JP2011066385A - Power module substrate, power module, and method of manufacturing the power module substrate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a power module substrate where a metal plate is reliably joined to a ceramics substrate and heat cycle reliability is high, and also to provide a power module including the power module substrate and a method of manufacturing the power module substrate. <P>SOLUTION: In the power module substrate, the metal plates 12, 13 made of pure aluminum are joined onto the surface of the ceramics substrate 11 made of Al<SB>2</SB>O<SB>3</SB>. On a junction interface 30 between the metal plates 11, 12 and the ceramics substrate 11, a Cu high concentration section 32, which has Cu concentration at least two times larger than that in the metal plates 12, 13, is formed. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a power module substrate used in a semiconductor device that controls a large current and a high voltage, a power module including the power module substrate, and a method of manufacturing the power module substrate.

A power module for supplying power among semiconductor elements has a relatively high calorific value, and as a substrate on which the power module is mounted, for example, a metal of Al (aluminum) on a ceramic substrate made of Al ₂ O ₃ (aluminum oxide). A power module substrate is used in which the plates are bonded via an Al—Si brazing material.
The metal plate is formed as a circuit layer, and a power element semiconductor chip is mounted on the metal plate via a solder material.
In addition, a metal plate made of Al or the like is bonded to the lower surface of the ceramic substrate to form a metal layer for heat dissipation, and the entire power module substrate is bonded to the heat sink via this metal layer. Yes.

  Conventionally, in order to obtain good bonding strength between the circuit layer and the metal plate as the metal layer and the ceramic substrate, for example, the following Patent Document 1 discloses a technique in which the surface roughness of the ceramic substrate is less than 0.5 μm. Has been.

Japanese Patent Laid-Open No. 3-234045

However, when the metal plate is bonded to the ceramic substrate, there is a disadvantage that a sufficiently high bonding strength cannot be obtained even if the surface roughness of the ceramic substrate is simply reduced, and the reliability cannot be improved. For example, even if the surface of the ceramic substrate is subjected to a honing process with Al ₂ O ₃ particles in a dry manner and the surface roughness is set to Ra = 0.2 μm, interface peeling may occur in the peeling test. I understood. Further, even when the surface roughness was set to Ra = 0.1 μm or less by the polishing method, there was a case where the interface peeling occurred in the same manner.
It is also known that when a thermal cycle is applied, cracking occurs in the ceramic substrate as well as separation of the bonding interface.

  In particular, recently, power modules have become smaller and thinner, and the usage environment has become harsh, and the amount of heat generated from electronic components tends to increase. It is necessary to dispose a module substrate. In this case, since the power module substrate is constrained by the heat radiating plate, a large shearing force acts on the bonding interface between the metal plate and the ceramic substrate at the time of thermal cycle load. There is a need for improvement in performance.

  The present invention has been made in view of the circumstances described above, and is a power module substrate having a high thermal cycle reliability in which a metal plate and a ceramic substrate are securely bonded, and a power module including the power module substrate. And it aims at providing the manufacturing method of this board | substrate for power modules.

In order to solve such problems and achieve the above object, the power module substrate of the present invention is for a power module in which a metal plate made of pure aluminum is bonded to the surface of a ceramic substrate made of Al ₂ O ₃ . It is a board | substrate, Comprising: The Cu high concentration part by which Cu density | concentration was made into 2 times or more of Cu density | concentration in the said metal plate was formed in the joining interface of the said metal plate and the said ceramic substrate. .

In the power module substrate having this configuration, the Cu concentration at which the Cu concentration is at least twice the Cu concentration in the metal plate at the bonding interface between the ceramic substrate made of Al ₂ O ₃ and the metal plate made of pure aluminum. Since the concentration portion is formed, it is possible to improve the bonding strength between the ceramic substrate and the metal plate by Cu atoms existing in the vicinity of the interface.
Note that the Cu concentration in the metal plate is the Cu concentration in a portion of the metal plate that is away from the bonding interface by a certain distance (for example, 5 nm).

