JPH09286681A - Metal-ceramic composite substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the composite substrate which has excellent heat cycle endurance and also resisting strength to vibration and is useful for mounting electronic parts by joining a specific metallic material to a ceramic substrate to form a composite substrate having specified bending strength. SOLUTION: This composite substrate is formed by joining an aluminum material to at least one surface of a ceramic substrate (such as aluminum nitride substrate) with e.g. a molten metal joining method, so that the resulting composite substrate has >=20kg/mm<2> bending strength when the distance between two supporting points is 30mm, at the time of applying a three-point bending load to the composite substrate. That is, the composite substrate is provided with a metallic part for mounting electronic parts and on the other hand, a heat radiation plate is joined to the lower surface of the substrate and further, a heat sink body is soldered to the radiation plate. In order to allow the heat sink body to tightly adhere to the fin material, the heat sink body is formed into a U-shape and its both ends are fastened by bolts. Therefore, at the time of fastening the heat sink body with bolts, unless the substrate has bending strength higher than a certain level, the adhesion between the heat sink body and the fin material is deteriorated and the heat radiation properties of the composite substrate is lowered and also, resisting strength to external force such as vibration is reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a metal-ceramic composite substrate suitable for mounting high-power electronic components such as power modules, and more particularly to automobile or train electronic components that require particularly excellent heat cycle resistance. An object of the present invention is to provide a composite substrate suitable for mounting.

[0002]

2. Description of the Related Art Conventionally, as a substrate used for mounting a high-power electronic component such as a power module, a copper-clad ceramic composite substrate produced by bonding a copper plate to a surface of a ceramic substrate has been used. This composite substrate further depends on the type of ceramic substrate used and its manufacturing method.
It is divided into a copper / alumina direct bonding substrate, a copper / aluminum nitride direct bonding substrate, a copper / alumina brazing substrate, and a copper / aluminum nitride brazing substrate.

Of these, the copper / alumina direct bonding substrate is:
As disclosed in JP-A-52-37914, copper oxide is used on the surface of an oxygen-free copper plate by using a copper plate containing oxygen or by using an oxygen-free copper plate and heating in an oxidizing atmosphere. After the generation, the copper plate and the alumina substrate are superposed and heated in an inert atmosphere to generate a composite oxide of copper and aluminum at the interface between the copper plate and the alumina substrate and join the copper plate and the alumina substrate. .

On the other hand, in the case of a copper / aluminum nitride direct bonding substrate, it is necessary to previously form an oxide on the surface of the aluminum nitride substrate. For example, as disclosed in Japanese Patent Application Laid-Open No. 3-93687, about 100
After treating the aluminum nitride substrate at a temperature of 0 ° C. to generate an oxide on the surface, the copper plate and the aluminum nitride substrate are joined via the oxide layer by the above-described method.

Further, the copper / alumina brazing substrate and the copper / aluminum nitride brazing substrate are joined together by using a brazing material having a low melting point between the copper plate and the ceramic substrate.
In addition to copper, an alloying element for lowering the melting point and an alloying element for improving the wettability with ceramics are added to the brazing material to be used. For example, active metal brazing materials such as Ag-Cu-Ti are often used. Have been.

Although the copper / ceramic composite substrate is widely used as described above, there are some problems during manufacturing and practically. The most serious problem among them is a failure due to the formation of cracks inside the ceramic substrate during the mounting and use of electronic components, and electrical conduction between the front and back of the substrate.

This is due to the fact that the coefficient of thermal expansion of copper is about one order of magnitude greater than that of ceramics. In the case of joining, when the ceramic substrate and copper are heated to nearly 1000 ° C. and cooled from the joining temperature to room temperature, A great deal of thermal stress is generated inside the composite substrate due to the difference in thermal expansion coefficient.

In recent years, with the development of power modules for electric vehicles or electric trains, the demand for composite substrates having excellent heat cycle resistance has been particularly increased. For example, electric vehicles are subject to severe temperature changes and large vibration. In this case, it is said that the heat resistance of the composite substrate needs to be 500 times or more, but the copper / ceramic composite substrate currently used cannot meet such a demand.

There has been a concept of using aluminum as a conductive circuit material having excellent electric and thermal conductivity similar to that of copper, and such a concept is described in, for example, Japanese Patent Laid-Open No. 59-121890. A brazing method is generally used for joining aluminum and ceramics, and aluminum-ceramics produced by the brazing method in Japanese Patent Laid-Open Nos. 3-125463, 4-12554 and 4-18746. A substrate is disclosed. According to this, the heat cycle resistance of the produced aluminum-ceramic substrate was about 200 times, and it was still not sufficiently applicable to the use requiring the high heat cycle resistance as described above.

