JP2002373955A - Power module substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power module substrate in which a ceramic basic material is not cracked even if a metallic brazing material is employed for bonding the ceramic basic material and a copper plate and for bonding the ceramic basic material and a heat sink plate. SOLUTION: In a power module substrate 10 where a heat sink plate 12 is formed on one surface and a circuit is formed on the other surface through metallization pattern layers 14 and 15 formed on the opposite sides of a ceramic basic material 11 or a copper plate 13 to be formed is bonded using metallic brazing materials 16 and 16a, the ceramic basic material 11 has non-bonded regions A18 and 18a extending from the outer circumferential end part 17 of the ceramic basic material 11 to the inside of the opposite surfaces.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power module substrate for mounting a semiconductor element which generates a large amount of heat, and more particularly, to reducing internal stress generated when a ceramic substrate is joined to a copper plate and a heat sink plate. It relates to a power module substrate.

[0002]

2. Description of the Related Art Power transistors used in the field of power electronics such as inverters and servo motors,
2. Description of the Related Art A power module in which an insulated gate bipolar transistor or the like is modularized uses a power module substrate in which a ceramic substrate having insulation and heat dissipation functions, a copper plate, and a heat sink plate are joined. A conventional power module substrate includes a copper plate on which a circuit is formed in advance by punching or etching on a front surface side of a ceramic base material made of aluminum nitride, and a copper plate having no circuit on the entire back surface. These copper plates are applied to a ceramic substrate,
For example, active metal brazing or DBC (Direct B
In this case, a heat sink plate made of copper was joined to the copper plate joined to the back surface side of the ceramic base material by using a solder without using a metallized layer. However, since solder is used for joining with the heat sink plate, for example, -65 to 150 ° C.
The temperature cycle test described above causes a problem that the solder deteriorates and the heat dissipation of the power module substrate is reduced.

Therefore, as shown in FIG. 4, a power module substrate 50 is formed by firstly forming a metallized pattern layer 53 having a pattern slightly larger than that of a circuit copper plate 52 on the upper surface of a ceramic base material 51 made of aluminum nitride. A metallized pattern layer 54 is formed using tungsten or the like on the entire lower surface of the ceramic substrate 51 in accordance with the outer dimensions of the ceramic substrate 51. Next, a circuit copper plate 52 is formed on the metallized pattern layer 53 on the upper surface side by using Au-Sn brazing material or A-Sn brazing material.
The joining is performed using a metal brazing material 55 made of g-Cu brazing or the like. Similarly, on the lower surface side of the ceramic base material 51, a heat sink plate 56 is
Metal brazing material 5 made of u-Sn brazing, Ag-Cu brazing, etc.
5. The heat sink plate 56 used here uses the metal brazing material 55 for joining with the ceramic base material 51. Therefore, in consideration of warpage at the time of joining by brazing, molybdenum having a thermal expansion coefficient similar to that of aluminum nitride is used. It is formed using. The ceramic base material 51, the circuit copper plate 52, and the metal brazing material 55 of the heat sink plate 56
Can be brazed all at once,
In some cases, brazing is performed twice.

[0004]

However, the above-mentioned conventional power module substrate has the following problems. In joining the ceramic base and the circuit copper plate, and the ceramic base and the heat sink plate made of molybdenum, since the metallized pattern layer of tungsten or the like is formed up to the end of the ceramic base, Ag-Cu
A metal brazing material such as brazing or Au-Sn brazing is also formed up to the end of the ceramic base material. Since metal brazing materials such as Ag-Cu brazing and Au-Sn brazing are materials that are not easily plastically deformed,
The difference in thermal expansion coefficient between the ceramic substrate such as aluminum nitride and the heat sink plate made of a copper plate, molybdenum or the like cannot be absorbed, and stress acts on the ceramic substrate to cause cracks at the ends of the ceramic substrate. The present invention has been made in view of such circumstances, and it is possible to generate a crack in a ceramic base even when a metal brazing material is used for joining a ceramic base and a copper plate, and a ceramic base and a heat sink plate. The aim is to provide a power module board without any.

