JP2019067804A - Ceramic circuit board - Google Patents

Abstract

To provide a ceramic circuit board equipped with durability with respect to a large current, heat dissipation, and thermal shock resistance.SOLUTION: A ceramic circuit board 101 includes: a ceramic substrate 1; and metal layers 2a, 2b which are provided on both sides of the ceramic substrate 1. The metal layers 2a, 2b have first metal layers 22a, 22b containing Al and second metal layers 23a, 23b containing Cu in this order from the ceramic substrate 1, and at least one of the metal layers 2a, 2b forms a metal circuit.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a ceramic circuit board, and more particularly to a ceramic circuit board suitable for mounting high power electronic components such as power modules.

  In recent years, with the advancement of the performance of industrial devices such as robots and motors, it has been required to increase the current and improve the efficiency of inverters. Under such circumstances, in the power module used for the inverter, the heat generated from the semiconductor element continues to increase. In order to efficiently diffuse the heat generated from the semiconductor element, a ceramic circuit board having good thermal conductivity is used.

  The power module is generally provided on the ceramic circuit board, the semiconductor element provided on one surface of the ceramic circuit board, and the other surface of the ceramic circuit board by soldering or the like, and Cu, which has excellent thermal conductivity, A base plate made of Cu-Mo, Cu-C, Al, Al-SiC, Al-C, etc., and a radiation fin provided by screwing or the like on the surface of the base plate opposite to the ceramic circuit board; Prepare.

  Power modules have been used initially for simple machine tools, but recently, like welding machines, train drives, and electric vehicles, durability and further miniaturization under harsher environmental conditions are required. It is intended to be used in

  In order to meet such requirements, in semiconductor devices used in power modules, SiC is being developed as a material to replace conventional Si, and in ceramic circuit boards, the thickness of metal circuits is increased, etc. Attempts have been made to increase the density. Further, as a material of the metal circuit portion of the ceramic circuit board, Cu is mainly used in order to correspond to a high voltage of several thousand volts and a high current of several hundreds of amperes.

  However, in such a power module, for example, when thermal shock from −45 ° C. to 235 ° C. is repeatedly applied, strain due to thermal stress due to the difference in thermal expansion coefficient between Cu and the ceramic accumulates in the grain boundary of Cu. This strain causes deviation of Cu grain boundaries, thereby increasing the surface roughness of the metal circuit surface. If the surface roughness of the metal circuit surface is increased, there is a concern that the bonding property with the SiC semiconductor element may be reduced and the power module may not operate properly. On the other hand, by reducing the thickness of the metal circuit portion, it is possible to suppress an increase in the surface roughness of the metal circuit surface accompanying the thermal shock (to improve the thermal shock resistance) (for example, non- Patent Document 1).

National Research and Development Corporation New Energy and Industrial Technology Development Organization, "New Material Power Semiconductor Project to Realize Low Oxygen Society" Business Register (released), p. III-572 (July 13, 2015)

  By reducing the thickness of the metal circuit portion in the ceramic circuit board, it is possible to suppress an increase in the surface roughness of the metal circuit surface accompanying the thermal shock to some extent, according to the study of the present inventors etc. It was found that such a ceramic circuit board has a decrease in durability against a large current and a decrease in heat dissipation.

  The present invention has been made in view of such circumstances, and it is an object of the present invention to provide a ceramic circuit board having durability against a large current, heat dissipation, and thermal shock resistance.

  The present invention comprises a ceramic base and a metal layer provided on both sides of the ceramic base, the metal layer including a first metal layer containing Al and a second metal layer containing Cu from the ceramic base A ceramic circuit board is provided, having in order, at least one of the metal layers forming a metal circuit.

  The ceramic circuit board is left in an environment of 235 ° C. for 30 minutes and then left in an environment of −45 ° C. for 30 minutes as one cycle, after the heat cycle test of 1000 cycles, the metal layer on the opposite side to the ceramic base The surface roughness Ra of the surface may be 1 μm or less.

The ceramic base may be made of AlN, Si ₃ N ₄ or Al ₂ O ₃ and may have a thickness of 0.2 to 1.5 mm.

  The thickness of the metal layer may be 0.1 to 6 mm.

  The end face of the first metal layer may be flush with the end face of the second metal layer, and the end face of the first metal layer may protrude outside the end face of the second metal layer.

  According to the present invention, it is possible to provide a ceramic circuit board having durability against a large current, heat dissipation and thermal shock resistance.

It is a sectional view showing one embodiment of a ceramic circuit board. It is a sectional view showing one embodiment of a ceramic circuit board. FIG. 2 is a cross-sectional view of one embodiment of a power module.

