JP4295409B2 - Manufacturing method of ceramic circuit board - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for manufacturing a ceramic circuit board in which an aluminum metal circuit board is bonded to a ceramic substrate with a brazing material.
[0002]
[Ohio's technology]
In recent years, as circuit boards such as power module boards and switching module boards, an active metal brazing material in which at least one of titanium, zirconia, hafnium and hydrides thereof is added to a silver-copper alloy on a ceramic board is used. A ceramic circuit board in which a metal circuit board made of copper or the like is directly bonded is used.
[0003]
Such a ceramic circuit board is generally made of an electrically insulating ceramic material such as an aluminum oxide sintered body, an aluminum nitride sintered body, a silicon nitride sintered body, and a mullite sintered body. In the case of a sintered material, it is specifically manufactured by the following method.
[0004]
That is,
(1) First, a brazing paste is prepared by adding an organic solvent and a solvent to an active metal powder obtained by adding at least one of titanium, zirconium, hafnium and hydrides thereof to a silver-copper alloy. .
(2) Next, a ceramic raw material powder such as aluminum oxide, silicon oxide, magnesium oxide, and calcium oxide is mixed with an appropriate organic binder, plasticizer, solvent, etc. to form a mud and this is a well-known doctor blade. After obtaining a plurality of ceramic green sheets by adopting a tape forming technique such as a method and a calender roll method, it is formed into a predetermined dimension, and then the ceramic green sheets are stacked up and down as necessary and in a reducing atmosphere. Firing is performed at a temperature of about 1600 ° C., and the ceramic green sheet is sintered and integrated to form a ceramic substrate made of an aluminum oxide sintered body.
(3) Next, a metal circuit board made of copper or the like is placed on the ceramic substrate with the brazing paste interposed therebetween.
(4) Finally, the brazing paste disposed between the ceramic substrate and the metal circuit board is heated to a temperature of about 900 ° C. in a non-oxidizing atmosphere, and the active metal powder is passed through the ceramic substrate. A ceramic circuit board is manufactured by joining a brazing material made of a silver-copper alloy and joining the brazing material to a metal circuit board.
[0005]
In order to effectively prevent oxidative corrosion on the exposed surface of the brazing material and the metal circuit board, and at the same time, to strengthen the bonding with an adhesive material such as solder for bonding and fixing an electronic component such as a semiconductor element to the metal circuit board, A metal such as nickel is deposited by using a technique such as plating.
[0006]
[Problems to be solved by the invention]
However, in this conventional ceramic circuit board, the metal circuit board is generally formed of copper, and the copper has a coefficient of thermal expansion of 18 ppm / ° C., and the aluminum oxide sintered body, the aluminum nitride sintered body, or the nitrided body. Thermal expansion coefficient of ceramic substrate made of silicon sintered body, mullite sintered body, etc. (aluminum oxide sintered body: 7 ppm / ° C., aluminum nitride sintered body, mullite sintered body: 4 ppm / ° C., nitriding (Silicon sintered body: 3 ppm / ° C.) When the thickness of the copper metal circuit board is increased, the metal circuit board is placed on the ceramic substrate due to its hardness and not easily deforming. After bonding, when heat is applied to the metal circuit board and the ceramic substrate, stress is generated between the metal circuit board and the ceramic substrate due to the difference in thermal expansion coefficient between the two, and the stress is weak. Cracks or fractures had a drawback that occurs in the ceramic substrate by acting on the ceramic substrate.
[0007]
In addition, the metal circuit board is bonded to the ceramic substrate by placing a metal circuit board of a predetermined pattern made of copper on the ceramic substrate with a brazing paste in between, and then heating it to a temperature of about 900 ° C. in a reducing atmosphere. Since the brazing paste is heated at a temperature equal to or higher than the liquidus temperature, the brazing paste spreads greatly, and the molten brazing paste causes an electrical short circuit between adjacent metal circuit boards. It had the disadvantage of doing.
