JP2001291809A - Heat dissipation components - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heat radiating component that has favorable adhesion with heat radiating fins and can achieve a heat radiating structure with excellent heat radiating property. SOLUTION: This heat radiating component is composed of a metal-ceramic complex constructed by impregnating a metal containing aluminum as a main component into a porous silicon carbide body. When two arbitrary points are assumed on one main surface, the main surface positioned between the two points is a planar plate shape having a positive radius of curvature.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat dissipating component comprising a silicon carbide-aluminum composite, which is used for dissipating heat in a hybrid integrated circuit using a ceramic circuit board.

[0002]

2. Description of the Related Art As semiconductor devices become more highly integrated and larger,
The amount of heat generated from electronic components such as semiconductor elements and circuits has been steadily increasing. Therefore, in order to sufficiently dissipate heat, a ceramic circuit board having high insulation and high heat dissipation is used.

[0003] In particular, aluminum nitride circuit boards are 10
Since it has a high thermal conductivity of 0 W / mK or more and has a thermal expansion coefficient close to that of silicon, it is widely used especially for high power applications.

[0004] The aluminum nitride circuit board is provided with a copper circuit in which electronic components such as semiconductor elements are joined to an aluminum nitride board by an active metal method or a DBC method.

[0005] FIG. 1 is a diagram showing a practical use of ceramic circuit boards including the aluminum nitride circuit board.
1 shows a typical heat dissipation structure for dissipating heat generated from electronic components and the like on a ceramic circuit board.

That is, the heat sink 3 is mounted on the radiating fins 4, and the ceramic circuit board 2 on which the electronic component 1 such as a semiconductor element is mounted at a desired position such as a circuit is mounted thereon. The electronic component 1 and the circuit on the ceramic circuit board, and the ceramic circuit board 2 and the heat sink 3 are joined by a joining material such as solder or brazing material as needed. The heat radiation fins and heat sinks are generally made of inexpensive metals having high thermal conductivity, such as copper and aluminum.

In manufacturing the heat dissipation structure,
After the structure above the heat sink is pre-assembled,
Furthermore, it is general that these and the radiation fins are fixed by screws with high thermal conductivity grease.
At this time, in order to maintain high heat radiation, it is necessary that the heat radiation fins 4 and the heat sink 3 (also called a base plate) are sufficiently adhered via grease.

However, the conventional structure in which a copper base plate and a ceramic circuit board are joined together has a problem in that cracks occur in the solder layer joining them, so-called solder cracks. Was. The solder layer is a copper base plate (17pp
m / K) and the thermal expansion coefficient of the ceramic substrate, which absorbs and relaxes the stress. However, as the number of cycles of high temperature and low temperature increases, cracks occur due to fatigue, and the cracks develop further. Therefore, there is a problem that reliability is deteriorated, for example, the heat radiation structure is broken or heat radiation characteristics are deteriorated.

For this reason, it is desired to develop a heat-dissipating component material such as a base plate having a high thermal conductivity and a coefficient of thermal expansion smaller than that of copper and close to that of a ceramic substrate. Composites (aluminum-silicon carbide composites) have been developed. The composite consisting of aluminum and silicon carbide has a coefficient of thermal expansion of 8 ppm / K
It is considerably smaller than the conventional copper of 17 ppm / K, and is attracting attention as a heat dissipating member capable of solving the problem of the solder crack.

However, according to the study of the present inventor, it has been found that some problems must be solved even in the heat-dissipating component composed of the above-described aluminum-silicon carbide composite before it can be put to practical use. Was.

First, the thermal conductivity of the aluminum-silicon carbide composite is as small as about half that of copper.
The challenge is to improve this. Regarding this problem, one having a thermal conductivity exceeding 200 W / mK has recently been developed.

The second is how to achieve a structure that easily dissipates heat in a series of structures from the semiconductor element to the heat radiation fins. The heat radiation component made of the aluminum-silicon carbide composite is warped in advance. The purpose of the present invention is to secure the heat radiation characteristics by improving the adhesion between the base plate and the heat radiation fins, which is a problem to be solved by the present invention.

