JP2005093803A - Ceramic circuit board and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To raise reliability to thermal stress and a heat cycle and enable etching processing to be applied to the formation of a circuit pattern, and reduce a manufacturing cost in a ceramic circuit board formed by joining a ceramic substrate and a metallic circuit board. <P>SOLUTION: The ceramic circuit board 1 has a metallic circuit board 4a joined to at least one surface 2a of both major surfaces (2a, 2b) of the ceramics substrate 2 via a junction layer 3. A corrugated outer circumferential part 5 of the junction layer 3 constituted of a brazing material layer, for example, is formed along a circuit pattern of the metallic circuit board 4. The corrugated outer circumferential part 5 of the junction layer 3 has a stress concentration relaxing function. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a ceramic circuit board used as a substrate for mounting various elements and modules, and a manufacturing method thereof.

  2. Description of the Related Art Conventionally, ceramic circuit boards having excellent insulation, heat dissipation, mechanical characteristics, and the like have been used as substrates for mounting various elements including semiconductor elements. In particular, it is common to apply a bonded substrate of a ceramic substrate and a metal plate to a ceramic circuit substrate on which a high-power semiconductor element such as a power transistor having a large calorific value or a power module is mounted. As a metal plate bonding method, a DBC method in which a ceramic substrate and a copper plate are directly bonded by heat treatment, a DBA method in which a ceramic substrate and an aluminum plate are directly bonded by heat treatment, or a brazing material containing an active metal is used. A method (active metal method) for bonding a ceramic substrate and a metal plate is known.

  In a ceramic-metal bonded substrate to which such a bonding method is applied, it is necessary to form a circuit pattern on a metal plate. As a metal circuit pattern formation method, a metal plate is processed into a desired circuit pattern in advance and then bonded to a ceramic substrate, or a metal plate is bonded to the ceramic substrate and then etched to form a desired circuit on the metal plate. A method of forming a pattern is known. However, when a ceramic substrate and a metal plate are bonded using a brazing material, the latter method is generally applied (see, for example, Patent Document 1). . The method of forming a circuit pattern by etching has an advantage that a high-definition metal circuit pattern can be formed with high accuracy.

  In the ceramic circuit board on which the metal circuit pattern is formed by applying the etching process described above, the shape of the metal circuit board and the shape of the bonding layer made of the brazing material are the same. By the way, in the present situation where high output transistors, intelligent power modules, and the like are being used, further improvement in reliability is required for ceramic circuit boards having metal circuit boards. In particular, for a ceramic circuit board obtained by bonding a ceramic board having a large difference in thermal expansion coefficient and a metal circuit board, it is strongly required to improve reliability against thermal stress and thermal cycle.

  That is, when a thermal cycle is applied to a ceramic circuit board obtained by bonding a ceramic substrate and a metal circuit board, thermal stress acts on the ceramic substrate side having a small thermal expansion coefficient. When such thermal stress is repeatedly applied, a crack is generated on the ceramic substrate side, resulting in a decrease in bonding strength, peeling of the metal circuit board, and destruction of the ceramic substrate. In particular, ceramic circuit boards on which high-power transistors and power modules are mounted tend to increase the thermal load and the associated thermal stress, and there is a strong demand for further improvements in thermal stress and thermal cycle reliability. ing.

In contrast, for example, in Patent Document 2, a thin wall portion is provided on the outer peripheral portion of the metal circuit board, or a hole or a groove is provided in the vicinity of the outer peripheral portion, thereby reducing thermal stress and generating cracks. It is described that suppresses. Although such a structure can relieve thermal stress, it is essential to process the metal circuit board in advance, which increases the manufacturing cost of the ceramic circuit board and forms the circuit pattern by the etching process described above. There is a drawback that the method cannot be applied.
Japanese Patent Laid-Open No. 11-340598 JP 2001-267447 A

  As described above, in the conventional ceramic circuit board, the thermal stress is relieved by processing the outer periphery of the metal circuit board in advance. However, in such a structure, when forming a complicated circuit pattern, an etching process capable of forming a high-definition metal circuit pattern with high accuracy cannot be applied, and the manufacturing cost is increased. There is a difficulty such as.

