20 to each other.

The adhesive layer 70 may contain at least one of epoxy resin, phenol resin and silicone resin as a main component. Epoxy resins are particularly preferred because they have well-balanced heat resistance, mechanical strength and chemical resistance. In order to preferably have these characteristics, the content of the epoxy resin as the main component is preferably 20 to 40 wt%, and the balance may be composed of subcomponents such as a curing agent. Specifically, the subcomponents include, for example, 1 to 10 wt% curing agent, 50 to 70 wt% inorganic filler, 0.5 to 2 wt% coupling agent, and 0.5 to 2 wt% catalyst. and 0.1-5 wt % of a 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 salts may be used as catalysts. Silicone may be used as a low stress agent. The adhesive layer 70 may have a bending elastic modulus smaller than that of the lid 80 .

As described above, as shown in FIGS. 1 and 2, a configuration is obtained in which the lid 80 seals the cavity CV. In other words, electronic device 90 (FIGS. 1 and 2) is obtained. The bottom surface BT (FIG. 2) of the heat sink 10 of the electronic device 90 will 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 penetrations (not shown) through which fasteners (eg, screws) pass for attachment to the support member.

FIG. 4 is a graph illustrating temperature dependence of CTE of each of Cu, Al ₂ O ₃ and CPC. Cu has a significantly higher CTE than that of Al ₂ O ₃ , while CPC has a comparable CTE. Therefore, if the frame for forming the cavity in the package is made of Al ₂ O ₃ and the heat sink is made of CPC instead of Cu, the difference in thermal expansion between the frame and the heat sink can be considerably suppressed. can. However, in order to enhance the heat dissipation performance of the heatsink, it may be desirable to use a material with a higher thermal conductivity than that of the CPC, typically substantially pure Cu, as the heatsink material. . Also, since CPC is a relatively expensive composite material, it may be desirable to use less expensive non-composite materials, typically substantially pure Cu. However, in the case of a configuration in which a frame made of Al ₂ O ₃ is simply bonded to a heat sink made of Cu with a bonding material, the difference in CTE is large, so under temperature changes during package manufacture or use, Thermal stress concentration tends to be a problem in packages.

According to this embodiment, the CTE ₃ of the buffer portion 22 is less than the CTE ₁ of the heat sink 10 and greater than the CTE ₂ of the ceramic portion 21 . Thereby, the thermal expansion difference between the heat sink 10 and the ceramic portion 21 is buffered by the buffer portion 22 . Therefore, it is possible to reduce the concentration of thermal stress on the package 51 under temperature changes during manufacture or use of the package 51 .

By including a metallic material (e.g., stainless steel) in the cushioning material, the cushioning under thermal stress is better than when the cushioning material does not include any metallic material (typically when the cushioning material is a ceramic material). Brittle fracture of the portion 22 can be prevented. When stainless steel is used, its composition control can easily tune the CTE ₃ of the buffer material to a value less than the CTE ₁ of the heat sink 10 and greater than the CTE ₂ of the ceramic portion 21 . Since the stainless steel contained in the buffer material contains Cr atoms at 11.5 wt % or more and 18 wt % or less, the CTE ₃ of the buffer material can be about 11 ppm/°C. This allows the CTE ₂ of the ceramic material to be a large value close to 11 ppm/° C. while satisfying the condition that the CTE ₂ of the ceramic material forming the ceramic portion 21 is smaller than the CTE ₃ of the buffer material. By selecting a ceramic material with a larger CTE ₂ , the thermal expansion difference between the ceramic part 21 made of the ceramic material and the heat sink 10 can be reduced.

When the CTE ₂ of the ceramic material is 9 ppm/K or more, the difference in thermal expansion between the ceramic portion 21 made of the ceramic material and the heat sink 10 having a relatively high CTE ₁ can be suppressed. By including zirconia in the ceramic material, the CTE ₂ of the ceramic material can be 9 ppm/K or higher.

The heat sink material has a thermal conductivity greater than 300 W/m·K. Thereby, the heat dissipation performance of the heat sink 10 can be improved. Thermal conductivities greater than about 300 W/m·K can readily be achieved by the heat sink material containing Cu at a purity of 95.0 wt % or greater. If the heatsink material is non-composite, the CTE ₁ of the heatsink material cannot be constrained by the material design of the composite. As a result, the difference in thermal expansion between the heat sink 10 and the ceramic portion 21 tends to increase. , the stress concentration in the package 51 can be reduced.

Buffer portion 22 is bonded to each of heat sink 10 and ceramic portion 21 using a bonding material. This bonding process normally requires heating and subsequent cooling, and the thermal stress concentration at that time can be reduced for the reasons described above. The bonding material may include resin or nano metal particles. In that case, the maximum temperature required for the joining process is lower than when the joining material is a typical brazing material. Thereby, the thermal stress generated in the bonding process can be reduced.

The coefficient of linear expansion can be obtained by measuring the displacement when the temperature is raised from 25° C. with an optical interferometric method or a push-rod dilatometer. Thermal conductivity is measured by the flash method. The ingredients of the material are measured by ICP (Inductively Coupled Plasma) analysis. Samples for measuring the various physical property values described above may be obtained by disassembling the electronic device 90 or the package 51 into individual components.

Next, a simulation of thermal stress due to the bonding process in package manufacture will be described below. Note that FIG. 5 is a plan view showing the dimensions of the configuration used for the simulation conditions. Table 1 below shows physical property values of materials assumed in the simulation. 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 a material that forms the heat sink 10 . SUS430 is a material that forms the buffer portion 22 . Note that Table 1 shows two types of CTE, one at 200° C. and one at 800° C., with 25° C. as the reference. In other words, a CTE between 25°C and 200°C and a CTE between 25°C and 800°C are shown.

