阅读说明：本技术 带散热片的功率模块用基板及带散热片的功率模块用基板的制造方法 (Substrate for power module with heat sink and method for manufacturing substrate for power module with heat sink ) 是由 山崎和彦 增山弘太郎 沼达也 石川雅之 于 2018-11-05 设计创作，主要内容包括：本发明提供一种带散热片的功率模块用基板(10),其具备：功率模块用基板(20)和散热片(40),所述功率模块用基板(20)具备绝缘基板(21)、形成在绝缘基板(21)的其中一个面的电路层(22)及形成在绝缘基板(21)的另一个面的金属层(23),所述散热片(40)通过接合层(30)被接合到功率模块用基板(20)的金属层(23)的与绝缘基板(21)相反侧的面,其中,接合层(30)为银粒子的烧结体,且为相对密度在60％以上且90％以下的范围内的多孔体,所述接合层的厚度在10μm以上且500μm以下的范围内。(The present invention provides a power module substrate (10) with a heat sink, which comprises: the power module substrate (20) is provided with an insulating substrate (21), a circuit layer (22) formed on one surface of the insulating substrate (21), and a metal layer (23) formed on the other surface of the insulating substrate (21), and the heat sink (40) is bonded to the surface of the metal layer (23) of the power module substrate (20) on the side opposite to the insulating substrate (21) by a bonding layer (30), wherein the bonding layer (30) is a sintered body of silver particles and is a porous body having a relative density of 60% to 90%, and the thickness of the bonding layer is 10 [ mu ] m to 500 [ mu ] m.)

1. A substrate with a heat sink for a power module, comprising a substrate for a power module and a heat sink, wherein the substrate for a power module comprises an insulating substrate, a circuit layer formed on one surface of the insulating substrate, and a metal layer formed on the other surface of the insulating substrate, and the heat sink is bonded to a surface of the metal layer of the substrate for a power module opposite to the insulating substrate via a bonding layer,

the bonding layer is a sintered body of silver particles, is a porous body having a relative density in the range of 60% to 90%, and has a thickness in the range of 10 μm to 500 μm.

2. The substrate for a heat sink-equipped power module according to claim 1,

the metal layer is composed of an aluminum plate made of aluminum or an aluminum alloy, or a copper plate made of copper or a copper alloy.

3. The substrate for a heat sink-equipped power module according to claim 2,

the metal layer is formed of the aluminum plate, and a silver plating layer or a gold plating layer is formed on a surface of the aluminum plate opposite to the insulating substrate.

4. A method for manufacturing a substrate for a power module with a heat sink according to claim 1, the method comprising the steps of:

a paste bonding material composition layer forming step of forming a layer of a paste bonding material composition containing silver particles having an average particle diameter in a range of 0.1 μm or more and 1 μm or less in an amount in a range of 70 mass% or more and 95 mass% or less on at least one of a surface of the metal layer of the power module substrate on the opposite side to the insulating substrate and a surface of the heat sink;

a laminating step of laminating the power module substrate and the heat sink with a layer of the paste bonding material composition; and

and a heating step of heating the laminated power module substrate and the heat sink at a temperature of 150 ℃ to 300 ℃ under a pressure of 1MPa or less in the laminating direction.

Technical Field

The present invention relates to a substrate with a heat sink for a power module and a method for manufacturing the substrate with the heat sink for the power module.

The present application claims priority based on patent application No. 2017-213917, which was filed in japan on 11/6/2017, and the contents of which are incorporated herein by reference.

Background

A power semiconductor device used for an inverter or the like generates a large amount of heat during operation. Therefore, a power module substrate including an insulating substrate made of a ceramic having high heat resistance, a circuit layer formed on one surface of the insulating substrate, and a metal layer formed on the other surface of the insulating substrate is used as a substrate on which a power semiconductor element is mounted.

In this power module board, the power semiconductor element is mounted on the circuit layer, the heat sink is brought into contact with the metal layer by the heat conductive material, and heat generated in the power semiconductor element is dissipated by the heat sink.

