JP2001308472A - Ceramic circuit board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve a problem of a conventional ceramic circuit board wherein heat generated from an electronic component can not be dissipated well to the outside and the electronic component malfunctions. SOLUTION: The ceramic circuit board is formed by fixing a metallic circuit board 3 to the surface of a ceramic substrate 1 through an active metal soldering material 2 wherein the ceramic substrate 1 comprises a sintered body of silicon nitride formed of silicon nitride as a principle component and a sintering auxiliaries and the area of the sintering auxiliaries exposed to the surface is not larger than 5% of the area of a surface where the metallic circuit board 3 is fixed.

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 in which a metal circuit board is joined to a ceramic substrate by brazing.

[0002]

2. Description of the Related Art In recent years, as a circuit board such as a power module board or a switching module board, a metallized metal layer adhered on a ceramic substrate is formed of a metal such as copper through a brazing material such as a silver-copper alloy. A ceramic circuit board to which a circuit board is bonded is used.

In such a ceramic circuit board, a metallized metal layer is generally adhered to the surface of a ceramic substrate made of an aluminum oxide sintered body, and a metal circuit board made of a metal material such as copper is applied to the metallized metal layer. It is formed by brazing through a brazing material such as brazing,
More specifically, for example, a raw material powder such as aluminum oxide, silicon oxide, magnesium oxide, and calcium oxide is mixed with a suitable organic binder, a plasticizer, a solvent, and the like to form a slurry, which is then mixed with a conventionally known doctor blade. A plurality of ceramic green sheets are obtained by adopting a tape forming technique such as a method or a calendar roll method, and then an appropriate organic binder and a solvent are added to the high melting point metal powder such as tungsten and molybdenum on the ceramic green sheets and mixed. The obtained metal paste is printed and applied in a predetermined pattern by employing a printing technique such as a screen printing method, and then the ceramic green sheets in which the metal paste is printed and applied in a predetermined pattern are vertically laminated as necessary. And firing in a reducing atmosphere at a temperature of about 1600 ° C. A metal substrate and a metal paste are sintered and integrated to form a ceramic substrate made of an aluminum oxide sintered body having a metallized metal layer on the surface, and finally a predetermined metal plate made of copper or the like is formed on the metallized metal layer on the surface of the ceramic substrate. The metal circuit board of the pattern is placed with a brazing material such as silver brazing interposed therebetween, and the metal circuit board is placed in a reducing atmosphere for about 90 minutes.
It is manufactured by heating to a temperature of 0 ° C. to melt the brazing material and joining the metallized metal layer and the metal circuit board with the molten brazing material.

[0004]

However, in this conventional ceramic circuit board, the ceramic substrate is generally formed of an aluminum oxide sintered body, and the aluminum oxide sintered body has a heat transfer coefficient of 20 W /
m · K, the heat generated during the operation of the electronic component mounted and fixed on the metal circuit board cannot be efficiently dissipated to the outside via the ceramic substrate. As a result, the electronic component becomes Has caused a problem that the electronic component is heated to a high temperature, which causes thermal destruction and deterioration of characteristics of the electronic component, so that the electronic component cannot be operated stably and reliably.

In order to solve the above problems, it is conceivable to form the ceramic substrate from a silicon nitride sintered body having a very high heat transfer coefficient of 60 W / m · K or more.

When such a ceramic substrate is formed of a silicon nitride-based sintered body, the silicon nitride-based sintered body is solid-phase sintered,
Since it does not contain much vitreous material and it is difficult to apply a metallized metal layer firmly, the attachment of a metal circuit board to a ceramic substrate made of silicon nitride-based sintered body reacts directly with the silicon nitride-based sintered body. An active metal brazing material containing at least one of titanium, zirconium, hafnium and / or a hydride thereof must be used.

However, the silicon nitride-based sintered body contains a large amount of a sintering aid in order to easily perform solid-phase sintering, and a part of the sintering aid is added to the surface of the silicon nitride-based sintered body by 15 to 20 parts. %
Since the sintering aid has poor wettability with the active metal brazing material, the metal circuit board is firmly bonded to the ceramic substrate made of silicon nitride sintered body via the active metal brazing material. It cannot be performed, and causes a disadvantage that the reliability as the ceramic circuit board is low.

