JP2004134493A - Ceramic circuit board - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a ceramic circuit board which is capable of markedly increasing a metal circuit layer in wiring density and current-carrying capacity and improving the functions and reliability of a high-power transistor, a power module, and a semiconductor device. <P>SOLUTION: The ceramic circuit board 1a composed of a ceramic board 2 and the metal circuit layer 4 bonded on the surface of the ceramic board 2 in one piece, is characterized in that, if the width and height of the metal circuit layer 4 are represented by W and H, respectively, the aspect ratio or the H/W ratio of the metal circuit layer 4 is 1 or more 1. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a ceramic circuit board mainly used for mounting a high-output transistor or a power module or mounted on a semiconductor device. In particular, it is possible to increase a wiring density by a metal circuit layer and greatly increase a current carrying capacity. And a ceramic circuit board capable of improving the function and reliability of a high-output transistor, a power module, and a semiconductor device.
[0002]
[Prior art]
Conventionally, a metal circuit board made of conductive copper or the like is integrally formed on a surface of a ceramic substrate having excellent insulation properties, such as an alumina (Al ₂ O ₃ ) sintered body, with a brazing material, an adhesive, or a metallized metal layer. A bonded ceramic circuit board is widely used as a substrate for a power transistor module or a substrate for a switching power supply module.
[0003]
However, in the above-mentioned ceramic circuit board, since a brazing material containing an active metal such as Ti, Zr, and Hf, an intervening agent such as an adhesive or a metallized layer exists between the metal circuit board and the ceramic substrate, both of them are present. However, there is a disadvantage that it is difficult to quickly radiate the heat generated by the semiconductor element provided on the metal circuit board to the outside of the system due to a large thermal resistance between them.
[0004]
In order to solve such problems, in recent years, without using the above-mentioned brazing material, adhesive or metallized layer, a metal circuit board punched into a predetermined shape is directly placed on a ceramic substrate, and is directly heated only by heating. The way to do it is also widespread. Specifically, a DBC method (Direct Bonding Copper method) for directly joining a ceramic substrate and a Cu plate, and a DBA method (Direct Bonding Aluminum method) for directly joining a ceramic substrate and an Al plate are employed.
[0005]
That is, the direct joining method is a method of directly joining ceramics and a metal plate without interposing a joining layer such as a brazing material layer, an adhesive layer, or a metallized layer. In this direct joining method, a eutectic liquid phase of a binder (oxygen in the case of copper) existing in the metal or on the surface of the metal and the metal is generated, and the two members are directly joined.
[0006]
Further, as described above, a brazing material layer containing an active metal such as Ti, Zr, or Hf is formed between the metal circuit board and the ceramic substrate, and the metal circuit board and the ceramic substrate are interposed via the brazing material layer. The active metal method of joining together is often used, and achieves excellent joining strength.
[0007]
FIG. 2 is a cross-sectional view showing a configuration example of a conventional ceramic circuit board 1. As a material of the ceramic substrate 2, an oxide ceramic sintered body such as alumina (Al ₂ O ₃ ), zirconia (ZrO ₂ ), mullite, or a nitride sintered body such as aluminum nitride (AlN) is used. . FIG. 2 shows a ceramic circuit board 1 in which a metal circuit board 3 made of copper containing no oxygen as a binder is directly bonded to the surface of an Al ₂ O ₃ substrate 2.
[0008]
When this ceramic circuit board 1 is used as a power module, a copper circuit board as a metal circuit board 3 is directly bonded to the surface side of the Al ₂ O ₃ substrate 2, while a copper plate as a back copper plate is also provided on the back side. Similarly, a structure is formed in which the semiconductor elements are directly joined, and the semiconductor elements are integrally joined at predetermined positions of the copper circuit board 3 on the front side via a solder layer (not shown).
[0009]
Note that the direct bonding method (DBC method) can be directly applied only to oxide-based ceramics such as Al ₂ O ₃ , and is not applicable to aluminum nitride (AlN) substrates and silicon nitride (Si ₃ N ₄ ) substrates. Even when applied directly to an oxide-based ceramic substrate, sufficient bonding strength of the metal circuit board cannot be obtained due to low wettability to the substrate.
[0010]
Therefore, when a non-oxide ceramic substrate is used, it is necessary to form an oxide layer on the surface of the ceramic substrate in advance to enhance wettability to the substrate. In this case, an oxide layer (Al ₂ O ₃ film) is formed on the entire surface of the AlN substrate by subjecting the AlN substrate to heat treatment in an oxidizing atmosphere in advance before the bonding operation of the metal circuit board.
