JP2012109315A - Power module substrate, power module substrate with cooler, and manufacturing methods of the power module and the power module substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power module substrate which easily and reliably joins a semiconductor element to a circuit layer made of copper or copper alloy through a solder material, and to provide the power module substrate with a cooler and manufacturing methods of the power module and the power module substrate.SOLUTION: In a power module substrate 10, a circuit layer 12 made of copper or copper alloy is disposed on one surface of an insulation layer (ceramic substrate 11), and a semiconductor element 3 is disposed on the circuit layer 12 through a solder layer 2. A conductive junction layer 30, formed by a sintered body of Ag paste containing glass, is formed on one surface of the circuit layer 12.

Description

  The present invention provides a power module substrate including a circuit layer on which a semiconductor element is mounted, a power module substrate with a cooler including the power module substrate, a power module using the power module substrate, and the power module The present invention relates to a method for manufacturing a substrate.

  Among various semiconductor elements, power elements for high power control used to control electric vehicles, electric vehicles, etc. generate a large amount of heat, so that the substrate (insulating layer) on which they are mounted is strong. In addition, a ceramic substrate made of ceramics, for example, AlN (aluminum nitride), which has not only excellent electrical insulation but also excellent heat resistance and relatively good thermal conductivity, has a conductive metal plate on the substrate. 2. Description of the Related Art Conventionally, power module substrates that are bonded as a circuit layer have been widely used. In such a power module substrate, a semiconductor element as a power element is usually mounted on the circuit layer via a solder material. As this type of power module substrate, a metal plate (heat radiating metal plate) with excellent thermal conductivity is also bonded to the lower surface of the ceramic substrate, and a cooler is bonded via the metal plate. A structure that dissipates heat is known.

  In such a power module substrate, aluminum or an aluminum alloy may be used as the metal plate constituting the circuit layer on one surface of the ceramic substrate and the metal plate for heat dissipation on the other surface. Copper (Cu) or a copper alloy is often used. A copper plate or copper alloy plate laminated on the surface of a ceramic substrate as a circuit layer is generally called a copper-clad substrate. Recently, a copper plate (copper foil) is used on the surface of a ceramic substrate. DBC substrates manufactured by a so-called direct bonding method, that is, a direct bonding copper (DBC) method, in which direct bonding is performed without using an adhesive, a brazing material, solder, or the like, are frequently used. Various specific methods for producing the DBC substrate have been proposed here. Basically, a small amount of oxide contained in the copper plate is used, and a Cu-O eutectic liquid phase is formed at the bonding interface with the ceramic substrate. And the eutectic liquid phase is used for bonding with ceramics. Since Cu-O eutectic is difficult to wet with non-oxides, if AlN is used as the ceramic, an oxide layer should be formed on the surface of AlN in advance to improve wettability. Etc. are also carried out.

    On the other hand, when a semiconductor element is mounted on a circuit layer made of copper or a copper alloy, the semiconductor element is generally joined via a solder material as described above. Conventionally, Pb-Sn so-called lead-containing solder is usually used as the solder material in that case, but recently, lead-free solder (lead-free solder) that does not contain lead from the viewpoint of environmental pollution. The tendency to use is increasing. As this lead-free solder, for example, Sn-Ag solder, Sn-In solder, Sn-Ag-Cu solder, Sn-Cu solder, Sn-Ag-In solder, Sn-Zn-Bi solder, Sn -Zn-Al solder. If such a solder material is used, a semiconductor element can be bonded to a circuit layer made of copper or a copper alloy with a high bonding strength. However, when these solder materials are used for joining, the circuit layer may be eroded by the molten solder material. This phenomenon is called erosion, and it has been relatively difficult for conventional lead-containing solders to occur, but lead-free solder has a problem that erosion cannot be overlooked. That is, when lead-free solder is used, the molten solder material component reacts with the copper on the surface of the circuit layer to cause an intermetallic compound, such as a Cu-In intermetallic compound, or a Sn-Cu intermetallic compound, Cu- While the Zn-based intermetallic compound or the like is generated, a phenomenon that the solder material component enters the circuit layer from the vicinity of the interface may occur. Here, since the intermetallic compound has low conductivity, if the above phenomenon (erosion) occurs, the electrical resistance of the circuit layer increases, and in an extreme case, the signal circuit is disconnected. As an element for a power module, a large amount of heat is generated from the circuit layer due to an increase in the electrical resistance of the circuit layer. There is a possibility that the calorific value becomes extremely large and inconveniences such as excessive temperature rise occur.

Therefore, conventionally, as disclosed in Patent Document 1, for example, a Ni plating film is formed on the surface of the circuit layer by a wet process such as electroless plating, and a solder material is disposed on the Ni plating film. Joining semiconductor elements has been performed.
Patent Document 2 proposes a technique for joining semiconductor elements using Ag nanopaste without using a solder material.

