JP7027095B2 - Ceramic circuit board - Google Patents

Description

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

In recent years, with the increase in performance of industrial equipment such as robots and motors, it has been required to increase the current and efficiency of inverters. Under such circumstances, the heat generated from semiconductor elements in power modules used for inverters is steadily increasing. 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 a ceramic circuit board, a semiconductor element provided on one surface of the ceramic circuit board, and on the other surface of the ceramic circuit board by soldering or the like, and has excellent thermal conductivity. A base plate made of Cu-Mo, Cu-C, Al, Al-SiC, Al-C, etc., and heat-dissipating fins provided on the surface of the base plate on the opposite side of the ceramic circuit board by screwing or the like. Be prepared.

Initially, power modules were used in simple machine tools, but nowadays, they are required to be durable and further miniaturized under harsher environmental conditions such as welders, train drives, and electric vehicles. It has come to be used for various purposes.

In order to meet such demands, the development of SiC as a material to replace conventional Si is being promoted in semiconductor devices used in power modules, and in ceramic circuit boards, currents such as increasing the thickness of metal circuits are being promoted. Attempts have been made to increase the density. Further, as a material for a metal circuit portion of a ceramic circuit board, Cu is mainly used in order to cope with a high voltage of several thousand volts and a high current of several hundred amperes.

However, in such a power module, when a thermal shock from −45 ° C. to 235 ° C. is repeatedly applied, for example, strain due to thermal stress due to the difference in thermal expansion rate between Cu and ceramics accumulates in the grain boundaries of Cu. This strain causes the grain boundaries of Cu to shift, thereby increasing the surface roughness of the metal circuit surface. If the surface roughness of the metal circuit surface increases, the bondability with the SiC semiconductor element deteriorates, and there is a concern that the power module may not operate normally. On the other hand, by reducing the thickness of the metal circuit portion, it is possible to suppress the increase in surface roughness of the metal circuit surface due to thermal shock (improve thermal shock resistance) (for example, non-heat impact resistance). See Patent Document 1).

National Research and Development Corporation New Energy and Industrial Technology Development Organization, "New Material Power Semiconductor Project for Realizing a Low-Oxygen Society" Business Ledger (Open), p. III-572 (July 13, 2015)

By reducing the thickness of the metal circuit portion of the ceramic circuit board, it is possible to suppress the increase in surface roughness of the metal circuit surface due to thermal shock to some extent, but according to the study by the present inventors, this is possible. It has been found that such ceramic circuit boards have 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 an object of the present invention is 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 material and metal layers provided on both sides of the ceramic base material, and the metal layer is a first metal layer containing Al and a second metal layer containing Cu from the ceramic base material. Provided is a ceramic circuit substrate which has in order and at least one of the metal layers forms 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. The surface roughness Ra of the surface may be 1 μm or less.

The ceramic base material may be formed of AlN, Si _{3N 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 and the end face of the second metal layer may be flush with each other, 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 sectional drawing which shows one Embodiment of a ceramics circuit board. It is sectional drawing which shows one Embodiment of a ceramics circuit board. It is sectional drawing which shows 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 material 1 and metal layers 2a and 2b provided on both sides of the ceramic base material 1. The metal layers 2a and 2b are in contact with the ceramic base material 1, respectively, and are formed on the first metal layers 22a and 22b containing Al and the first metal layers 22a and 22b, respectively, and the second metal layer 23a containing Cu is formed. , 23b. That is, the ceramic base material, 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 present inventors consider the reason why a ceramic circuit board having such characteristics can suppress an increase in surface roughness of a metal circuit surface even after repeated thermal shocks. ..

First, the conventional ceramic circuit board is formed by bonding a metal layer containing Cu to a ceramic base material, but as described above, when it is repeatedly subjected to thermal shock, heat caused by the difference in thermal expansion rate between Cu and ceramics is generated. The strain due to stress accumulates in the grain boundaries of Cu, and this strain causes the deviation of the grain boundaries of Cu, 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 material, 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 it is generated between the second metal layer containing Cu and the ceramic base material even when it is repeatedly subjected to thermal shock. It is considered that the thermal stress can be buffered. As a result, the present inventors consider that the deviation of the grain boundaries of Cu can be suppressed and the increase in the surface roughness of the surface of the metal circuit can be suppressed.