Here, the mass ratio of Al, Cu, and O obtained by analyzing the bonding interface including the Cu high concentration portion by energy dispersive X-ray analysis is Al: Cu: O = 50 to 90 wt%: 1 to 10 wt%: It is preferably 0 to 45 wt%.
If the mass ratio of Cu atoms existing at the bonding interface exceeds 10 wt%, a reaction product of Al and Cu is generated excessively, and this reaction product may hinder the bonding. On the other hand, when the mass ratio of Cu atoms is less than 1 wt%, there is a possibility that the bonding strength by Cu atoms cannot be sufficiently improved. Therefore, the mass ratio of Cu atoms at the bonding interface is preferably in the range of 1 to 10 wt%.

Here, since the spot diameter at the time of performing the analysis by the energy dispersive X-ray analysis method is extremely small, measurement is performed at a plurality of points (for example, 10 to 100 points) on the bonding interface, and the average value is calculated. . Further, when measuring, the bonding interface between the crystal grain boundary of the metal plate and the ceramic substrate is not measured, but only the bonding interface between the crystal grain and the ceramic substrate is measured.
The analytical value by the energy dispersive X-ray analysis method in this specification is the energy dispersive X-ray fluorescence element analyzer NORAN manufactured by Thermo Fisher Scientific Co., Ltd. mounted on the electron microscope JEM-2010F manufactured by JEOL. The acceleration was performed at 200 kV using System7.

A power module according to the present invention includes the above-described power module substrate and an electronic component mounted on the power module substrate.
According to the power module having this configuration, the bonding strength between the ceramic substrate and the metal plate is high, and the reliability can be drastically improved even when the usage environment is severe.

The power module substrate manufacturing method of the present invention is a method for manufacturing a power module substrate in which a metal plate made of pure aluminum is bonded to the surface of a ceramic substrate made of Al ₂ O ₃ , wherein the ceramic substrate And the metal plate through a Cu layer having a thickness of 0.15 μm or more and 3 μm or less, and the ceramic substrate and the metal plate that are stacked are pressed and heated in the stacking direction, and the ceramic substrate is heated. And a melting step for forming a molten aluminum layer at the interface of the metal plate, and a solidification step for solidifying the molten aluminum layer by cooling. In the melting step and the solidification step, the ceramic substrate and the metal plate A Cu high concentration portion in which the Cu concentration is at least twice the Cu concentration in the metal plate is formed at the bonding interface with It is characterized by that.

  According to the method for manufacturing a power module substrate of this configuration, the ceramic substrate and the metal plate are stacked via the Cu layer, and the stacked ceramic substrate and the metal plate are pressed and heated in the stacking direction. The eutectic reaction between Cu in the Cu layer and Al in the metal plate lowers the melting point in the vicinity of the bonding interface, and it is possible to form a molten aluminum layer at the interface between the ceramic substrate and the metal plate even at a relatively low temperature. A board | substrate and a metal plate can be joined. That is, the ceramic substrate and the metal plate can be joined without using a brazing material made of an Al—Si alloy or the like.

Further, if the thickness of the Cu layer is less than 0.15 μm, there is a possibility that the molten aluminum layer cannot be sufficiently formed at the interface between the ceramic substrate and the metal plate. Further, when the thickness of the Cu layer exceeds 3 μm, a reaction product of Cu and Al is excessively generated at the bonding interface, and the vicinity of the bonding interface of the metal plate is strengthened more than necessary. There is a possibility that cracks may occur in the ceramic substrate made of Al ₂ O ₃ . For this reason, in the case of a ceramic substrate made of Al ₂ O ₃ , the thickness of the Cu layer is preferably 0.15 μm or more and 3 μm or less.

The Cu layer is preferably formed by interposing a copper foil between the ceramic substrate and the metal plate in the laminating step.
Alternatively, the Cu layer is preferably formed by a Cu fixing step of fixing Cu to at least one of the bonding surfaces of the ceramic substrate and the metal plate before the laminating step.
According to these means, a Cu layer having a desired thickness can be formed between the ceramic substrate and the metal plate, and the ceramic substrate and the metal plate can be reliably bonded.

Here, in the Cu fixing step, it is preferable that Al is fixed together with Cu.
In this case, since Al is fixed together with Cu, the formed Cu layer contains Al, and in the heating process, this Cu layer is preferentially melted to reliably form a molten metal region. Thus, the ceramic substrate and the metal plate can be firmly bonded. In order to fix Al together with Cu, Cu and Al may be vapor-deposited at the same time, or sputtering using an alloy of Cu and Al as a target.

