JP2002043478A - Ceramic circuit board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem that a semiconductor element is peeled from a metal circuit board and cannot be operated normally. SOLUTION: The metal circuit board 3 is attached to the upper face of a ceramic board 1, a projection part 3a mounting a semiconductor element 5 is formed on the upper face of the metal circuit board 3, and the projection part 3a satisfies the following equation. 200 μm>=H>=50 μm, L>=100 μm, S>=40%, H: height of the projection part, L: (the outer periphery of the semiconductor element)-(the outer periphery of the projection part) and S: a ratio of the area of the upper face of the projection part to the area of the lower face of the semiconductor element).

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 formed by joining a metal circuit board 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 made of copper or the like via a brazing material such as a silver-copper alloy. A ceramic circuit board with a circuit board bonded, or silver
A ceramic circuit board is used in which a metal circuit board made of copper or the like is directly joined to a copper eutectic alloy via an active metal brazing material obtained by adding titanium, zirconium, hafnium or a hydride thereof.

[0003] Such a ceramic circuit board, for example, a ceramic circuit board in which a metal circuit board made of copper or the like is joined to a metallized metal layer adhered on the ceramic board via a brazing material, is generally made of an aluminum oxide sintered body. A metallized metal layer is applied to the surface of a ceramic substrate made of an electrically insulating ceramic material such as an aluminum nitride sintered body, a silicon nitride sintered body, a mullite sintered body, etc.
The metallized metal layer is formed by brazing a metal circuit board made of a metal material such as copper via a brazing material such as silver brazing. Specifically, for example, a ceramic substrate is made of an aluminum oxide sintered body. In the case of consisting of, raw material powders such as aluminum oxide, silicon oxide, magnesium oxide and calcium oxide are mixed with an appropriate organic binder, a plasticizer, a solvent and the like to form a slurry, which is then mixed with a conventionally known doctor blade method. A plurality of ceramic green sheets are obtained by adopting a tape forming technique such as or a calender roll method, and then an appropriate organic binder, a plasticizer, and a solvent are added to the high melting point metal powder such as tungsten or molybdenum on the ceramic green sheets. The metal paste obtained by mixing is subjected to a predetermined pattern by employing a thick film forming technology such as screen printing. Then, the ceramic green sheets, on which the metal paste is printed and applied in a predetermined pattern, are laminated one on top of the other as necessary and fired at a temperature of about 1600 ° C. in a reducing atmosphere. To form a ceramic substrate made of an aluminum oxide sintered body having a metallized metal layer on the surface, and finally a metal circuit board of a predetermined pattern made of copper or the like on the metallized metal layer on the surface of the ceramic substrate. And a brazing material such as a silver brazing material is interposed therebetween and heated in a reducing atmosphere at a temperature of about 900 ° C. to melt the brazing material, and the metallized metal layer and the metal circuit board are melted with the molten brazing material. It is produced by joining

In order to effectively prevent oxidative corrosion on the exposed surface of the metallized metal layer and the metal circuit board and to firmly connect the semiconductor element to the metal circuit board via an adhesive such as solder, nickel or the like is used. A metal having excellent corrosion resistance and good wettability to an adhesive such as solder is applied to a predetermined thickness by using a technique such as a plating method.

[0005] The bonding of the semiconductor element to the metal circuit board is performed by printing a solder paste formed by adding an organic solvent and a solvent to the solder powder on the metal circuit board, and using a printing technique such as screen printing. By using the solder paste, the semiconductor element is placed on the solder paste on which the solder paste has been printed and applied, and then the semiconductor element is heated to a predetermined temperature (about 180 ° C.). ,
This is performed by causing a solvent or the like to scatter and melting the solder, and joining the metal circuit board and the semiconductor element with the melted solder.

[0006]

However, in this conventional ceramic circuit board, when the semiconductor element is bonded to the upper surface of the metal circuit board via an adhesive such as solder, the solder is largely melted on the surface of the metal circuit board. Spread and thickness is 50
μm, and as a result, it is difficult to firmly attach the semiconductor element to the metal circuit board, and when heat acts on the metal circuit board and the semiconductor element, The difference between the two thermal expansion coefficients (for example, copper: 18
(ppm / ° C., silicon: 4 ppm / ° C.), which has a disadvantage that a large thermal stress is generated and the semiconductor element is separated from the metal circuit board by the thermal stress.

