JP2003258167A - Structure - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a heat dissipation structure suitable for power module in which high reliability and long term heat dissipation properties can be sustained. <P>SOLUTION: The heat dissipation structure comprises a metallic frame having an opening, a ceramic substrate provided with metal layers on the opposite sides thereof, and a metallic base plate placed on one metal layer of the ceramic substrate wherein the ceramic substrate and/or the metallic base plate are/is arranged at the opening of the metallic frame and the metallic base plate is secured to the metallic frame. Difference of thermal expansion coefficient is set in the range of 6-23 ppm between the ceramic substrate and the metallic base plate. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention has a ceramic substrate and is capable of mounting a high-power semiconductor element. Therefore, various high powers such as a power source mounted on a mobile device such as an automobile are provided. The present invention relates to a heat dissipation structure capable of providing electric parts suitable for uses such as a power supply, and a manufacturing method thereof.

[0002]

2. Description of the Related Art Conventionally, in a power module using semiconductor elements such as IGBTs and MOSFETs, heat generated in those semiconductor elements is released to the outside so that the temperature of the semiconductor elements does not rise above a predetermined temperature. Therefore, aluminum oxide (Al ₂ O ₃ ), silicon nitride (Si ₃ N ₄ ),
It has been common to use a heat dissipation structure in which a ceramics circuit board made of aluminum nitride (AlN) or the like is soldered to a base plate made of metal such as copper (Cu) or aluminum (Al).

However, for power modules for electric railways and electric vehicles including hybrid cars, higher heat dissipation and reliability are required, and heat dissipation by soldering the ceramic circuit board and the metal base plate is required. Depending on the usage conditions, the structure may crack the ceramic substrate,
It is known that cracks (hereinafter referred to as solder cracks) occur in the solder layer, which may cause problems in heat dissipation and reliability.

Cracks generated in the ceramic substrate cause insulation failure, and cracks generated in the solder layer deteriorate heat dissipation, and as a result, the temperature of the semiconductor element rises to make it inoperable. There is a strong demand for a heat dissipation structure (hereinafter, also simply referred to as a structure) that realizes a highly reliable power module for a long period of time in which such a phenomenon does not occur.

Aluminum (Al), which has excellent stress relaxation property, is used to prevent cracks from occurring in the ceramic substrate.
An aluminum-silicon carbide (Al-SiC) composite having a coefficient of thermal expansion close to that of a ceramic substrate is used in order to use a metal as a circuit metal and to reduce stress generated in a solder layer between a ceramic circuit substrate and a base plate. It has been considered to use a material such as a metal or a copper-molybdenum (Cu-Mo) composite material as a base plate.

A power module using a combination of a ceramic substrate with an aluminum circuit and a base plate made of a composite material has high reliability and is suitable for electric railway vehicles and hybrid cars, but is expensive. Is a big drawback, and it is a shackle for expanding applications.
The composite materials such as Al-SiC and Cu-Mo have to be manufactured by a special method as compared with the conventional metal base plate, and the cost of the processing process and the surface treatment process is high, and the metal base plate is made. This is because it will be several times more expensive.

However, as described above, regarding the power module using the inexpensive metal base plate, the solder layer is cracked or the solder is deteriorated due to the thermal stress received in the assembly process and the actual use conditions. Is known to occur.

In view of these problems, it is considered that the use of solder for joining the ceramic circuit board and the base plate itself causes a decrease in reliability. Therefore, a brazing material is used in place of the solder to form the base plate. It is also considered to improve reliability by adopting a structure in which the ceramic circuit board is directly joined (Japanese Patent Laid-Open Nos. 9-97865 and 1).
0-270596).

However, the inventors of the present invention have examined the heat dissipation structure having the above-mentioned structure. As a result, the heat resistance at the initial stage of actual use may be higher than that of the heat dissipation structure constructed by normal soldering, It has been found that there are problems to be solved such as thermal resistance increasing if the cycle is subjected to a long period of time.

The present inventor has made various studies on the above-mentioned problems, and it is derived from the warp of the lower surface of the base plate (the surface opposite to the surface on which the ceramic circuit board is bonded) and the fixing method of the heat dissipation structure. And when mounting a heat-generating electrical component such as a semiconductor on the circuit of the ceramic circuit board,
It has been found that there are cases where cracks occur in the solder used for joining the circuit and the heat-generating electric component.

