JP2024043165A - Ceramic circuit board and method of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ceramic circuit board that has a proper porous part on a surface of a ceramic substrate and that is suitable for a power module and the like.

SOLUTION: A ceramic circuit board in which a metal circuit is bonded onto a surface of a ceramic substrate with a brazing material has a porous part on a surface of an exposure part of the ceramic substrate exposed by formation of the metal circuit. A thickness of the porous part is 1 to 30 μm in a depth direction of the ceramic substrate.

SELECTED DRAWING: Figure 1

COPYRIGHT: (C)2024,JPO&INPIT

Description

The present invention relates to a ceramic circuit board suitable for power modules and the like, and a method for manufacturing the same.

In recent years, the trend towards hybrid and electric vehicles and the introduction of power generation methods that utilize natural energy such as wind and solar power has expanded, and power modules that play an essential role in these systems, such as converting and controlling electrical energy, have been attracting attention. Ceramic circuit boards are one of the components of these power modules, and their general structure consists of a substrate made of ceramic plate material with excellent electrical insulation, a circuit layer on one side of which a metal plate with excellent conductivity is bonded to form an arbitrary circuit pattern, and a heat dissipation layer on the other side of which a metal material for a heat sink is bonded.

Here, a joining technique using a brazing material is widely used as one of the means for joining ceramics and metal. Ag-Cu-Sn brazing filler metals, which are mainly composed of silver (Ag) and mixed with copper (Cu), tin (Sn), etc. to lower the melting point, are known. Since it is not possible to bond with ceramics, materials containing about 0.2 to 2 wt% of titanium (Ti) have been mainly used for the purpose of activating the bonding interface with ceramics and increasing bonding strength. However, since it contains a large amount of Ag and Ti, the brazing filler metal becomes very expensive, and there is a problem in that the cost required for joining becomes very high. Therefore, in recent years, various new brazing materials have been studied as a solution to this problem.

For example, Patent Document 1 discloses that it contains 0.1 to 2.0 wt% of Ti, 0.07 to 12.0 wt% of silicon (Si), and the remainder consists of aluminum (Al) and unavoidable impurities. An Al-Si-Ti brazing material (Al-based brazing material) is disclosed. According to Patent Document 1, by using inexpensive Al as the main component and utilizing the Al oxidation prevention effect of Si and the oxide film activation effect of Ti, a highly reliable bonded body can be obtained at low cost. is listed.
Furthermore, Patent Document 2 proposes a ceramic circuit board in which a ceramic substrate and a copper plate are bonded using a Cu--Mg--Ti brazing material (Cu-based brazing material) that does not contain Ag. According to Patent Document 2, Mg in the Cu--Mg--Ti alloy is sublimed and does not remain at the bonding interface, resulting in a good bonded body.

Japanese Patent Application Publication No. 4-294890 Japanese Patent Application Publication No. 2005-305526

As described in Patent Document 1 and Patent Document 2, by using Al-based brazing filler metal or Cu-based brazing filler metal that does not contain Ag, which is a noble metal, the cost of the brazing filler metal itself can be reduced, and it is possible to bond ceramic circuit boards. It becomes possible to significantly reduce the cost in the process compared to the conventional method. However, in the circuit formation process of forming a circuit layer after bonding, various problems arise because Ag is not included.

Here, a copper-bonded ceramic circuit board in which a copper plate is bonded to a ceramic substrate using a brazing material will be explained as an example. During the copper etching (melting) process performed in the circuit formation process, even the ceramic parts melt and become porous, and if the degree of melting is large, the strength of the ceramic substrate will be lower than before. was there. When using a conventional Ag-based brazing filler metal whose main component is Ag, when observing the cross section of a ceramic circuit board, a phase with a high proportion of Ag (Ag-rich phase) is formed between the ceramic circuit board and the copper plate. This can be confirmed. Since this Ag-rich phase is chemically stable, it does not dissolve even when it comes into contact with the processing solution used for etching copper plates, and as a result, this Ag-rich phase acts as a barrier layer to protect the surface of the ceramic substrate. It fulfills its role. Therefore, when the Ag-based brazing material was used, the ceramic substrate was hardly dissolved during the etching process of the copper plate.