Further, the thickness of the solder as an adhesive is increased in advance (for example, 250 μm), and the bonding strength of the semiconductor element to the metal circuit board is determined by setting an appropriate amount of solder interposed between the metal circuit board and the semiconductor element. May be strengthened.

However, if the thickness of the solder as the adhesive is increased, when the solder is melted and the semiconductor element is joined to the metal circuit board, the molten solder flows out from the metal circuit board onto the ceramic substrate and is adjacent thereto. Or short circuit between the metal circuit boards, or a thick adhesive made of solder having a low thermal conductivity is interposed between the semiconductor element and the metal circuit board, and the heat generated during operation of the semiconductor element is generated by the metal circuit board and It cannot be efficiently transmitted to the ceramic substrate, and has a drawback that the semiconductor element is heated to a high temperature to cause thermal destruction and thermal degradation of the semiconductor element.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned drawbacks, and has as its object to firmly join a semiconductor element to a metal circuit board and to keep the semiconductor element joined to the metal circuit board at an appropriate temperature for a long time. An object of the present invention is to provide a ceramic circuit board that can be normally and stably operated over a long period of time.

[0010]

According to the present invention, a metal circuit board is attached to an upper surface of a ceramic substrate, and a convex portion on which a semiconductor element is mounted is formed on the upper surface of the metal circuit plate.
The convex portion satisfies the following expression.

200 μm ≧ H ≧ 50 μm L ≧ 100 μm S ≧ 40% H: Height of convex portion L: (periphery of semiconductor device) − (periphery of convex portion) S: Upper surface area of convex portion relative to lower surface area of semiconductor device According to the ceramic circuit board of the present invention, the convex portion on which the semiconductor element is mounted is formed on the upper surface of the metal circuit board, the height of the convex portion is 50 μm to 200 μm, and the outer periphery of the convex portion is The ratio of the upper surface area of the convex portion to the lower surface area of the semiconductor device was set to 40% or more while the external size of the convex portion was made smaller than the external size of the semiconductor device so that a difference of 100 μm or more was formed between the semiconductor device and the outer periphery of the device. Therefore, when the semiconductor element is mounted on the convex portion provided on the metal circuit board and is bonded via solder as an adhesive, the lower surface of the semiconductor element, the side surface of the convex portion, and the upper surface of the metal circuit board around the convex portion are formed. Moderately in between A space having a volume is formed, and solder is filled and interposed in the space and between the lower surface of the semiconductor element and the upper surface of the convex portion. As a result, soldering of the semiconductor element to the convex portion provided on the metal circuit board is performed. The three-dimensional bonding can be made extremely strong, and the semiconductor element can be securely and firmly bonded to the upper surface of the projection.

When a semiconductor element is simultaneously joined to a convex portion provided on a metal circuit board via solder as an adhesive,
The semiconductor element and the protrusion come into contact with an appropriate area, and the heat generated during operation of the semiconductor element is efficiently transmitted to the metal circuit board and the ceramic substrate. As a result, the semiconductor element always has an appropriate temperature, and Can operate normally and stably over a long period of time.

[0013]

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 the ceramic circuit board of the present invention, wherein 1 is a ceramic board,
2 is a metallized metal layer and 3 is a metal circuit board.

The ceramic substrate 1 has a square shape,
A metallized metal layer 2 is adhered on the upper surface, and a metal circuit board 3 is brazed to the metallized metal layer 2.

The ceramic substrate 1 functions as a support member for supporting the metal circuit board 3, and is made of aluminum oxide sintered body, silicon nitride sintered body, aluminum nitride sintered body, silicon carbide sintered body, mullite. It is formed of an electrically insulating material such as a porous sintered body.

When the ceramic substrate 1 is formed of, for example, an aluminum oxide sintered body, an organic binder, a plasticizer, and a solvent suitable for a raw material powder such as aluminum oxide, silicon oxide, magnesium oxide, and calcium oxide are used. Is mixed and formed into a slurry, and the slurry is formed into a ceramic green sheet (green ceramic sheet) by employing a conventionally known doctor blade method or calender roll method. A punching process is performed, a predetermined shape is formed, and a plurality of sheets are laminated as necessary to form a molded body. Thereafter, the molded body is fired at a high temperature of about 1600 ° C., or is applied to a raw material powder such as aluminum oxide. The raw material powder is prepared by adding and mixing an organic solvent and a solvent. By molding techniques and molded into a predetermined shape, and thereafter, is manufactured by firing the molded body at a temperature of about 1600 ° C..

