JP2019165100A - Method for manufacturing substrate for heat sink-equipped power module - Google Patents

Abstract

To reliably join a substrate for a power module to a heat sink composed of an aluminum silicon carbide composite at a temperature of 500°C or below.SOLUTION: A method for joining, by diffusion, a metal layer of a substrate for a power module to a heat sink through a copper layer, provided that the substrate is arranged by joining a circuit layer to one face of a ceramic substrate and the metal layer made of aluminum or aluminum alloy to the other face, and the heat sink is composed of an aluminum silicon carbide composite formed by impregnating aluminum alloy into a porous body of silicon carbide comprises the step of joining the substrate for a power module and the heat sink together in a state in which a piece of metal foil of aluminum alloy with magnesium added thereto at a concentration of 0.02 mass% or more and 3.0 mass% or less is interposed between the metal layer of the substrate for a power module and the copper layer.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a method for manufacturing a power module substrate with a heat sink used in a semiconductor device that controls a large current and a high voltage.

As a power module substrate, a circuit layer is bonded to one surface of an insulating layer made of a ceramic substrate such as aluminum nitride, and an aluminum heat sink is bonded to the other surface via an aluminum plate. A power module substrate is known.
For example, in a power module substrate with a heat sink disclosed in Patent Document 1, a circuit layer made of a pure aluminum plate, an aluminum alloy plate, a pure copper plate, a copper alloy plate, or the like is bonded to one surface of an insulating layer made of a ceramic substrate. A metal layer made of pure aluminum or an aluminum alloy metal plate is bonded to the other surface of the insulating layer, and a heat sink made of aluminum or an aluminum alloy is bonded to the metal layer via a copper layer. In this case, the insulating layer and the metal layer are bonded using a brazing material, and the metal layer and the heat sink are bonded by solid phase diffusion between the copper layer interposed therebetween.

  In such a power module substrate with a heat sink, porous silicon carbide disclosed in Patent Document 2 is used as a heat sink material in order to prevent warping due to joining of members having different thermal expansion coefficients such as a ceramic substrate and an aluminum plate. It has been proposed to use a low expansion coefficient composite (aluminum silicon carbide composite) obtained by impregnating a molded body with a metal mainly composed of aluminum.

JP 2014-60215 A JP 2000-281465 A

By the way, it is preferable that the metal layer of the power module substrate is made of relatively high purity aluminum (particularly high purity aluminum having a purity of 99.99% by mass or more) in order to relieve stress accompanying thermal expansion and contraction. On the other hand, since the aluminum silicon carbide composite described in Patent Document 2 uses a relatively low-purity aluminum alloy containing silicon, magnesium or the like in order to obtain a dense and high-strength composite by high temperature casting or the like, this A temperature required for solid phase diffusion of the aluminum silicon carbide composite and copper is, for example, about 500 ° C.
However, when trying to join the metal layer of the power module substrate and the aluminum silicon carbide composite at the same time at a temperature of about 500 ° C. via the copper layer, it is insufficient for joining the metal layer and the copper layer, Intermetallic compounds (CuAl ₂ , CuAl, etc.) do not grow sufficiently between the metal layer and the copper layer, and joint failure tends to occur. In order to solve this, if an attempt is made to increase the bonding temperature, a part of the aluminum silicon carbide composite may be melted.

  The present invention has been made in view of such circumstances, and an object thereof is to reliably bond a power module substrate and a heat sink made of an aluminum silicon carbide composite at a temperature of 500 ° C. or lower.

In the method for manufacturing a power module substrate with a heat sink of the present invention, a circuit layer is bonded to one surface of a ceramic substrate, and a metal layer made of aluminum or an aluminum alloy is bonded to the other surface of the ceramic substrate. By diffusion bonding the metal layer in the power module substrate and a heat sink made of an aluminum silicon carbide composite formed by impregnating a silicon carbide porous body with an aluminum alloy through a copper layer, the power module substrate A metal foil made of an aluminum alloy in which magnesium is added between the metal layer and the copper layer of the power module substrate. With the power module substrate and the heat module interposed therebetween. Bonding the heat sink.
In this case, the magnesium concentration of the metal foil is 0.02 mass% or more and 3.0 mass% or less.

