JP2024059207A - Metal-ceramic bonded substrate, manufacturing method thereof, and power module - Google Patents

Abstract

[Problem] To provide a large-sized metal-ceramic bonding substrate that is free of cracks and has little warping, and a method for manufacturing the same. [Solution] The metal-ceramic bonding substrate has one heat-dissipating Cu plate, a plurality of AlN substrates having one main surface bonded to one main surface of the heat-dissipating Cu plate via a brazing material, and a plurality of circuit pattern Cu plates bonded to the other main surface of each of the plurality of AlN substrates via a brazing material. [Selected Figure] Figure 1

Description

The present invention relates to a metal-ceramic bonded substrate, a method for manufacturing a metal-ceramic bonded substrate, and a power module.

Conventionally, metal-ceramic bonded substrates have often been used for the insulated circuit parts of power semiconductor devices (power modules) such as IGBT (Insulated Gate Bipolar Transistor) modules, in which a copper plate with a specified circuit pattern is bonded to one main surface of a ceramic substrate, and a copper plate on the heat dissipation side is bonded to the other main surface.

Figure 6 is a cross-sectional view explaining an example of a conventional power module (IGBT module). The lower surface of the semiconductor chip 100 in which the IGBT is built is bonded by high-temperature solder 700 onto the circuit pattern Cu plate 400 bonded to one main surface of the ceramic substrate 300 via the brazing material 600. The heat dissipation side Cu plate 500 is bonded to the other main surface of the ceramic substrate 300 via the brazing material 600. The ceramic substrate 300 is bonded to the Cu heat sink plate (Cu base plate) 200 via the heat dissipation side Cu plate 500 by low-temperature solder 800 such as eutectic solder. The electrodes formed on the upper surface of the semiconductor chip 100 and the circuit pattern Cu plate 400, and further, depending on the model, the electrodes (not shown) provided on the case (housing) of the power module and the circuit pattern Cu plate 400 are electrically connected by bonding wires (not shown) made of Al or the like.

In recent years, in order to simplify the assembly process of power modules, there is a demand for larger metal-ceramic substrates (for example, the surface area of the main surface of the heat-dissipating Cu plate is 25 ^cm2 or more).

Conventionally, when manufacturing large power modules for high power, for example, the heat dissipation side Cu plates of multiple metal-ceramic bonding substrates, to which semiconductor chips are bonded via high-temperature solder, are each soldered onto a large Cu heat sink plate (Cu base plate) using low-temperature solder, and then the electrodes of the semiconductor chips are connected to the circuit pattern Cu plate, and the circuit pattern Cu plate is connected to the electrodes formed on the case of the power module using bonding wires such as Al.

In this case, when mounting electronic components such as semiconductor chips, positioning and handling are required for each of the multiple metal-ceramic substrates. In addition, multiple metal-ceramic bonded substrates need to be soldered to the Cu heat sink plate with high positioning accuracy, which requires a positioning jig and a positioning process for each metal-ceramic bonded substrate. Therefore, there is a demand to increase the size of metal-ceramic bonded substrates, reduce steps such as positioning and handling in the assembly process, and improve production efficiency.

For example, Patent Document 1 discloses a silicon nitride circuit board in which metal plates are bonded to both sides of a silicon nitride substrate having a three-point bending strength of 500 MPa or more, where the thickness of the metal plate on the front side is t1 and the thickness of the metal plate on the back side is t2, and at least one of the thicknesses t1 and t2 is 0.6 mm or more, satisfying 0.10≦|t1-t2|≦0.30 mm, and the silicon nitride substrate has a warpage in the range of 0.1 to 0.5 mm in both the long side direction and the short side direction. This document discloses examples of ceramic substrates having a size of 25 ^cm2 or more, and even large substrates exceeding ¹⁰⁰ cm2.

Patent Publication No. WO2017/056666

However, as in Patent Document 1, when using a silicon nitride substrate, the thermal conductivity is lower than that of an aluminum nitride (AlN) substrate, and improvements in heat dissipation are required. In addition, when an AlN substrate with high thermal conductivity is used, there are problems such as the substrate cracking or large warping occurring after bonding, making it impossible to use as an insulating substrate, or causing problems with assembly such as mounting electronic components or soldering to a Cu heat sink plate. It has also been found that even with a high-strength AlN substrate with a three-point bending strength of 500 MPa or more (for example, about 590 MPa), the above problems occur when making a large metal-ceramic bonded substrate, possibly because the AlN substrate has inferior toughness compared to a silicon nitride substrate.

The present invention aims to provide a large metal-ceramic bonded substrate (copper (Cu)-aluminum nitride (AlN) bonded substrate) that has excellent heat dissipation and dielectric strength, is free of cracks after bonding, and has little warping, and a manufacturing method thereof, for use in semiconductor devices such as power modules that are equipped with a metal-ceramic bonded substrate in which a metal plate is bonded to a ceramic substrate.

The first aspect of the present invention is a method for producing a cellular membrane comprising the steps of:
One heat dissipation side Cu plate,
On one main surface of the heat dissipation side Cu plate,
A plurality of AlN substrates having one main surface bonded to each other via a brazing material;
On the other main surface of each of the plurality of AlN substrates,
A plurality of circuit pattern Cu plates joined via a brazing material;
The metal-ceramic bonding substrate has the following structure.

A second aspect of the present invention is a method for producing a composition comprising the steps of:
The area of the other main surface of the heat dissipation side Cu plate is 25 ^cm2 or more.
The metal/ceramic bonding substrate according to the first aspect.

A third aspect of the present invention is a method for producing a composition comprising the steps of:
The thickness of the heat dissipation side Cu plate and the circuit pattern Cu plate is 0.3 mm or more and 1.2 mm or less.
The metal/ceramic bonding substrate according to the first or second aspect.

A fourth aspect of the present invention is a method for producing a composition comprising the steps of:
The thermal conductivity of the plurality of AlN substrates is 100 W/(m·K) or more.
The metal/ceramic bonding substrate according to the first or second aspect.