The warp of the base plate is caused by the difference in thermal expansion between the base plate and the ceramic substrate. That is, when a metal base plate such as copper (coefficient of thermal expansion is 17 ppm / ° C.) is used, the coefficient of thermal expansion is the coefficient of thermal expansion of the ceramic substrate (4 pp
m / ° C.), so that when soldered at around 300 ° C or brazed at around 600 ° C to 900 ° C and then cooled to around room temperature, the bonded body of the base plate and the ceramics circuit board largely warps. Since the warp causes the lower surface of the base plate to be concave, when further attempting to join the joined body to the heat dissipation block, a gap is generated between the heat dissipation block and the lower face of the base plate, and heat dissipation grease is present in the gap. Even so, the thermal conductivity deteriorates, and the temperature of electronic components such as semiconductor elements constituting the power module rises.

In order to make the warp of the base plate convex downward and to an appropriate range, there is a method in which the base plate is previously convex warped downward and soldered to the circuit board. In some cases, many solder voids are generated in the layer, which may lead to an increase in thermal resistance. A method of brazing while sandwiching it with a jig with a curvature is conceivable, but even if a convex warp is attached to the base plate in this way, the method of fixing the heat dissipation structure to the heat dissipation block or heat Depending on the cycle conditions, the bottom surface of the base plate may not be sufficiently pressed against the heat dissipation block. For example, when a brazing integrated structure of an aluminum circuit board and a metal base plate is used, when the semiconductor element (also referred to as a semiconductor chip) is heated and cooled in the soldering process, the base plate warps before and after that. It has been found that it can change significantly. When such a phenomenon occurs, in order to make the lower surface of the base plate flat after soldering, it is necessary to make it convex downward before soldering, but if the warp variation is large, It is necessary to make the initial warp largely convex downward, and therefore, when heated in the soldering process, it is largely warped downward, resulting in uneven solder layer thickness and in the solder layer. May cause voids to occur. in any case,
In such a method, since the warp shape changes intricately depending on the size and arrangement of the circuit board, it may be difficult to appropriately warp.

Further, when the heat dissipation structure is exposed to a heat cycle for a long period of time, a warp is repeatedly generated due to a difference in thermal expansion between the ceramic substrate and the base plate.
There is a case where the heat dissipation grease is unevenly distributed or an air layer is formed between the base plate and the heat dissipation block. In the case of the heat dissipation structure in which the ceramic circuit board and the base plate are directly joined to each other, there is no solder layer acting as a stress relaxation layer between the ceramic circuit board and the base plate. However, there is a tendency that the repeated change of the warp during the heat cycle becomes large, and the bias of the grease and the formation of the air layer tend to occur easily. Such a phenomenon is expected to occur remarkably when the change in warpage caused by the thermal cycle is large.

In addition, even if the ceramic circuit board and the base plate are directly joined, the heat-generating electric parts such as semiconductor elements are still soldered to the circuits on the ceramic circuit board. Therefore, since the ceramic circuit board and the base plate are directly bonded to each other without a solder layer having a stress relaxation function, the stress applied to the ceramic board becomes larger than that of the conventional power module, and the ceramic circuit board Since the stress applied to the solder layer between the semiconductor element and the semiconductor element also increases, solder cracks are more likely to occur. It is considered that the generated stress increases as the difference in the coefficient of thermal expansion between the substrate and the base plate increases, but is affected not only by the coefficient of thermal expansion but also by the amount of change in warpage due to the heat treatment.

The occurrence of these problems deteriorates the dissipation of heat generated from electric parts and circuits such as semiconductor elements in the module and raises the temperature of the semiconductor elements, causing malfunction of the semiconductor elements and the life of the semiconductor elements. This causes a phenomenon such as shortening, which is not practically preferable.

[0016]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and clarifies the relationship between the heat dissipation structure used in a power module and its reliability, and provides high reliability and long-term heat dissipation. The purpose is to provide a structure that can maintain the property.

[0017]

DISCLOSURE OF THE INVENTION The inventors of the present invention have made extensive studies in view of the above circumstances, and have produced various structures as prototypes in combination with a ceramic circuit board, a metal base plate, and a metal frame. , By evaluating its reliability, the structure having a specific structure has a small amount of change in its warp even after undergoing thermal history such as soldering, and consequently, solder cracks and substrate cracks are unlikely to occur, and it is possible to maintain a long period of time. The inventors of the present invention have found that they have excellent heat dissipation properties and have arrived at the present invention.

That is, the present invention comprises a metal frame having an opening, a ceramics substrate provided with metal layers on both sides, and a metal base plate provided on one metal layer of the ceramics substrate. A structure in which the ceramics substrate and / or the metal base plate is arranged in the opening of the metal frame, and the metal base plate is fixed to the metal frame, the coefficient of thermal expansion of the ceramics substrate And the difference in the coefficient of thermal expansion between the metal base plate and the metal base plate is 6 to 23 ppm.