  Hereinafter, some embodiments of the present invention will be described in detail. However, the present invention is not limited to the following embodiments.

  FIG. 1 is a cross-sectional view showing an embodiment of a ceramic circuit board. As shown in FIG. 1, the ceramic circuit board 101 has a ceramic base 1 and metal layers 2 a and 2 b provided on both sides of the ceramic base 1. The metal layers 2a and 2b are in contact with the ceramic base 1, respectively, and the first metal layers 22a and 22b containing Al and the second metal layer 23a containing Cu formed on the first metal layers 22a and 22b. , 23b. That is, the ceramic base, the first metal layer and the second metal layer are laminated in this order. At least one of the metal layers 2a and 2b forms an electric circuit (metal circuit).

  The inventors consider as follows the reason why the ceramic circuit board having such characteristics can suppress the increase of the surface roughness of the metal circuit surface even after repeated thermal shocks. .

  First, the conventional ceramic circuit substrate is a ceramic substrate on which a metal layer containing Cu is joined. However, as described above, when a thermal shock is repeatedly received, the heat resulting from the difference in coefficient of thermal expansion between Cu and the ceramic Strain due to stress accumulates on Cu grain boundaries, and this strain causes deviation of Cu grain boundaries, thereby increasing the surface roughness of the metal circuit surface. On the other hand, in the ceramic circuit board according to the present invention, the first metal layer containing Al is first bonded to the ceramic base, and the second metal layer containing Cu is formed via the first metal layer. ing. Although the difference in thermal expansion coefficient between Al and ceramics is large, Al is a soft metal, so even if it is subjected to repeated thermal shocks, it is generated between the second metal layer containing Cu and the ceramic base It is believed that thermal stress can be buffered. As a result, the present inventors believe that the shift of the grain boundary of Cu was suppressed and the increase in the surface roughness of the metal circuit surface was able to be suppressed.

  Further, in the ceramic circuit board according to the present invention, the increase in surface roughness of the metal circuit surface can be suppressed by adopting the above configuration, and it is not necessary to reduce the thickness of the metal circuit portion as in the prior art It is considered that the decrease in durability against a large current and the decrease in heat dissipation due to the reduction of the thickness can be suppressed.

In order to obtain such a ceramic circuit board 101, for example, the ceramic base 1 is preferably formed of AlN, Si ₃ N ₄ or Al ₂ O ₃ . The thickness of the ceramic base 1 is preferably 0.2 to 1.5 mm, and more preferably 0.25 to 1.0 mm. When the thickness of the ceramic base 1 is less than 0.2 mm, the thermal shock resistance tends to decrease, and when it exceeds 1.5 mm, the heat dissipation tends to decrease.

  Moreover, although 1st metal layer 22a, 22b contains Al, it should just contain Al as a main component. Here, the term "main component" means a component contained at 70% by mass or more based on the total mass of the first metal layers 22a and 22b. The proportion of the main component may be 90% by mass or more, or 95% by mass or more. In addition, the first metal layer may contain a small amount of unavoidable impurities.

  The other components contained in the first metal layers 22a and 22b are not particularly limited as long as the effects of the present invention are not impaired. For example, an alloy containing Cu, Cu and Mo, Cu and W Alloys and the like. The first metal layers 22a and 22b may be formed of the same kind of material or different kinds of materials, but are formed of the same kind of material from the viewpoint of facilitating the manufacture of the ceramic circuit board. Is preferred.

  The thickness of the first metal layers 22a and 22b is preferably 0.1 to 3 mm, and more preferably 0.15 to 1 mm. If the thickness of the first metal layers 22a and 22b is less than 0.1 mm, the thermal stress generated between the second metal layer containing Cu and the ceramic base can not be buffered, and if it exceeds 3 mm, The thickness of the ceramic circuit board becomes larger than necessary, which makes it difficult to miniaturize the power module. The thicknesses of the first metal layers 22a and 22b may be substantially the same or different, but are preferably substantially the same from the viewpoint of facilitating the production of the ceramic circuit board.

  The second metal layers 23a and 23b contain Cu, but may contain Cu as a main component. Here, the “main component” means a component contained at 70% by mass or more based on the total mass of the second metal layers 23 a and 23 b. The proportion of the main component may be 90% by mass or more, or 95% by mass or more. The second metal layer may also contain a small amount of unavoidable impurities.