The simulation was carried out on No. 1 shown in Table 2 below. 1 to No. 5 are performed. Note that the bonding temperature is the temperature at which a bonding material for bonding between members is applied. Regarding the bonding temperature, 200° C. is a temperature assuming that the bonding material contains resin or nano metal particles, and 800° C. is a bonding temperature assuming a typical brazing material as the bonding material.

FIG. 6 is a graph showing a simulation result of the maximum thermal stress of the ceramic portion of the frame. The values in the graph are No. 1 results are normalized. From this result, it can be seen that the maximum value of the thermal stress is reduced by applying the buffer portion 22 . Also, it can be seen that the maximum value of the thermal stress is reduced by reducing the bonding temperature.

FIG. 7 is a graph showing the tendency of the thermal stress distribution of the ceramic portion 21 of the frame 20 in the simulation results. In the figure, darker black indicates greater thermal stress. From this result, it can be seen that the thermal stress tends to concentrate on the bent portion BD in the ceramic portion 21 .

<Embodiment 2>
FIG. 8 is a schematic cross-sectional view showing the structure of the package 52 according to the second embodiment. In the present embodiment, at least part of the inner edge PI of the ceramic surface SC is separated from the buffer portion 22 in plan view. In particular, the bent portion BD (see FIG. 1) of the inner edge PI is separated from the buffer portion 22 in plan view.

At least part of the outer edge PE of the ceramic surface may overlap the buffer portion 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 of the buffer portion 22 (the surface facing the ceramic surface SC). It is regarded as a type of configuration that visually overlaps the buffer portion 22 .

Since the configuration other than the above is substantially the same as the configuration of the first embodiment described above, 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: Embodiment 2) may be used instead of package 51 (FIG. 3: Embodiment 1).

According to the present embodiment, the bent portion BD of the inner edge PI of the ceramic surface SC of the ceramic portion 21 is separated from the buffer portion 22 in plan view. Thereby, the concentration of thermal stress (see FIG. 7) on the bent portion BD can be suppressed.

At least a portion of the outer edge PE of the ceramic surface SC of the ceramic portion 21 may overlap the buffer portion 22 in plan view. As a result, while the buffer portion 22 is designed such that the bent portion BD of the inner edge PI of the ceramic surface SC is deviated from the buffer portion 22 in a plan view, the width dimension of the buffer portion 22 is prevented from being excessively small. It becomes easy to sufficiently secure the rigidity of the portion 22 .

It is preferable that the outer surface of the frame 20 does not protrude beyond the side surface of the heat sink 10 . In other words, in plan view, the frame 20 is preferably arranged only within the range where the heat sink 10 is arranged. As a result, when the electronic device 90 (see FIG. 2) is attached to its support member (not shown), there is a risk that the frame 20 will come into contact with some structure (for example, a printed circuit board) provided on the support member. can be reduced. This applies not only to the second embodiment, but also to the first embodiment described above.

As described above, since the inner edge PI is separated from the buffer portion 22 in plan view, the dimension LA and the dimension LB are expressed by the following formula: 0.1≤LB/LA≤0.6
is preferably satisfied. Here, the dimension LA is the width dimension (perpendicular to the thickness direction) of the ceramic surface SC of the ceramic portion 21 . A dimension LB is a dimension by which the inner edge PI of the ceramic surface SC protrudes from the buffer portion 22 . Dimension LA and dimension 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. By satisfying 0.1≦LB/LA, the effect of alleviating thermal stress concentration becomes more sufficient. By satisfying LB/LA≦0.6, it becomes easy to sufficiently secure the rigidity of the cushioning portion 22 .

8: electronic component 9: wire (wiring member)
REFERENCE SIGNS LIST 10: heat sink 20: frame 21: ceramic part 22: buffer part 30: lead frame (metal terminal)
51, 52: package 70: adhesive layer 80: lid 90: electronic device BD: bent portion CV: cavity PE: outer edge PI: inner edge SC: ceramic surface

Claims (13)

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 plan view;
with
The frame 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 made of a buffer material disposed between the ceramic portion and the heat sink and 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. including,
package. The buffer material comprises a second metallic material different from the first metallic material,
The package of Claim 1. the buffer material comprises stainless steel;
3. Package according to claim 1 or 2. The stainless steel contains 11.5% by mass or more and 18% by mass or less of chromium atoms.
4. Package according to claim 3. The second linear expansion coefficient of the ceramic material is 9 ppm/K or more,
5. A package according to any one of claims 1-4. the ceramic material comprises zirconia;
6. A package according to any one of claims 1-5. the first metallic material has a thermal conductivity greater than 300 W/mK;
7. A package according to any one of claims 1-6. The first metal material contains copper with a purity of 95.0 weight percent or more,
A package according to any one of claims 1-7. wherein the first metallic material is a non-composite material;
9. A package according to any one of claims 1-8. The buffer portion is bonded to each of the heat sink and the ceramic portion using a bonding material,
10. A package according to any one of claims 1-9. The bonding material contains resin or nano metal particles,
11. Package according to claim 10. The ceramic part has a ceramic surface facing toward the heat sink, the ceramic surface having an inner edge surrounding the cavity, the inner edge including a bent portion, the bent portion in plan view. detached from the buffer at
A package according to any one of claims 1 to 11. 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 plan view.
13. Package according to claim 12.

Images