In the present invention, the metal frame is made of iron, aluminum, copper or an alloy containing iron, aluminum or copper as a main component, and the ceramic substrate is silicon nitride or aluminum nitride. In the above structure, the base plate is made of aluminum, copper, or an alloy containing aluminum or copper as a main component. Furthermore, the method of fixing the metal base plate to the metal frame is press fitting,
The structure is characterized in that it is either shrink-fitting or caulking.

As a preferred embodiment of the present invention,
A metal layer provided on both sides of the ceramic substrate, wherein the metal layer on the side of the ceramic substrate facing the metal base plate and the metal base plate are joined by a brazing material. Are both high-purity aluminum, the metal layer on the side of the metal layer facing the metal base plate, the structure characterized in that it is equal to or more than the thickness of the metal layer on the opposite side. is there.

Further, as a preferred embodiment of the present invention, the joining of the ceramics substrate and the metal layer on the side facing the metal base plate, and the joining of the metal layer and the metal base plate,
All of the above structures are characterized in that they are joined by a brazing material made of an aluminum alloy containing one or more of Mg, Ag and Cu.

Further, according to the present invention, by using the above-mentioned structure, a metal layer on the side of the ceramic substrate which does not face the metal base plate is formed into a circuit, and one or more semiconductor elements are mounted on the circuit. A module characterized by

Further, according to the present invention, (1) a step of producing a ceramic substrate having metal layers on both sides thereof, and (2) a base plate made of metal provided on any of the metal layers of the ceramic substrate. The process of making an integrated ceramics substrate,
(3) A step of preparing a metal frame having an opening having a size capable of accommodating the ceramic substrate and / or the metal base plate in advance, (4) The ceramic substrate and / or metal of the base plate-integrated ceramic substrate A method of manufacturing a structure, comprising the step of disposing a base plate made of metal in the opening of the metal frame and fixing and integrating the metal frame and the metal base plate.

In addition, in the present invention, the step (4) is
The metal frame is heated, and the metal base portion of the base plate integrated ceramics substrate is stored in the opening of the metal frame,
The method of manufacturing a structure as described above, which is a step of fixing and integrating the metal frame base plate and the metal base plate of the ceramic substrate integrated with the metal frame base plate by cooling.

[0025]

BEST MODE FOR CARRYING OUT THE INVENTION The ceramic substrate used in the present invention may be of any type as long as it satisfies the required characteristics such as electrical insulation characteristics, thermal conductivity and mechanical strength, but high thermal conductivity. Aluminum nitride (AlN), which is a ceramic having C, or silicon nitride (Si ₃ N ₄ ) having both high strength and relatively high thermal conductivity is more preferable. In particular, when the base plate and the circuit board are directly brazed, it is preferable to use a silicon nitride substrate having excellent mechanical properties.

The metal plate which is provided on one surface of the ceramic substrate and has a heat-generating electric component mounted on a part thereof as a circuit may be any metal having good conductivity, but it is inexpensive and has a high thermal conductivity. High copper and aluminum are preferably used. Further, as the copper or aluminum, those of high purity, which have high thermal conductivity and electrical conductivity and high plastic deformability with respect to stress generation, are preferable.

In the present invention, the metal plate provided on the base plate side of the ceramic substrate so as to be in contact with the base plate is preferably a metal having a tensile strength of 200 MPa or less and an elongation of 20% or more, more preferably 150 MPa. A metal having the following tensile strength and an elongation of 30% or more is selected. That is, the presence of the metal plate is mainly intended to improve the bonding force between the ceramic substrate and the base plate as well as heat dissipation, but according to the results of the experimental study by the present inventor,
When selecting one having the above-mentioned characteristics, it is possible to obtain a module having excellent stress relaxation property and having high reliability even if it is subjected to repeated thermal history under actual use, and the effect of the present invention is more easily achieved. Because. Examples of the metal plate include aluminum, tin, lead, zinc, vanadium, yttrium, cadmium, calcium, indium, platinum, palladium, silver, gold and alloys thereof. Among them, aluminum, zinc, tin and alloys thereof are preferably used from the viewpoint of easy availability and low cost. Among aluminum alloys, aluminum with a purity of 99% or more, JI
S designations 3003, 8011 and the like are particularly preferably used.