A fifth aspect of the present invention is a method for producing a composition comprising the steps of:
The dielectric strength between the heat dissipation side Cu plate and the circuit pattern Cu plate is 2.5 kV or more;
a warpage conversion value on the other main surface of the heat-dissipating side Cu plate, expressed by the following formula (1), is 0 mm or more and 2.5×10 ⁻³ mm or less;
The metal/ceramic bonding substrate according to the first or second aspect.
Warpage conversion value (mm)=warpage amount of Cu plate on heat dissipation side (mm)×thickness of AlN substrate (mm)/diagonal length of Cu plate on heat dissipation side (mm) (1)

A sixth aspect of the present invention is a method for producing a composition comprising the steps of:
On one main surface of one Cu plate for forming a heat dissipation side Cu plate,
A plurality of AlN substrates are arranged with one main surface thereof interposed therebetween by a brazing material,
On the other main surface of each of the plurality of AlN substrates,
One main surface of each of a plurality of Cu plates for forming a circuit pattern Cu plate is arranged via a brazing material,
forming a laminate in which the Cu plate for forming the heat dissipation side Cu plate, the plurality of AlN substrates, and the plurality of Cu plates for forming the circuit pattern Cu plate are laminated in order via a brazing material;
After heating the laminate in a state where a stress of 0.001 kgf/ ^cm2 or more and 0.1 kgf/cm2 or ^less is applied in the thickness direction,
and cooling the laminate, and bonding the Cu plate for forming the heat dissipation side Cu plate, the plurality of AlN substrates, and the plurality of Cu plates for forming the circuit pattern Cu plate, respectively, via brazing material.

A seventh aspect of the present invention is a method for producing a composition comprising the steps of:
The method further includes a step of forming an etching resist corresponding to a predetermined circuit pattern on the other main surface of the Cu plate for forming the plurality of circuit pattern Cu plates bonded to the plurality of AlN substrates, and then removing a part of the Cu plate for forming the plurality of circuit pattern Cu plates by etching to form a plurality of circuit pattern Cu plates.
A method for producing the metal/ceramic bonding substrate according to the sixth aspect.

An eighth aspect of the present invention is a method for producing a composition comprising the steps of:
The method further includes a step of forming an etching resist having a predetermined shape on the other main surface of the Cu plate for forming the heat dissipation side Cu plate to which the plurality of AlN substrates are bonded, and then removing a part of the Cu plate for forming the heat dissipation side Cu plate by etching to form a heat dissipation side Cu plate.
A method for producing a metal/ceramic bonding substrate according to the sixth or seventh aspect.

A ninth aspect of the present invention is a method for producing a composition comprising the steps of:
The area of the other main surface of the heat dissipation side Cu plate is 25 ^cm2 or more.
A method for producing the metal/ceramic bonding substrate according to the eighth aspect.

A tenth aspect of the present invention is a method for producing a composition comprising the steps of:
The thickness of the plurality of circuit pattern Cu plates is 0.3 mm or more and 1.2 mm or less;
A method for producing the metal/ceramic bonding substrate according to the seventh aspect.

An eleventh aspect of the present invention is a method for producing a composition comprising the steps of:
The thickness of the heat dissipation side Cu plate is 0.3 mm or more and 1.2 mm or less.
A method for producing the metal/ceramic bonding substrate according to the eighth aspect.

A twelfth aspect of the present invention is a method for producing a composition comprising the steps of:
The thermal conductivity of the plurality of AlN substrates is 100 W/(m·K) or more.
A method for producing the metal/ceramic bonding substrate according to the sixth aspect.

A thirteenth aspect of the present invention is a method for producing a composition comprising the steps of:
A power module incorporating the metal/ceramic bonding substrate according to the first or second aspect.

The present invention provides a semiconductor device such as a power module that is equipped with a metal-ceramic bonded substrate in which a metal plate is bonded to a ceramic substrate, and a large metal-ceramic bonded substrate that has excellent heat dissipation and dielectric strength, is free of cracks after bonding, and has little warping, as well as a method for manufacturing the same.

FIG. 1( a ) is a cross-sectional view that typically shows one example of a metal-ceramic bonding substrate 1 according to a first embodiment of the present invention, FIG. 1( b ) is a top view that typically shows one example of a metal-ceramic bonding substrate 1 according to a first embodiment of the present invention, and FIG. 1( c ) is a bottom view that typically shows one example of a metal-ceramic bonding substrate 1 according to a first embodiment of the present invention. FIG. 2 is a flow chart showing an example of a method for manufacturing the metal/ceramic bonding substrate 1 according to the first embodiment of the present invention. FIG. 3 is an explanatory diagram showing the laminate formation step S101 in the first embodiment of the present invention. FIG. 4 is an explanatory diagram showing the bonding step S102 in the first embodiment of the present invention. FIG. 5 is a cross-sectional view that illustrates a schematic example of a metal/ceramic bonding substrate 2 according to another embodiment of the present invention. FIG. 6 is a cross-sectional view for explaining an example of a conventional power module (IGBT module).

[Details of the embodiment of the present invention]
Next, an embodiment of the present invention will be described below with reference to the drawings. Note that the present invention is not limited to these examples, but is defined by the claims, and is intended to include all modifications within the meaning and scope of the claims.

First Embodiment of the Present Invention
(1) Configuration of metal-ceramic bonding substrate First, the configuration of the metal-ceramic bonding substrate 1 of this embodiment will be described. Fig. 1(a) is a cross-sectional view that shows a schematic example of the metal-ceramic bonding substrate 1 of this embodiment, Fig. 1(b) is a top view that shows a schematic example of the metal-ceramic bonding substrate 1 of this embodiment, and Fig. 1(c) is a bottom view that shows a schematic example of the metal-ceramic bonding substrate 1 of this embodiment.

As shown in FIG. 1( a ), the metal-ceramic bonding substrate 1 of this embodiment includes one heat-dissipating-side Cu (copper) plate 50, a plurality of (e.g., two in FIG. 1 ) AlN (aluminum nitride) substrates 30 having one main surface bonded to one main surface of the heat-dissipating-side Cu (copper) plate 50 via a brazing material 60, and a plurality of (e.g., two in FIG. 1 ) circuit pattern Cu (copper) plates 40 bonded to the other main surfaces of each of the plurality of AlN (aluminum nitride) substrates 30 via the brazing material 60.
The main surface of the Cu plate or AlN substrate, which is a plate material, refers to the plate surface (a surface perpendicular to the thickness direction of the plate material, not a side surface), and there is a front main surface and a back main surface.