  The present invention has been made in order to cope with such problems, and it is possible to apply an etching process capable of forming a circuit pattern with high accuracy while improving reliability against thermal stress and thermal cycle, and It is an object of the present invention to provide a ceramic circuit board and a method for manufacturing the same that reduce the manufacturing cost.

  A ceramic circuit board according to the present invention includes a ceramic substrate and a metal circuit board bonded to at least one of both main surfaces of the ceramic substrate via a bonding layer as described in claim 1. In the circuit board, the bonding layer has a corrugated outer periphery formed along a circuit pattern of the metal circuit board.

  In the ceramic circuit board of the present invention, the waveform provided on the outer peripheral portion of the bonding layer preferably has a curved shape as described in claim 2, and the waveform forming period is in the range of 0.1 to 5 mm. In addition, it is preferable that the corrugated width is 0.05 to 2 mm. Moreover, as a joining layer in the ceramic circuit board of this invention, the brazing material layer used for joining to a ceramic substrate and a metal circuit board is mentioned, for example, as described in Claim 3.

  The method for manufacturing a ceramic circuit board according to the present invention includes a method for manufacturing a ceramic circuit board by bonding a metal circuit board to at least one surface of both main surfaces of the ceramic substrate, as described in claim 5. On the main surface of the ceramic substrate, corresponding to the circuit pattern of the metal circuit board, a step of applying a bonding material so that the outer peripheral portion has a waveform, and a metal plate is disposed on the coating layer of the bonding material, The method includes a step of bonding the ceramic substrate and a metal plate, and a step of forming the metal circuit plate by processing the metal plate in correspondence with the circuit pattern.

  In the ceramic circuit board of the present invention, the outer peripheral shape of the bonding layer is corrugated along the circuit pattern of the metal circuit board. According to the joining layer having such a corrugated outer peripheral portion, the length of the joining end of the ceramic substrate and the metal circuit board can be apparently increased, so that stress concentration at the joining end can be reduced. it can. Furthermore, based on the corrugated shape provided on the outer peripheral portion of the bonding layer, the metal circuit board has a portion that is not bonded to the ceramic substrate, and the stress concentration is mitigated by the buffering action against the thermal contraction of this portion. The

  Such a stress concentration relaxation effect can suppress the generation of cracks in the ceramic substrate, the growth of the generated cracks, and the like. Therefore, it is possible to greatly increase the reliability of the ceramic circuit board against thermal stress and thermal cycle. Furthermore, since the stress concentration mitigating effect of such a bonding layer can be obtained by simply changing the bonding material formation pattern (coating pattern) in advance, the circuit pattern can be made more accurate without increasing the manufacturing cost. It is also possible to apply an etching process that can be formed.

  According to the ceramic circuit board of the present invention, the reliability against thermal stress and thermal cycle can be improved. In addition, it is possible to apply an etching process that can form a circuit pattern with high accuracy, and it is possible to suppress an increase in manufacturing cost, thereby improving both practicality and reliability with respect to thermal history. A ceramic circuit board can be provided.

BEST MODE FOR CARRYING OUT THE INVENTION

  Hereinafter, modes for carrying out the present invention will be described. 1 and 2 are views showing a configuration of a ceramic circuit board according to an embodiment of the present invention. FIG. 1 is a plan view of the ceramic circuit board, and FIG. 2 is a cross-sectional view taken along the line AA. The ceramic circuit board 1 shown in these drawings has a ceramic substrate 2. Metal circuit boards 4 (4a, 4b) are bonded to both main surfaces (both front and back surfaces) 2a, 2b of the ceramic substrate 2 via bonding layers 3, respectively.

  A desired circuit pattern is formed on the metal circuit board 4 a bonded to the surface 2 a side of the ceramic substrate 2. That is, a metal circuit board 4 a having a circuit pattern corresponding to a semiconductor element or other element mounted on the ceramic circuit board 1 is bonded to the surface 2 a side of the ceramic substrate 2. On the other hand, on the back surface 2b side of the ceramic substrate 2, for example, a back side metal circuit board 4b serving as a joined portion to a heat sink or a warp preventing member is joined. Here, a simple plate-shaped metal plate is applied to the back side metal circuit board 4b. However, for example, when a module is formed, a circuit pattern having a desired shape is also formed on the back side metal circuit board 4b.