[0005]

A power module substrate according to the present invention, which meets the above object, has a heat sink plate on one surface and a circuit board on the other surface via metallized pattern layers formed on both surfaces of a ceramic substrate. In a power module substrate in which a copper plate on which is formed or formed is bonded using a metal brazing material, the ceramic base has a non-bonded region A from the outer peripheral end of the ceramic base to the inside of both surfaces. Thereby, the metallized pattern layer and the metal brazing material are not formed up to the end of the surface of the ceramic base material, and even if the plastic deformation of the metal brazing material is small, the stress concentration of the ceramic base material can be reduced, so that the ceramic The generation of cracks from the end of the substrate can be prevented.

Here, the copper plate preferably has at least a non-joining region portion B protruding further outward from a joint portion between the copper plate and the ceramic base material and facing the non-joining region portion A of the ceramic base material. As a result, the bonding area between the copper plate and the ceramic substrate can be reduced, and the difference in the coefficient of thermal expansion between the ceramic substrate and the copper plate can be reduced, so that the stress on the ceramic substrate can be reduced. Cracks can be prevented from occurring. Further, when the circuit copper plate is formed by etching, it can be easily formed without requiring time for alignment.

[0007] Each circuit copper plate forming a circuit of the copper plate preferably has a non-joining region C over the entire periphery of the circuit copper plate and is joined to the ceramic base material. As a result, the bonding area between the copper plate and the ceramic substrate can be further reduced, and the difference in thermal expansion coefficient between the ceramic substrate and the copper plate can be reduced. The occurrence of cracks in the material can be prevented.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be described with reference to the accompanying drawings to provide an understanding of the present invention. 1A and 1B are a cross-sectional view and a plan view, respectively, of a power module substrate according to an embodiment of the present invention, and FIG. 2 is a partially enlarged cross-sectional view of a modified example of the power module substrate. FIG. 3 is a partially enlarged sectional view of another modified example of the power module substrate.

As shown in FIGS. 1A and 1B, a power module substrate 10 according to one embodiment of the present invention has a ceramic substrate 11 made of aluminum nitride. The ceramic substrate can be formed using silicon nitride, aluminum nitride, boron nitride, alumina, or a composite material containing these components, such as mullite or cordierite, as a main component. Preferred are alumina and aluminum nitride, with aluminum nitride being most suitable as the ceramic substrate. On the ceramic base material 11, a copper plate 13 for forming a circuit on the upper surface side via a metallized pattern layer
Bonded using a metal brazing material 16 such as g-Cu brazing or Au-Sn brazing, and connecting the heat sink plate 12 to a metal brazing material 16a such as Ag-Cu brazing or Au-Sn brazing via a metallized pattern layer 15 on the lower surface side. To form the power module substrate 10. Copper plate 1 with circuit formed
A semiconductor element is mounted at a predetermined position on 3 and functions as a power module.

In joining the ceramic base 11 and the copper plate 13, and the ceramic base 11 and the heat sink plate 12, a non-joined area portion that is not joined from the outer peripheral end 17 of the ceramic base 11 to the inside of the upper surface side. (Non-joining area portion A) 18 and outer peripheral end portion 1 of ceramic base material 11
A non-joining region portion (non-joining region portion A) 18a that is not joined is provided from 7 to the inner surface on the lower surface side.
These non-joining region portions 18 and 18a provided from the outer peripheral end portion 17 of the ceramic base 11 to the inside of both surfaces.
As a result, the occurrence of cracks at the corners of the end portions of the ceramic base material 11 is prevented, the highly reliable power module substrate 10 can be formed, and the heat generated from the semiconductor elements can be efficiently radiated from the heat sink plate 12. Can operate normally.