  The other components contained in the second metal layers 23a and 23b are not particularly limited as long as the effects of the present invention are not impaired. For example, an alloy containing Al, Al and Mo, Cu and W Alloys and the like. The second metal layers 23a and 23b may be formed of the same kind of material or different kinds of materials, but are formed of the same kind of material from the viewpoint of facilitating the production of the ceramic circuit board. Is preferred.

  It is preferable that it is 0.2-3 mm, and, as for the thickness of 2nd metal layer 23a, 23b, it is more preferable that it is 0.3-2 mm. When the thickness of the second metal layers 23a and 23b is less than 0.2 mm, it becomes difficult to flow a large current, and when it exceeds 3 mm, the generated thermal stress becomes large and the thermal stress in the first metal layer containing Al Buffering can be difficult. The thicknesses of the second metal layers 23a and 23b may be substantially the same or different, but are preferably substantially the same from the viewpoint of facilitating the production of the ceramic circuit board.

  The thickness of the metal layers 2a and 2b is preferably 0.1 to 6 mm, more preferably 0.2 to 3 mm, still more preferably 0.4 to 2 mm, and 0.5 to 0.5 mm. Particular preference is given to 1 mm. If the thickness of the metal layers 2a and 2b is less than 0.1 mm, the flowable current is limited, and if it exceeds 6 mm, the thermal shock resistance tends to decrease. The thicknesses of the metal layers 2a and 2b may be substantially the same or different, but are preferably substantially the same from the viewpoint of facilitating the production of the ceramic circuit board.

  The ceramic circuit board 101 according to the present embodiment described above is a metal layer after 1000 cycles of heat cycle test, where one cycle is an operation of leaving in an environment of −35 ° C. for 30 minutes after leaving in an environment of 235 ° C. for 30 minutes. It is possible to suppress an increase in surface roughness Ra of the surface opposite to the ceramic base of the above. The value of Ra after the heat cycle test may be, for example, 1 μm or less, may be 0.9 μm or less, and may be 0.5 μm or less. The lower limit of the above-mentioned Ra is not particularly limited, but is, for example, 0.1 μm or more.

  In this specification, surface roughness Ra in the surface on the opposite side to the ceramic base material of a metal layer can be measured by the method based on JIS-B0601-1994 using a surface roughness measuring machine. As a surface roughness measuring machine, for example, a trade name “SJ-400” manufactured by Mitutoyo Co., Ltd. can be used.

  The ceramic circuit board 101 is obtained, for example, by bonding the ceramic base 1 and the first metal layers 22a and 22b and then forming the second metal layers 23a and 23b on the first metal layers 22a and 22b. Can.

  As a method of bonding the ceramic base 1 and the first metal layers 22a and 22b, there is a method using an adhesive method in which both are adhered, an active metal method, a thermal spraying method, etc. alone or in combination. It can be mentioned.

  The bonding method is a method of bonding both using an adhesive, and for example, a method of forming a circuit by an etching method if desired after bonding a metal plate with an acrylic adhesive on both sides of a ceramic base.

  The active metal method includes, for example, a method of forming a circuit by an etching method if desired after bonding an Al plate on both sides of a ceramic base at a temperature of 630 ° C. using an Al-Cu-Mg clad foil as a brazing material. .

  In the thermal spraying method (cold spray method), for example, the metal powder composed of a plurality of metal particles is heated to 10 to 270 ° C. and accelerated to a speed of 250 to 1050 m / s and then sprayed to form a ceramic substrate. And a step of heat-treating the ceramic base and the metal layer formed on the ceramic base in an inert gas atmosphere. When the first metal layer containing Al is formed by a thermal spraying method, Al particles may be used as the metal constituting the metal powder.

  Further, as a method of forming the second metal layers 23a and 23b on the first metal layers 22a and 22b, as in the case of the first metal layer, an adhesion method in which both are adhered using an adhesive, an active metal method, A method of using a thermal spraying method etc. singly or in combination may be mentioned, and the redundant description will be omitted here.

In the active metal method, as a method of forming a second metal layer containing Cu, for example, a brazing material of Ag (90%)-Cu (10%)-TiH ₂ (3.5%) is used. After bonding a Cu plate on the first metal layer at a temperature of 800 ° C., a method of forming a circuit by an etching method can be mentioned, if desired.

  Although the metal layers 2a and 2b each have the first metal layers 22a and 22b and the second metal layers 23a and 23b in the above-described embodiment, the present invention is not limited to the above embodiments, for example. The metal layers 2a and 2b may each have three or more metal layers, such as having another metal layer between the first metal layer and the second metal layer. When such other metal layer is provided, the metal layer may be, for example, a metal layer containing Ni. By having another metal layer, the reaction in a high temperature environment of the first metal layer containing Al and the second metal layer containing Cu can be suppressed.