JP 2004-172378 A JP 2006-202938 A

As described in the aforementioned Patent Document 1, in the power module substrate in which the Ni plating film is formed on the surface of the circuit layer, the surface of the Ni plating film deteriorates due to oxidation or the like in the process until the semiconductor element is bonded. There is a possibility that the reliability of bonding with a semiconductor element bonded via a solder material may be lowered.
In addition, when the cooler is joined to the power module substrate by brazing, the Ni plating film deteriorates if brazing or the like is performed after forming the Ni plating film on the circuit layer surface. After a power module substrate and a cooler are brazed to form a power module substrate with a cooler, the entire power module substrate with a cooler is immersed in a plating bath. In this case, the Ni plating film is also formed on portions other than the circuit layer. However, when the cooler is made of aluminum or an aluminum alloy, the Ni plating film is placed between the cooler made of aluminum and the Ni plating film. There is a risk of electric corrosion. Therefore, in the Ni plating process, it was necessary to perform a masking process so that the Ni plating film was not formed on the cooler part. There is a problem that a great amount of labor is required for the process only for forming the plating film, and the manufacturing cost of the power module is greatly increased.

  On the other hand, as disclosed in Patent Document 2, when joining a semiconductor element using Ag nano paste without using a solder material, the layer made of Ag nano paste is formed thinner than the solder material. For this reason, the stress at the time of thermal cycle load tends to act on the semiconductor element, and the semiconductor element itself may be damaged.

  The present invention has been made in the background as described above, and in joining a semiconductor element on a circuit layer made of copper or a copper alloy via a solder material, the corrosion of the solder material on the surface of the circuit layer is caused. A power module substrate, a power module substrate with a cooler, a power module, and a power module capable of easily and surely joining semiconductor elements while reducing costs by eliminating the need for Ni plating on the circuit layer surface An object is to provide a method for manufacturing a power module substrate.

  As a result of intensive experiments and research on the solution to the above problems, the present inventors formed a conductive bonding layer made of a sintered body of Ag paste containing glass on a circuit layer made of copper or a copper alloy. Thus, the present inventors have found that it is effective to arrange a solder material through the conductive bonding layer and bond the semiconductor elements to solve the above-mentioned problems, and have made the present invention.

Therefore, the power module substrate according to the basic form (first form) of the present invention is:
In a power module substrate in which a circuit layer made of copper or a copper alloy is disposed on one surface of an insulating layer, and a semiconductor element is disposed on the circuit layer via a solder layer, one of the circuit layers A conductive bonding layer made of a fired body of an Ag paste containing glass is formed on the surface.

According to the power module substrate of the basic form of the present invention, a conductive bonding layer (Ag fired layer) made of a fired body of Ag paste containing glass is formed on one surface of the circuit layer. Therefore, the semiconductor element can be bonded to the circuit layer made of copper or copper alloy via the conductive bonding layer via the solder material. That is, a conductive bonding layer (Ag fired layer) is formed as an alternative to the Ni plating film in the prior art, and this conductive bonding layer (Ag fired layer) is used as a solder underlayer. Therefore, it is not necessary to immerse the power module substrate in a plating solution or the like, and troublesome work such as masking processing can be reduced.
In addition, since the solder material for joining semiconductor elements does not directly contact the circuit layer made of copper or copper alloy, even when a lead-free solder material is used as the solder material, the circuit layer is eroded by the solder material component (erosion). Therefore, it is possible to prevent an increase in electrical resistance, disconnection, or increase in the amount of heat generated due to erosion by the solder material. Moreover, since there is no risk of erosion even if lead-free solder is used, lead-free solder is used as a solder material for joining semiconductor elements as a power module substrate using copper or copper alloy for the circuit layer. It can be actually used, which is advantageous from the viewpoint of preventing environmental pollution.
Furthermore, since the solder material is used for joining the semiconductor elements, it is possible to form a thick solder material, and it is possible to suppress the stress on the semiconductor element from acting on the thermal cycle load, and the semiconductor element itself Breakage can be prevented.

    A power module substrate according to a second aspect of the present invention is the power module substrate according to the first aspect, wherein the conductive bonding layer includes a glass layer formed on the circuit layer, and an upper surface of the glass layer. And the conductive layer is dispersed in the glass layer.

  In the power module substrate according to the second embodiment, the glass layer of the conductive bonding layer is provided with conductivity by conductive particles, and therefore the entire conductive bonding layer also exhibits conductivity in the thickness direction. In addition, electrical conduction can be ensured between the circuit layer and the semiconductor element.

Furthermore, in the power module substrate according to the third aspect of the present invention, in the power module substrate according to the first or second aspect, the electric resistance value P in the thickness direction of the conductive bonding layer is set to 0.5Ω or less. It is characterized by being.
In this embodiment, since the electric resistance value P in the thickness direction of the conductive bonding layer is 0.5Ω or less, electricity is reliably conducted between the semiconductor element and the circuit layer via the conductive bonding layer and the solder material. Therefore, a highly reliable power module can be configured. Furthermore, in order to ensure electrical continuity between the semiconductor element and the circuit layer, the electrical resistance value P in the thickness direction of the conductive bonding layer is preferably 0.2Ω or less.
In the present invention, the electric resistance value P in the thickness direction of the conductive bonding layer is the electric resistance between the upper surface of the conductive bonding layer and the upper surface of the circuit layer. This is because the electrical resistance of copper or copper alloy constituting the circuit layer is much smaller than the electrical resistance in the thickness direction of the conductive bonding layer. The electrical resistance value P is measured by separating the conductive bonding layer from the center of the upper surface of the conductive bonding layer and the distance H from the central point of the upper surface of the conductive bonding layer to the end of the conductive bonding layer by H. Between the points on the circuit layer.