Next, a method of manufacturing the power module substrate 10 according to one embodiment of the present invention will be described. First, a ceramic base material 11 is prepared by adding a plasticizer, a binder, and a solvent to a powder obtained by adding an appropriate amount of a sintering aid to ceramic powder for forming aluminum nitride, kneading the mixture sufficiently, and defoaming to prepare a slurry. Then, it is formed from a ceramic green sheet in a roll shape having a desired thickness, for example, 0.1 to 1.0 mm, by an ordinary doctor blade method or the like.

[0012] The roll-shaped ceramic green sheet is
A metallized pattern for joining the copper plate 13 and the heat sink plate 12 with the metal brazing materials 16 and 16a is cut on the obtained blank ceramic green sheet by cutting to a desired appropriate size. Are formed on both surfaces by screen printing or the like, and the ceramic green sheet and the high melting point metal are simultaneously fired to form the ceramic base material 11 having the metallized pattern layers 14 and 15. The metallized pattern layers 14, 15
In the formation of the outer peripheral end portion 17 of the ceramic base material 11,
To the inside of both surfaces from which the metallized pattern layers 14 and 15 having a width of about 0.1 to 2.0 mm are not formed, that is, the non-bonded region portions (non-bonded region portions A) 18 and 1
8a are provided. In addition, as a method of forming the non-joining region portions (non-joining region portions A) 18 and 18a, an insulating paste of the same material as that of the ceramic green sheet is used and formed by screen printing so as to cover the end of the large metallized pattern. You can also. In order to make the ceramic substrate 11 have a desired thickness, two ceramic green sheets are formed and bonded so that the metallized pattern layers 14 and 15 are on the outer surface of the ceramic substrate 11. In order to obtain a thickness, a desired number of ceramic green sheets may be sandwiched between two ceramic green sheets, laminated, and fired.

Next, the metallized pattern layers 14, 15
A copper plate 13 on which a circuit pattern is formed by punching, etching, or the like by applying Ni plating to the surface of
The metal brazing material 16 such as g-Cu brazing or Au-Sn brazing is placed via the brazing material 16, and the metal brazing material 16 is heated and melted and joined. In addition, a heat sink plate 12 made of molybdenum or the like in contact with the metallized pattern layer 15 on the lower surface side of the ceramic base material 11 is placed via a metal brazing material 16a such as Ag-Cu brazing or Au-Sn brazing, Metal brazing material 16
a is heated and melted and joined by brazing. The heating and melting of the metal brazing materials 16 and 16a are usually performed by heating the ceramic substrate 1
1 is performed simultaneously on both the upper surface side and the lower surface side, but the upper surface side and the lower surface side may be separately and twice separately brazed. In the case of brazing using Au—Sn brazing, the metallized pattern layer 14,
The surface of No. 15 is plated with Ni and Au.

The heat sink plate 12 used for bonding to the above-mentioned ceramic substrate 11 has a coefficient of thermal expansion similar to that of the ceramic substrate 11, for example, molybdenum, kovar (Fe
-Ni-Co alloy, trade name "Kovar"), a metal plate made of 42 alloy (Fe-Ni alloy) or the like,
It is formed into a desired size by punching or cutting with a press die. The heat sink plate 12 has an Ag-
In the case of brazing and joining using Cu brazing, Ni plating is applied, and in the case of brazing and joining using Au-Sn brazing, Ni plating and Au plating are applied.

As shown in FIG. 2, a power module substrate 10a according to a modification of the above-described embodiment has a ceramic substrate 11 and a copper plate 13 and a ceramic substrate 11 and a heat sink plate 12 which are joined together. From the outer peripheral end 17 to the inside of both the upper surface side and the lower surface side, a non-bonded region portion that is not bonded (non-bonded region portion A)
18, 18a are provided. Further, in joining the copper plate 13 and the ceramic substrate 11, the copper plate 13 protrudes outward from a joint portion between the ceramic substrate 11 and the copper plate 13, and forms a non-joining region (non-joining region A non-joining area (non-joining area B) 19 is provided opposite to A) 18. Reference numeral 14a indicates a metallized pattern layer formed on the ceramic base material 11, and reference numeral 16b indicates a metal brazing material for joining the metallized pattern layer 14a and the copper plate 13.