In the present invention, the metal layers provided on both surfaces of the ceramic substrate are made of high-purity aluminum, and high-purity aluminum having a purity of 99.9% or more is particularly preferable. This is because, as described above, high-purity aluminum has both the properties that a metal plate to be a circuit should have and the properties that a metal plate provided on the base plate side of a ceramic substrate in contact with the base plate should have. Is. Also,
It is desirable that the metal layer of the metal layer on the side facing the metal base plate has a thickness equal to or greater than that of the metal layer on the opposite side. This is not enough to reduce the difference in the coefficient of thermal expansion between the ceramic substrate and the base plate unless the metal layer on the side facing the base plate has a certain thickness, resulting in poor long-term reliability such as heat cycles. Because there are things.

The difference between the coefficient of thermal expansion of the base plate and the coefficient of thermal expansion of the ceramic substrate used in the present invention is selected to be 6 to 23 ppm. This is because in a combination of materials having a difference in thermal expansion coefficient of more than 23 ppm, stress and warpage due to the difference in thermal expansion coefficient increase, and reliability is impaired. On the other hand, when the difference in the coefficient of thermal expansion is small, the change in the warpage due to the thermal history is small, and it is relatively easy to ensure reliability without using a frame material, and the need for the present invention is eliminated. If a material such as Al-SiC composite material or Cu-Mo composite material is used as the base plate, the cost is higher than the metal base plate, and the cost is higher than the metal frame material. However, since the coefficient of thermal expansion becomes small and the reliability of the integrated structure may be poor, the object of the present invention can be clearly achieved at 6 to 23 ppm.

Generally, the coefficient of thermal expansion of metals is larger than that of ceramics, and aluminum nitride and silicon nitride have a coefficient of thermal expansion of 3 to 5 pp.
m is 15 to 25 pp for copper and aluminum
Since it is about m, a combination of these materials can be used in the present invention. The structure of the present invention is epoch-making in that long-term reliability can be maintained even with a combination of materials having such a large difference in coefficient of thermal expansion.

In the structure of the present invention, preferably, the metal layer on the side of the ceramic substrate facing the metal base plate and the metal base plate are joined with a brazing material. This is because brazing has higher joint reliability and joint strength than soldering. More preferably, the joining of the ceramic substrate and the metal layer on the side facing the metal base plate, and the joining of the metal layer and the metal base plate are made of Mg, Ag, and Cu.
It is preferable that they are joined by a brazing material made of an aluminum alloy containing one or more of the above. By using such a brazing material, more reliable joining can be realized.

In the heat dissipation structure of the present invention, the size of the metal plate in contact with the base plate is 1 mm or more on one side (hereinafter the same) of the external shape of the heat-generating electric component mounted on the surface circuit of the ceramic circuit board (hereinafter the same). That is, it is preferable that both sides are 2 mm larger. If long-term reliability is required, it is desirable that the size be 2.0 mm or more. This is because when this requirement is satisfied, the heat dissipation from the heat-generating electric component can be easily maintained reliably, and the object of the present invention can be achieved more reliably.

In the module, most of the heat generated in the heat-generating electric parts such as semiconductor elements escapes to the outside through the ceramic substrate and the base plate. At that time, it is important to secure a sufficiently large area to dissipate the heat in order to secure the heat dissipation. In particular, when the base plate and the ceramic circuit board are joined without using solder, as described above, the partial warpage caused by the temperature difference caused by heat generation is promoted. In order to secure a sufficient contact area for radiation, the size of the metal plate in contact with the base plate needs to be larger than the outer circumference of the heating element by 1 mm or more.

The size of the metal plate on the side in contact with the base plate is -2.0 m based on the outer shape of the ceramic substrate.
It is preferable to make it larger than m. The reason for this is that if the metal plate is too smaller than the ceramic substrate, it becomes difficult to secure the heat dissipation from the heat-generating electrical components, the placement of the heat-generating electrical components is limited, or the ceramic is used in the nickel plating process after joining. This is because a plating solution may easily remain in the clearance between the substrate and the base plate, which may cause inconvenience. It should be noted that the size of the metal plate is preferably not larger than +4.0 mm or more with respect to the outer shape of the ceramics substrate, because if the metal plate is too large, the stress concentrated on the outer periphery of the metal plate causes irregularity of the metal plate. This is because deformation may occur, or a joint failure with the base plate may occur. Most preferably, it is -1.5 to +1.0 mm based on the outer shape of the ceramic substrate.