Furthermore, the power module substrate according to the fourth aspect of the present invention is the power module substrate according to any one of the first to third aspects, wherein the glass is lead oxide, zinc oxide, silicon oxide, It is characterized by containing one or more selected from boron oxide, phosphorus oxide, and bismuth oxide.
In this case, the softening point of the glass becomes relatively low, the Ag paste can be fired at a low temperature, and the circuit layer made of copper or a copper alloy can be prevented from being deteriorated by heat during firing of the Ag paste.

Furthermore, the power module substrate according to the fifth aspect of the present invention is the power module substrate according to any one of the first to fourth aspects, wherein the insulating layer includes AlN, Si ₃ N ₄ and Al. It is a ceramic substrate made of one or two or more ceramics selected from ₂ O ₃ .
A ceramic substrate selected from these AlN, Si ₃ N ₄ and Al ₂ O ₃ is excellent in insulation and strength, and at the same time has excellent heat resistance and relatively good thermal conductivity. By using it, the reliability of the power module substrate can be improved. In addition, a circuit layer can be easily formed by bonding a metal plate made of copper or a copper alloy on the ceramic substrate by a direct bonding method (DBC) or the like.

The sixth aspect of the present invention relates to a power module substrate with a cooler.
The power module substrate with a cooler according to the sixth embodiment includes the power module substrate according to any one of the first to fifth embodiments and the other surface of the insulating layer of the power module substrate. And a cooler disposed on the side.
Here, the cooler does not need to be directly joined to the other surface of the insulating layer, but a heat dissipation metal layer (heat dissipation metal plate) made of copper or copper alloy similar to the circuit layer, aluminum or aluminum alloy. Or what is necessary is just to join to the other surface side of an insulating layer through the buffer layer which consists of composite materials (for example, AlSiC etc.) containing aluminum.

The seventh aspect of the present invention relates to a power module. The power module according to the seventh aspect is disposed on the one surface side of the circuit layer of the power module substrate of any one of the first to fifth aspects and the power module substrate. The semiconductor element is bonded via a solder layer.
In the power module of this form, since the semiconductor element is joined via the solder material, the stress at the time of thermal cycle loading is relieved by the solder material, and damage to the semiconductor element due to the thermal stress can be suppressed. Therefore, the thermal cycle reliability can be greatly improved, and since it is not necessary to form a Ni plating film as in the prior art, the production cost can be greatly reduced.

The eighth aspect of the present invention relates to a method for manufacturing a power module substrate.
In the power module substrate manufacturing method according to the eighth embodiment, a circuit layer made of copper or a copper alloy is disposed on one surface of an insulating layer, and a semiconductor element is disposed on the circuit layer via a solder layer. A method for manufacturing a power module substrate, comprising: an application step of applying an Ag paste containing glass powder to one surface of the circuit layer; and heat treatment in a state where the Ag paste is applied to the Ag paste. And a conductive bonding layer made of a fired body of an Ag paste containing glass is formed on one surface of the circuit layer.

  According to the method for manufacturing a power module substrate of this embodiment, in order to form a conductive bonding layer on the circuit layer at a stage before the semiconductor element is bonded to the circuit layer made of copper or a copper alloy with a solder material, When the semiconductor elements are joined by the solder material, the solder material does not directly contact the circuit layer, and therefore it is possible to effectively prevent the circuit layer from being eroded (eroded) by the solder material. Accordingly, the Ni plating film as in the case of the prior art becomes unnecessary, and as a result, it is not necessary to immerse the power module substrate in a plating solution or the like, and troublesome work such as masking treatment can be reduced.

Furthermore, in the method for manufacturing a power module substrate according to the ninth aspect of the present invention, in the method for manufacturing a power module substrate according to the eighth aspect, the firing temperature in the firing step is 350 ° C. or higher and 645 ° C. or lower. It is characterized by.
In the manufacturing method of this embodiment, since the firing temperature in the firing step is 350 ° C. or higher, the conductive bonding layer can be reliably formed by firing the Ag paste. Moreover, since the firing temperature is 645 ° C. or lower, it is possible to prevent deterioration of the circuit layer made of copper or a copper alloy in the firing step.

  According to the present invention, when a semiconductor element is joined to a circuit layer made of copper or a copper alloy via a solder material, the solder material does not directly contact the circuit layer made of copper or a copper alloy. No erosion of the layer occurs, so it is possible to prevent inconveniences such as an increase in electrical resistance and disconnection of the circuit layer due to the erosion of the solder material, and an increase in the amount of heat generated. It is possible to use lead-free solder, which is considered to be prone to occur, without any trouble, and it is advantageous for prevention of environmental pollution by using lead-free solder. Moreover, in the present invention, the Ni plating film as in the case of the prior art is not formed on the circuit layer, and a conductive bonding layer made of a fired body of Ag paste is formed. In forming such a conductive bonding layer, Since there is no need to immerse in a plating solution or the like as in the case of forming a Ni plating film, troublesome work such as masking can be reduced. Therefore, according to the present invention, the semiconductor element can be securely and securely disposed on the circuit layer made of copper or copper alloy without causing inconveniences such as an increase in electrical resistance of the circuit layer, disconnection, an increase in the amount of heat generation, and a significant cost increase. A power module substrate that can be easily joined, a power module substrate with a cooler, a power module, and a method of manufacturing the power module substrate can be provided.