Moreover, in the case of this method, the joining must be performed in vacuum, and in the case of non-oxide ceramics, pretreatment must be performed in advance to form an oxide on the surface of the ceramics. Also, there were some points that were not satisfactory in terms of thermal conductivity.

[0011]

In the composite substrate obtained by the above-mentioned manufacturing method, a metal portion 3 for mounting an electronic component is usually provided on a circuit, and a semiconductor chip is mounted on the metal portion 3.
On the contrary, the heat sink 5 is joined to the lower surface and further soldered to the heat sink. The heat sink material is U-shaped so that the heat sink material and the fin material are in close contact with each other and bolted at both ends.

In this case, if the composite substrate does not have a bending strength of a certain degree or more and is bolted, the heat radiation is deteriorated due to poor adhesion between the heat sink and the fin material.
Further, when these are mounted, there is a problem that cracks are generated in the ceramic substrate because they are weak against external force such as vibration.

[0013]

[Means for Solving the Problems] As a result of intensive research to solve the above-mentioned problems, a metal-ceramic composite substrate obtained by joining molten aluminum to a ceramic substrate and solidifying it was compared with a conventional copper-clad substrate. It was found that when used, it has appropriate bending strength and is excellent in heat cycle resistance, and was able to provide the present invention.

That is, according to the present invention, a ceramic substrate and a ceramic composite substrate in which an aluminum material is bonded to at least one surface of the ceramic substrate have a fulcrum distance of 30 when a three-point bending load is applied to the composite substrate.
The invention relates to a metal-ceramic composite substrate having a bending strength of 20 kg / mm ² or more.

[0015]

The substrate used in the present invention is a ceramic substrate made of alumina, aluminum nitride, silicon carbide, zirconia or the like, glass or the like. In this case, a high-purity material is even more preferable.

The metal used as the base in the present invention is aluminum or an aluminum alloy, which improves conductivity and obtains softness.
In this case, the higher the purity, the higher the conductivity, but on the contrary, the price becomes higher, so 99.9% (3N) of pure aluminum was used in the present invention.

The metal and the ceramic substrate are joined by the melt joining method, whereby a composite substrate having high joining strength and few uncontacted defects can be obtained. In addition, since the bonding can be performed in a nitrogen atmosphere, it is not necessary to perform the process in a vacuum as in the conventional method, so that the manufacturing cost is reduced. Further, the surface of aluminum nitride substrates and silicon carbide substrates can be modified. It can be directly joined without using.

Regarding the relationship between the thickness of the ceramic substrate and the thickness of the aluminum metal, the thickness of the metal is further increased as compared with the conventional copper-clad ceramic composite substrate.
On the contrary, the thickness of the ceramic substrate can be reduced, so that the metal / ceramic thickness ratio can be further increased as compared with the conventional product. As a result, it is easily conceivable that the heat dissipation of the composite substrate of the present invention and the amount of flowing current increase.

An etching resist is thermocompression-bonded to one main surface of the metal-ceramic composite substrate obtained by the above-mentioned molten metal joining method, and after light-shielding and developing treatment is performed to form a desired pattern, a ferric chloride solution is used. Circuit 4 after etching
To form

No crack is generated even when a power module body using the thus obtained metal-ceramic composite substrate having a bending strength of 20 kg / mm ² or more (when the distance between fulcrums is 30 mm) is mounted. Furthermore, it was confirmed that the heat cycle resistance also has a heat cycle characteristic of 1000 times or more, which has not been obtained in the past.

In this case, in order to measure the bending strength, as shown in FIG. 2, the heat dissipation plate 5 on the lower surface of the ceramic substrate is directed upward, the circuit surface is directed downward, and the circuit board is supported at two points. It is measured by applying a pressing force of 0.5 mm / min. In the case of the aluminum-ceramic composite substrate of the present invention, the bending strength is 20 kg.
If it is less than / mm ² , the adhesion to the fin material is poor, and the resistance to external force such as vibration is low.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION A composite substrate of the present invention (hereinafter referred to as a metal-ceramics direct bonding substrate) will be described below with reference to the drawings.
Will be described in detail.

(Example 1)

FIG. 4 is a principle diagram of equipment for manufacturing the aluminum-ceramics direct bonding substrate of the present invention.
The aluminum 2 having a purity of 99.9% is set in the crucible 6, the lid 9 is closed, and the inside of the case 8 is filled with nitrogen gas. The crucible 6 is heated to 750 ° C. by a heater to melt the aluminum, and then the ceramic substrate 1 is formed from the left inlet of the guide integrated die 10 provided in the crucible.
A 6 mm × 52 mm × 0.635 mm AlN substrate was inserted in order. A molten aluminum was brought into contact with the AlN substrate contained in the crucible and then solidified on the outlet side to obtain a metal-ceramics direct bonding substrate in which aluminum plates having a thickness of 0.5 mm were bonded to both surfaces.