However, when using an Al-based or Cu-based brazing filler metal whose main component is an element other than Ag, such a barrier layer is not formed between the copper plate and the ceramic substrate. The liquid easily penetrates into the ceramic substrate, excessively dissolving the ceramic substrate, and causing the ceramic substrate to become porous deep inside, resulting in a significant decrease in strength and damage to the pores formed by dissolution. There was a problem that foreign matter remained behind, causing quality deterioration such as discoloration and poor insulation.

On the other hand, if the surface of such a ceramic substrate is porous, it has certain advantages such as better adhesion with the sealing material filled in the module when used as a power module component. Therefore, it would be ideal to be able to appropriately control the degree of porosity.

Therefore, an object of the present invention is to provide a ceramic circuit board that has an appropriate porous portion on the surface of the ceramic circuit board and is suitable for power modules and the like.

The present invention provides a ceramic circuit board in which a metal circuit is bonded to the surface of a ceramic substrate using a brazing material, the ceramic circuit board having a porous portion on the surface of the exposed portion of the ceramic substrate exposed by the formation of the metal circuit; The thickness of the porous portion is 1 to 30 μm in the depth direction of the ceramic substrate.

Further, it is preferable that the Ag content of the brazing filler metal is 50% by mass or less.

The method for manufacturing a ceramic circuit board of the present invention includes a metal-bonded ceramic substrate preparation step in which a metal-bonded ceramic substrate is prepared by bonding a metal and a ceramic substrate with a brazing material, and a protective film is formed on necessary portions of the metal. a film forming step; and a metal circuit forming step in which a predetermined portion of the metal and the brazing material of the metal bonded ceramic substrate are melted by a treatment liquid to form a metal circuit, and the metal circuit forming step is performed multiple times. It is characterized by being carried out in stages.

Further, in the metal circuit forming step carried out in multiple steps, after dissolving the metal and the brazing material by the processing liquid, the metal bonding ceramic substrate is cleaned, and the metal and the brazing material are again melted by the processing liquid. This is preferably carried out by dissolving.

Further, in the metal circuit forming step performed in multiple stages, it is preferable to interrupt the melting after 50% or more of the thickness of the metal has been melted.

According to the present invention, it is possible to provide a ceramic circuit board that has an appropriate porous portion on the surface of the ceramic substrate and is suitable for power modules and the like.

FIG. 1 is a schematic cross-sectional view showing an example of a ceramic circuit board of the present invention. 1A to 1C are schematic cross-sectional views showing an example of a method for producing a ceramic circuit board of the present invention. FIG. 2 is a schematic diagram showing the copper-bonded ceramic substrate and resist processing positions of Example 1. 1 is a cross-sectional SEM image of the ceramic circuit board obtained in Example 1. 2 is a cross-sectional SEM image of the exposed ceramic portion of the ceramic circuit board obtained in Example 1. 2 is a cross-sectional SEM image of the ceramic circuit board obtained in Example 2. 1 is a cross-sectional SEM image of a ceramic exposed portion of a ceramic circuit board obtained in Example 2. 1 is a cross-sectional SEM image of a ceramic circuit board obtained in Comparative Example 1.

The ceramic circuit board of the present invention and its manufacturing method will be described below with reference to the schematic diagrams shown in FIGS. 1 and 2.

As shown in FIG. 1, in order to produce a ceramic circuit board 101, first, a metal bonded ceramic substrate 100 is prepared in which a metal 10 and a ceramic substrate 11 are bonded together using a brazing material 12 (metal bonded ceramic substrate preparation step). A protective film 13 such as a resist is formed on the necessary portions of the metal 10 ((protective film forming step T1). Next, the exposed metal 10 and the brazing material 12 are immersed in a treatment liquid 14 such as acid or alkali. By chemically dissolving (etching) and removing the portion (predetermined location), a metal circuit 10b is formed using the undissolved metal 10 (metal circuit forming step T2), and a ceramic circuit board 101 is obtained (T3). ).
At this time, if the Ag content of the brazing filler metal 12 is 50% by mass or less, a barrier layer made of Ag will not be sufficiently formed, so the treatment liquid 14 will reach the ceramic substrate 11 during the formation of the metal circuit 10b. The surface of the ceramic substrate 11 is also partially dissolved. As a result, a porous portion 15 is formed on the surface (exposed portion 11a) of the ceramic substrate 11 exposed by the formation of the metal circuit 10b. This porous portion 15 extends from the surface of the ceramic substrate 11 in the depth direction. In the present invention, the depth of this development, that is, the thickness of the porous portion 15 is 1 to 30 μm in the depth direction of the ceramic substrate over the entire range. If the depth of development is more than 30 μm, there is a problem that the insulation required for the ceramic circuit board is insufficient or the mechanical strength is weak and the ceramic circuit board is broken.