  Various ceramic sintered bodies can be applied to the ceramic substrate 2 constituting the ceramic circuit board 1, and it is not particularly limited to the constituent materials. That is, as a constituent material of the ceramic substrate 2, for example, a non-oxide ceramic sintered body such as an aluminum nitride sintered body or a silicon nitride sintered body, an alumina sintered body, a composite sintered body of alumina and zirconia, or the like. It is possible to use various ceramic sintered bodies up to oxide-based ceramic sintered bodies.

  Of the various ceramic sintered bodies described above, when high heat dissipation is required for the ceramic circuit board 1, a ceramic made of a nitride ceramic sintered body such as an aluminum nitride sintered body or a silicon nitride sintered body. It is preferable to use the substrate 2. In particular, an aluminum nitride sintered body having a thermal conductivity of 100 W / m K or more is effective for increasing the heat dissipation of the ceramic circuit board 1 and is particularly suitable for use as a mounting substrate for high-power transistors, power modules, and the like. It is. Moreover, according to the silicon nitride sintered body, the mechanical strength can be greatly improved while improving the heat dissipation of the ceramic circuit board 1. The thickness of the ceramic substrate 2 varies depending on the material used, but is preferably in the range of 0.3 to 1.5 mm, for example.

  The metal circuit board 4 can be composed of various metal plates in accordance with the use application or usage form of the ceramic circuit board 1, and for example, a Cu plate or a Cu alloy plate, an Al plate or an Al alloy plate is preferably used. . However, the constituent material of the metal circuit board 4 is not limited to these, and metal materials other than Cu and Al, for example, Ni and Ni alloys, refractory metals such as W and Mo and alloys thereof, Cu, It is also possible to use an alloy of Al, Ni or the like and a refractory metal, a clad material or the like. According to the bonding method to which the bonding layer 3 is applied, the metal circuit board 4 made of various metal materials can be bonded to the ceramic substrate 2. The thickness of the metal circuit board 4 is preferably in the range of 0.1 to 0.5 mm, for example.

  The ceramic substrate 2 and the metal circuit board 4 as described above are bonded via the bonding layer 3. The bonding layer 3 is not necessarily limited, but generally a brazing material layer is applied. The brazing material constituting the bonding layer 3, that is, the brazing material that joins the ceramic substrate 2 and the metal circuit board 4 is appropriately selected according to the type of the ceramic substrate 2, and for example, Ti, Zr, Hf At least one active metal selected from Nb, Al, etc. (for example, contained in the range of 0.5 to 10% by weight with respect to the total amount of the brazing filler metal) is an Ag—Cu eutectic composition or a composition in the vicinity thereof. It is preferable to use an active metal brazing material blended with a brazing filler metal component such as a brazing filler metal or a Cu brazing filler metal. The active metal brazing material may contain an appropriate amount of Sn or In (for example, 2 to 7% by weight based on the total amount of the brazing material).

  A corrugated pattern is formed on the outer peripheral portion 5 of the bonding layer 3 made of the brazing material described above. As shown in the cross-sectional view of the main part in FIG. 3 (transverse cross-sectional view cut in the plane direction at the portion of the bonding layer 3), the outer peripheral portion 5 of the bonding layer 3 is the outer peripheral shape of the metal circuit board (each metal plate) 4, A wave shape is formed along the metal circuit pattern. In other words, the outer peripheral portion 5 of the bonding layer 3 has a waveform that is concave in the inner direction with respect to the outer peripheral shape of the metal circuit board 4. The waveform provided on the outer peripheral portion 5 of the bonding layer 3 is preferably a wave shape constituted by a smooth curve such as a sine wave.

  Thus, by making the outer peripheral portion 5 of the bonding layer 3 into a wave shape, the length of the bonding end between the ceramic substrate 2 and the metal circuit board 4 can be apparently increased. The occurrence of cracks or breakage of the ceramic substrate 2 due to thermal stress, thermal cycle, etc., corresponds to the ceramic portion corresponding to the joint end of the metal circuit board 4 (substantially equivalent to the outer periphery of the joint layer in the conventional ceramic circuit board). This is caused by concentration of stress on the surface. With respect to such a point, the stress concentration at the joining end of the ceramic substrate 2 and the metal circuit board 4 is reduced by apparently increasing the length of the outer peripheral portion 5 of the joining layer 3 based on the outer peripheral shape of the waveform. Can be relaxed.

