JP4191860B2 - Ceramic circuit board - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a ceramic circuit board in which a metal circuit board is joined to a ceramic board by brazing.
[0002]
[Prior art]
In recent years, a metal circuit board made of copper or the like is bonded to a metallized metal layer deposited on a ceramic substrate through a brazing material such as a silver-copper alloy as a circuit board such as a power module substrate or a switching module substrate. Ceramic circuit board or ceramic circuit in which a metal circuit board made of copper or the like is directly joined to the ceramic board via an active metal brazing material in which titanium, zirconium, hafnium or a hydride thereof is added to a silver-copper eutectic alloy. A substrate is used.
[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 bonded to a metallized metal layer deposited on the ceramic board via a brazing material is generally an aluminum oxide sintered body, aluminum nitride A metallized metal layer is deposited on the surface of a ceramic substrate made of an electrically insulating ceramic material such as a sintered carbonaceous material, a silicon nitride sintered material, and a mullite sintered material, and copper or the like is applied to the metalized metal layer. It is formed by brazing a metal circuit board made of a metal material through a brazing material such as silver brazing. Specifically, for example, when the ceramic substrate is made of an aluminum oxide sintered body, aluminum oxide is used. Add appropriate organic binder, plasticizer, solvent, etc. to raw powder such as silicon oxide, magnesium oxide, calcium oxide, etc. Along with this, a plurality of ceramic green sheets are obtained by adopting a tape forming technique such as a doctor blade method or a calender roll method that is conventionally known, and then suitable for refractory metal powders such as tungsten and molybdenum on the ceramic green sheet. A metal paste obtained by adding and mixing an organic binder, a plasticizer, and a solvent is printed and applied in a predetermined pattern by employing a thick film forming technique such as a screen printing method, and then the metal paste is printed and applied in a predetermined pattern. The ceramic green sheets are stacked one above the other as needed and fired in a reducing atmosphere at a temperature of about 1600 ° C., and the ceramic green sheets and metal paste are sintered and integrated to have a metallized metal layer on the surface. A ceramic substrate made of a sintered body is formed, and finally the ceramic is A metal circuit board having a predetermined pattern made of copper or the like is placed on the metallized metal layer on the surface of the substrate with a brazing material such as silver solder interposed therebetween, and this is heated to a temperature of about 900 ° C. in a reducing atmosphere. It is manufactured by melting a material and joining a metallized metal layer and a metal circuit board with the melted brazing material.
[0004]
The exposed surfaces of the metallized metal layer and the metal circuit board are nickel nickel to effectively prevent oxidative corrosion and to firmly connect electronic components such as semiconductor elements to the metal circuit board via an adhesive such as solder. A metal having excellent corrosion resistance such as solder and wettability with respect to an adhesive such as solder is applied to a predetermined thickness by using a technique such as plating.
[0005]
The electronic component is connected to the metal circuit board by first using a printing technique such as a well-known screen printing method with a solder paste formed by adding an organic solvent and a solvent to the solder powder on the metal circuit board. A printed pattern is printed and applied, and then the electrodes of the electronic component are placed on and abutted on the printed and applied solder paste, and then heated to a predetermined temperature (about 180 ° C.), and the solder paste organic solvent, It is performed by volatilizing the solvent and the like, melting the solder, and joining the metal circuit board and the electrode of the electronic component with the melted solder.
[0006]
[Problems to be solved by the invention]
However, in this conventional ceramic circuit substrate, the thermal expansion coefficient of the ceramic substrate is about 3 ppm / ° C. to 7 ppm / ° C. (aluminum oxide sintered body: about 7 ppm / ° C., aluminum nitride based sintered body: about 4 ppm / ° C. The silicon nitride-based sintered body is about 3 ppm / ° C., whereas the thermal expansion coefficient of the metal circuit board made of copper, aluminum or the like is about 18 ppm / ° C. to 23 ppm / ° C. ((copper: about 18 ppm / ° C., (Aluminum: about 23 ppm / ° C), and the thermal expansion coefficients of the ceramic substrate and the metal circuit board are greatly different. Therefore, the metal circuit board is attached to the metallized metal layer deposited on the upper surface of the ceramic substrate with a brazing material such as silver brazing. When attaching to the metal circuit board, a large stress is generated between the ceramic substrate and the metal circuit board due to the difference in thermal expansion coefficient between the two. As a result, the ceramic substrate in the region where the outer peripheral portion of the metal circuit board is located is cracked in the depth direction and grows to cause cracks in the ceramic substrate. Had.
[0007]
The present invention has been devised in view of the above drawbacks, and its purpose is to effectively prevent the ceramic substrate from cracking, and to operate electronic components such as semiconductor elements reliably and stably. It is to provide a ceramic circuit board.