[0008]
In order to prevent the brazing material paste from spreading, it is conceivable that the brazing material paste has a thickness of, for example, less than 10 μm.
[0009]
However, if the thickness of the brazing paste is reduced, when the metal circuit board is mounted on the ceramic substrate, the stress caused by the difference in thermal expansion coefficient between the ceramic substrate and the metal circuit board is reduced. The material cannot be absorbed effectively, and a large stress acts on the ceramic substrate, which induces a defect that cracks and cracks are generated in the ceramic substrate.
[0010]
The present invention has been devised in view of the above drawbacks, and its purpose is to generate a metal circuit board on a ceramic substrate without causing an electrical short circuit between adjacent metal circuit boards, and to generate a crack or the like in the ceramic substrate. It is an object of the present invention to provide a method for manufacturing a ceramic circuit board that can be firmly bonded without any problem.
[0011]
[Means for Solving the Problems]
The method for producing a ceramic circuit board of the present invention comprises:
(1) Contains aluminum powder, brazing powder composed mainly of silicon powder and / or aluminum-silicon alloy powder, and an aggregate formed by joining high melting point metal powder having a melting point of 950 ° C. or higher by point joining. Producing a brazing paste; and
(2) placing an aluminum metal circuit board on the ceramic substrate with the brazing paste interposed therebetween;
(3) A brazing paste disposed between the ceramic substrate and the aluminum metal circuit board is heated in a non-oxidizing atmosphere, and the main component is an aluminum-silicon alloy containing aggregates on the ceramic substrate. Joining the brazing material and joining the brazing material to the aluminum metal circuit board;
It is characterized by comprising.
[0012]
The method for producing a ceramic circuit board according to the present invention is characterized in that the agglomerates are contained in an amount of 3 to 20% by weight based on the brazing material.
[0013]
Furthermore, the method for producing a ceramic circuit board according to the present invention is characterized in that the aggregate has an average diameter of 10 to 100 μm.
[0014]
According to the method for manufacturing a ceramic circuit board of the present invention, since the metal circuit board is formed of soft aluminum, after the metal circuit board is bonded onto the ceramic board, heat is applied to the metal circuit board and the ceramic board. Even if a stress due to the difference in thermal expansion coefficient between them is generated, the stress is absorbed by deforming the metal circuit board. As a result, a large stress does not act on the ceramic substrate. It is possible to effectively prevent the occurrence of cracks and cracks.
[0015]
According to the method for manufacturing a ceramic circuit board of the present invention, the metal circuit board is bonded to the ceramic board by an average diameter formed by joining refractory metal powder having a melting point of 950 ° C. or higher on the ceramic board by spot bonding. After placing a metal circuit board having a predetermined pattern made of aluminum with a brazing paste containing 3 to 20% by weight of agglomerates of 10 to 100 μm on the brazing material, this was placed in a reducing atmosphere at about 600 ° C. Therefore, even if the brazing paste is heated at a temperature equal to or higher than the liquidus temperature of the brazing material, the agglomerates are formed between the ceramic substrate and the metal circuit board. The brazing material paste does not melt and spread greatly, and as a result, the occurrence of an electrical short between adjacent metal circuit boards is effectively prevented.
[0016]
At the same time, a space having a predetermined thickness is secured between the metal circuit board and the ceramic substrate by the aggregate obtained by bonding the high melting point metal powder having a melting point of 950 ° C. or higher by spot bonding, and a predetermined amount of brazing material is provided in the space. Due to the interposition, the stress generated by the difference in thermal expansion coefficient between the metal circuit board and the ceramic substrate is also absorbed by the brazing material, and the generation of cracks and cracks in the ceramic substrate is further effectively prevented.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Next, the present invention will be described in detail with reference to the accompanying drawings.