Further, as described above, the thickness of the metal plate on the side of the base plate to be joined to the circuit board is preferably thicker than the thickness of the metal plate on the side of the circuit. From the practical point of view, it is preferable that the thickness of the metal plate on the base plate side is about 1 to 3 times the thickness of the metal plate on the circuit side. More preferably 1.2 times to 2.
It is good to set it to 5 times, more preferably 1.4 to 2 times.
By doing so, an integrated product of the substrate and the base plate can be obtained in which the warpage is less likely to change due to a thermal cycle such as a soldering process.

Regarding the heat dissipation characteristics of the heat dissipation structure, it is important to make the contact area between the base plate of the constituent material and the ceramics circuit board sufficiently large in order to reduce the thermal resistance from the initial stage under actual use conditions. However, at the same time, it is very important from the perspective of ensuring long-term heat dissipation and therefore reliability. Regarding the latter, for example, the tendency can be grasped by continuing the heat cycle of −40 ° C. to 125 ° C. for a long period of time.

Regarding the metal frame used in the present invention, iron,
It is preferably made of aluminum, copper, or an alloy containing iron, aluminum, or copper as a main component. Since it is preferable to use a frame material with as high rigidity as possible,
An alloy is preferable to a pure metal, and a work-hardened material is preferable. Iron is preferably used for the frame material in terms of cost and rigidity.

As described above, the heat dissipation structure of the present invention adopts a specific structure, so that even if it is subjected to repeated heat fluctuations, no cracks or breaks occur in the ceramic substrate or the solder layer, It has the characteristics that the radiation is secured and that it can exhibit high reliability for a long period of time.

Further, the present invention uses the heat dissipation structure,
A module characterized in that a circuit is formed in a metal layer on a side of the ceramic substrate in the heat dissipation structure that does not face the metal base plate, and one or more semiconductor elements are mounted on the circuit. Is. The module of the present invention is a highly reliable module because it uses the heat dissipation structure having the characteristics described above, but this characteristic is remarkable in a module in which one or more semiconductor elements are mounted on the circuit. Is. However, a module equipped with a semiconductor element is used for power control in a power source application, and is subject to extremely severe repeated thermal fluctuations in this application.
The module of the present invention is suitable, for example, as a power control module for use as a power source for mobile devices such as automobiles. The module of the present invention naturally includes a module having a plurality of metal base plates in one frame and a plurality of ceramic substrates on the metal base plates.

Next, a method of obtaining the heat dissipation structure of the present invention will be described by taking the method of manufacturing the structure of the present invention as an example.

In the structure of the present invention, the ceramic substrate may be joined after the frame and the base plate are integrated, or the ceramic substrate may be joined to the base plate and then joined to the frame. Further, the metal layers provided on both sides of the ceramic substrate may be joined at the same time when they are joined to the base plate.

The method of manufacturing a structure of the present invention includes (1) a step of manufacturing a ceramic substrate having metal layers on both sides,
(2) A step of forming a base plate-integrated ceramic substrate by providing a metal base plate on any metal layer of the ceramic substrate, (3) the ceramic substrate and /
Or a step of preparing a metal frame having an opening of a size capable of accommodating a metal base plate, (4) a ceramic substrate of the base plate integrated ceramic substrate and / or a metal base plate of the metal frame. And a step of fixing the metal frame and the metal base plate to integrate them by arranging them in the opening.

By adopting this combination of steps,
Since the temperature to which the frame material is exposed is lower than when the ceramic substrate is joined after the frame and base plate are integrated,
The rigidity of the frame material can be kept high, and the effect of suppressing the deformation of the base plate due to the frame material, which is one of the objects of the present invention, can be exhibited.

In general, the surface of the base plate is often covered with a nickel-plated film, but it is not always necessary unless problems such as corrosion occur in the environment of use. Whether or not the base plate needs to be plated before brazing also depends on the manufacturing method used. Further, the frame material may be plated if necessary. When using iron, it is advisable to carry out anticorrosion treatment such as chromate treatment.

In the step (1) of producing a ceramic substrate having metal layers on both sides, it is not necessary to specifically limit the method of producing the ceramic substrate, and a known method can be used. For example, when the metal layer is aluminum, an aluminum alloy containing magnesium and at least one element selected from the group consisting of copper, germanium, and silicon may be used for the brazing material. Particularly, if a JIS No. 2017 foil is inserted between a metal plate and a ceramic substrate and heated to 600 ° C. or higher while applying pressure, highly reliable bonding is possible. When using a metal having a lower melting point than aluminum as the metal plate, if appropriate,
It is desirable to use a low melting point brazing filler metal or to jointly use a surface reaction promoting means such as ultrasonic wave or plasma treatment.

