JP2001144224A - Metal-ceramic composite substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a metal-ceramic composite substrate having excellent heat cycle resistant characteristics. SOLUTION: The metal-ceramic composite substrate is produced by solidifying molten aluminum directly on a ceramic substrate. A specified circuit is formed by etching aluminum solidified on the composite substrate.

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 a power module, and more particularly, to an electronic component for an automobile which requires particularly excellent heat cycle resistance. It is an object 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 the 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.

A copper / alumina brazing substrate and a copper / aluminum nitride brazing substrate are joined between a copper plate and a ceramic substrate by using a brazing material having a low contact point.
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. Among them, the most serious problem is a failure due to the formation of cracks inside the ceramic substrate during mounting and use of electronic components, and electrical conduction between the front and back of the substrate.

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

Further, when mounting electronic components such as power modules, the copper / ceramic composite substrate is heated to nearly 400 ° C., and the temperature of the composite substrate constantly changes due to the use environment and heat generation during use. Then, a fluctuating thermal stress is applied to the composite substrate. Cracks occur in the ceramic substrate due to these thermal stresses.

One of the important evaluation items of the composite substrate is heat cycle resistance. This is indicated by the number of circulations until cracks occur in the substrate due to the thermal stress during heating and cooling when the substrate is repeated from −40 ° C. to 125 ° C. The copper / ceramic composite substrate manufactured by the direct bonding method is After about 50 cycles, the characteristic value of the composite substrate manufactured by the brazing method is 50 cycles or less.

Furthermore, in order to obtain such characteristics, there is a restriction condition that the thickness of the ceramic substrate is increased by the sum of the thicknesses of the copper plates bonded to both main surfaces. There has been a problem that the thickness must be at least twice as large as necessary to maintain electrical insulation. Conversely, the thermal conductivity, which is another important characteristic of the composite substrate, is sacrificed at present.

In recent years, with the development of power modules for electric vehicles, the demand for composite substrates having excellent heat cycle resistance has been particularly increased. For example, in the case of use conditions in which temperature changes are severe and vibrations are large like electric vehicles. It is said that the heat cycle resistance of the composite substrate is required to be 3000 times or more, but the copper / ceramic composite substrate currently used cannot meet such a demand.

The concept of using aluminum having excellent electrical and thermal conductivity similar to that of copper as a conductive circuit material has been known for a long time. The brazing method is used for joining aluminum and ceramics.
No. 63, JP-A-4-12554 and JP-A-4-187
No. 46 discloses an aluminum-ceramic substrate produced by a brazing method. According to this, the heat cycle resistance of the manufactured aluminum-ceramic substrate was about 200 times, and it was still not possible to sufficiently cope with the use requiring the high heat cycle resistance as described above.

In addition, in the case of this method, the joining must be performed in a vacuum, and in the case of non-oxide ceramics, a pre-treatment must be performed in advance to form an oxide on the surface of the ceramics. In addition, there were also points where the thermal conductivity was not satisfactory.

[0014]

As described above, conventional copper / ceramic direct substrates and aluminum brazed substrates conventionally manufactured have not been suitable as substrates for electric vehicles from the viewpoint of heat cycle resistance. An object of the present invention is to provide a novel substrate having a heat cycle resistance of 3000 times or more for electric vehicles.

[0015]

The present inventors have focused on the fact that the brazing material used for brazing is harder than the metal to be joined. The use of a hard brazing material impairs the stress relaxation function of the metal itself, generates relatively large thermal stress in the substrate, and reduces heat cycle resistance and the like. In order to develop a substrate having low thermal stress and excellent heat cycle resistance, the present inventors have further improved one of the previous inventions (Japanese Patent Application No. 4-355211), and
A ceramic direct bonding substrate was fabricated. When evaluating these substrates, excellent heat cycle resistance was confirmed,
The invention could be submitted.