1 and 2 are sectional views showing an embodiment of a ceramic circuit board manufactured by the manufacturing method of the present invention, wherein 1 is a ceramic substrate, 2 is a brazing material layer, and 3 is a metal circuit board.
[0018]
The ceramic substrate 1 is made of an electrically insulating material such as a silicon nitride sintered body, an aluminum nitride sintered body, an aluminum oxide sintered body, a mullite sintered body, a silicon carbide sintered body, and a metal on the upper surface thereof. The circuit board 3 is brazed via the brazing material layer 2.
[0019]
The ceramic substrate 1 functions as a support member for supporting the metal circuit board 3 brazed to the upper surface thereof.
[0020]
The metal circuit board 3 brazed to the upper surface of the ceramic substrate 1 is made of aluminum and serves to supply electric signals and electric power to electronic components such as semiconductor elements mounted on the ceramic circuit substrate.
[0021]
Further, the brazing material for brazing the metal circuit board 3 to the upper surface of the ceramic substrate 1 is formed of a brazing material mainly composed of an aluminum-silicon alloy, and is bonded to the upper surface of the ceramic substrate 1 and the lower surface of the metal circuit board 3. Thus, the metal circuit board 3 is attached to the ceramic substrate 1.
[0022]
Thus, according to the above-described ceramic circuit board, electronic components such as semiconductor elements are electrically connected to the metal circuit board 3 on the upper surface of the ceramic substrate 1 through an adhesive such as solder, and the metal circuit board 3 is used as an external electric circuit. If connected, electronic components such as semiconductor elements are electrically connected to an external electric circuit through the metal circuit board 3.
[0023]
Next, a method for manufacturing the ceramic circuit board will be described.
(1) First, the ceramic substrate 1 is manufactured.
[0024]
The ceramic substrate 1 is made of an electrically insulating material such as a silicon nitride sintered body, an aluminum nitride sintered body, an aluminum oxide sintered body, a mullite sintered body, a silicon carbide sintered body, and the like, for example, silicon nitride In the case of a sintered material, a suitable organic binder, plasticizer and solvent are added to and mixed with raw material powders such as silicon nitride, aluminum oxide, magnesium oxide and yttrium oxide to form a mud and the mud A ceramic green sheet (ceramic green sheet) is formed by adopting a well-known doctor blade method or calender roll method. After that, the ceramic green sheet is subjected to appropriate punching processing and a plurality of layers are laminated to form a nitrogen atmosphere. It is manufactured by baking at a high temperature of 1600 to 2000 ° C.
(2) Next, the metal circuit board 3 is manufactured.
[0025]
The metal circuit board 3 is made of aluminum. For example, the metal circuit board 3 is manufactured in a predetermined pattern shape having a thickness of 500 μm by applying a conventionally known metal processing method such as a rolling method or a punching method to an aluminum ingot. The
(3) Next, a brazing paste is produced.
[0026]
The brazing paste has an average diameter obtained by joining a refractory metal powder having a melting point of 950 ° C. or higher to a brazing powder containing aluminum powder and silicon powder and / or aluminum-silicon alloy powder as a main component by spot joining. It is manufactured by adding 3 to 20% by weight of an aggregate 2a of 10 to 100 μm, an appropriate organic solvent, a solvent, and kneading.
(4) Next, the brazing paste is applied to the upper surface of the ceramic substrate 1 in a predetermined pattern with a thickness of, for example, 30 to 50 μm using a conventionally known screen printing technique. The metal circuit board 3 is placed on the brazing material paste.
(5) Finally, the brazing material paste disposed between the ceramic substrate 1 and the metal circuit board 3 is subjected to a hydrogen gas atmosphere or hydrogen. In a non-oxidizing atmosphere of a nitrogen gas atmosphere, it is heated to 600 ° C. to disperse the organic solvent and solvent of the brazing material paste and melt the brazing material to form the upper surface of the ceramic substrate 1 and the lower surface of the metal circuit board 3. By joining, the metal circuit board is attached to the upper surface of the ceramic substrate 1.
