JPH07288296A - Ceramic circuit substrate - Google Patents

Abstract

PURPOSE:To provide a ceramic circuit substrate having high heat radiation, which can be fabricated in a method which is excellent in resistance against thermal impact and excellent in economy. CONSTITUTION:A conductor circuit formed from a copper plate 0.1mm thick or thicker is jointed to at least one of surfaces of a ceramic substrate by silicone adhesive containing inorganic filler and/or metallic filler. Heat conductivity of the silicone adhesive is 1X10<-3>cal/cm.sec. deg.C or more. In addition, thickness of the silicone adhesive for jointing the ceramic substrate to the conductor circuit is 30mum or less.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ceramic circuit board used for mounting power transistors and the like.

[0002]

2. Description of the Related Art Bipolar transistor, power MOS
Since a substrate for a power module on which a power transistor such as an FET is mounted requires high heat dissipation and high dielectric strength reliability, a ceramic substrate such as alumina or aluminum nitride is generally used. Since the current flowing through the power transistor is large, it is 0.1
A copper plate having a thickness of mm or more (usually a thickness of about 0.2 to 0.3 mm) is used. The DBC method (direct joining method: for example, Japanese Patent Publication No.
7-13515 method) and the active metal brazing method.
By these methods, a ceramic circuit board having a low thermal resistance has been obtained. What is common to these joining methods is that chemical bonding between a ceramic material and a metal material is used for joining the ceramic substrate and the copper plate. Therefore, the joining requires heat treatment at a very high temperature of 1065 to 1083 ° C. by the DBC method and 800 to 900 ° C. by the active metal brazing method. Furthermore, in the case of the DBC method, a mixed gas atmosphere of N ₂ gas and a trace amount of O ₂ gas is required as an atmosphere during heat treatment, and particularly, the partial pressure of O ₂ gas requires strict control. Also in the active metal brazing method, an atmosphere of an inert gas such as N ₂ or Ar or a vacuum atmosphere is required.

[0003]

In the conventional method of joining a ceramic substrate and a copper plate, as described above, high-temperature heat treatment and atmosphere control are required, so the equipment becomes complicated and expensive, and the running cost is also high. There was the problem of becoming expensive. Furthermore, in the circuit board obtained by the conventional joining method, the ceramic substrate and the copper plate are chemically strongly joined together, and since there is no buffer layer, the stress due to the difference in coefficient of thermal expansion between the ceramic substrate and the copper plate is Since the stress is applied directly to the ceramics substrate and the stress is repeated, cracks or fractures occur in the ceramics substrate, and finally there is a problem that the ceramics substrate and the copper plate are separated from each other, or the substrate is dielectrically broken down.

In view of the above circumstances, an object of the present invention is that it has high heat dissipation required for ceramics circuit boards, is excellent in thermal shock resistance, and does not require special atmosphere control, etc. Another object of the present invention is to provide a ceramics circuit board that can be manufactured by an excellent method.

[0005]

According to a first aspect of the present invention, there is provided a ceramic circuit board, wherein a conductor circuit made of a copper plate having a thickness of 0.1 mm or more is provided on at least one surface of the ceramic board with an inorganic filler and / or a metal. It is characterized in that it is adhered by a silicone adhesive containing a filler.

In the ceramic circuit board according to claim 2 of the present invention, the silicone adhesive has a thermal conductivity of 1 × 10 ⁻³ ca.
The ratio is 1 / cm · second · ° C. or higher, and
Alternatively, it is the ceramic circuit board according to claim 1.

The ceramic circuit board according to claim 3 of the present invention is characterized in that the thickness of the silicone adhesive for adhering the ceramic circuit and the conductor circuit is 30 μm or less. It is a ceramic circuit board.