As shown in FIG. 3, a power module substrate 10b according to another modification of the present embodiment has a ceramic substrate 11 and a copper plate 13 and a ceramic substrate 11 and a heat sink plate 12 which are connected to each other. Non-joining region portion (non-joining region portion A) that is not joined from the outer peripheral end portion 17 of the base material 11 to the inside of both the upper surface side and the lower surface side.
18, 18a are provided. Further, in joining the copper plate 13 and the ceramic base material 11, a non-joining region portion (non-joining portion) extends from the outer peripheral end portion 20 of the circuit copper plate 13 a forming an individual circuit of the copper plate 13 to the inner side of the joining surface side. A region part C) 21 is provided. Reference numeral 14
Reference numerals b and 16c denote a metallized pattern layer and a brazing metal, respectively. In these joinings, the joining area between the ceramic substrate 11 and the copper plate 13 can be reduced,
The concentration of stress on the ceramic base 11 generated from the difference in thermal expansion coefficient between the ceramic base 11 and the copper plate 13 can be reduced.

When the ceramic substrate 11 and the copper plate 13 are bonded together, the non-bonded region (non-bonded region B) 1 of the copper plate 13
9 and the method of forming the non-joining region portion (non-joining region portion C) 21 of each circuit copper plate 13a include metal brazing materials 16b, 16
In order to prevent the molten metal c from flowing to the end face of the surface of the copper plate 13 and the circuit copper plate 13a when it is melted, blackening treatment or the like is performed on the portions to be non-joined regions 19 and 21 so that the metal brazing materials 16b and 16c are removed. A portion that does not wet the copper plate 13 or the circuit copper plate 13a is formed. Alternatively, a groove is formed in the copper plate 13 or the circuit copper plate 13a to prevent a flow when the metal brazing materials 16b and 16c are melted. The copper plate 13 and the circuit copper plate 13a
Are formed on the ceramic substrate 11 by forming metallized pattern layers 14a and 14b having a pattern corresponding to the formation of the respective non-bonded regions 19 and 21.

As a method of joining a copper plate for forming a circuit to the ceramic base, a metallized pattern layer having a non-joined area A on the upper surface of the ceramic base is formed.
Ag-C on the metalized pattern layer
After joining with a metal brazing material such as u-brazing or Au-Sn brazing,
With the etching resist layer provided and the circuit portion masked, the copper plate portion is first etched using an etching solution such as cupric chloride, and then further etched with an etching solution such as a fluoride and hydrogen peroxide solution. There is also a method of etching a metal brazing part to form a copper plate having a circuit.
The ceramic substrate can also be used by forming a granular ceramic raw material formed by granulating a ceramic powder, a binder and the like with a spray drier into a plate shape by a press molding machine using a press die.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The inventor of the present invention measured the stress generated in the joint between a ceramic base material and a heat sink plate by simulation for the power module substrate according to the present invention and the conventional power module substrate. The components of each power module board are as follows. (1) Example Ceramic substrate: size 30 x 30 mm, thickness 0.64
mm aluminum nitride base metallized pattern layer: tungsten metallized down about 0.5 mm from the end Heat sink plate: size 80 × 80 mm, thickness 3.0 m
m-Molybdenum plate Metal brazing material: Ag-Cu brazing (joining temperature of about 800 ° C) (2) Conventional example Ceramic substrate: size 30 x 30 mm, thickness 0.64
mm aluminum nitride base material Metallized pattern layer: Tungsten metallized heat sink plate of the same size as ceramic substrate Heat sink plate: size 80 x 80 mm, thickness 3.0 m
m-Molybdenum plate Metal brazing material: Ag-Cu brazing (joining temperature of about 800 ° C)

Table 1 shows the results of simulated measurement of the stress in the vertical direction of the ceramic substrate and the stress applied to the metallized pattern layer after bonding the ceramic substrate and the heat sink plate to the above-described embodiment and the conventional example. As a result, in the example, it can be demonstrated that cracks do not occur in the ceramic substrate because the stress in the vertical direction of the ceramic substrate is reduced as compared with the conventional example.