Furthermore, when focusing on the dissolution process of the metal 10, for reasons described below, the dissolution rate of the metal 10 tends to be uneven and slow, and it is easy for some areas of the ceramic substrate 11 to be exposed to the treatment liquid 14 for long periods of time and other areas to be exposed. Therefore, by allowing the dissolution of the metal 10 to proceed uniformly over the entire surface and controlling the dissolution rate, it is possible to control the porous portion 15 caused by the dissolution of the ceramic substrate 11.

Note that the ceramic substrate referred to here includes silicon nitride, aluminum nitride, zirconia-containing alumina, alumina, etc., and the metals that form the metal circuit include various metals such as copper, aluminum, and nickel, as well as dissimilar materials such as carbon nanotubes. This refers to things that are composites of and various alloys.

Referring to FIG. 2, the melting process of copper 10a in forming a metal circuit will be described using as an example a copper-bonded ceramic substrate 100a in which copper 10a is bonded to ceramic substrate 11 using a brazing material. Intermediate products 20 such as copper ions and copper oxide are deposited on the surface of the copper 10a during dissolution, and these interfere with the progress of dissolution of the copper 10a (t1). Therefore, in order to control the dissolution of the ceramic substrate 11, the intermediate product 20 is removed from the surface of the copper 10a so that the dissolution of the copper 10a proceeds uniformly over the entire surface, and the dissolution rate is further increased or controlled. It is effective to minimize the time during which the material contacts the processing liquid 14.
However, in reality, the shape of the copper 10a (metal circuit) to be formed in the metal circuit forming process may be a thin line, a pit with a small diameter, or the copper is thick and the area to be etched is narrow. Alternatively, due to shape dependence such as depth, the removal of the intermediate product 20 from the portion to be etched is not performed well, and as a result, phenomena such as a slow dissolution rate of copper or non-uniformity are likely to occur.

One way to eliminate this phenomenon and suppress dissolution of the ceramic substrate 11 is to stop the process when etching the copper 10a when 50% or more of the thickness of the copper 10a has been etched (dissolved). , the surface of the copper-bonded ceramic substrate 100a is once cleaned (washed) with the rinsing liquid 21 to form the ceramic circuit board 101b (t2), and then the etching process is performed again to completely remove the copper 10a and the brazing material 12. An example of this method is to remove the ceramic substrate 11 and expose the ceramic substrate 11 (t3, t4). As a result, even if the area near the surface of the etched copper 10a has a shape such as a narrow width or a deep groove, the intermediate product 20 that has remained there can be completely removed during the process, and the etching process can be performed after removal. When the process is restarted, the dissolution of copper can proceed uniformly and rapidly over the entire surface. It is also effective in terms of work efficiency to perform cleaning immediately before the ceramic substrate 11 is exposed, for example, after 65 to 85% of the copper thickness to be removed by etching has been processed. As a result, the ceramic circuit board 11 is prevented from excessive contact with the processing liquid 14 and dissolved in the metal circuit forming process, and has a suitable porous portion 15, and is of good quality and suitable for power modules. It becomes possible to create.

At this time, the copper-bonded ceramic substrate 100a may be dried each time, or may be subjected to various treatments while being kept in a wet state. Further, etching and cleaning may be performed by a general immersion method, or by spraying or atomizing various liquids. Further, the cleaning process may be performed only once, or may be performed in multiple steps by alternately repeating cleaning and etching.

Furthermore, changing the composition of the processing liquid (etching liquid) is also one of the methods for producing a ceramic circuit board in which dissolution of the ceramic substrate is suppressed. Etching solutions containing hydrochloric acid as a main component are generally used, and hydrochloric acid easily dissolves various types of ceramics. Therefore, dissolution of ceramics can also be suppressed by using copper sulfate, an oxidizing acid, or an alkaline etching solution as the treatment solution.

Each of these methods may be applied singly or in combination. For example, as a multi-step example, 75% of the copper thickness is treated with an etching solution of ferric chloride + hydrochloric acid, and after cleaning is treated with an etching solution of copper sulfate (processing is done in two stages by changing the type of solution). It is also effective to bond the copper plate and the ceramic using a brazing filler metal to which a small amount of Ag is added, and to perform the etching process in a multi-step manner. These can be selected depending on the specifications such as the constituent materials and dimensions of the circuit board and the equipment specifications.
Furthermore, since the melting of ceramics as described above is caused by the composition of the brazing material, the solution presented here is applicable not only when the metal to be joined is copper, but also when the metal to be joined is aluminum, etc. It can be applied without any problem.