[0011]
According to the ceramic circuit board in which the metal circuit board is joined to the ceramic substrate by the above direct joining method, since the brazing material or the adhesive layer is not interposed at the joint interface, the heat resistance between both members is small, and the circuit has excellent heat dissipation. A substrate is obtained. In addition, since it has a simple structure in which a Mo plate or the like is not interposed between ceramics and metal, it has advantages that a small size and high mounting can be achieved, and that a work process can be shortened.
[0012]
In addition, as a method of forming a metal plate into a circuit shape to form a metal circuit board, as described above, a method of forming a circuit by punching a metal plate into a predetermined shape by a punching press or the like before joining or a method of forming a metal plate on a ceramic substrate A method of forming a circuit by performing an etching process after joining is generally adopted.
[0013]
[Problems to be solved by the invention]
In recent years, technical demands for higher output, higher function, higher reliability, and smaller size of high output transistors, power modules and semiconductor devices have been further increased, and the current carrying capacity is higher than before. The demand for ceramic circuit boards having fine circuit patterns has increased significantly.
[0014]
However, in the above-mentioned conventional ceramic circuit board, when a circuit is formed on the metal plate before the metal plate and the ceramic substrate are joined, and the prepared fine metal circuit board is joined to the ceramic substrate, a predetermined circuit pattern is formed. It has been extremely difficult to stably join a large number of fine metal circuit boards to predetermined positions on a ceramic substrate while maintaining the shape. In particular, it is necessary to stably and accurately join a metal circuit layer having a height higher than a width such that an aspect ratio defined by a ratio of a height to a width of the metal circuit board is 1 or more, with high positional accuracy. It was virtually impossible.
[0015]
On the other hand, when a circuit is formed by an etching method after joining a metal plate to a ceramic substrate, the etching liquid is simultaneously eroded not only in the thickness direction of the metal plate but also in the horizontal direction. Will be limited. That is, if the thickness of the metal plate is 0.5 mm, the gap (pitch) between adjacent metal circuit layers becomes as rough as 0.5 mm, and a fine metal circuit layer cannot be formed. In particular, it has been impossible at all to prepare a metal circuit layer having a high height with a high shape precision as compared with a width having an aspect ratio defined by a ratio of the height to the width of the metal circuit layer of 1 or more. .
[0016]
Therefore, in the conventional ceramic circuit board, as shown in FIG. 2, the cross-sectional shape of each of the metal circuit boards 3 is limited to a shape having a width extending in the plane direction of the ceramic substrate 2, so that the metal circuit It is impossible to form a metal circuit layer having a height H larger than the width W such that the aspect ratio defined by the ratio of the height H to the width W of the plate 3 is 1 or more. Was in the range of approximately 0.01 to 0.8. Specifically, the width W of the metal circuit board having the minimum width is about 0.5 mm, the height H is about 0.3 mm, the aspect ratio is about 0.6, and most of those have the maximum value. is there. As a result, the number of metal circuit layers that can be formed per unit surface area of the ceramic substrate is small, making it difficult to improve the wiring density. In addition, by increasing the current carrying capacity, it is possible to achieve higher output, higher function, and smaller size of the semiconductor device. There was a problem that it was difficult.
[0017]
The present invention has been made in order to solve the above problems, and in particular, it is possible to increase the wiring density by a metal circuit layer and greatly increase a current carrying capacity, and to provide a high output transistor, a power module, and a semiconductor device. It is an object of the present invention to provide a ceramic circuit board capable of improving function and reliability.
[0018]
[Means for Solving the Problems]
In order to achieve the above object, the present inventors diligently studied a method of forming a metal circuit layer having a fine circuit width and a sufficient height in a stable state with high accuracy. As a result, after forming a brazing metal layer along a predetermined circuit pattern on the ceramic substrate, a thick resist is further applied on the entire surface of the ceramic substrate, and the resist corresponding to the circuit pattern is removed. It has been found that, when metal plating is applied by electroforming, a fine pitch metal circuit layer having a high height to width ratio (aspect ratio) can be formed in a stable state with high shape accuracy for the first time.
[0019]
The present invention has been completed based on the above findings. That is, in the ceramic circuit board according to the present invention, in a ceramic circuit board in which a metal circuit layer is integrally joined on at least one surface of the ceramic substrate, an aspect ratio which is a ratio of a height to a width of the metal circuit layer is 1 It is characterized by the above.