In the step (2) in which the metal base plate is provided on any of the metal layers of the ceramic substrate to form the base plate-integrated ceramic substrate, a brazing material is appropriately selected according to the material to be joined. Then, brazing can be performed, or in some cases, solid state diffusion bonding can be used without using a brazing material. Preferably, when the metal layer is aluminum, the bonding with the metal base plate is Mg,
It is preferable that they are joined by a brazing material made of an aluminum alloy containing one or more of Ag and Cu. By using such a brazing material, more reliable bonding can be realized. To join copper and aluminum, you can stack copper and aluminum plates without using brazing material,
Bonding can be performed by heating near the eutectic temperature of copper and aluminum, or bonding can be performed using a brazing material having a low melting point containing magnesium, zinc, or the like. Solid phase diffusion bonding is particularly useful for bonding metals having a low melting point.

The heat dissipation structure of the present invention can be obtained by joining a ceramic circuit board and a base plate, which are obtained by joining metal plates in advance, but the metal plate, the ceramic substrate and the base plate can be obtained at once. It can also be manufactured by joining. That is, between the concave and convex surfaces of a mold having a concave surface having a desired shape and a convex surface facing the concave surface, a metal plate to be a circuit is provided on one main surface, and a desired metal plate is provided on the opposite surface. With or without the circuit board and the brazing material,
The base plate is arranged and fixed to a jig, and heated so that a part of the brazing material is melted or while the surfaces of the desired metal plate and the base plate are reacted, and the ceramic circuit board and the base plate are heated. , It is also possible to obtain a heat dissipation structure used in the present invention, also between the concave and convex surfaces of a mold having a concave surface of a desired shape and a convex surface facing it, a metal plate to be a circuit, The brazing material, the ceramic substrate, the brazing material, the metal plate, the brazing material, and the base plate are laminated in this order and fixed to a jig so that a part of the brazing material is melted or the surfaces of the desired metal plate and base plate are It is also possible to obtain a heat dissipation structure used in the present invention by heating while reacting to bond the ceramic circuit board and the base plate.

In the step (3) of preparing the metal frame having the opening, various known methods can be used for forming the opening. The most general method is a method of punching a metal plate using a press machine and a die. The size of the opening needs to be determined in consideration of the difference in thermal expansion coefficient between the base plate and the metal plate, and also depends on the method of assembling the base plate and the frame.

The conventional power module is used by attaching it to a water cooling block or a heat radiation fin with a screw by using a hole provided in the base plate. In the power module using the structure of the present invention, it is possible to similarly tighten the screws by using the mounting holes provided in the frame. At this time, the base plate to which the circuit board is attached needs to have a structure in which a sufficient pressing force is exerted so that the base plate is in close contact with the water cooling block and the heat radiation fin. Therefore, it is preferable to provide a step or a taper on the surface where the base plate and the frame face each other as shown in FIG.

In the step (4), various known methods can be used, but press fitting, shrink fitting, or caulking is preferable. Press-fitting is a method in which an opening having substantially the same size as the base plate is provided in the frame member and the base plate is pushed into the opening using a press or the like. At this time, if the size of the opening is smaller than that of the base plate by 5 to 40 μm, the adhesion between the base plate and the frame is improved, which is convenient for dissipating heat and the reliability is also increased.

Shrink-fit is a process in which a metal frame provided with an opening slightly smaller than the size of the base plate is heated and expanded, and the metal base plate is stored and cooled in the place where the opening is enlarged. A method of fixing and integrating a metal frame and a base material. This method is preferable because it does not require any expensive equipment and is excellent in mass productivity as compared with other methods.

The crimping is a method of mechanically deforming a part of the frame material or the base plate to form a protrusion, and thereby fixing the frame and the base plate. In the case of caulking and integrating, if the thermal expansion coefficient of the frame material is larger than that of the base plate, the bonding force between the frame and the base plate may be reduced due to heating in normal outer peripheral caulking, which may cause a problem. In this case, one or a plurality of holes may be opened in the base plate, a boss formed in the frame material may be inserted into the hole, and the boss may be crushed from above and below with a pressing machine. This point-type caulking method is suitable when there is a difference in thermal expansion coefficient between the frame material and the base plate. In order to avoid the generation of new stress due to the difference in thermal expansion coefficient between the frame material and the base plate, it is necessary to provide a gap between the inner circumference of the opening and the outer circumference of the base plate to absorb the dimensional change during heating and cooling. In this case, the caulking on the outer periphery of the base plate is inferior in reliability. Further, the smaller the number of points to be crimped, the more stress is not generated, so that the reliability of the structure can be increased.