It is a schematic explanatory drawing of the power module using the board | substrate for power modules which is embodiment of this invention. It is explanatory drawing which shows the board | substrate for power modules which is embodiment of this invention. FIG. 3 is an enlarged explanatory diagram of a circuit layer surface in the power module substrate of FIG. 2. In embodiment of this invention, it is upper surface explanatory drawing which shows the measuring method of the electrical resistance value P of the thickness direction of a conductive joining layer. In embodiment of this invention, it is side explanatory drawing which shows the measuring method of the electrical resistance value P of the thickness direction of a conductive joining layer. It is a flowchart which shows the manufacturing method of Ag paste. It is a flowchart which shows the manufacturing method of the power module of FIG.

Hereinafter, the present invention will be described in more detail with reference to the drawings.
FIG. 1 shows a power module that is a basic embodiment of the present invention.
The power module 1 includes a power module substrate 10 on which a circuit layer 12 is disposed, a semiconductor chip (semiconductor element) 3 bonded to the surface of the circuit layer 12 via a solder layer 2, and a cooler 40. I have.

The power module substrate 10 is made of a ceramic substrate 11 constituting the insulating layer described above, and copper (Cu) or a copper alloy (Cu alloy) disposed on one surface (the upper surface in FIG. 1) of the ceramic substrate 11. And a heat dissipation metal layer 13 disposed on the other surface (lower surface in FIG. 1) of the ceramic substrate 11.
The ceramic substrate 11 prevents electrical connection between the circuit layer 12 and the metal layer 13 for heat dissipation, has high insulation, high strength, excellent heat resistance, and heat conduction. It is made of AlN (aluminum nitride) having relatively good properties. In addition, the thickness of the ceramic substrate 11 is set within a range of 0.2 to 1.5 mm, and in this embodiment is set to 0.635 mm.

  The circuit layer 12 is formed by joining a metal plate made of copper or copper alloy, which is a metal having excellent conductivity, to one surface of the ceramic substrate 11. In the present embodiment, the circuit layer 12 is formed by joining a copper plate made of a rolled plate of pure copper (for example, oxygen-free copper) having a purity of 99.99% or more to the ceramic substrate 11.

The heat radiating metal layer 13 is formed by bonding a metal plate made of a metal having good thermal conductivity to the other surface of the ceramic substrate 11. In the present embodiment, the heat dissipating metal layer 13 is joined to the ceramic substrate 11 by a copper plate made of a rolled plate of pure copper (for example, oxygen-free copper) having a purity of 99.99% or more, like the circuit layer 12. Is formed by.
Here, in order to form the circuit layer 12 and the heat radiating metal layer 13 on each surface of the ceramic substrate 11, means for joining the copper plate to each surface of the ceramic substrate 11 is not particularly limited. Applying a direct bonding method (DBC method) for directly bonding a copper plate to a ceramic substrate without interposing an organic resin adhesive, a brazing material, a solder material, etc. between each surface of the substrate 11 and the copper plate, A so-called DBC substrate is desirable. Further, means for joining a copper plate as the circuit layer 12 to one surface of the ceramic substrate 11 and means for joining a copper plate as the metal layer 13 for heat dissipation to the other surface of the ceramic substrate 11 are not necessarily limited. Although not necessarily the same, if the same means is applied, a copper plate as the circuit layer 12 can be bonded to one surface of the ceramic substrate 11 and simultaneously a copper plate as the heat dissipation metal layer 13 can be bonded to the other surface. In addition, the number of manufacturing steps can be reduced to reduce the cost. Particularly when the DBC method is applied, it is advantageous to directly bond the copper plates to both surfaces of the ceramic substrate 11 at the same time.

  The cooler 40 is for cooling the power module substrate 10 described above. The top plate portion 41 joined to the power module substrate 10 and the top plate portion 41 are suspended downward. The heat radiation fin 42 and the flow path 43 for distribute | circulating a cooling medium (for example, cooling water) are provided. The cooler 40 (top plate portion 41) is preferably made of a material having good thermal conductivity, and is made of A6063 (aluminum alloy) in the present embodiment.

  In the present embodiment, a buffer layer 15 made of aluminum, an aluminum alloy, or a composite material containing aluminum (for example, AlSiC) is provided between the top plate portion 41 of the cooler 40 and the heat radiating metal layer 13. ing.

In the power module 1 shown in FIG. 1, a conductive bonding layer (Ag fired layer) made of an Ag paste fired body formed by firing Ag paste described later on the surface of the circuit layer 12 (upper surface in FIG. 1). The semiconductor chip 3 is bonded to the surface of the conductive bonding layer 30 via the solder layer 2. That is, the conductive bonding layer (Ag fired layer) 30 functions as a solder underlayer.
Here, as the solder material for forming the solder layer 2, it is allowed to use Pb—Sn-based lead-containing solder, but normally, from the viewpoint of preventing environmental pollution, lead-free solder not containing lead, For example, Sn-Ag solder, Sn-In solder, Sn-Ag-Cu solder, Sn-Cu solder, Sn-Ag-In solder, Sn-Zn-Bi solder, Sn-Zn-Al solder It is preferable to use solder or the like. When these lead-free solders are used, if they come into direct contact with the copper plate during brazing heating (solder melting), the copper plate may be eroded as described above. Is not in direct contact with the copper plate, the copper plate is not eroded during brazing heating, and therefore, lead-free solder can be used without any problem.
As shown in FIG. 1, the conductive bonding layer 30 is not formed on the entire surface of the circuit layer 12 but is selectively formed only on a portion where the semiconductor chip 3 is disposed.