The present invention has been devised in view of the above-mentioned drawbacks, and has as its object to strengthen the bonding between a ceramic substrate and a metal circuit board, and to efficiently dissipate heat generated by mounted electronic components to the outside. It is to provide a ceramic circuit board which can be used.

[0009]

SUMMARY OF THE INVENTION The present invention is a ceramic circuit board comprising a ceramic substrate and a metal circuit board attached to the surface of the ceramic substrate via an active metal brazing material. It is made of a silicon nitride sintered body formed of silicon and a sintering aid, and the area of the surface of the sintering aid that is exposed on the surface relative to the area of the surface to which the metal circuit board is attached. It is characterized by being 5% or less.

According to the ceramic circuit board of the present invention, since the ceramic substrate is formed of a silicon nitride sintered body having a very high heat transfer coefficient of 60 W / m · K or more, it is mounted and fixed on a metal circuit board. Even if the electronic components generate a large amount of heat during operation, the heat is satisfactorily dissipated into the atmosphere through the metal circuit board and the ceramic substrate. It is possible to operate normally.

Further, according to the ceramic circuit board of the present invention, the area of the sintering aid exposed on the surface of the ceramic substrate surface on which the metal circuit board is attached is set to 5% or less. Therefore, the bonding area between the ceramic substrate and the active metal brazing material becomes large, and as a result, the attachment of the metal circuit board to the ceramic substrate can be made extremely strong.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described in detail based on embodiments shown in the accompanying drawings.

FIG. 1 shows an embodiment of a ceramic circuit board according to the present invention, wherein 1 is a ceramic board, 2 is an active metal brazing material, and 3 is a metal circuit board.

The ceramic substrate 1 has a square shape,
A metal circuit board 3 is brazed to the upper surface via an active metal brazing material 2.

The ceramic substrate 1 functions as a supporting member for supporting the metal circuit board 3, and is formed of a silicon nitride sintered body.

The ceramic substrate 1 made of the silicon nitride sintered body has a heat transfer coefficient of 60 W / m · K or more and is easy to conduct heat. Even if the electronic components generate a large amount of heat, the heat is satisfactorily dissipated into the atmosphere via the metal circuit board 3 and the ceramic substrate 1, and as a result, the electronic components have an appropriate temperature, and the electronic components are always stable and normal. Can be operated.

The ceramic substrate 1 made of the silicon nitride-based sintered body includes raw material powders such as silicon nitride, aluminum oxide, and magnesium oxide, yttrium oxide, cesium oxide, and the like.
An appropriate organic binder, a plasticizer, and a solvent are added to a sintering aid powder composed of a rare earth element such as samarium oxide, erbium oxide, ytterbium oxide, and ruthenium oxide to form a slurry and mix the slurry with a conventionally known doctor. A ceramic green sheet (ceramic green sheet) is formed by employing a blade method or a calendar roll method, and then the ceramic green sheet is subjected to an appropriate punching process to form a predetermined shape, and a plurality of sheets are laminated as necessary. Then, it is formed into a molded body.
It is manufactured by firing at a high temperature of ° C.

A ceramic circuit board 3 made of a silicon nitride sintered body has a metal circuit board 3 attached to the upper surface thereof by brazing via an active metal brazing material 2.

The metal circuit board 3 is made of a metal material such as copper or aluminum. By applying a conventionally known metal working method such as a rolling method or a punching method to an ingot of copper or aluminum, for example, , Thickness 500μ
m, it is manufactured in a predetermined pattern shape.

In the case where the metal circuit board 3 is made of copper, if the metal circuit board 3 is formed of oxygen-free copper, the surface of the copper during the brazing is reduced by the oxygen existing in the copper. The wettability with the active metal brazing material 2 is improved without being oxidized, and the bonding to the ceramic substrate 1 via the active metal brazing material 2 is strengthened. Therefore, it is preferable that the metal circuit board 3 is formed of oxygen-free copper.

When the metal circuit board 3 is coated with a metal having good conductivity and good corrosion resistance and good wettability with the active metal brazing material 2 by plating on the surface thereof, the metal A good electrical connection between the circuit board 3 and an external electric circuit can be achieved, and an electronic component such as a semiconductor element can be firmly bonded to the metal circuit board 3 via solder. Therefore, it is preferable that the metal circuit board 3 be coated with a metal made of nickel and having good conductivity, good corrosion resistance and good wettability with the active metal brazing material 2 by plating.