In the conventional method, a base plate having no or little warping has been directed. However, when a ceramic circuit board and a base plate are joined by using a base plate having a flat surface, the base plate is bent. Due to the stress generated due to the difference in thermal expansion between the base plate and the ceramic circuit board, the surface of the base plate that is brought into close contact with the radiating fins is warped in a concave shape. For this reason, in the next step, when fixing the base plate on which the ceramic circuit board is fixed to the radiation fins, a sufficient contact area cannot be obtained, the heat radiation fins have satisfactory heat radiation properties, and the The heat dissipation structure that can maintain the heat dissipation has not yet been obtained.

As a means for solving the above problem, the present applicant previously warps the surface of the base plate to be in close contact with the radiating fins into a convex shape, and makes the base plate adhere to the radiating fins even after joining the ceramic substrate. It has been considered that the side surface is maintained as a convex warp, and this is fixed to a radiating fin by screwing to secure a sufficient contact area to release heat.

So far, warped aluminum
The present applicant has made various proposals on a method for producing a silicon carbide composite (hereinafter, referred to as a composite), and a method of subjecting the composite after the production to machining to impart warpage,
In a composite in which the aluminum layer is coated on the front and back of the composite, the thickness of the aluminum layer on the front and back is changed during the production of the composite, and a method of imparting warpage by stress generated from the difference in the aluminum thickness on the front and back, and the dispersed phase of the composite A method of preparing a composite after pre-grading the density and composition of the preformed silicon carbide preform, giving a warp from the difference in composition and density, and further subjecting the composite to heat treatment while applying stress and plastic deformation Have proposed a method of warping.

[0016]

However, in a warped base plate manufactured by the above-described method or the like, the shape of the warp (how the surface is warped) is various.
Therefore, the shape of the base plate after the actual mounting process such as bonding of the ceramic circuit board cannot sufficiently achieve the purpose of maintaining the surface on the side to be in close contact with the radiation fins in a convex warpage. The situation is happening frequently.

FIG. 2 is a diagram for explaining the above situation. After the ceramic circuit board is joined, the surface on the side that is in close contact with the radiation fins has a convex warp overall, but shows a typical warp shape that does not provide sufficient adhesion when screwed to the radiation fins This shows a conventional example in which screwing does not work effectively because the outer peripheral portion of the portion where the substrates are joined has warped to the concave side.

[0018]

Means for Solving the Problems The inventors of the present invention have prepared a base plate having various warping shapes, although it is entirely convex, with respect to the adhesion between the base plate and the radiation fins. Performing the board joining, and measuring the warped shape after the joining, as a result of evaluating the presence or absence of the concave portion in the plane, in the state before the circuit board joining, those having a certain specific shape,
Even after the circuit board is joined, the concave portion does not occur in the plane and the convex shape is maintained, and a heat radiation structure having characteristics very close to the original heat dissipation property and maintaining the same is obtained. The present inventors have obtained the knowledge that the present invention can be performed, and completed the present invention.

That is, the present invention relates to a heat-dissipating component comprising a metal-ceramic composite in which a silicon carbide-based porous body is impregnated with a metal containing aluminum as a main component. When taken, the heat radiating component is characterized in that the main surface located between the two points is a flat plate having a positive radius of curvature.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the heat-radiating component of the present invention, the warped shape of the base plate before the substrate bonding is specified as described above. As a result, the base after the ceramic circuit substrate bonding is completed. The state of the plate is such that a surface side in contact with a cooling component such as a radiation fin has a convex warpage, and has a feature in which a partial concave portion does not occur in the surface. Therefore, the close contact between the base plate and the radiating fins can be enhanced, and a heat radiating structure exhibiting a heat radiating property very close to the original heat radiating property and maintaining this can be easily obtained.

The present inventor has prepared a base plate having a convex shape but various warp shapes, joined the circuit boards, measured the warped shape after the joining, and determined the occurrence of concave portions in the plane. As a result of examining the presence / absence, the one having a warped shape including a linear portion before joining the circuit board may generate a concave portion from the linear portion, and as shown in FIG. , That is, a flat plate whose main surface located between two points has a positive radius of curvature when any two points are taken on one main surface. It has been found that the adhesion between the base plate and the heat radiating components such as the heat radiating fins becomes good only when the requirement of the heat radiating structure is satisfied, and the original characteristics of the heat radiating structure can be exhibited.