[0020]
When the aspect ratio, which is the ratio of the height to the width of the metal circuit layer, is less than 1, the number of metal circuit layers arranged per unit area of the ceramic substrate is reduced, and it is difficult to sufficiently increase the wiring density. Become. As the aspect ratio is increased, the cross-sectional area of the metal circuit layer can be increased and the conduction capacity can be increased.
[0021]
However, if the aspect ratio is excessively increased, the structural strength of the metal circuit layer is apt to decrease. Therefore, the aspect ratio is set to 5 or less, though it depends on the width of the metal circuit layer. A more preferred aspect ratio is in the range of 1.2 to 2.5. Specifically, the width W of the metal circuit layer is preferably in the range of 0.3 to 0.5 mm, while the height H of the metal circuit layer is preferably in the range of 1 to 1.5 mm.
[0022]
In the ceramic circuit board, it is preferable that the metal circuit layer is made of copper or aluminum. That is, the metal constituting the metal circuit layer has a good wettability with a brazing metal layer such as a simple substance of copper, aluminum, iron, nickel, chromium, silver, molybdenum, and cobalt, or an alloy thereof. The metal is not particularly limited as long as it can be applied, but copper, aluminum or an alloy thereof is particularly preferable from the viewpoints of conductivity and cost.
[0023]
Further, in the ceramic circuit board, a metal brazing layer containing at least one of Ag, Cu, Ti and Zr is provided between the metal circuit layer and the ceramic substrate, and the metal brazing layer is interposed through the metal brazing layer. It is preferable that the circuit layer and the ceramic substrate are integrally joined. The bonding strength between the metal circuit layer and the ceramic substrate can be increased by the metal brazing material layer, and a ceramic circuit substrate having excellent durability and reliability can be obtained.
[0024]
The joining method using the active metal method as described above joins a ceramic substrate and a metal circuit layer via a metal brazing material layer containing at least one active metal selected from, for example, Ti, Zr, Hf, and Nb. How to As the composition of the active metal-containing brazing material to be used, for example, an Ag-Cu eutectic composition (72 wt% Ag-28 wt% Cu) or a composition in the vicinity thereof is mainly composed of an Ag-Cu brazing material or a Cu brazing material. A composition in which at least one active metal selected from Ti, Zr, Hf, Nb and the like is added in an amount of 1 to 10% by weight can be exemplified. In addition, a low melting point metal such as In may be added to the active metal-containing brazing material.
[0025]
Further, in the above-mentioned ceramic circuit board, it is preferable that the ceramic board is made of any one of aluminum nitride, silicon nitride, alumina, and a compound of alumina and zirconia (commonly called argyl).
[0026]
That is, the ceramic substrate used for the ceramic circuit board according to the present invention is not particularly limited, and electrical strength such as strength, heat dissipation (thermal conductivity), dielectric constant, and breakdown voltage required for the circuit board is required. It is selected according to the characteristics. Specifically, in addition to an oxide-based ceramic substrate such as aluminum oxide (alumina: Al ₂ O ₃ ), a nitride such as aluminum nitride (AlN), silicon nitride (Si ₃ N ₄ ), titanium nitride (TiN), etc. Or a non-oxide ceramic substrate such as a carbide such as silicon carbide (SiC) or titanium carbide (TiC), or a boride such as lanthanum boride. These ceramic substrates may contain a sintering aid such as yttrium oxide.
[0027]
In the ceramic circuit board, it is preferable that a plating layer made of at least one of Ni, Ag and Au is formed on the surface of the metal circuit layer. It is sufficient that the thickness of the plating layer is about 1 to 5 μm. By forming the plating layer, the corrosion resistance of the metal circuit layer can be greatly increased, and the durability and reliability of the ceramic circuit board can be greatly improved.
[0028]
The ceramic circuit board according to the present invention can be manufactured, for example, by the following procedure. That is, first, a metal brazing material paste is printed on the surface of the ceramic substrate by a screen printing method or the like, and a metal brazing material layer having a predetermined circuit pattern is formed on the ceramic substrate.
[0029]
Here, in order to increase the bonding strength of the metal brazing material layer to the ceramic substrate, it is preferable to perform a heat treatment at a temperature suitable for the bonding condition of the printed brazing material, that is, at a temperature of 700 to 900 ° C. for about 10 minutes to 1 hour. This brazing material layer may be formed on the entire surface of the ceramic substrate at first, and after forming the metal circuit layer, the brazing material layer other than the circuit pattern may be removed.
