JPH0369569A - Method for joining metal to ceramic - Google Patents

Abstract

PURPOSE:To make it possible to stably join a metal sheet to a ceramic substrate by putting a laminate obtd. by superposing the ceramic substrate on the metal sheet on a pedestal coated with ceramic powder, joining the sheet to the substrate by heating to a high temp. in an inert atmosphere and removing the ceramic powder by acid treatment. CONSTITUTION:A ceramic substrate such as an alumina substrate is superposed on a metal sheet such as a Cu sheet. The resulting laminate is put on a pedestal coated with alumina powder and the metal sheet is joined to the ceramic substrate by holding at a high temp. in an inert atmosphere. The alumina powder melt-bonded to the metal sheet is then removed by acid treatment.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for directly bonding a metal plate to a ceramic substrate, and in particular uses alumina powder to cleverly prevent welding between the bonded metal plate and the pedestal. The present invention relates to a method for joining metals and ceramics that has been improved to be suitable for industrial mass production.

[Prior Art] Conventionally, the method of joining an alumina substrate as a ceramic substrate and a copper plate as a metal plate is to apply a copper paste containing a binder onto the alumina substrate, dry and bake it, and form a glass shape in the alumina substrate. A method of bonding by reacting a substitute substance with a binder in a copper paste and also reacting the reaction product with copper, or a method of sandwiching a reactive metal (brazing material) between an alumina substrate and a copper plate, A known method is to cause a diffusion reaction between an alumina substrate and a reactive metal, and between a copper plate and a reactive metal, at a temperature higher than the melting point.

However, recently, semiconductor devices have been progressing toward higher power, higher integration, and modularization, and in response to the demands for higher heat dissipation of ceramic substrates, simplification of semiconductor devices, and higher reliability, the above-mentioned A method of directly bonding a copper circuit board onto an alumina substrate without using copper paste or braze is now being used.

The method of directly bonding copper and a ceramic substrate described in British Patent Publication No. 761045 involves strongly oxidizing copper in advance, placing the copper on an alumina substrate, and bonding the two together in a 1.
The process involves heating at a temperature higher than 0.83°C (the melting point of copper) and lower than the melting point of cuprous oxide (about 1.200°C). During the heating cycle, most of the cupric oxide is converted to cuprous oxide, so the copper plate reaches its melting point and melts, but the cuprous oxide is not melted, and the cuprous oxide remains in the interfacial region between the alumina substrate and the copper. It is stated that there will be one copper layer.

In addition, in the "Method of bonding copper parts to a ceramic substrate" disclosed in Japanese Patent Publication No. 60-43.54, before bonding and arranging a copper plate or a ceramic substrate, the copper parts surface or the ceramic substrate must be bonded in advance. A copper oxide layer with a thickness of 200 to 5,000 is formed on top, and then the copper member and the ceramic substrate are stacked and placed in an inert atmosphere, and the copper part is deposited at the interface between the copper part rail and the ceramic substrate. The temperature at which a hypoeutectic melt of copper oxide and copper oxide is formed is 1,065°C (Cu
A direct bonding method is described that consists of heating to a temperature between -0 eutectic temperature) and 1.083°C followed by cooling.

Furthermore, in JP-A No. 63-166774 "Method for manufacturing a bonded body of a copper plate and an alumina substrate" written by the present inventor, a copper plate and an alumina substrate that are brought into contact with each other are brought into contact with each other in an inert atmosphere.
．． ．． By heating to a temperature lower than 0.83°C,
A direct bonding method is disclosed in which a compound is formed between copper and alumina and a glass-forming substance on the surface of an alumina substrate without forming a eutectic liquid phase of copper and copper oxide at the contact portion, and then cooling. ing. In this case, when carrying the copper plate and alumina substrate to be directly bonded into a conveyor furnace, the stacked pieces are placed on a SiC pedestal.
The pieces are brought in and heat treated for bonding in a conveyor furnace.