  Furthermore, the Cu fixing step fixes Cu to at least one of the bonding surfaces of the ceramic substrate and the metal plate by means selected from vapor deposition, CVD, sputtering, plating, or application of Cu paste. Is preferred.

  ADVANTAGE OF THE INVENTION According to this invention, the metal plate and the ceramic substrate are reliably joined, and the power module board | substrate with high thermal cycle reliability, the power module provided with this power module board | substrate, and the manufacturing method of this power module board | substrate are provided. It becomes possible to do.

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 a schematic diagram of the junction interface of the circuit layer of the board | substrate for power modules which is embodiment of this invention, a metal layer (metal plate), and a ceramic substrate. It is explanatory drawing which shows the manufacturing method of the board | substrate for power modules which is embodiment of this invention. It is explanatory drawing which shows the joining interface vicinity of the metal plate in FIG. 3, and a ceramic substrate. It is a schematic explanatory drawing of the power module using the board | substrate for power modules which is the 2nd Embodiment of this invention. It is the schematic diagram of the junction interface of the circuit layer of the board | substrate for power modules which is the 2nd Embodiment of this invention, a metal layer (metal plate), and a ceramic substrate. It is explanatory drawing which shows the manufacturing method of the board | substrate for power modules which is the 2nd Embodiment of this invention. It is explanatory drawing which shows the joining interface vicinity of the metal plate in FIG. 7, and a ceramic substrate. It is a figure which shows the evaluation result of the crack of the ceramic substrate in an Example. It is a figure which shows the evaluation result of the joining reliability in an Example.

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 shows a power module substrate 10 and a power module 1 according to a first 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 3 bonded to the surface of the circuit layer 12 via a solder layer 2, and a heat sink 4. Here, the solder layer 2 is made of, for example, a Sn—Ag, Sn—In, or Sn—Ag—Cu solder material. In the present embodiment, a Ni plating layer (not shown) is provided between the circuit layer 12 and the solder layer 2.

The power module substrate 10 has a ceramic substrate 11, a circuit layer 12 disposed on one surface (the upper surface in FIG. 1) of the ceramic substrate 11, and the other surface (lower surface in FIG. 1) of the ceramic substrate 11. And a disposed metal layer 13.
The ceramic substrate 11 prevents electrical connection between the circuit layer 12 and the metal layer 13, and is made of Al ₂ O ₃ (alumina) having a high insulating property. 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 bonding a conductive metal plate 22 to one surface of the ceramic substrate 11. In the present embodiment, the circuit layer 12 is formed by joining a metal plate 22 made of a rolled plate of aluminum (so-called 4N aluminum) having a purity of 99.99% or more to the ceramic substrate 11.

  The metal layer 13 is formed by bonding a metal plate 23 to the other surface of the ceramic substrate 11. In the present embodiment, the metal layer 13 is formed by joining a metal plate 23 made of a rolled plate of aluminum (so-called 4N aluminum) having a purity of 99.99% or more, like the circuit layer 12, to the ceramic substrate 11. Is formed.

The heat sink 4 is for cooling the power module substrate 10 described above, and includes a top plate portion 5 joined to the power module substrate 10 and a flow path 6 for circulating a cooling medium (for example, cooling water). It has. The heat sink 4 (top plate portion 5) is preferably made of a material having good thermal conductivity, and in this embodiment, is made of A6063 (aluminum alloy).
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 5 of the heat sink 4 and the metal layer 13. .

  When the bonding interface 30 between the ceramic substrate 11 and the circuit layer 12 (metal plate 22) and the metal layer 13 (metal plate 23) is observed with a transmission electron microscope, as shown in FIG. A Cu high concentration portion 32 in which Cu is concentrated is formed. In the Cu high concentration portion 32, the Cu concentration is higher than the Cu concentration in the circuit layer 12 (metal plate 22) and the metal layer 13 (metal plate 23). The Cu concentration is set to be twice or more the Cu concentration in the circuit layer 12 and the metal layer 13. Here, in this embodiment, the thickness H of the Cu high concentration portion 32 is 4 nm or less.

Note that, as shown in FIG. 2, the bonding interface 30 observed here is a lattice image of the interface layer side edge of the lattice image of the circuit layer 12 (metal plate 22) and the metal layer 13 (metal plate 23) and the ceramic substrate 11. The center between the interface side end of the reference surface S is defined as a reference plane S.
The Cu concentration in the circuit layer 12 (metal plate 22) and the metal layer 13 (metal plate 23) is constant from the bonding interface 30 in the circuit layer 12 (metal plate 22) and the metal layer 13 (metal plate 23). This is the Cu concentration in a portion separated by a distance (5 nm in this embodiment).