A metallized metal layer 2 is adhered to the surface of the ceramic substrate 1, and the metallized metal layer 2 acts as a base metal layer when the metal circuit board 3 is brazed to the ceramic substrate 1.

The metallized metal layer 2 is made of a high melting point metal material such as tungsten, molybdenum, manganese or the like. For example, a metal paste obtained by adding a suitable organic binder, a plasticizer and a solvent to tungsten powder and mixing the resultant is fired. A predetermined pattern and a predetermined thickness (10 to 50 μm) are formed on the upper surface of the ceramic substrate 1 by printing and applying a predetermined pattern on a surface of a ceramic green sheet (ceramic raw sheet) serving as the ceramic substrate 1 in advance by a conventionally known screen printing method. Is adhered to.

If the metallized metal layer 2 is coated with a metal such as nickel or gold having good conductivity, good corrosion resistance and good wettability with the brazing material by plating, the metallized metal layer 2 is formed. The oxidation corrosion of the layer 2 can be effectively prevented, and the metallized metal layer 2 and the metal circuit board 3 can be effectively prevented.
Can be extremely firmly brazed. Accordingly, in order to effectively prevent the metallized metal layer 2 from being oxidized and corroded and to firmly braze the metallized metal layer 2 and the metal circuit board 3, nickel,
It is preferable that a metal such as gold having good conductivity, good corrosion resistance and good wettability with the brazing material is applied to a thickness of 1 to 20 μm.

The metallized metal layer 2 has a metal circuit board 3 attached to the upper surface thereof with a brazing material 4 interposed therebetween.

The metal circuit board 3 is made of a metal material such as copper or aluminum. The metal circuit board 3 is formed on a metallized metal layer 2 formed on the surface of the ceramic substrate 1 by, for example, a silver brazing material (silver: 72 wt. %, Copper: 28% by weight) and aluminum brazing material (aluminum: 88% by weight, silicon: 1)
2% by weight) and then placed in a vacuum or in a neutral or reducing atmosphere at a predetermined temperature (about 900 ° C. for silver brazing, about 900 ° C. for aluminum brazing) Is heated at about 600 ° C.) to melt the brazing material 4 and join the upper surface of the metallized metal layer 2 and the lower surface of the metal circuit board 3 to be attached to the surface of the ceramic substrate 1.

The metal circuit board 3 made of copper, aluminum, or the like has a thickness, for example, by subjecting an ingot of copper, aluminum, or the like to a conventionally known metal working method such as a rolling method or a punching method. Is 500 μm, and is manufactured in a predetermined pattern shape corresponding to the pattern shape of the metallized metal layer 2.

When the metal circuit board 3 is also made of copper,
When the metal circuit board 3 is formed of oxygen-free copper, the oxygen-free copper has good wettability with the brazing material 4 without being oxidized by the oxygen existing in the copper surface during brazing. Becomes
Bonding to the metallized metal layer 2 via the brazing material 4 is strengthened. Therefore, it is preferable that the metal circuit board 3 is formed of oxygen-free copper.

Further, the metal circuit board 3 has a convex portion 3a on which the semiconductor element 5 is mounted on its upper surface. The convex portion 3a functions to support the semiconductor element and to operate the semiconductor element 5. The heat generated at this time is transmitted and dissipated through the metal circuit board 3.

The convex portion 3a is formed at the same time when the metal circuit board 3 is formed by applying a conventionally known metal working method such as a rolling method or a punching method to an ingot (lumps) of copper, aluminum, or the like. Alternatively, the metal circuit board 3 is subjected to a pressing method, an etching method, or the like, so that the metal circuit board 3
It is formed in a predetermined shape at a predetermined position on the upper surface.

The height (H) of the projection 3a is 50 μm.
m to 200 μm, the difference (L) between the outer circumference of the projection 3 a and the outer circumference of the semiconductor element 5 is 100 μm or more, and the ratio of the area of the upper surface of the projection 3 a to the area of the lower surface of the semiconductor element 5 is 40% or more.