The present invention will be described in detail below. As a result of studying the improvement of the above-mentioned problems of the prior art, the inventors have performed a method of bonding a ceramics substrate and a copper plate with a silicone adhesive to provide excellent thermal shock resistance and special atmosphere control. It was found that the ceramic circuit board can be obtained by a method which does not require the above, that is, which is excellent in economic efficiency. Furthermore, the increase in thermal resistance as a ceramic circuit board due to the presence of the silicone adhesive between the ceramic substrate and the copper plate is achieved by filling the silicone adhesive with a high thermal conductive inorganic filler and / or a metal filler. The present invention has also been found to be improved by using a silicone adhesive having high thermal conductivity.

In the ceramic circuit board of the present invention, a copper plate having a thickness of 0.1 mm or more is adhered to at least one surface of the ceramic board with a silicone adhesive. Examples of the copper plate used in the present invention include electrolytic copper foil and rolled copper plate, and the thickness thereof is limited to 0.1 mm or more because of the necessity as a power module substrate on which a power transistor is mounted. The bonding conditions may be selected according to the type of silicone adhesive, but even when a type of silicone adhesive that cures by heating is used,
Since the curing temperature is usually about 120 to 150 ° C., there is no need for a large-scale heat treatment furnace as in the above-mentioned prior art, and since there is no copper oxidation due to heat, it is not necessary to use an inert gas atmosphere. Can be adhered. It should be noted that the silicone adhesive may be cured in a vacuum atmosphere if necessary, for example, in order not to leave voids in the silicone adhesive, but in such a case, a high temperature as in the conventional technique is required. Since it does not require an expensive heat treatment furnace, the running cost is low, and the production can be performed by an economical method.

Next, matters relating to thermal resistance will be described below. When heat is transferred from the copper plate to the ceramic substrate, the thermal resistance between the copper plate and the ceramic substrate is
0 in the DBC method (direct joining method) because there is nothing in between
In the active metal brazing method, the thermal resistance of the brazing material layer becomes
In the present invention, the heat resistance of the silicone adhesive layer is obtained. Comparing the thermal conductivities of the brazing material and the silicone adhesive, the brazing material has a thermal conductivity of approximately 7 × 10 ⁻¹ cal / cm · sec · ° C, whereas the silicone adhesive does not contain a filler. The type is usually about 4 × 10 ⁻⁴ cal / cm · second · ° C., and it is unavoidable that the silicone adhesive method is disadvantageous in terms of heat resistance as compared with the conventional method.

Therefore, in the ceramic circuit board of the present invention, in order to improve the increase in thermal resistance due to the silicone adhesive existing between the ceramic board and the copper conductor circuit, the silicone adhesive is an inorganic filler and / or Alternatively, it is important that the metal filler is filled. The filler to be filled may be insulative or conductive, but the high thermal conductivity of the filler itself and the high filling rate mean that the thermal resistance of the silicone adhesive layer is high. Is required, that is, in order to provide the ceramic circuit board with high heat dissipation. Examples of the inorganic filler include alumina, aluminum nitride, silicon carbide, silicon nitride, boron nitride, titanium oxide, zirconium oxide, mullite, cordierite, and the like, and examples of the metal filler include copper, silver, tungsten, molybdenum. , Carbon and the like. These fillers may be filled individually or as a mixture of a plurality of types.

The silicone adhesive having a high thermal conductivity containing the above-mentioned inorganic filler and / or metal filler has a thermal conductivity of 1 × 10 ⁻³ cal / cm · sec · ° C. or more. It is desirable in order to reduce the thermal resistance of the agent layer and not to impair the high heat dissipation characteristic of the ceramic circuit board.

The thickness of the silicone adhesive layer in the present invention is not particularly limited, but the thickness after curing is preferably 30 μm or less. Because the thermal resistance of the silicone adhesive layer is proportional to the thickness of the layer and inversely proportional to the thermal conductivity of the silicone adhesive, the greater the thickness of the layer, the greater the thermal resistance. This is because some high heat dissipation is impaired.