[0027]
In this case, the bonding mechanism of the brazing material to the ceramic substrate 1 is not clear, but the aluminum in the brazing material reacts with magnesium oxide or silicon oxide as a sintering aid contained in the ceramic substrate 1. However, it is assumed that the reaction is performed by forming a reaction layer.
[0028]
Further, when the ceramic substrate 1 and the metal circuit board 3 are joined via a brazing material, an aggregate 2a formed by joining refractory metal powder having a melting point of 950 ° C. or higher by spot joining in the brazing material paste. Because of the addition, a space of a predetermined thickness is secured between the ceramic substrate 1 and the metal circuit board 3 so that the brazing material does not melt and spread widely. The occurrence of a short circuit is effectively prevented. At the same time, a space having a predetermined thickness is secured between the metal circuit board 3 and the ceramic substrate 1 by the agglomerate 2a formed by joining high melting point metal powders having a melting point of 950 ° C. or higher by spot bonding, and a predetermined amount is provided in the space Since the brazing material is interposed, a part of the stress generated by the difference in thermal expansion coefficient between the metal circuit board 3 and the ceramic substrate 1 is absorbed by the brazing material, and the ceramic substrate 1 is cracked or cracked. There is no.
[0029]
The brazing material powder mainly composed of aluminum powder and silicon powder and / or aluminum-silicon alloy powder of the brazing material paste is, for example, a eutectic alloy containing 88% by weight and 18% by weight of aluminum and silicon, respectively. Thus, magnesium may be added as an additive, or an active metal powder composed of at least one of titanium, zirconium, hafnium and hydrides thereof may be added. In the case of adding magnesium as an additive to the brazing paste, alloys having aluminum, silicon, and magnesium of 90% by weight, 7.5% by weight, and 2.5% by weight are preferably used, and titanium, zirconium, When adding an active metal powder made of hafnium and at least one of these hydrides, the amount of the active metal powder is set to 2 to 5% by weight, whereby the bonding with the ceramic substrate 1 can be further strengthened.
[0030]
Further, when the particle size of the brazing material powder is less than 1 μm, the specific surface area of the brazing material powder is increased, and a large amount of oxygen is present in the oxide film formed on the surface of the brazing material powder. There is a risk that the wettability with respect to the ceramic substrate 1 and the metal circuit board 3 is lowered, and the bonding strength between the ceramic substrate 1 and the metal circuit board 3 is lowered. Accordingly, the particle size of the brazing material powder is preferably 1 μm or more.
[0031]
Further, the agglomerate 2a added to the brazing material paste is formed of a high melting point metal powder having a melting point of 950 ° C. or higher such as copper, silver, gold, tungsten, molybdenum, manganese, etc. If the metal powder is molybdenum, it is heated to a temperature of about 2000 ° C. in a reducing atmosphere and held for about 5 minutes to join the powders by point bonding and then gradually cool to room temperature to obtain a predetermined diameter. It is produced by classifying it.
[0032]
Since the refractory metal has a melting point of 950 ° C., which is sufficiently higher than the liquidus temperature of the brazing material, the aggregate 2a melts even when the brazing material is heated to a temperature higher than the liquidus temperature. A space having a predetermined thickness can be reliably ensured between the ceramic substrate 1 and the metal circuit board 3 without any problems.
[0033]
If the diameter of the agglomerate 2a is less than 10 μm, it is difficult to secure a space of a predetermined thickness between the ceramic substrate 1 and the metal circuit board 3, and if it exceeds 100 μm, the brazing paste is applied to the upper surface of the ceramic substrate 1. In addition, when printing is applied using a printing technique such as a conventionally known screen printing method, it is difficult for the aggregate 2a to be caught on the mesh of the screen and to be printed and applied in a predetermined pattern. Therefore, the diameter of the aggregate 2a is preferably in the range of 10 to 100 μm, more preferably in the range of 20 to 50 μm.