The heat dissipation side Cu plate 50 is made of, for example, a rolled Cu plate with high thermal conductivity and a purity of 99.9% by mass or more (preferably 99.99% by mass or more), and is used as a heat dissipation plate. In addition, it is preferable that the outer shape of the heat dissipation side Cu plate 50 is approximately rectangular.

The area (surface area) of the other main surface of the heat-dissipating-side Cu plate 50 (the side opposite to the surface to which the AlN substrate 30 is bonded) is preferably ²⁵ cm2 or more, and more preferably ⁵⁰ cm2 or more. This allows the metal-ceramic bonding substrate 1 to be made larger, and the steps of positioning and handling in the assembly process to be reduced, making it more efficient. The upper limit of the area of the other main surface of the heat-dissipating-side Cu plate 50 is not particularly limited, but may be, for example, ²⁰⁰ cm2 or less, or 150 ^cm2 or less.

The thickness of the heat dissipation side Cu plate 50 is preferably 0.3 mm or more and 1.2 mm or less, and more preferably 0.5 mm or more and 1.0 mm or less. This makes it possible to improve heat dissipation while suppressing cracking of the AlN substrate 30.

The AlN substrate 30 preferably has a thermal conductivity of 100 W/(m·K) or more, more preferably 130 W/(m·K) or more, and even more preferably 170 W/(m·K) or more. As a result, the Cu-AlN bonded substrate (metal-ceramic bonded substrate 1) of this embodiment can significantly improve heat dissipation compared to Cu-ceramic bonded substrates that use alumina substrates (commercially available mass-produced products have a thermal conductivity of about 20 W/(m·K)) or silicon nitride substrates (commercially available mass-produced products have a thermal conductivity of at most about 90 W/(m·K)) as the ceramic substrate.

The shape of the AlN substrate 30 is not particularly limited, but for example, a roughly rectangular shape is often used. The thickness of the AlN substrate 30 is, for example, 0.25 mm to 3.0 mm, preferably 0.3 mm to 2.0 mm, and more preferably 1.5 mm or less.

The circuit pattern Cu plate 40 is made of a rolled Cu plate with a purity of 99.9% by mass or more (preferably 99.99% by mass or more) and high electrical and thermal conductivity, and has a predetermined circuit pattern (for example, a substantially rectangular shape in FIG. 1). The circuit pattern Cu plate 40 is configured to mount a semiconductor chip or the like. In addition, the circuit pattern Cu plate 40 is preferably smaller in area than the AlN substrate 30, and multiple circuit pattern Cu plates 40 may be formed on the other main surface of one AlN substrate 30.

The thickness of the circuit pattern Cu plate 40 is preferably 0.3 mm or more and 1.2 mm or less, and more preferably 0.5 mm or more and 1.0 mm or less. A large thickness of the heat dissipation side Cu plate 50 and the circuit pattern Cu plate 40 is advantageous for heat dissipation. On the other hand, in the metal-ceramic bonding substrate 1 (Cu-AlN bonding substrate), if the Cu plate to be bonded is too thick, there is a risk of cracks occurring in the ceramic substrate (AlN substrate 30) after bonding, so the sum of the thicknesses of the heat dissipation side Cu plate 50 and (one) circuit pattern Cu plate 40 is preferably 0.6 mm or more and 2.0 mm or less, and more preferably 0.8 mm or more and 1.8 mm or less.
In order to suppress deterioration over time of the surface of the circuit pattern Cu plate 40 and/or the heat dissipation side Cu plate 50, a coating such as Ni or Ni alloy plating may be formed.
In addition, it is preferable that the dielectric strength between the heat-dissipating side Cu plate 50 and the circuit pattern Cu plate 40 is 2.5 kV or more.

The brazing material 60 is preferably an active metal-containing brazing material that is generally used to join metals and ceramics, and for example, Ag-Cu-Ti and Ag-Cu-Sn-Ti brazing materials can be used. In particular, it is preferable to use a brazing material with an active metal or other metal element added to a composition near the Ag-Cu eutectic. The thickness of the brazing material 60 is preferably 5 μm or more and 30 μm or less, and more preferably 10 μm or more and 20 μm or less.

In the metal-ceramic bonded substrate 1 of this embodiment shown in FIG. 1, two AlN substrates 30 are bonded to one heat dissipation side Cu plate 50 via a brazing material 60. That is, two AlN substrates 30 equipped with a circuit pattern Cu plate 40 are connected by the heat dissipation side Cu plate 50, and can be handled as one metal-ceramic bonded substrate 1 (Cu-AlN bonded substrate) in the manufacturing process of the power module. This contributes to the efficiency of the assembly process of the power module components, such as bonding a semiconductor chip to the other surface of the circuit pattern Cu plate 40, bonding a Cu heat sink plate (Cu base plate) to the other surface of the heat dissipation side Cu plate 50, and connecting the circuit pattern Cu plate 40 and the terminal of the case by wire bonding, and also makes it easy to keep the dimensional accuracy of positioning and the like within a predetermined range. In addition, three or more AlN substrates 30 equipped with circuit pattern Cu plates 40 may be bonded to one heat dissipation side Cu plate 50. In addition, from the viewpoint of suppressing cracking of the ceramic substrate and reducing warping, it is preferable to arrange the multiple AlN substrates 30 in line symmetry with respect to the (virtual) center line of the plate surface (main surface) of the heat dissipation side Cu plate 50, and it is preferable that the multiple AlN substrates 30 are the same size.

