JPH05275566A - Manufacture of ceramic circuit board for power module - Google Patents

Abstract

PURPOSE:To provide a ceramic circuit board for a power module having high quality, high performance and a low cost. CONSTITUTION:A patterned copper-plated copper-tungsten alloy plate and an alumina board having a thickness of 30-150mum are laminated, and heated at 1065-1085 deg.C in an oxidative atmosphere to be connected. Since the ultrathin alumina board is used, a problem of thermal conductivity due to the alumina board is improved, and a ceramic circuit board having high heat dissipation out of a system is provided. Since such an ultrathin alumina board is connected to a copper-plated copper-tungsten alloy plate by oxidation heating, thermal expansion coefficients of the circuit board and the alumina board can be equalized, and problems of a crack, peeling due to a difference of the coefficients of both the boards are solved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a ceramic circuit board for a power module such as a module equipped with a power IC, a power transistor or the like, or a circuit board for a switch power supply module, and more particularly to a ceramic board and a copper plate. The present invention relates to a method for manufacturing a ceramic circuit board for a power module, which is obtained by direct bonding and is provided with high quality, high performance and low cost.

[0002]

2. Description of the Related Art In recent years, in a module equipped with a power IC, a power transistor, etc. and a module for a switch power source, the amount of power used has been increased and a large amount of power has been used. There has been a demand for a circuit board for a power module that has high heat dissipation and high reliability.

Conventionally, this kind of power module circuit board generally has a thickness of about 0.6 to 1 mm and a surface roughness Ra.
While contacting an alumina substrate having a thickness of about 0.5 to 0.6 μm with a circuit copper plate having a thickness of 0.3 to 0.5 mm,
A so-called DBC circuit board, which is manufactured by heating at a eutectic temperature of copper-oxygen, that is, a temperature of 1060 to 1090 ° C. and directly bonding in a nitrogen atmosphere containing a small amount of oxygen, has been commercialized.

Since this DBC circuit board has a relatively thin bonding layer between the alumina board and the copper plate and is formed of copper or copper oxide, it has the advantage of being relatively excellent in heat dissipation. It is used as a circuit board for power modules.

[0005]

However, the above-mentioned DBC circuit board has the following drawbacks. There is variation in the bonding force between the alumina substrate and the copper plate,
If it is weak, peeling may occur. It is considered that this is because it is difficult to control the amount of oxygen in the firing nitrogen atmosphere and the contact surface of the bonding layer is small because the surface roughness of the alumina substrate is large.

Since the thickness of the alumina substrate used is large, the thermal conductivity is low, and the heat dissipation to the outside of the system is not sufficient, which causes a thermal problem.

Since the thermal expansion coefficient of the substrate and that of the copper plate are greatly different, the circuit board bonded to each other is vulnerable to heat shock, and cracks or breakage of the alumina substrate itself may occur due to soldering, for example. Peeling between copper plates may occur.

As described above, all the conventional circuit boards have problems in terms of quality, performance, price and the like.

The present invention solves the above-mentioned conventional problems, and provides a method of manufacturing a high-quality, high-performance and inexpensive power module circuit board suitable as a power hybrid circuit board for high power and large power. With the goal.

[0010]

According to a first aspect of the present invention, there is provided a method of manufacturing a ceramic circuit board for a power module, comprising: a patterned copper-tungsten alloy plate having a copper coating;
It is characterized in that an alumina substrate having a thickness of 0 to 150 μm is laminated and bonded by heating at 1065 to 1085 ° C. in an oxygen atmosphere.

According to a second aspect of the present invention, there is provided a method of manufacturing a ceramic circuit board for a power module according to the first aspect, wherein the copper-tungsten alloy plate contains 5 to 30% by weight of copper.

According to a third aspect of the present invention, there is provided a method of manufacturing a ceramic circuit substrate for a power module according to the first or second aspect, wherein a surface roughness Ra of a laminated surface of the alumina substrate with the copper-tungsten alloy plate is 0.2 μm or less. It is characterized by being.

The present invention will be described in detail below. The copper-tungsten alloy plate used in the present invention is, for example,
It is a composite material produced by sintering tungsten powder into a porous body and infiltrating copper into the porous body, and its thermal expansion coefficient can be arbitrarily changed to some extent depending on the compounding ratio of copper and tungsten. There are commercial products of such copper-tungsten alloy plates, which can be purchased and used. The copper content in the copper-tungsten alloy suitable for the coefficient of thermal expansion of alumina is preferably in the range of 5 to 30% by weight, and particularly preferably in the range of 10 to 30% by weight.