Ceramic circuit boards were produced under various conditions, and the thickness of the porous part of the ceramic exposed during circuit formation was confirmed. A summary of the implementation conditions and results is shown in Table 1.

The specific details of each embodiment are given below.
Example 1
A copper plate having a thickness of 1.2 mm was bonded to both sides of a silicon nitride substrate having a size of 50 mm x 50 mm and a thickness of 0.32 mm using a brazing material made of Cu (64 mass%)-Mg-Sn-Ti to prepare a copper-bonded ceramic substrate. Then, an etching resist was applied to the copper surface of the substrate in the shape shown in FIG.
Next, the substrate was immersed in an etching solution consisting of cupric chloride and hydrochloric acid, and copper was dissolved for 25 minutes while the solution was vigorously stirred. After that, the substrate was washed with pure water, and then immersed in the etching solution again and treated for another 10 minutes. This multi-step process produced a ceramic circuit substrate.
A cross section of the fabricated ceramic circuit board was cut out and observed using a scanning electron microscope (FE-SEM, JEOL JSM-7001F). As shown in Figure 4, the end of the copper plate dissolved and removed by etching had a typical flared shape (fillet shape), and the ceramic portion exposed by etching had almost no brazing material layer. As shown in Figure 5, it was confirmed that the ceramic was dissolved and made porous on the exposed ceramic surface. The depth of dissolution of the ceramic (porous portion thickness) at this time was about 22 μm.

(Example 2)
A copper-bonded ceramic substrate was produced in the same manner as in Example 1. Thereafter, an etching resist was applied to the surface of the copper plate in the shape shown in FIG. 3, and an etching solution consisting of ferric chloride and hydrochloric acid was sprayed onto the surface to dissolve the copper for 5 minutes. Thereafter, after cleaning with pure water, the etching solution was again sprayed on the substrate in multiple steps, and these treatments were repeated four times in total to produce a ceramic circuit board.
A cross section of the produced ceramic circuit board was cut out and observed using a scanning electron microscope (FE-SEM, JSM-7001F manufactured by JEOL). As shown in Figure 6, the edge of the copper plate that was dissolved and removed by etching has a typical widening shape (fillet shape), and the ceramic portion exposed by etching has almost no brazing material layer. Ta. As shown in FIG. 7, it was confirmed that the surface layer of the exposed ceramic portion was melted and made porous. The melting depth of the ceramic at this time was approximately 2 μm.

(Example 3)
A copper plate with a thickness of 1.2 mm is bonded to both sides of a silicon nitride substrate with a size of 190 mm x 140 mm and a thickness of 0.32 mm using a brazing material made of Cu (60 mass%)-Mg-Sn-Ti. A ceramic substrate was fabricated.
After printing an etching resist on the fabricated substrate, an etching solution consisting of cupric chloride and hydrochloric acid was sprayed onto the substrate to dissolve the copper for 5 minutes. Thereafter, after washing with pure water, an etching solution was sprayed again, and these processes were repeated four times in total, thereby performing multi-step processing to produce a ceramic circuit board.
A cross section of the produced ceramic circuit board was cut out and observed in the same manner as in Example 1. The end of the copper plate that had been dissolved and removed by etching had a typical widening shape (fillet shape), and the ceramic portion exposed by etching had almost no brazing material layer. It was also confirmed that the surface layer of the exposed ceramic portion had become porous due to melting of the ceramic. The melting depth of the ceramic at this time was about 28 μm.

Example 4
A copper plate having a thickness of 0.2 mm was bonded to both sides of a silicon nitride substrate having a size of 50 mm×50 mm and a thickness of 0.32 mm using a brazing material made of Cu (70 mass%)-Mg-Sn-Ti to prepare a copper-bonded ceramic substrate. Then, an etching resist was applied to the surface of the copper plate in the shape shown in FIG.
Next, the substrate was immersed in an etching solution consisting of cupric chloride and hydrochloric acid, and copper was dissolved for 20 minutes while the solution was vigorously stirred. After that, the substrate was washed with pure water, and then immersed in the etching solution again and treated for another 3 minutes. This multi-step process produced a ceramic circuit substrate.
The cross section of the produced ceramic circuit board was cut out and observed in the same manner as in Example 1. The end of the copper plate dissolved and removed by etching had a typical flared shape (fillet shape), and the ceramic portion exposed by etching had almost no brazing material layer. It was confirmed that the ceramic was dissolved and made porous on the surface of the exposed ceramic portion. The depth of the dissolved ceramic was about 10 μm.