In the present invention, the absolute amount of warpage, that is, the amount of warpage, cannot be uniquely determined due to various definitions. For example, if a typical definition of the amount of warpage is given, For a line parallel to the longitudinal direction of the base plate and passing through the center of the base plate, the height of both ends of the base plate is measured, and when the height of each is set to zero, the line is sandwiched between both ends. There is a method in which the highest value of the heights of the points on the line segment is used as the amount of warpage, and a method of obtaining the amount of warp in the short direction or diagonal direction by a similar method.

In the present invention, the degree of warpage is determined experimentally by the area and thickness of the base plate, the material, shape and thickness of the ceramic circuit board to be joined, and other mounted parts. You only have to decide. that time,
After joining the ceramic circuit boards, it is necessary to determine the amount of warping so that the surface of the base plate to which the heat radiating components such as the heat radiating fins are bonded does not become concave. If the base plate has an appropriate amount of warpage, the warped base plate of the present invention will not be concavely warped, and no in-plane recess will be formed.

According to the experimental results of the present inventors, for example, the size of the base plate is 120 × 80 mm and the thickness is 4 m.
m, and the circuit board is an aluminum nitride substrate on which a copper circuit board is formed, the dimensions of which are: 70 × 50 mm, 0.65 mm thick aluminum nitride;
When a circuit of mm is formed, the suitable amount of warpage of the base plate is 50 to 200 μm in the longitudinal direction and 50 in the transverse direction.
１５０150 μm.

As described above, the method of manufacturing the heat radiating component of the present invention includes a method in which the silicon carbide-aluminum composite after fabrication is machined to impart a warp, and an aluminum layer is formed on both sides of the composite. In the coated composite, change the thickness of the aluminum layer on the front and back during composite production,
A method of imparting warpage by the stress resulting from the thickness difference between the front and back aluminum layers, or preparing a composite after preliminarily inclining the density and composition of the silicon carbide preform that is the dispersed phase of the composite, Any method may be used, such as a method of giving a warp due to a difference in density, or a method of applying a stress to a composite body, performing a heat treatment, plastically deforming and giving a warp.

As an example of the method for producing a warped base plate of the present invention, a method of forming a warp by applying heat to the above-mentioned composite while applying a stress to the composite and plastically deforming the composite will be exemplified.

As a method for producing a silicon carbide preform used in the present invention, a mixed powder in which a silicon carbide powder is mixed with an organic binder and an inorganic binder to maintain the strength after firing is formed, and then mixed in air. Or a method of baking in an inert atmosphere to form a preform, a method of adding water, a solvent and a plasticizer, a dispersant, etc. to the mixed powder, kneading, extruding, baking, reducing the viscosity of the mixture, A publicly known method such as an injection method of injecting and baking the mixture, followed by firing can be employed.

In order to obtain an aluminum-silicon carbide composite having a high thermal conductivity and a low coefficient of thermal expansion, a preform may be prepared by any of the above methods.
It is desirable that the relative density of the preform be 50% or more, more preferably 60% or more. And, for that purpose, the silicon carbide raw material having a different particle size distribution 2
It is effective to appropriately mix more than one kind of raw material powder.

As a method of impregnating a silicon carbide preform with a metal containing aluminum as a main component to form a composite, a so-called melt forging method in which molten aluminum is poured into a silicon carbide preform and impregnated with high pressure, Conventionally known methods include a die casting method for rapidly injecting and impregnating aluminum into a preform to form a composite, and a powder metallurgy method for producing a dense body by mixing, molding and sintering silicon carbide and aluminum powder. The method can be adopted. Regarding the surface properties of the composite produced by the above method, the composite structure may be exposed on the surface, or the surface or a part thereof may be coated with aluminum. Relative density of silicon is 60-80
% Of the preform can be used, and as a result,
It is preferable because it has a feature that a composite having a high thermal conductivity of about 160 to 200 W / mK can be easily obtained.