[Problems to be Solved by the Invention] However, it has been found that when using a pedestal made of SiC with the above-mentioned means, there are the following problems.

First, the production of the SiC pedestal itself, that is, the sintering of SiC, is difficult, and free Si and free C are generated during the SiC powder manufacturing process and sintering, and these are contained in the pedestal. If an alumina substrate stacked with a copper plate is placed on the pedestal and the bonding process is performed in an inert atmosphere, an appropriate atmosphere cannot be maintained, and especially if free Si is present, the copper plate and free Si will alloy and become golden. It was found that there were problems such as: In addition, this alloying causes the copper plate and the SiC pedestal to be welded together, making it difficult or impossible to remove it from the pedestal, and even if it could be removed, the resulting bonded body would no longer be able to be marketed as a product. ,wait.

On the other hand, the presence of free C creates a local reducing atmosphere at a part of the contact surface between the copper plate and the aluminum plate, inhibiting the formation of oxides that should be formed at the bonding interface. It was found that this part is likely to become a non-bonded part.

Therefore, if this method were to be used for mass production, the inspection process to prevent quality deterioration would be large-scale, which would lead to high costs, so some kind of solution was needed.

[Means for Solving the Problems] The present inventors conducted intensive research to solve the problems, and found that they used alumina as the ceramic pedestal and further coated alumina powder on the surface of the alumina pedestal. The inventors have discovered that by arranging and using the invention, both problems can be solved, and the present invention has been achieved.

That is, the present invention, in its most preferred embodiment,
A method of bonding a laminate consisting of at least one metal plate and at least one ceramic substrate stacked in contact with each other in an inert atmosphere, the metal plate at the bottom of the laminate being supported. An alumina pedestal is used as the pedestal, and alumina powder is placed on the first pedestal.
Process: A laminate of a metal plate and a ceramic substrate that are in contact with each other is placed on the alumina powder and heat treated to bond them in an inert atmosphere.The second step is welding to the metal plate at the bottom of the laminate. A third step of dissolving and removing the alumina powder obtained by the alumina powder by acid treatment is provided. However, in the present invention, after obtaining a laminate as a bonded body by placing ceramic powder on a ceramic pedestal, placing a laminate to be bonded on top of the ceramic powder and heat-treating, the metal surface of the bonded body is Since the present invention provides a method characterized in that ceramic powder welded to the metal surface is removed by acid treatment of the metal surface, it is preferable to use a ceramic base and ceramic powder made of alumina, but it is not necessarily limited to alumina. It is not something that will be done.

[Function] The material of the pedestal used in the method of the present invention is a stable material that does not disturb the atmosphere during bonding, that is, it does not decompose or dissociate at high temperatures, and is industrially stable. Second, any material may be used as long as the bonded product obtained after the bonding process can be easily removed.

Non-oxide ceramic materials are thought to be appropriate for ceramic substrates that do not react with the copper plate at high temperatures, but actual tests show that some decomposition and dissociation occur at high temperatures (7
In addition, free components are often generated during the production of raw material powder and the production of sintered bodies of ceramic materials.

The inventors conducted numerous experiments using non-oxide ceramic materials, and found that in many cases, the tough pitch copper used was partially reduced due to the formation of a local reducing atmosphere. did. Therefore, we decided to abandon the use of non-oxide ceramic materials and consider using oxide ceramic materials.

However, oxide-based ceramic materials are bonded to steel materials under appropriate temperature and atmospheric conditions. Therefore, if this is used as an abrasive material for a pedestal, the pedestal will stick to the product and it will not become a product. Moreover, since the adhesive strength is quite high, it cannot be easily separated.

Therefore, the present inventors have found that by using a pedestal made of an oxide-based ceramic material and further placing appropriate ceramic powder on the surface of the pedestal that should be in contact with the metal plate, the pedestal and the copper plate can be directly bonded. In addition, since the alumina powder bonded to the copper plate is separated from the pedestal, we conducted an experiment assuming that the resulting bonded body would easily separate from the pedestal, and found that the effect was as expected. This has been confirmed to be possible.