The height of the projection 3a is set to 50 μm to 200 μm.
μm, and the lower surface of the semiconductor element 5 while the outer dimension of the convex part 3a is smaller than the outer dimension of the semiconductor element 5 so that a difference of 100 μm or more is formed between the outer circumference of the convex part 3a and the outer circumference of the semiconductor element 5. When the ratio of the upper surface area of the protrusion 3a to the area is 40% or more, when the semiconductor element 5 is mounted on the protrusion 3a provided on the metal circuit board 3 and joined via the solder 6 as an adhesive. A space having an appropriate volume is formed between the lower surface of the semiconductor element 5, the side surface of the convex portion 3a, and the upper surface of the metal circuit board 3 around the convex portion 3a, and within the space and the lower surface of the semiconductor element 5 and the upper surface of the convex portion 3a. And the solder 6 is interposed between them, and as a result, the bonding of the semiconductor element 5 to the convex portion 3a provided on the metal circuit board 3 via the solder 6 becomes three-dimensional, and the bonding strength is reduced. Very strong,
The semiconductor element 5 can be securely and firmly joined to the upper surface of the projection 3a.

At the same time, the projection 3a provided on the metal circuit board 3
When the semiconductor element 5 is joined to the semiconductor element 5 via a solder 6 as an adhesive, the semiconductor element 5 and the projection 3a come into contact with an appropriate area, and the heat generated when the semiconductor element 5 is operated causes the metal circuit board 3 and The power is efficiently transmitted to the ceramic substrate 1, and as a result, the semiconductor element 5 always has an appropriate temperature, and the semiconductor element 5 can operate normally and stably for a long period of time.

The height of the projection 3a is 50 μm.
When the value is less than the predetermined value, the volume of the space formed between the lower surface of the semiconductor element 5, the side surface of the projection 3a, and the upper surface of the metal circuit board 3 around the projection 3a becomes narrower, and the semiconductor element 5 is firmly joined to the upper surface of the projection 3a. If the thickness exceeds 200 μm, the volume of the space formed between the lower surface of the semiconductor element 5, the side surface of the protrusion 3 a, and the upper surface of the metal circuit board 3 around the protrusion 3 a becomes too large, and the solder is formed in the space. 6 cannot be completely filled, and the semiconductor element 5 cannot be firmly joined to the upper surface of the projection 3a. Therefore, the height of the projection 3a is specified in the range of 50 μm to 200 μm.

When the difference (L) between the outer periphery of the convex portion 3a and the outer periphery of the semiconductor element 5 is less than 100 μm, the lower surface of the semiconductor element 5, the side surface of the convex portion 3a, and the upper surface of the metal circuit board 3 around the convex portion 3a. And the volume of the space formed between the semiconductor element 5 and the semiconductor element 5 cannot be firmly joined to the upper surface of the projection 3a. Therefore, the difference (L) between the outer periphery of the protrusion 3a and the outer periphery of the semiconductor element 5 is specified to be 100 μm or more.

Further, if the area of the upper surface of the projection 3a is less than 40% of the area of the lower surface of the semiconductor element 5, the heat generated by the semiconductor element 5 cannot be efficiently transmitted to the metal circuit board 3 and the ceramic substrate 1. In addition, the temperature of the semiconductor element 5 becomes high, causing the semiconductor element 5 to undergo thermal destruction and thermal degradation in characteristics. Therefore, the area of the upper surface of the projection 3a is specified to be 40% or more of the area of the lower surface of the semiconductor element 5.

Further, the metal circuit board 3 having the projections 3a is coated on its surface with a metal made of nickel and having good conductivity, good corrosion resistance and good wettability with the brazing material by plating. When the metal circuit board 3 is electrically connected to an external electric circuit, the electrical connection is good, and when the semiconductor element 5 is joined to the metal circuit board 3 via the solder 6, the joining is firmly performed. It can be. Therefore,
It is preferable that the metal circuit board 3 having the protrusions 3a is coated with a metal having good conductivity and good corrosion resistance and good wettability with the brazing material by a plating method.

In the case where a plating layer made of nickel is applied to the surface of the metal circuit board 3, the metal circuit board 3 contains 8 to 15 phosphorus therein.
When the amorphous alloy of nickel-phosphorus is contained in an amount of 0.5% by weight, the oxidation of the surface of the plating layer made of nickel can be prevented well, and the wettability with the brazing material 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, it is preferable to contain 8 to 15% by weight of phosphorus therein to form a nickel-phosphorus amorphous alloy.

When a plating layer made of a nickel-phosphorus amorphous alloy is applied to the surface of the metal circuit board 3, if the content of phosphorus with respect to nickel is less than 8% by weight or more than 15% by weight, nickel is added. 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 nickel plating layer 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.