  Further, in the ceramic circuit board 101 shown in FIG. 1, the end face 22E of the first metal layer 22a, 22b and the end face 23E of the second metal layer 23a, 23b are flush, but the ceramic circuit board is more excellent From the viewpoint of having excellent thermal shock resistance, like the ceramic circuit board 102 shown in FIG. 2, the end face 22E of the first metal layers 22a and 22b is outside the end face 23E of the second metal layers 23a and 23b, that is, the ceramic base It may be protruded to the end side of the material 1. The width of the portion where the end face 22E protrudes beyond the end face 23E may be, for example, 1 to 1000 μm.

  The ceramic circuit board described above is suitably used in a power module, and can suppress the reduction in durability against a large current and the reduction in heat dissipation.

  FIG. 3 is a cross-sectional view of an embodiment of a power module. As shown in FIG. 3, the power module 200 includes a base plate 3, a ceramic circuit board 103 joined to the base plate 3 via the first solder 4, and a second solder 5 on the ceramic circuit board 103. And the semiconductor element 6 joined via the

  The ceramic circuit board 103 includes a ceramic base 1 and metal layers 2 a and 2 b provided on both sides of the ceramic base 1. The base plate 3 is joined to the metal layer 2 b via the first solder 4. The semiconductor element 6 is joined to a predetermined portion of the metal layer 2a via the second solder 5, and is joined to a predetermined portion of the metal layer 2a by a metal wire 7 such as an aluminum wire (aluminum wire). . In the power module shown in FIG. 3, the metal layer 2a forms an electric circuit (metal circuit). The metal layer 2b may or may not form a metal circuit.

  Each of the above-described components provided on the base plate 3 is covered with, for example, a hollow box-shaped resin case 8 whose one surface is open, and is accommodated in the case 8. The hollow portion between the base plate 3 and the housing 8 is filled with a filler 9 such as silicone gel. An electrode 10 penetrating through the housing 8 is joined to a predetermined portion of the metal layer 2 a via a third solder 11 so as to be electrically connected to the outside of the housing 8.

  At an edge portion of the base plate 3, for example, a mounting hole 3 a for screwing when attaching a heat dissipation component to the power module 200 is formed. The number of mounting holes 3a is, for example, four or more. At the edge of the base plate 3, instead of the mounting hole 3a, a mounting groove may be formed such that the side wall of the base plate 3 has a U-shaped cross section.

  Since the power module 200 includes the ceramic circuit board according to the above-described embodiment, the power module 200 is suitably used as a driving inverter of a train or an automobile where high withstand voltage, high output and the like are required.

  Hereinafter, the present invention will be more specifically described by way of examples. However, the present invention is not limited to these examples.

Example 1
An aluminum nitride (AlN) substrate (size: 50 mm × 60 mm × 0.635 mm t) was used as a ceramic substrate. An Al plate (0.2 mm in thickness) was bonded to both surfaces of the ceramic base at a temperature of 630 ° C. using an Al—Cu—Mg clad foil as a brazing material, and an Al circuit was formed by etching. Subsequently, a Cu circuit having a thickness of 0.3 mm was laminated by a thermal spraying method (cold spray method), annealing was performed at a temperature of 300 ° C., and electroless Ni plating was performed to fabricate a ceramic circuit board.

Example 2
An Al circuit having a thickness of 0.2 mm was laminated on both sides of the same ceramic base as in Example 1 by a thermal spraying method (cold spray method), and annealing was performed at a temperature of 500 ° C. Subsequently, a Cu circuit having a thickness of 0.3 mm was laminated by a thermal spraying method (cold spray method), annealing was performed at a temperature of 300 ° C., and electroless Ni plating was performed to fabricate a ceramic circuit board.

[Example 3]
An Al circuit having a thickness of 0.2 mm was laminated on both sides of the same ceramic base as in Example 1 by a thermal spraying method (cold spray method), annealing was performed at a temperature of 500 ° C., and a circuit was formed by etching. Subsequently, a Cu plate (thickness 0.3 mm) having a circuit pattern shaped thereon was adhered to an Al plate with an acrylic adhesive, and then electroless Ni plating was performed to prepare a ceramic circuit board.

Comparative Example 1
Using Ag-Cu-TiH ₂ brazing material, bonding the Cu plate (thickness 0.3 mm) at a temperature 800 ° C. on both sides of the same ceramic base material as that used in Example 1, after forming a Cu circuit by etching, no Electrolytic Ni plating was performed to prepare a ceramic circuit board.