Further, according to the conventional method, when a copper plate is bonded to only one surface of the ceramic substrate, the ceramic substrate is warped due to the stress caused by the difference in coefficient of thermal expansion between the copper plate or the brazing material and the ceramic substrate at the time of bonding. It was That is, since the contracting force of the copper plate and the brazing material is applied to the side where the copper plates are joined during cooling, warpage occurs because the joining surface side is concave. In order to prevent this phenomenon, it is necessary to bond a copper plate not only on the side where a conductor circuit is required, but also on the other side to balance the stress on both the front and back surfaces of the ceramic substrate. However, according to the present invention, since stress is hardly applied to the ceramics substrate at the time of joining the copper plates,
It is possible to bond the copper plate only to the side where the conductor circuit is required, which has the advantage of reducing the amount of copper plate used and the number of steps.

The method for forming a circuit on a copper plate in the present invention is not particularly limited. For example, a circuit board may be formed by etching after adhering to a ceramic substrate, or a circuit board may be preliminarily punched to form a circuit board on a ceramic substrate. You may make it adhere to.

[0016]

The deterioration of the thermal shock resistance of the ceramics circuit board is mainly due to the difference in thermal expansion between the ceramics board and the conductor circuit made of the copper plate. For example, the coefficient of thermal expansion of alumina ceramics is 7.2 (× 10 ^-6 / ° C), while the coefficient of thermal expansion of copper is 17.0 (× 10 ^-6 / ° C), which shows a large difference between the two. is there. In the conventional DBC method (direct joining method), a ceramic substrate and a copper plate are directly joined, and in the case of the active metal brazing method, an active metal brazing layer containing silver and copper as a main component is provided between the ceramic substrate and the copper plate. It exists and its coefficient of thermal expansion is about 18 (× 10 ⁻⁶ / ° C.). Therefore, in the conventional joining method, the stress caused by the difference in the coefficient of thermal expansion acts on the joining interface and destroys the ceramics which are more brittle than the metal.

Since the silicone adhesive used in the present invention is a rubber material having a high elasticity after being hardened, it is necessary to interpose it between the ceramic substrate and the conductor circuit made of the copper plate due to the difference in the coefficient of thermal expansion. It acts to relieve the stress on the interface and thus improves the thermal shock resistance of the ceramic circuit board.

Further, the bonding of the conductor circuit composed of the ceramic substrate and the copper plate with a silicone adhesive serves to bond the ceramic substrate and the copper plate without requiring a large-scale heat treatment furnace and an inert gas atmosphere unlike the prior art. do.

Furthermore, the inclusion of an inorganic filler and / or a metal filler in the silicone adhesive and the thickness of the silicone adhesive layer being 30 μm or less have the effect of increasing the thermal conductivity of the silicone adhesive layer. As a result, high heat dissipation as a ceramic circuit board is achieved.

[0020]

EXAMPLES The present invention will be described below based on Examples and Comparative Examples.

The silicone adhesives used in the following examples and comparative examples are the following four types. Silicone Adhesive A: Alumina Filler Filled Silicone Adhesive, 1-Liquid, Addition Reaction Heat Curing Type, Thermal Conductivity = 2.5 × 10 ⁻³ cal / cm · sec · ° C. Silicone Adhesive B: Alumina Filler Filled Silicone Adhesive Agent, 1 liquid type, addition reaction heat curing type, thermal conductivity = 4.0 × 10 ⁻³ cal / cm · sec · ° C. Silicone adhesive C: carbon filler filled silicone adhesive, 1 liquid type, addition reaction heat curing Mold, thermal conductivity = 3.0 × 10 ⁻² cal / cm · sec · ° C. Silicone adhesive D: filler-unfilled silicone adhesive, one-component, addition reaction heat curing type, thermal conductivity = 4.0 × 10 ^-4 cal / cm ・ sec ・ ° C

Example 1 Alumina substrate (30 × 40 m)
m, thickness 0.635 mm), the above silicone adhesive A was screen-printed in a circuit pattern on the upper surface, and a 0.2 mm-thick copper plate whose adhesive surface was chemically polished was placed thereon,
Heat treatment was performed at 150 ° C. for 30 minutes in a vacuum atmosphere to cure the silicone adhesive A and bond the alumina substrate and the copper plate. Then, a silicone adhesive A was solidly screen-printed on the entire surface of the alumina substrate on which the copper plate of the obtained substrate was not bonded, and the adhesive surface was chemically polished in the same manner as above. A 2 mm thick copper plate was joined.
After that, an etching method using a resist is used to form a circuit pattern only on the copper plate on one side of the copper plates bonded to both sides of the alumina substrate, and then electroless Ni plating is applied only on the copper plate to form a ceramic circuit. A substrate was obtained. The thickness of the silicone adhesive layer was set to about 20 μm.