In the metal-ceramic bonding substrate 1 of this embodiment, it is preferable that the dielectric strength between the heat dissipation side Cu plate 50 and the circuit pattern Cu plate 40 is 2.5 kV or more, and the warpage equivalent value expressed by the following formula (1) on the other main surface of the heat dissipation side Cu plate 50 is 0 mm or more and 2.5 × 10 ^-3 mm or less.
Warpage conversion value (mm)=warpage amount (mm) of heat-dissipating-side Cu plate 50×thickness (mm) of AlN substrate 30/diagonal length (mm) of heat-dissipating-side Cu plate 50 (1)

In a conventional power module (IGBT module) such as that shown in FIG. 6, when the metal-ceramic bonding substrate is enlarged, cracking and warping of the ceramic substrate become an issue. In contrast, in the metal-ceramic bonding substrate 1 of this embodiment, multiple AlN substrates 30 (for example, two in FIG. 1) are bonded to a single heat dissipation Cu plate 50 via brazing material 60, thereby suppressing cracking of the ceramic substrate and realizing a metal-ceramic bonding substrate 1 with small warping despite its large area.

(2) Manufacturing Method of Metal-Ceramic Bonding Substrate Next, a manufacturing method of the metal-ceramic bonding substrate 1 of this embodiment will be described. Fig. 2 is a flow chart showing an example of a manufacturing method of the metal-ceramic bonding substrate 1 of this embodiment. As shown in Fig. 2, the manufacturing method of the metal-ceramic bonding substrate 1 of this embodiment includes, for example, a laminate formation step S101, a bonding step S102, and a pattern formation step S103.

(Laminate formation process S101)
As shown in FIG. 3, in the laminate formation process S101, for example, one main surface of a plurality of (e.g., two) AlN substrates 30 are arranged on one main surface of a single Cu plate 51 for forming a heat dissipation side Cu plate via a brazing material 60, and one main surface of a plurality of (e.g., two) Cu plates 41 for forming a circuit pattern Cu plate are arranged on the other main surface of each of the plurality of AlN substrates 30 via the brazing material 60 to form a laminate 5 in which the Cu plate 51 for forming the heat dissipation side Cu plate, the plurality of AlN substrates 30, and the plurality of Cu plates 41 for forming the circuit pattern Cu plate are sequentially stacked via the brazing material 60.

As the Cu plate 51 for forming the heat dissipation side Cu plate and the Cu plate 41 for forming the circuit pattern Cu plate, it is preferable to use, for example, a rolled Cu plate with a purity of 99.9% by mass or more (preferably 99.99% by mass or more) and high thermal conductivity and electrical conductivity.

The AlN substrate 30 preferably has a thermal conductivity of 100 W/(m·K) or more, more preferably 130 W/(m·K) or more, and even more preferably 170 W/(m·K) or more. The three-point bending strength of the AlN substrate 30 is preferably 450 MPa or more, and even more preferably 500 MPa or more. The shape of the AlN substrate 30 is not particularly limited, but for example, a roughly rectangular shape is often used. The thickness of the AlN substrate 30 is, for example, 0.25 mm or more and 3.0 mm or less, preferably 0.3 mm or more and 2.0 mm or less, and even more preferably 1.5 mm or less.

The brazing material 60 is an active metal-containing brazing material that is generally used to join metals and ceramics, and for example, Ag-Cu-Ti and Ag-Cu-Sn-Ti brazing materials can be used. In particular, it is preferable to use a brazing material in which an active metal or other metal element is added to a composition near the Ag-Cu eutectic. The brazing material 60 is preferably in the form of a paste or foil, and more preferably in the form of a paste. If the brazing material 60 is in the form of a paste, it can be applied to the AlN substrate 30 by a simple method such as screen printing. The thickness of the brazing material 60 is preferably 5 μm or more and 30 μm or less, and more preferably 10 μm or more and 20 μm or less.

(Joining step S102)
4, in the bonding process S102, the laminate 5 is placed on a lower base plate 70 made of a stainless steel plate such as SUS304, an upper base plate 71 made of a stainless steel plate such as SUS304 is placed on the laminate 5, and a weight (not shown) is placed on the upper base plate 71 as necessary, so that a stress of 0.001 kgf/ ^cm2 or more and 0.1 kgf/cm2 or less is applied in the thickness direction of the laminate 5 (with respect to the area of one main surface of the plurality of AlN substrates ³⁰ ). It is more preferable to set the load to 0.005 kgf/cm2 or ^more . In this stressed state, for example, the laminate 5 is inserted into a vacuum furnace and heated, and then cooled, and the Cu plate 51 for forming the heat dissipation side Cu plate, the plurality of AlN substrates 30, and the plurality of Cu plates 41 for forming the circuit pattern Cu plate are bonded via the brazing material 60.

The stress applied in the thickness direction of the laminate 5 in the bonding process S102 of the present invention is small, and there is no need to use a special pressure tool during bonding. In addition, by stacking multiple laminates 5 in the thickness direction of the laminate 5 with spacers such as ceramic substrates in between and then placing the upper base plate 71, it becomes possible to bond a large number of laminates 5 with good productivity, and mass production is also excellent.

(Pattern formation step S103)
In the pattern formation process S103, for example, an etching resist corresponding to a predetermined circuit pattern is formed on the main surface of each of the plurality of Cu plates 41 for forming the circuit pattern Cu plates bonded to the plurality of AlN substrates 30, and then a portion (unnecessary portion) of the plurality of Cu plates 41 for forming the circuit pattern Cu plates (and/or the brazing material 60) is removed by etching to form the plurality of circuit pattern Cu plates 40.

In the pattern formation process S103, for example, an etching resist of a predetermined shape (a shape corresponding to the shape of the heat dissipation side Cu plate 50) is formed on the other main surface of the Cu plate 51 for forming the heat dissipation side Cu plate to which multiple AlN substrates 30 are bonded, and then a part (unnecessary part) of the Cu plate 51 for forming the heat dissipation side Cu plate (and/or the brazing material 60) is removed by etching to form the heat dissipation side Cu plate 50. If necessary, an etching resist of a predetermined shape may also be formed on one of the main surfaces of the Cu plate 51 for forming the heat dissipation side Cu plate.