[0034]
Further, the high melting point metal powder such as copper, silver, gold, tungsten, molybdenum and manganese forming the agglomerate 2a has a large specific surface area when the diameter is less than 1 μm and is formed on the surface of the high melting point metal powder. There is a large amount of oxygen in the oxide film, and the oxygen reduces the wettability of the brazing material to the ceramic substrate 1 and the metal circuit board 3, thereby reducing the bonding strength between the ceramic substrate 1 and the metal circuit board 3. When the thickness exceeds 6 μm, the number of joints between the high melting point metal powders is small, and the mechanical strength of the aggregate 2a is weakened. When the metal circuit board 3 is brazed to the ceramic substrate 1, the aggregate 2a As a result, it becomes difficult to secure a space having a predetermined thickness between the ceramic substrate 1 and the metal circuit board 3. Therefore, it is preferable that each refractory metal powder forming the aggregate 2a has a diameter in the range of 1 to 6 μm.
[0035]
If the amount of the aggregate 2a added to the brazing material is less than 3% by weight, it becomes difficult to ensure a space of a predetermined thickness between the ceramic substrate 1 and the metal circuit board 3, and exceeds 20% by weight. In addition, the bonding area of the brazing material to the ceramic substrate 1 and the metal circuit board 3 becomes narrow, and the brazing strength of the metal circuit board 3 to the ceramic substrate 1 tends to decrease. Therefore, the amount of the aggregate 2a added to the brazing material is preferably in the range of 3 to 20% by weight.
[0036]
Furthermore, when copper, silver, or gold is selected as the refractory metal powder forming the agglomerate 2a, the copper, silver, and gold have a high thermal conductivity of about 300 W / m · K. When a large amount of heat is generated during operation of the electronic component bonded and fixed to the ceramic, the heat can be satisfactorily transmitted and dissipated to the ceramic substrate 1 through the aggregate 2a in the brazing material. Therefore, it is preferable to use the aggregate 2a having a high thermal conductivity of about 300 W / m · K or more, such as copper, silver, or gold.
[0037]
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. For example, in the above-described embodiment, the ceramic substrate 1 is made of silicon nitride. Although an example in which the sintered body is formed is shown, when the electronic component generates a large amount of heat and it is desired to efficiently remove this heat, the ceramic substrate 1 is formed of an aluminum nitride sintered body having a high thermal conductivity. The ceramic substrate 1 may be formed of a mullite sintered body having a low dielectric constant when it is desired to propagate an electric signal to the metal circuit board 3 at a high speed.
[0038]
Further, if a metal made of nickel and having good conductivity, corrosion resistance and good wettability with the brazing material is deposited on the surface of the metal circuit board 3 by a plating method, the metal circuit board 3 and the external electric circuit 3 The electrical connection with the circuit is good, and electronic components such as semiconductor elements can be firmly bonded to the metal circuit board 3.
[0039]
When nickel plating is applied to the aluminum metal circuit board 3, if the aluminum metal circuit board 3 is subjected to zincate treatment as a nickel plating pretreatment, the nickel plating layer is uniformly and firmly applied to the aluminum metal circuit board 3. Can be attached. Accordingly, when the aluminum metal circuit board 3 is subjected to nickel plating, it is preferable that the aluminum metal circuit board 3 is subjected to a zincate treatment. As the zincate treatment, for example, the aluminum metal circuit board 3 is immersed for 30 seconds in a zincate bath using commercially available AD-3-1F 3X manufactured by Uemura Kogyo Co., Ltd. Zinc deposited on the surface of the circuit board 3 is dissolved and finally immersed in the zincate bath again for 30 seconds.