According to a first aspect of the present invention, there is provided a metal-ceramic composite substrate having at least one main surface of a ceramic substrate formed with a metal portion for electrical conduction and mounting of electronic components. The present invention relates to a metal-ceramic composite substrate characterized in that a predetermined circuit is formed by etching a metal plate on a composite substrate which has been solidified and joined, and a second invention relates to the above-mentioned ceramic substrate. This uses an aluminum nitride substrate.

[0017]

The substrate used in the present invention is a ceramic substrate such as alumina, aluminum nitride, silicon carbide, or zirconia, or glass. In this case, a high-strength material is still more preferable.

The metal used in the present invention is a pure metal of aluminum, which improves the conductivity and obtains softness. In this case, the higher the purity, the higher the conductivity, but the higher the price. Conversely, 99.9% (3N) pure aluminum was used in the present invention.

The joining between the metal and the ceramic substrate is performed by a molten metal joining method, whereby a composite substrate having high joining strength and few unconnected defects can be obtained. In addition, since the bonding can be performed in a nitrogen atmosphere, there is no need to perform in a vacuum as in the conventional method, so that the manufacturing cost is reduced. Further, the bonding is directly performed on an aluminum nitride substrate without surface modification. be able to.

Regarding the relationship between the thickness of the ceramic substrate and the thickness of the aluminum metal, it is necessary to further increase the thickness of the metal while reducing the thickness of the ceramic substrate in comparison with the conventional copper-clad ceramic composite substrate. Therefore, the thickness ratio of metal / ceramics can be made larger than that of 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.

The composite substrate of the present invention (hereinafter referred to as an aluminum-ceramic direct bonding substrate) will be described in detail with reference to the drawings.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION

(Example 1)

FIG. 7 is a diagram showing the principle of equipment for manufacturing the aluminum-ceramic direct bonding substrate of the present invention.
Aluminum having a purity of 99.9% is set in the crucible 10, the lid 13 is closed, and the inside of the case 12 is filled with nitrogen gas. After heating to 750 ° C. with the heater 11 to melt the aluminum, a 36 mm × 52 mm × 0.635 mm alumina substrate was sequentially inserted as the ceramic substrate 1 from the left entrance of the integrated guide die 14 provided in the crucible 10. . The molten aluminum was brought into contact with the alumina substrate contained in the crucible 10 and then solidified at the outlet side to obtain an aluminum-alumina direct bonding substrate having a 0.5 mm-thick aluminum plate bonded to both surfaces.

Next, on the aluminum portion on the composite substrate,
The etching resist was heated and pressed, subjected to light shielding and development processing to form a desired pattern, and then etched with a ferric chloride solution to form a circuit. Further, the circuit surface was replaced with Zn and subjected to Ni plating to obtain an aluminum-ceramic direct bonding substrate having a shape as shown in FIG.

When the properties of the composite substrate were measured, the following results were obtained.

Peeling characteristic> 30 kg / cm (aluminum breaks)

Heat cycle> 3000 times (no crack)

Bending strength: 69 kg / mm ²

Deflection: 286 μm (see FIG. 5)

(Comparative Example 1)

A copper plate 7 having a thickness of 0.3 mm is formed of 36 mm × 52
It was directly bonded to the upper and lower surfaces of an alumina substrate 6 of mm × 0.635 mm to obtain a copper-alumina direct bonding substrate having a shape shown in FIG. 3 is an oxide (Al-Cu-Si-O).

When the characteristics shown in Example 1 were similarly obtained,

Peeling characteristic> 10 kg / cm (cut at the interface between alumina and Cu)

Heat cycle: cracks occur 50 times, copper plate peels off 600 times

Bending strength: 49 kg / mm ²

Deflection: 172 μm.

(Example 2)

As the ceramic substrate 1, an aluminum nitride plate (36 mm × 52 mm × 0.63) was used instead of alumina.
An aluminum-aluminum nitride direct bonding substrate was obtained in the same manner as in Example 1 except that 5 mm) was used.

The characteristics of this composite substrate are as follows:

Peeling characteristic> 20 kg / cm

Heat cycle> 3000 times

Flexural strength: 53 kg / mm ²

Deflection: 230 μm

As described above, the heat cycle resistance was favorable for use in automobiles.