Then, an etching resist is thermocompression-bonded to the aluminum portion on the composite substrate, shielded from light and developed to form a desired pattern, and then etched with a ferric chloride solution to form a circuit. 1a and 1
The metal-ceramics direct bonding substrate shown in FIG. 2b was obtained, and the bending strength of this substrate was determined by the equation shown in FIG.
It was 6 kg / mm ² , and the measured value is shown in FIG.

The obtained bonded substrate is placed in a furnace atmosphere under H ₂ atmosphere.
/ N ₂ = 1: 1, and the bending strength was measured after passing through the furnace with the peak temperature adjusted to 360 ° C. for 5 minutes.
It became 1.8 kg / mm ² . The measured bending strength of an AlN substrate having a thickness of 0.635 mm is 42.8 kg / mm ² as shown in FIG. 3 for reference, and the bending strength of an aluminum bonded substrate is better than that of a single substrate. Was found to be high.

(Comparative Example 1)

For comparison, the AlN substrate shown in Example 1 was used, and a copper plate having a thickness of 0.3 mm was Ag-Cu on both surfaces of the substrate.
The composite substrate obtained by heat bonding at 780 ° C. through a Ti-active metal brazing material was etched to obtain a copper-clad composite substrate having the same circuit as shown in FIG. 1a. When measured in the same manner as in Example 1, it was 29.5 kg / mm ² as shown in FIG. 3, and the bending strength after passing through the furnace was 15.3 kg / mm ² , which is considerably lower than that in Example 1. Met.

(Example 2)

A shown in Example 1 as a ceramic substrate
When a target metal-ceramics direct bonding substrate was obtained under the same conditions as in Example 1 except that an alumina substrate having the same size was used instead of the 1N substrate and the bending strength of these was measured. As shown in 3, the alumina substrate alone is 5
0.8 kg / mm ² , 62.0 kg / m for this bonded substrate
m ² and 51.0 kg / mm after passing through the furnace
The bending strength was ² .

(Comparative Example 2)

For comparison, the alumina substrate shown in Example 2 was used, and a copper plate was joined to both surfaces of the alumina substrate in a furnace at 1063 ° C. to obtain a substrate, which was subjected to etching treatment to obtain the same circuit as shown in FIG. 1a. A copper-clad composite substrate having the following characteristics was obtained, and the bending strength of these was measured to be 37.8 kg / mm ² .
After passing through the furnace, the pressure was 28.3 kg / mm ² , and the bending strength was lower than that of the directly bonded substrate of the present invention.

(Example 3)

A shown in Example 1 as a ceramic substrate
Under the same conditions as in Example 1 except that a 36 mm × 52 mm × 0.4 mm thick thin alumina substrate was used in place of the 1N substrate, the desired metal-ceramic direct bonding substrate was obtained and the bending strength of these was measured. However, as shown in FIG.
Was 4.6 kg / mm ^2, was also the bending strength of 55.4kg / mm ² in the same manner after which was further passages through furnace.

The heat cycle resistance was determined using the direct bonding substrates of the present invention shown in Examples 1 to 3. This is indicated by the number of cycles until the substrate is repeatedly cracked from -40 ° C to 125 ° C and due to thermal stress during heating / cooling, but the substrate of the present invention does not crack even after 1000 times. On the other hand, in the copper-clad substrate of the comparative example, cracks were observed about tens to hundreds of times.

[0036]

As described above, since the direct bonding substrate of the present invention can reduce the thermal stress by utilizing the softness peculiar to the aluminum material, it has a larger bending strength value than the conventional copper-clad composite substrate. Therefore, the adhesion between the heat sink body and the fin material is improved, and finally the heat cycle resistance is improved.

[Brief description of drawings]

FIG. 1a is a schematic plan view of a metal-ceramic composite substrate according to the present invention.

FIG. 1b is a schematic bottom view of a metal-ceramic composite substrate according to the present invention.

FIG. 2 is a schematic view showing a state of bending strength measurement of the substrate of the present invention.

FIG. 3 is a measurement diagram showing a change in bending strength of a substrate of the present invention obtained by using an AlN substrate, an alumina substrate, and a thin alumina substrate.

FIG. 4 is a principle view of a substrate manufacturing apparatus of the present invention.

[Explanation of symbols]

 1 Ceramics substrate 2 Aluminum 3 Metal part 4 Circuit 5 Heat sink 6 Crucible 7 Heater 8 Case 9 Lid 10 Guide integrated die

Claims (1)

[Claims] 1. A ceramics substrate and a ceramics composite substrate in which an aluminum material is bonded to at least one surface of the ceramics substrate, and the bending strength of the composite substrate is in the range of 20 kg / mm ² or more. Metal-ceramic composite substrate.