  The mass ratio of Al, Cu, and O when the bonding interface 30 is analyzed by energy dispersive X-ray analysis (EDS) is Al: Cu: O = 50 to 90 wt%: 1 to 10 wt%: 0. It is set within the range of 45 wt%. In addition, the spot diameter at the time of performing analysis by EDS is 1 to 4 nm, the bonding interface 30 is measured at a plurality of points (for example, 100 points in the present embodiment), and the average value is calculated. Further, the bonding interface 30 between the crystal grain boundaries of the metal plates 22 and 23 constituting the circuit layer 12 and the metal layer 13 and the ceramic substrate 11 is not measured, and the metal plate 22 constituting the circuit layer 12 and the metal layer 13 Only the bonding interface 30 between the crystal grains 23 and the ceramic substrate 11 is a measurement target.

Such a power module substrate 10 is manufactured as follows. As shown in FIG. 3, a metal plate 22 (4N aluminum rolled plate) serving as a circuit layer 12 is formed on one surface of a ceramic substrate 11 made of Al ₂ O ₃ with a thickness of 0.15 μm to 3 μm (this embodiment). In this embodiment, a metal plate 23 (4N aluminum rolled plate) that is laminated on the other surface of the ceramic substrate 11 and has a thickness of 0.15 μm to 3 μm (in this embodiment) 3 μm) of copper foil 25.

The laminated body 20 thus formed is charged and heated in a vacuum furnace in a state of being pressurized (pressure 1 to 5 kg / cm ² ) in the laminating direction (pressure / heating process). Here, the degree of vacuum in the vacuum furnace is 10 ⁻³ Pa to 10 ⁻⁵ Pa, and the heating temperature is 610 ° C. to 650 ° C. As shown in FIG. 4, the surface layers of the metal plates 22 and 23 that become the circuit layer 12 and the metal layer 13 and the copper foils 24 and 25 are melted by this pressurizing / heating process, and molten aluminum is formed on the surface of the ceramic substrate 11. Layers 26 and 27 are formed.

Next, the laminated body 20 is cooled to solidify the molten aluminum layers 26 and 27 (solidification step). By this pressurization / heating step and solidification step, a Cu high concentration portion 32 in which the Cu concentration is higher than the Cu concentration in the metal plates 22 and 23 constituting the circuit layer 12 and the metal layer 13 is formed at the bonding interface 30. Generated.
In this way, the power module substrate 10 according to the present embodiment is manufactured.

In the power module substrate 10 and the attached power module 1 according to the present embodiment configured as described above, the Cu concentration at the bonding interface 30 between the circuit layer 12 and the metal layer 13 and the ceramic substrate 11 is the circuit layer. 12 and the Cu concentration in the metal layer 13 is formed to be twice or more of the Cu concentration, so that Cu atoms intervene at the bonding interface 30, thereby causing the ceramic substrate 11 made of Al ₂ O ₃ and It is possible to improve the bonding strength between the circuit layer 12 and the metal layer 13.

  Furthermore, in this embodiment, the mass ratio of Al, Cu, and O when the bonding interface 30 is analyzed by the energy dispersive X-ray analysis method is Al: Cu: O = 50 to 90 wt%: 1 to 10 wt%: 0. Since it is set to ˜45 wt%, it is possible to prevent the reaction product of Al and Cu from being excessively generated at the bonding interface 30 to inhibit the bonding, and to sufficiently exert the effect of improving the bonding strength by Cu atoms. be able to.

In addition, it is laminated on one surface of the ceramic substrate 11 made of Al ₂ O ₃ via a metal plate 22 to be the circuit layer 12 and a copper foil 24 having a thickness of 0.15 μm to 3 μm (3 μm in this embodiment). The metal plate 23 (4N aluminum rolled plate) to be the metal layer 13 is laminated on the other surface of the ceramic substrate 11 via a copper foil 25 having a thickness of 0.15 μm to 3 μm (3 μm in this embodiment), Since this laminated body is pressurized and heated, the Cu of the copper foils 24 and 25 and the Al of the metal plates 22 and 23 undergo a eutectic reaction, whereby the copper foils 24 and 25 and the metal plates 22 and 23 are Since the melting point of the surface layer portion is lowered, it becomes possible to form the molten aluminum layers 26 and 27 at the interface between the ceramic substrate 11 and the metal plates 22 and 23 even at a relatively low temperature (610 ° C. to 650 ° C.). It is possible to join the box substrate 11 and the metal plates 22 and 23.