Hereinafter, the production of the aluminum-silicon carbide composite of the present invention will be described in more detail by way of a melt forging method.

After the silicon carbide preform prepared by the above method is set in a mold, molten aluminum is charged into the mold, and the molten aluminum is pressed. , And cooling in that state, an aluminum-silicon carbide composite can be obtained.

In the above operation, the preform is preheated in advance for smooth impregnation. The aluminum material to be impregnated is an aluminum-silicon alloy containing 5 to 14% by mass of silicon for the purpose of lowering the melting temperature, facilitating the impregnation, and improving the mechanical properties of the obtained composite. Further, an aluminum-silicon-magnesium alloy to which magnesium is added in an amount of 0.1 to 2.0% by mass for the purpose of further improving the wettability with the preform is used. Which alloy to use can be selected arbitrarily,
Generally, the aluminum alloy melted at 800 ° C. to 900 ° C. is impregnated.

The aluminum-silicon carbide composite produced by the above method is processed as it is, or after its surface and outer periphery are processed into a predetermined shape, to obtain a base plate having a desired shape but almost no warpage. Becomes

Next, the base plate is warped. As a method thereof, plastic deformation may be caused by heating while applying a stress to a part or the entire surface of the base plate. At this time, the method of applying the stress may be determined experimentally, but in order to obtain the warped shape of the present invention, the convex surface and the concave surface having a constant radius of curvature in a spherical shape or a desired direction are used. It is preferable to apply a load by using a mold having a base plate sandwiched between both surfaces.

The heat treatment is performed at a temperature of 300 ° C. or more, preferably 350 ° C. or more. If the temperature is less than 300 ° C., the material is not easily deformed even if stress is applied. If heated at a temperature exceeding 350 ° C., the material is easily deformed and the productivity is excellent. Although the upper limit of the heating temperature is not particularly limited, it goes without saying that the heating is performed at a temperature lower than the temperature at which the aluminum component constituting the composite is melted.

[0036]

The present invention will be described below with reference to examples. Example 1 A 4.3 mm-thick preform made of silicon carbide having a relative density of 65% was set in a mold.
Molten aluminum containing 5% by weight of silicon and 0.5% of magnesium is poured into the mold and pressed under high pressure to impregnate the voids in the preform with an aluminum alloy to form an aluminum-silicon carbide. A composite was made. By processing the resulting composite, a size of 12
0 mm (longitudinal direction) x 80 mm (short direction) and thickness 4
mm base plate. The surface composition at this time was composed of an aluminum alloy and silicon carbide.

Next, in order to give a warp to the obtained base plate, an uneven mold having a curved surface with the same curvature was prepared. The base plate described above was inserted between the concave surface and the convex surface, and the base plate was tightened by a tightening jig, so that the base plate was shaped into a concave and convex curved surface. Next, the base plate in such a state is removed by 450.
After heating at 1 ° C. for 1 hour, cooling, releasing the tightening, the warpage was measured.

The warpage was measured by a surface roughness meter, and the measurement span was 115 mm in the longitudinal direction and 75 mm in the transverse direction. The measurement position in both the longitudinal and transverse directions was a line passing through the center of the base plate. As a result of measuring the warpage, one surface has a convex shape in both the longitudinal direction and the short direction, and the opposite surface has a concave warp shape, and after bonding the ceramic circuit board, on the convex measuring line to be bonded to a heat radiating component such as a heat radiating fin. Regardless of which two points were zero, all points in between had positive heights. The maximum height when the height of both ends of the measurement span is zero, that is, the amount of warpage is 151 μm in the longitudinal direction.
m, and 110 μm in the transverse direction.

Next, after nickel plating was applied to the base plate, an aluminum nitride circuit board was soldered to the concave side of the base plate. At the time of soldering, the longitudinal direction of the base plate was made parallel to the longitudinal direction of the aluminum nitride circuit board, and the circuit board was arranged at the center of the base plate. The aluminum nitride circuit board used here had dimensions of 70 mm × 50 mm and a thickness of 0.6 mm.
A circuit is formed by bonding a 0.3 mm copper plate to a 5 mm aluminum nitride substrate.