As the heat conductive material, paste (grease) having high heat conductivity is widely used. When the power module substrate and the heat sink are brought into contact with each other by the paste, if the power module substrate is warped due to a heat cycle caused by ON/OFF of the power semiconductor element, a gap may be formed between the power module substrate and the paste, and the heat conductivity between the power module substrate and the heat sink may be reduced.

Therefore, direct bonding of the metal layer of the power module substrate and the heat sink using a solder material has been studied. Patent document 1 describes a substrate for a power module with a heat sink, In which the substrate for a power module and the heat sink are bonded to each other using various solder materials such as Sn — Ag based, Sn — In based, or Sn — Ag — Cu based solder materials.

Patent document 1: japanese laid-open patent publication No. 2014-222788 (A)

When a conventional substrate for a power module with a heat sink, in which a substrate for a power module and a heat sink are bonded using a solder material, is subjected to a cooling-heating cycle for a long time, the solder material is broken due to internal stress generated by a difference in linear expansion coefficient between the substrate for a power module and the heat sink, and the thermal conductivity between the substrate for a power module and the solder material may be locally reduced. If this local decrease in thermal conductivity occurs, the thermal resistance between the power module substrate and the heat sink increases, heat is easily accumulated in the power module substrate, the temperature of the semiconductor element increases, the power module substrate is damaged, and the insulating substrate may be broken.

Disclosure of Invention

The present invention has been made in view of the above circumstances, and an object thereof is to provide a substrate for a power module with a heat sink and a method for manufacturing the substrate for a power module with a heat sink, which can suppress an increase in thermal resistance or a crack in an insulating substrate due to a load of a cooling and heating cycle for a long time.

In order to solve the above problem, a substrate for a power module with a heat sink according to the present invention includes a substrate for a power module and a heat sink, the substrate for a power module including an insulating substrate, a circuit layer formed on one surface of the insulating substrate, and a metal layer formed on the other surface of the insulating substrate; the heat sink is bonded to a surface of the power module substrate opposite to the insulating substrate, the surface being a surface of the metal layer, the surface being a sintered body of silver particles, the surface being a porous body having a relative density of 60% to 90%, the surface being a surface of the power module substrate opposite to the insulating substrate, the surface being a surface of the power module substrate opposite to the surface of the metal layer, the surface being a surface of the power module substrate opposite to the insulating substrate, the surface being a.

According to the power module substrate with a heat sink of the present invention having such a structure, the bonding layer is made of a sintered body of silver particles, and therefore has a high melting point and is difficult to melt. Further, since the sintered body of silver particles constituting the bonding layer is a porous body having a relative density in the range of 60% to 90% and has a thickness in the range of 10 μm to 500 μm, internal stress due to a difference in linear expansion coefficient between the power module substrate and the heat sink is relaxed during a cooling-heating cycle load, and the bonding layer is less likely to be broken. Therefore, the substrate for a power module with a heat sink according to the present invention can suppress an increase in thermal resistance or a crack in the insulating substrate due to a load of a cooling-heating cycle for a long period of time.

In the substrate for a power module with a heat sink according to the present invention, the metal layer is preferably formed of an aluminum plate made of aluminum or an aluminum alloy or a copper plate made of copper or a copper alloy.

In this case, since the metal layer is made of an aluminum plate made of aluminum or an aluminum alloy or a copper plate made of copper or a copper alloy, thermal conductivity is high, and heat generated in the semiconductor element mounted on the circuit layer can be efficiently transferred to the heat sink.

In the substrate for a power module with a heat sink according to the present invention, when the metal layer is formed of the aluminum plate, a silver plating layer or a gold plating layer is preferably formed on a surface of the aluminum plate opposite to the insulating substrate.

In this case, since the silver plating layer or the gold plating layer is formed on the surface of the aluminum plate (metal layer) opposite to the insulating substrate, the bonding force between the metal layer and the bonding layer (sintered body of silver particles) is increased.