Next, a second embodiment of the present invention will be described.
FIG. 5 shows a power module substrate 110 and a power module 101 according to the second embodiment of the present invention.

The power module substrate 110 includes a ceramic substrate 111, a circuit layer 112 disposed on one surface of the ceramic substrate 111 (upper surface in FIG. 5), and the other surface (lower surface in FIG. 5) of the ceramic substrate 111. And a disposed metal layer 113.
The ceramic substrate 111 prevents electrical connection between the circuit layer 112 and the metal layer 113, and is made of highly insulating Al ₂ O ₃ (alumina). 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 112 is formed by bonding a conductive metal plate 122 to one surface of the ceramic substrate 111. In the present embodiment, the circuit layer 112 is formed by joining a metal plate 22 made of a rolled plate of aluminum (so-called 4N aluminum) having a purity of 99.99% or more to the ceramic substrate 111.

  The metal layer 113 is formed by bonding a metal plate 123 to the other surface of the ceramic substrate 111. In this embodiment, similarly to the circuit layer 112, the metal layer 113 is formed by joining a metal plate 123 made of a rolled plate of aluminum (so-called 4N aluminum) having a purity of 99.99% or more to the ceramic substrate 111. Is formed.

  When the bonding interface 130 between the ceramic substrate 111 and the circuit layer 112 (metal plate 122) and the metal layer 113 (metal plate 123) is observed with a transmission electron microscope, as shown in FIG. , Cu high concentration portion 132 enriched with Cu is formed. In the Cu high concentration portion 132, the Cu concentration is higher than the Cu concentration in the circuit layer 112 (metal plate 122) and the metal layer 113 (metal plate 123). The Cu concentration is set to be twice or more the Cu concentration in the circuit layer 112 and the metal layer 113. Here, in this embodiment, the thickness H of the Cu high concentration portion 132 is 4 nm or less.

Note that the bonding interface 130 observed here is a lattice image of the ceramic substrate 111 and the interface side end of the lattice image of the circuit layer 112 (metal plate 122) and the metal layer 113 (metal plate 123), as shown in FIG. The center between the interface side end of the reference surface S is defined as a reference plane S.
In addition, the Cu concentration and the oxygen concentration in the circuit layer 112 and the metal layer 113 are the Cu concentration and the oxygen in a part of the circuit layer 112 and the metal layer 13 that are apart from the bonding interface 130 by a certain distance (5 nm in this embodiment). Concentration.

  The mass ratio of Al, Cu, and O when the bonded interface 130 is analyzed by energy dispersive X-ray analysis (EDS) is Al: Cu: O = 50 to 90 wt%: 1 to 10 wt%: 0. It is set within the range of 45 wt%. In addition, the spot diameter at the time of performing the analysis by EDS is 1 to 4 nm, the bonding interface 130 is measured at a plurality of points (for example, 100 points in the present embodiment), and the average value is calculated. Further, the bonding interface 130 between the crystal grain boundaries of the metal plates 122 and 123 constituting the circuit layer 112 and the metal layer 113 and the ceramic substrate 111 is not measured, and the metal plate 122 and the metal layer 122 constituting the circuit layer 112 and the metal layer 113. Only the bonding interface 130 between the crystal grains 123 and the ceramic substrate 111 is set as a measurement target.

Such a power module substrate 110 is manufactured as follows. As shown in FIG. 7, Cu fixing is performed on both surfaces of a ceramic substrate 111 made of Al ₂ O ₃ by vacuum deposition to form 0.15 μm to 3 μm thick Cu fixing layers 124 and 125. (Cu fixing step). A metal plate 122 (4N aluminum rolled plate) serving as the circuit layer 112 is laminated on one surface of the ceramic substrate 111 on which the Cu fixing layers 124 and 125 are formed, and the metal layer 113 is formed on the other surface of the ceramic substrate 111. A metal plate 123 (4N aluminum rolled plate) is laminated (lamination step).