In the pattern formation process S103, it is preferable to form the heat-dissipation-side Cu plate 50 so that the area of the other main surface of the heat-dissipation-side Cu plate 50 is 25 ^cm2 or more. It is also preferable to form the heat-dissipation-side Cu plate 50 so that the thickness of the heat-dissipation-side Cu plate 50 is 0.3 mm or more and 1.2 mm or less. It is also preferable to form the multiple circuit pattern Cu plates 40 so that the thickness of the multiple circuit pattern Cu plates 40 is 0.3 mm or more and 1.2 mm or less.

By carrying out the above steps, the metal-ceramic bonding substrate 1 of this embodiment can be manufactured.

<Other embodiments of the present invention>
Although the embodiment of the present invention has been specifically described above, the present invention is not limited to the above-mentioned embodiment, and various modifications can be made without departing from the gist of the present invention.

For example, in the above embodiment, as shown in FIG. 1(c), the case where the heat dissipation side Cu plate 50 is smaller than the outer periphery of the AlN substrate 30 has been described. FIG. 5 is a cross-sectional view showing an example of a metal-ceramic bonding substrate 2 (Cu-AlN substrate) according to another embodiment of the present invention. The difference from the above-mentioned first embodiment is that the heat dissipation side Cu plate 50 is larger than the outer periphery of the AlN substrate 30 when viewed from a direction perpendicular to the main surface of the circuit pattern Cu plate 40 (from above). The metal-ceramic bonding substrate 2 of this embodiment may have a Cu heat sink plate (Cu base plate) bonded to the other surface of the heat dissipation side Cu plate 50 as in the first embodiment, or the heat dissipation side Cu plate 50 itself may be substituted for the Cu base plate. In the latter case, soldering between the Cu base plate and the metal-ceramic substrate can be omitted.

Next, examples of the present invention will be described. These examples are merely examples of the present invention, and the present invention is not limited to these examples.

[Example 1]
(Laminate Forming Process)
As the ceramic substrate, two rectangular aluminum nitride substrates (AlN substrates with a thermal conductivity of 170 W/(m·K) or more, a three-point bending strength of 588 MPa, and a deflection at break of 0.659 mm in a three-point bending strength test) with a length of 48 mm, a width of 58 mm, and a thickness of 0.38 mm were prepared. In addition, two rectangular oxygen-free Cu plates with a length of 50 mm, a width of 60 mm, and a thickness of 0.8 mm were prepared as the Cu plates for forming the circuit pattern Cu plates, and one oxygen-free copper plate with a length of 100 mm, a width of 60 mm, and a thickness of 0.6 mm was prepared as the Cu plate for forming the heat dissipation side Cu plate. In addition, the brazing material was prepared as a metal powder (total of 100 mass%) consisting of 10 mass% Cu powder, 5 mass% Sn powder, 2 mass% Ti powder (as an active metal component), and the remainder Ag powder. A vehicle consisting of an acrylic binder and a solvent was added to these metal powders and kneaded to prepare a paste-like brazing material containing active metals.

The brazing material was applied to almost the entire front and back surfaces of the AlN substrate by screen printing to a thickness of 20 μm, and then dried to form brazing material on both sides of the AlN substrate.

The two AlN substrates on which the brazing material was formed were arranged (at the center of the Cu plate for forming the heat-dissipating side Cu plate) with a gap of 2 mm (as shown in FIG. 3) on one surface (main surface) of the Cu plate for forming the heat-dissipating side Cu plate. In other words, the entire surface of one surface (main surface) of the two AlN substrates was in contact with one surface (main surface) of the Cu plate for forming the heat-dissipating side Cu plate via the brazing material. Next, the two Cu plates for forming the circuit pattern Cu plate were arranged so that the entire surface of the other surface (main surface) of the two AlN substrates on which the brazing material was formed was covered, and a laminate consisting of the Cu plate for forming the heat-dissipating side Cu plate, the AlN substrate, and the Cu plate for forming the circuit pattern Cu plate was obtained.

(Joining process)
Next, (as shown in FIG. 4 ) the above laminate was placed (mounted) on a lower stainless steel plate (lower base plate) made of SUS304 so that the other surface of the Cu plate for forming the heat dissipation side Cu plate was in contact with it, and further an upper stainless steel plate (upper base plate) made of SUS304 was placed (mounted) on the laminate, and the laminate was heated to 850° C. in a vacuum while a stress of 0.01 kgf/cm ² was applied in the thickness direction of the laminate (with respect to the main surface of the AlN substrate) (a state in which the weight of the upper stainless steel plate was applied), and then cooled, thereby bonding the Cu plate for forming the heat dissipation side Cu plate and the Cu plate for forming the circuit pattern Cu plate to both surfaces of the AlN substrate.

(Pattern Forming Process)
Next, a (substantially rectangular) ultraviolet-curing alkaline peelable resist corresponding to the shape of the specified heat-dissipating-side Cu plate was applied by screen printing to the surface (other main surface) of the Cu plate for forming the heat-dissipating-side Cu plate bonded to the AlN substrate. Also, the above resist corresponding to the shape of the specified circuit-pattern Cu plate (circuit-shaped, approximately rectangular in this embodiment) was applied by screen printing to the surface (other main surface) of the Cu plate for forming the circuit pattern Cu plate bonded to the other surface of the AlN substrate.

After these resists were hardened by irradiating them with ultraviolet light, unnecessary parts of the Cu plate were etched using an etching solution consisting of copper chloride, hydrochloric acid, and the remaining part water. The resist was then removed using an aqueous solution of sodium hydroxide. Next, unnecessary brazing material remaining on the surface of the AlN substrate was removed using a known etching solution containing EDTA (ethylenediaminetetraacetic acid). The surface of the Cu plate was then chemically polished using a commercially available chemical polishing solution to remove any unevenness in the appearance of the surface, and the heat dissipation side Cu plate and the circuit pattern Cu plate were formed.