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

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

Further, although the first metal layers 22a and 22b contain Al, they may contain Al as a main component. Here, the "main component" means a component contained in an amount of 70% by mass or more based on the total mass of the first metal layers 22a and 22b. The ratio of the main component may be 90% by mass or more, or 95% by mass or more. Further, the first metal layer may contain a trace amount of unavoidable impurities.

The other components contained in the first metal layers 22a and 22b are not particularly limited as long as they do not impair the effects of the present invention, but are not particularly limited, and are, for example, alloys containing Cu, Cu and Mo, Cu and W. Examples include alloys containing. The first metal layers 22a and 22b may be formed of the same type of material or different materials, respectively, but are formed of the same type of material from the viewpoint of facilitating the production of the ceramic circuit board. Is preferable.

The thickness of the first metal layers 22a and 22b is preferably 0.1 to 3 mm, 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 substrate cannot be buffered, and if it exceeds 3 mm, The thickness of the ceramic circuit board becomes larger than necessary, making it difficult to reduce the size of the power module. The thicknesses of the first metal layers 22a and 22b may be substantially the same or different from each other, but are preferably substantially the same from the viewpoint of facilitating the manufacture 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 in an amount of 70% by mass or more based on the total mass of the second metal layers 23a and 23b. The ratio of the main component may be 90% by mass or more, or 95% by mass or more. Further, the second metal layer may contain a trace amount of unavoidable impurities.

The other components contained in the second metal layers 23a and 23b are not particularly limited as long as they do not impair the effects of the present invention, but are not particularly limited, and are, for example, alloys containing Al, Al and Mo, Cu and W. Examples thereof include alloys containing. The second metal layers 23a and 23b may be formed of the same type of material or different materials, respectively, but are formed of the same type of material from the viewpoint of facilitating the production of the ceramic circuit board. Is preferable.

The thickness of the second metal layers 23a and 23b is preferably 0.2 to 3 mm, more preferably 0.3 to 2 mm. If the thickness of the second metal layers 23a and 23b is less than 0.2 mm, it becomes difficult to pass a large current, and if it exceeds 3 mm, the generated thermal stress becomes large, and the thermal stress in the first metal layer containing Al becomes large. Can be difficult to buffer. The thicknesses of the second metal layers 23a and 23b may be substantially the same or different from each other, but are preferably substantially the same from the viewpoint of facilitating the manufacture 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, further preferably 0.4 to 2 mm, and 0.5 to 0.5 to 2. It is particularly preferably 1 mm. If the thickness of the metal layers 2a and 2b is less than 0.1 mm, the current that can be passed is limited, and if it exceeds 6 mm, the thermal impact resistance tends to decrease. The thicknesses of the metal layers 2a and 2b may be substantially the same or different from each other, 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 above-described embodiment has a metal layer after a heat cycle test of 1000 cycles, in which the operation of leaving the ceramic circuit board 101 in an environment of 235 ° C. for 30 minutes and then leaving it in an environment of −45 ° C. for 30 minutes is one cycle. It is possible to suppress an increase in the surface roughness Ra of the surface opposite to the ceramic substrate. The value of Ra after the heat cycle test may be, for example, 1 μm or less, 0.9 μm or less, and 0.5 μm or less. The lower limit of Ra is not particularly limited, but is, for example, 0.1 μm or more.

In the present specification, the surface roughness Ra on the surface of the metal layer opposite to the ceramic substrate can be measured by a method according to JIS-B0601-1994 using a surface roughness measuring machine. As the surface roughness measuring machine, for example, the trade name "SJ-400" manufactured by Mitutoyo Co., Ltd. can be used.

The ceramic circuit board 101 can be obtained, for example, by joining the ceramic base material 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, respectively. Can be done.

As a method for joining the ceramic base material 1 and the first metal layers 22a and 22b, a method of bonding the two together using an adhesive, an active metal method, a thermal spraying method, or the like may be used alone or in combination. Can be mentioned.

The bonding method is a method of adhering the two together using an adhesive, and is a method of adhering a metal plate to both sides of a ceramic base material with, for example, an acrylic adhesive, and then forming a circuit by an etching method, if desired.