Since this copper-tungsten alloy plate is used for a circuit, it is patterned by punching in a pattern with a press or by etching to form a pattern. The thickness of such a copper-tungsten alloy plate is usually 0.3 to
The thickness is preferably about 0.5 mm, but the thickness may be outside this range.

Such a copper-tungsten alloy plate is preferably coated with copper to a thickness of about 100 μm for bonding with an alumina substrate. The copper coating can be formed by electroplating or electroless plating, and further by sputtering, ion plating or the like.

On the other hand, the alumina substrate has a thickness of 30 to 150 μm.
m, the surface roughness (hereinafter, simply referred to as “surface roughness”) Ra of the laminated surface with at least the copper-coated copper-tungsten alloy plate Ra is preferably 0.2 μm or less.
If the thickness of the alumina substrate is less than 30 μm, the mechanical properties of the substrate cannot be satisfied, and if it exceeds 150 μm, the effect of improving the heat dissipation property of the present invention cannot be sufficiently obtained.

Further, the surface roughness Ra of the alumina substrate is 0.
If it exceeds 2 μm, the contact area of the bonding layer between the alumina substrate and the copper-coated copper-tungsten alloy plate cannot be sufficiently obtained, and the problem of peeling cannot be reliably solved.

Such an ultrathin film alumina substrate is difficult to manufacture by the conventional alumina powder method, and preferably, a manufacturing method using a colloidal substance of aluminum hydroxide as a starting material, for example, an alkoxide hydrolysis method. It is advantageous to manufacture

In the case of the alkoxide hydrolysis method, after synthesizing an aluminum alkoxide, water is added to this to hydrolyze it to form boehmite. Further, an acid is added to this to peptize it to produce a colloid of ultrafine particles.
Then, an organic binder is added to this to adjust the viscosity, and after molding and drying, the obtained green sheet is fired to obtain an extremely thin alumina having a surface roughness Ra of 0.2 μm or less and an ultrathin thickness of 30 to 150 μm. A substrate can be obtained.

Of course, the method for producing an alumina substrate according to the present invention is not limited to the above-mentioned alkoxide hydrolysis method, and it is possible to use an inorganic salt hydrolysis method or other conventional general production method such as a powder method. It can also be manufactured by polishing the obtained alumina substrate as needed.

To bond the copper-coated copper-tungsten alloy plate and the alumina substrate, the copper-coated copper-tungsten alloy plate and the alumina substrate are heated in a laminated state to directly form a copper oxide layer on the laminated surface. It is done by joining.

This heat bonding is performed in an oxidizing atmosphere at 1065.
-1085 ° C, 5-30 minutes, preferably 10-2
Do about 0 minutes. The oxidizing atmosphere during heating is
Air, oxygen, or a mixed gas of oxygen and an inert gas can be used.

If the heating bonding temperature is less than 1065 ° C., sufficient bonding strength cannot be obtained, and if it exceeds 1085 ° C., copper begins to melt. After the heat treatment, the product is cooled and, if necessary, the oxide film formed on the surface of the copper-coated copper-tungsten alloy plate is removed by acid treatment or the like to obtain a product.

[0024]

In the present invention, since an ultrathin alumina substrate having a thickness of 30 to 150 μm is used, the problem of thermal conductivity due to the alumina substrate is improved, and a ceramic circuit board having high heat dissipation to the outside of the system is provided. It

Moreover, since such an ultra-thin alumina substrate is used as a circuit substrate to oxidize and bond with a copper-coated copper-tungsten alloy plate, the circuit substrate and the alumina substrate can have the same coefficient of thermal expansion. The problems of cracking and peeling due to the difference in the coefficient of thermal expansion between the plates are solved.

In particular, according to the method of claim 2, the coefficient of thermal expansion of the copper-coated copper-tungsten alloy plate is made to match the coefficient of thermal expansion of the alumina substrate, and cracks caused by the difference in the coefficient of thermal expansion between the two plates. The problem of peeling and peeling can be more reliably prevented.