(Comparative Example 2)

As shown in FIG.
3mm copper plate is coated with active metal brazing material (Ag-Cu-Ti) 5
The characteristics were measured in the same manner as in Example 2 using a copper-aluminum nitride soldered substrate obtained by bonding to an aluminum nitride plate 8 through

Peeling characteristic> 30 kg / cm

Heat cycle: cracks occur 40 times, copper plate peels 500 times

Flexural strength: 42 kg / mm ²

Deflection: 140 μm

Although the peel characteristics were excellent, the desired heat cycle resistance was far from required.

(Embodiment 3)

The alumina amount of 0.5 mm was formed on one side of the alumina substrate having a thickness of 0.635 mm used in Example 1, and the amount of warpage was measured after passing through a continuous heating furnace heated to 360 ° C. The measurement was performed as shown in FIG. 5, and the same operation was repeated. The amounts of warpage of the substrate were summarized for each number of times and shown in FIG. The atmosphere in the heating furnace was H ₂ : N ₂ = 1: 4.

(Comparative Example 3)

Except for a copper-clad alumina substrate directly bonded using a copper plate having a thickness of 0.3 mm instead of aluminum,
The amount of warpage was measured by the means shown in Example 3, and the result was shown in FIG.
Are also shown.

As a result, as compared with the copper-clad alumina substrate of Comparative Example 3, the amount of warpage of the aluminum / alumina substrate according to the present invention was about 1/3. Since the amount of warpage increases as the stress inside the substrate increases, it was found that the stress inside the aluminum / alumina substrate was much smaller than that of the copper-clad alumina substrate.

[0058]

As described above, the aluminum / ceramic direct bonding substrate according to the present invention is rich in heat cycle resistance, which cannot be obtained with a conventional composite substrate, and is preferable as a power module substrate for electric vehicles.

[Brief description of the drawings]

FIG. 1 is a schematic view of an aluminum / ceramic direct bonding substrate according to the present invention.

FIG. 2 is a schematic view of a conventional copper / alumina direct bonding substrate.

FIG. 3 is a schematic view of a conventional copper / alnium nitride direct bonding substrate.

FIG. 4 is a schematic view of a conventional metal / ceramic brazing substrate.

FIG. 5 is a schematic view of a warpage amount measurement in a third embodiment.

FIG. 6 is a diagram illustrating a warpage amount with respect to the number of times of furnace passing in Example 3 and Comparative Example 3.

FIG. 7 is a principle view of an apparatus for manufacturing a composite substrate according to the present invention.

[Explanation of symbols]

 Reference Signs List 1 ceramic substrate 2 aluminum 3 oxide (Al-Cu-Si-O) 4 oxide on aluminum nitride surface 5 metal brazing material 6 alumina substrate 7 copper plate 8 aluminum nitride plate 9 metal plate 10 crucible 11 heater 12 case 13 lid 14 guide Integrated die

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Masami Sakuraba 1-8-2 Marunouchi, Chiyoda-ku, Tokyo Dowa Mining Co., Ltd. (72) Inventor Nagatoshi Nagata 1-8-2 Marunouchi, Chiyoda-ku, Tokyo Same as above Inside Wa Mining Co., Ltd.

Claims (2)

[Claims] 1. A metal-ceramic composite substrate having at least one principal surface of a ceramic substrate formed with a metal portion for electrical conduction and mounting of electronic components, wherein the molten aluminum is directly solidified on the ceramic substrate and joined. A metal-ceramic composite substrate, wherein a predetermined circuit is formed by etching an upper metal plate. 2. A metal-ceramic composite substrate having at least one principal surface of an aluminum nitride substrate formed with a metal portion for electrical conduction and mounting of electronic components, wherein an aluminum melt is directly solidified and joined to the aluminum nitride substrate. A metal-ceramic composite substrate, wherein a predetermined circuit is formed by etching a metal plate on the composite substrate.