Comparative Example 2
As a ceramic substrate, a silicon nitride (Si ₃ N ₄ ) substrate (size: 50 mm × 60 mm × 0.32 mm t) was used. A Cu plate (0.3 mm thick) is bonded to both sides of the ceramic base using an Ag-Cu-TiH ₂ brazing material at a temperature of 800 ° C, and after forming a Cu circuit by etching, electroless Ni plating is applied, A ceramic circuit board was produced.

Comparative Example 3
A Cu plate (0.3 mm thick) is adhered to both sides of the same ceramic base as in Comparative Example 2 using an acrylic adhesive, and a Cu circuit is formed by etching, and then electroless Ni plating is performed to form a ceramic circuit board. Was produced.

Comparative Example 4
After laminating a 0.3 mm thick Al circuit by thermal spraying (cold spray) on both sides of the same ceramic base as in Example 1 and annealing at a temperature of 500 ° C., electroless Ni plating is applied to the ceramic. A circuit board was produced.

  Table 1 shows the details of the ceramic circuit boards of the examples and the comparative examples.

<Measurement of surface roughness Ra>
The obtained ceramic circuit substrate was left in an environment of 235 ° C. for 30 minutes, and then left in the environment of −40 ° C. for 30 minutes as one cycle to conduct a heat cycle test of 1000 cycles. With respect to the ceramic circuit boards of Examples 1 to 3 and Comparative Examples 2 to 4 after the heat cycle test, using a surface roughness measuring machine (Mittoyo Co., Ltd., trade name “SJ-400”, JIS-B0601-1994) The surface roughness Ra was measured by the method according to Example 1. In the ceramic circuit boards of Examples 1 to 3, the surface roughness Ra was increased as compared with the ceramic circuit boards of Comparative Examples 2 to 4 even after the heat cycle test. It was shown that the ceramic circuit board of Comparative Example 1 had peeling of the circuit after the heat cycle test and breakage of the ceramic base, and the surface was rough. Could not measure Ra.

  The evaluation results of the ceramic circuit board are shown in Table 2.

  After bonding the Si semiconductor element and the electrodes with high temperature solder to the ceramic circuit substrates of Examples 1 to 3 and Comparative Examples 1 to 4, the Al-SiC base plate is further bonded to the ceramic circuit substrate using eutectic solder. did. Next, the Al wire is ultrasonically bonded to the Si semiconductor element and the ceramic circuit board and wired, then the resin case is adhered to the base plate with an adhesive, and then the resin case is filled with silicone gel to form the power module. Made.

  Next, this power module was tightened to a 140 mm × 190 mm × 50 mm transparent resin block with six M6 mounting bolts and mounted at a torque of 10 N. The obtained power module was subjected to a conduction test after a heat cycle test of 1000 cycles with one cycle of a temperature of −45 ° C. × 30 minutes and a temperature of 235 ° C. × 30 minutes. In the power module using the above, the durability and the heat dissipation to a large current are not sufficient, and the temperature of the semiconductor element rapidly rises, causing a malfunction.

  DESCRIPTION OF SYMBOLS 1 ... ceramic base material, 2a, 2b ... metal layer, 22a, 22b ... 1st metal layer, 23a, 23b ... 2nd metal layer, 22E ... end surface of 1st metal layer, 23E ... end surface of 2nd metal layer, 101 , 102 ... ceramic circuit board.

Claims (6)

A ceramic base, and a metal layer provided on both sides of the ceramic base, the metal layer including a first metal layer containing Al and a second metal layer containing Cu from the ceramic base in this order Have,
A ceramic circuit board, wherein at least one of the metal layers forms a metal circuit.   After leaving in an environment of 235 ° C. for 30 minutes and taking 30 minutes in an environment of −45 ° C. as one cycle, after the heat cycle test of 1000 cycles, the surface of the metal layer opposite to the ceramic base surface The ceramic circuit board according to claim 1, wherein the roughness Ra is 1 μm or less. The ceramic circuit board according to claim 1, wherein the ceramic base is formed of AlN, Si ₃ N ₄ or Al ₂ O ₃ .   The ceramic circuit board according to any one of claims 1 to 3, wherein the thickness of the ceramic base is 0.2 to 1.5 mm.   The ceramic circuit board according to any one of claims 1 to 4, wherein the thickness of the metal layer is 0.1 to 6 mm.   The end face of the first metal layer is flush with the end face of the second metal layer, or the end face of the first metal layer protrudes outside the end face of the second metal layer. The ceramic circuit board as described in any one of -5.

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