2 and 3 show the power module substrate 10 before the semiconductor chip 3 is joined via the solder layer 2 (but after firing the Ag paste).
In this power module substrate 10, Ag powder, glass powder, resin, solvent, dispersant, as described in detail later on the surface of the circuit layer 12 (upper surface in FIGS. 2 and 3). A conductive bonding layer 30 made of a fired body obtained by firing an Ag paste containing the above is formed. The conductive bonding layer 30 made of this Ag paste fired body is formed on the circuit layer 12 side as shown in FIG. 3 in a state before the semiconductor chip 3 is bonded via the solder layer 2 after baking the Ag paste. The upper and lower glass layers 31 and the Ag layer 32 formed on the glass layer 31 have a two-layer structure, of which the lower glass layer 31 has a fine particle size of about several nanometers. Conductive particles 33 are dispersed. The conductive particles 33 are crystalline particles containing at least one of Ag and Cu. And since the electroconductive particle 33 is disperse | distributing in the glass layer 31 in this way, the glass layer 33 also shows electroconductivity, and it is electroconductive in the thickness direction also as the electroconductive joining layer 30 which consists of Ag paste baking bodies. Is shown. The conductive particles 33 in the glass layer 31 can be observed and measured by, for example, a transmission electron microscope (TEM).

  The electric resistance value P in the thickness direction of the conductive bonding layer 30 is set to 0.5Ω or less. Here, in the present embodiment, the electric resistance value P in the thickness direction of the conductive bonding layer 30 is an electric resistance value between the upper surface of the conductive bonding layer 30 and the upper surface of the circuit layer 12. This is because the electric resistance of pure copper such as oxygen-free copper constituting the circuit layer 12 is much smaller than the electric resistance in the thickness direction of the conductive bonding layer 30. When measuring the electrical resistance, as shown in FIGS. 4 and 5, the upper surface center point of the conductive bonding layer 30 and the distance from the upper surface center point of the conductive bonding layer 30 to the end portion of the conductive bonding layer 30. The electrical resistance between the point on the circuit layer 12 that is separated by H from the end of the conductive bonding layer 30 with respect to H is measured.

  In the present embodiment, since the circuit layer 12 is made of pure copper having a purity of 99.99%, the conductive bonding layer 30 is formed on the surface of the circuit layer 12 (upper surface in FIG. 3). That is, the pure copper constituting the circuit layer 12 and the glass layer 31 are directly bonded. In the present embodiment, the thickness tg of the glass layer 31 is 0.01 μm ≦ tg ≦ 5 μm, the thickness ta of the Ag layer 32 is 1 μm ≦ ta ≦ 100 μm, and the total thickness tg + ta of the conductive bonding layer 30 is It is desirable to configure so as to be within each range of 1.01 μm ≦ tg + ta ≦ 105 μm.

Next, an Ag paste for forming an Ag paste fired body as the conductive bonding layer 30 will be described.
This Ag paste contains Ag powder, glass powder, resin, solvent and dispersant, and the content of the powder component consisting of Ag powder and glass powder is 60% by mass of the entire Ag paste. The content is preferably in the range of 90% by mass or less, and the remainder is made of resin, solvent and dispersant. In addition, in this embodiment, content of the powder component which consists of Ag powder and glass powder is 85 mass% of the whole Ag paste.
The viscosity of the Ag paste is preferably adjusted to 10 Pa · s or more and 500 Pa · s or less, more preferably 50 Pa · s or more and 300 Pa · s or less.

The Ag powder preferably has a spherical shape with a particle size of 0.05 μm or more and 1.0 μm or less. In this embodiment, an Ag powder having an average particle size of 0.8 μm was used.
The glass powder contains, for example, any one or more of lead oxide, zinc oxide, silicon oxide, boron oxide, phosphorus oxide and bismuth oxide, and the softening temperature is 600 ° C. or less. In the present embodiment, glass powder made of bismuth oxide, zinc oxide and boron oxide and having an average particle size of 0.5 μm was used.
The weight ratio A / G between the weight A of the Ag powder and the weight G of the glass powder is desirably adjusted within a range of 80/20 to 99/1. In this embodiment, A / G = 80 / It was set to 5.

A solvent having a boiling point of 200 ° C. or higher is suitable. In this embodiment, diethylene glycol dibutyl ether is used.
The resin is used to adjust the viscosity of the Ag paste, and a resin that decomposes at 500 ° C. or higher is suitable. In this embodiment, ethyl cellulose is used.
In this embodiment, a dicarboxylic acid-based dispersant is added. In addition, you may comprise Ag paste, without adding a dispersing agent.

Next, the manufacturing method of Ag paste is demonstrated with reference to the flowchart shown in FIG. First, the above-mentioned Ag powder and glass powder are mixed to produce a mixed powder (mixed powder forming step S1). Moreover, a solvent and resin are mixed and an organic mixture is produced | generated (organic substance mixing process S2).
Then, the mixed powder, the organic mixture, and the dispersant are premixed by a mixer (preliminary mixing step S3). Next, the preliminary mixture is mixed while being kneaded using a roll mill (kneading step S4). The obtained kneading is filtered with a paste filter (filtration step S5). In this way, the aforementioned Ag paste is produced.