Examples of the active metal method include a method in which an Al-Cu-Mg clad foil is used as a brazing material, an Al plate is bonded to both sides of a ceramic substrate at a temperature of 630 ° C., and then a circuit is formed by an etching method, if desired. ..

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

Further, as a method for forming the second metal layers 23a and 23b on the first metal layers 22a and 22b, respectively, as in the case of the first metal layer, an adhesive method for adhering the two with an adhesive, an active metal method, and the like. Examples thereof include a method in which a thermal spraying method or the like is used alone or in combination, and redundant description will be omitted here.

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

In the above-described embodiment, the case where the metal layers 2a and 2b have the first metal layers 22a and 22b and the second metal layers 23a and 23b, respectively, has been described, but the present invention is not limited to the above-described embodiment, 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 having such another metal layer, the metal layer may be, for example, a metal layer containing Ni. By having another metal layer, it is possible to suppress the reaction between the first metal layer containing Al and the second metal layer containing Cu in a high temperature environment.

Further, in the ceramic circuit board 101 shown in FIG. 1, the end faces 22E of the first metal layers 22a and 22b and the end faces 23E of the second metal layers 23a and 23b are flush with each other, but the ceramic circuit board is more excellent. From the viewpoint of having thermal shock resistance, the end faces 22E of the first metal layers 22a and 22b are outside the end faces 23E of the second metal layers 23a and 23b, that is, ceramic groups, as in the ceramic circuit board 102 shown in FIG. It may protrude to the end side of the material 1. The width of the portion of the end face 22E protruding from 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 a decrease in durability against a large current and a decrease in heat dissipation.

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

The ceramic circuit board 103 includes a ceramic base material 1 and metal layers 2a and 2b provided on both sides of the ceramic base material 1. The base plate 3 is joined to the metal layer 2b via the first solder 4. The semiconductor element 6 is bonded to a predetermined portion of the metal layer 2a via a second solder 5, and is bonded 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 components provided on the base plate 3 is covered with, for example, a hollow box-shaped resin housing 8 having an open surface, and is housed in the housing 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 the housing 8 is bonded to a predetermined portion of the metal layer 2a via a third solder 11 so as to be electrically connected to the outside of the housing 8.

At the edge of the base plate 3, for example, a mounting hole 3a for screwing when mounting a heat radiating component to the power module 200 is formed. The number of mounting holes 3a is, for example, four or more. Instead of the mounting hole 3a, a mounting groove may be formed at the edge of the base plate 3 so 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 present embodiment described above, it is suitably used as a drive inverter for a train or an automobile, which is required to have high withstand voltage, high output, and the like.

Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to these examples.

[Example 1]
As the ceramic substrate, an aluminum nitride (AlN) substrate (size: 50 mm × 60 mm × 0.635 mmt) was used. An Al-Cu-Mg clad foil was used as a brazing material, and an Al plate (thickness 0.2 mm) was bonded to both sides of a ceramic substrate at a temperature of 630 ° C., and an Al circuit was formed by etching. Subsequently, Cu circuits having a thickness of 0.3 mm were laminated by a thermal spraying method (cold spray method), annealed at a temperature of 300 ° C., and then electroless Ni-plated to prepare a ceramic circuit board.

[Example 2]
An Al circuit having a thickness of 0.2 mm was laminated on both sides of a ceramic substrate similar to that in Example 1 by a thermal spraying method (cold spray method), and annealed at a temperature of 500 ° C. Subsequently, Cu circuits having a thickness of 0.3 mm were laminated by a thermal spraying method (cold spray method), annealed at a temperature of 300 ° C., and then electroless Ni-plated to prepare a ceramic circuit board.

[Example 3]
An Al circuit having a thickness of 0.2 mm was laminated on both sides of a ceramic substrate similar to that in Example 1 by a thermal spraying method (cold spray method), annealed at a temperature of 500 ° C., and then an etching was performed to form the circuit. Subsequently, a Cu plate (thickness 0.3 mm) having a circuit pattern formed was bonded to the 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, a Cu plate (thickness 0.3 mm) was bonded to both sides of a ceramic substrate similar to Example 1 at a temperature of 800 ° C., and a Cu circuit was formed by etching. Electroless Ni plating was applied to produce a ceramic circuit board.