Generally, an aluminum oxide film is formed on the surface of the metal layer in the power module substrate and the surface of the aluminum silicon carbide composite of the heat sink, which prevents the formation of an intermetallic compound between aluminum and copper, resulting in poor bonding. Cause.
According to this manufacturing method, the metal foil made of aluminum or aluminum alloy to which magnesium is added is interposed between the metal layer and the copper layer of the power module substrate, so that the solid solution magnesium diffuses in the metal foil. Then, it reacts with the oxide film on the surface of the metal layer or the heat sink to destroy the aluminum oxide film and disperse as magnesium oxide (MgAl ₂ O ₄ or MgO). In this case, since the metal foil is an aluminum alloy in which magnesium is dissolved, the magnesium oxide produced by destroying the aluminum oxide film on the aluminum surface is dispersed as fine particles at the interface between aluminum and copper. It becomes. Therefore, it is suppressed that this magnesium oxide inhibits the formation of an intermetallic compound between aluminum and copper. As a result, the growth of the intermetallic compound between aluminum and copper is promoted, and the power is reduced even at a low temperature of 500 ° C. or lower. The module substrate and the heat sink can be firmly bonded.

  In this case, if the magnesium concentration in the metal foil is less than 0.02% by mass, the magnesium oxide is not sufficiently formed, and there is a risk of poor bonding. On the other hand, if the magnesium concentration in the metal foil exceeds 3.0% by mass, rolling becomes difficult.

As a preferred embodiment of the method for producing a power module substrate with a heat sink of the present invention, the thickness of the metal foil is preferably 3.0 μm or more and 300.0 μm or less.
In this case, when the thickness of the metal foil is less than 3.0 μm, it is difficult to roll, and when the thickness exceeds 300.0 μm, the stress caused by the difference in linear expansion between the metal foil (rolled foil) and the ceramic is large. And may cause peeling.

In the method for manufacturing a power module substrate with a heat sink according to another aspect of the present invention, the metal foil may further contain silicon, and the silicon concentration may be 10.5% by mass or less.
Silicon can also diffuse into the aluminum of the metal layer or aluminum silicon carbide composite to increase the bonding strength. However, if the silicon concentration of the metal foil exceeds 10.5% by mass, rolling becomes difficult.

  According to the present invention, the magnesium component of the metal foil breaks the aluminum oxide film on the surface of the metal layer and the aluminum silicon carbide composite and disperses as fine magnesium oxide, so that the intermetallic compound of aluminum and copper Growth is promoted, and the power module substrate and the heat sink can be firmly bonded at a temperature of 500 ° C. or lower.

It is sectional drawing which shows the whole structure of the board | substrate for power modules with a heat sink which concerns on one Embodiment of this invention. It is sectional drawing which shows the state before joining about the board | substrate for power modules of FIG. It is sectional drawing which shows the state before joining a heat sink to the board | substrate for power modules in the manufacturing method of the said embodiment.

Hereinafter, embodiments of the present invention will be described.
In FIG. 1, the board | substrate 1 for power modules with a heat sink manufactured by the manufacturing method of this embodiment is shown. In the power module substrate 1 with a heat sink, the power module substrate 10 and the heat sink 20 are bonded in a laminated state via a copper layer 30.

The power module substrate 10 includes a ceramic substrate 11, a circuit layer 12 bonded to one surface (front surface) 11a of the ceramic substrate 11, and a metal layer 13 bonded to the other surface (back surface) 11b of the ceramic substrate 11. And have.
The ceramic substrate 11 is an insulating material that prevents electrical connection between the circuit layer 12 and the metal layer 13, and is formed of, for example, AlN (aluminum nitride), silicon nitride Si ₃ N ₄ or the like, and has a thickness of 0. .2 mm to 1.5 mm.