As a result of the above, a metal-ceramic bonding substrate was obtained in which two AlN substrates were bonded onto a roughly rectangular heat dissipation side Cu plate measuring 96 mm in length, 56 mm in width, and 0.6 mm in thickness, and a roughly rectangular circuit pattern Cu plate measuring 46 mm in length, 56 mm in width, and 0.8 mm in thickness was formed on the surfaces (other faces) of the two AlN substrates.
As shown in FIG. 1, the minimum distance W1 between the end of the circuit pattern Cu plate and the end of the AlN substrate was 1 mm, and the minimum distance W2 between the end of the heat dissipation side Cu plate and the end of the AlN substrate (excluding the side where the side surfaces of the AlN substrate face each other) was 1 mm.

(evaluation)
Cracks in the Substrate When the obtained metal/ceramic bonding substrate was visually observed, no cracks were found in the ceramic substrate.
Dielectric strength: Electrodes were provided on the circuit pattern Cu plate (front side) and the heat dissipation side Cu plate (back side) of this metal-ceramic bonding substrate, and the AC voltage applied between these electrodes (front and back) in the atmosphere was gradually increased and the voltage at which a leakage current of 1 mA or more flowed was measured as the dielectric strength. No dielectric breakdown occurred even at 2.5 kV, and the dielectric strength was 2.5 kV or more.
When a voltage of 2.5 kV was applied, a rating of O (dielectric strength 2.5 kV or more) was given if the insulation was maintained, and a rating of X (dielectric strength less than 2.5 kV) was given if the insulation was destroyed. This example was rated as O (dielectric strength 2.5 kV or more).
Amount of warpage: Using a KEYENCE 3D one-shot measuring device (VR-5000), the height data of the surface (other main surface) of the heat dissipation side Cu plate of the metal-ceramic bonding substrate was measured over the entire surface. Using the software attached to the device, a flat reference plane was set from each height data using the least squares method, and each height data was corrected so that the set reference plane was horizontal, and further offset in the height direction so that the height of the reference plane became 0. Using the height data corrected and offset by the processing of the software, height data of the diagonal of the approximately rectangular heat dissipation side Cu plate was obtained. The maximum and minimum differences of the height data on the two diagonals of this heat dissipation side Cu plate were calculated, and the larger of the two was taken as the amount of warpage of the metal-ceramic bonding substrate. As a result, the amount of warpage was 0.652 mm, which was good.
Using the amount of warpage (mm) of the other main surface of the heat-dissipating-side Cu plate calculated above, the thickness (mm) of the AlN substrate, and the diagonal length (mm) of the heat-dissipating-side Cu plate, the value expressed by the following formula (1) was determined as the equivalent warpage value. As a result, the equivalent warpage value was 2.2×10 ⁻³ mm.
In Example 1, the amount of warping of the other main surface of the heat-dissipating Cu plate is 0.652 mm, the thickness of the AlN substrate is 0.38 mm, and the diagonal length of the heat-dissipating Cu plate is 111.14 mm.
Warpage conversion value (mm)=warpage amount of Cu plate on heat dissipation side (mm)×thickness of AlN substrate (mm)/diagonal length of Cu plate on heat dissipation side (mm) (1)

[Comparative Example 1]
A metal-ceramic bonded substrate was produced in the same manner as in Example 1, except that the stress applied in the thickness direction of the laminate during bonding (with respect to the main surface of the AlN substrate) was 4.17 kgf/ ^cm2 . The stress was applied to the laminate by using a jig that tightened bolts between the upper and lower stainless steel plates on which the laminate was placed. Specifically, holes were formed in the four corners of the upper and lower stainless steel plates, and bolts were passed through the holes in the upper and lower stainless steel plates and tightened with nuts.

When the obtained metal-ceramic bonding substrate was visually observed in the same manner as in Example 1, cracks were confirmed in the ceramic substrate, and the dielectric strength between the front and back Cu plates was × (less than 2.5 kV). Furthermore, when the amount of warping and the equivalent value of warping were evaluated in the same manner as in Example 1, the amount of warping was 0.620 mm, and the equivalent value of warping was 2.1×10 ⁻³ mm.

[Comparative Example 2]
(Laminate Forming Process)
As the ceramic substrate, one approximately rectangular aluminum nitride substrate (AlN substrate with thermal conductivity of 170 W/(m·K) or more, three-point bending strength of 588 MPa, and deflection at break in a three-point bending strength test of 659 μm) with a length of 96 mm, a width of 58 mm, and a thickness of 0.38 mm was prepared. In addition, as the Cu plate for forming the circuit pattern Cu plate, one approximately rectangular oxygen-free Cu plate with a length of 100 mm, a width of 60 mm, and a thickness of 0.8 mm was prepared, and as the Cu plate for forming the heat dissipation side Cu plate, one oxygen-free Cu plate with a length of 100 mm, a width of 60 mm, and a thickness of 0.6 mm was prepared.

The brazing material was applied to almost the entire front and back surfaces of the AlN substrate by screen printing to a thickness of 20 μm, and then dried to form brazing material on both sides of the AlN substrate.

One AlN substrate on which the brazing material was formed was placed in the center of one surface of the Cu plate for forming the heat dissipation side Cu plate. In other words, the entire surface of one surface of the AlN substrate was in contact with one surface of the Cu plate for forming the heat dissipation side Cu plate via the brazing material. Next, one Cu plate for forming the circuit pattern Cu plate was placed so that the entire surface of the other side of the one AlN substrate on which the brazing material was formed was covered, and a laminate was obtained consisting of the Cu plate for forming the heat dissipation side Cu plate, the AlN substrate, and the Cu plate for forming the circuit pattern Cu plate.

(Joining process)
Next, the above-mentioned laminate was placed on a lower stainless steel plate made of SUS304 so that the other surface of the Cu plate for forming the heat dissipation side Cu plate was in contact with the laminate, and an upper stainless steel plate made of SUS304 was placed on the laminate. The laminate was then heated to 850°C in a vacuum while being subjected to a stress of 0.01 kgf/ ^cm2 in the thickness direction of the laminate (with respect to the main surface of the AlN substrate) (a state in which the weight of the upper stainless steel plate was applied), and then cooled, thereby bonding the Cu plates to both surfaces of the AlN substrate.