[Comparative Example 2]
As the ceramic substrate, a silicon nitride (Si ₃ N ₄ ) substrate (size: 50 mm × 60 mm × 0.32 mmt) was used. Using Ag-Cu-TiH ₂ brazing material, a Cu plate (thickness 0.3 mm) is bonded to both sides of a ceramic substrate at a temperature of 800 ° C., a Cu circuit is formed by etching, and then electroless Ni plating is applied. A ceramic circuit board was manufactured.

[Comparative Example 3]
A Cu plate (thickness 0.3 mm) is adhered to both sides of a ceramic substrate similar to Comparative Example 2 using an acrylic adhesive, a Cu circuit is formed by etching, and then electroless Ni plating is applied to the ceramic circuit board. Was produced.

[Comparative Example 4]
An Al circuit with a thickness of 0.3 mm is laminated on both sides of a ceramic substrate similar to Example 1 by a thermal spraying method (cold spray method), annealed at a temperature of 500 ° C., electroless Ni plating is applied, and the ceramics are subjected to. A circuit board was manufactured.

Table 1 shows the details of the ceramic circuit boards of each Example and Comparative Example.

<Measurement of surface roughness Ra>
The obtained ceramic circuit board was left in an environment of 235 ° C. for 30 minutes and then left in an environment of −40 ° C. for 30 minutes, and a heat cycle test of 1000 cycles was performed. JIS-B0601-1994 using a surface roughness measuring machine (Mitutoyo Co., Ltd., trade name "SJ-400") for the ceramic circuit boards of Examples 1 to 3 and Comparative Examples 2 to 4 after the heat cycle test. The surface roughness Ra was measured by a method according to the above. Even after the heat cycle test, the surface roughness Ra of the ceramic circuit boards of Examples 1 to 3 was increased as compared with the ceramic circuit boards of Comparative Examples 2 to 4. It was shown that the ceramic circuit board of Comparative Example 1 had peeling of the circuit and damage of the ceramic base material after the heat cycle test, and the surface roughness of the ceramic circuit board of Comparative Example 1 was shown to be good. Ra could not be measured.

Table 2 shows the evaluation results of the ceramic circuit board.

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

Next, this power module was fastened to a transparent resin block of 140 mm × 190 mm × 50 mm with six M6 mounting bolts, and mounted with a torque of 10 N. The obtained power module was subjected to a heat cycle test of 1000 cycles with a temperature of −45 ° C. × 30 minutes and a temperature of 235 ° C. × 30 minutes as one cycle, and then an energization test was performed. It cannot be said that the power module using the above has sufficient durability and heat dissipation against a large current, and the temperature of the semiconductor element rises sharply, causing a malfunction.

1 ... Ceramic substrate, 2a, 2b ... Metal layer, 22a, 22b ... First metal layer, 23a, 23b ... Second metal layer, 22E ... First metal layer end face, 23E ... Second metal layer end face, 101 , 102 ... Ceramic circuit board.

Claims (5)

A ceramic base material and metal layers provided on both sides of the ceramic base material are provided, and the metal layer comprises a first metal layer containing Al and a second metal layer containing Cu in this order from the ceramic base material. Have and
At least one of the metal layers forms a metal circuit and
The thickness of the first metal layer is 0.1 to 3 mm, and the thickness is 0.1 to 3 mm.
After leaving it in an environment of 235 ° C for 30 minutes and then leaving it in an environment of −45 ° C for 30 minutes as one cycle, after a heat cycle test of 1000 cycles, the surface of the surface of the metal layer opposite to the ceramic substrate. A ceramic circuit board having a roughness Ra of 1 μm or less . The ceramic circuit board according to claim 1 _, wherein the ceramic substrate is made of AlN, Si 3N ₄ or Al ₂ O ₃ . The ceramic circuit board according to claim 1 or 2 , wherein the thickness of the ceramic substrate is 0.2 to 1.5 mm. The ceramic circuit board according to any one of claims 1 to 3 , wherein the metal layer has a thickness of 0.1 to 6 mm. Claim 1 in which the end face of the first metal layer and the end face of the second metal layer are flush with each other, or the end face of the first metal layer protrudes outside the end face of the second metal layer. The ceramic circuit board according to any one of 4 to 4 .

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