[0030]
Next, a photoresist is applied to the surface of the ceramic substrate so as to have a thickness equal to or greater than the thickness of the finally formed metal circuit layer, thereby forming a resist film. Thereafter, the resist film at the portion where the metal circuit layer is to be formed is removed by photolithography or the like to form a void along the wiring pattern. At this time, a wiring pattern-like void having a depth larger than the width of the void is formed so that the metal brazing material layer formed at the bottom of the void can be directly observed from the resist film surface direction.
[0031]
Next, a metal having good wettability with respect to the metal constituting the brazing metal layer is deposited and filled to a predetermined thickness in the above-mentioned gap by plating to form a metal circuit layer. After that, the resist film remaining on the parts other than the metal circuit layer is removed with a stripping solution, so that the metal circuit layer having a high height to width ratio (aspect ratio) and excellent shape accuracy is integrally joined. The manufactured ceramic circuit board can be manufactured in a stable state.
[0032]
According to the ceramic circuit board according to the above configuration, since the metal circuit layer having a high height to width (aspect ratio) is formed in a stable state with high shape accuracy, wiring of the metal circuit layer on the ceramic substrate is performed. Density can be increased and current carrying capacity can be significantly increased despite high-definition metal circuit layers, and the function and reliability of high-output transistors, power modules, and semiconductor devices can be improved. become.
[0033]
BEST MODE FOR CARRYING OUT THE INVENTION
Next, an embodiment of a ceramic circuit board according to the present invention will be specifically described with reference to the accompanying drawings.
[0034]
As shown in FIG. 3A, an alumina (Al ₂ O ₃ ) substrate, a silicon nitride (Si ₃ N ₄ ) substrate having a thickness of 0.635 mm, an aluminum nitride (AlN) substrate having a thickness of 0.9 mm, An alumina-zirconia compound substrate having a thickness of 0.9 mm is prepared as the ceramic substrate 2, and a brazing material paste is printed on the surface of each ceramic substrate 2 using a screen printing method, and as shown in FIG. Is 0.2 mm, a metal brazing material layer 5 having a predetermined circuit pattern was formed. In addition, BAg-18 (Ag / Cu / Sn-based brazing material) composition was applied as the brazing material paste.
[0035]
Further, each ceramic substrate 2 on which the brazing material paste is printed is subjected to a heat treatment at a temperature of 800 ° C. for 15 minutes in a heating furnace having a degree of vacuum of 1 × 10 −4 Torr or less, so that the ceramic substrate 2 of each metal brazing material layer 5 is formed. The bonding strength for
[0036]
Thereafter, as shown in FIG. 3C, a 0.5 mm-thick photoresist film 6 is applied to the surface of the ceramic substrate 2 on which the metal brazing material layer 5 is formed by applying an ultraviolet curing photoresist. Formed. Next, the portions other than the circuit pattern are selectively irradiated with ultraviolet rays according to the desired wiring pattern shape to cure the resist film in the irradiated portion, while the resist film in the wiring pattern portion has a predetermined shape. By cleaning with a cleaning liquid, a void 7 was formed along the wiring pattern as shown in FIG.
[0037]
Next, by performing an electroplating process on the ceramic substrate on which the voids 7 are formed, as shown in FIG. 3E, a height corresponding to the thickness (0.5 mm) of the photoresist film 6 is obtained. A metal circuit layer (copper circuit layer) 4 having a height H was formed. Thereafter, as shown in FIG. 3F, the cured resist film 6 was removed by washing with a predetermined stripper. Further, by dissolving and removing the metal brazing material layer 5 remaining on the substrate surface other than the wiring pattern of the metal circuit layer (copper circuit layer) 4, the width as shown in FIG. Each of the ceramic circuit boards 1a according to the examples having the metal circuit layer 4 having a height of 0.5 mm was prepared.
[0038]
In addition to the above embodiment, the metal circuit layer was processed under the same conditions as in the above embodiment except that the width W of the metal circuit layer was changed to a range of 0.3 to 0.5 mm and the height was changed to a range of 1 to 1.5 mm. A large number of ceramic circuit boards 1a according to the respective examples were prepared.
[0039]
As shown in FIG. 1, the ceramic circuit board 1a according to each embodiment prepared as described above has a large number of fine metal circuit layers 4 integrally joined on the upper surface side of each ceramic substrate 2, and each metal circuit layer In the cross-sectional shape of No. 4, the width W was in the range of 0.3 to 0.5 mm and the height H was in the range of 1 to 1.5 mm, so that the aspect ratio was in the range of 2 to 5.