(Pattern Forming Process)
Next, a UV-curable alkaline peelable resist (approximately rectangular) corresponding to the shape of the heat-dissipating Cu plate was applied by screen printing to the surface of the Cu plate for forming the heat-dissipating Cu plate bonded to the AlN substrate. Also, the above resist (circuit-shaped, approximately rectangular in this embodiment) corresponding to the shape of the predetermined circuit pattern was applied by screen printing to the surface of the Cu plate for forming the circuit pattern Cu plate bonded to the other side of the AlN substrate.

After these resists were hardened by irradiating them with ultraviolet light, unnecessary parts of the Cu plate were etched using an etching solution consisting of copper chloride, hydrochloric acid, and the remainder water, and the resist was removed using an aqueous sodium hydroxide solution. Next, unnecessary brazing material remaining on the surface of the AlN substrate was removed using a known etching solution containing EDTA (ethylenediaminetetraacetic acid), forming the heat dissipation side Cu plate and the circuit pattern Cu plate.

As a result of the above, a metal-ceramic bonded substrate was obtained in which one AlN substrate was bonded onto a roughly rectangular heat-dissipating Cu plate measuring 96 mm in length, 56 mm in width, and 0.6 mm in thickness, and a roughly rectangular circuit pattern Cu plate measuring 96 mm in length, 56 mm in width, and 0.8 mm in thickness was formed on the surface (other side) of the one AlN substrate.

(evaluation)
The obtained metal-ceramic bonding substrate was visually observed to find no cracks in the ceramic substrate, and the dielectric strength between the front and back Cu plates was ◯ (2.5 kV or more). Furthermore, when the amount of warping and the equivalent warping value were evaluated in the same manner as in Example 1, the amount of warping was 1.031 mm, and the equivalent warping value was 3.5×10 ⁻³ mm, which means that the warping was large and poor.

[Comparative Example 3]
A metal-ceramic bonded substrate was produced in the same manner as in Comparative Example 2, except that the stress applied in the thickness direction of the laminate during bonding (with respect to the main surface of the AlN substrate) was 4.17 kgf/ ^cm2 . The stress was applied to the laminate by fastening bolts between the upper and lower stainless steel plates on which the laminate was placed. Specifically, holes were formed in the four corners of the upper and lower stainless steel plates, and bolts were passed through the holes in the upper and lower stainless steel plates and fastened with nuts.

When the obtained metal-ceramic bonding substrate was visually observed in the same manner as in Example 1, cracks were confirmed in the ceramic substrate, and the dielectric strength between the front and back Cu plates was × (less than 2.5 kV). Furthermore, when the amount of warping and the equivalent value of warping were evaluated in the same manner as in Example 1, the amount of warping was 0.672 mm, and the equivalent value of warping was 2.3×10 ⁻³ mm.

[Example 2]
A metal-ceramic bonding substrate was produced in the same manner as in Example 1, except that two approximately rectangular aluminum nitride substrates (AlN substrates having a thermal conductivity of 170 W/(m K) or more, a three-point bending strength of 593 MPa, and a deflection at break of 0.467 mm in a three-point bending strength test) measuring 48 mm in length, 58 mm in width, and 0.635 mm in thickness were used as the ceramic substrates.

The obtained metal-ceramic bonding substrate was visually observed in the same manner as in Example 1, and no cracks were found in the ceramic substrate, and the dielectric strength between the front and back Cu plates was good (2.5 kV or more). Furthermore, when the amount of warping and the equivalent warping value of the metal-ceramic substrate were evaluated in the same manner as in Example 1, the amount of warping was 0.273 mm, and the equivalent warping value was 1.6× ^10-3 mm, which was small and good.

[Comparative Example 4]
A metal-ceramic bonded substrate was produced in the same manner as in Example 2, except that the stress applied in the thickness direction of the laminate during bonding (with respect to the main surface of the AlN substrate) was 4.17 kgf/ ^cm2 . The stress was applied to the laminate by fastening bolts between the upper and lower stainless steel plates on which the laminate was placed. Specifically, holes were formed in the four corners of the upper and lower stainless steel plates, and bolts were passed through the holes in the upper and lower stainless steel plates and fastened with nuts.

When the obtained metal-ceramic bonding substrate was visually observed in the same manner as in Example 1, cracks were confirmed in the ceramic substrate, and the dielectric strength between the front and back Cu plates was × (less than 2.5 kV). Furthermore, when the amount of warping and the equivalent value of warping were evaluated in the same manner as in Example 1, the amount of warping was 0.149 mm, and the equivalent value of warping was 0.9×10 ⁻³ mm.

[Comparative Example 5]
A metal-ceramic bonding substrate was produced in the same manner as in Comparative Example 2, except that a roughly rectangular aluminum nitride substrate (AlN substrate with a thermal conductivity of 170 W/m·K or more) measuring 96 mm in length, 58 mm in width, and 0.635 mm in thickness was used as the ceramic substrate.

(evaluation)
The obtained metal-ceramic bonding substrate was visually observed to find no cracks in the ceramic substrate, and the dielectric strength between the front and back Cu plates was ◯ (2.5 kV or more). Furthermore, when the amount of warping and the equivalent warping value were evaluated in the same manner as in Example 1, the amount of warping was 0.526 mm, and the equivalent warping value was 3.0×10 ⁻³ mm, which means that the warping was large and poor.

[Comparative Example 6]
A metal-ceramic bonded substrate was produced in the same manner as in Comparative Example 5, except that the stress applied in the thickness direction of the laminate during bonding (with respect to the main surface of the AlN substrate) was 4.17 kgf/ ^cm2 . The stress was applied to the laminate by fastening bolts between the upper and lower stainless steel plates on which the laminate was placed. Specifically, holes were formed in the four corners of the upper and lower stainless steel plates, and bolts were passed through the holes in the upper and lower stainless steel plates and fastened with nuts.

The obtained metal-ceramic bonding substrate was visually observed to find no cracks in the ceramic substrate, and the dielectric strength between the front and back Cu plates was rated as "good" (2.5 kV or more). Furthermore, when the amount of warping and the equivalent warping value were evaluated in the same manner as in Example 1, the amount of warping was 0.555 mm, and the equivalent warping value was 3.2× ^10-3 mm, which were large.