In the examples, alumina powder was used as the ceramic powder used in the method of the present invention, which is (1) inexpensive;
2) Since it is made of the same material as the pedestal on which the alumina powder is applied, it has the same heat capacity, making it easy to control the temperature when the temperature of the bonded body increases. (3) Alumina material is stable at high temperatures and creates a reducing atmosphere. Due to reasons such as no. Furthermore, the reason for using an alumina pedestal as the pedestal on which the alumina powder is applied is substantially the same as in (1) to (3) above.

The above alumina powder has a particle size of 1. (bzm ~ number m
It has been confirmed through experiments that it is preferable to use

Through the heat treatment for bonding, the copper plate in the laminate placed on the pedestal via the ceramic powder and the alumina substrate are directly bonded, and the alumina powder placed on the pedestal also becomes part of the copper plate. Join. However, it was confirmed that the alumina pedestal itself did not bond with the alumina powder spread on it, nor did it bond with the steel material that was in contact with it through the alumina powder. Therefore, it was easy to separate the joined body from the pedestal.

] 0 There are mechanical removal methods such as polishing and vibration to remove the alumina powder bonded to the copper plate, but these methods are undesirable because they give a shock to the bonded body, and they also cause scratches on the surface of the copper plate. This tends to result in unsuitable products. Therefore, the inventors of the present invention took advantage of the property that copper plates are etched by acid and thought of immersing the entire bonded body in an acid solution to dissolve the entire copper surface and remove the alumina powder. be.

In this case, the alumina powder and the copper plate are joined in a point contact state, so when the joined body is immersed in an acid solution, the acid quickly circulates from around the point joint and dissolves the copper. The point-bonded alumina powder could be easily removed.

Although the part that was point-bonded to the alumina powder was in contact with the etching solution for a shorter time than the surrounding area, it was confirmed that no traces that would pose a problem as a product remained in the spot-bonded part. Under the bonding temperature range adopted in the method of the present invention, the alumina powder is not sintered, and some of the alumina powder bonded to the copper plate has a wide contact surface and is removed by etching. There was nothing difficult about it.

Hereinafter, it will be explained in detail using examples.

[Example]-] As a copper plate and an alumina substrate to be bonded to each other, tough pitch copper with a thickness of 0.3 mm and a size of 28 mm x 40 mm and a tough pitch copper with a thickness of 0.635 mm and a size of 30 mm x 4 are used.
A 2 mm 96% alumina substrate was prepared.

As a pedestal, a 96% alumina plate measuring 50 mm x 50 mm x 135 mm is used, and as shown in Fig. 1, the surface of the pedestal 4 is coated with alumina powder 3 having a particle size of 2 to 10 μm. ), then a copper plate 22 and an alumina substrate 1 are placed on this pedestal from below as shown in FIG.
, the copper plates 21 stacked one on top of the other in the order of 1. ．． 063°C11,067°C
, 1,075° C. (second step).

After the obtained joined body was cooled, it was taken out into the atmosphere and the bonding state between the -1 joined body and the pedestal was examined. Table 1 shows the results.

In this case, the bonding condition was evaluated using two samples each.
After heat treatment using 0 pieces, when the pedestal is rotated 90 degrees and stood up so that the contact surface with the laminate is vertical, the number of pieces that the bonded laminate naturally separates from the pedestal is `` Items other than those listed are listed in the column ``Not joined to the pedestal'' and other items are recorded in the column ``Joined to the pedestal.''

From Table 1, it can be seen that there was no bonding between the laminate and the pedestal after the bonding was completed.

The cross-sectional structure of the bonded body obtained in the second step is as shown in FIG. are joined.

The copper plate 22 in the figure is placed on a pedestal in the method of the present invention, and the alumina powder 3 of the pedestal 2 is attached to the copper plate in a point-bonded state.