(Example 5)
An aluminum bonded ceramic substrate was manufactured by bonding a silicon nitride substrate and an aluminum plate using Al (97 mass%)-Ti as a brazing material.
A part of the substrate was cut out and immersed in an etching solution consisting of cupric chloride and hydrochloric acid to perform aluminum dissolution treatment for 5 minutes. Thereafter, after cleaning with pure water, the substrate was immersed in an etching solution again and treated for an additional 3 minutes, thereby producing a ceramic circuit board in multiple stages.
A cross section of the produced ceramic circuit board was cut out and processed, and observed in the same manner as in Example 1. The edge of the aluminum that was dissolved and removed by etching had a typical widening shape (fillet shape), and the ceramic portion exposed by etching had almost no brazing material layer. It was also confirmed that the surface layer of the exposed ceramic portion had become porous due to melting of the ceramic. The melting depth of the ceramic at this time was approximately 15 μm.

(Comparative Example 1)
A copper plate having a thickness of 1.2 mm was bonded to both sides of a silicon nitride substrate having a size of 50 mm×50 mm and a thickness of 0.32 mm using a brazing material made of Cu (64 mass%)-Mg-Sn-Ti to prepare a copper-bonded ceramic substrate. Then, an etching resist was applied to the surface of the copper plate in the shape shown in FIG.
Next, the substrate was immersed in an etching solution consisting of cupric chloride and hydrochloric acid, and the stirring speed was set to twice that of Example 1, and the treatment was continued until the copper was completely dissolved (one-step treatment, requiring 40 minutes), thereby producing a ceramic circuit substrate.
The cross section of the produced ceramic circuit board was cut out and observed in the same manner as in Example 1. As shown in Fig. 8, the end of the copper plate dissolved and removed by etching had a typical flared shape (fillet shape), and the ceramic portion exposed by etching had almost no brazing material layer. The ceramic was dissolved and made porous on the surface of the exposed ceramic portion, but the depth of the dissolution varied depending on the location. At the deepest part, the depth of the dissolution of the ceramic was about 33 μm.

100 Metal bonded ceramic substrate 100a Copper bonded ceramic substrate 101, 101a Ceramic circuit board 101b Ceramic circuit board 10 Metal 10a Copper 10b Metal circuit 11 Ceramic substrate 11a Exposed portion 12 Brazing material 13 Resist 14 Processing liquid 15 Porous portion 20 Intermediate product 21 rinse liquid

Claims (5)

A ceramic circuit board in which a metal circuit is bonded to the surface of a ceramic substrate using a brazing material,
A porous portion is provided on the surface of the exposed portion of the ceramic substrate exposed by the formation of the metal circuit, and the thickness of the porous portion is 1 to 30 μm in the depth direction of the ceramic substrate. Ceramic circuit board. The ceramic circuit board according to claim 1, wherein the brazing filler metal has an Ag content of 50% by mass or less. A method for manufacturing a ceramic circuit board in which a metal circuit is bonded to the surface of a ceramic substrate using a brazing material,
a metal-bonded ceramic substrate preparation step of preparing a metal-bonded ceramic substrate in which a metal and a ceramic substrate are bonded with a brazing material;
a protective film forming step of forming a protective film on necessary parts of the metal;
a metal circuit forming step in which predetermined locations of the metal and the brazing material of the metal bonded ceramic substrate are melted by a treatment liquid to form a metal circuit;
A method of manufacturing a ceramic circuit board, characterized in that the metal circuit forming step is performed in multiple stages. In the metal circuit forming step carried out in multiple stages, after dissolving the metal and the brazing material by the processing liquid is interrupted, the metal bonding ceramic substrate is cleaned, and the metal and the brazing material are melted by the processing liquid again. 4. The method of manufacturing a ceramic circuit board according to claim 3, wherein the method is carried out by: The method for manufacturing a ceramic circuit board according to claim 3 or 4, characterized in that, in the metal circuit forming step performed in multiple stages, melting is interrupted after 50% or more of the thickness of the metal is melted. .