Further, when a plating layer made of nickel is applied to the surface of the metal circuit board 3, phosphorus is added in an amount of 8 to 15 μm.
When the nickel-phosphorus amorphous alloy is contained in an amount of about 0.5% by weight, the surface oxidation of the plating layer made of nickel can be prevented well, and the wettability with the active metal brazing material 2 can be maintained for a long time. Therefore, when a plating layer made of nickel is applied to the surface of the metal circuit board 3, phosphorous is added to the inside thereof.
It is preferable that the content of the nickel-phosphorus amorphous alloy is set to be contained in an amount of about 15% by weight.

When a plating layer made of a nickel-phosphorus amorphous alloy is deposited on the surface of the metal circuit board 3, when the content of phosphorus with respect to nickel is less than 8% by weight or more than 15% by weight, There is a danger that it becomes difficult to form an amorphous alloy of phosphorus and the solder cannot be firmly bonded to the plating layer. Therefore, when a plating layer made of a nickel-phosphorus amorphous alloy is applied to the surface of the metal circuit board 3, the content of phosphorus with respect to nickel is preferably set in the range of 8 to 15% by weight, and more preferably. The range of 10 to 15% by weight is good.

The plating layer made of nickel, which is deposited on the surface of the metal circuit board 3, has a thickness of 1.5 μm.
If it is less than 3, the surface of the metal circuit board 3 cannot be completely covered with the plating layer made of nickel, and there is a risk that oxidation corrosion of the metal circuit board 3 cannot be effectively prevented. If it exceeds, the intrinsic stress existing inside the plating layer made of nickel becomes large, and the ceramic substrate 1 will be warped or cracked. In particular, when the thickness of the ceramic substrate 1 is as thin as 700 μm or less, warpage or cracking of the ceramic substrate 1 becomes remarkable. Therefore, the thickness of the plating layer made of nickel deposited on the surface of the metal circuit board 3 is 1.5 μm to
It is preferable to set the range to 3 μm.

Further, a metal circuit board 3 is provided on the ceramic substrate 1.
The active metal brazing material 2 for brazing is used as a bonding material for bonding the ceramic substrate 1 and the metal circuit board 3, and for example, silver brazing material (silver: 72% by weight, copper: 28% by weight) or aluminum A brazing material made of a brazing material (aluminum: 88% by weight, silicon: 12% by weight) or the like is preferably used in which at least one of titanium, tungsten, hafnium and / or a hydride thereof is added in an amount of 2 to 5% by weight. You.

The attachment of the metal circuit board 3 to the ceramic substrate 1 by the active metal brazing material 2 involves placing the metal circuit board 3 on the ceramic substrate 1 with the active metal brazing material 2 interposed therebetween.
Next, this is heat-treated in a vacuum or in a neutral or reducing atmosphere at a predetermined temperature (about 900 ° C. for silver brazing material or about 600 ° C. for aluminum brazing material) to obtain an active metal brazing material 2.
Is melted and bonded to the upper surface of the ceramic substrate 1 and the lower surface of the metal circuit board 3.

In the present invention, it is important that the area of the sintering aid exposed on the surface of the ceramic substrate 1 on which the metal circuit board 3 is attached is set to 5% or less.

When the area of the sintering aid on the surface of the ceramic substrate 1 to which the metal circuit board 3 is attached is set to 5% or less, the metal circuit board 3 is attached to the ceramic substrate 1 via the active metal brazing material 2. In this case, the bonding area between the ceramic substrate 1 and the active metal brazing material 2 becomes large, and as a result, the attachment of the metal circuit board 3 to the ceramic substrate 1 can be made extremely strong.

When the area of the sintering aid on the surface of the ceramic substrate 1 exceeds 5%, the bonding area between the ceramic substrate 1 and the active metal brazing material 2 decreases, and the ceramic substrate 1 and the active metal brazing material 2 And the bonding strength with the metal is weak. Therefore, the metal circuit board 3 of the ceramic substrate 1
Is specified in the range of 5% or less.