[0040]
Furthermore, when the nickel plating layer is made of a nickel-phosphorus amorphous alloy containing 8 to 15% by weight of phosphorus, the surface oxidation of the nickel layer can be satisfactorily prevented. Therefore, when a nickel plating layer is applied to the aluminum metal circuit board 3, the nickel plating layer is preferably made of a nickel-phosphorus amorphous alloy containing 8 to 15% by weight of phosphorus.
[0041]
Furthermore, when a nickel plating layer is applied to the surface of the metal circuit board 3, the nickel plating layer completely covers the surface of the metal circuit board 3 with the nickel plating layer when the thickness is less than 1.5 μm. There is a risk that it will be difficult to effectively prevent oxidative corrosion of the metal circuit board 3, and if it exceeds 3 μm, the internal stress inside the nickel plating layer will increase and the ceramic substrate 1 will be damaged. There is a risk of warping or cracking. 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. Therefore, when a nickel plating layer is deposited on the surface of the metal circuit board 3, the thickness of the nickel plating layer is preferably set in the range of 1.5 μm to 3 μm.
[0042]
【The invention's effect】
According to the method for manufacturing a ceramic circuit board of the present invention, since the metal circuit board is formed of soft aluminum, after the metal circuit board is bonded onto the ceramic board, heat is applied to the metal circuit board and the ceramic board. Even if a stress due to the difference in thermal expansion coefficient between them is generated, the stress is absorbed by deforming the metal circuit board. As a result, a large stress does not act on the ceramic substrate. It is possible to effectively prevent the occurrence of cracks and cracks.
[0043]
According to the method for manufacturing a ceramic circuit board of the present invention, the metal circuit board is bonded to the ceramic board by an average diameter formed by joining refractory metal powder having a melting point of 950 ° C. or higher on the ceramic board by spot bonding. After placing a metal circuit board having a predetermined pattern made of aluminum with a brazing paste containing 3 to 20% by weight of agglomerates of 10 to 100 μm on the brazing material, this was placed in a reducing atmosphere at about 600 ° C. Therefore, even if the brazing paste is heated at a temperature equal to or higher than the liquidus temperature of the brazing material, the agglomerates are formed between the ceramic substrate and the metal circuit board. The brazing material paste does not melt and spread greatly, and as a result, the occurrence of an electrical short between adjacent metal circuit boards is effectively prevented.
[0044]
At the same time, a space having a predetermined thickness is secured between the metal circuit board and the ceramic substrate by the aggregate obtained by bonding the high melting point metal powder having a melting point of 950 ° C. or higher by spot bonding, and a predetermined amount of brazing material is provided in the space. Due to the interposition, the stress generated by the difference in thermal expansion coefficient between the metal circuit board and the ceramic substrate is also absorbed by the brazing material, and the generation of cracks and cracks in the ceramic substrate is further effectively prevented.
[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.
FIG. 2 is an enlarged view of an essential part of a sectional view showing an embodiment of the ceramic circuit board of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Ceramic substrate 2 ... Brazing material layer 2a ... Aggregate 3 ... Metal circuit board

Claims (3)

(1) It contains a brazing material powder mainly composed of aluminum powder, silicon powder and / or aluminum-silicon alloy powder, and an aggregate formed by joining refractory metal powder having a melting point of 950 ° C. or higher by spot joining. Producing a brazing paste; and
(2) placing an aluminum metal circuit board on the ceramic substrate with the brazing paste interposed therebetween;
(3) A brazing paste disposed between the ceramic substrate and the aluminum metal circuit board is heated in a non-oxidizing atmosphere, and the main component is an aluminum-silicon alloy containing aggregates on the ceramic substrate. Joining the brazing material and joining the brazing material to the aluminum metal circuit board;
A method of manufacturing a ceramic circuit board comprising: 2. The method of manufacturing a ceramic circuit board according to claim 1, wherein the aggregate is contained in an amount of 3 to 20% by weight based on the brazing material. 2. The method of manufacturing a ceramic circuit board according to claim 1, wherein an average diameter of the aggregate is 10 to 100 [mu] m.

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