The laminated body 120 formed in this manner is charged in the lamination direction (pressure 1 to 5 kg / cm ² ) in a vacuum furnace and heated (pressure / heating process). Here, the degree of vacuum in the vacuum furnace is 10 ⁻³ Pa to 10 ⁻⁵ Pa, and the heating temperature is 610 ° C. to 650 ° C. As shown in FIG. 8, the pressurizing / heating process melts the surface layers of the metal plates 122 and 123 and the Cu fixing layers 124 and 125 to be the circuit layer 112 and the metal layer 113, and melts aluminum on the surface of the ceramic substrate 111. Layers 126, 127 are formed.

Next, the laminated body 120 is cooled to solidify the molten aluminum layers 126 and 127 (solidification step). By this pressurization / heating process and solidification process, a Cu high concentration portion 132 in which the Cu concentration is higher than the Cu concentration in the metal plates 122 and 123 constituting the circuit layer 112 and the metal layer 113 is formed at the bonding interface 130. Generated.
In this way, the power module substrate 110 according to the present embodiment is manufactured.

In the power module substrate 110 and the attached power module 101 according to the present embodiment configured as described above, the Cu concentration at the bonding interface 130 between the circuit layer 112 and the metal layer 113 and the ceramic substrate 111 is changed to the circuit layer. 112 and the Cu high concentration portion 132 having a concentration twice or more the Cu concentration in the metal layer 113 is formed, so that Cu atoms intervene at the bonding interface 130, so that the ceramic substrate 111 made of Al ₂ O ₃ and It is possible to improve the bonding strength between the circuit layer 112 and the metal layer 113.

  Furthermore, in this embodiment, the mass ratio of Al, Cu, and O when the bonding interface 130 is analyzed by the energy dispersive X-ray analysis method is Al: Cu: O = 50 to 90 wt%: 1 to 10 wt%: 0. Since it is set to ˜45 wt%, it is possible to prevent the reaction product of Al and Cu from being excessively generated at the bonding interface 130 to inhibit the bonding, and to sufficiently exert the effect of improving the bonding strength by Cu atoms. be able to.

Further, Cu is fixed to both surfaces of the ceramic substrate 111 made of Al ₂ O ₃ by vacuum deposition, and the metal plate 122 (the circuit layer 112 is formed on one surface of the ceramic substrate 111 on which the Cu fixing layers 124 and 125 are formed. 4N aluminum rolled plate), a metal plate 123 (4N aluminum rolled plate) to be the metal layer 113 is laminated on the other surface of the ceramic substrate 111, and this laminate is pressed and heated. The eutectic reaction between Cu in the Cu fixing layers 124 and 125 and Al in the metal plates 122 and 123 lowers the melting point of the surface layer portion of the metal plates 122 and 123, and ceramics even at relatively low temperatures (610 ° C. to 650 ° C.). It becomes possible to form the molten aluminum layers 126 and 127 at the interface between the substrate 111 and the metal plates 122 and 123, and the ceramic substrate 11. It can be bonded to the metal plate 122 and 123 and.

  Further, since Cu is directly fixed to the ceramic substrate 111, the oxide film is formed only on the surfaces of the metal plates 122 and 123, and exists at the interface between the metal plates 122 and 123 and the ceramic substrate 111. Since the total thickness of the oxide film is reduced, the yield of initial bonding is improved. Further, even in an inert gas atmosphere, the ceramic substrate 111 and the metal plates 122 and 123 can be bonded.

As mentioned above, although embodiment of this invention was 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 metal layer has been described as a rolled plate of pure aluminum having a purity of 99.99%, but is not limited to this, and aluminum having a purity of 99% (2N aluminum) It may be.

Moreover, in 2nd Embodiment, although Cu fixed to what was performed to both surfaces of a ceramic substrate, it was not limited to this, Cu may be fixed to the joint surface of a metal plate, and metal Cu may be fixed to both the plate and the ceramic substrate.
Furthermore, although it demonstrated as what fixes Cu by vacuum evaporation, it is not limited to this, You may fix Cu by means, such as sputtering, CVD, plating, application | coating of a copper paste.

Further, the ceramic substrate and the metal plate have been described as being bonded using a vacuum heating furnace, but the present invention is not limited to this, and the ceramic substrate and the metal plate can be used in an N ₂ atmosphere, an Ar atmosphere, a He atmosphere, or the like. You may join with.