  As the circuit layer 12 and the metal layer 13, either aluminum or an aluminum alloy can be applied. However, for the metal layer 13, pure aluminum having a purity of 99.00% by mass or more or a purity of 99.99% by mass or more is used for stress relaxation. Is particularly preferred. The plate thickness of the circuit layer 12 and the metal layer 13 is preferably 0.1 mm to 1.0 mm. The circuit layer 12 and the metal layer 13 are bonded together by laminating aluminum plates on both surfaces of the ceramic substrate 11 through, for example, an Al—Si brazing material, and pressing and heating them in the laminating direction.

Heat sink 20 is formed of an aluminum silicon carbide composite formed by impregnating a silicon carbide porous body with an aluminum alloy. The silicon carbide porous body is obtained by mixing silicon carbide powder and a binder, forming a plate shape, and sintering. An aluminum silicon carbide composite is produced by impregnating the silicon carbide porous body with a molten aluminum alloy containing magnesium or silicon at a high pressure. It has both the characteristics of aluminum and silicon carbide, has good thermal conductivity as a heat sink, has a low thermal expansion coefficient, and is bonded to the power module substrate 10 so that thermal expansion and contraction can be achieved. The occurrence of warpage or the like can be suppressed in balance with the 10 ceramic substrates 11.
As the heat sink 20, a flat plate is preferably used, and the thickness thereof is preferably 0.4 mm to 6.0 mm.
Note that a skin layer (not shown) made of an impregnated aluminum alloy is formed on the surface of the heat sink 20, and the skin layer and the copper layer 30 are joined.
Moreover, as an aluminum alloy to be impregnated, for example, A356 (ASTM standard), ADC12, 6063, 3003, etc. (JIS standard) can be used.
The copper layer 30 is not particularly limited, but is preferably made of pure copper in terms of thermal conductivity. For example, it is formed of a rolled plate of oxygen-free copper and has a thickness of 0.05 mm or more and 3.0 mm or less.

Next, the manufacturing method of the board | substrate 1 for power modules with a heat sink of this embodiment is demonstrated.
The manufacturing method includes a power module substrate forming step of bonding the circuit layer 12 and the metal layer 13 to the ceramic substrate 11 to form the power module substrate 10, and a heat sink bonding step of bonding the heat sink 20 to the power module substrate 10. It consists of. Hereinafter, it demonstrates in order of this process.

(Power module substrate formation process)
As shown in FIG. 2, an aluminum plate 12A to be a circuit layer 12 is formed on one surface 11a of the ceramic substrate 11, an aluminum plate 13A to be a metal layer 13 is formed on the other surface 11b, and an Al—Si brazing filler metal foil 15 is provided. The circuit layer 12 is bonded to one surface 11a of the ceramic substrate 11 and the metal layer 13 is bonded to the other surface 11b by heating the stacked body in a state of being pressed in the stacking direction and then cooling. The power module substrate 10 is formed. The brazing filler metal foil 15 is melted by heating, diffuses into the circuit layer 12 and the metal layer 13, and is firmly bonded to the ceramic substrate 11.
The bonding conditions at this time are not necessarily limited, but the pressure in the stacking direction is 0.3 MPa to 1.0 MPa in a vacuum atmosphere, and the heating temperature is 640 ° C. or more and 650 ° C. or less for 1 minute or more and 60 minutes. It is preferable to hold the minute or less.

(Heat sink bonding process)
As shown in FIG. 3, the heat sink 20 is bonded to the metal layer 13 of the power module substrate 10 via the copper layer 30. This bonding is a solid phase diffusion bonding of the aluminum of the metal layer 13 and the heat sink 20 and the copper of the copper layer 30.
In addition, the metal foil 40 is inserted between the metal layer 13 and the copper layer 30 for this joining. This metal foil 40 is a metal foil formed of an aluminum alloy to which magnesium is added.
The metal foil 40 is interposed between the metal layer 13 and the copper layer 30 and heated while being pressed in the laminating direction, thereby joining the metal layer 13 and the heat sink 20 by diffusion bonding of aluminum and copper. . The bonding conditions at this time are not necessarily limited, but the pressure in the stacking direction is 0.3 MPa or more and 3.5 MPa or less in a vacuum atmosphere, and is maintained at a heating temperature of 400 ° C. or more and less than 500 ° C. for 5 minutes or more and 240 minutes or less. It is preferable to do this.

