JPS61270269A - Method of joining ceramic substrate to metal piece - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a method of joining a ceramic substrate and a metal piece.

[Background technology]

Conventionally, as a method for bonding a metal piece to a ceramic substrate such as alumina, for example, M o -M n is made into a paste and printed on the ceramic substrate, and the paste is heated at 130° C. in humidified hydrogen.
Methods that have been used include metallizing at a temperature of 0 to 1700°C, applying nickel plating to the surface, and brazing the metal pieces with a brazing filler metal to join them.

In recent years, these methods have been replaced by methods in which a metal piece is brought into direct contact with a ceramic substrate and bonded by heating in a gas atmosphere containing a binder such as oxygen, or a method in which a metal piece containing a binder is bonded to a ceramic substrate. A method is known in which the substrate is brought into contact with the substrate and heated in a non-oxidizing atmosphere. The former method requires heating at a high temperature below the melting point of the metal and above the eutectic point of the eutectic alloy of the metal and the binder. Therefore, when this method is used, problems arise in that bubble-like non-adhesive spots (blisters or bulges) occur and that the metal surface on the side other than the bonding surface is covered with a thick metal oxide layer. On the other hand, the latter method uses a metal piece containing a binder in advance, such as tough pitch copper in the case of copper, and heats it in a non-oxidizing atmosphere. It is difficult to obtain a strong bond in a completely non-oxidizing atmosphere such as the atmosphere, and even if bonding is achieved, the problem of blistering still remains. In addition, in the method of heating tough pitch copper in an oxidizing atmosphere, tough pitch copper is very easily oxidized (therefore, the metal surface on the side that is not the bonding surface is likely to be covered with a thick oxide layer. The coarsening of the crystals due to recrystallization is significant, and extremely fine control of conditions is required.

There is also a method of using a copper piece with only the surface oxidized in advance, but even in this method, when joining by heating in a non-oxidizing atmosphere, when the heat is removed, the copper oxide becomes CuO-
Since Cu is decomposed into 20-pc u, considerable rapid heating is required, and even if it is heated in an oxidizing atmosphere, a step of preliminary oxidation is required.
This complicates the process and causes high costs.

[Purpose of the invention]

The present invention was made in view of the current situation, and an object of the present invention is to provide a method for joining a ceramic substrate and a metal piece without blisters and without covering the exposed metal surface with oxide. do.

[Disclosure of the invention]

In order to achieve the above object, the present invention places metal pieces on a ceramic substrate in contact with each other, and under a controlled reactive gas atmosphere, the substrate is heated to a temperature lower than the melting point of the metal and capable of reacting with metal and metal. The temperature is raised to a temperature higher than the eutectic point of the compound formed between the reactive gases, held at that temperature for a while to form a eutectic, and then the atmosphere is made non-reactive and cooled. The gist of the method is to complete the bonding between a ceramic substrate and a metal piece, the method comprising crimping the metal piece and the substrate while the temperature of the substrate is rising. This invention will be explained in detail below based on FIGS. 1 and 2, taking as an example the case where copper or copper alloy is selected as the material of the metal piece, alumina is selected as the material of the ceramic substrate, and oxygen is selected as the reactive gas. explain. The figure shows a case where a pressure roller is used as a pressure bonding means.

(2) A plate-shaped metal piece 2 of copper or copper alloy is placed in contact with the alumina ceramic substrate 1 and inserted into a heating furnace.

■ Create an inert gas atmosphere containing oxygen from 20 ppm to 1100 ppm in the heating furnace. As an inert gas,
Nitrogen is generally used, but argon, helium, etc. may also be used. If the oxygen content is less than 20 ppm, the metal piece 2 and the ceramic substrate 1 will not be bonded. Also, 11
If it exceeds 00pp, the exposed metal surface will be covered with oxide,
Furthermore, the metal piece 2 melts and loses its original shape.