Next, the manufacturing method of the power module 1 which is this embodiment is demonstrated with reference to the flowchart shown in FIG.
First, a copper plate to be the circuit layer 12 and a copper plate to be the heat-dissipating metal layer 13 are prepared, and these copper plates are laminated on one surface and the other surface of the ceramic substrate 11 and directly bonded by the DBC method. The direct bonding process and conditions are not particularly limited, but an oxide layer is formed on the surface of the ceramic substrate 11 in advance by a technique such as baking heat treatment in the air, and copper plates are formed on both surfaces of the ceramic substrate. Each copper plate and the ceramic substrate 11 can be directly joined by laminating, heating at a high temperature of about 1050 ° C. to 1080 ° C. in an inert atmosphere such as nitrogen, and then cooling. Specifically, in this embodiment, as the bonding conditions by the DBC method for bonding the copper plates to both surfaces of the ceramic substrate made of AlN, the conditions of N ₂ gas atmosphere and 1060 ° C. were applied ( Circuit layer bonding step S11).

    Next, the cooler 40 (top plate portion 41) is joined to the other surface side of the heat radiating metal layer 13 via the buffer layer 15 via the brazing material (cooler joining step S12). The brazing temperature of the cooler 40 is preferably in the range of 590 ° C to 610 ° C.

    And the above-mentioned Ag paste is apply | coated to the surface of the circuit layer 12 (Ag paste application | coating process S13). In addition, when apply | coating Ag paste, various means, such as a screen printing method, an offset printing method, and a photosensitive process, are employable. In this embodiment, the Ag paste is formed in a pattern by a screen printing method.

In a state where the Ag paste is applied to the surface of the circuit layer 12, the Ag paste is charged into the heating furnace and the Ag paste is fired (firing step S <b> 14). In addition, it is preferable to set the calcination temperature at this time to 350 to 645 degreeC.
The conductive bonding layer 30 having the glass layer 31 and the Ag layer 32 is formed by the firing step S14. At this time, fine conductive particles 33 having a particle size of about several nanometers are dispersed inside the glass layer 31. The conductive particles 33 are crystalline particles containing at least one of Ag and Cu, and are presumed to have precipitated in the glass layer 31 during firing.

  Thus, the power module substrate 10 having the conductive bonding layer 30 formed on the surface of the circuit layer 12 and the power module substrate with a cooler are produced.

Then, the semiconductor chip 3 is placed on the surface of the conductive bonding layer 30 via a solder material, and soldered in a reduction furnace (solder bonding step S15). At this time, part or all of the Ag layer 32 of the conductive bonding layer 30 is melted in the solder layer 2 formed of the solder material.
Thereby, the power module 1 in which the semiconductor chip 3 is bonded onto the circuit layer 12 through the solder layer 2 is produced.

  In the power module substrate 10 and the power module 1 according to the present embodiment configured as described above, the surface of the circuit layer 12 formed by directly bonding a copper plate having a purity of 99.99% or more to the ceramic substrate 11. In addition, since the conductive bonding layer 30 made of a fired body of Ag paste containing glass is formed, the solder layer 2 can be formed on the conductive bonding layer 30 so that the semiconductor chip 3 can be bonded reliably and easily. it can. Therefore, it is not necessary to form a Ni plating film as shown in the prior art, and the semiconductor chip 3 can be bonded onto the circuit layer 12 relatively easily and reliably. Therefore, the trouble which arises when forming the Ni plating film as in the prior art is eliminated, and the power module 1 can be produced satisfactorily.

Here, as shown in FIG. 3, the conductive bonding layer 30 includes a glass layer 31 and an Ag layer 32 formed on the glass layer 31. Since the fine conductive particles 33 having a size of about nanometer are dispersed, the glass layer 31 can also have conductivity. Specifically, in this embodiment, the electrical resistance value P in the thickness direction of the conductive bonding layer 30 including the glass layer 31 is set to 0.5Ω or less.
Therefore, it is possible to reliably conduct electricity between the semiconductor chip 3 and the circuit layer 12 via the conductive bonding layer 30 and the solder layer 2, and the highly reliable power module 1 can be configured.

  Further, the Ag paste constituting the conductive bonding layer 30 contains Ag powder and glass powder composed of lead oxide, zinc oxide and boron oxide, and the softening temperature of the glass powder is set to 600 ° C. or less. Therefore, the Ag paste can be fired at a relatively low temperature. Specifically, the firing temperature can be set to 350 ° C. or higher and 645 ° C. or lower. Therefore, troubles such as deterioration of the circuit layer 12 and reduction in bonding strength between the circuit layer 12 and the ceramic substrate 11 due to the firing of the Ag paste can be prevented, and the high-quality power module substrate 10 and the power module 1 can be prevented. Can be produced.

  Furthermore, since the viscosity of the Ag paste is adjusted to 10 Pa · s or more and 500 Pa · s or less, more preferably 50 Pa · s or more and 300 Pa · s or less, the Ag paste applying step for applying the Ag paste to the surface of the circuit layer 12 In S13, a screen printing method or the like can be applied, and the conductive bonding layer 30 can be selectively formed only on the portion where the semiconductor chip 3 is disposed. Therefore, the amount of Ag paste used can be reduced, and the manufacturing cost of the power module substrate 10 and the power module 1 can be greatly reduced.