Moreover, although demonstrated as what provided the buffer layer which consists of aluminum, the aluminum alloy, or the composite material containing aluminum (for example, AlSiC etc.) between the top-plate part of a heat sink and a metal layer, even if this buffer layer is not provided Good.
Furthermore, although the heat sink has been described as being made of aluminum, it may be made of aluminum alloy, copper or copper alloy. Further, although the description has been given of the heat sink having a cooling medium flow path, the structure of the heat sink is not particularly limited.

A confirmation experiment conducted to confirm the effectiveness of the present invention will be described.
Cu was fixed to both surfaces of a 40 mm square and 0.635 mm thick ceramic substrate made of Al ₂ O ₃ by vacuum deposition, and a metal plate made of 4N aluminum having a thickness of 0.6 mm was attached to both surfaces of the ceramic substrate. Laminated and heated in a vacuum furnace (vacuum degree: 10 ⁻³ Pa to 10 ⁻⁵ Pa) in a state pressurized at a pressure of 1 to 5 kg / cm ² in the laminating direction, and provided with a ceramic substrate, a circuit layer, and a metal layer Produced a power module substrate.
Similarly, Cu is fixed to one side of a metal plate made of 4N aluminum having a thickness of 0.6 mm by vacuum deposition, and both sides of the ceramic substrate made of Al ₂ O ₃ having a thickness of 40 mm square and a thickness of 0.635 mm are attached. In addition, the vapor deposition sides of both metal plates are laminated so as to be on the Al ₂ O ₃ side, respectively, and a vacuum furnace (vacuum degree: 10 ⁻³ Pa to 10 ⁻³ ) in a state of being pressurized with a pressure of 1 to 5 kg / cm ² in the lamination direction ^The substrate for power module provided with the ceramic substrate, the circuit layer, and the metal layer was produced by heating at ⁻⁵ Pa).
Here, the adhesion amount (Cu thickness) of Cu by vacuum deposition is set to five levels of 0.1 μm, 0.5 μm, 1.0 μm, 2.0 μm, and 3.0 μm, and the heating temperatures are 610 ° C., 630 ° C., A total of 30 types of power module substrates were formed at three levels of 650 ° C.

On the metal layer side of the power module substrate thus molded, aluminum of 4N aluminum, 50 mm × 60 mm equivalent to the top plate of the heat sink, and 5 mm thick through a buffer layer having a thickness of 0.9 mm The plate (A6063) was joined.
The test piece was loaded 3000 times with a thermal cycle of −40 ° C. to 105 ° C. to confirm the presence or absence of cracks in the ceramic substrate. Two power module substrates of the same level were used for the test. The result is shown in FIG. In FIG. 9, all the test specimens were not cracked by the ceramic substrate, ◯, even if at least one ceramic substrate was cracked, and all the test specimens were cracked by the ceramic substrate. What was done was made into x.

Moreover, the above-mentioned thermal cycle was loaded 3000 times and the joining area ratio in that case was calculated | required. The result is shown in FIG. In FIG. 10, the case where the bonding area ratio after loading the heat cycle 3000 times is 85% or more, the case where the bonding area ratio after loading the heat cycle 3000 times is 70% or more and less than 85%, Δ The case where the bonding area ratio after the thermal cycle was loaded 3000 times was less than 70% was evaluated as x.
The bonding area ratio was calculated by the following formula. Here, the initial bonding area is an area to be bonded before bonding.
Bonding area ratio = (initial bonding area-peeling area) / initial bonding area

As shown in FIG. 9, when the Cu thickness formed in the Cu fixing step is increased, it is confirmed that the ceramic substrate made of Al ₂ O ₃ tends to be cracked. Moreover, in the test piece whose Cu thickness is 2 micrometers, the tendency for the crack of ceramics to be suppressed is confirmed, so that heating temperature is high.
On the other hand, as shown in FIG. 10, it is recognized that the higher the heating temperature, the higher the bonding reliability. Further, when the Cu thickness is about 1 μm, it is confirmed that the bonding reliability is improved even when the heating temperature is low.
From these test results, it was confirmed that in the ceramic substrate made of Al ₂ O ₃ , it is preferable that the Cu thickness existing at the interface between the metal plate and the ceramic substrate at the time of bonding is 2.5 μm or less.