[0053]

Example 1 As a ceramic substrate, the thermal conductivity measured by a laser flash method was 65 W / mK, 3
A silicon nitride substrate (dimensions 45 × 30 × 0.635 mm) having an average point bending strength of 720 MPa was prepared. Also, the dimensions are 45 × 30 × 0.4 mm and the purity is 99.99.
% Aluminum plate was prepared. The aluminum plates are stacked on both sides of the silicon nitride substrate via JIS nominal 2017 aluminum alloy foil, and set on a jig.
The aluminum plate and the silicon nitride plate were bonded together in a vacuum while applying pressure. After the joining, an etching resist was screen-printed on a desired portion of the surface of the aluminum plate, and a pattern was formed by performing an etching treatment to produce a ceramic circuit board.

Next, as a base plate, dimensions 55 × 40 ×
A 4 mm thick aluminum alloy JIS No. 6063 material was prepared. Then, a JIS name 2017 aluminum alloy foil is placed between the ceramic circuit board and the aluminum alloy base plate, arranged so that each part has the shape shown in FIGS. 1 and 2, and set on a graphite jig. did. The graphite jig is a pair of a plate having a concave surface and a plate having a convex surface,
The uneven surface had a span of 50 mm and 100 μm. Bonding was performed under a heating condition of 590 ° C. × 4 min while pressing with a graphite jig to obtain an integrated product of the circuit board and the base plate.

An aluminum alloy JIS No. 6063 having a thickness of 4 mm was prepared as a frame material, an opening 20 μm smaller than the external dimensions of the integrated product was provided near the center, and four screw holes were provided in the outer peripheral portion. A plate of 115 × 80 mm was prepared. The above integrated product was pushed into this frame with a press machine to obtain a structure.

To evaluate the heat dissipation of the structure, a 10 mm square silicon semiconductor element (hereinafter referred to as a silicon element) was soldered to a predetermined position on the circuit board. Before and after soldering, the shape in the longitudinal direction passing through the center of the base plate on the back surface of the structure was measured with a contour shape measuring instrument, and the difference was obtained. Then, an aluminum heat dissipation unit was fastened to the bottom surface of the structure with four screws via silicone grease. The module tightened with this screw, -40 ℃ ~ 1
A heat cycle test was performed at 25 ° C., and the change in thermal resistance was examined every predetermined number of cycles. The thermal resistance was determined by cooling the heat dissipation unit with water and measuring the temperature of the silicon element and the temperature of the aluminum heat dissipation unit while applying a constant current in the thickness direction of the silicon element. Table 1 shows the amount of change in warpage before and after soldering and the number of cycles in the heat cycle test when the thermal resistance reached 120% of the initial value.

[0057]

[Table 1]

Example 2 A steel frame material produced in the same manner as in Example 1 was heated to 300 ° C. to be expanded, and the integrated article produced in the same manner as in Example 1 was quickly pushed into the central hole. After cooling, a structure was produced. Evaluation was performed in the same manner as in Example 1, and the results are shown in Table 1.

[Example 3] A step was provided on the outer peripheral portion of a base plate made of an aluminum alloy, and a frame with steps capable of pressing the step from above was made of a steel material. In addition, a hole having a diameter of 3 mm for caulking is made in the base plate, and a boss is provided on the frame side so as to fit in the caulking hole of the base plate when the base plate and the frame are assembled. A boss was struck from the top and bottom using a mold and crushed and crimped to produce a structure (see FIG. 3). Evaluation was performed in the same manner as in Example 1, and the results are shown in Table 1.

Example 4 In Example 1, the silicon nitride plate was replaced with an aluminum nitride plate, the base plate was replaced with nickel-plated oxygen-free copper, and the frame material was copper alloy CDAN.
o. In place of 19210, a structure was obtained in the same manner as above. Evaluation was carried out in the same manner as in Example 1, and the results are shown in Table 1.
It was shown to.

[Embodiment 5] A structure is obtained in the same manner as in Embodiment 4, except that the step of integrating the aluminum nitride circuit board and the base plate in Embodiment 4 is performed by soldering instead of brazing. It was Evaluation was performed in the same manner as in Example 1, and the results are shown in Table 1.

Example 6 A 99.99% high-purity aluminum plate having a thickness of 0.4 mm was formed on one surface of a silicon nitride substrate.
A structure was prepared in the same manner as in Example 1 except that a high-purity aluminum plate having a thickness of 0.8 mm was bonded to one surface and an Al—Ag—Mg-based brazing material was used to bond the circuit board and the base plate. . Evaluation was performed in the same manner as in Example 1, and the results are shown in Table 1.