In order to reduce the area of the sintering aid exposed on the surface of the ceramic substrate 1 to 5% or less, the sintering aid is softer than the silicon nitride forming the ceramic substrate 1 and the ceramic sintering aid is used. This is performed by subjecting the surface of the substrate 1 to a special blasting treatment and selectively removing the sintering aid.

As the special blast treatment, specifically, a solution of water or the like to which an appropriate amount of an abrasive such as alumina spherical powder having a particle diameter of 20 to 250 μm is added is 0.1 to 0.5M.
1 to 1 on the upper surface of the ceramic substrate 1 with a blowing pressure of Pa
The blasting process is performed by spraying for 0 minute, and the sintering aid area on the surface of the ceramic substrate 1 is 5%
It is as follows.

In the blasting process, when the particle diameter of the alumina spherical powder is less than 20 μm, it is difficult to efficiently remove the sintering aid exposed on the surface of the ceramic substrate 1 and the area of the exposed sintering aid is reduced. If the thickness exceeds 250 μm, residual stress exceeding 20 MPa is present on the surface of the ceramic substrate 1, and the metal circuit board 3 is stably and firmly joined to the ceramic substrate 1. There is a risk of not being able to do so. Therefore, it is preferable that the particle diameter of the alumina spherical powder is in the range of 20 to 250 μm.

When the blowing pressure is less than 0.1 MPa, it is difficult to efficiently remove the sintering agent exposed on the surface of the ceramic substrate 1 and the area of the exposed sintering agent is 5% or less. There is a danger that you will not be able to
If it exceeds 0.5 MPa, residual stress exceeding 20 MPa is present on the surface of the ceramic substrate 1, and there is a risk that the metal circuit board 3 cannot be stably and firmly joined to the ceramic substrate 1. Therefore, it is preferable that the spray pressure be in the range of 0.1 to 0.5 MPa.

Thus, according to the above-described ceramic circuit board, the electrodes of the electronic component are brought into contact with the upper surface of the metal circuit board 3 with the solder interposed therebetween, and then the electrode is brought to a predetermined temperature (about 18).
0 ° C.) to melt the solder and join the melted solder to the metal circuit board 3 and the electrodes of the electronic component, whereby the electronic component is electrically connected to the metal circuit board 3 and the metal circuit board 3 When connected to an external electric circuit, the electronic component is electrically connected to the external electric circuit via the metal circuit board 3.

It should be noted that the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention. The ceramic substrate 1 is subjected to a blast process of spraying a solution containing an abrasive on the surface.
The sintering aid exposed on the surface of the substrate was selectively removed. However, the present invention is not limited to this. The ceramic substrate 1 is put into a container containing a medium made of water and alumina powder, and then Alternatively, the container may be rotated or vibrated to remove the medium by bringing the medium into contact with a sintering aid that exposes the surface of the ceramic substrate 1, that is, a method such as a so-called rotary barrel treatment or vibration barrel treatment may be used.

[0036]

According to the ceramic circuit board of the present invention,
Since the ceramic substrate is formed of a silicon nitride sintered body having a very high heat transfer coefficient of 60 W / m · K or more, the electronic components mounted and fixed on the metal circuit board generate a large amount of heat during operation. Also, the heat is satisfactorily dissipated into the atmosphere via the metal circuit board and the ceramic substrate. As a result, the electronic component is at an appropriate temperature, and the electronic component can always be operated stably and normally.

According to the ceramic circuit board of the present invention, the area of the sintering aid exposed on the surface of the ceramic substrate on which the metal circuit board is attached is set to 5% or less. Therefore, the bonding area between the ceramic substrate and the active metal brazing material becomes large, and as a result, the attachment of the metal circuit board to the ceramic substrate can be made extremely strong.

[Brief description of the drawings]

FIG. 1 is a sectional view showing one embodiment of a ceramic circuit board of the present invention.

[Explanation of symbols]

 1. Ceramic substrate 2. Active metal brazing material 3. Metal circuit board

Claims (1)

[Claims] 1. A ceramic circuit board comprising a ceramic circuit board and a metal circuit board attached to the surface thereof via an active metal brazing material, wherein said ceramic board comprises silicon nitride as a main component and a sintering aid. The surface of the sintering aid exposed to the surface is 5% or less with respect to the area of the surface to which the metal circuit board is attached, which is formed of the formed silicon nitride-based sintered body. Ceramic circuit board.