In particular, according to the method of claim 3, since the surface of the alumina substrate is smooth, it is possible to secure a large contact area with the copper-coated copper-tungsten alloy plate and to further enhance the bonding strength. ..

[0028]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to the following examples as long as the gist thereof is not exceeded.

Example 1 Using an ultrafine particle boehmite sol as a starting material, an alumina substrate was prepared by an alkoxide hydrolysis method. Specifically, an aluminum ingot and alcohol were reacted to synthesize an aluminum alkoxide, which was hydrolyzed, and then an acid was further added for peptization to generate a boehmite sol. An organic binder was added to this to make a slurry, which was then molded and dried while casting through a doctor blade to obtain a green sheet. After that, it is cut into a predetermined shape and fired in an electric furnace to have a surface roughness Ra of 0.2.
A dense alumina substrate having a thickness of 100 μm and a thickness of 100 μm was obtained.
Since the alumina substrate thus obtained was composed of fine particles, it did not generate pinholes even when it was thin, had a small surface roughness, and had very good smoothness. .. Moreover, the thickness could be easily controlled to a desired thickness.

1 by electroplating with this alumina substrate
A patterned copper-tungsten alloy plate (copper 10% by weight, tungsten 90% by weight, thickness 0.5 mm) on which a copper coating having a thickness of 00 μm was formed was placed in a stack in a heating furnace and contained 100 ppm of oxygen. 1065 ° C in nitrogen atmosphere
At 20 ° C. for 20 minutes and then cooled.

The alumina substrate with a circuit thus obtained could be suitably used as a ceramic circuit substrate for a power module for high power.

Example 2 By the same sol-gel method as in Example 1, the surface roughness Ra0.
An alumina substrate having a thickness of about 1 μm and a thickness of 50 μm was produced. This alumina substrate and a patterned copper-tungsten alloy plate (copper 20% by weight, tungsten 80% by weight, thickness 0.5 mm) having a copper coating with a thickness of 100 μm were laminated and placed in a batch type heating furnace. , Oxygen 500pp
After heating in a nitrogen gas atmosphere containing m at 1080 ° C. for 10 minutes, it was cooled. The alumina substrate with a circuit thus obtained could be suitably used as a ceramic circuit substrate for power modules for high power.

Example 3 By the same sol-gel method as in Example 1, the surface roughness Ra0.
An alumina substrate having a thickness of about 05 μm and a thickness of 30 μm was produced. This alumina substrate and a patterned copper-tungsten alloy plate (copper 30% by weight, tungsten 70% by weight, thickness 0.5 mm) having a copper coating with a thickness of 100 μm were laminated and placed in a continuous heating furnace to obtain oxygen. After heating at 1070 ° C. for 10 minutes in a nitrogen gas atmosphere containing 200 ppm, it was cooled. The circuitized alumina substrate thus obtained is
It could be suitably used as a ceramic circuit board for power modules for high power.

[0034]

As described above in detail, according to the method for manufacturing a ceramic circuit board for a power module of the present invention, the bonding strength between the copper-coated copper-tungsten alloy plate for a circuit and the alumina board is high, and the heat dissipation is high. Provided is a ceramic circuit board for power modules, which has good performance, high reliability, high performance, high quality, and low cost.

According to the method of manufacturing a ceramic circuit board for a power module of claim 2, the copper-coated copper-tungsten alloy plate and the alumina substrate can have the same thermal expansion coefficient, and the difference between the thermal expansion coefficients of the two plates. The problem of cracking and peeling due to the is further reliably prevented.

According to the method for manufacturing a ceramic circuit board for a power module of claim 3, the bonding strength is further improved.

Claims (3)

[Claims] 1. A patterned copper-tungsten alloy plate having a copper coating and an alumina substrate having a thickness of 30 to 150 μm are laminated, and the mixture is placed in an oxygen atmosphere at 1065 to 1085 ° C.
A method for manufacturing a ceramics circuit board for a power module, which comprises bonding the substrates by heating them to each other. 2. The method for producing a ceramic circuit board for a power module according to claim 1, wherein the copper-tungsten alloy plate contains 5 to 30% by weight of copper. 3. A ceramic circuit board for a power module according to claim 1, wherein the surface roughness Ra of the laminated surface of the alumina substrate with the copper-tungsten alloy plate is 0.2 μm or less. Method.