In the present embodiment, since the ceramic substrate 11 made of AlN (aluminum nitride) having excellent insulation and strength, excellent heat resistance, and relatively good thermal conductivity is used as the insulating layer, the power module is used. The reliability of the substrate 10 can be improved. Moreover, the circuit layer 12 can be easily formed by directly bonding a copper plate on the ceramic substrate 11 by the DBC method.
Further, in the present embodiment, the cooler 40 is disposed on the other side (lower side in FIG. 1) of the ceramic substrate 11 via the heat dissipation metal layer 13 and the buffer layer 15. It can prevent that the power module 1 becomes high temperature by heat_generation | fever.

  Hereinafter, the result of the confirmation experiment conducted to confirm the effect of the present invention will be shown as an example of the present invention together with a comparative example. The following examples are for explaining the effects of the present invention, and it goes without saying that the configurations, processes, and conditions described in the examples do not limit the technical scope of the present invention.

As Example 1 of the present invention, the power module substrate described in the above embodiment was prepared.
That is, Invention Example 1 was obtained by forming a conductive bonding layer made of an Ag paste fired body on a circuit layer made of a copper plate having a purity of 99.99% or more. Incidentally, as the glass powder in this case, the _Bi 2 _{O 3} 90.6 wt%, the ZnO 2.6 _wt%, the B 2 _{O 3} 6.8 wt%, with lead-free glass powder containing. Further, ethyl cellulose was used as the resin, and diethylene glycol dibutyl ether was used as the solvent. Furthermore, a dicarboxylic acid-based dispersant was added. Further, in joining a copper plate as a circuit layer to a ceramic substrate made of AlN, the DBC method under the above conditions was applied.
As a conventional example, a power module substrate described in the above embodiment was prepared by forming a Ni plating film having a thickness of 5 μm on the surface of the circuit layer instead of the conductive bonding layer made of the Ag paste fired body.

With respect to these inventive example 1 and the conventional example, the solder wettability was evaluated. The evaluation of the solder wettability was performed by a spread test defined in JIS Z 3197. The spreading rate S is determined by placing a ball-shaped solder material having a diameter d on a sample (a conductive bonding layer or Ni plating film made of an Ag paste fired body) and heating the same to a predetermined temperature. The height h is measured and is an index calculated by (d−h) / d × 100. The larger the spreading ratio S, the better the wettability with the solder material, and the stronger the semiconductor chip can be bonded via the solder layer.
Here, in this example, the height of the solder layer after being held at 350 ° C. for 0.1 hour was measured using Sn-3.0 wt% Ag-0.5 wt% Cu as the solder material. The results are shown in Table 1.

In the conventional example in which the Ni plating film is formed, the spreading rate S is 67 to 70%.
On the other hand, in Example 1 of the present invention in which the conductive bonding layer made of the Ag paste fired body was formed, the spreading rate S was 69 to 73%, and the solder wettability was equal to or higher than that of the conventional example. It was confirmed that
Further, it was confirmed that the bonding property of the conductive bonding layer itself made of the Ag paste fired body to the circuit layer made of the copper plate was good in the case of the present invention example 1.
Therefore, also in the present invention example 1 in which the conductive bonding layer made of the Ag paste fired body is provided on the circuit layer made of the copper plate, the semiconductor chip is surely disposed through the solder layer as in the conventional example in which the Ni plating film is formed. It was confirmed that it was possible to form a power module by bonding.

Next, the results of measuring the electrical resistance value P in the thickness direction of the conductive bonding layer made of the Ag paste fired body in the power module substrate described in the above embodiment will be described.
In the present invention, the Ag layer thickness ta and the glass layer thickness tg of the conductive bonding layer made of the Ag paste fired body are changed, and the weight ratio A / G between the weight A of the Ag powder and the weight G of the glass powder is changed. Example 2-11 was produced. As the glass powder of Example 2-6 at this time, PbO: 77.6 wt%, ZnO: 5.7 _wt%, SiO 2: using lead glass powder containing 16.7% by weight. As the glass powder of Example _7-11, Bi ₂ O 3: 90.6 wt%, ZnO: 2.6 _{wt%, B} 2 O 3: Using lead-free glass powder containing 6.8 mass% . In any of Examples 1-11, ethyl cellulose was used as the resin, diethylene glycol dibutyl ether was used as the solvent, and a dicarboxylic acid-based dispersant was further added. Then, the conductive bonding layer was formed into a square shape having a side length of 15 mm as viewed from above.
With respect to the sample of the present invention example 2-11 thus obtained, a conductive bonding layer comprising an Ag paste fired body using a tester (manufactured by KEITHLEY: 2010 MULTITIMER) by the method described in FIGS. The electrical resistance value P in the thickness direction was measured. The measurement results are shown in Table 2.

  In any of Invention Examples 2-11, it was confirmed that the electric resistance value P in the thickness direction of the conductive bonding layer made of the Ag paste fired body was 0.5Ω or less. In addition, it was confirmed that the electrical resistance value P in the thickness direction of the conductive bonding layer made of the Ag paste fired body was reduced by forming the glass powder ratio small and the glass layer thickness tg thin. .