A method for manufacturing a substrate for a power module with a heat sink according to the present invention is a method for manufacturing a substrate for a power module with a heat sink, the substrate for a power module including an insulating substrate, a circuit layer formed on one surface of the insulating substrate, and a metal layer formed on the other surface of the insulating substrate, the method comprising: a paste bonding material composition layer forming step of forming a layer of a paste bonding material composition containing silver particles having an average particle diameter in a range of 0.1 μm or more and 1 μm or less in an amount in a range of 70 mass% or more and 95 mass% or less on at least one of a surface of the metal layer of the power module substrate on the opposite side to the insulating substrate and a surface of the heat sink; a laminating step of laminating the power module substrate and the heat sink with a layer of the paste bonding material composition; and a heating step of heating the laminated power module substrate and the heat sink at a temperature of 150 ℃ to 300 ℃ in a lamination direction under a pressure of 1MPa or less.

According to the method for manufacturing a substrate for a power module with a heat sink of the present invention having such a configuration, the stacked body of the substrate for a power module and the heat sink is stacked by the layer of the paste-like bonding material composition containing silver particles having an average particle diameter in a range of 0.1 μm or more and 1 μm or less in an amount in a range of 70 mass% to 95 mass%, and is heated at a temperature of 150 ℃ to 300 ℃ under a pressure of 1MPa or less in the stacking direction, so that the silver particles are not excessively densified and can be reliably sintered. As a result, a bonding layer, which is a sintered body of silver particles and is a porous body having a relative density in the range of 60% to 90%, can be formed between the metal layer of the power module substrate and the heat sink.

According to the present invention, it is possible to provide a substrate for a power module with a heat sink and a method for manufacturing the substrate for a power module with a heat sink, which can suppress an increase in thermal resistance or a crack in an insulating substrate due to a load of a cooling and heating cycle for a long time.

Drawings

Fig. 1 is a schematic explanatory view of a power module using a substrate for a power module with a heat sink according to an embodiment of the present invention.

Fig. 2 is a flowchart of a method for manufacturing a substrate for a heat sink-equipped power module according to an embodiment of the present invention.

Fig. 3 is a cross-sectional SEM photograph of the bonding layer of the substrate for a power module with a heat sink manufactured in inventive example 9.

Fig. 4 is a cross-sectional SEM photograph of the bonding layer of the substrate for a power module with a heat sink manufactured in inventive example 17.

Detailed Description

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

Fig. 1 is a schematic explanatory view of a power module using a substrate for a power module with a heat sink according to an embodiment of the present invention.

In fig. 1, a power module 1 includes a power module substrate 10 with a heat sink and a semiconductor element 3 bonded to one surface (upper side in fig. 1) of the power module substrate 10 with a heat sink via a solder layer 2. The solder layer 2 is, for example, a Sn — Ag solder material, a Sn — In solder material, or a Sn — Ag — Cu solder material (so-called lead-free solder material).

The substrate 10 for a power module with a heat sink includes a substrate 20 for a power module and a heat sink 40 joined by a bonding layer 30.

The power module substrate 20 includes an insulating substrate 21, a circuit layer 22 formed on one surface of the insulating substrate 21, and a metal layer 23 formed on the other surface of the insulating substrate 21.

The insulating substrate 21 prevents electrical connection between the circuit layer 22 and the metal layer 23, and is made of, for example, AlN (aluminum nitride), Si₃N₄(silicon nitride) and Al₂O₃Ceramics having high insulation properties such as (alumina). The thickness of the insulating substrate 21 is set to be in the range of 0.2mm to 1.5mm, in the present embodimentWherein the thickness of the resin composition is 0.635 mm.

The circuit layer 22 is formed by bonding an aluminum plate made of aluminum or an aluminum alloy, or a copper plate made of copper or a copper alloy, to one surface (an upper surface in fig. 1) of the insulating substrate 21. As the aluminum plate, aluminum having a purity of 99 mass% or more (e.g., a1050 and a 1080) and high-purity aluminum having a purity of 99.99 mass% or more (4N — Al) can be used. As the copper plate, oxygen-free copper and high-purity copper (6N — Cu) having a purity of 99.9999 mass% or more can be used. The thickness of the circuit layer 22 is set to be in the range of 0.1mm to 1.0mm, and in the present embodiment, 0.3 mm. A circuit pattern is formed on the circuit layer 22, and one surface (an upper surface in fig. 1) thereof is a mounting surface 22A on which the semiconductor element 3 is mounted. In the present embodiment, a nickel plating layer (not shown) may be provided between the mounting surface 22A of the circuit layer 22 and the solder layer 2.