As described above, an aluminum oxide film is present on the surfaces of the metal layer 13 and the heat sink 20, which hinders solid phase diffusion bonding with the copper layer 30. In this joining step, since magnesium atoms are contained in the aluminum alloy in the metal foil 40, the magnesium atoms destroy the aluminum oxide film on the surfaces of the metal layer 13 and the heat sink 20, and spinel (MgAl ₂ O ₄ ). To produce magnesium oxide. Therefore, the surface of the metal layer 13 and aluminum silicon carbide aluminum from which the aluminum oxide film has been removed and the surface of the copper layer 30 are in contact with each other to be diffusion bonded.

  Further, since the magnesium oxide generated at this time is formed by diffusion of magnesium atoms, it is a fine particle and dispersed in the plane direction along the interface between the metal layer 13 and the copper layer 30. It is formed. Therefore, the diffusion bonding between the aluminum of the metal layer 13 or the heat sink 20 and the copper of the copper layer 30 is hardly hindered, the diffusion bonding between aluminum and copper is promoted, and the metal layer 13 and the heat sink 20 are firmly bonded. Is done.

This metal foil 40 is a rolled foil of an Al—Si alloy (aluminum alloy) to which magnesium is added, and the thickness is preferably 3.0 μm or more and 300.0 μm or less. When the thickness of the metal foil 40 is less than 3.0 μm, it is difficult to roll, and when the thickness exceeds 300.0 μm, the stress caused by the difference in linear expansion between the metal foil 40 (rolled foil) and the ceramic becomes large. May cause peeling.
In addition, although the metal foil 40 was comprised with the Al-Si alloy to which magnesium was added, it is preferable that the content rate of the silicon in the Al-Si alloy is 10.5 mass% or less. When the content ratio of silicon in the Al—Si alloy exceeds 10.5 mass%, rolling becomes difficult.
Moreover, in the said embodiment, although the material of the metal foil 40 was made into the Al-Si alloy to which magnesium was added, you may use the other aluminum alloy to which magnesium was added, and pure aluminum to which magnesium was added. There may be.

The density | concentration of magnesium in the metal foil 40 is set to the ratio from which magnesium will be 0.02 mass% or more and 3.0 mass% or less.
If the magnesium concentration is less than 0.02% by mass, magnesium oxide is not sufficiently formed at the interface between aluminum and copper. As a result, an aluminum oxide film remains and diffusion bonding between aluminum and copper is inhibited, resulting in poor bonding. There is a fear.
On the other hand, when the concentration of magnesium increases, the concentration of aluminum relatively decreases and the metal layer 40 becomes harder, so that rolling becomes difficult.

  In this way, the metal layer 13 of the power module substrate 10 and the heat sink 20 are solid-phase diffusion bonded via the copper layer 30, whereby the power module substrate 1 with a heat sink in which these are integrated is manufactured. .

  According to this manufacturing method, by interposing the metal foil 40 made of an aluminum alloy to which magnesium is added, the copper layer 30 connects the metal layer 13 of the power module substrate 10 and the heat sink 20 made of the aluminum silicon carbide composite. Thus, it is possible to perform solid phase diffusion bonding at a low temperature of 500 ° C. or less, and it is possible to firmly bond both the metal layer 13 and the heat sink 20 made of the aluminum silicon carbide composite.

In addition, the detailed configuration is not limited to the configuration of the embodiment, and various modifications can be made without departing from the spirit of the present invention.
In the present embodiment, the heat sink 20 is a flat plate, but the shape is not particularly limited. For example, a liquid-cooled cooler having a water channel inside may be used.