[0021]

[Table 1]

[0022]

The power module substrate according to any one of claims 1 to 3 has a non-joining region A from the outer peripheral end of the ceramic base material to the inside of both surfaces. The pattern layer, and the metal brazing material are not formed, and even if the plastic deformation of the metal brazing material is small, the stress concentration of the ceramic base material can be reduced,
It is possible to prevent the occurrence of cracks from the ends of the ceramic substrate.

In particular, in the power module board according to the second aspect, the copper plate protrudes further outward from the bonding portion between the copper plate and the ceramic base, and further includes a non-bonding region B opposed to the non-bonding region A of the ceramic base. Since it has at least, by reducing the bonding area of the copper plate and the ceramic substrate,
The difference in the coefficient of thermal expansion between the ceramic base and the copper plate can be reduced, the stress on the ceramic base can be reduced, and the occurrence of cracks in the ceramic base can be prevented. When the circuit copper plate is formed by etching, it can be easily formed.

In particular, in the power module substrate according to the present invention, each circuit copper plate forming a circuit of the copper plate has a non-joining region C over the entire periphery of the circuit copper plate and is joined to the ceramic base. Therefore, by reducing the bonding area between the copper base and the ceramic base, the difference in the coefficient of thermal expansion between the ceramic base and the copper base can be reduced, the stress on the ceramic base can be reduced, and cracks in the ceramic base can be reduced. Generation can be prevented.

[Brief description of the drawings]

FIGS. 1A and 1B are a cross-sectional view and a plan view, respectively, of a power module substrate according to an embodiment of the present invention.

FIG. 2 is a partially enlarged sectional view of a modified example of the power module substrate.

FIG. 3 is a partially enlarged cross-sectional view of another modified example of the power module substrate.

FIG. 4 is a cross-sectional view of a conventional power module substrate.

[Explanation of symbols]

10, 10a, 10b: power module substrate, 11:
Ceramic substrate, 12: heat sink plate, 13: copper plate,
13a: circuit copper plate, 14, 14a, 14b, 15: metallized pattern layer, 16, 16a, 16b, 16c: metal brazing material, 17: outer peripheral end, 18, 18a: non-joining area (non-joining area A) , 19: non-joining area (non-joining area B), 20: outer peripheral end, 21: non-joining area (non-joining area C)

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Masanori Nagahiro 2701-1, Iwakura, Omine-cho, Omine-cho, Mine-shi, Yamaguchi F-term in Sumitomo Metal Electronics Device Co., Ltd. 4G026 BA03 BA06 BA07 BB16 BB17 BB18 BB21 BB22 BB25 BC01 BC02 BD02 BD14 BF15 BF16 BG02 BH07 5E338 AA01 AA18 BB71 BB75 CC01 CC04 CC06 CD11 EE02 EE28 5F036 AA01 BA03 BA23 BB01

Claims (3)

[Claims] 1. A heat sink plate is formed on one surface via a metallized pattern layer formed on both surfaces of a ceramic substrate, and a copper plate on which a circuit is formed or formed on the other surface is formed using a metal brazing material. In the power module substrate to be joined, the ceramic substrate has a non-joining region portion A from the outer peripheral end of the ceramic substrate to the inside of both surfaces. 2. The non-joined power module board according to claim 1, wherein the copper plate protrudes further outward from a joint between the copper plate and the ceramic base, and faces the non-joined area A of the ceramic base. A power module substrate having at least a region section B. 3. The power module board according to claim 1, wherein each of the circuit copper plates forming the circuit of the copper plate has a non-joining region portion C over the entire periphery of the circuit copper plate.
A power module substrate, which is bonded to the ceramic base.