[Example 3]
A metal-ceramic bonding substrate was produced in the same manner as in Example 1, except that the stress applied in the thickness direction of the laminate during bonding (to the main surface of the AlN substrate) was 0.03 kgf/ ^cm2 . The stress applied to the laminate was adjusted by placing a weight on the upper base plate.

The obtained metal-ceramic bonding substrate was visually observed in the same manner as in Example 1, and no cracks were found in the ceramic substrate, and the dielectric strength between the front and back Cu plates was O (2.5 kV or more). Furthermore, when the amount of warping and the equivalent warping value were evaluated in the same manner as in Example 1, the amount of warping was 0.664 mm, and the equivalent warping value was 2.3× ^10-3 mm.

[Example 4]
A metal-ceramic bonding substrate was produced in the same manner as in Example 2, except that the stress applied in the thickness direction of the laminate during bonding (with respect to the main surface of the AlN substrate) was 0.03 kgf/ ^cm2 . The stress applied to the laminate was adjusted by placing a weight on the upper base plate.

The obtained metal-ceramic bonding substrate was visually observed in the same manner as in Example 1, and no cracks were found in the ceramic substrate, and the dielectric strength between the front and back Cu plates was O (2.5 kV or more). Furthermore, when the amount of warping was evaluated in the same manner as in Example 1, the amount of warping was 0.382 mm, and the equivalent warping value was 2.2× ¹⁰

From the above, it was confirmed that by bonding multiple AlN substrates (two in this example) to one heat dissipation Cu plate using brazing material, it is possible to realize a metal-ceramic bonded substrate with small warping and suppressing cracking of the ceramic substrate, even though it is large in area.

Reference Signs List 1, 2 Metal-ceramic bonding substrate 5 Laminated body 30 AlN substrate 40 Circuit pattern Cu plate 41 Circuit pattern Cu plate forming Cu plate 50 Heat dissipation side Cu plate 51 Heat dissipation side Cu plate forming Cu plate 60 Brazing material 70 Lower base plate 71 Upper base plate 100 Semiconductor chip 200 Cu heat sink plate (Cu base plate)
300 Ceramic substrate 400 Circuit pattern Cu plate 500 Heat dissipation side Cu plate 600 Brazing material 700 High temperature solder 800 Low temperature solder S101 Laminate formation process S102 Bonding process S103 Pattern formation process

Claims (13)

One heat dissipation side Cu plate,
On one main surface of the heat dissipation side Cu plate,
A plurality of AlN substrates having one main surface bonded to each other via a brazing material;
On the other main surface of each of the plurality of AlN substrates,
A plurality of circuit pattern Cu plates joined via a brazing material;
A metal-ceramic bonding substrate having the above structure. The area of the other main surface of the heat dissipation side Cu plate is 25 ^cm2 or more.
2. The metal/ceramic bonding substrate according to claim 1. The thickness of the heat dissipation side Cu plate and the circuit pattern Cu plate is 0.3 mm or more and 1.2 mm or less.
3. The metal/ceramic bonding substrate according to claim 1 or 2. The thermal conductivity of the plurality of AlN substrates is 100 W/(m·K) or more.
3. The metal/ceramic bonding substrate according to claim 1 or 2. The dielectric strength between the heat dissipation side Cu plate and the circuit pattern Cu plate is 2.5 kV or more;
a warpage conversion value on the other main surface of the heat-dissipating side Cu plate, expressed by the following formula (1), is 0 mm or more and 2.5×10 ⁻³ mm or less;
3. The metal/ceramic bonding substrate according to claim 1 or 2.
Warpage conversion value (mm)=warpage amount of Cu plate on heat dissipation side (mm)×thickness of AlN substrate (mm)/diagonal length of Cu plate on heat dissipation side (mm) (1) On one main surface of one Cu plate for forming a heat dissipation side Cu plate,
A plurality of AlN substrates are arranged with one main surface thereof interposed therebetween by a brazing material,
On the other main surface of each of the plurality of AlN substrates,
One main surface of each of a plurality of Cu plates for forming a circuit pattern Cu plate is arranged via a brazing material,
forming a laminate in which the Cu plate for forming the heat dissipation side Cu plate, the plurality of AlN substrates, and the plurality of Cu plates for forming the circuit pattern Cu plate are laminated in order via a brazing material;
After heating the laminate in a state where a stress of 0.001 kgf/ ^cm2 or more and 0.1 kgf/cm2 or ^less is applied in the thickness direction,
and cooling the laminate, and bonding the Cu plate for forming the heat dissipation side Cu plate, the plurality of AlN substrates, and the plurality of Cu plates for forming the circuit pattern Cu plate via brazing material. The method further includes a step of forming an etching resist corresponding to a predetermined circuit pattern on the other main surface of the Cu plate for forming the plurality of circuit pattern Cu plates bonded to the plurality of AlN substrates, and then removing a part of the Cu plate for forming the plurality of circuit pattern Cu plates by etching to form a plurality of circuit pattern Cu plates.
The method for producing a metal/ceramic bonding substrate according to claim 6. The method further includes a step of forming an etching resist having a predetermined shape on the other main surface of the Cu plate for forming the heat dissipation side Cu plate to which the plurality of AlN substrates are bonded, and then removing a part of the Cu plate for forming the heat dissipation side Cu plate by etching to form a heat dissipation side Cu plate.
The method for producing a metal/ceramic bonding substrate according to claim 6 or 7. The area of the other main surface of the heat dissipation side Cu plate is 25 ^cm2 or more.
The method for producing a metal/ceramic bonding substrate according to claim 8. The thickness of the plurality of circuit pattern Cu plates is 0.3 mm or more and 1.2 mm or less;
The method for producing a metal/ceramic bonding substrate according to claim 7. The thickness of the heat dissipation side Cu plate is 0.3 mm or more and 1.2 mm or less.
The method for producing a metal/ceramic bonding substrate according to claim 8. The thermal conductivity of the plurality of AlN substrates is 100 W/(m·K) or more.
The method for producing a metal/ceramic bonding substrate according to claim 6. 3. A power module incorporating the metal/ceramic bonding substrate according to claim 1 or 2.