As a power module substrate, a ceramic substrate made of an aluminum nitride plate and a circuit layer made of a pure aluminum plate (4N-Al) and a metal layer bonded to each other are used. The layers were joined. For joining the power module substrates, an Al-7.5 mass% Si brazing foil having a thickness of 12 μm was used and held at a temperature of 640 ° C. to 660 ° C. for 30 minutes at a pressure of 0.6 MPa.
The presence or absence of addition of Mg, the concentration of silicon and the concentration of magnesium, and the foil thickness in the metal foil formed when joining the metal layer and the copper layer of the power module substrate in Examples 1 to 8 and Comparative Example 1 are as follows. One. In the conventional example, the metal foil is not used for connection between the metal layer and the copper layer of the power module substrate.
In joining the metal layer and the copper layer of this power module substrate, the pressure was 2.1 MPa and the temperature was kept at 490 ° C. for 150 minutes.

About the obtained sample, the joining rate (DBA / Cu joining rate) of a metal layer and a copper layer was evaluated.
The bonding rate was a ratio obtained by binarizing the ultrasonic flaw detection image on the bonding surface to obtain the bonded area excluding the peeled portion, and dividing this by the area of the interface to be bonded.
Moreover, about the obtained data, the joining rate (AIN / back Al joining rate) of a ceramic substrate and a metal layer was evaluated as cooling cycle reliability. The bonding rate between the ceramic substrate and the metal layer is a numerical value after executing a temperature cycle test that is changed 3000 times between −40 ° C. and 150 ° C.
These results are shown in Table 1.

As is clear from Table 1, the magnesium concentration of the aluminum foil to which magnesium was added or the Al-Si foil to which magnesium was added was 0.02% by mass to 3.0% by mass (Examples 1 to 8). ) Has a bonding rate (DBA / Cu bonding rate) between the metal layer and the copper layer of more than 90%, and it was possible to obtain a bond having no practical problem even at a temperature of 500 ° C. or lower.
Further, the bonding rate (AIN / back Al bonding rate) between the ceramic substrate made of aluminum nitride of Examples 1 to 8 and the metal layer made of pure aluminum exceeds 75%, and the thermal cycle reliability is also high. it was high. In particular, in Examples 1 to 7, the bonding ratio of AIN / back Al exceeded 80%, and the foil pressure of the aluminum foil added with magnesium or the Al-Si foil added with magnesium was 3.0 μm or more and 300 By setting the thickness to 0.0 μm or less, the cooling cycle reliability could be further improved.

1 Power Module Substrate with Heat Sink 10 Power Module Substrate 11 Ceramic Substrate 12 Circuit Layer 13 Metal Layer 20 Heat Sink 30 Copper Layer 40 Metal Foil 50 Bonding Layer

Claims (3)

  A circuit layer is bonded to one surface of the ceramic substrate, and a metal layer made of aluminum or an aluminum alloy is bonded to the other surface of the ceramic substrate. A heat sink joining step for joining the power module substrate and the heat sink by diffusion bonding a heat sink made of an aluminum silicon carbide composite formed by impregnating the body with an aluminum alloy through a copper layer. The heat sink joining step includes a metal made of an aluminum alloy in which magnesium is added at a concentration of 0.02 mass% or more and 3.0 mass% or less between the metal layer and the copper layer of the power module substrate. The power module substrate and the heat sink are connected with a foil interposed. Method of manufacturing a substrate for a power module with a heat sink, characterized by.   The thickness of the said metal foil is 3.0 micrometers or more and 300.0 micrometers or less, The manufacturing method of the board | substrate for power modules with a heat sink of Claim 1 characterized by the above-mentioned.   The method for manufacturing a power module substrate with a heat sink according to claim 1 or 2, wherein the metal foil further contains silicon, and the concentration of the silicon is 10.5 mass% or less.

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