  Furthermore, the metal circuit board 4 has a portion that is not joined to the ceramic substrate 2 based on the corrugated shape provided on the outer peripheral portion 5 of the joining layer 3 described above. In other words, between the metal circuit board 4 and the ceramic substrate 2, as shown in an enlarged view in FIG. 4, the gap 6 ( A portion where the bonding layer 3 does not exist) is provided. A portion of the metal circuit board 4 that is not bonded or fixed to the ceramic substrate 2, that is, a portion corresponding to the gap portion 6 exhibits a buffering action against thermal contraction due to the thermal cycle. The stress concentration with respect to can be reduced.

  As described above, by forming the outer peripheral portion 5 of the bonding layer 3 into a waveform along the metal circuit pattern, the stress concentration that causes cracks in the ceramic substrate 2, that is, the heat generated when a thermal cycle is applied. The concentration of stress on the joint end can be alleviated. Concentration relaxation of thermal stress suppresses the generation and growth of cracks, thereby preventing a decrease in bonding strength between the ceramic substrate 2 and the metal circuit board 4, peeling of the metal circuit board 4, and destruction of the ceramic substrate 2. Is possible. Therefore, the thermal cycle characteristics of the ceramic circuit board 1, that is, the reliability with respect to the thermal history can be greatly improved. In addition, an etching process or the like that can form a circuit pattern with high accuracy can be applied, and the manufacturing cost can be reduced.

  When the corrugated outer peripheral portion 5 of the bonding layer 3 is provided with a stress concentration relaxation function, it is preferable that the corrugated outer peripheral portion 5 has a wave shape constituted by a smooth curve such as a sine wave as described above. Although the present invention does not necessarily exclude a triangular waveform, stress concentration occurs in that portion when the apex angle becomes an acute angle, so that the effect of improving thermal cycle characteristics is reduced. When applying a triangular waveform, it is preferable to make the apex angle an obtuse angle, but it is desirable to apply a waveform composed of a smooth curve in terms of the function of reducing stress concentration. As for the specific shape of the corrugated outer peripheral portion 5, as shown in FIG. 5, the wave formation period p is in the range of 0.1 to 5 mm, and the wave formation width w is in the range of 0.05 to 2 mm. preferable.

  When the formation period p of the corrugated outer peripheral portion 5 is less than 0.1 mm, stress concentration tends to occur due to the narrowed crest portion. On the other hand, when the formation period p of the corrugated outer peripheral portion 5 exceeds 5 mm, the effect of apparently increasing the joint end length described above is reduced. The formation period p of the corrugated outer periphery 5 is more preferably in the range of 0.5 to 2 mm. Further, even when the formation width w of the corrugated outer peripheral portion 5 is less than 0.05 mm, the apparent increase effect of the joining end length described above is reduced. On the other hand, if the formation width w of the corrugated outer peripheral portion 5 exceeds 2 mm, the portion of the metal circuit board 4 that is not bonded to the ceramic substrate 2 increases excessively, which may cause a decrease in bonding strength. The formation period p of the corrugated outer periphery 5 is more preferably in the range of 0.1 to 1 mm.

  In this embodiment, the ceramic circuit board 1 in which the metal circuit boards 4a and 4b are joined to the front and back surfaces 2a and 2b of the ceramic board 2 is shown. However, the ceramic circuit board of the present invention is limited to such a structure. is not. The ceramic circuit board of the present invention may be obtained by bonding a metal circuit board only to one main surface of the ceramic substrate 2. Even in such a configuration, by making the outer peripheral portion 5 of the bonding layer 3 corrugated, the reliability with respect to the thermal history can be enhanced based on the stress concentration mitigating effect.

  Next, a method for manufacturing the ceramic circuit board of the above-described embodiment will be described with reference to FIGS. First, as shown in FIGS. 6A and 7A, for example, a brazing material is applied as a bonding material to the metal plate bonding surface (the main surface 2a in FIGS. 6 and 7) of the ceramic substrate 2. At this time, the brazing material is applied in advance so as to correspond to the shape of the metal circuit pattern 11 and is applied so that the outer peripheral portion formed along the metal circuit pattern 11 has a waveform.