  Next, in FIG. 10, a test piece (Cu thickness 0.1 μm, bonding temperature 650 ° C.) having a bonding area ratio of less than 70% after 3000 cycles of thermal cycling is referred to as Comparative Examples 1 and 2, and thermal cycling is performed. The test pieces (Cu thickness: 1.0 μm, bonding temperature: 650 ° C.) having a bonding area ratio after loading of 3000 times of 3,000 times were designated as Invention Examples 1 and 2, and these Comparative Examples 1, 2 and Invention Examples About 1 and 2, the joining interface was observed using the transmission electron microscope (the JEOL make: JEM-2010F) in the state before a heat cycle load. The Cu concentration (Cu mass ratio) at the bonded interface was analyzed by energy dispersive X-ray analysis (EDS). The Cu concentration (Cu mass ratio) at a position 5 nm away from the bonding interface in the metal plate was analyzed by energy dispersive X-ray analysis (EDS). The analysis value by the energy dispersive X-ray analysis method is accelerated using an energy dispersive X-ray fluorescence element analyzer NORAN System 7 manufactured by Thermo Fisher Scientific Co., Ltd. mounted on an electron microscope JEM-2010F manufactured by JEOL. The voltage was 200 kV. The results are shown in Table 1.

In Comparative Examples 1 and 2, the Cu concentration (Cu mass ratio) at the bonding interface is less than twice the Cu concentration (Cu mass ratio) in the metal plate, and the improvement in bonding strength by Cu atoms is insufficient. It was confirmed that.
On the other hand, in Inventive Examples 1 and 2, the Cu concentration (Cu mass ratio) at the bonding interface is set to be twice or more the Cu concentration (Cu mass ratio) in the metal plate. It was confirmed that improvement was achieved.

1 Power module 3 Semiconductor chip (electronic component)
DESCRIPTION OF SYMBOLS 10 Power module substrate 11 Ceramic substrate 12 Circuit layer 13 Metal layers 22, 23 Metal plates 24, 25 Copper foil (Cu layer)
26, 27 Molten aluminum layer 30 Bonding interface 32 Cu high concentration part

Claims (8)

A power module substrate in which a metal plate made of pure aluminum is bonded to the surface of a ceramic substrate made of Al ₂ O ₃ ,
A power module substrate, wherein a Cu high concentration portion in which a Cu concentration is twice or more of a Cu concentration in the metal plate is formed at a bonding interface between the metal plate and the ceramic substrate.   The mass ratio of Al, Cu, and O obtained by analyzing the bonding interface including the Cu high-concentration portion by energy dispersive X-ray analysis is Al: Cu: O = 50 to 90 wt%: 1 to 10 wt%: 0 to 45 wt. The power module substrate according to claim 1, wherein the power module substrate is a percentage.   A power module comprising: the power module substrate according to claim 1; and an electronic component mounted on the power module substrate. A method of manufacturing a power module substrate in which a metal plate made of pure aluminum is bonded to the surface of a ceramic substrate made of Al ₂ O ₃ ,
A laminating step of laminating the ceramic substrate and the metal plate via a Cu layer having a thickness of 0.15 μm or more and 3 μm or less, and pressurizing and heating the laminated ceramic substrate and the metal plate in the laminating direction; A melting step of forming a molten aluminum layer at an interface between the ceramic substrate and the metal plate, and a solidification step of solidifying the molten aluminum layer by cooling,
In the melting step and the solidifying step, a Cu high-concentration portion in which the Cu concentration is twice or more the Cu concentration in the metal plate is formed at the bonding interface between the ceramic substrate and the metal plate. A method for manufacturing a power module substrate.   5. The method for manufacturing a power module substrate according to claim 4, wherein the Cu layer is formed by interposing a copper foil between the ceramic substrate and the metal plate in the laminating step.   The Cu layer is formed by a Cu adhering step of adhering Cu to at least one of the bonding surfaces of the ceramic substrate and the metal plate before the laminating step. A method for manufacturing a power module substrate.   The power module substrate manufacturing method according to claim 6, wherein in the Cu fixing step, Al is fixed together with Cu.   In the Cu fixing step, Cu is fixed to at least one of the bonding surfaces of the ceramic substrate and the metal plate by means selected from vapor deposition, CVD, sputtering, plating, or application of Cu paste. A method for manufacturing a power module substrate according to claim 6 or 7.

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