[0008]
The present invention is a ceramic circuit board in which a metal circuit board made of a metal having a thermal expansion coefficient larger than that of the ceramic substrate is bonded to the upper surface of the ceramic substrate, and is 1/3 of the thickness of the ceramic substrate from the upper surface of the ceramic substrate. An electrically independent metallized layer is disposed at the position of the inner distance A, and the outer periphery of the metallized layer is larger than the area smaller than the outer periphery of the metal circuit board by the distance A and the outer periphery of the metal circuit board. It is characterized by being made smaller .
[0009]
Further, the present invention is characterized in that the metallized layer has a thickness of 5 μm to 50 μm.
[0010]
According to the ceramic circuit board of the present invention, the metallized layer is disposed at a distance A that is within 1/3 of the thickness of the ceramic substrate from the upper surface of the ceramic substrate, and the outer periphery of the metalized layer is the outer periphery of the metal circuit board. Since the distance A is larger than the smaller region, the ceramic substrate and the metal circuit board are deeply formed in the region where the outer peripheral portion of the metal circuit board is located due to the large stress generated due to the difference in thermal expansion coefficient between the ceramic board and the metal circuit board. Even if a crack is generated in the vertical direction, the growth of the crack is effectively prevented by the metallized layer, and as a result, no crack is generated in the ceramic substrate. Therefore, the ceramic circuit board of the present invention can securely and securely connect the electrodes of the electronic component on the metal circuit board, and the electronic component connected to the metal circuit board can operate normally and stably over a long period of time. It becomes possible to make it.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Next, the present invention will be described in detail based on embodiments shown in the accompanying drawings.
FIG. 1 shows a cross-sectional view of an embodiment of the ceramic circuit board of the present invention, wherein 1 is a ceramic substrate, 2 is a metallized metal layer, and 3 is a metal circuit board.
[0012]
The ceramic substrate 1 has a rectangular shape, and a metallized metal layer 2 is deposited on the upper surface thereof, and a metal circuit board 3 is brazed to the metallized metal layer 2.
[0013]
The ceramic substrate 1 acts as a support member for supporting the metal circuit board 3, and is an aluminum oxide sintered body, a mullite sintered body, a silicon carbide sintered body, an aluminum nitride sintered body, and a mullite sintered body. It is made of an electrically insulating material such as
[0014]
For example, when the ceramic substrate 1 is formed of an aluminum oxide sintered body, an appropriate organic binder, plasticizer, and solvent are added to and mixed with raw material powders such as aluminum oxide, silicon oxide, magnesium oxide, and calcium oxide. Then, a ceramic green sheet (green ceramic sheet) is formed by adopting a conventionally well-known doctor blade method or calendar roll method, and then a suitable punching process is performed on the ceramic green sheet. And forming a molded body by laminating a plurality of sheets as necessary, and then firing the molded body at a high temperature of about 1600 ° C., or an organic solvent suitable for a raw material powder such as aluminum oxide Add and mix the solvent to adjust the raw material powder and apply the raw material powder to press molding technology It was molded into a predetermined shape, and thereafter, is manufactured by firing the molded body at a high temperature of about 1600 ° C..
[0015]
The ceramic substrate 1 has a metallized metal layer 2 deposited on the surface thereof, and the metallized metal layer 2 functions as a base metal layer when the metal circuit board 3 is brazed to the ceramic substrate 1.
[0016]
The metallized metal layer 2 is made of a refractory metal material such as tungsten, molybdenum, manganese, etc. For example, a ceramic paste is obtained by firing a metal paste obtained by adding and mixing an appropriate organic binder, plasticizer, and solvent to tungsten powder. A predetermined pattern and a predetermined thickness (10 to 50 μm) are deposited on the upper surface of the ceramic substrate 1 by applying a predetermined pattern to the surface of the ceramic green sheet (ceramic green sheet) in advance by a well-known screen printing method. Is done.
[0017]
The metallized metal layer 2 is formed by depositing a metal having good conductivity such as nickel and gold and having good corrosion resistance and wettability with a brazing material to a thickness of 1 μm to 20 μm by plating. Further, the oxidative corrosion of the metallized metal layer 2 can be effectively prevented, and the brazing between the metallized metal layer 2 and the metal circuit board 3 can be extremely strengthened. Therefore, in order to effectively prevent the oxidative corrosion of the metallized metal layer 2 and to strengthen the brazing between the metallized metal layer 2 and the metal circuit board 3, the surface of the metallized metal layer 2 has good conductivity such as nickel and gold. Thus, it is preferable to deposit a metal having good corrosion resistance and wettability with the brazing material to a thickness of 1 μm to 20 μm.
[0018]
The metallized metal layer 2 has a metal circuit board 3 attached to the upper surface thereof via a brazing material.