A base to which a ceramic circuit board is soldered
The warpage of the surface of the substrate not bonded to the circuit board was measured. The warp measurement is performed by a surface roughness meter with the measurement surface facing upward, and the measurement span is 115 in the longitudinal direction.
mm, and 75 mm in the lateral direction. The measurement position in both the longitudinal and transverse directions was a line passing through the center of the base plate. As a result of the measurement of the warp, both the longitudinal direction and the transverse direction show a convex (ie, positive) warp shape, and even if any two points on the measurement line are set to zero, all points between them show a positive height. The maximum height when the height at both ends of the measurement span is zero, that is, the amount of warpage is 52 μm in the longitudinal direction,
It was 39 μm in the transverse direction.

Further, an aluminum block plate is prepared as a heat dissipating component, a heat dissipating grease is applied thereon to a thickness of 50 μm, the base plate on which the ceramic circuit board is mounted is disposed, and the four corners are tightened with a 6N tightening force. Screwed. Thereafter, the fastening was removed, and the adhesion area between the base plate mounted on the ceramic circuit board and the heat radiating component was evaluated by measuring the area of the grease adhering to the back surface of the base plate. Table 1 shows the above results.

[0042]

[Table 1]

Example 2 5.3 mm thick preform
A base plate to which a ceramic circuit board was joined was produced in the same manner as in Example 1 except that the base plate was impregnated and the thickness of the base plate was changed to 5 mm. Warpage was measured in the same manner as in Example 1. In addition, even if any two points on the convex side measurement line after the warp was applied to the base plate were set to zero, all points between them had a positive height. Table 1 shows the measurement results of the warpage on the convex surface side after the base plate was warped and after the ceramic circuit board was joined, and the results of examining the adhesion between the base plate and the heat radiating component.

[Embodiment 3] A preform having a thickness of 4.9 mm
Except that the aluminum alloy was left on the surface of the composite during the processing of the composite after impregnation, and the base plate was 5 mm thick, and that the warping was performed at 400 ° C. A base plate to which a ceramic circuit board was joined was manufactured in the same manner as in Example 1. Warpage was measured in the same manner as in Example 1. In addition, even if any two points on the convex side measurement line after the warp was applied to the base plate were set to zero, all points between them had a positive height. Bee
Table 1 shows the measurement results of the warpage on the convex surface side after the warp was applied to the base plate and the bonding of the ceramic circuit board, and the results of examining the adhesion between the base plate and the heat radiating component.

[Embodiment 4] A preform having a thickness of 2.9 mm
Except that the aluminum alloy was left on the surface of the composite during the processing of the composite after impregnation, a base plate with a thickness of 3 mm was formed, and the warping was performed at 400 ° C. A base plate to which a ceramic circuit board was joined was manufactured in the same manner as in Example 1. Warpage was measured in the same manner as in Example 1. In addition, even if any two points on the convex side measurement line after the warp was applied to the base plate were set to zero, all points between them had a positive height. Bee
Table 1 shows the measurement results of the warpage on the convex surface side after the warp was applied to the base plate and the bonding of the ceramic circuit board, and the results of examining the adhesion between the base plate and the heat radiating component.

Example 5 A base plate was produced in the same manner as in Example 1. When the base plate is to be warped, it is placed on a setter such that each of the four sides of the base plate serves as a fulcrum, and the center of the base plate is pressed at right angles to the same surface. The heat treatment and the bonding of the ceramic circuit board were performed under the same conditions as in Example 1. Warpage was measured in the same manner as in Example 1. It should be noted that even if any two points on the convex side measurement line after the base plate is warped are set to zero,
All points in between had a positive height. Table 1 shows the measurement results of the warpage on the convex surface side after the base plate was warped and after the ceramic circuit board was joined, and the results of examining the adhesion between the base plate and the heat radiating component.