The metal layer 23 is formed by bonding an aluminum plate made of aluminum or an aluminum alloy or a copper plate made of copper or a copper alloy to the other surface (lower surface in fig. 1) of the insulating substrate 21. As the aluminum plate, aluminum having a purity of 99 mass% or more (e.g., a1050 and a 1080) and high-purity aluminum having a purity of 99.99 mass% or more (4N — Al) can be used. As the copper plate, oxygen-free copper and high-purity copper (6N — Cu) having a purity of 99.9999 mass% or more can be used. The thickness of the metal layer 23 is set to be in the range of 0.1mm to 1.0mm, and in the present embodiment, 0.3 mm.

In the present embodiment, the surface of the metal layer 23 opposite to the insulating substrate 21 side is a bonding surface 23A to which the heat sink 40 is bonded by the bonding layer 30. When the metal layer 23 is made of an aluminum plate, a silver plating layer or a gold plating layer (not shown) is preferably provided on the bonding surface 23A. By providing the silver plating layer or the gold plating layer, the bonding force between the metal layer 23 and the bonding layer 30 is enhanced, and the reliability of the power module substrate with a heat sink can be further improved. The thickness of the silver plating layer and the gold plating layer is preferably in the range of 0.05 μm to 1 μm. In the case where the metal layer 23 is formed of a copper plate, a silver plating layer or a gold plating layer may be provided on the bonding surface 23A.

The heat sink 40 is used for cooling the power module substrate 20. One surface (upper surface in fig. 1) of the heat sink 40 is a top plate portion 41 bonded to the metal layer 23 of the power module substrate 20 via the bonding layer 30. The heat sink 40 includes a flow path 42 through which a cooling medium flows. Instead of providing the flow path 42, the surface of the heat sink 40 other than the top plate 41 may have a fin structure.

The heat sink 40 is composed of aluminum or an aluminum alloy or copper or a copper alloy. In the present embodiment, the fins 40 are made of an aluminum alloy. As the aluminum alloy, an a3003 alloy, an a1100 alloy, an a3003 alloy, an a5052 alloy, an A7N01 alloy, and an a6063 alloy can be used. The top plate 41 of the heat sink 40 may have a silver plating layer or a gold plating layer (not shown) on its surface. By providing the silver plating layer or the gold plating layer, the bonding force between the heat sink 40 and the bonding layer 30 is enhanced, and the reliability of the power module substrate with a heat sink can be further improved.

The bonding layer 30 is made of a sintered body of silver particles. The fine silver particles are sintered at a relatively low temperature, but the sintered body of the silver particles has improved thermal stability and is not melted by heat generated from a general power semiconductor element. The sintered body of the silver particles constituting the bonding layer 30 is a porous body having a plurality of pores, and has a relative density in the range of 60% to 90%, preferably 62% to 90%, and more preferably 80% to 88%. The bonding layer 30 has a lower elastic modulus than bulk (bulk) silver due to the pores in the bonding layer 30, and internal stress due to a difference in linear expansion coefficient between the power module substrate 20 and the heat sink 40 is relaxed during a cooling-heating cycle load. Therefore, the bonding layer 30 is less likely to be broken during a thermal cycling load. If the relative density is less than 60%, the mechanical strength of the sintered body, that is, the bonding layer 30, is reduced, and there is a possibility that the bonding layer 30 is damaged during a load of a cooling-heating cycle. On the other hand, if the relative density exceeds 90%, the elastic modulus of the bonding layer 30 is about the same as that of the bulk silver, and there is a possibility that the function of relaxing the internal stress caused by the bonding layer 30 during the cooling-heating cycle load is lowered. The relative density of the bonding layer 30 is a percentage of the density (measured value) of the bonding layer 30 with respect to the true density of silver.