Next, the point-bonded alumina powder 3 was held in a 50% nitric acid solution for a certain period of time to dissolve and remove it (third step).
. In this case, we tried varying the retention time in the liquid to determine the appropriate retention time, and found that if the retention time was kept for 30 seconds or more, the alumina powder remaining on the surface of the copper plate 22 would be completely gone, and the surface of the copper plate would be healthy. I found out that it will happen.

When the thickness of the bonded body (copper plate 2, alumina substrate 1, and copper plate 22 integrated) immersed in the liquid for 30 seconds was measured with a micrometer, it was approximately 2I1 compared to the thickness before immersion.
Although it was made thinner, there were no problems with the dimensions of the joined product.

In addition, although 50% nitric acid solution was used as the acid solution, since the alumina substrate is a material with excellent oxidation resistance,
There was no possibility that the alumina substrate itself would be eluted.

[Example 2] As in Example 1, an experiment was conducted using a pedestal made of 96% alumina material to investigate ceramic powder suitable for coating on the pedestal. The ceramic powder used was 2 to t.
OIIm particle size A, ll' 203 , A, 12 N.

There are five types: SiC, BN, and Si2N4, but especially S
As for the iC, commercially available products from three companies were used, so the symbols A, B, and C were added to the SiC to distinguish them. Table 2 shows the results of a test in which a laminate of a copper plate and an alumina substrate similar to that in Example 1 was placed on the ceramic powder coated on these pedestals to obtain a bonded body. The obtained joined body was evaluated as "O" if the copper plate and alumina substrate were soundly joined, and "X" if the copper plate and alumina board were not joined soundly.

(Left below) Table 2 The grain boundaries of the copper sheets that were not joined at this time had smaller grain boundaries rlJ than those of the joined copper sheets, and when observed with an optical microscope, it was found that they exist in tough pitch copper. The expected Cu2O phase was not observed.

This is SiCC%AJ7N coated on an alumina pedestal.
This is thought to be due to deoxidation of tough pitch copper due to dissociation and decomposition of ceramic powders such as , BN, Si3N4, etc. From this, A, Q2 as ceramic powder
It can be seen that not only the use of 03 powder but also the use of alumina material as the material of the pedestal creates a stable atmosphere during bonding.

This is because alumina material is a very stable substance.

[Effects of the Invention] As described above, according to the present invention, a copper plate and an alumina substrate can be heated and bonded in a stable atmosphere. In addition, not only can inexpensive alumina material be used as the pedestal, but the simple method of using ceramic powder is effectively used to prevent the pedestal from joining with the copper plate. , can bring about a reduction in manufacturing costs.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing an example of the arrangement of a laminate of a copper plate and an alumina substrate on a pedestal before being put into a furnace. FIG. 2 is a sectional view showing an example of a bonded body of a copper plate and an alumina substrate. FIG. 3 is a schematic cross-sectional view showing the dissolved state of the surface of the copper plate after the bonded body shown in FIG. 2 is immersed in acid. Explanation of symbols 1...Alumina substrate 2 (...Copper plate 22...Copper plate 3...Alumina powder 4...Alumina pedestal

Claims (3)

[Claims] (1) A method in which a laminate consisting of at least one metal plate and at least one ceramic substrate stacked alternately is held at high temperature in an inert atmosphere and bonded, the metal at the bottom of the laminate being bonded. The first step is to place the ceramic powder on a pedestal for contacting and supporting the plate; placing the laminate of the metal plate and the ceramic substrate on the ceramic powder and holding it at high temperature in an inert atmosphere; A second step of joining the metal plate and the ceramic substrate; and a third step of dissolving and removing the ceramic powder welded to the metal plate at the bottom of the laminate by acid treatment of the surface of the metal plate. How to join with ceramic. (2) The method for joining metal and ceramic according to claim 1, wherein the inert atmosphere in the second step is an inert atmosphere containing 1% or less oxygen. (3) The method according to claim 1 or 2, wherein the pedestal is an alumina pedestal, and the ceramic powder is alumina powder.