  FIGS. 6A and 7A show a brazing material coating layer 13 corresponding to the shape of the metal circuit pattern 11 and having a corrugated outer peripheral portion 12. The waveform of the outer peripheral portion 12 is preferably a shape having the formation period p and the formation width w as described above. Further, the brazing material coating layer 13 can be easily applied to various shapes by, for example, adding a suitable amount of an organic binder and a solvent to the brazing material to form a paste, and screen-printing the brazing material paste.

  Next, the metal plate 14 is disposed on the brazing material coating layer 13 described above. This metal plate 14 is a plate-like body before forming a circuit pattern. As shown in FIG. 6B and FIG. 7B, the laminate of the ceramic substrate 2 and the metal plate 14 is heat-treated in a temperature and atmosphere according to the type of brazing material applied. Then, a joined body of the ceramic substrate 2 and the metal plate 14 is produced. Here, the bonding layer 3 made of the brazing material has a shape corresponding to the shape of the metal circuit pattern 11 based on the shape of the brazing material applied, and a waveform is formed on the outer peripheral portion 5 thereof.

  Thereafter, a resist corresponding to the metal circuit pattern 11 is formed on the metal plate 14, and portions other than the circuit pattern are removed, for example, by etching, as shown in FIGS. 6C and 7C. Then, a metal circuit board 4 having a desired circuit pattern is formed to obtain a target ceramic circuit board 1. As described above, the ceramic circuit board 1 having the bonding layer 3 provided with the wave shape showing the stress relaxation effect on the outer peripheral portion 5 can be obtained only by changing the application shape of the brazing material as the bonding material. There is no increase in manufacturing cost.

  Furthermore, since the stress relaxation effect is obtained based on the shape of the bonding layer 3, an etching process capable of increasing the definition of the pattern can be applied to the formation of the metal circuit pattern. Here, the metal circuit board 4 can also be formed by placing each metal plate processed into a circuit pattern in advance on the brazing material coating layer 13 and performing heat treatment in this state. The position of the metal plate is likely to be displaced, and the accuracy of the metal circuit pattern may be reduced. On the other hand, a complicated circuit pattern can be formed with high accuracy by performing an etching process after bonding.

  Next, specific examples of the present invention and evaluation results thereof will be described.

Example 1
First, a brazing paste was applied to the surface of an aluminum nitride (AlN) substrate having a thickness of 0.635 mm by applying a screen printing method. For this brazing material paste, an Ag-Cu eutectic brazing material (active metal brazing material) containing 2% by mass of Ti, which is made by pasting an appropriate amount of an organic binder and a solvent, is used. It was applied so that the thickness of the layer was 20 μm. Further, the brazing paste was applied so as to correspond to the shape of the metal circuit pattern, and the outer peripheral portion formed along the metal circuit pattern was corrugated. The specific shape of the waveform formed on the outer peripheral portion was a sine wave having a wave formation period p of 1 mm and a wave formation width w of 0.5 mm.

  Next, a 0.2 mm thick Cu plate was placed on the AlN substrate coated with the brazing paste, and this laminate was heat-treated in a vacuum atmosphere of 0.01 Pa or less at 800 ° C. for 15 hours. Then, the AlN substrate and the Cu plate were joined. Thereafter, an ultraviolet curable resin was applied on the Cu plate so as to correspond to the circuit pattern, and this was cured by irradiation with ultraviolet rays. By using this resin layer as a resist and etching the Cu plate into a circuit pattern, a wave shape is formed along the circuit pattern on the outer periphery of the target ceramic circuit board, that is, the bonding layer made of the brazing material layer. A ceramic circuit board was obtained.

Comparative Example 1
In Example 1 described above, a ceramic circuit board was produced in the same manner as in Example 1 except that the brazing material paste was applied over the entire surface corresponding to the size of the Cu plate. In the ceramic circuit board of Comparative Example 1, the brazing material layer has the same shape as the metal circuit pattern by the etching process.