As mentioned above, although embodiment and the Example of this invention were described, this invention is not limited to this, It can change suitably in the range which does not deviate from the technical idea of the invention.
For example, the metal plate constituting the circuit layer and the heat dissipation metal layer has been described as using a rolled plate made of pure copper having a purity of 99.99% or more. However, the present invention is not limited to this, and the purity is less than that. It is also acceptable to use copper, or a copper alloy aluminum or aluminum alloy to which an alloy element such as Cr or Be is added.
Further, in some cases, copper or copper alloy is used for the metal plate of the circuit layer, while aluminum or aluminum alloy is allowed to be used as the metal plate constituting the heat dissipation metal layer.

Moreover, about the raw material and compounding quantity of Ag paste, it is not limited to what was described in embodiment, You may use another glass powder, resin, a solvent, and a dispersing agent.
For example, if the glass powder contains one or more of lead oxide, zinc oxide, silicon oxide, boron oxide, phosphorus oxide, and bismuth oxide as the main component, other alkali metals and transition metals In the case of the present invention, the glass transition temperature is 300 ° C. or higher and 450 ° C. or lower, the softening temperature is lower than the melting point of copper, preferably 600 ° C. or lower, and crystallization is performed. It is desirable to use glass having a temperature of 450 ° C. or higher.
From the viewpoint of preventing environmental pollution, it is desirable to use glass that does not contain lead, that is, lead-free glass, as the glass powder blended in the raw material of the Ag paste.

    Further, the resin blended in the Ag paste is not particularly limited, but usually an acrylic resin, an alkyd resin, or the like may be used. Furthermore, α-terpineol, butyl carbitol acetate, or the like can be used as a solvent blended in the Ag paste.

Further, the thickness ratio of the glass layer and the Ag layer in the conductive bonding layer formed of the Ag paste fired body to be formed is not limited to that illustrated in FIG.
Further, it is described that uses a ceramic substrate made of AlN as an insulating layer, is not limited thereto, using a ceramic substrate made of Si 3 _N 4 _(silicon nitride) Al 2 _O 3 _(alumina) or the like In other cases, the insulating layer may be made of an insulating resin.

  In addition, it was explained that a copper plate to be a circuit layer is bonded to a ceramic substrate by the DBC method and a conductive bonding layer made of a fired Ag paste is formed on the circuit layer after brazing a cooler. The conductive bonding layer may be formed before the copper plate is bonded to the ceramic substrate or before the cooler is brazed.

Moreover, although it demonstrated as what provided the buffer layer which consists of a composite material (for example, AlSiC etc.) containing aluminum, aluminum alloy, or aluminum between the top plate part of the cooler and the metal layer for heat dissipation, this buffer layer Can be omitted.
Furthermore, although it demonstrated as what comprises the top-plate part of a cooler with aluminum, you may be comprised with the aluminum alloy, the composite material containing aluminum, copper, copper alloy, etc. further. The structure of the cooler has been described as having heat radiation fins and a cooling medium flow path, but the structure of the cooler is not particularly limited.

1 Power Module 2 Solder Layer 3 Semiconductor Chip (Semiconductor Element)
DESCRIPTION OF SYMBOLS 10 Power module substrate 11 Ceramic substrate 12 Circuit layer 30 Conductive joining layer 31 Glass layer 32 Ag layer 33 Conductive particle 40 Cooler

Claims (9)

In a power module substrate in which a circuit layer made of copper or a copper alloy is disposed on one surface of an insulating layer, and a semiconductor element is disposed on the circuit layer via a solder layer;
A power module substrate, wherein a conductive bonding layer made of a sintered body of an Ag paste containing glass is formed on one surface of the circuit layer.   The power module substrate according to claim 1, wherein the conductive bonding layer includes a glass layer formed on the circuit layer and an Ag layer formed on the glass layer.   3. The power module according to claim 1, wherein an electric resistance value P in the thickness direction of the conductive bonding layer is set to 0.5Ω or less. 4. substrate.   The said glass contains any 1 type, or 2 or more types chosen from lead oxide, zinc oxide, a silicon oxide, a boron oxide, phosphorus oxide, and a bismuth oxide, The Claims 1- Claim characterized by the above-mentioned. Item 4. The power module substrate according to any one of Items 3 to 3. The insulating layer is an insulating substrate made of one or more ceramics selected from AlN, Si ₃ N ₄ and Al ₂ O _3. 5. The power module substrate according to any one of the above.   A power module substrate according to any one of claims 1 to 5, and a cooler disposed on the other surface side of the insulating layer of the power module substrate. A substrate for a power module with a cooler.     A power module substrate according to any one of claims 1 to 5 and a semiconductor element disposed on one surface side of the circuit layer of the power module substrate, the semiconductor A power module, wherein the elements are joined via a solder layer. In the method for manufacturing a power module substrate, wherein a circuit layer made of copper or a copper alloy is disposed on one surface of the insulating layer, and a semiconductor element is disposed on the circuit layer via a solder layer;
An application step of applying an Ag paste containing glass on one surface of the circuit layer; and a baking step of baking the Ag paste by heat treatment in a state where the Ag paste is applied,
A method for producing a power module substrate, comprising: forming a conductive bonding layer made of a fired body of an Ag paste containing glass on one surface of the circuit layer.   The method for producing a power module substrate according to claim 8, wherein a firing temperature in the firing step is 350 ° C. or more and 645 ° C. or less.

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