[0040]
On the other hand, a conventional ceramic circuit board 1 as shown in FIG. 2 was prepared as a comparative example. That is, a copper circuit board having a thickness of 0.3 mm is directly bonded as a metal circuit board 3 to the surface of an alumina substrate having the same dimensions as the ceramic substrate 2 used in each embodiment by the DBC method, and the cross-section of the wiring pattern which is further minimized. Ceramics according to Examples and Comparative Examples prepared using ceramic substrates of the same size, which were patterned so that width W was 0.5 mm and height was 0.3 mm (aspect ratio was 0.6 or less) When the wiring density and the current carrying capacity of the circuit board were compared, the wiring density of the ceramic circuit board according to each example increased from 2.1 times to 3.5 times as compared with the comparative example. The current carrying capacity increased from 2.5 times to 4.7 times as compared with the comparative example.
[0041]
However, also in the ceramic circuit board according to each embodiment, when the aspect ratio, which is the ratio of the height H to the width W of the metal circuit layer 4, approaches 2.5 to 5, the structural strength of the metal circuit layer 4 decreases. However, since the deformation is likely to occur, the aspect ratio of the metal circuit layer 4 is preferably in the range of 1.0 to 2.2.
[0042]
In each of the examples, the arrangement pitch of the adjacent metal circuit layers can be made as fine as 50 to 250 μm, but the arrangement pitch in the comparative example was as coarse as 0.3 mm.
[0043]
As described above, in each embodiment, after forming a metal brazing material layer having a circuit pattern on a ceramic substrate, a fine circuit pattern is formed by applying a photoresist, and metal plating is performed along the circuit pattern. Thus, a ceramic circuit board having a metal circuit layer having a pitch smaller than the thickness (height) of the metal circuit layer can be realized. As a result, the wiring density is more than doubled as compared with the related art, and high-performance transistors, power modules, and semiconductor devices can be achieved, and the reliability can be further improved.
[0044]
Further, at least one type of plating layer (not shown) of Ni, Ag, or Au is formed on the metal circuit layer 4 of the ceramic circuit board of each embodiment by an electroless plating method in a thickness of 2 to 6 μm. And the corrosion resistance could be improved.
[0045]
【The invention's effect】
As described above, according to the ceramic circuit board of the present invention, since the metal circuit layer having a high height to width (aspect ratio) is formed in a stable state with high shape accuracy, The wiring density of the metal circuit layer can be increased, and the current carrying capacity can be greatly increased despite the high-definition metal circuit layer, and the function and reliability of high-output transistors, power modules, and semiconductor devices can be improved. It can be improved.
[Brief description of the drawings]
FIG. 1 is a sectional view showing a configuration example of one embodiment of a ceramic circuit board according to the present invention.
FIG. 2 is a cross-sectional view showing a configuration example of a conventional ceramic circuit board.
3A and 3B are cross-sectional views illustrating a process of manufacturing a ceramic circuit board according to the present invention, wherein FIG. 3A illustrates a ceramic substrate, FIG. 3B illustrates a state in which a brazing metal layer is formed, and FIG. (D) shows a state in which the photoresist film along the circuit pattern is removed, and (e) shows a state in which a metal plating layer is deposited and filled in a portion where the photoresist film has been removed. (F) is a cross-sectional view showing a state in which the photoresist film other than the circuit pattern is removed, and (g) is a state showing the state in which the remaining metal brazing material layer is removed.
[Explanation of symbols]
1, 1a, 1b Ceramic circuit substrate 2 Ceramic substrate (Al ₂ O ₃ substrate, Si ₃ N ₄ substrate, AlN substrate, alumina-zirconia compound substrate)
3 metal circuit board (copper circuit board)
4 Metal circuit layer (copper circuit layer)
5 Brazing metal layer 6 Photoresist film 7 Void

Claims (5)

A ceramic circuit board in which a metal circuit layer is integrally bonded on at least one surface of a ceramic substrate, wherein an aspect ratio which is a ratio of a height to a width of the metal circuit layer is 1 or more. . 2. The ceramic circuit board according to claim 1, wherein said metal circuit layer is made of copper or aluminum. 2. The ceramic circuit board according to claim 1, wherein a metal brazing material layer containing at least one of Ag, Cu, Ti and Zr is provided between the metal circuit layer and the ceramic substrate, and the metal brazing material layer is interposed therebetween. A ceramic circuit board, wherein the metal circuit layer and the ceramic substrate are integrally joined. 2. The ceramic circuit board according to claim 1, wherein said ceramic substrate is made of any one of aluminum nitride, silicon nitride, alumina, and a compound of alumina and zirconia. 2. The ceramic circuit board according to claim 1, wherein a plating layer made of at least one of Ni, Ag and Au is formed on the surface of the metal circuit layer.

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