The thickness of the bonding layer 30 is set to be in the range of 10 μm to 500 μm. If the thickness of the bonding layer 30 is less than 10 μm, the ability to relax the internal stress in the bonding layer 30 during the cooling-heating cycle load may be reduced, and the bonding layer 30 may be damaged. On the other hand, if the thickness of the bonding layer 30 exceeds 500 μm, the mechanical strength of the bonding layer 30 decreases, and there is a possibility that the bonding layer 30 is damaged during a cooling-heating cycle load.

The bonding layer 30 preferably has a thickness in the range of 10 μm or more and 100 μm or less, and more preferably has a thickness in the range of 15 μm or more and 50 μm or less.

Next, a method for manufacturing a substrate for a heat sink-equipped power module according to the present embodiment will be described with reference to fig. 2.

Fig. 2 is a flowchart of a method for manufacturing a substrate for a heat sink-equipped power module according to an embodiment of the present invention. The method for manufacturing a substrate for a power module with a heat sink according to an embodiment of the present invention includes a paste bonding material composition layer forming step S01, a laminating step S02, and a heating step S03.

(paste bonding material composition layer Forming step S01)

In the paste adhesive composition layer forming step S01, a layer of the paste adhesive composition is formed on at least one of the surface of the metal layer of the power module substrate opposite to the insulating substrate and the surface of the heat sink. As a method for forming the layer of the paste bonding material composition, a coating method, a dipping method, or the like can be used. In the heating step S03 described later, the bonding layer 30 is generated by heating the paste bonding material composition layer.

The paste bonding material composition includes a solvent and silver particles.

The solvent of the paste bonding material composition is not particularly limited as long as it can be evaporated and removed in the heating step S03 described later. As the solvent, for example, an alcohol-based solvent, an ethylene glycol-based solvent, an acetic acid-based solvent, a hydrocarbon-based solvent, and an amine-based solvent can be used. Examples of the alcohol solvent include α -terpineol and isopropyl alcohol. Examples of the glycol-based solvent include ethylene glycol, diethylene glycol, and polyethylene glycol. Examples of the acetic acid-based solvent include butyl carbitol acetate. Examples of the hydrocarbon solvent include decane, dodecane, and tetradecane. Examples of the amine solvent include hexylamine, octylamine, and dodecylamine. These solvents may be used alone or in combination of two or more.

The silver particles used have an average particle diameter in the range of 0.1 μm to 1 μm. If the average particle diameter of the silver particles is less than 0.1 μm, it is difficult to increase the thickness of the paste bonding material composition layer, and sintering of the silver particles is facilitated in the heating step S03 described later, which may result in an excessively high relative density of the bonding layer 30 to be formed. On the other hand, if the average particle diameter of the silver particles exceeds 1 μm, sintering of the silver particles becomes difficult in the heating step S03 described later, and the relative density of the bonding layer 30 to be formed may become too low. The average particle diameter of the silver particles is preferably in the range of 0.2 μm to 0.5 μm.

The silver particles may also be coated with a protective material to prevent oxidation and agglomeration. As the protective material, an organic material having 2 to 8 carbon atoms can be used. The organic substance is preferably a carboxylic acid. Examples of the carboxylic acid include glycolic acid, citric acid, malic acid, maleic acid, malonic acid, fumaric acid, succinic acid, and tartaric acid. The content of the protective material is preferably 1 mass% or less, assuming that the silver particles are 100 mass%.

The content of the silver particles in the paste bonding material composition is in the range of 70 mass% to 95 mass% when the paste bonding material composition is set to 100 mass%. If the amount is less than 70 mass%, the viscosity of the paste bonding material composition becomes too low, and it becomes difficult to increase the thickness of the paste bonding material composition layer, and sintering of the silver particles becomes difficult in the heating step S03 described later, and there is a possibility that the relative density of the bonding layer 30 to be formed becomes too low. On the other hand, if the content of the silver particles exceeds 95 mass%, the viscosity of the paste adhesive composition becomes too high, and there is a possibility that it becomes difficult to form a paste adhesive composition layer. The content of the silver particles in the paste bonding material composition is preferably an amount in the range of 70 mass% to 90 mass%, and more preferably an amount in the range of 85 mass% to 90 mass%.