[Comparative Example 1] Except for applying the warp to the base plate in the same manner as in Example 5, all of the fabrication of the base plate itself, the joining of the ceramic circuit board, and the measurement of the warp were performed in Example 1. The procedure was performed in the same manner as described above. When the warpage of the convex side after the warp was applied to the base plate was measured, the center of the base plate showed a positive height when the height at both ends of the measurement span in the longitudinal direction was set to zero. Although,
A concave portion was present on a line from the center of the base plate toward one end. Table 1 shows the measurement results of the warpage on the convex surface side after the base plate was warped and after the ceramic circuit board was joined, and the results of examining the adhesion between the base plate and the heat radiating component.

COMPARATIVE EXAMPLE 2 Except for applying the warp to the base plate in the same manner as in Example 5, all of the fabrication of the base plate itself, the joining of the ceramic circuit board, and the measurement of the warp were performed in Example 2. The procedure was performed in the same manner as described above. When the warpage of the convex side after the warp was applied to the base plate was measured, the center of the base plate showed a positive height when the height at both ends of the measurement span in the longitudinal direction was set to zero. Although,
On the line from the center of the base plate to both ends, one portion had a linear shape, and the other had a concave portion. Table 1 shows the measurement results of the warpage on the convex surface side after the base plate was warped and after the ceramic circuit board was joined, and the results of examining the adhesion between the base plate and the heat radiating component.

[Comparative Example 3] Except for applying the warp to the base plate in the same manner as in Example 5, the fabrication of the base plate itself, the joining of the ceramic circuit board, and the measurement of the warp were all performed in Example 3. The procedure was performed in the same manner as described above. When the warpage was measured on the convex side after the base plate was warped, the center of the base plate showed a positive height when the height at both ends of the measurement span in the short direction was set to zero. Although
A concave portion was present on a line from the center of the base plate toward one end. Table 1 shows the measurement results of the warpage on the convex surface side after the base plate was warped and after the ceramic circuit board was joined, and the results of examining the adhesion between the base plate and the heat radiating component.

[Comparative Example 4] Except for applying the warp to the base plate in the same manner as in Example 5, all of the fabrication of the base plate itself, the joining of the ceramic circuit board, and the measurement of the warp were performed in Example 4. The procedure was performed in the same manner as described above. When the warpage of the convex side after the warp was applied to the base plate was measured, the center of the base plate showed a positive height when the height at both ends of the measurement span in the longitudinal direction was set to zero. Although,
There was a linear portion on a line from the center of the base plate toward one end. Table 1 shows the measurement results of the warpage on the convex surface side after the base plate was warped and after the ceramic circuit board was joined, and the results of examining the adhesion between the base plate and the heat radiating component.

Comparative Example 5 A method similar to that in Example 5 was used, such as applying a warp to the base plate, manufacturing the base plate itself, joining the ceramic circuit board, and measuring the warp. When the warpage was measured on the convex side after the base plate was warped, the center of the base plate showed a positive height when the height at both ends of the measurement span in the short direction was set to zero. However, there was a concave portion on a line from the center of the base plate toward one end. Table 1 shows the measurement results of the warpage on the convex surface side after the base plate was warped and after the ceramic circuit board was joined, and the results of examining the adhesion between the base plate and the heat radiating component.

[0052]

The base plate made of the aluminum-silicon carbide composite of the present invention has a warped shape in consideration of the improvement of the adhesion to the heat radiating component, and thus is suitably used as a base plate for a circuit board. Is done.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a heat dissipation structure in practical use of a ceramic circuit board.

FIG. 2 is a cross-sectional view showing a conventional example of the shape of a base plate in which a ceramic circuit board is integrated.

FIG. 3 is a diagram illustrating terms of the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 electronic component 2 ceramic circuit board 3 base plate (heat sink) 4 radiating fin

Claims (1)

[Claims] 1. A heat-dissipating component comprising a metal-ceramic composite in which a silicon carbide-based porous body is impregnated with a metal containing aluminum as a main component, wherein two arbitrary points are taken on one main surface. A heat dissipating component, wherein a main surface located between the two points is a flat plate having a positive radius of curvature.