(2) The temperature of the heating furnace is raised, and when the temperature inside the furnace reaches the eutectic point of copper and copper oxide or higher, the pressure roller 3 is applied to press the metal piece 2 onto the ceramic substrate 1.

Blisters are formed between the ceramic substrate 1 and the metal piece 2 because the metal-metal oxide eutectic liquid 4 generated on the contact surface between the metal piece 2 and the ceramic substrate 1 coats the ceramic substrate surface. This is thought to be due to the fact that air bubbles 5 are trapped inside during wetting, and that portion remains as a non-adherent area after bonding. Therefore, if the metal piece 2 and the ceramic substrate 1 are pressed together while they are wetted by the eutectic liquid 4 and the air bubbles 5 trapped inside are pushed out, the generation of blisters can be prevented. In this example, the pressure roller 3 used as a pressure bonding means has its surface in direct contact with the metal piece 2 at a temperature higher than the eutectic point.
The material is a non-oxide ceramic that has poor wettability with the eutectic liquid 4 and is difficult to cause a chemical reaction, or a surface coated with a high melting point metal such as tungsten.
Alternatively, it is preferable to use one made entirely of such a material.

In addition, the crimping pressure needs to be set at a constant pressure according to the thickness of the copper plate to be used, so that the copper plate softened at high temperatures is not rolled and the thickness of the copper plate becomes too thin.

The temperature at which the pressure bonding is performed is not particularly limited, but if the temperature is below the eutectic point, the eutectic liquid 4 will not be sufficiently generated at the interface between the metal piece 2 and the ceramic substrate 1, and the pressure roller 3 will be applied to the metal piece 2. Even if the ceramic substrate 1 is pressure-bonded, the temperature will exceed the reconstruction melting point, and when sufficient eutectic liquid 4 is generated at the interface, there is a risk that bubbles 5 that will cause blisters will be trapped inside again. It is preferable to perform crimping after the above conditions have been reached.

In the present invention, pressure may be applied to the metal piece 2 by a method other than a pressure roller, such as a press.

■ Raise the temperature to a specified temperature and maintain the temperature of the heating furnace for a certain period of time. This holding time needs to be long enough to generate the eutectic composition in a molten state, and the thicker the metal piece, the longer the time required. Here, the eutectic composition is
An atomic mixture of a metal and a reactive gas, or an atomic mixture of a metal and a compound formed between the metal and a reactive gas, such as, in the case of this example, a mixture of copper and copper oxide. It is. This eutectic composition then wets the adjoining ceramic substrate and metal. This eutectic composition strongly bonds the ceramic substrate and metal when cooled.

■ Stop oxygen from entering the heating furnace and cool it in a pure nitrogen atmosphere. Cooling in a non-oxidizing atmosphere (non-reactive atmosphere)
This is done because oxygen is not required for bonding during cooling and to reduce the excess oxide layer on the exposed metal surface.

By the way, alumina substrates can be used for semiconductor integrated circuits or
Although specifically mentioned here because of its high thermal conductivity, which is useful in high-power electrical circuits, other non-metallic refractory materials can also be used in this invention, and the metal strip material is also limited to copper. It's not a thing. In the present invention, a reactive gas atmosphere other than an oxygen-containing atmosphere, such as a sulfur-containing atmosphere or a phosphorus-containing atmosphere, may be used depending on the conditions. Further, in the above embodiment, nitrogen was used as the inert gas (non-reactive atmosphere), but an inert gas such as argon or 1 helium may be used.

As described above, in the method of joining a ceramic substrate and a metal piece of the present invention, the metal piece is pressed and crimped onto the ceramic substrate when the temperature rises, so that bubbles that occur when the temperature rises are avoided. By this pressure bonding, non-adherent spots (blisters or bulges) can be removed, and a strong bond can be obtained between the substrate and the metal piece. Since the bonding conditions are the same as for normal bonding methods, the process is not complicated, the metal pieces used in normal bonding methods can be used, and there is no risk of oxidation on exposed metal surfaces, reducing costs. It is also possible to make it lower.