(Examples 2 to 6) As shown in Table 1 below, an alumina substrate or an aluminum nitride substrate was used as a ceramic substrate. The size and thickness of these ceramic substrates were the same as those of the alumina substrate used in Example 1. Then, as shown in Table 1, any of the above-mentioned silicone adhesive A, silicone adhesive B, or silicone adhesive C was used as the silicone adhesive. Other conditions were the same as in Example 1 to obtain a ceramic circuit board. The thickness of the silicone adhesive layer was set to about 20 μm.

Comparative Example 1 The above silicone adhesive D was used as the silicone adhesive. Other conditions were the same as in Example 1 to obtain a ceramic circuit board. In addition,
The thickness of the silicone adhesive layer was set to about 20 μm.

Comparative Example 2 The above silicone adhesive D was used as the silicone adhesive, and the thickness of the silicone adhesive layer was set to 35 μm. Other conditions were the same as in Example 1 to obtain a ceramic circuit board.

(Comparative Examples 3 and 4) As shown in Table 1 below, an alumina substrate or an aluminum nitride substrate was used as a ceramic substrate. The size and thickness of these ceramic substrates were the same as those of the alumina substrate used in Example 1. Copper plates having a thickness of 0.2 mm were bonded to both surfaces of these substrates by the active metal brazing method. The conditions after the joining with the copper plate was completed were the same as in Example 1 to obtain a ceramics circuit board.

Thermal shock resistance and thermal resistance were evaluated as performances of the ceramic circuit boards obtained in each of the above Examples and Comparative Examples, and the results are shown in Table 1. The respective evaluation methods are shown below.

(Evaluation method of thermal shock resistance) The number of cycles until the cracks can be visually confirmed in the ceramics or the peeling of the copper plate can be confirmed by conducting a thermal shock test with the treatment under the following series of conditions as one cycle. I checked.

First treatment: -60 ° C for 30 minutes Second treatment: Room temperature for 10 minutes Third treatment: 150 ° C for 30 minutes

(Method of Evaluating Thermal Resistance) A TO-220 type transistor is soldered on a ceramic circuit board, and an aluminum radiation fin in an ideal heat radiation state is soldered on the lower surface of the substrate to energize the transistor. The thermal resistance of the ceramics circuit board was determined from the temperature rise of the transistor when energized and the collector loss of the transistor.

[0031]

[Table 1]

As can be seen from the results in Table 1, the examples of the present invention have lower thermal resistance than Comparative Examples 1 and 2 and have better thermal shock resistance than Comparative Examples 3 and 4. confirmed.

[0033]

Since the ceramic circuit board according to claims 1 to 3 of the present invention is constructed as described above, according to the present invention, it has a high heat dissipation property, an excellent thermal shock resistance, and Since a ceramics circuit board that can be manufactured by a highly economical method can be obtained, it is useful in applications such as circuit boards for power modules.

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Claims (3)

[Claims] 1. A conductor circuit comprising a copper plate having a thickness of 0.1 mm or more on at least one surface of a ceramic substrate,
A ceramic circuit board characterized by being bonded by a silicone adhesive containing an inorganic filler and / or a metal filler. 2. The silicone adhesive has a thermal conductivity of 1 × 10.
3. The ceramic circuit board according to claim 1, which has a temperature of ^-3 cal / cm.sec..degree. C. or more. 3. The ceramic circuit board according to claim 1, wherein the thickness of the silicone adhesive that bonds the ceramic board and the conductor circuit is 30 μm or less.