The thickness of the paste bonding material composition layer is not uniformly specified because it varies depending on the average particle diameter or content of the silver particles of the paste bonding material composition, but the thickness of the bonding layer formed by heating in the heating step S03 described later may be in the range of 10 μm to 500 μm. The thickness of the bonding layer is preferably in the range of 10 μm or more and 100 μm or less.

(laminating step S02)

In the laminating step S02, the power module substrate and the heat sink are laminated by the paste adhesive composition layer formed in the paste adhesive composition layer forming step S01. The thickness of the paste adhesive composition layer interposed between the stacked power module substrate and heat sink is preferably uniform.

(heating step S03)

In the heating step S03, the laminate of the power module substrate and the heat sink sheet laminated in the laminating step S02 is heated.

The heating temperature of the laminate is 150 ℃ to 300 ℃, preferably 170 ℃ to 270 ℃. If the heating temperature is lower than 150 ℃, the silver particles in the paste bonding material composition layer may be difficult to sinter, and the bonding layer may not be formed. On the other hand, if the heating temperature exceeds 300 ℃, the sintering of the silver particles in the paste bonding material composition layer proceeds excessively, and the relative density of the bonding layer to be formed may become excessively high.

The heating of the laminate is performed under a pressure of 1MPa or less in the lamination direction. The laminate may not be pressed in the laminating direction. If the laminate is heated in a state where the laminate is pressurized with a pressure exceeding 1MPa in the laminating direction, sintering of the silver particles proceeds excessively, and the relative density of the bonding layer to be formed may become excessively high.

By heating the laminate in this manner, the silver particles in the paste bonding material composition layer are sintered to produce the substrate for a power module with a heat sink as the present embodiment.

According to the substrate 10 for a power module with a heat sink of the present embodiment configured as described above, the metal layer 23 of the substrate 20 for a power module is formed of an aluminum plate made of aluminum or an aluminum alloy, and therefore, heat generated by the semiconductor element 3 mounted on the circuit layer 22 can be more efficiently transferred to the heat sink 40. Further, since the bonding layer 30 is made of a sintered body of silver particles, it has a high melting point and is difficult to melt. Further, since the sintered body of the silver particles constituting the bonding layer 30 is a porous body having a relative density in the range of 60% to 90%, and has a thickness in the range of 10 μm to 500 μm, the internal stress generated by the difference in linear expansion coefficient between the power module substrate 20 and the heat sink 40 during the cooling-heating cycle load is relaxed, and the bonding layer 30 is less likely to be broken. Therefore, the substrate 10 for a power module with a heat sink according to the present embodiment can suppress an increase in thermal resistance and a crack in the insulating substrate 21 due to a load of a cooling-heating cycle for a long period of time.

Further, according to the method for manufacturing the substrate 10 for a power module with a heat sink of the present embodiment, the substrate 20 for a power module and the heat sink 40 are laminated by the layer of the paste-like bonding material composition containing silver particles having an average particle diameter in the range of 0.1 μm or more and 1 μm or less in the amount in the range of 70 mass% or more and 95 mass% or less, and the laminated body formed is heated at a temperature of 150 ℃ or more and 300 ℃ or less under a pressure of 1MPa or less in the laminating direction, so that the silver particles are not excessively densified and can be reliably sintered. As a result, the bonding layer 30, which is a sintered body of silver particles and is a porous body having a relative density of 60% to 90%, can be formed between the metal layer 23 of the power module substrate 20 and the heat sink 40.

The embodiments of the present invention have been described above, but the present invention is not limited to these embodiments, and can be modified as appropriate within a range not departing from the technical spirit of the present invention.

For example, in the substrate 10 for a power module with a heat sink of the present embodiment, the semiconductor element 3 is mounted on the circuit layer 22, but the present invention is not limited thereto, and for example, electronic components other than the semiconductor element such as an LED may be mounted.