  For the ceramic circuit boards of Example 1 and Comparative Example 1 described above, first, the bonding strength of the Cu circuit board was measured. Further, thermal cycle characteristics were measured and evaluated using the ceramic circuit boards of the respective examples manufactured under the same conditions. Thermal cycle characteristics: -40 ° C x 30 minutes + room temperature (RT) x 10 minutes + 125 ° C x 3 minutes + RT x 10 minutes 1 cycle of thermal cycle test (TCT) repeated 250 cycles, then the amount of cracks generated Was evaluated by measuring. The amount of crack generation is indicated by the ratio (X / L × 100 (%)) of the length X of the crack generation portion (development development portion) to the total outer peripheral length L of each Cu circuit pattern portion.

  In the above evaluation results, the bonding strength of the Cu circuit board of Example 1 was almost the same as that of Comparative Example 1. On the other hand, regarding the thermal cycle characteristics, the crack generation amount of the ceramic circuit board according to Example 1 was about 10%, whereas the crack generation amount of the ceramic circuit board according to Comparative Example 1 was about 15%. From this evaluation result, it can be seen that in Example 1, the number of TCT cycles is improved by about 33% in a relative comparison with Comparative Example 1. Thus, by forming a wave shape along the circuit pattern on the outer peripheral portion of the bonding layer made of the brazing material layer, it becomes possible to obtain a ceramic circuit board having high bonding strength and excellent thermal cycle characteristics. .

It is a top view which shows schematic structure of the ceramic circuit board by one Embodiment of this invention. It is sectional drawing of the ceramic circuit board shown in FIG. It is the cross-sectional view which cut | disconnected the ceramic circuit board shown in FIG. 1 in the plane direction in the part of the joining layer. It is a principal part expanded sectional view of the ceramic circuit board shown in FIG. It is a figure for demonstrating the outer peripheral part shape of the joining layer in the ceramic circuit board of this invention. It is a top view which shows the principal part manufacturing process of the manufacturing method of the ceramic circuit board by one Embodiment of this invention. It is a figure which shows the principal part manufacturing process of the ceramic circuit board shown in FIG. 6 in a cross section.

Explanation of symbols

    DESCRIPTION OF SYMBOLS 1 ... Ceramic circuit board, 2 ... Ceramic board, 3 ... Bonding layer, 4 (4a, 4b) ... Metal circuit board, 5 ... Waveform outer periphery of bonding layer, 11 ... Metal circuit pattern, 13 ... ... brazing material coating layer, 14 ... metal plate.

Claims (7)

In a ceramic circuit board comprising a ceramic substrate and a metal circuit board bonded to at least one surface of both main surfaces of the ceramic substrate via a bonding layer,
The ceramic circuit board, wherein the bonding layer has a corrugated outer periphery formed along a circuit pattern of the metal circuit board. The ceramic circuit board according to claim 1,
The waveform provided on the outer peripheral portion of the bonding layer has a curved shape, and the wave formation period is in the range of 0.1 to 5 mm, and the wave formation width is in the range of 0.05 to 2 mm. A ceramic circuit board characterized by that. In the ceramic circuit board according to claim 1 or 2,
The ceramic circuit board, wherein the bonding layer is made of a brazing material layer. In the ceramic circuit board according to any one of claims 1 to 3,
The ceramic substrate is made of an aluminum nitride sintered body, a silicon nitride sintered body, an alumina sintered body, or a composite sintered body of alumina and zirconia, and the metal circuit board is made of a copper plate or an aluminum plate. Ceramic circuit board. In manufacturing a ceramic circuit board by joining a metal circuit board to at least one of the two main surfaces of the ceramic board,
Applying a bonding material on the main surface of the ceramic substrate so as to correspond to the circuit pattern of the metal circuit board so that the outer peripheral portion has a waveform;
Arranging a metal plate on the coating layer of the bonding material, and bonding the ceramic substrate and the metal plate;
Forming the metal circuit plate by processing the metal plate in correspondence with the circuit pattern. A method for manufacturing a ceramic circuit board, comprising: In the manufacturing method of the ceramic circuit board of Claim 5,
A method for manufacturing a ceramic circuit board, wherein the bonding material is applied so that a waveform forming period is in a range of 0.1 to 5 mm and a forming width is in a range of 0.05 to 2 mm. In the manufacturing method of the ceramic circuit board of Claim 5 or Claim 6,
A method of manufacturing a ceramic circuit board, wherein a brazing material is used as the bonding material.

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