Next, examples according to the present invention will be described together with comparative examples.

(Example) On a plate-shaped alumina substrate with a thickness of 50 fins
A plate-shaped oxygen-free copper piece (copper foil) with a thickness of 1111 mm was placed on it and inserted into a heating furnace. Next, nitrogen containing 20 ppm of oxygen was flowed into the furnace to purge the inside of the furnace, and then heating was started while overflowing. When the temperature in the furnace exceeded the eutectic point of copper-copper oxide (1065° C.), a pressure roller made of silicon nitride was driven to press the copper foil onto the alumina substrate. The temperature continues to rise even after the completion of crimping, and the temperature inside the furnace reaches 1070℃.
The temperature increase was stopped when the temperature rose to .degree. C., and this temperature was maintained for 5 minutes. After holding for 5 minutes, the mixing of oxygen into the heating furnace was stopped, and only pure nitrogen overflowed to gradually cool the furnace, and the work was completed.

Under the above conditions, experiments were repeated using pressure rollers of three different weights: 100 g, 150 g, and 300 g.

The bonded product of the alumina substrate and copper foil obtained in the above operation had no blisters or blisters under any pressure conditions, and the adhesion between the substrate and the metal piece was strong.

(Comparative Example) When a bonded body was produced in the same manner as in the example except that crimping was not performed, cracking occurred and good bonding could not be obtained.

〔Effect of the invention〕

The method of joining a ceramic substrate and a metal piece according to the present invention is as follows:
With the above structure, bonding can be performed under the same conditions as normal bonding methods, so the exposed metal surface will not be oxidized, and since the metal piece and ceramic substrate are crimped together when the temperature rises, blisters and blisters will not occur. This does not occur and a strong bond can be obtained, and since the steps other than crimping are the same as normal bonding methods, the process does not become complicated.

[Brief explanation of drawings]

FIG. 1 is a perspective view of an example of the crimping work of this invention.
FIGS. 2A to 2B are schematic diagrams illustrating the extrusion of bubbles in this example. 1...Ceramic substrate 2...Metal piece 3...Pressure mouth agent Takehiko Matsumoto February 4, 1988, Komagi Utsukai No. 113573 2, Name of the invention, Method for joining a ceramic substrate and metal piece 3, Related to the case of the person making the amendment Patent application: 1048 Kadoma, Kadoma City, Osaka Prefecture Name: (583) Representative of Matsushita Electric Works Co., Ltd. (4) MJ actor Sadao Ii 4, no agent 6, Specification subject to amendment 7, Contents of amendment (1) Specification page 3, line 11 to page 3 In line 12, the phrase "metal oxide layer" is corrected to "metal oxide layer."

Claims (5)

[Claims] (1) A metal piece is placed in contact with a ceramic substrate, and in a controlled reactive gas atmosphere, the substrate is heated to form a compound having a temperature lower than the melting point of the metal and formed between the metal and the reactive gas. The temperature is raised to a temperature higher than the eutectic point with
This is a method in which the bonding between the substrate and the metal piece is completed by holding the temperature for a while to generate a eutectic and then cooling the atmosphere to a non-reactive atmosphere. A method for joining a ceramic substrate and a metal piece, characterized by crimping the piece and the substrate. (2) The method of joining a ceramic substrate and a metal piece according to claim 1, wherein the temperature at which the pressure bonding is performed is at least the eutectic point or higher. (3) A method for joining a ceramic substrate and a metal piece according to claim 1 or 2, wherein the pressure bonding is performed by a pressure roller. (4) The method for joining a ceramic substrate and a metal piece according to any one of claims 1 to 3, wherein the reactive gas atmosphere is an inert gas atmosphere containing 20 to 100 ppm oxygen. (5) The method for joining a ceramic substrate and a metal piece according to any one of claims 1 to 4, wherein the metal piece is either copper or a copper alloy.