[0019]
The metal circuit board 3 is made of a metal material such as copper or aluminum, and the metal circuit board 3 is formed on the metallized metal layer 2 formed on the surface of the ceramic substrate 1, for example, a silver brazing material (silver: 72% by weight, copper : 28% by weight) or aluminum brazing material (aluminum: 88% by weight, silicon: 12% by weight), etc., and then placed, and after that, in vacuum or in a neutral or reducing atmosphere Heat treatment is performed at a temperature (about 900 ° C. for silver brazing material and about 600 ° C. for aluminum brazing material) to melt the brazing material and bond it to the upper surface of the metallized metal layer 2 and the lower surface of the metal circuit board 3. As a result, it is attached to the surface of the ceramic substrate 1.
[0020]
The metal circuit board 3 made of copper, aluminum, or the like has a thickness of, for example, 500 μm by applying a conventionally known metal processing method such as a rolling method or a punching method to an ingot (lumb) such as copper or aluminum. A predetermined pattern shape corresponding to the pattern shape of the metallized metal layer 2 is manufactured.
[0021]
When the metal circuit board 3 is also made of copper, if the metal circuit board 3 is made of oxygen-free copper, the oxygen-free copper is oxidized by oxygen present in the copper during brazing. Therefore, the wettability with the brazing material is improved, and the bonding to the metallized metal layer 2 through the brazing material is strengthened. Therefore, the metal circuit board 3 is preferably formed of oxygen-free copper.
[0022]
Further, when the metal circuit board 3 is coated with a metal having good conductivity made of nickel and having good corrosion resistance and wettability with a brazing material on the surface thereof, the metal circuit board 3 and the external electric circuit 3 are connected. The electrical connection with the circuit is good, 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 is coated with a metal having good conductivity made of nickel and having good corrosion resistance and wettability with the brazing material on the surface thereof.
[0023]
In the case where a plating layer made of nickel is deposited on the surface of the metal circuit board 3, if the nickel-phosphorus amorphous alloy containing phosphorus in an amount of 8 to 15% by weight is formed, surface oxidation of the plating layer made of nickel is improved. Thus, 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 inside to form a nickel-phosphorus amorphous alloy.
[0024]
When a plating layer made of a nickel-phosphorus amorphous alloy is applied to the surface of the metal circuit board 3, the nickel-phosphorus amorphous alloy is used when the phosphorus content relative to nickel is less than 8% by weight or more than 15% by weight. There is a risk that it becomes difficult to form solder and the solder cannot be firmly adhered to the plating layer.
[0025]
Accordingly, when a plating layer made of an amorphous alloy of nickel-phosphorus is applied on the surface of the metal circuit board 3, the phosphorus content relative to nickel is preferably in the range of 8 to 15% by weight, preferably 10 A range of ˜15% by weight is preferred.
[0026]
Furthermore, when the thickness of the plating layer made of nickel deposited on the surface of the metal circuit board 3 is less than 1.5 μm, the surface of the metal circuit board 3 is completely covered with the plating layer made of nickel. And there is a risk that the oxidative corrosion of the metal circuit board 3 cannot be effectively prevented. When the thickness exceeds 3 μm, the internal stress in the plated layer made of nickel increases, and the ceramic substrate 1 Warpage or cracking will occur. In particular, when the thickness of the ceramic substrate 1 is as thin as 700 μm or less, warping or cracking of the ceramic substrate 1 becomes remarkable.
[0027]
Therefore, the plating layer made of nickel deposited on the surface of the metal circuit board 3 preferably has a thickness in the range of 1.5 μm to 3 μm.
[0028]
The ceramic substrate 1 to which the metal circuit board 3 is attached on the upper surface is further provided with a metallized layer 4 at a distance A within 1/3 of the thickness of the ceramic substrate 3 from the upper surface. 4 is formed so that the outer periphery thereof is larger than the region where the distance A is smaller than the outer periphery of the metal circuit board 3. Therefore, when the metal circuit board 3 is attached to the metallized metal layer 2 deposited on the upper surface of the ceramic substrate 1 via a brazing material such as silver brazing, the heat of both of the ceramic substrate 1 and the metal circuit board 3 is heated. A large stress is generated due to the difference in the expansion coefficient, which is concentrated on the outer peripheral portion of the metal circuit board 3 and cracks are generated in the depth direction in the ceramic substrate 1 in the region where the outer peripheral portion of the metal circuit board 3 is located. Even so, the growth of the crack is effectively prevented by the metallized layer 4, and as a result, no crack is generated in the ceramic substrate 1.
[0029]
This is because cracks generated in the depth direction of the ceramic substrate 1 develop at an angle lower than 45 ° in the depth direction of the ceramic substrate 1 starting from the outer peripheral portion of the metal circuit board 3. This is because if the metallized layer 4 is formed at a position of a distance A larger than the region A smaller than the outer periphery of the metal circuit board 3, the metallized layer 4 can reliably catch the progress of cracks.