A semiconductor element 5 is joined to the convex portion 3a of the metal circuit board 3 via a solder 6. The solder 6 includes a tin-lead eutectic alloy, a tin-lead alloy, a gold-tin alloy, A metal material such as a gold-germanium alloy is preferably used.

The bonding of the semiconductor element 5 to the projection 3a via the solder 6 is performed when the solder 6 is made of, for example, a tin-lead eutectic alloy (tin: 60% by weight, lead: 40% by weight). An organic solvent and a solvent are added to and mixed with a tin-lead eutectic alloy powder to prepare a solder paste, and the solder paste is formed on the upper surface of the convex portion 3a using a conventionally known printing technique such as screen printing. Then, the semiconductor element 5 is placed on the solder paste that has been deposited to a predetermined thickness,
This is performed by heating to 80 ° C. and melting the solder.

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. Although an example in which the semiconductor element 5 is formed of an aluminum oxide sintered body is shown, when the semiconductor element 5 generates a large amount of heat and the heat is to be efficiently removed, the ceramic substrate 1 is sintered with an aluminum nitride based material having a high heat transfer coefficient. The ceramic substrate 1 may be formed of a mullite sintered body having a low dielectric constant when it is desired to transmit an electric signal to the metal circuit board 3 at high speed.

In the above-described embodiment, the metallized metal 2 is previously applied to the surface of the ceramic substrate 1 and the metal circuit board 3 is brazed to the metallized metal layer 2 to form a ceramic circuit board. Is attached directly to the surface of the ceramic substrate 1 via an active metal brazing material obtained by adding titanium or titanium hydride to a silver-copper eutectic alloy in an amount of 2 to 5% by weight, for example. May be formed.

Further, in the above-described embodiment, the projection 3a formed on the upper surface of the metal circuit board 3 is formed integrally with the metal circuit board 3. However, the projection 3a is formed separately by the same material and method as the metal circuit board 3. The protrusions 3a may be formed on the body, and the protrusions 3a may be bonded and fixed to the upper surface of the metal circuit board 3 via an adhesive such as brazing material.

[0041]

According to the ceramic circuit board of the present invention,
A convex portion on which the semiconductor element is mounted is formed on the upper surface of the metal circuit board, the height of the convex portion is set to 50 μm to 200 μm, and 100 μm is provided between the outer periphery of the convex portion and the outer periphery of the semiconductor element.
Since the ratio of the upper surface area of the convex portion to the lower surface area of the semiconductor device is set to 40% or more while the external size of the convex portion is made smaller than the external size of the semiconductor device so that a difference of not less than μm is formed, the convex portion is provided on the metal circuit board. When the semiconductor element is mounted on the convex part and joined via solder as an adhesive,
A space having an appropriate volume is formed between the lower surface of the semiconductor element, the side surface of the convex portion, and the upper surface of the metal circuit board around the convex portion, and solder is filled in the space and between the lower surface of the semiconductor device and the upper surface of the convex portion. As a result, the bonding of the semiconductor element to the protrusion provided on the metal circuit board via solder becomes three-dimensional, and the bonding strength becomes extremely strong. It can be securely and firmly joined.

At the same time, when the semiconductor element is bonded to the projection provided on the metal circuit board via solder as an adhesive,
The semiconductor element and the protrusion come into contact with an appropriate area, and the heat generated during operation of the semiconductor element is efficiently transmitted to the metal circuit board and the ceramic substrate. As a result, the semiconductor element always has an appropriate temperature, and Can operate normally and stably over a long period of time.

[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]

 DESCRIPTION OF SYMBOLS 1 ... Ceramic substrate 2 ... Metallized metal layer 3 ... Metal circuit board 3a ... Convex part 5 ... Semiconductor element 6 ... Solder

Claims (1)

[Claims] 1. A metal circuit board is mounted on an upper surface of a ceramic substrate, and a convex portion on which a semiconductor element is mounted is formed on the upper surface of the metal circuit plate, wherein the convex portion satisfies the following expression. A ceramic circuit board characterized by the above-mentioned. 200 μm ≧ H ≧ 50 μm L ≧ 100 μm S ≧ 40% H: Height of convex portion L: (periphery of semiconductor device) − (periphery of convex portion) S: Ratio of upper surface area of convex portion to lower surface area of semiconductor device