[Comparative Example] The size of the base plate is 115 × 80 m.
A structure was produced in the same manner as in Example 1 except that m was used and no frame material was used. The amount of change in warpage before and after soldering and the heat cycle test were performed, and the thermal resistance was 120% of the initial value.
The number of occurrences is shown in Table 1.

[0064]

The structure of the present invention is characterized by high reliability and high heat dissipation, and has a small change in warpage during soldering of semiconductor elements, and solves the problems in the power module assembly process due to the warpage. In addition, the module obtained using this has the characteristic of maintaining high heat dissipation even after a long-term heat cycle, so a power module for power control that requires both high reliability and high heat dissipation performance. In particular, it can be suitably used as a power module for power control of mobile equipment such as automobiles and trains, and is industrially useful.

[Brief description of drawings]

FIG. 1 is a plan view of an example of a structure of the present invention.

FIG. 2 is a sectional view of an example of a structure of the present invention.

FIG. 3 is a sectional view of a structure according to a third embodiment of the present invention.

[Explanation of symbols]

1 (Metal) base plate 2 Ceramic circuit board 3 Ceramic substrate 4 Metal plate (circuit) 5 metal plates 6 Bonding layer 7 Solder layer 8 Semiconductor elements 9 screw holes 10 (Metal) frame 11 openings 12 Caulking hole 13 Boss 14 steps

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Takuya Okada             3-5 Asahi-cho, Machida-shi, Tokyo Electrification             Gakkou Central Research Institute F term (reference) 5F036 AA01 BB08 BC06 BD01 BD03                       BD14

Claims (9)

[Claims] 1. A ceramic substrate comprising a metal frame having an opening, a ceramic substrate having metal layers on both sides thereof, and a metal base plate provided on one metal layer side of the ceramic substrate. And / or a structure in which a metal base plate is arranged in the opening of the metal frame, and the metal base plate is fixed to the metal frame, wherein the coefficient of thermal expansion of the ceramic substrate and the metal base. A structure characterized in that the difference in the coefficient of thermal expansion of the plates is 6 to 23 ppm. 2. The metal frame is made of iron, aluminum, copper, or an alloy containing iron, aluminum, or copper as a main component, the ceramic substrate is silicon nitride or aluminum nitride, and the metal base plate is The structure according to claim 1, comprising aluminum, copper, or an alloy containing aluminum or copper as a main component. 3. The structure according to claim 1, wherein the method of fixing the metal base plate to the metal frame is any of press fitting, shrink fitting, and caulking. 4. The metal layer on the side of the ceramic substrate facing the metal base plate and the metal base plate are joined by a brazing material, claim 1, or claim 2. The structure according to 3. 5. The metal layers provided on both sides of the ceramic substrate are made of high-purity aluminum, and the metal layer of the metal layer facing the metal base plate is equivalent to the metal layer on the opposite side. The structure according to claim 1, claim 2, claim 3, or claim 4 having the above thickness. 6. The bonding of the ceramics substrate and the metal layer on the side facing the metal base plate, and the bonding of the metal layer and the metal base plate are all one or more of Mg, Ag and Cu. The structure according to claim 4 or 5, wherein the structure is joined by a brazing material made of an aluminum alloy containing a. 7. The structure according to claim 1, claim 2, claim 3, claim 4, claim 5 or claim 6 is used, which is located on the side not facing the metal base plate on the ceramic substrate. A module, wherein a metal layer is formed into a circuit, and one or more semiconductor elements are mounted on the circuit. 8. A base plate-integrated ceramics substrate comprising: (1) a step of producing a ceramics substrate having metal layers on both sides thereof; and (2) a metal base plate provided on one of the metal layers of the ceramics substrate. And (3) preparing a metal frame having an opening having a size capable of accommodating the ceramic substrate and / or the metal base plate in advance,
(4) a step of arranging the ceramic substrate of the base plate-integrated ceramic substrate and / or the metal base plate in the opening of the metal frame, and fixing and integrating the metal frame and the metal base plate. A method of manufacturing a structure, comprising: 9. In the step (4), the metal frame is heated, the metal base portion of the base plate-integrated ceramics substrate is stored in the opening of the metal frame, and the metal frame is cooled. 9. The method for manufacturing a structure according to claim 8, which is a step of fixing and integrating the frame base plate and the metal base plate of the ceramic substrate.