[0030]
The metallized layer 4 is formed at the position of the distance A from the upper surface of the ceramic substrate 1 by the same material and method as the metallized metal layer 2, and the outer periphery thereof is larger than the region where the distance A is smaller than the outer periphery of the metal circuit board 3. Yes.
[0031]
If the metallized layer 4 is disposed at a position exceeding 1/3 of the thickness of the ceramic substrate 1, the mechanical strength of the ceramic substrate 1 is remarkably lowered by cracks extending to the metallized layer 4. The reliability as is lost. Therefore, the metallized layer 4 is specified to be disposed within a range of １ ／ from the upper surface of the ceramic substrate 1 with respect to the thickness of the ceramic substrate 1.
[0032]
Further, if the metallized layer 4 is formed smaller than a region having a distance A smaller than the outer periphery of the metal circuit board 3, the metallized layer 4 starts from the outer periphery of the metal circuit board 3 and is 45 ° in the depth direction of the ceramic substrate 1. A crack that develops at a lower angle cannot be reliably received, and the ceramic substrate 1 is cracked. Therefore, it is specified that the metallized layer 4 is formed larger than a region having a distance A smaller than the outer periphery of the metal circuit board 3.
[0033]
Further, if the thickness of the metallized layer 4 is less than 5 μm, it tends to be difficult to effectively prevent the cracks from developing in the metallized layer 5, and if the thickness exceeds 50 μm, the metallized layer 4 is between the metalized layer 4 and the insulating substrate 1. There is a risk of peeling. Therefore, it is preferable that the metallized layer 4 has a thickness in the range of 5 μm to 50 μm.
[0034]
Thus, according to the above-described ceramic circuit board, an electronic component such as a semiconductor element is bonded and fixed to the metal circuit board 3 attached to the upper surface of the ceramic substrate 1 via an adhesive such as solder, so that an electrode such as a semiconductor element is formed. Is electrically connected to the metal circuit board 3 via an electrical connection means such as a bonding wire, and electronic components such as semiconductor elements are mounted on the ceramic circuit board and connected to an external electric circuit via the metal circuit board 3. Is done.
[0035]
It should be noted that the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention. For example, in the above-described embodiments, the ceramic substrate 1 is made of an aluminum-based ceramic. In the example shown in the figure, the electronic component generates a large amount of heat, and when it is desired to efficiently remove this heat, the ceramic substrate 1 is made of an aluminum nitride sintered body or silicon nitride having high thermal conductivity. The ceramic substrate 1 may be formed of a mullite sintered body having a low dielectric constant when the electric signal is to be propagated through the metal circuit board 3 at a high speed.
[0036]
Further, in the above-described embodiment, the metallized metal 2 is previously deposited on 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 substrate. A ceramic circuit board is formed on the surface of the substrate 1 by directly attaching the metal circuit board 3 through an active metal brazing material in which, for example, 2-5% by weight of titanium or titanium hydride is added to a silver-copper eutectic alloy. May be.
[0037]
【The invention's effect】
According to the ceramic circuit board of the present invention, the metallized layer is disposed at a distance A that is within 1/3 of the thickness of the ceramic substrate from the upper surface of the ceramic substrate, and the outer periphery of the metalized layer is the outer periphery of the metal circuit board. Since the distance A is larger than the smaller region, the ceramic substrate and the metal circuit board are deeply formed in the region where the outer peripheral portion of the metal circuit board is located due to the large stress generated due to the difference in thermal expansion coefficient between the ceramic board and the metal circuit board. Even if a crack is generated in the vertical direction, the growth of the crack is effectively prevented by the metallized layer, and as a result, no crack is generated in the ceramic substrate. Therefore, the ceramic circuit board of the present invention can securely and securely connect the electrodes of the electronic component on the metal circuit board, and the electronic component connected to the metal circuit board can operate normally and stably over a long period of time. It becomes possible to make it.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing an embodiment of a ceramic circuit board according to the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Ceramic substrate 2 ... Metallized metal layer 3 ... Metal circuit board 4 ... Metallized layer

Claims (2)

A ceramic circuit board in which a metal circuit board made of a metal having a thermal expansion coefficient larger than that of the ceramic substrate is bonded to the upper surface of the ceramic substrate, and is a distance within one third of the thickness of the ceramic substrate from the upper surface of the ceramic substrate An electrically independent metallization layer is disposed at the position A, and the outer periphery of the metallization layer is larger than the region smaller than the outer periphery of the metal circuit board by the distance A and smaller than the outer periphery of the metal circuit board. Ceramic circuit board.   The ceramic circuit board according to claim 1, wherein the metallized layer has a thickness of 5 μm to 50 μm.

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